analytical hierarchy process applied to maintenance strategy selection for offshore platforms in...

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Analytical Hierarchy Process applied to maintenance strategy selection for offshore

platforms in challenging environments.

Nnaemeka NwogbeS1538433MSc Mechanical Engineering with Manufacturing.Glasgow Caledonian University

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ABSTRACT

Maintenance policy selection is a very important task for any engineering industry.

An attempt to formulate an effective maintenance management framework in order to

cope with challenges of extreme environment is of significance to the offshore

industry. That being said the offshore industry faces a challenging situation in

maintaining a level of production at isolated and often harsh locations as is common

offshore. Maintenance is of utmost importance not only in order to achieve

prolongation of the life of platforms, but also for environment and for general health

and safety of personnel aboard the not easily accessible oil platforms. The aim of this

research was to integrate the Analytical Hierarchy Process (AHP), to select the most

appropriate maintenance strategy for a challenging environment faced by offshore

platforms. Whilst providing new insight into the capability of the AHP methodology.

This aim has been accomplished utilizing interview response from shell Maintenance

and Inspection supervisors and two case studies based on: Petronas and Analysis of

the failure of an offshore compressor crankshaft.

As a result from this research, the maintenance strategy based on information

obtained was produced using the AHP multi criteria decision weighing methodology

as implemented on a compressor in a corrosive environment.


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ACKNOWLEDGEMENTS

Ending a four-month journey of research, but also personal growth, there are some

reflections to be made. I would like to thank my supervisor Dr. Babakalli, for his

support and advice through this trying time. I would also like to thank the

maintenance and Inspection supervisors that took part in the interview, my brother

Nnadozie Nwogbe for setting it all up and for all his support, my brother Obinna

Nwogbe for keeping an eye on my progress and making sure I was on track, my

parents for all their love and support.


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CONTENTS

CHAPTER 1.............................................................................................................................................................6

INTRODUCTION AND POSITIONING..........................................................................................................6

1.1. Background..............................................................................................................................................6

1.1. Shell............................................................................................................................................................ 9

1.2. Problem Statement and Scope.....................................................................................................10

1.3. Aim and objectives.............................................................................................................................11

1.4. Research questions..........................................................................................................................11

1.5. Delimitations.......................................................................................................................................12

1.6. Structure of paper...............................................................................................................................12

CHAPTER 2..........................................................................................................................................................14

LITERATURE REVIEW....................................................................................................................................14

2.1. Challenges met in an offshore environment..........................................................................14

2.2. Selecting a maintenance approach using AHP multiple criteria decision-making.............................................................................................................................................................................. 17

2.3. Maintenance strategy utilized on an offshore oil platform..............................................18

CHAPTER 3..........................................................................................................................................................24

OVERVIEW.......................................................................................................................................................... 24

3. Oil and Gas Industry...................................................................................................................................24

3.1. Offshore Industry..........................................................................................................................25

3.1.1. Offshore Exploration and Planning.....................................................................26

3.1.2. Offshore Production...................................................................................................28

3.2. Offshore platforms..............................................................................................................................30

3.3.1. Platform Type and Design....................................................................................30

3.4. Critical equipment in the Oil and Gas Industry.....................................................................36

3.4.1. Safety Critical...............................................................................................................36

3.4.2. Safety critical equipment.......................................................................................38

3.4.3. Operation Critical.......................................................................................................47

CHAPTER 4..........................................................................................................................................................50

RESEARCH METHODOLOGY........................................................................................................................50

4. Research Overview....................................................................................................................................50

4.1. Research Approach......................................................................................................................50


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4.2. Research Process.................................................................................................................................51

4.2.1. Delphi Interview Technique...................................................................................52

4.2.2. Case study..................................................................................................................55

4.3. Validity.....................................................................................................................................................56

4.4. Findings.............................................................................................................................................56

4.5. Corrosion..........................................................................................................................................56

4.5.1. Environmental influences.....................................................................................57

4.5.2. Contribution of process and equipment conditions..................................58

4.6. Corrosion Maintenance..................................................................................................................60

4.6.1. Corrosion maintenance tasks...............................................................................61

4.7. Corrosion maintenance strategy.................................................................................................62

4.7.1. Corrective Maintenance.........................................................................................62

4.7.2. Preventative Maintenance....................................................................................63

4.7.3. Predictive Maintenance or Condition-Based Maintenance.....................63

4.7.4. Reliability-Centered Maintenance.....................................................................64

4.8. Compressor............................................................................................................................................64

4.9. Analytical Hierarchy Process (AHP)..........................................................................................65

Chapter 5..............................................................................................................................................................71

DATA ANALYSIS................................................................................................................................................71

5. Application of the Analytical Hierarchy Process..........................................................................71

CHAPTER 6..........................................................................................................................................................80

DISCUSSION & CONCLUSIONS....................................................................................................................80

6.1. Discussion........................................................................................................................................80

6.2. Conclusion........................................................................................................................................81

6.3. Future Research Work..................................................................................................................83

6.3.1. Analytical Network Process (ANP)......................................................................84

6.3.2. Fuzzy AHP.......................................................................................................................84

REFERENCE........................................................................................................................................................85

APPENDIX............................................................................................................................................................97

Appendix A.....................................................................................................................................................97

Appendix B..................................................................................................................................................... 98

Appendix C......................................................................................................................................................99

Appendix D.................................................................................................................................................. 103

Appendix E...................................................................................................................................................105


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CHAPTER 1

INTRODUCTION AND POSITIONING.

This chapter is intended to give the reader an insight and understanding into the aim,

objective and expected results of the dissertation. This is accomplished by explaining

the relevance of the topic to the industry, academia and in most cases the economy.

1.1. Background.

To appreciate the purpose of this dissertation it is vital to understand the role of the oil

and gas industry. According to Kendrick Oil Company (2015), oil provides one-third

of the world’s energy supply and the addition of natural gas, increases that to over 50

percent. Both of the world’s alternative energy sources; wind and solar power, cannot

compare in production to that of petroleum. In 2010, petroleum production was over

5,700 gigawatts compared to 24 gigawatts of wind and 3.4 gigawatts of solar power

produced the same year. What this implies is that without ongoing production of what

is recognized as the dominant source of energy in today’s society. The result would be

an economical downfall.

That being said, the management of maintenance operations in the oil and gas

industry is of severe importance to both its effectiveness and efficiency. The oil and

gas industry is one recognized for its expensive specialized equipment and strict

environmental considerations. The industry is often antagonized with ever changing

rules and regulations. Answerable to a number of regulatory bodies, that deal with


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environmental impact as well as health and safety. Irrespective of the efforts made by

many companies to put in place an effective maintenance and safety culture, an

incident occurs that often involves a massive loss of life and property and leaves

many devastated and fearful of the possibility that it may happen again.

The consequence of poor maintenance practice stems even further; Steve Sonnenberg,

president of Emerson Process Management states, “Chief executives are seeing the

need to better manage physical assets for improved profitability.” He goes on to

explain that “With the right strategy, the typical $1 billion USD plant can save $12

million or more annually in maintenance costs – not including the corresponding

operational and production benefits from reduced downtime.”

Boschee (2013) compares the US industrial average downtime, which ranges from 3%

to 5%, with that of oil and gas industry’s, which have an estimated downtime ranging

from 5% to 10%. This indicates a need for improvement in reliability and

maintenance of facilities, equipment, and processes. Robert MacArthur, head of ABS

Group’s asset and maintenance optimization practice, states, “I have been on offshore

platforms that were in a crisis mode of operation, running at 30% unplanned

downtime.” He goes on to estimate that the oil and gas industry may also fail to meet

high standards for another key performance indicator (KPI) – assets meeting their

engineered life expectancy. He explains that the “Midstream and Downstream asset

life expectancy is about 65%, but offshore is estimated to be somewhat lower,” This

begs the question, why is there a significant result of poor maintenance in the offshore

industry?

The Offshore industry is a large and diverse sector that has seen rapid growth since

the very first platform was installed in 1947. These developments are evident

particularly in the exploration and development of offshore oil and gas fields in deep

waters. According to the international Energy Agency around 30% of the 85 million

barrels per day of oil consumed are sourced from offshore oil wells with a tendency to

increase. The offshore output has more significance for those outside the organization

of the petroleum exporting countries causing them to rely primarily on production.


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The industry faces a challenging situation in maintaining a level of production at

isolated and often harsh locations as is common offshore. Maintenance is of utmost

importance not only in order to achieve prolongation of the life of platforms, but also

for environment and for general health and safety of personnel aboard the not easily

accessible oil platforms. According to Lo (2016), there has been a major decline in

production efficiency and lost revenues. He makes reference to a 2014 report

published by consulting firm Mckinsey & Company and cited data from the UK

Department of Energy and Climate Change, that states that the production efficiency

on the UK Continental Shelf (UKCS) had declined from 81% in 2004 to 60% in 2012.

It can be understood that the challenging conditions in certain offshore sites directly

affect the maintenance strategy implemented at those sites. Craig Wiggins, head of

UK maintenance, modifications and operations for oilfield services company Aker

solutions explains that the weather conditions on offshore sites can be very difficult.

“Poor weather often disrupts travel and causes logistical challenges as well as

increasing HSE risks.” These harsh weather conditions often affect the equipment of

offshore platforms causing a reduction in reliability and increasing the frequency of

required maintenance. (Maybe add some more on equipment)




industry. An improper selection can have a detrimental effect on a company due to an

increased operating budget and unplanned maintenance costs. For this purpose it is

rather important to consider a number of criteria such as safety, cost, added value,

mean time between failures (MTBF), and mean time to repair (MTTR). When

reviewing maintenance procedures, management is typically asked to select the best

maintenance policy for each piece of equipment or system from a set of alternatives.

For example, corrective, preventative, opportunistic, condition based, predictive

maintenance, etc. This selection process is dependent on a number of criteria; the

decision will affect the allocation of resource, technology selection, management and

organization process, etc. Therefore, In order to select a suitable strategy, it is

necessary to make a decision based on facts. Decision-making process and judgment


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regarding selection of maintenance strategy are often discontinuous, complex and

unstructured (Hajshirmohammadi and Wedley, 2004). To solve this problem several

decision approaches have been developed. Almeida and Bohoris (1995) deliberate the

use of a decision making theory to maintenance, paying close attention to multiple

utility theory. Triantaphaphyllou et al. (1997) suggests using an analytical hierarchy

process that takes into consideration only four maintenance criteria: cost, reparability,

reliability and availability. The Reliability Centered Maintenance is a widely utilized

maintenance policy selection that has had much success in the offshore industry.

Rausand and Vatn (2008) suggest that a major advantage of the RCM analysis process

is a structured, and traceable approach to determine the optimal type of preventative

maintenance (PM). Achieved through a detailed analysis of failure modes and failure

causes. Bevilacqua and Braglia (2000) presented an application of the Analytical

Hierarchy Process (AHP) for maintenance strategy selection in an Italian oil refinery

processing plant, combining many features which are important in the selection of the

maintenance policy: economic factors, applicability and costs, safety, etc. Using this

approach, the selection of a maintenance policy can be accomplished by combining

qualitative and quantitative considerations in a systematic framework.

1.1. Shell

Shell is an Anglo-Dutch multinational oil and gas Company, with its headquarters in

the Netherlands and integrated in the United Kingdom. It is recognized as the seventh

largest company in the world, in terms of revenue as of 2016. As of 2013, shell’s

revenue was equal to 85.4% of the Netherlands $555.8 billion GDP; furthermore

they’re one of the world most valuable companies. With operations in over 90

countries, producing around 3.1 million barrels of oil equivalent per day and have

44,000 service stations worldwide.


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1.2. Problem Statement and Scope.Based on the information supplied in the background, it is clear that an optimal

maintenance strategy is required. However, there is limited research on the

effect extreme environments have on the maintenance strategy in the offshore

oil and gas industry. In offshore oil production preventative maintenance is

recognized as one of the major activities in maintaining the highest output of oil

produced at a low cost. The challenge in the offshore industry is the appropriate

preventative maintenance/inspection intervals of offshore platforms, and even

more so platforms in extreme conditions. The offshore industry recognized that

the predicted structure loads and its effect as well as the resistance of a platform

would be subject to uncertainties. The harsh environment creates the need for a

specialized logistic and maintenance strategy capable of overcoming the

difficulties. Factors such as, corrosive environments, cold or hot temperatures,

high pressures, difficult accessibility, etc. are all critical factors when developing

a suitable and cost-effective offshore maintenance and support strategy. This

strategy will take into consideration the environmental influence on

performance of maintenance activities in order to guarantee the shortest

possible downtimes and less costly intervention services.

This study focuses on the effects a challenging environment has on the

maintenance strategy developed in the offshore oil and gas industry. Interviews

with Maintenance and Inspection staff from Shell Assen as well as intensive

research have been carried out. Due to the information obtained and significant

corrosion issues dealt with offshore, the maintenance strategy is developed for a

fixed offshore platform located in a corrosive environment. Using the

information obtained from the investigation, a suitable maintenance strategy is

developed using the Analytic hierarchy process (AHP).


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1.3. Aim and objectives.

The aim of this research is to integrate the Analytical Hierarchy Process (AHP), to

select the most appropriate maintenance strategy for a challenging environment faced

by offshore platforms. Whilst providing new insight into the capability of the AHP

methodology.

In order to achieve this aim:

1. Explore the challenges met in the offshore environment.

2. Examine the capabilities of the AHP methodology.

3. Research the maintenance strategies utilized on an offshore platform.

4. Investigate the critical equipment on an offshore platform.

5. Interview offshore maintenance and inspection supervisors at on oil and gas

company. (Shell Assen)

1.4. Research questions. The following research questions were framed in order to fulfill the aim of the

research.

RQ1: What are the critical maintenance issues that occur in an extreme

environment on an offshore oil platform?

In an extreme offshore environment, maintenance issues are a major challenge. With

the temperature extremes and conditions faced in places such as the North Sea, Arctic,

and other equatorial settings, the challenges of operating in an offshore setting

increases. Hence, it is vital maintenance personnel are aware of the possible critical

maintenance issues a platform may run into in specific environments, in order to be

better prepared and avoid unplanned maintenance.


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In seeking answers to the major question the study will also address the following

sub-questions:

RQ 2: What current maintenance strategies exist for extreme environments?

Extreme environments are faced by many structures or different equipment’s, such as

marine vehicles utilized in sub sea functions, wind turbines, etc. An awareness of the

possible strategies used to counter similar maintenance issues confronted in different

industries is of great significance in order to identify capable strategies.

RQ 3: What challenges are faced in an offshore environment?

The demand for energy, together with the lack of supplies of traditional fossil fuels

specifically in locations where they are easily accessed, has pushed oil and gas

industry to explore new geographical areas. This search has progressed towards some

of the earths most remote, extreme and vulnerable environments where temperature,

water and drilling depths have all been altered dramatically.

1.5. Delimitations

The research conducted focuses on the maintenance of the offshore platform in

extreme environments. This scope has been to provide a suitable maintenance strategy

using the Analytical Hierarchy Process (AHP). The researcher has limited the

dissertation to case studies and interviews due to time constraints involving company

clearance to obtain relevant data showing downtime and maintenance issues on an oil

platform.

1.6. Structure of paper

Chapter 2 presents Literature review based on the aim of research and methodology.

Chapter 3 offers a brief overview of the offshore oil and gas industry. Chapter 4


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summarizes the methodology utilized in the dissertation as well as findings from the

methodologies carried out. Then, Chapter 5 presents the data analysis section, where

the steps, calculations and results are illustrated. Finally, in chapter 6, the discussion,

conclusion as well as further work obtained from the conducted research is presented.


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CHAPTER 2

LITERATURE REVIEW

This section contains a review of state of literature for the topics that will be

presented in the thesis. The topics addresses the influence of the uncertainty caused

by offshore environmental challenges as well as the proposed method for optimizing

offshore platforms. It also contains a review of studies analysing the Swiss cheese

model, a safety critical model developed my James Reason.

2.1. Challenges met in an offshore environment.

Studies have shown that offshore industry face regular engineering and functional

challenges due to its harsh offshore environments.

The operations of the offshore industry are quite complex (Omoh and Haugen, 2013)

and the growing offshore sector presents a series of on-going challenges (maritime).

Patrick Philips (2015) analogy states that " Onshore is the mission control centre and

offshore is the space shuttle". The offshore and onshore models operate in contrasting

work environments (Patrick and Philip, 2015).

There are major challenges that has to be overcome " to ensure the space shuttle and

their control centre are working in tandem"

2.1 A. Structural damage

“The main hazards on offshore installations are the process fluids and processing

operations, the sea environment, and the process links between the reservoir and other

installations.” (Khan and Amyotte, 2002). Concluding that, “Little can be done to Nnaemeka NwogbeS1538433MSc Mechanical Engineering with Manufacturing.Glasgow Caledonian University

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eliminate or reduce the environmental hazards, except building the installation

onshore...” The authors objective is to present a complete picture of inherent safety

application in offshore oil and gas activities. They determine that the elimination of

hazards on an offshore facility will be met with resilient difficulty because the hazards

are related directly to the function of the facility. “Some important design

considerations are peak loads created by hurricane wind and waves, fatigue loads

generated by waves over the platform lifetime and the motion of the platform.”

(Sadeghi, 2007). Furthermore Sadeghi (2007) stressed that the hazards in the offshore

industry are predominantly functional.

Mansfield (1992) analyses environmental effects on structural integrity. In

relation to onshore environments, Mansfield indicates that “Onshore the relevant

building regulations and experience should ensure adequate design for normal

and exceptional environmental loads such as snow and wind loadings.” In

comparison to the offshore environment he reiterates, “Offshore the greater

severity and uncertainties of environmental conditions place a high demand on

the structures and their foundations.” Bar-Cohen and Zacny (2009) touch on

structural threats generated by the offshore environment “The seafloor represents

some of the most extreme environments for drilling on earth.” They justify this

statement by describing the seafloor as a combination of high pressures and

temperature extremes in a corrosive and electrically conductive medium. Dey et al.,

(2004) makes reference to frequent corrosion from recurrent contact with seawater,

“The chemical reaction between the pipe metal and the seawater causes an

external corrosion.” This ties in with the functional hazards mentioned by Khan

and Amyotte as described above in paragraph 2.1a. (2002). Dey et al., (2004)

reiterated that external erosion is a non-malicious damage. “ Which is caused by

solid substances in the sea water when they come in contact with the pipelines.”

(Dey et al., 2004).

2.2 B. Logistic challenges

“Logistics typically refers to activities that occur within the boundaries of a single


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organization.” (Hugos, 2011). Hugos goes on to define the activities that occur within

an organization. “ Also, traditional logistics focuses its attention on activities such as

procurement, distribution, maintenance, and inventory management.” That being said,

“Logistical planning of the offshore supply chain can be a real challenge. Multiple

disruptions and incidents may happen in every state without the planners being able to

foresee situations that may arise.” (Oleivsgard, 2013). “Logistics management of

maintenance is a very critical task in the offshore wind energy industry. It also

becomes more crucial for wind farms located in cold, icy or remote areas where the

accessibility for maintenance is restricted.” (Shaifee, 2014). “Any failure to deliver

proper maintenance logistics due to lack of spare parts, unavailability of means of

transportation, or insufficient staffing may adversely affect the wind farm availability

and thereby reducing power output as well as profitability.” (Shaifee, 2015). Lindqvst

and Lundin, in their study on spare part logistics and optimization for wind turbines

(WT) state that “Inadequate spare part stocks can lead to WT unavailability and loss

of revenue if subsystems or items fail and cannot be replaced.” (Lindqvst and Lundin,

2010). They suggested that “ when a spare part is needed but missing in stock, it has

to be ordered from a supplier. Depending on the lead-time of the spare part this causes

operational downtime.” (Lindqvst and Lundin, 2010). Nadili (2002) examined the

logistical as well as inventory challenges of floating offshore wind farms based on

data of components in a wind turbine. (Nadili, 2002) concluded that, available spare

part is one challenge in terms of providing flexible solution to ensure a short lead-time

for spare parts delivery. “The availability of onshore wind turbines is typically in the

range of 95-99% while for early offshore projects an availability as low as 60% has

been observed at some wind farms due to serial failures and harsh weather

conditions.” (Besnard, 2013).

From the literature supplied the authors agree that the offshore environment is one

plagued with uncertainties. These uncertainties have a negative effect on both the

offshore structure and logistics of the industry.


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2.2. Selecting a maintenance approach using AHP

multiple criteria decision-making.

“The AHP is a method that derives ratio scales from reciprocal comparisons. It is a

method of breaking down a complex situation into its component parts, arranging

these parts, or variables, into a hierarchic order, assigning numerical values to

subjective judgments on the relative importance of each variable, and synthesizing the

judgments to determine the overall priorities of the variables.” (Labib et.al, 1998).

However, Studies on maintenance systems in practice show that some managers are

unaware of the different types of maintenance policies (Shorrocks and Labib, 2000)

and selection methods.

Labib et.al. Propose “a three stage system that can handle multiple criteria decision

analysis, conflicting objectives, and subjective judgments. Moreover, the

methodology facilitates and supports a group decision-making process. This

systematic, and adaptable, approach will determine what specific actions to perform

given current working conditions.”Arunraj and Maiti (2010) used AHP and goal

programming to select a maintenance policy in a chemical factory. They concluded

that, by choosing risk as a criterion, predictive maintenance is favored as a periodic

maintenance strategy. Likewise, when cost is chosen as a criterion. Additionally,

Triantaphyllou et al. (1997) proposed using the AHP system primarily with respect to

the four criteria of cost, reliability, repair capability and availability.

“In the conventional AHP, the pairwise comparison is made by using a ratio scale.

Even though the discrete scale has the advantages of simplicity and ease of use, it

does not take into account the uncertainty associated with the mapping of one’s

perception (or judgment) to a number.” (Erkayman et.al. 2012). Deng (1999)

suggests a fuzzy approach to tackle the uncertainty and inaccuracy of human

behavior. Wang et.al. (2006) Also proposes a fuzzy AHP approach to mitigate the

“imprecise judgments of the decision makers…” Although, a new fuzzy prioritization Nnaemeka NwogbeS1538433MSc Mechanical Engineering with Manufacturing.Glasgow Caledonian University

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method is deduced “In order to avoid the fuzzy priority calculation and fuzzy ranking

procedures....”

Pariazar et.al. (2008) Illustrates the use of an AHP improved by the Rough set theory

to eliminate the inconsistency commonly existing in the AHP method. They consider

the use of the concept of attribute significance in rough sets theory proposed by Wang

(2001) to eliminate evaluation bias problem in AHP. Pariazar et.al. Makes use of a

case study to demonstrate the application of the various steps of the proposed

methodology.

Zaim et.al. (2012) Investigates, two of the commonly utilized methods for decision-

making, namely the Analytical Network Process (ANP) and the Analytical Hierarchy

Process (AHP), are used for the selection of the best maintenance policy. He

determines that, “The ANP method is useful for getting more accurate and effective

results in complex and crucial decision making problems.” However, Bevilacqua and

Braglia (2000) describe an application of the Analytical Hierarchy Process (AHP) for

selecting an ideal maintenance strategy for a major Italian oil refinery. They intend to

improve the effectiveness of the AHP methodology by coupling the AHP

methodology with a sensitivity analysis; this is a determination technique, used to

conclude if an independent variable will impact a particular dependent variable under

a given set of assumptions.

From the Literature supplied, it is clear that the AHP method can be implemented

using different schemes to better select a suitable maintenance strategy. The authors

agree that the uncertainty created by the decision maker will upset the effectiveness of

the AHP method. Additionally, the selection of the criterion is based on the industry.

Nevertheless, cost is a likely to be considered.

2.3. Maintenance strategy utilized on an offshore oil

platform


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Here papers relating to the maintenance strategies used in the offshore oil and gas

industry will be reviewed. Some of which include case studies that exemplify

maintenance strategy applications on static equipment’s such as pipelines and

pressure vessels and rotating assets such as pumping systems and certain topside

process components.

According to Mandal and Syan (2016), The Oil & Gas industry is a case that requires

an industry specific maintenance approach. “Mainly the upstream gas industry can

make significant headway in asset maintenance by adopting philosophies and

strategies, especially with respect to offshore platforms...” (Alsaidi et al., 2014).

Alsaidi (2014) goes on to suggest, “Present maintenance strategies are not

commensurate with ever increasing magnitude of complex equipment maintenance.”

The author proposes that by utilizing TQM (Total Quality Maintenance), equipment’s

could be well maintained and avoid running into trouble in the future. Alsaidi believes

that with a TQM environment, leadership substitutes supervision. It “eliminates

distances among departments and sections, and promotes self improvement measures

as education and training for all concerned.”

“Reliability is the probability that a product or service will operate properly for a

specified period of time (design life) under the design operating

considerations…”(Elsayed, 1996). According to (Andrews and Fecarotti, 2015) “the

reliability performance of any system is a function of its design and the maintenance

strategy employed.” Retd (2012) coincides with this and infers that, “Operation and

maintenance strategies are strongly linked to the reliability and accessibility of the

operating assets.” Rasusand (1998), discusses the Reliability centered maintenance

approach (RCM) as well as the steps in that approach. His research details the

applicability of the approach, “RCM has now been applied with considerable success

for more than 20 years; first within the aircraft industry, and later within the military

forces, the nuclear power industry, the offshore oil and gas industry, and many other

industries.”(Rasusand, 1998). In his article on Strategic Maintenance Planning, Kelly Nnaemeka NwogbeS1538433MSc Mechanical Engineering with Manufacturing.Glasgow Caledonian University

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(2006) referred to an RCM study on an oil and gas extraction platform. He explained

that the entire operation was broken into just over 100 subsystems before finding out

that 24 of the subsystems accounted for over 80% of the total maintenance man-hours

expanded. Furthermore Kelly (2016), detailed that the maintenance regime for half of

the 24 subsystems were dictated by either legislative or code-of-practice mandatory

requirements and could not be changed. This limited the RCM study to “the

remaining dozen subsystems, which accounted for approximately 50% of the man

hours.” (Kelly, 2016). He reiterated that the final result of the study revealed a

predicted workload cut in half and a reduction in the total expected maintenance

workload for the platform.

“Many companies are investigating the broader implementation of automation to

reduce the number of employees required and the risks they are subjected to in a bid

to improve efficiency and decrease human error and risks.” (Telford, 2011).

Furthermore, Telford (2011) suggests that Proactive or preventative maintenance

(PM) strategies are an essential component of an effective maintenance program. He

goes on to state “There is also an increase in un-manned facilities, particularly in

remote locations. These two trends will inevitably increase operating costs.” (Telford,

2011). “CBM strategies are currently a major focus of maintenance and maintenance

management research due to the aforementioned trends and challenges, as well as

increased complexity in industrial technologies.” (Swanson, 1997). “The PM strategy

known as condition-based maintenance (CBM) provides a dynamic understanding of

equipment condition while in operation and is used to predict failure in mechanical

systems through fault diagnosis from condition monitoring signals using diagnostics

and prognostics.” (Heng et al., 2009).

Gola and Nystad (2011) consider a practical case study concerning maintenance of

choke valves in offshore oil platforms. They aim to develop a condition monitoring

system capable of providing reliable calculations of the erosion state based on

collected measurements of physical parameters related to the choke erosion. As well

as to develop a prognostic system that can accurately estimate the remaining useful

life of the choke. Padmanabhan (2009) refers to Reciprocating Compressor as “the

workhorse of refineries, petrochemical and oil production units.” The author expands


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on the implementation of the CBM approach and illustrates monitoring parameters

utilized on rotating equipment located on an oil platform.

“Any downtime on offshore oil and gas platforms is expensive, which is why planned

maintenance is essential” (Marathon Oil UK). A case study was used to illustrate

maintenance performance on the three platforms utilizing the new technology. The

case study report explains that “The system carries out routine daily checks that flag

up any delays or problems, allowing planners to reschedule work as and when

required to maximize efficiency, safety and resources” (Marathon Oil UK). Marathon

Oil UK’s drive to improve efficiency in maintenance planning as well as managing

unexpected complications led to the invention of an advanced solution based on

Microsoft Project Server and SharePoint technologies.

2.4. Application of the Swiss Cheese Model

Articles explaining the application of the Swiss cheese model are presented and

analyzed. Modifications to the model to fit different industry specifications are also

reviewed.

The Swiss cheese model is an organizational model used to analyze and represent the

causes of systematic failures or accidents (Reason, 2000).

“In practice however, such accident modeling based on the Reason model proved

difficult to apply, resulting in an increasing amount of varieties and simplifications.”

(Sklet, 2004). “Most of the models restrict themselves to the work and technical

systems levels and exclude the technological nature and development of the inherent

hazards.” (Stoop and Dekker, 2010). “Much of the accident data are conceptually

flawed because of the inadequacies of underlying accident models in existing

programs.” (Benner, 1985). “Despite some criticism, the simple model has been

widely taken up in risk analysis and risk management, especially in safety critical

fields where human operators play an important role in incidents, for example, in

aviation, nuclear, petrochemicals industries and, indeed, healthcare.” (Li and

Thimbleby, 2014).


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Ayyub (2014) sates that the methodology is commonly used in aviation, engineering,

and health care, and is capable of describing a scenario that can lead to a series of

events that must occur in a specific order and manner that will ultimately result in an

accident. “The principle idea of the model basically like cheese slice, has holes of or

latent condition.” (Hassan, 2014), “If holes can be visualized and the relationship

between holes and latent conditions can become clear, then it is possible to control the

occurrence of holes. “ (Fukuoka and Furusho, 2016). The authors carried out their

research to determine the relationship between latent conditions and the

characteristics of holes by analyzing 84 serious marine accidents. In their study they

define latent conditions as the following “(1) inadequate passage planning, (2)

inadequate procedures, (3) inadequate rules or deviations from rules, (4) inadequate

human–machine interface, (5) inadequate condition of equipment, (6) adverse

environment, (7) inadequate conditions of operators, (8) inadequate communication,

(9) inadequate team work at a local workplace, and (10) inadequate management in an

organization.” (Fukuoka and Furusho, 2016).

“Reason’s Swiss cheese model was originally developed for domains such as oil and

gas, aviation, railways, and nuclear power generation.” (Beuzekon et al., 2010)

Kujath et al., (2010) present and discusses accident prevention model for offshore oil

and gas processing environments. In their study they discuss the application of the

Swiss cheese model by collecting data on offshore oil and gas process accidents in

order to compile a listing of hazards and to evaluate risk. “The predominant reported

reasons for hydrocarbon releases are: loose bolts on flanges, loose flanges, damaged

flange seals, incorrect welds, loose fittings, faulty valves, switching generator fuels,

overfilling of tanks, open access/vent/valve, safety instrumented system failures,

damaged hoses, equipment start up, seal failures, and pump over- pressure. The

reported sources of ignition are: turbine gas leak, hot manifold, short circuit due to

water ingress in electrical panel, welding and grinding, and bearing overheating.”

(Khan et al., 2010). They further state that other possible causes of accidental

hydrocarbon releases are: vibration, corrosion and release of inert nitrogen from

within a tank. Khalique (2016) explore basic offshore safety and express the

importance of incorporating asset integrity barriers, to an asset integrity management


23

system (AIMS). They suggest doing so with a Swiss Cheese Model; “ Each

component within a system whose failure can lead to an accident is referred to as a

‘safety critical element’ and therefore considered as a barrier to prevent accident.”

(Khalique, 2016). “High technology systems have many defensive layers: some are

engineered (alarms, physical barriers, automatic shutdowns, etc.), others rely on

skilled individuals (anaesthetists, surgeons, pilots, control room operators, etc.), and

yet others depend on procedures and administrative controls.” (Beuzekon et al., 2010)


24

CHAPTER 3

OVERVIEW

This chapter covers a brief summary of the Oil and Gas industry. Whilst focusing on

the offshore industry, its platforms and the critical equipment’s located aboard the

offshore structures.

3. Oil and Gas IndustryThe oil and Gas industry is vital to the economy and to our everyday life. According

to UKOG oil has become the world’s most important source of energy since the mid-

1950s. As it continues to fuel our cars, heat our homes and cook our food, just to

name a few. It is a large and diverse industry made up of three integral sectors:

Upstream, Midstream and Downstream.


25

Figure 1: Illustration of the three integral sectors of the Oil and Gas Industry.

(https://media.licdn.com/mpr/mpr/shrinknp_800_800/

AAEAAQAAAAAAAAXqAAAAJDVhYTgwOGUyLTgxNjEtNDZkOS04MGFk

LWE3OTA3Y2I3YzdlMg.jpg)

Midstream

The mid stream sector includes some parts of the upstream and downstream sectors,

but its main function is the gathering and storing of the unrefined oil and natural gas

also referred to as the raw produced products. They are gathered and stored before

being transported by pipeline or boat to refineries.

Downstream

The Down stream sector is also referred to as the refining sector. Here the refining of

crude oil and the selling and distribution of natural gas and products attained from

crude oil, takes place. The downstream sector is made up of oil refineries,

petrochemical plants, petroleum distribution outlets, retail outlets and natural gas

distribution companies. This sector is in direct link with the consumers.

Upstream

The upstream sector also known as the Exploration and Production (E&P) sector is

the part of the industry that deals with obtaining the crude oil and natural gas from

under ground or underwater (Onshore and Offshore) and bringing it up to the surface.

It involves exploration of potential oil and gas fields including the drilling and

operation of those wells. This sector is pivotal to the structure of the industry due to

its rewarding yet complex and risky quality. This sector is greatly affected by external

elements such as, political instabilities, international conflicts, and even seasonal

weather patterns.

3.1. Offshore IndustryMore than two thirds of the earth’s surface is covered in water. This begs to reason

that oil and gas are found and produced not only on land but also at sea. According to


https://media.licdn.com/mpr/mpr/shrinknp_800_800/AAEAAQAAAAAAAAXqAAAAJDVhYTgwOGUyLTgxNjEtNDZkOS04MGFkLWE3OTA3Y2I3YzdlMg.jpg



26

EDP Solutions, in the oil and gas industry, “Offshore” refers to the development of oil

fields and natural gas deposits under the ocean. Offshore oil and gas production,

Involves extracting oil and gas from beneath the sea, it is a critical component of the

world’s energy supply. “Offshore has provided nearly 70% of the major oil and gas

discoveries worldwide in the last decade.” (Sandrea and Sandrea, 2010). This

industry is responsible for twenty percent of oil reserves and 45% of gas reserves.

According to the Organisation of Economic Co-operation and Development, in 2014

Offshore oil production amounted to 21.5 million barrels per day and offshore gas

production amounted to 90 billion cubic feet per day (BCFD) which in turn accounted

for approximately one quarter of the worlds oil and gas production. In Planete

Energies report “The challenges of Oil and Gas Production” (2015), it is implied that

the offshore industry accounts for 30% of global oil production and 27% of global gas

production. The report suggests that these percentages have remained stable since the

early 2000s and are unlikely to change any time soon.

3.1.1. Offshore Exploration and Planning.The purpose of exploration is to identify commercially viable resources of oil and gas.

Locating such reservoirs and estimating the likelihood of them being a possible

resource is a time consuming and complicated process. This process requires the use

of a range of techniques, such as deep and shallow geophysical (seismic) surveys,

shallow drilling and coring, aero-magnetic/gravity surveys and exploration and

appraisal drilling. The most popular combination utilized by most oil companies is,

seismic surveys and exploratory drilling.


27

Figure 2: Diagram showing Seismic survey.

(https://krisenergy.com/images/offshore%20seismic%20survey.jpg)

Once exploration discovers oil and gas reserves with a prospect for a good economic

return, the next step is to figure out the best way to extract it. The target location for

drilling is determined, specific objectives are devised early in the planning phase

where the nature and cost of the well to be drilled is defined. This is a long and

strenuous process that can take even longer than the exploration process. These

objectives determine how long the well will take, the range of tests required as well as

the surface hole location (rig positioning). Before a well is drilled information is

gathered on the stability of the surface sediments and potential subsurface hazards.


https://krisenergy.com/images/offshore%20seismic%20survey.jpg

28

Furthermore, before a drilling operation can be scheduled the following are taken into

account:

• The weather and current conditions

• Seasonal environmental conditions and license conditions

• Availability of rigs

• Commitments made to government

• Other company internal constraints and objectives

(Department of Trade and Industry, 2001).

3.1.2. Offshore Production.Before the production process can begin a well must be drilled to reach the reservoir.

This process is specifically carried out by a mobile drilling platform. After the drilling

platform is removed a production platform is then installed over the borehole using a

barge equipped with heavy lift cranes. The oil and gas are extracted and then

processed.

Extraction

The retrieval of oil and gas from deposits deep in the sea floor requires the use of

sophisticated equipment and highly skilled personnel. Offshore oil extraction is

carried out using offshore drills and involves the operation of wells on the continental

shelf; this sometimes occurs in waters that are hundreds of feet deep. Once the well

has been drilled, a production casing is installed. This casing is fixed to close the well

and control the flow of petroleum. Explosives are then sent below the ground to crack

the production casing at different depths allowing oil and gas to enter the well in a

controlled manner and moved to the surface at a reasonable pressure. When initially

drilled, the pressure produced by the reservoir is enough to transport oil to the surface

but as time passes the pressure drops and pumps are needed for this process to

continue. Different methods are used to the pressure and flow of oil to the surface;

sometimes water or gas is pumped into the reservoir, or in some cases steam is sent

down to the well to heat the petroleum. Because the liquid brought up to the platform


29

is a mixture of crude oil, natural gas, water, and sediments. Offshore processing of the

raw material takes place.

Production

The aim of the processing is it to convert raw produce or well fluid into a marketable

product (Crude oil, gas, and condensate). Initially, Subsea hydrocarbon equipment

was only utilized for oil extraction. Gas was separated from liquid hydrocarbons

under water, and then the extracted liquid hydrocarbons were pumped to the surface

and gas also under its own pressure. Currently, offshore production technologies are

highly capable. The offshore production process is made up of a number of operations

that allow for a safe and reliable production of petroleum and natural gas from

flowing wells. The fundamental operations that are carried out on an offshore

platform include:

Produced hydrocarbon separation;

Gas processing;

Oil and gas export;

Well testing;

Produced water treatment and injection;

Seawater lift for cooling duty and injection; and

Utilities to support these processes.

(Azeri et al., 2004)

The figure below shows operations in different stages.


30

Figure 3: Production process

(http://www.offshorepost.com/resource/production-process-overview/)

3.2. Offshore platforms. “Around the world, until 2013, there are more than 6500 offshore oil and gas

installations distributed in about 53 countries.” (Misra, 2016) Offshore platforms are

massive structures equipped with facilities to drill and extract oil and gas from wells.

With onshore drilling the ground provides a platform from which to drill, however at

sea an artificial drilling platform must be constructed. That being said, it should be

noted that an oil rig and oil platform are completely different. An oil rig is in most

cases is part of an oil platform that deals primarily with drilling and completion of

wells whilst an oil platform covers many more facilities. Including having an oil rig,

it includes a wellhead, helipad, utility systems, quarter etc. (Dalvi, 2015).

3.3.1. Platform Type and DesignAccording to Sammie (2016) the systems and equipment installed in an offshore

platform depends on its planned functions and crude oil type or composition.

Furthermore, is the offshore platform is intended for oil or gas plants? Does it perform

any processing or is it simply a wellhead platform? Does it also include an enhanced

oil recovery (EOR) package? Is it a living quarter platform? These facilities are

located on the topside of the offshore platform as seen in Figure 2. Because the

Topside is designed to accommodate wellheads, trees, piping manifolds, wellhead

control panel, and any other required facility, the size of the platform depends on

those facilities required.

Many permanent offshore platforms are equipped with a full oil production facility

onboard. It is in this facility that the processing of production fluids from oil wells is

carried out. A process system can be located on a production or wellhead platform,

the main intention of the system is to separate the key components such as; gas, oil

and water or to guide crude flow by pressure, temperature and volume regulation.

Before they are prepared for export to offshore or floating loading facilities.


31

Figure 4: An example of offshore platform structure and its facilities. (Northwest

Hutton field Platform).

(http://www.offshore-technology.com/projects/hutton-field/hutton-field2.html)


http://www.offshore-technology.com/projects/hutton-field/hutton-field2.html

32

The type of platform used depends primarily on the depth of the water and the

environmental conditions. Drilling for oil and gas offshore in most cases hundreds of

miles away from land presents a number of challenges compared to drilling onshore;

where vast water depths does is not influence onshore platforms. The platform and

rigs used in shallow waters are very different from those used in deep-water. Figure 3

illustrates the different platforms and rigs available and the depths at which they are

used.

Figure 5: Offshore oil platforms designed for different water depths.

(http://cdn2.hubspot.net/hubfs/514555/images/blog/offshore-cables-topside-

modules1.jpg)


http://cdn2.hubspot.net/hubfs/514555/images/blog/offshore-cables-topside-modules1.jpg

http://cdn2.hubspot.net/hubfs/514555/images/blog/offshore-cables-topside-modules1.jpg

33

According to the US Mineral Management Service (MMS), the water depth can be

classified as shown below.

Shallow water < 350 m

Deep water < 1500 m

Ultra deep water > 1500 m

There are two types of offshore drilling rigs and platforms. They are known as a

moveable (Floating) or fixed platform. Offshore platforms can be classified as fixed

platforms, compliant towers, jack-up platforms, semi-submersible platforms, tension-

leg platforms (TLPs) and SPAR platforms. Due to the scope of this research the focus

will be on the Fixed platform.

Fixed Platform

A fixed platform is a type of offshore platform capable of working in depths of up to

1,500 feet, which offers stability in place of mobility. They are costly to build and

often require a large oil discovery to justify their construction. A fixed platform can

be described as being made up of two main components; the “substructure” and

“Superstructure”. The “Superstructure” which is also referred to as the topside, acts as

home to drilling rigs and production facilities such as gas turbines, generating sets,

pumps, compressors, a gas flare stack, revolving cranes, survival craft, helicopter pad

and also offer accommodation facilities for crew. The tops side can weigh up to

40,000 tonnes. That being said it is only expected that the base structure also known

as the “substructure” is designed to handle such a considerable weight.


34

Figure 6: Fixed Concrete Offshore Platform.

(https://wikiocean.wordpress.com/2012/02/13/troll-a-platform-the-tallest-

construction-ever-moved-by-mankind/)

The fixed platform is typically built on steel or concrete legs that are fitted and

supported by the seabed. With some concrete platforms, the weight of the legs and

seafloor platform is so great that it allows the platform to rest on its on mass instead

of being attached to the seafloor. In most cases a fixed offshore oil and gas production

platform is made up of steel legs also known as a “ steel tubular jacket”.


https://wikiocean.wordpress.com/2012/02/13/troll-a-platform-the-tallest-construction-ever-moved-by-mankind/

https://wikiocean.wordpress.com/2012/02/13/troll-a-platform-the-tallest-construction-ever-moved-by-mankind/

35

Figure 7: Fixed steel “Jacket” Platform.

(http://www.esru.strath.ac.uk/EandE/Web_sites/98-9/offshore/rig.jpg)

(http://www.2b1stconsulting.com/wp-content/uploads/2012/08/

Jacket_Platform.jpg)


http://www.2b1stconsulting.com/wp-content/uploads/2012/08/Jacket_Platform.jpg

http://www.2b1stconsulting.com/wp-content/uploads/2012/08/Jacket_Platform.jpg

http://www.esru.strath.ac.uk/EandE/Web_sites/98-9/offshore/rig.jpg

36

3.4. Critical equipment in the Oil and Gas Industry.“An effective maintenance program is founded on a critical equipment list developed

through a rigorous analysis of the probability of failure and the consequences of

failure.”(Townsend, 2011). According to Alexis and Rounds (2016) critical

equipment is any equipment or a machine that is capable of significantly impairing

the ability for a business to safely meet its objectives, adversely affect quality levels

and violate environmental standards of the business organization.

Critical equipment in the oil and gas industry can be categorized into two main

sections; Safety critical and Operation critical.

3.4.1. Safety Critical. Health and Safety is an important factor for every industrial sector, but this is

particularly so for the offshore oil and gas industry where there is high potential for a

major accident. The HSE (Health and Safety Executive) describe the safety critical

Elements as “parts of an installation and such of its plant (including computer

programmes), or any part of thereof-

(a) The failure of which could cause or contribute substantially to; or

(b) A purpose of which is to prevent, or limit the effect of a major accident. “

(HSE, 2016).

What this implies is that any structure, plant equipment, system; including computer

software or component part whose failure can contribute to a major accident or impair

or limit the effect of a major accident, is classified as safety critical. In the figure

below reference is made to the Integrity Barrier “Swiss Cheese” Model of Shell EP.


37

Figure 13: Integrity Barrier “Swiss Cheese” Model of Shell EP

In the early nineties, James Reason developed the Swiss cheese model. The model

acts as an illustration for accident causation utilized in risk analysis and risk

management, in sectors such as aviation, engineering, healthcare, and as the standard

behind layered security. The ideology is a comparison of human systems to multiple

slices of Swiss cheese, stacked side by side, in which the different layers represent the

types of defense put in place to relieve the risk of a threat becoming reality. In theory,

a lapse or weakness; which are characterized, as the holes in one defense should not

allow a risk to materialize, because another defense also exists, to prevent a particular

point of weakness. The original Swiss cheese model can be seen in Appendix A.


38

The model in Figure 12 is an incorporation of that model to the safety critical

elements at shell. The safety critical elements are listed under each threat and

escalation category

3.4.2. Safety critical equipment

The SCE (safety critical elements) in figure 12 have been divided into “Hardware

barriers”: Structural integrity, Process containment, Ignition control, Detection

systems, Protection systems, shutdown systems, emergency response and life saving.

According to the “Safety Critical Element Interpretation Document NAM Asset Land”

and “ONEgas Asset East (NL)”, each element has been categorized under certain

discipline of accountability. For the purpose of this study the main focus will be on

the mechanical safety critical equipment’s on an offshore production platform.

Hardware Barrier: Structural integrityStructural integrity is described as the ability of an item to hold under a constant

load. Dr. Steve Roberts describes it as the “the science and technology of the margin

between safety and disaster.”

Heavy lift crane

A heavy lift crane is simply a type of machine equipped with a hoist rope, wire rope

or chains, and sheaves capable of transporting and handling items that typically weigh

over 100 tons and of widths and heights of over 100 meters. In the offshore industry

these include parts of rigs and production platforms. Overhead cranes or any

mechanical handling equipment at an offshore location are safety critical equipment

since failure could cause or contribute to a major accident or harm personnel.

“Dropped objects from cranes are one of the major risks on offshore installations.”

(Dropsafe, 2016)


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Figure 14: A Heavy Lift Crane

(http://www.cargotec.com/en-global/newsroom/media-bank/solutions/

HighResolutionImage/hires_offshore-2012-05.jpg)

Hardware Barrier: Process ContainmentProcess containment in the oil and gas industry indicates equipment that contains

dangerous substances, such as highly toxic and flammable properties. These

containment systems are considered safety critical if they provide primary

containment under normal operating conditions and if failure directly causes a loss of

containment into the atmosphere or into non-hazardous system, resulting in the

release or over pressurization which may in turn result to a fire or explosion with the

potential to cause death or serious harm and a serious environmental impact.Nnaemeka NwogbeS1538433MSc Mechanical Engineering with Manufacturing.Glasgow Caledonian University

http://www.cargotec.com/en-global/newsroom/media-bank/solutions/HighResolutionImage/hires_offshore-2012-05.jpg

http://www.cargotec.com/en-global/newsroom/media-bank/solutions/HighResolutionImage/hires_offshore-2012-05.jpg

40

Pressure Vessels

Pressure vessels are normally designed, constructed and installed according to the

recognized pressure vessel code or standard. They contain hydrocarbons, chemicals or

other substances that are required under normal operating conditions. An Offshore

platform typically has a number of safety critical pressure vessels. Such as, slug

catchers, separators and flare knock out drums and flare stacks.

Slug catcher

A slug catcher is a static equipment that plays an important role in oil production. It is

an essential equipment located at the receiving terminal of a multiphase-flow

processing plant. It is used to accumulate liquids that have settled in flow lines to

prevent an overload in the plant.

Figure 15: Slug catcher

(http://www.europipe.com/fileadmin/europipe-modern/images/europipe-slug-catcher-

grafik.png)


http://www.europipe.com/fileadmin/europipe-modern/images/europipe-slug-catcher-grafik.png

http://www.europipe.com/fileadmin/europipe-modern/images/europipe-slug-catcher-grafik.png

41

Separators

An oil and gas separator is a cylindrical pressure vessel used to separate oil, gas and

water from a well stream. A separator can be vertical or horizontal and classified as a

two-phase or three-phase separator. A two-phase separator deals only with oil and

gas, while the three-phase deals with oil, water and gas.

Figure 16: Illustration of a three-phase Horizontal Separator

(http://www.piping-engineering.com/crude-oil-processing-offshore-

facilities.html)


http://www.piping-engineering.com/crude-oil-processing-offshore-facilities.html

http://www.piping-engineering.com/crude-oil-processing-offshore-facilities.html

42

Flare Knockout drums

A knock out drum is a crucial part of a flare system (A system that collects and

discharges gas from pressurized process safely into the atmosphere). It is located

before the flare ahead as shown in Figure 15. This process containment vessel is put

in place to prevent liquids from entering the flare stack, which in turn prevent

spewing out burning liquid into the atmosphere.

Figure 17: Flare system

(http://www.flarenotice.com/images/flaringinfo/clip_image004.png)


http://www.flarenotice.com/images/flaringinfo/clip_image004.png

43

Figure 18: Illustration of a Flare system on a platform

(http://www.thecyberhawk.com/wordpress/wp-content/uploads/2012/07/Offshore-live-

flare-inspection-3.jpg)

Heat Exchangers

Heat exchangers that contain hydrocarbons or another dangerous substance in at least

one side of the exchanger are considered safety critical. The goal is to maintain

integrity of the pressure-bearing envelope. The typical scope of a safety critical heat


http://www.thecyberhawk.com/wordpress/wp-content/uploads/2012/07/Offshore-live-flare-inspection-3.jpg

http://www.thecyberhawk.com/wordpress/wp-content/uploads/2012/07/Offshore-live-flare-inspection-3.jpg

44

exchanger is the pressure-containing envelope, that is the shell and supports and all

welded connections or tapings connected to it, including nozzles, instrument and

small-bore appendages up to and including the first mechanical joint(s).

Typical safety critical heat exchangers are process hydrocarbon heat exchangers, like

inlet gas cooler, gas or gas heat exchanger and off-gas cooler and chemical treatment

heat exchangers, like glycol dehydration systems.

Figure 19: Gas Exhaust Heat Exchanger.

(http://www.power-technology.com/features/feature109722/feature109722-5.html)

Rotating Equipment


http://www.power-technology.com/features/feature109722/feature109722-5.html

45

Rotating equipment is safety critical equipment because failure of any component can

cause a loss of containment resulting in a fire, explosion or release of a dangerous

substance with potential to cause death or serious injury to one or more persons. It

covers pumps, compressors, turbo-expanders and gas turbines for generating electrical

power. The typical scope of a safety critical pump, compressor or turbo-expander is

the pressure-containing envelope. That is the equipment shell including the suction

and discharge flanges or mechanical joints and all welded connections or tapings

connected to it, including all nozzles, instrument and small-bore appendages and

supports.

Some examples of safety critical rotating equipment are process hydrocarbon pumps,

compressors, Gas turbines, water or natural gas condensate loading pumps and

process drain pumps. These are all mechanical equipment’s that essentially move

materials by adding kinetic energy to their process. (Schematics and diagram)

Piping Systems

The idea behind a safety critical pipework is the pressure-containing casing between

the various items of equipment, i.e. all pipework, fittings, flanges, valves, instrument

tapping, instrument tubing, flexible hoses and pipe supports. Critical piping systems

will generally be those, which may contain flammable or hazardous fluids under

normal or abnormal conditions. Piping is considered safety critical if release of a

toxic material represents an immediate risk to one or more persons. A primary

element of instrumentation that is integral part of the piping system (e.g. venturi

flowmeters) and in direct contact with the hazardous medium is also classified as a

safety critical piping system.

Relief System


46

Relief systems located on safety critical process containment systems are safety

critical in Asset Land. The relief system is designed to protect equipment from over

pressurization if the process control system fails or in case of heat input from outside

to a blocked-in containment. Safety critical relief components comprise all pressure,

thermal, fire relief valves or discs (also on atmospheric storage tanks), including

associated relief pipework. Elements, which directly influence the capability of the

relief valves and/or rupture of discs, are also safety critical. These include heat tracing

of relief valve pilot lines, control valves (where the valve Cv determines the relief

valve capacity), high-pressure trips and non-return valves.

The figure below shows the schematics for the arrangement of a compress system,

including the relief systems put in place. The symbols in the PI&D (Piping and

instrumentation drawing) have been supplied in Appendix B.

Figure 20: A typical arrangement for a centrifugal compressor system.

(http://www.enggcyclopedia.com/2012/02/typical-pid-arrangement-centrifugal-compressor-

systems/)


http://www.enggcyclopedia.com/2012/02/typical-pid-arrangement-centrifugal-compressor-systems/

http://www.enggcyclopedia.com/2012/02/typical-pid-arrangement-centrifugal-compressor-systems/

47

Hardware Barrier: Protection Systems

These are systems that have been put in place to reduce the consequences of failures

by providing greater safety and protection in order to prevent loss, damage and

destruction.

Fire Water Pumps

Due to the production process carried out on an offshore process facility, extremely

reliable and effective fire fighting systems must be available. Firewater pumps, if

present are put in place to limit the effects and consequences of fires. It is a pump

system located around the platform connected to a detection system, which In the

event of a fire, open up a valve or series of valves to allow water to flow through to

the fire. Traditional, firewater pumps are conventional, vertical line shaft-pumps

driven by a diesel engine or electric motor. The reliability of a plant’s firewater

pumps is a frequent oversight; this oversight is capable of resulting in a significant

consequence. According to a Rotating Equipment consultant Amin Almasi, a

firewater pump system can account for 15 to 35 percent of insurance deficiency rating

points for a plant. With no thorough planning and the correct equipment, facilities

could see production process slowed down or stopped completely due to uncontrolled

fires leaving themselves vulnerable to high insurance costs.

3.4.3. Operation Critical.

Although there is no direct comparison between the importance of operation critical

and safety critical equipment, it is clear that due to legal requirements and regulations

safety critical equipment pertaining to the oil and gas sector must be clearly managed

and maintained. That being said, failure to properly manage and maintain operation

critical equipment has its consequences. Their availability and capacity to alter

operational efficiency is key to the success of an organization.


48

Difficulty arises in classifying operation critical equipment in the offshore industry

because they are classed based on location. A particular piece of equipment at a low

temperature environment may not stand as operation critical equipment at a high

temperature environment. According to Narayanan and Joshy, R.H. Clifton suggested

a five level priority rating based on the basis of efficient operation of the equipment

vital to the production process. That being said, Campos et al., (2015) mentions some

key operation critical equipment in the oil and gas industry. They explain that in oil

and gas facilities the pumping and compression systems require a considerably high

level of availability. Therefore faults that could result in their shutdown must be

minimized and even eliminated. Faults in the critical systems mentioned can lead to

loss in production “as large as 200,00 bbl to certain production limits.” (Campos

et.al., 2015). The issue of failure in a heat exchanger is also considered a major

concern, especially pertaining to offshore platforms as their ability to control the

crude oil temperature affects the efficiency of the separators.


49

Figure 21: Gas treatment process on a WD143 Offshore Platform.

(http://images.pennwellnet.com/ogj/images/ogj2/9632jla02.gif)

Table 1: Gas treatment controller systems

PC Pressure controller

FC Flow controller

LC Level controller

SC Surge controller

Figure 21. Illustrates an example of a production critical process where a compressor,

heat exchanger and pumps are utilized. The gas treatment process is a key step in gas

processing; the gas collected from the high-pressure separator undergoes treatment to

remove water. This involves cooling by heat exchanger and compression of the gas

before using glycol to remove any remaining moisture. This step is important in

preventing hydrate formation and corrosion within the gas pipeline.

Power generators are also key components in production on an oil platform. They

provide electrical power for all drilling operations, production operations and all of

the platform utility systems. The Rolls Royce gas turbine generator used on a shell

fixed platform costs approx. 3-4million euros to replace, and its availability is key to

the production of the platform.


http://images.pennwellnet.com/ogj/images/ogj2/9632jla02.gif

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CHAPTER 4

RESEARCH METHODOLOGY

The methodology used in carrying out the research is explained in this

chapter as well as well as a brief explanation on the findings.

4. Research Overview

In this thesis, the Multi Criteria Decision Making method based on the Analytical

Hierarchy Process (AHP), is proposed to select the most appropriate maintenance

strategy for major extreme environments faced by offshore platforms taking into

consideration the environmental influence on performance of maintenance activities.

Whilst providing new insight into the capability of the AHP methodology. The

research was conducted in response to the following research questions (1) What are

the critical maintenance issues that occur in an extreme environment on an offshore

oil platform (2) What current maintenance strategies exist for challenging

environments? (3) What are the challenges faced in an offshore environment?

4.1. Research Approach.

The research presented in this dissertation is predominantly based on qualitative data;

this form of research is specifically exploratory research. Used to gain an

“understanding of a subject and its contextual setting, provide explanation of reasons

and associations, evaluate effectiveness and aid the development of theories or

strategies.” (Office for National Statistics). Maxwell (2005) describes five scientific

goals for which a qualitative approach is suited.


51

Understanding the meaning of the events, situations, experiences and actions

the participants of the study are involved in.

Understanding the context within which the participants act and how this

context influences their actions.

Identifying unanticipated phenomena and influences, and generating new

grounded theories about the latter.

Understanding the process by which events and actions take place.

Developing casual explanations.

The Qualitative research method will consist of in-depth interviews on maintenance

and inspection staff for Shell Assen, followed by a case study based on the primary

equipment that the proposed methodology will be based on. The interview will be

carried out on both rotation and static maintenance staff including an Inspection staff

member for Shell, Assen, Netherlands. The instrument for this data collection method

is a questionnaire personally designed and generally based on a “criticality analysis”

method. Taking into account the following parameters. (1) Safety critical (2)

Production critical (3) maintenance costs (4) failure frequency (5) downtime length

The design and nature of the interview and case studies further explained in the

following section.

4.2. Research Process.

After researching existing literature based on the research questions mentioned in

section 1.4, an interview is proposed to analyze the basis and importance of

formulating a maintenance strategy suitable for a specific challenging environment.


52

4.2.1. Delphi Interview TechniqueIn-depth interviews are optimal for collecting data on individuals’ personal histories,

perspectives, and experiences, particularly when sensitive topics are being explored.

(Tripathy and Tripathy, 2015). An interview questionnaire was framed, after

researching existing literature on challenging offshore environments as well as the

maintenance strategies applied. The interview process was carried out using the

Figure 22: Delphi method framework

Delphi Method. The Delphi technique is recognized as a systematic, interactive

forecasting method, which typically utilizes a group of experts in order to answer a

series of questions in two or more rounds. The participants of the Delphi method are


53

typically experts with a professional insight on the topic. The Delphi method is

exceptionally useful in areas of limited research, since survey instruments and ideas

are generated from a knowledgeable participant pool (Hasson et al., 2000), and it is

suited to explore areas where controversy, debate or a lack of clarity exists.

The performed interview was structured according to the framework shown in Figure

22. The structure is aimed at obtaining a broad range of opinions from the experts

interviewed. The responses obtained from the first round of questions are summarized

and used as the foundation for the second round of questions. Subsequently the results

from the second round feed into the final round.

The steps carried out are presented below:

Step 1: Choose a facilitator.

The researcher in this case acted as the facilitator of the interview.

Step 2: Identify your experts.

The expert is, “ any individual with relevant knowledge and experience of a particular

topic.” (Cantrill et al., 1996). In this case the experts chosen for the panel were a

rotation and static maintenance supervisor as well as an inspection supervisor.

Step 3: Define the Problem.

This step focuses on the problem or issues the research questions aims to understand.

The experts are made aware of the problem at hand and the aim of the research. Here

the researcher explains the need for a robust maintenance strategy in a challenging

offshore environment.

Step 4: Round one questions.

General questions are asked to gain a general understanding of the experts view

relating to the problem at hand. The questions asked of the Maintenance and

inspection supervisors varied. The maintenance staff was asked (1) what environment


54

they find the most challenging in regards to maintenance issues? (2) What the critical

equipment on the platforms are? (3) What type of maintenance strategies are used on

the critical equipment’s mentioned?

Whilst the Inspection supervisor was asked to answer (1) what environment they find

the most challenging in regards to maintenance issues and inspection? (2) What

equipment requires frequent inspection? 3) What inspection strategy is employed? (4)

What other factors influence inspection?

The complete phase 1 questionnaire and response from both Maintenance and

Inspection supervisors can be seen in Appendix C.

Step 5: Round two questions.

From the response achieved from the first questionnaire, the second round will delve

deeper to clarify specific issues in order to develop a clear consensus from a common

ground. Due to the primary scope of study pertaining particularly to maintenance

strategies, the following follow up questions were asked only of the maintenance

supervisors. (1) What critical equipment experiences frequent failures/maintenance

calls in the company’s most challenging environment? (2) How long is the downtime

for the critical equipment mentioned? (3) Most expensive equipment to replace or

carry out maintenance?

The complete phase 2 questionnaire and response from both Maintenance and

Inspection supervisors can be seen in Appendix D.

Step 6: Act on findings

In this step the findings are analyzed and a conclusion is made.


55

4.2.2. Case study. These well-documented case studies indicate the effects and capabilities of corrosion

in the offshore industry.

PETRONAS

The Malaysian state owned global energy giant at the heart of B.C.’S LNG ambitions,

was informed in late 2013 that it was going through “very serious” safety and

integrity issues throughout its offshore Malaysian operations. A 732 page internal

audit presented to the senior management on Oct.24, 2013, brought attention to a

number of problems on Petronas oil and gas platforms in three major oil and gas

fields. Four of the issues were described by the auditors as being “almost certain,” if

not fixed, to cause “catastrophic” events. Including what was described as

“systematic” problems relating to the lack of staff, competence and training there

were also more than a dozen references to “severe” cases of corrosion threatening the

structural integrity of the facilities. Auditors found six “pressure vessels” – containers

that hold pressurized gas or liquid--- that had internal corrosion and had not been

inspected for at least 20 years. According to the Vancouver sun, Petronas has cited

concerns about a number of accidents and deaths since 2011, which according to a

sun source led to ordering the 2013 internal audit.

Analysis of the failure of an offshore compressor crankshaft.

Due to the detection of an oil leak on a compressor crankshaft, located on an offshore

oil and gas platform, an inspection was carried out. During the inspection of a North

Sea oil and gas platform a crack was identified on the crankshaft of a compressor. The

crankshaft had been in services for 8 months and after detection of the crack, was


56

decommissioned for a failure examination and material analysis to determine the

mechanism of failure. Localized corrosion attack, similar to pitting, was discovered

on the bulk of the crankshaft surface. Along with chlorine residue, located in the base

of the pit like features. This led to the conclusion that the primary mechanism of

failure was undoubtedly corrosion fatigue paired with torsional loading.

4.3. Validity.

The term validity describes to what extent a researcher‘s chosen method is feasible for

the studies of the intended phenomenon (Gummesson, 2000). Based on the capability

of the analytical method (AHP), in utilizing qualitative data to reach a decision, the

research methods of choice are proved valid.

4.4. Findings.

From the Delphi technique and case study utilized in this research, it was concluded

that a corrosive environment is a major challenging environment attributed to the

offshore industry. The research methodologies employed also obtained response

regarding the maintenance strategies used on certain critical equipment on an offshore

platform. It was established that RCM, Preventative Maintenance (PM), Predictive

Maintenance/Condition Based Maintenance (PdM/CBM) and Corrective Maintenance

(CM), were some of the frequently applied maintenance strategy in situations where

corrosion was a factor. Six crucial factors to implementing an optimal maintenance

strategy were established: Safety, Personnel training/capabilities, Loss of production,

inventory and fault identification.

4.5. Corrosion.


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Shaw and Kelly (2006) describe corrosion as the degradation of materials’ properties

due to interactions with their environments...” According to the Shell inspection

supervisor, in the last 3 years Shell offshore platforms have seen 450 occasions of

reported corrosion, 400 of which were external compared to the onshore platforms

where 280 corrosion occasions were reported with only 30 pertaining to external

corrosion issues. In accordance with the Inspection supervisor, both rotation and static

Maintenance supervisors refer to a corrosive environment as the most challenging

offshore environment. As reported by Wood et al., (2013) 137 major refinery

accidents reported by EU countries to the EMARS (EU major accident report system)

database since 1984, around 20% indicated corrosion failure as an important

contributing factor. In consonance with eMars this proportion of refinery accidents

has remained constant well into the 21st century. Corrosion is capable of causing a

release of hazardous substances and components or reducing both the performance

and reliability of equipment until their immanent failure. In essence, the presence of

corrosion is capable of introducing risk to the safety and well being of both plant

employees and the general public as well as lead to severe damage of process units,

and in some cases shutdown of refinery operations.

4.5.1. Environmental influences.

Corrosion develops due to hostile environmental conditions during the life cycle of a

range of industrial structures, e.g., offshore oil platforms, ships, and desalination

plants. There are a number of environmental corrosion factors that are in some ways

unique to oil and gas production. Crude oil and natural gas are made up of a number

of naturally corrosive products, such as carbon dioxide (CO2 ¿, hydrogen Sulfide ¿),

and water (H 2O ¿ . Furthermore, other unique aspects are the extreme temperatures

and pressures encountered. Oil and gas production has come a long way. Due to

advancement of technology, deep-water exploration is now a regular factor in the

production of oil and gas. According to Garverick (1994) in deep gas wells; measured

at 6000m (20,000ft.) temperature approaching 230 C (450 F) have been measured,

and partial pressures of CO2 and H 2 S of the order of 20.7 MPa (3000 psi) and 48


58

MPa (7000 psi), respectively, have been encountered. Although oxygen is typically

absent from depths greater than approximately 100 m (330 ft) below the surface. It is

however responsible for the external corrosion of offshore platforms and drilling rigs.

Corrosion can become apparent in two forms, uniform or localized corrosion.

Uniform corrosion, also known as general corrosion is the typical form of corrosion

where an entire surface area undergoes thinning of the metal. “In chemical processing

industries uniform corrosion is considered the least dangerous form of corrosion

because it is easily visible long before it is degraded enough to fail.”(Frankel, 19983)

However, uniform corrosion in some cases are the cause of accidents if taken for

granted, for example, in pipelines that are located in remote locations, underground,

or otherwise and not frequently inspected or maintained, uniform corrosion may

remain undetected.

“Localized corrosion is the accelerated attack of a passive metal in a corrosive

environment at discrete sites where the otherwise protective passive film has broken

down.” (Frankel, 1998) Thus, the effects of localized corrosion can be more

detrimental than that of uniform corrosion due to the increased possibility of failure.

Characteristically, localized corrosion occurs between joints also known as crevice

corrosion or under a paint coating or insulation. Stress corrosion cracking and

hydrogen assisted stress corrosion are both forms of localized corrosion.

4.5.2. Contribution of process and equipment conditions.

The Petroleum Industry is made up of a large variety of corrosive environments.

Prabha et al., (2014) states that corrosion problems occur in the petroleum industry in

at least three general areas: (1) Production, (2) transportation and storage, and (3)

refinery operations. As corrosion in the petroleum industry is vast in all sectors and in

most cases similar, it begs to reason that the damage mechanism of a refinery holds

some similarities with that of Production. That being said the American Petroleum

Institute Recommended Practice 571 (API 571) mentions several characteristic

corrosion damage mechanisms to industrial activity including those specific to

refineries. The table below shows the damage mechanisms found in a refinery.


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Operating conditions in the oil and gas industry, due to its nature are likely to instigate

corrosion failure to initiate a chain of events leading to a major accident. Corrosion is

a serious development capable of creating holes in tubing walls, causing the release of

highly flammable chemicals. Contamination is another leading cause for surface

degradation also known as localized corrosion. Such contamination are in most cases

caused by the introduction of iron particles from welding and grinding operations;

surface deposits from handling, drilling, and blasting; and from sulfur-rich diesel

exhaust. The periodic seawater deluge testing carried out on an offshore platform,

especially in combination with insufficient freshwater cleansing, can leave behind

unwanted chloride-laden deposits, which will promote corrosion.

Table 3: Stress corrosion cracking damage mechanisms proposed by API 571.Damage

Mechanism

Velocity,

Temperature and

pH Influences

Substances

Involved

Other Influences Processes Affected

Mechanical and Metallurgical Failure Mechanisms

Erosion-

corrosion

High velocity, High

Temperature, High

Temperature, High,

Low pH.

Varied Particularly occurs

in pockets, elbows

and similar

configurations.

Affects all types of

equipment exposed

to moving fluids,

gas‐borne catalytic

particles.

Uniform or Localized loss of Thickness (Generic)

Galvanic

corrosion

Varied

Atmospheric

corrosion

Low temperature Cyclic: Fluctuation

between ambient

and < or >

temperature.

Cooling

water

corrosion

Low velocity, High

temperature.

Fresh or salt water,

potential chlorides

High Temperature Corrosion (Generic)


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Sulphidation High temperature Sulphur

concentration

FCC, coker,

vacuum distillation,

visbreaker and

hydro-processing.

High

temperature

H2/H2S

High temperature H 2∧H 2 S Desulphurizers,

hydrpocessing,

hydrotreaters,

hydrocracking

Nitiriding High temperature Nitrogren

compounds

4.6. Corrosion Maintenance.

According to NACE International, the worldwide corrosion authority. It is widely

recognized within the oil and gas industry that effective management of corrosion will

contribute towards achieving the following benefits:

Statutory or Corporate compliance with Safety, Health and Environmental

policies

Reduction in leaks

Increased plant availability

Reduction in unplanned maintenance

Reduction in costs of delay.

Corrosion can account for 60% of offshore maintenance costs; these cost implications

as defined by the HSE (Health & Safety Executive) are direct and indirect costs.

Direct costs pertain to inspection, chemical inhibition, corrosion monitoring and

coating maintenance. Where as indirect costs include Increased maintenance, deferred

production, plant non-availability and logistics. “The goal of corrosion management

is to achieve the desired level of service at the least cost.” (Rogerge, 2007)


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Legislation governing activities for topside processing facilities for offshore

installations are important for every offshore platform. These regulations provide a

framework where risks are identified by means of a structured approach and

accompanied by an appropriate set of risk control measures to manage them. The

regulations place an emphasis on the management of corrosion to ensure system

integrity and in turn the safe operation of facilities. This infers that management

systems must include suitable procedures to identify corrosion risks, and where they

pose a threat to the safety or integrity of the facilities, in order to manage those risks.

There are three corrosive zones on an offshore platform, each of which have its own

distinctive corrosion problems: (1) the atmospheric zone (above water), (2) the splash

zone (tidal), and (3) the subsea zone (underwater and sea bottom). For the purpose of

the research the main focus is the critical equipment located on the atmospheric zone

also known as topside.

4.6.1. Corrosion maintenance tasks.

Cathodic protection is one of the most widely used maintenance techniques in

countering corrosion concerns. The offshore industries rely on cathodic protection to

guarantee the integrity and durability of their assets, such as, offshore platforms,

subsea pipelines and marine terminals. Due to the high conductivity presented by

seawater, the cathodic protection method is extremely appropriate for this condition.

Although it cannot be used to prevent atmospheric corrosion, it is used on the interior

surfaces of water-storage tanks and water-circulating systems.


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4.7. Corrosion maintenance strategy.

A major challenge for maintenance managers is to guarantee that an optimal

maintenance strategy is in place, by proficiently applying available and potentially

scarce resources to maintenance requirements. “Prioritizing maintenance activities is

central to a methodical, structured maintenance approach, in contrast to merely

addressing maintenance issues in reactive, short-term mode.” (Roberge, 2007). The

most critical requirements must be addressed first, before then prioritizing persisting

maintenance needs.

Repair and rehabilitation activities are put in place in order to restore damaged

structures or equipment to their working condition and remedy the problems caused

by corrosion. Maintenance is understood to be a regular and essential activity that

comes with its cost. Nevertheless, corrosion monitoring represents a consequential

part of maintenance and asset management. Four remedial types of maintenance

strategies can be identified, namely corrective maintenance (CM), preventative

maintenance (PM), predictive or condition-based maintenance (PdM or CBM) and

reliability-centered maintenance (RCM).

4.7.1. Corrective Maintenance

Corrective Maintenance can be described as maintenance tasks performed to return an

equipment or structure to its original state. This strategy may refer to maintenance

due to breakdown or maintenance identified by a condition-monitoring program.

Maintenance due to a breakdown can be categorized as planned where equipment

have been allowed to run-to-failure or unplanned maintenance where a breakdown has

occurred due to an ineffective preventative maintenance procedure. According to

Kholy (2006), Maintenance experts have pointed out that there may be a "natural

tendency" to intuitively follow the corrective maintenance approach, even though it

may be (cost) ineffective in ensuring reliability. This maintenance strategy can be

described as a retroactive approach hence why corrosion-monitoring programs do not Nnaemeka NwogbeS1538433MSc Mechanical Engineering with Manufacturing.Glasgow Caledonian University

63

utilize this strategy. It is characterized by costs of repair (replacement components,

labor, consumables), lost production and lost sales.

4.7.2. Preventative Maintenance

Like it name suggests, preventative maintenance is an approach that aims to service

equipment before it fails. The goal of this strategy is to eliminate unnecessary

inspection and maintenance tasks, by establishing predetermined schedules.

“Preventive maintenance aims to eliminate unnecessary inspection and maintenance

tasks, to implement additional maintenance tasks when and where needed and to

focus efforts on the most critical items.” (Roberge, 2007). This suggests that the high

the consequence of failure, the higher the level of preventative maintenance required.

A Corrosion monitoring program may assist in improving the planned maintenance

schedule, as inspection plays a crucial role in the success of a preventative

maintenance strategy. Inspection of components for corrosion or other damages and

monitoring the condition of a component in order to identify the need for corrective

action before failure occurs, are essential to the maintenance approach.

4.7.3. Predictive Maintenance or Condition-Based MaintenancePredictive maintenance is maintenance based on the actual condition of a component

and not according to fixed schedules. The aim of this approach is to minimize or

eliminate unnecessary maintenance and inspection activities and to focus maintenance

efforts when and where they’re essential. This strategy is gleamed as highly proactive

with an emphasis on predicting when and where maintenance actions are required.

Utilizing corrosion sensors and monitoring activities are imperative in obtaining

information on the actual condition of a component. A rather domestic example

would be oil change in an automobile, changing the oil based on an oil analysis would

signify, predictive maintenance. As changing the oil would be based on the

degradation of the oil or wear and debris found in the oil.


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4.7.4. Reliability-Centered Maintenance Reliability-centered maintenance involves creating a maintenance program in the

most cost-effective and technically practical way. This maintenance approach exploits

a systematic, structured method based on failure consequences. It defers greatly from

the typical time based maintenance approach and highlights the functional importance

of system components and their failure/maintenance history. The potential benefits of

the reliability-centered maintenance approach involve preserving high levels of

system reliability and availability, whilst minimizing unnecessary maintenance tasks,

providing a documented basis for maintenance decision making and identifying the

most cost-effective inspection, testing and maintenance methods.

4.8. Compressor. “Compressors can be classified into two basic categories, reciprocating and rotary.”

(Scales, 1997). A Reciprocating compressor is utilized in compressing natural gases

and other process gases when the required pressures are higher than the current gas

flow rate. Reciprocating compressors compress the gas by using a piston to physically

reduce the volume of gas contained in a cylinder. As gas volume decreases, there is a

consequential increase in pressure. This form of a compressor is referred to as a

positive displacement compressor. Similarly a Rotary compressor is described as a

positive displacement or dynamic compressor. Gas compression performance and

throughput is a critical aspect of production in the offshore oil and gas industry. Oil

platforms that utilize gas lift become essentially reliant on gas compression in order to

attain good production figures. Gas compression uptime and throughput are directly

related with oil production volumes. Therefore, an efficient and stable compression

system is the foundation of good production. Compression systems are one of the

more complex systems on an offshore installation.


65

4.9. Analytical Hierarchy Process (AHP).

Multi-criteria Decision Making (MCDM) is the decision-making methodology

utilized in this research and the Analytical Hierarchy Process (AHP) weighing method

is applied. “Decision-making is the act or process of choosing a preferred option or

course of action from a set of alternatives.” (kitajima and Toyota, 2013). A decision

making process is made up of the following steps:

1. Identifying the goal of the decision making process.

2. Selection of the required criteria.

3. Selection of the Alternative course of actions.

4. Selection of the weighing methods to represent importance

5. Method of Aggregation.

6. Decision-making based on the Aggregation results.

The MCDM approach is applied to a problem made up of multiple criteria. The

purpose is to support decision makers facing problems regarding decision and

planning. Since there is no unique optimal solution for such problems, it is necessary

to use decision maker’s preferences to differentiate between solutions. “To make a

decision, set priorities, and allocate resources we often have to rank and select among

available options (“alternatives”).” (Aragón, 2013). In order to accomplish this a

criteria is developed, weighed, and alternative actions are evaluated against them. The

more important criteria are assigned higher weights and are therefore derived using

science-based, objective measurements and methods.

The Analytical Hierarchy Process (AHP) was developed by Saaty in the early 1970s.

The process has sustained its popularity in aiding numerous corporate and

government decision makers. It is used in deriving the weights of the criteria in the

decision making process, here a pairwise comparison of criteria with respect to their

importance, likelihood, or preference is conducted. The AHP process allows for the

integration of the decision makers interpretation of evidence (data testimony, etc.);

this implies the applicability of quantitative and qualitative data. Where comparisons


66

are taken from actual measurements or from a fundamental scale, which reflects the

relative strength of preferences and feelings. Although the AHP is recognized as the

most popular multi-criteria decision making (MCDM) method. It is not widely used in

making decisions regarding maintenance strategies in the oil and gas industry.

Goal Perspective Main Criteria Sub-Criteria Alternative

Figure 23. Illustration of the AHP model

To demonstrate the suitability of the approach a case study on the corrosion on the

crankshaft of a compressor in an offshore platform is used. The AHP model utilized

in this study is illustrated in Figure 23.

The criteria developed were obtained by paring research with findings from interview

response regarding the maintenance strategy selection for a fixed shell offshore

platform as well as case studies applied to the chosen challenging environment. The

three criteria applied are analyzed as follows:

Safety (C1)

Safety levels required are often high in oil and gas industry. The relevant factors

describing the Safety are:


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(C11) Personnel: The failure of many machines can lead to serious damage of

personnel on site, such as high-pressure vessels.

(C12) Facilities: For example, the sudden breakdown of a corrosion inhibitor pump

will result in increased corrosion of your pipes and in some cases, equipment.

(C13) Environment: The failure of equipment with poisonous liquid or gas can

damage the environment.

Cost (C2)

Different maintenance strategies come with different expenditure for hardware,

software, and personnel training.

(C21) Hardware: For preventative and condition or predictive maintenance, a number

of sensors and computers are required.

(C22) Software: Software is needed when analyzing data for measured parameters

when utilizing condition-based or predictive maintenance strategies. For example,

vibration and oil analysis.

(C23) Personnel training: Sufficient training is required for maintenance staff to be

fully capable of using the required tools and techniques, needed to reach the

maintenance goals.

Added-value (C3)

A good maintenance program can produce added value, this criteria deals with the

indirect benefit of a particular maintenance policy. This category includes low

inventories of spare parts, small production loss, and quick fault identification.

(C31) Spare parts inventories: Generally, corrective maintenance need more spare

parts than other maintenance strategies. Spare parts for some machines cost more than

others.

(C32) Production loss: The failure of production critical machinery often leads to a

higher cost production loss. Selecting a suitable maintenance strategy for such a

machine can reduce loss of production.


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(C33) Fault identification: Fault diagnostic and predictive techniques used in

condition-based, Reliability-Centered Maintenance and predictive maintenance

strategies aim to quickly tell maintenance engineers where and why fault occurs. As a

result, the maintenance time can be reduced, and the availability of the production

system may be improved. This indicates an improvement of Mean time between

repair. (MTBR).

“Rather than prescribing a “correct” decision, the AHP helps decision makers find

one that best suits their goal and their understanding of the problem.” (Majunder,

2015). Different forms of the AHP methodology exists, this research will be

conducted using the “original” AHP version developed by Dr. Thomas L. Saaty. A

brief description of the steps utilized in an AHP process is shown below

1) The implementation of the AHP first requires a decomposition of the

decision problem into a hierarchy of sub-problems that can be individually

analyzed. The “goal" is located at the top of the hierarchy, the intermediate

level is made up of the “criteria” and “sub-criteria” and the subsequent level,

recognized as the lowest level are the “alternatives”.

2) Once the hierarchy is constructed and elements of the hierarchy are

identified, the decision maker systematically evaluates the various elements

by means of pair comparison with respect to their impact on an element

above them in the hierarchy. The criteria, sub-criteria and alternatives are

weighed as a function of their importance to the goal. The AHP

accomplishes this by exploiting pair wise comparisons to determine weights

and ratings. “One of the questions which might arise when using a pairwise

comparison is: how important is the “maintenance policy cost” factor with

respect to the “maintenance policy applicability” attribute, in terms of the

“maintenance policy selection” (i.e. the problem goal)? The answer may be

“equally important”, “moderately more important”, etc.” (Bevilacqua and

Braglia, 2000). The response is based on qualitative intensity and are

quantified and translated into scores. Table 3 illustrates a 9-points scale

utilized by Bevilacqua and Braglia (2000).


69

Table 3: Judgment scores in AHP (Bevilacqua and Braglia, 2000).

Judgment Explanation Score

Equally Two attribute contribute

equally to the upper-level

criteria

1

2

Moderately Experience and judgment

slightly favour one

attribute over another

3

4

Strongly Experience and judgment

strongly favour one

attribute over another

5

6

Very strongly An attribute is strongly

favoured and its

dominance demonstrated

in practice.

7

8

Extremely The evidence favouring

one attribute over another

is of the highest possible

order of affirmation.

9

The judgment score is referred to by Saaty (1980) as the intensity

score (ij); a ratio with valid reciprocal values (1/ij).

(2,4,6,8: represent the intermediate values)

“Let C = {Cj |j = 1, 2,...., n} be the set of criteria. The result of the pairwise

comparison on n criteria can be summarized in an (n_n) evaluation matrix A

in which every element aij (i,j = 1,2,..., n) is the quotient of weights of the

criteria.” (Amiri, 2010)


70

3) The criteria priority weights are then developed following the construction

of a judgment matrix. The eigenvector approach is used in computing the

weights of the sub-criteria required for the pairwise comparison matrix. The

corresponding weights are given by the vector (W) that agrees with the

maximum eigenvalue (λmax). “It should be noted that the quality of the

output of the AHP is strictly related to the consistency of the pairwise

comparison judgments.” (Özkhan et al., 2011). The consistency is viewed as

the relationship between the elements being compared. The consistency

index CI is: CI =(λmax-n)/(n-1). The final consistency ratio (CR); which

indicates if the evaluation is sufficiently consistent can be calculated by

finding the ratio of CI and the random index (CI/RI). An inconsistency ratio

of 0.1 or more may require further investigation.

4) The weights of the main and sub-criteria are found; these weights are then

multiplied, providing the global weights of the criteria. Before then the

comparing the sub criteria to the alternatives.


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Chapter 5

DATA ANALYSIS

The data analysis chapter contains the proposed AHP methodology for selecting the

most appropriate maintenance strategy for an offshore platform, implemented based

on research and interview response.

5. Application of the Analytical Hierarchy Process.

An offshore production platform is a very complex facility, with a lot of different

machines and equipment with very different operating conditions. Deciding on the

best maintenance policy is not an easy matter, since the maintenance program must

combine technical requirements with the firm’s managerial strategy. By interviewing

the maintenance and inspection supervisors, it is concluded that the criteria in chapter

4 can be accepted. Therefore, the AHP hierarchy scheme is constructed

correspondingly. Next, the selection of the optimum maintenance strategy for a

compressor is presented as an example. In the following steps of the decision-making

process, the AHP comparison judgment matrices are decided according to the

suggestions of the maintenance staff. There are 3 main criteria, 9 sub-criteria and 4

Maintenance alternatives. Indicating 13 pairwise comparison matrices in all: One for

the criteria with respect to the goal of the research, which is shown in Table 5, three

for the sub-criteria, one for the sub-criteria with respect to safety: Personnel, Facilities

and Environment, is shown in Table 6. Another for the sub-criteria of Cost: Hardware,

Software and Personnel training and Added value: Spare parts inventories, Production

loss and fault identification. (See complete results in Appendix E). Then, there are 9

comparison matrices for the four alternatives with respect to its allocated criteria. The

9 covering criteria in this study are: Personnel, facility, environment, hardware, Nnaemeka NwogbeS1538433MSc Mechanical Engineering with Manufacturing.Glasgow Caledonian University

72

software, personnel training, spare parts inventories, production loss and fault

identification. Each of the 3 criteria has been allocated with 3 sub-criteria given a total

criterion of 9. Only 3 out of the 13 matrices leading to the rankings are shown in

Table 5, 6 and 7.

Table 5: Pairwise comparison matrix of the criteria with respect to the Goal.

CR: 0.038 (OK if CR<= 0.1), λmax= 3.0

Table 6: Pairwise comparison matrix for the sub criteria with respect to safety.

SAFETY (C11) (C12) (C13) w i Global Priority

Personnel (C11) 1 8 5 0.733

Facilities (C12) 0.125 1 0.25 0.068

Environment (C13) 0.2 4 1 0.199

GOAL Safety (C1) Cost (C2) Added-Value (C3) w i

Safety (C1) 1 8 3 0.661

Cost (C2) 0.125 1 0.20 0.067

Added-Value (C3) 0.33 5 1 0.272

CR: 0.081 (OK if CR<= 0.1), λmax= 3.09

Table 7: Pairwise comparison matrix for the alternatives with respect to

personnel.

PERSONNEL A1 A2 A3 A4 w i

Preventative (A1) 1 8 4 9 0.618

RCM (A2) 0.125 1 0.2 5 0.089

Predictive (A3) 0.25 5 1 7 0.258

Corrective (A4) 0.111 0.2 0.143 1 0.036

CR: 0.127 (OK if CR<= 0.1), λmax= 4.34


73

The calculations used in obtaining Table 5, Table 6, Table 7, Table 8 and the AHP

Results (Table 9), are shown below and broken up into levels 1, 2 and 3:

Level 1: Develop the weights for the criteria.

In order to obtain the weights; also known as the eigenvector of relative importance,

of the main criteria shown in Table 5. A single pair-wise comparison matrice was

developed. By utilizing the judgment table in section 4, then multiplying the values in

each row together and calculating the nth root of said product. Then dividing the

aforementioned nth root of the products by the total to obtain the weight.

Develop rating for main criteria:

Safety (C1) is extremely strong in importance compared to Cost (C2); Added value

(C3) is strong in importance compared to cost (C2); and Safety (C1) is moderately

more important than added value (C3). (See Table 3.)

The nth root of product values in each row are calculated as follows:

Let C = {Cj |j = 1, 2,...., n} be the set of criteria

n= number of criteria being compared. (n=3)

C 1 j=1× 8× 5=(24)1 /3

C 2 j=0.125× 1× 0.20=(0.025)1/3

C 3 j=0.333 ×5 ×1=(1.667)1/3

Each of the aforementioned nth root of product are then added together.

(24 )13+(0.025)1/3+(1.667)1 /3=4.363


74

The nth roots of product from the previous step are then normalized to obtain

the appropriate weights for each criterion. The weights (eigenvector) for each

criteria are calculated as follows:

C 1=(24 )

13

4.362=0.661

C 2=(0.025 )

13

4.362=0.067

C 3=(1.667 )

13

4.362=0.272

Note when calculated correctly the sum of the weights of each criteria must

equal 1.

The consistency ratio is then calculated and checked to ensure that it is equal

to or below. 10% (0.1) this indicates an acceptable inconsistency of the subject

judgment. Calculating the consistency is a 4-step process as show below.

Step 1: The pair-wise comparison values for each column are added together

to obtain the “Sum” values. Then each sum is then multiplied by the respective

weight (Priority vector) for those criteria. Particularly,

C 1=(1+0.125+0.333 )=1.458

C 2=(8+1+5 )=0.938=0.938

C 3=(3+0.20+1 )=1.142

Note the row labeled “Sum*PV” shown in the table below. Each value in this

row shows the result of multiplying the respective sum (Sum) by the

respective weigh for that given criteria (Priority vector).

(C 1 ) :∑ ¿ PV =1.458 ×0.661=0.964

(C 2 ) :∑ ¿ PV =0.938 ×0.067=0.939


75

(C 3 ) :∑ ¿ PV =1.142 ×1.186=1.142

Step 2: The aforementioned values obtained from ∑ ¿PV are added together

to 3.044. This value is known as λmax

Table 8: Main criteria pair-wise comparison with Consistency Ratio.

Safety

(C1)

Cost

(C2)

Added-

Value

(C3)

3rd root-of-

product

Priority Vector

Safety (C1) 1 8 3 2.884 0.661

Cost (C2) 0.125 1 0.20 0.292 0.067

Added-Value (C3) 0.333 5 1 1.186 0.272

Sum 1.458 14 4.2 4.363 1.000

Sum*PV 0.964 0.939 1.142 3.044

CI (Consistency

Index)

0.022

RI (Random

Consistency Index)

0.58

CR (Consistency

Ratio)

0.038

λmax=0.964+0.939+1.142=3.044

Table 9: Random Indices (RI).

n 1 2 3 4 5 6 7 8 9 10

RI 0 0 0.58 0.9 1.12 1.24 1.32 1.41 1.45 1.49

Step 3: The Consistency index (CI) is calculated using the formula below:


76

Let n= number of criteria being compared

λmax=¿3.044 (As calculated in the previous step for the sub criteria)

CI=( λmax−n)/(n−1)

n=3

CI=3.044−32

=0.022

Step 4: Lastly, the consistency ratio (CR) is calculated by diving the consistency

index obtained in step 3 by a random index (RI), which is determined from Table 9.

Consistency Ratio (CR )=CI /RI

Because n=3, the random index (RI) for the pair wise comparison matrix is equal to

0.58. Therefore,

CR=CIRI

=0.0220.58

=0.038 < 0.1 (OK.)

The Consistency ratio obtained makes the decision-maker aware of the consistency of

the pair-wise comparison. A higher number (>0.1) would indicate less consistency

and a lower number (<0.1) would indicate higher consistency.

Develop the weights for each sub criteria:

The weights for each sub-criteria are created by developing a pair wise comparison

matrix for each sub-criterion. An example of the values obtained for the sub-criteria

with respect to safety can be seen in Table 6. These values are attained by going

through the steps previously described.


77

The additional column (Global Priority) in Table 6 was calculated using the step

below:

Personnel (C 11¿=0.733 ×0.485=¿ 0.485

Facilities (C 12¿=0.068× 0.067=¿0.045

Environment (C 13)=0.199× 0.272=0.132

Here the global priorities are calculated by simply multiplying the priority vectors

obtained for the sub criteria by the respective main criteria.

Level 2: Develop the weights for each decision alternative for each criterion.

Here the weights for each decision alternative for each sub criterion is achieved by

developing a pair wise comparison of the performance of each decision alternative on

each criterion, as shown in Table 7. Within each sub criteria matrix the pair wise

system will rate each alternative relative to every other alternative. The weights are

then calculated using the steps described previously. The judgment score is first

assigned to each pair-wise comparison. Table 7 indicates that in respect to safety,

personnel is “very strong” in importance that facilities, personnel is “strong”

compared to Environment and Environment is “moderately” important in compared

to facilities. (See Table 3.)

Level 3: Determine the overall priority for each sub criteria (criteria)

In the final phase the overall priority for each alternative is determined by multiplying

the Global priority weights in Table 6, by that of the alternative weights in Table 7

(only one of the matrices leading to the rankings was given, in Table 7) then adding

the respective products. This step is referred to in AHP as the “The Principle

Composition of Priorities.”

The column in matrix C represent the eigenvectors of the pair wise comparisons of

the project alternatives with respect to all the evaluation criteria placed above them in

the hierarchy. Matrix C is then multiplied by the global priority vector w for the


78

evaluation criteria, in order to obtain the final preference vector X for the 4 project

alternatives being considered as shown below.

X=Cw [0.617 0.617 0.617 0.274 0.0810.055 0.560 0.355 0.0620.089 0.1130.1130.102 0.172 0.648 0.105 0.087 0.5320.258 0.234 0.234 0.580 0.6980.187 0.300 0.521 0.3510.036 0.035 0.035 0.044 0.0480.1100.034 0.036 0.054 ][

0.4850.0450.1320.0130.0050.0490.0250.0260.220

]X=[0.451986

0.2190310.2850070.043263]

Criteria

Global weight

(Criteria*Sub

criteria)

Safety (C1)

0.661

Cost (C2)

0.067

Added-Value (C3)

0.272

Overall

Priority

C11

0.485

C12

0.045

C13

0.132

C21

0.013

C22

0.005

C23

0.049

C31

0.025

C32

0.026

C33

0.220

w i

A1 0.617 0.617 0.617 0.274 0.081 0.055 0.560 0.355 0.062 0.452

A2 0.089 0.113 0.113 0.102 0.172 0.648 0.105 0.087 0.532 0.219

A3 0.258 0.234 0.234 0.580 0.698 0.187 0.300 0.521 0.351 0.285

A4 0.036 0.035 0.035 0.044 0.048 0.110 0.034 0.026 0.054 0.043

Table 10: Synthesizing to obtain the final results.

Table 10. Shows the global weight of each criteria and the eigenvectors of the

pairwise comparisons used to get the Overall priority for each Alternative. Table 11

below shows the AHP results in percentages, with the Alternatives illustrated

according to priority, from highest to lowest priority.

Maintenance strategy Priority %

Preventative Maintenance (A1) 45.2Nnaemeka NwogbeS1538433MSc Mechanical Engineering with Manufacturing.Glasgow Caledonian University

79

Predictive/Condition based Maintenance (A3) 28.5

RCM (A2) 21.9

Corrective Maintenance (A4) 4.3

Table 11. AHP Results.


80

CHAPTER 6

DISCUSSION & CONCLUSIONS.

This chapter offers a discussion on results presented in the data analysis section as

well as a conclusion of the conducted research and any other future work.

6.1. Discussion.

The present study was designed to integrate the Analytical Hierarchy Process (AHP)

in a decision-making procedure, regarding maintenance strategy selection for

corrosion in a compressor. The percentage of priority value declares the alternatives

ability to capture the set goal, therefore each alternative that has the highest points

value has the most power to capture the goal defined. Table 9. Shows Preventive

maintenance with a priority percentage of 45.2%, which indicates that it is the best

maintenance strategy in this case, due to its higher percentage priority value.

Corrective maintenance obtained the lowest priority percentage of 4.3%, signifying a

lack off efficiency in tackling the presented goal.

It can be observed from the results that the sub-criteria’s have played a pivotal role in

the priority weight for each main criteria. Specifically, the Added value (C3)

presented a priority weight of 0.272 compared to Cost (C2), which presented a value

of 0.067. It can be perceived that the sub criteria’s chosen for the added value; due to

their indirect correlation with safety and cost, were effective in increasing the

judgment score during a pair wise comparison which in turn effected the priority

weight of the criteria. The results achieved correlate with similar findings by Saaty

(1994) where he expresses that each element in the hierarchy structure are considered

to be independent of all the others, and hence, the interactions and feed backs which

might be present in the system are ignored. Previous researches have proved a

relationship between the consistency ratio (CR) and the number of pair wise


81

comparisons (n). After studying the consistency in random matrices of different sizes

Alonso and Lamata (2006) proposed the development of a system that utilizes saaty’s

max eigenvalue, yet accepts different levels of consistency that is based on the

dimension of the matrix.

The correlation suggested in their research was made apparent in the results obtained

in the data analysis section; as the consistency ratio of each associated pair wise

comparison presented a consistency ratio of around 0.1. Higher than that, produced by

a 3 by 3 pair wise comparison. The increased proved a direct relationship between the

pairwise comparison and the consistency ratio. Indicating that as the number of

pairwise comparisons increase, so also does the inconsistency in judgment relating to

the comparison matrix in question.

6.2. Conclusion.




industry. An optimal maintenance strategy will enable increased availability and

reliability of a plant or equipment, as well as safety, reduction of maintenance costs

and production loss. That being said the offshore industry faces a challenging

situation in maintaining a level of production at isolated and often harsh locations as

is common offshore. Maintenance is of utmost importance not only in order to

achieve prolongation of the life of platforms, but also for environment and for general

health and safety of personnel aboard the not easily accessible oil platforms. With this

in mind the aim of this research was to integrate the Analytical Hierarchy Process

(AHP), to select the most appropriate maintenance strategy for a challenging

environment faced by offshore platforms. Whilst providing new insight into the

capability of the AHP methodology.

As a means to fulfill the objectives of the dissertation, three research questions were

formulated:


82

RQ1: What are the critical maintenance issues that occur in an extreme

environment on an offshore oil platform?

RQ 2: What current maintenance strategies exist for extreme

environments?

RQ 3: What challenges are faced in an offshore environment?

A qualitative research method was adopted in order to answer the research questions

presented above. A combination of the Delphi technique, research and case studies

was utilized in aim to answer the questions presented. Through the manipulation of

information gained through research, the interview question required for phase 1 of

the Delphi technique was developed. From phase 1(See Appendix C), corrosion was

obtained as the most challenging environment faced by maintenance engineers on a

Shell offshore platform. Additionally, the responses and information obtained from

the panel of specialists (Inspection and Maintenance supervisors), led to the

development of a list of safety critical and production critical equipment, suitable

criteria for maintenance strategy and a list of maintenance strategies used in

countering corrosion. Further investigation was done in order to bolster the

information obtained and phase 2 (See Appendix D) was developed. Due to the scope

of study the mechanical critical equipment’s were further investigated to aid in

developing maintenance criteria for equipment corrosion on an offshore platform.

Two case studies were used in supporting the acquired evidence. Both studies present

corrosion as an unfavorable concern in the Offshore Industry. Case study 1, based on

PETRONAS; the Malaysian state owned global energy giant. Illustrates the effect

corrosion and a poor maintenance strategy has on the success of an industry. Whilst

Case study 2, investigates corrosion detected on the crankshaft of a compressor; one

of the many critical equipment’s located onboard an offshore platform. The

conclusion drawn from the case studies encourages the development of an optimal

maintenance strategy for corrosion in a compressor.

In this research, the Analytical Hierarchy Process (AHP) proposed by Dr. Saaty was

applied to the Maintenance criteria’s: Personnel (C11), facilities (C12), environment


83

(C13), hardware (C21), software (C22), personnel training (C23), Spare parts

inventory (C31), Production loss (C32), and fault identification (C33). Each of which

were divided into 3 main criterion: Safety (C1), Cost (C2) and Added Value (C3) and

compared against 4 alternative maintenance strategies applicable to corrosion:

Preventative maintenance (PM), Reliability-centered maintenance (RCM), Predictive

maintenance/condition based maintenance (PdM/CBM) and Corrective maintenance

(CM). With the ability to incorporate qualitative data, the AHP methodology resulted

in a reliable outcome that showed Preventative maintenance strategy holding the

highest percentage of 45.2% in points, Predictive maintenance with 28.5%,

Reliability-centered maintenance with 21.9% and Corrective maintenance with 4.3%.

This study has shown that when integrated with a research and interview response

from maintenance and inspection supervisors, the AHP technique has proved to be a

valid support for the selection of a suitable maintenance strategy. The hierarchical

structure of the proposed AHP combines many features, which are important for the

selection of the maintenance policy, such as: Safety, Cost, added value, etc. The result

attained from the maintenance strategy derived via the proposed methodology,

confirms the competencies of the AHP methodology. It validates the theory that AHP

is capable of developing and improving the understanding of the dynamics of a

complex case and can act as an efficient approach in reaching a decision.

6.3. Future Research Work.

Previous research has shown the capabilities of a number of analytical and decision-

making methods where the standard AHP methodology fails. Some of these

techniques are the Fuzzy pairwise comparison (Fuzzy AHP) and Analytical Network

Process (ANP).


84

6.3.1. Analytical Network Process (ANP).

The ANP method is described as “an improved version of AHP method.”(Zaim et al.,

2012). The ANP method is capable of carrying out a systematic evaluation of all the

relationships in the decision-making process. This technique does not only enable the

pair-wise comparisons of sub-criteria linked to specific main criteria, but also enables

an independent comparison of all the interacting sub-criteria’s. Further research has

shown that the decision-making that takes place in companies cannot easily be

explained by a simple hierarchical structure due to the capability of interactions

between criteria and alternatives. In order to combat these circumstances, complicated

analyses can be a necessary procedure in finding a suitable alternative. The ANP

technique is used for such a problem, as it is based on pairwise comparisons; similar

to that of AHP. Although in an ANP model all components and relationships are

defined and the relationships determined as two-way interactions. In the model the

network structure is used and all the relationships between criteria are considered and

each relationship divided into individual clusters of relating criteria. Due to such

relationships, the ANP method is useful for obtaining a more precise and effective set

of results in a complex and critical decision making situation.

6.3.2. Fuzzy AHP.

The AHP methodology is often criticized due to its unbalanced judgment scale and its

failure of properly handling the uncertainty brought about by the pairwise comparison

process. Deng (1999) presents the fuzzy approach for tackling problems with

qualitative multi-criteria decision analysis presents. The method was intended to

adequately model the uncertainty and imprecision of the human behavior. In essence

eliminate the uncertainty provided by the decision maker.


85

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APPENDIX


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Appendix A


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Appendix B

(https://

chemengineering.wikispaces.com/file/view/PFD_Symbols.png/246373095/

PFD_Symbols.png)

Appendix C


https://chemengineering.wikispaces.com/file/view/PFD_Symbols.png/246373095/PFD_Symbols.png



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INTERVIEW QUESTIONS PHASE 1(STATIC)

1) What environment do you find the most challenging in regards to maintenance

issues? (High temperature, low temperature. Etc.)

Answer: Salty Air: Corrosive Environment

2) What are the critical equipment’s on the platform? (Static and rotating) (Fixed

platform)

Answer: Major issue External Corrosion on pressurized equipment.

(These are all safety critical equipment)

List Below:

a. Pressure vessel

b. Pipes

c. __________________________________

d. __________________________________

3) What type of maintenance strategy are used on the critical equipment’s?

(Listed in question 2)

Answer: Time based Maintenance and Planned Maintenance

(Annual inspection on everything)


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INTERVIEW QUESTIONS PHASE

1(ROTATION)

1) What environment do you find the most challenging in regards to maintenance

issues? (High temperature, low temperature. Etc.)

Answer: Salty Air: Corrosive Environment

2) What are the critical equipment’s on the platform? (Static and rotating) (Fixed

platform)

List Below:

Safety critical

e. Emergency generators

f. Fire water pumps

Production critical

g. Power generator

h. Gas compressors

i. Export pumps

Safety critical

a. Inspection once a month (TBM functional tests and TBPM) Emergency

gen.

b. Failure functional tests

Two types of fire water pumps

Diesel engine---PM

Electrical--- No PM, only functional tests carried out once a month

and corrective maintenance

Production critical


101

c. Power generator--- Preventative maintenance and condition based

maintenance.

d. Gas compressors—PM, CBM, RCM, CM

(2 types, Depends on size of platform)

Centrifugal pump (Main pump)—CBM and PM for luber support

Reciprocating—PM based

INTERVIEW QUESTIONS PHASE

1(INSPECTION)

1) What environment they find the most challenging in regards to maintenance

issues and inspection?

Answers:

Salty environment 2.2 mm/yr--- (high corrosive environments)

2) What equipment requires frequent inspection?

Answers:

High risk vessels have high inspection

3) What inspection strategy is employed?

Answers:

Risk Based Inspection

4) What other factors influence inspection?

Answers:

Can’t go and leave whenever you want. (Logistic Challenge)


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Big Pressure vessels are inspected on the platform you can’t move

them.

> Separation vessels

> Heat exchangers

> Sand fielders

> Boilers

Additional information:

According to shell:

In the Last 3 years there have been:

Offshore:

450 occasions where reported corrosion

400 external corrosion

Onshore:

280 occasions where reported corrosion

30 external corrosion


103

Appendix D

Interview questions phase 2 (Rotation)

1) What critical equipment experiences frequent failures/maintenance calls in the

company’s most challenging environment?

Answer: Usually Instrumentation issues on smaller equipment’s such as Pressure

gauge failures caused by wear or vibration.

(Wear—PM to catch it out , Vibration- no PM in place (Break down maintenance/

corrective maintenance) .)

2) How long is the Downtime for the equipment mentioned?

Answer

a) No production (1-2 days to swap) (Emergency gen.)

b) No production loss (redundancy) (Fire water pumps)

c) Redundancy (no downtime) 1day—2months (need spare) (always ad spares)

( 6 months to send away) 1 week 5-7 days for swap (boat) (Power gen.)

d) One spare unit/stand by (without downtime)--- 1 week/ corrective (very very

long) (Gas compressors)

e) One spare unit/stand by (without downtime)--- 1 week/ corrective (very very

long) (Export pumps)

3) Most expensive equipment to replace?


104

Answer:

Rolls Royce drive power gen engine most expensive

Interview questions phase 2 (Static)

1) How often is Time based Maintenance and Planned Maintenance carried out?

ANSWER: Annually

Based on result from time based inspections which are carried out annually

to remove and replace insulation due to insulation degradation. Also a turn around

shut down every 3-4 years.

2) What critical equipment experiences frequent failures maintenance calls in the

company’s most challenging environment?

Answer: In corrosive environments insulated pressurized equipment degrade

quickly.

(Backlog of external corrosion maintenance issues)

3) How long is the Downtime for the pressurized equipment?

Answer: Depends on corrosion severity


105

Appendix E

Pair wise comparison of Main criteria

Pair wise comparison of Sub criteria in respect to Safety

Pairwise comparison of sub criteria in respect to Added value


106

Pairwise comparison of sub criteria in respect to Cost.


107

Pairwise comparison of each Alternative in respect to each safety sub criteria


108

Pairwise comparison of each Alternative in respect to each Cost sub criteria


109

Pairwise comparison of each Alternative in respect to each Added value sub

criteria.


110
