Implementation of the API RP 584 Integrity Operating Windows Methodology at the Gibson Island

Ammonia Manufacturing Plant*

A process gas leak outside of the primary reformer caused a serious fire incident at the Gibson Island

Works (GIW) ammonia manufacturing plant in Brisbane, Australia. As part of their global reliability

improvement strategy, Incitec Pivot Ltd. (IPL) selected GIW as a pilot for the pending API RP 584 In-

tegrity Operating Windows (IOW) standard. An all-inclusive review of plant performance was conduct-

ed, including a creep remnant life assessment and stress analyses of the primary reformer. This paper

presents a safety overview of the GIW facility and presents a case study of how the IOW standard was

implemented at the facility. The steps used to mitigate risk and improve the methods used for additional

facilities are also covered.

L. Bateman, D. Keen

Incitec Pivot /Dyno Nobel, Brisbane Qld, Australia

Q. Rowson^, B. Fletcher*, O. Kwon^, C. Thomas^, A. Saunders-Tack^, A. Karstensen#

Quest Integrity Group, ^Lower Hutt, New Zealand, *Boulder, Co, USA, #Brisbane, Qld, Australia

*Presented at the Nitrogen + Syngas 2014 Conference in Paris, France

failure led to a significant fire outside

of the primary reformer at Incitec Pivot

Ltd. (IPL) Gibson Island ammonia

plant (GIW) in December 2010. The

impact of this incident on the plant reliability

and safety management processes led to the de-

cision to pilot the implementation of the API RP

584 Integrity Operating Windows standards

(IOW) best practice [1]. This paper describes

the implementation process for this standard for

the reforming section of the plant.

INTRODUCTION & BACKGROUND

To properly understand the nature of the IOW

implementation process, a basic understanding

of the equipment involved is required. The pro-

cess loop in question is the fired section of the

front end steam reformer at GIW in Brisbane

Australia. The front end is made up of a generic

type fired pre-heater up-stream of a typical

1960s vintage Foster Wheeler terrace-wall fired radiant section reformer, complete with a mixed

feed coils and an auxiliary fired convection

bank. The items of equipment and their configu-

ration are shown in Figure 1 in the simplified

process flow diagram excerpt. The items of

equipment addressed in the IOW process in-

clude the preheat furnace (EF602) and the steam

reformer (R601). The reason that this loop is a

focus for the IOW process is because it is the

highest risk loop in the plant in addition to it

having experienced the incident in December

2010.

A

Figure 1. P&ID excerpt of the reforming loop, EF602 furnace left, R601 right

OUTLINE OF THE INCIDENT LEADING

TO IOW PROGRAM

The outlet pigtails and manifold are contained

within a coffin box located at the bottom of the furnace. The pigtail connections to the

catalyst tubes are located approximately 900

mm (35.43 in) above the bottom of the tubes

which extend outside the bottom of the coffin box and are fitted with a bottom flange as shown in Figure 1.

An outlet pigtail weldolet suffered a creep

failure in December 2010 [2]. The partially

reformed process gas leaked into the coffin-box section of the reformer and directly impinged on the fabric seal at the bottom of the

tubes. The jet of leaking gas quickly pierced the

fabric seal as it is only designed to seal the

slightly negative-pressure furnace. The instant

that the H2-rich gas (at 760C (1400 F)), met

the oxygen-rich atmosphere outside the furnace,

it immediately ignited. The sudden increase in

temperature at the bottom of the tube caused the

stud bolts on the bottom flanges to soften and

stretch, leading to another leak at the flanges in

the vicinity of the failed pigtail. This also

ignited, causing the next tube flange studs to

soften and leak, resulting in a chain reaction

along the bottom of the reformer. The fire was

clearly visible on the outside of the furnace box.

The instant the condition was noted by the

control room, the feed was shut off immediately

and the plant safely ramped down to allow

further investigation.

The root cause analysis clearly indicated a creep

failure was responsible for the original leak at

the pigtail. Micrographs of the failed pigtail

Coffin box section

showed that the material of a single pigtail

contained extensive creep voids, while nearby

pigtails were in good condition. The root cause

of the incident was extended operation at high

temperatures meaning operation had been above

a safe Operating Window. The pigtails were installed in 2007, had under gone 10 thermal

cycles in that time and had a design pressure

and temperature of 2.75MPa (0.4 ksi) and 815C (1500 F) respectively. This conclusion led to

the development of an IOW programme

involving analysis of all the components and

pipework within the front end of the ammonia

plant.

EXPLANATION OF THE IOW

PROGRAMME

IOW Definition:

The definition, monitoring and control of key

process as well as operational parameters,

commonly referred to as the plant Integrity

Operating Window (IOW). This is an essential

step in ensuring optimal reliability, availability

and profitability of critical plant equipment.

Purpose:

To provide sustained operational reliability and

understanding of the relationship between

campaign life, production rates, and

opportunities for improvement.

Deliverables:

A clear understanding of likely failure modes,

remaining life and integrity of components

under controllable process variables (e.g.

temperature, pressure, flow, etc.) and

operational guidelines outlining the upper and

lower bounds of these limitations.

The end goal of the IOW process is illustrated in

Figure 2 below.

Figure 2. Integrity Operating Window limits

IOW PROCESS AS EXECUTED BY

IPL/QUEST INTEGRITY

The IOW process consists of series of steps used

to limit operational variables that govern the

most likely failure mechanism for a given item

of equipment.

The actual process begins similarly to the Risk

Based Inspection (RBI) program [3] as outlined

in Figure 3. A team of experts assesses the risk

of failure with respect to a given mode and

mechanism of failure. RBI then branches off to

create Inspection Test Plans (ITPs) and

inspection schedules to reduce these risks.

The IOW program uses the initial work of the

RBI process of defining and ranking the risk of

particular failure modes and mechanisms. This

part of the analysis was already completed in the

form of root cause analysis and updated RBI

risk assessments following the serious incident

in December 2010.

The condition of the vessels was assessed by

Non-Destructive Examination (NDE) and

inspection, and the remaining life was assessed

with respect to the process variable that governs

the failure mechanism (e.g. temperature for

creep failure). This analysis is carried out in a

variety of ways, from API579 [4] level 1

screening (e.g. go/no-go assessment) through to

complete computational fluid dynamics and

finite element models encompassed by an

API579 level 3 assessment. Consumed life

based on past operating history is subtracted

from the total life, and the IOW limits are

agreed upon by all the original stakeholders.

Figure 3. RBI and IOW Process Flow Charts

WHY IOW WAS CHOSEN BY IPL

An IOW program was chosen to ensure the

safety, reliability, availability and profitability

of critical plant equipment via the prevention of

unexpected failure.

The entire program is a synergistic multi-

discipline approach used to establish the plant

IOW, as an essential prerequisite and integral

part of RBI implementation. There are many

stakeholders in the IOW process as it affects

numerous aspects of the operation. How this

strategy fits into IPLs systems is shown in Figure 4.

Figure 4. How IOW fits into the plant operational groups

IPL identified that a failure to properly define,

monitor and control the IOW may have severe

or even catastrophic impact on plant integrity. In

addition, it can discredit the gains in safety,

reliability and availability offered by RBI. The

pigtail failure in December 2010 was an

example in point.

A well-executed IOW and RBI work process is

essential to increase the flexibility and

profitability of plant operations.

ANALYSIS PERFORMED AT GIBSON

ISLAND FACILITY

In order for IPL to implement the IOW

standard, first a comprehensive understanding of

actual operating conditions was required.

Detailed Computational Fluid Dynamics (CFD)

modeling of the radiant and convective sections

of the ammonia front end were preformed. This

determined actual temperature variations along

the pipe work, dead spaces and bends. CFD

findings were then used as the input conditions

to develop Finite Element Analysis (FEA)

models of the front end. The FEA Models were

used to determine the state of stress of the unit

under creep conditions, taking into account all

system load and supports of the unit. Results

from this stress analysis were then used as input

into API579 fitness-for-service assessments

which were used to determine the safe operating

conditions and laterdefined the IOW to API RP

584 draft standard.

Computational Fluid Dynamics (CFD)

Computational Fluid Dynamics (CFD) is a

simulation tool that is used to numerically solve

and analyze problems that deal with fluid flow

in detail. CFD modeling was used to understand

observed uneven temperature distributions in

the radiant and convection sections of the

primary reformer. The main objective of the

CFD modeling was to provide the steady state

flow field distribution inside the steam reformer

while operating under typical firing conditions.

In this study, three-dimensional steady state

CFD models were developed to determine the

flow field solution distribution (pressure,

temperature, velocity, etc.) throughout the

primary reformer. The CFD modeling included

the combustion of hydrocarbons as well as

radiation heat transfer in an effort to accurately

predict the flue gas distribution in the

convection and radiant sections of the reformer.

The overall geometry of the CFD model is

presented in Figure 5.

Figure 5. Isometric view of the CFD model.

The CFD analysis predicted flue gas

distributions containing large vortex structures

spinning at low velocities in the radiant section

of the unit [5]. Low flue gas velocities were

expected since the heat transfer mechanism is

predominately governed by radiation rather than

forced convection in this region. The modeling

predicted cooler flue gas temperatures for the

catalyst tubes adjacent to the end walls in the

radiant section; these lower temperatures were

also observed by IPL through the use of infrared

imagery. Figures 6 and 7 shows significantly

lower flue gas temperatures predicted at the end

walls at the lower portion of the radiant section.

The CFD modeling indicated the flow

emanating from the lower radiant burners

closest to the end walls were slowed down and

pushed away from the wall by standing vortices

located at the bottom of the radiant section.

These vortices were caused by the flow being

slowed down due to the presence of the catalyst

tubes.

Figure 6. Flue gas temperature distribution in

the radiant section.

Figure 7. Flue gas temperature distribution in

the radiant section.

Similar insights for other flow distribution

issues within the unit as well as burner

performance observations were obtained from

the CFD modeling. The use of the CFD analysis

has provided IPL with understanding on how

the reformer tube and burner layout and

configuration affected the temperature

distribution within the unit. This model can be

used to make future operational decisions

increasing the safe and economic operation of

the unit, such as investigating the remaining life

for a given flow-embedded component using

CFD-predicted heat loads when updating the

design or operating conditions. The added value

of having an existing CFD model of the unit is

that it can be readily used to understand the

implication on the flue gas heat distribution for

possible design modifications during upcoming

shutdowns as well as modifications to the units operating conditions (such as: increasing the

burner firing rates, upgrading the fan at the

stack, etc.).

Finite Element Analysis (FEA)

The temperature information obtained from the

CFD analysis was used as input in the Finite

Element Analysis (FEA) to determine the

critically stressed areas, which will be the life

limiting locations. FEA can determine the state

of stress in components, due to external and

internal loads and is invaluable when the

problem to be solved is statically indeterminate.

The front end of the ammonia plant required the

creation of finite element analysis (FEA) global

1D piping-element model of the radiant section.

This was then broken out into detailed FEA 3D

solid-element sub-models of critically high

stressed areas where the simplified global 1D

piping model was unable to satisfactorily

resolve the state of stress in a specific location.

Figure 8 shows an example of the mixed feed

coil outlet manifold.

Figure 8. Maximum von Mises stress location in mixed feed coil outlet manifold prior to stress

relaxation of 250.9 MPa (36.4 ksi), units of contour plot in MPa.

Fitness-For-Service (FFS) Assessments

The stress determined from the FEA was used

as input to FFS assessments which were

undertaken to the requirements of

API579/ASME FFS-1. Due to the high metal

temperatures that the radiant section and

associated pipework operates under, creep was

the predominant failure mechanism of concern.

For the example of the mixed feed coil outlet

manifold [6], the high level of stress (250.9 MPa

(36.4 ksi) von Mises stress) was mainly caused

by the system loading and throughout one year

of operation, the initial maximum stress, 250

MPa (36.3 ksi) was predicted to relax to 41 MPa

(5.9 ksi) due to creep. It is worth noting that the

stress had already relaxed below 50 MPa (7.3

ksi) after 3000 hours. The evolution of the stress

at the peak stress location from start-up has been

shown over an uninterrupted 40,000 hour time

period of operation in Figure 9 and the

evolutionary changes in the stress was used in

the remnant life calculations.

Figure 9. Maximum von Mises stress location

in mixed feed coil outlet manifold

during stress relaxation during

operation.

This component has operated for 231,108 hours

and has undergone 46 thermal cycles. Installed

in 1982, its first 18 years of life were at an

operating and design temperature of 560C (1040 F). Operating conditions changed in the

year 2000. Based on thermocouple

measurements its remaining 11 years in service

have been at an average operating temperature

of 573.6C (1064.5 F) a temperature well above the original design

temperature. These thermocouples are located in

the mixed feed coil outlet manifold and inlet

header. It was assumed that the average

operating hours between each thermal cycle as

represented by a start-up and shut-down

sequence of 5522 hours (7.5 months), with 29

thermal cycles occurring prior to the year 2000

and 17 thermal cycles occurring post the year

2000. This has been

summarized in Table 1.

Operation Temperature

(C)

Pressure

(MPa)

Number of

Start

(thermal

cycles)

occurred

Duration

of

operating

hours

between

starts,

hours

pre 2000

(18 yrs.)

560

(1040 F)

2.93

(0.4 ksi) 29 5522

post 2000

(11 yrs.)

573.6

(1064.5 F)

2.93

(0.4 ksi) 17 5522

Table 1. Assumed historic use for start

frequency (thermal cycles) and time

between starts.

Analysis assuming mean creep properties

Using mean Omega creep parameters from

API579 under the historic conditions specified

in Table 1, the critical location in the mixed feed

outlet manifold was assessed to have already

reached 85% of its life. With the 15% life

remaining, various scenarios of pressure and

temperature were considered. This has been

summarized in Table 2. The future on-line time

for the unit was assumed high, close to 8760

hours of operation are obtained each year. This

means that even if the operating temperature

and pressures were reduced to design

conditions, the mixed feed coil would have a

remaining life of approximately 6 more years

(52,540/8760) before failure is predicted.

Remaining life

(hr.)

Temperature

C (F)

Pressure:

2.69 MPa

(0.39 ksi)

Pressure:

2.96 MPa

(0.43 ksi)

560

(1040 F) 52,540 50,747

573.6

(1064.5 F) 26,223 25,023

578.6

(1073.5 F) 19,764 18,794

583.6

(1082.5 F) 14,759 14,027

588.3

(1091.5 F) 11,147 10,582

593.6

(1100.5 F) 6,208 5,777

598.3

(1109.5 F) 6,096 5,777

603.6

(1118.5 F) 4,416 4,183

Table 2. Mixed feed coil outlet manifold

remaining operating hours versus

operating temperatures and

pressures with mean creep

properties.

As a result of the IOW process the FFS analysis

led to the repair of the mixed feed coil outlet

manifold, with a schedule redesign and

replacement prior to the next major outage.

Items considered for the redesign of this

manifold, are:

Materials selection

Replacement of a fixed mounting with a

spring hanger so that it reduces the sys-

tem loading

Change of position at which the stub

tubes enter the manifold.

These changes will reduce the peak stresses that

led to the short predicted life of the original

manifold for the operating conditions

considered. However, a detailed assessment of

the extent of life increase due to these changes

has not been completed.

HOW IOW RESULTS WERE

IMPLEMENTED AT GIW

The intent of an IOW study is not necessarily to

produce a lower set of programmable limits

within the plants distributed control system (DCS). Rather, the IOW results create a range of

operating set points with regard to the governing

process variable that influences the failure

mode/mechanism. All stakeholders were invited

to an IOW workshop where these process

variable ranges are presented and the best limit

is agreed upon.

The best way to illustrate this is by example

such as the mixed feed coil outlet pass tube row

(hottest tubes).

Using the Level 2 creep analysis of Part 10 in

API-579/ASME-FFS-1 [4], a table of metal skin

temperatures vs. remnant life was created (much

like Table 2). This table was presented to the

stakeholders as the IOW results, and the implementation of these results were agreed

upon in a stakeholder workshop. For example,

operations process engineers ruled out the lower

and upper-most temperatures because they were

unachievable in the current plant firing

configuration. Maintenance engineers/managers

preferred the lower temperatures as they

resulted in longer equipment life and therefore

greater campaign life between change-outs.

Process development engineers preferred the

higher operating temperatures because hotter

mixed feed gas before the primary reformer

catalyst tubes means a greater rate of conversion

i.e. greater steam reforming of CH4 to produce

more H2 per unit volume. Plant management

and business analysts (accountants) calculated

the optimized operating temperature based on

the trade-off between extra production output

and the cost of increased maintenance/change-

outs, (i.e. 10-15 year life was optimal as the cost

of the more frequent change-outs was exceeded

substantially by the increased production

output).

In this instance the IOW limit as implemented

was actually a higher temperature than current

operating temperatures because the

understanding of the condition and equipment

life expectancy was enhanced and well

documented after completion of the IOW.

The other type of IOW result is capital works

required for sustained operation. The study

found on two occasions that the serviceable

lifespan of the equipment in question had either

expired or was close to failure. The intended

course of action is then further inspection,

modification or replacement. This is illustrated

by way of the three following examples:

1) Further Inspection: The inlet header tee IOW

result indicated that the stress at a particular

location would have resulted in a consumption

of creep life in order of 30% had the metal

exhibited minimum creep properties. If this was

the case the microstructure would have

contained some creep voids/fissuring on the

grain boundaries and the item would require

immediate replacement. Replication was carried

out on the area of high stress plus three other

locations for comparison and all showed

acceptable microstructure with no voids or

fissuring on the grain boundaries. Shear wave

UT was also conducted to ensure there were no

crack-like flaws. Hardness testing was

completed to restore confidence in the

materials strength. The item was added to the change-out list for the 2015 turn-around, with

the new design possibly using a better material

metallurgy. No further action was required,

other than limiting the operating temperature at

a nearby temperature indicator.

2) Modification: The mixed feed coil outlet

manifold was found to have an extremely high

stress relaxation magnitude that may have

exceeded yield in the one location of highest

combined stress as illustrated in Figure 8. This

area was un-inspectable due to its location on

the intrados of the branch connection. The risk

was unacceptable to the stakeholders, so a

modification plan was initiated. An FEA was

done to assess the feasibility of jacketing the

header with thick rolled plate to reduce stress by

increasing cross-sectional area; and to provide a

secondary containment in the event of a

creep/fatigue failure at the original location. The

management of change procedure was initiated

and the modification was completed. The item

was added to the change-out list for the 2015

turn-around, with the new design possibly using

a better material metallurgy

3) Replacement: The outlet header was installed

new in 2011; however the old spring support

system was reused. The IOW results indicated

that the support was inadequate at the ends and

the manifold drooped somewhat in service. This consequently put excess bending strain on

the end pigtails as well as the outlet manifold to

Bull Tee welds, reducing the pigtails serviceable lives. The upgrade of the support

system and modification was added to the

capital list for the 2015 turn-around, with the

new design intent to take load off the pigtails

and re-establish their lives.

The IOW study revealed some points of

weakness under the current operating

conditions. When these weaknesses are

addressed and the plant is run at higher rates, the

IOW results should also show the next level of

weakness. The IOW study is therefore a useful

tool for operations and development groups who

will be making up-rate improvements overtime.

As a result operations and development groups

should fully understand the effect their changes

will have on the upstream and downstream

items of equipment.

BENEFITS OF THE IOW PROGRAM

The root cause analysis for the fire incident

highlighted a number of systemic issues relating

to the management of pressure equipment that

required attention. Although RBI and Reliability

Centered Maintenance (RCM) practices were in

place and implemented, there was opportunity

for improvement on the integration and

implementation of individual integrity

management practices within the plant

environment. In particular, processes which

drove a holistic approach to integrity

management integrating the respective plant

disciplines around operations, process

technology, maintenance and inspection were

largely missing within the procedural

framework.

Draft best practice API RP 584 IOW was

reviewed and found to provide a key procedural

driver for improving plant processes in this

respect.

Implementation of the API RP 584 IOW meant

an improved appreciation of the consequences

of operating the plant in a particular fashion. It

also defined key parameters through a

multidisciplinary approach that allowed the

implementation of the shared supervision of

plant integrity and performance management. In

some cases it meant being able to run plant

components beyond their original design life or

above their original design pressures and

temperatures in a controlled, safe and monitored

manner. This is due to the conservatism inherent

in the original design.

One of the great successes that highlighted the

value of implementing the IOW program

internally was the determination of the

remaining life expectancy of the mixed feed

outlet manifold based on historic operational

and support settings. Determination that this

was the life limiting component, and that a

repair was needed in order to get to the next

major shutdown, so that a re-design manifold

could then be fitted, brought tangible

appreciation for the IOW program, as well as

having better operational control limits on the

plant, allowing it to be run in a more optimized

state, with increased production.

When the repair of the manifold was being

carried out, everybody, from the CEO to the

trades assistant helping the welder, knew that

this repair was necessary due to the findings of

the IOW and without it there was a possibility

of another catastrophic event before the next

major shutdown.

Another notable outcome was the hip coil outlet

tubes. In 2007 these tubes were replaced with

304 material. The CFD study completed as part

of the IOW project revealed that the temperature

on these tubes was in excess of the design

allowable temperature, because of a

concentration of flow (channeling) through the

Dietrich arch. The following FFS analysis

showed the tubes were very close to failing by

creep fatigue and they were scheduled for

change-out with Incoloy 800H tubes. Inspection

of the removed 304 tubes showed some creep

damage from only 3-4 yrs. operation, meaning

the change-out was very well warranted.

FINAL WORDS

Based on the successful implementation of the

IOW process at the GIW plant, IPL is in the

process of completing the IOW process at two

of their other plants. The current API579 creep

assessment failure criteria were found to be

wanting and the R5 code [7] was used in its

place. Efforts are being made to improve the

creep assessment methodology as its rolled out at other plants/facilities.

The main damage mechanisms at each plant

need to be given the highest consideration and

are not all the same. For example, one of the

plants for which analysis is still being

performed shows that metal dusting of key

components is likely to be the life limiting

factor of safe plant life.

REFERENCES

1. API RP 584 Integrity Operating Windows

standard.

2. Private communication.

3. API 581 Risk Based Inspection Standard

4. API 579/ASME FFS-1 Fitness-For-Service

Standard.

5. Quest Integrity CFD report number 101317-

Rev02 issued April 2010.

6. Quest Integrity FEA/FFS report number

101303.01 Issued October 2011.

7. British Energys R5 code, Assessment procedure for the high temperature response

of structures.