ia final report
TRANSCRIPT
Industrial Attachment Final Report – Singapore Technologies Electronics Ltd.
NANYANG TECHNOLOGICAL UNIVERSITY Page 1 of 63
Industrial Attachment Final Report
24/01/2011-24/06/2011
Prepared by: CHU WEI XIN (DESIGN STREAM)
Student No: U0920905B
Company: SINGAPORE TECHNOLOGIES ELECTRONICS LTD.
Institution / Organization: NANYANG TECHNOLOGICAL UNIVERSITY
Faculty / School: MECHANICAL ENGINEERING / SCHOOL OF
MECHANICAL AND AEROSPACE ENGINEERING
Date: June 2011
Semester of Study: Year 3 Semester 2
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TABLE OF CONTENTS
Page
ABSTRACT……………………………………………………………………………………….…...4
ACKNOWLEDGEMENTS…………………………………………………………………...…….…5
LIST OF FIGURES……………………………………………………………………………………6
CHAPTER 1 – INTRODUCTION
1.1 – Aim………………………………………………………….………………..7
1.2 - Scope………………………………………………………………….………8
CHAPTER 2 – SINGAPORE TECHNOLOGIES ELECTRONICS LTD.
2.1- About the Company…………………………………………………………...9
2.2 – Defense Business Unit………………………………………………………10
CHAPTER 3 – THE DESIGN PROCESS..…………………………………………………………..12
CHAPTER 4 – AUTONOMOUS UNDERWATER VEHICLE (AUV) LAUNCH AND RECOVERY
SYSTEM (LARS)
4.1 - Launch and Recovery System Overview……………………………………14
4.2 - Challenges of the Existing Hoop Design……………………………………15
4.3 - Conceptual Design Phase……………………………………………………16
4.4 – Detail Design Phase
4.4.1 – General Dimensions of Selected Concept Design……………….18
4.4.2 – Simplified Detail Calculations…………………………………...20
CHAPTER 5 – ON-SITE / IN-OFFICE ASSIGNMENTS
5.1 - Force Protection (FP) Work Desk Layout…………………………………..22
5.2 – Force Protection (FP) Heavy Machine Gun (HMG)………………………..23
5.3 - AC DC Converter Bracket and Cover Design………………………………24
5.3.1 – Engineering Drawings…………………………………………...25
5.4 – Modeling of Existing Products……………………………………………...26
5.5 – Bow Thruster Removal Manual…………………………………………….27
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5.6 – Building of Mock-Ups………………………………………………………28
5.7 – Marine Corrosion Control…………………………………………..29
5.8 – Thrusters…………………………………………………………….30
CHAPTER 6 – CONCLUSION…………………………………………………………….31
APPENDICES
APPENDIX A- Bow Thruster Removal Manual…………………………A1
APPENDIX B- Corrosion Control Research Paper………………………B1
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ABSTRACT
This report record the experience gained by the student throughout the 22 weeks of
Industrial Attachment in Defense Business Unit, Singapore Technologies
Electronics Ltd (Ang Mo Kio).
It describes the nature of the job scope of the student, the projects that the student
has handled and the invaluable lessons that could not be obtained in school.
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ACKNOWLEDGEMENTS
The student would like to send out his heart-felt gratitude for the opportunity to
work in the company. The student would like to express appreciation to his
supervisors, for the guidance and patience they has shown in all the projects
assigned to him and their willingness to impart their valuable experience, knowledge
and skill to the student.
Special thanks too to the supervisor-in-charge in NTU, A/P Yeo Khim Teck from
the School of Mechanical and Aerospace Engineering for the time spent in
reviewing the reports and the interest that he has shown in our projects.
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LIST OF FIGURES
Figure Page
1. The Design Process………………………………………………………………….12
2. Challenges of the Existing Hoop Design……………………………………………14
3. Launch and Recovery System (LARS) Concept Design 1…………………………..16
4. Launch and Recovery System (LARS) Concept Design 2…………………………..17
5. Launch and Recovery System (LARS) Concept Design 3…………………………..17
6. Selected Concept Design for Launch and Recovery System ……………………….19
7. Force Protection (FP) Work Desk Layout…………………………………………..22
8. Force Protection (FP) Heavy Machine Gun.………………………………………..23
9. AC DC Converter Bracket and Cover………………………………………………24
10. AC DC Converter Bracket and Cover Engineering Drawings…………….………..25
11. Modeling of Existing Products…………………………………………….………..26
12. Mock-up……………………………………………………………………………..28
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CHAPTER 1 – INTRODUCTION
1.1 AIM
The purpose of this report is to present and inform the reader about the projects that
the student have been assigned during the 22 weeks, 24th
January 2011 – 24 June
2011, at Singapore Technologies Electronics Ltd (Ang Mo Kio).
Major Projects assigned are namely:
Autonomous Underwater Vehicle (AUV) Launch and Recovery System (LARS)
Force Protection (FP)
On-Site Assignments
Marine Corrosion Control Research Paper
The main aim of the projects is to allow the students to first, familiarize themselves
with the design process. This involves the conceptual design phase, detail design
phase and the final design phase. Another aim is to allow the students to be
proficient with SolidWorks, which is a 3D Computer Aided Design (CAD) software
that is being utilized by engineers in their design. And lastly, by having on-site work,
it not only allows the student to see and understand the constraints faced in their
design, it also allow the students to gain hands on experience that cannot be
experienced in the design studio. In writing this report, the student has to make
certain assumptions due to the lack of knowledge in a certain field of study and
hence, have to do their own self-reading to understand more about the concepts.
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1.2 SCOPE
Chapter 2, the company, Singapore Technologies Electronics Ltd (Ang Mo Kio)
background is being introduced.
Chapter 3 introduces the entire Design Process, from Conceptual Design to the
Manufacturing Phase.
Chapter 4 records down the assigned Design Project to the student, the Launch and
Recovery System (LARS) for the Autonomous Underwater Vehicle (AUV). It
illustrates how the final design was selected from several conceptual designs.
Chapter 5 is a compilation of the various short assignments and research that the
student has assisted / accomplished during his stay in the office / site.
Chapter 6 is a conclusion of what the student has learnt and experienced during the
entire 22 week internship.
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Chapter 2 – SINGAPORE TECHNOLOGIES ELECTRONICS
LTD.
2.1 ABOUT THE COMPANY
Established in 1969, Singapore Technologies Electronics Limited (ST Electronics) is a
leading Information Communications Technologies (ICT) System provider in the region.
The company’s strategic thrust is in the three key business areas of Satellite & Broadband
Communications (satcoms); e-Government & e-Enterprise; and Eco-enabling ICT. Its core
capabilities lie in its design, development and integration of advanced electronics systems
for commercial, industrial, defence, government and public services applications worldwide.
With its satcoms, e-Government and e-Enterprise, and eco-enabling ICT capabilities
and expertise, ST Electronics offers wired and wireless communication solutions,
rail and traffic management systems, real-time C4I (command, control,
communication, computing and intelligence) solutions, modelling and training
simulation, intelligent building management systems, homeland security solutions
and managed services. It undertakes continuing research and development to help
create cost-effective purpose-built products at both system and sub-system levels for
customers.
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ST Electronics’ unique strength and track records have made it a trusted partner of
its customers, both government and commercial. With more than 5000 staff, it has
accumulated extensive experience and skills in designing mission critical real-time
systems and in delivering complex security and infrastructure projects. Our solutions
empower government agencies to optimise scarce resources and increase operational
efficiencies. We also provide the best communication infrastructure for effective
crises management.
2.2 DEFENSE BUSINESS UNIT
In Defense Systems, we continuously build on our cumulative experience acquired
over the past 40 years of integrating, maintaining and upgrading weapons and
electronic systems.
We provide System Life Cycle Solutions to defence and non-defence customers.
ST Electronics' involvement in major platform building and multi combat systems
integration programmes cover a full spectrum of system life cycle activities. This
cycle continues into system upgrades, obsolescence management and/or acquisition
of new systems.
ST Electronics provides innovative systems integration services for combat systems
for various naval platforms as well as air defence systems. With today’s demand for
highly integrated combat suites, System of Systems (SoS) integration has become an
increasing important activity and capability that would enhance the overall value
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and capability of defence combat systems. We have the experience and competency
in interface design management for multi-systems integration.
System integration activities would include:
System interface definition, specification and design
Inter/Intra system interface testing
Installation, checkout, integration and testing (ICIT)
Technical studies and consultancy
Our core capabilities include:
Electronic systems integration for naval platform (MCV, LST, Frigate)
Electronic Systems Integration for weapon systems
Integration of mobile radar systems
Technical studies and consultancy
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CHAPTER 3 – THE DESIGN PROCESS
Figure 1. The Design Process
Design Brief
The design brief is typically a statement of intent. I.e. “We will design and make an
AUV Deployment System”.
Product Design Specification
During this phase, the customer states the requirements that they desire to come out
with a successful product. The designer should constantly refer back to this
document to ensure that the designs are appropriate.
Producing the Product Design Specification would require you to research the
problem and analyse competing products and all-important points.
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Concept Design
Using the Product Design Specification as the basis, the designer will come out with
an outline of the key components and their arrangement with the details of the
design left for a later stage. During this stage it is important that we consider not
only the product design specification but also consider the activities after the design
stage. These include namely the manufacturing, sales and transportation. By
considering all these in the early design stages would eliminate problems that can
occur later on in the design stages. This stage of the design involves drawing up a
number of different viable concept designs which satisfy the requirements of the
product outlined in the product design specifications and then evaluating them to
decide on the most suitable to develop further. Hence, concept design can be seen as
a two-stage process of concept generation and concept evaluation.
Detail design
In this stage of the design process, the chosen concept design is designed in detailed
with all the dimensions and specifications necessary to make the design specified on
a detailed drawing of the design. It may be necessary to produce prototypes to test
ideas at this stage. The designer should also work closely with manufacture to
ensure that the product can be made.
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Chapter 4 – AUTONOMOUS UNDERWATER VEHICLE (AUV)
LAUNCH AND RECOVERY SYSTEM (LARS)
4.1 LAUNCH AND RECOVERY SYSTEM OVERVIEW
As the usage of Autonomous Underwater Vehicle (AUV) become more widespread,
it can be foreseen in the near future, AUVs will be deployed in fully autonomous
scenarios, i.e. the systems do not have human intervention from deployment of AUV
to mission execution to recovery of AUV. Hence it is necessary for the Launch and
Recovery Systems (LARS) to be reliable as they will aid in the recovery, recharging
and transfer of data from the AUV onto the supporting platform.
The AUV after its mission will proceed to the rendezvous point where it will be in
close proximity with the mechanical guidance hoop that will retrieve the AUV out
from the water. But due to the water currents and unforeseen weather conditions, it
was necessary to have some sort of system that would guide the AUV safely into the
mechanical guidance hoop. This can be achieved by, installing three acoustic
receivers which will seek acoustic contact with the AUV transponders.
The mechanical guidance hoop is concerned with the position of itself, relative to
the AUV, and with that, it can maneuver itself to a position where the AUV will
enter the mechanical guidance hoop safely.
This mechanical guidance hoop will be the equipment that is used to launch and
recover the AUV before / after a mission. Hence it is important that the mechanical
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guidance hoop can hold the required hardware on board, at the same time, be
reasonably small enough to reduce the storage space on the deck.
This is a joint project between ST Electronics and NUS Acoustic Research Lab,
supervised by DSO.
4.2 CHALLENGES OF THE EXISTING HOOP DESIGN
Diameter: 1500 mm
Rear View
1586 mm
Side View
Isometric View
Figure 2(a). Figure 2(b).
Figure 2(c).
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The existing guidance hoop design takes up a significant amount of space on the
platform on which it is operating from. This makes the hoop rather clumsy to
operate due to the large diameter. The diameter of the hoop is preferably, be variable
so that it can be collapsed inwards to reduce the diameter after recovery / stored on
the platform. And during deployment / pre-recovery, the hoop opens up to form a
‘basket’. The student then goes through the full design process (Conceptual Design,
Detail Design, Final Design).
4.3 CONCEPTUAL DESIGN PHASE
Concept 1
Figure 3(a). Figure 3(b).
The working mechanism Concept 1 is obtained from an umbrella. During recovery,
the winch will pull the mechanical guidance hoop / basket that we see on the Figure
1(a). Once the struts contact the side of the cylinder / cage, the struts will then
collapse inwards, reducing the diameter of the mechanical guidance hoop. During
deployment, the struts will move out of the cylinder / cage, the individual struts will
spread open by having spring mechanisms.
Winch
Cylinder / Cage
Struts
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Concept 2
Figure 4(a). Figure 4(b).
Concept 2 is operated by a slider mechanism (in green), when the slider slides along
the guides, it will cause the struts to open and close, changing the diameter of the
mechanical hoop. This slider will be actuated by a hydraulic / pneumatic actuator.
Concept 3
Figure 5(a). Figure 5(b).
Concept 3 is being operated by 4 hydraulic actuators. Upon extension of the
hydraulic actuators, it will cause the mechanical linkages to be spread open, forcing
Slider Sliding Guides
Struts
Hydraulic Actuator
Struts
Mechanical Linkage
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the struts to move away and apart from each other. The vice versa will happen
during retraction of the hydraulic actuators.
Based on the above conceptual ideas, Concept 3 has been chosen as the preferred
working principle for the LARS. With the selected Concept 3, the student will
proceed into the detail design phase.
4.4 DETAIL DESIGN PHASE
As this is a joint project between ST Electronics and NUS Acoustic Research Lab,
the two parties will have to work together closely. NUS Acoustic Research Lab will
be in-charge of determining the types of hardware that will be installed and its
quantity, which will be installed on the mechanical guidance hoop. As NUS has yet
to confirm the hardware and its quantity that will be installed onto the mechanical
guidance hoop, the student did an assumption on the hardware to be installed based
on existing designs from the North Atlantic Treaty Organization (NATO). This will
allow the student to gauge the amount of hydraulic pressure the system has to
provide in order to open the mechanical guidance basket. This will have significant
impact on the design of the hydraulic circuit as well as the specification of the
hydraulic pump / system.
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4.4.1 GENERAL DIMENSIONS OF CONCEPT 3 (SELECTED
CONCEPT DESIGN)
As compared to the initial design that had a diameter of 1500mm. The proposed
design had a storage diameter of approximately 500mm. This is a significant
reduction, it would reduce the clumsiness in handling this equipment as well as the
storage space on deck.
Figure 6(a). Figure 6(b).
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4.4.2 SAMPLE DETAIL CALCULATIONS
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CHAPTER 5 – ON – SITE ASSIGNMENTS
5.1 FORCE PROTECTION (FP) WORK DESK LAYOUT
The purpose of doing a SolidWorks layout of the
Force Protection (FP) work desk is necessary to
have a visual representation of how the hardware is
to be placed. This would not only allow the designer
to see the amount of space required to place all the
hardware, but also allow the designer to take into
consideration human factors such that the operator
of the system can work comfortably and at ease.
Factors such as whether the operator can reach each
and every hardware easily are the screens tilted
sufficiently such that the operator can see both
screens without having to turn the head much. At
the same time are the screens sufficiently elevated
so that the operator wouldn’t get strained neck from
prolonged usage.
Isometric View
Back View
Front View Top View
Figure 7(a).
Figure 7(b).
Figure 7(c). Figure 7(d).
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5.2 FORCE PROTECTION (FP) HEAVY MACHINE GUN (HMG)
This is an alternative method of getting the information of a certain component that
is available in the market. Unlike requesting the manufacturer / supplier to send a
dimensioned drawing, an engineer could model out the component using a picture
that is easily available from the internet. After which, he will identify all the vital
dimensions / information that he / she requires. This engineering drawing shown
below shows the general shape of the component, and its vital dimensions /
information required. All that is required of the manufacturer / supplier is to fill in
the table on the bottom right. In this case, a M2 Browning 50 Caliber Heavy
Machine Gun (http://en.wikipedia.org/wiki/M2_Browning) is being used.
Figure 8(a).
Figure 8(b).
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5.3 AC DC CONVERTER BRACKET AND COVER DESIGN
The student was tasked to design a bracket to hold the AC DC Converter as well as a
‘cover’ to protect the AC DC Converter from seawater that may leak into the
compartment. This AC DC Converter was to be attached into the left compartment
of the Unmanned Surface Vehicle (USV). Hence it was required that the bracket
would hold on to the AC DC Converter firmly. This assignment has exposed the
student to basic bracket design, how to use the hole features in SolidWorks as well
as to know the key requirements for proper engineering drawing.
Isometric View Front View
Bracket Design
AC DC
Converter
Cover
Bracket
Figure 9(a). Figure 9(b).
Figure 9(c).
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5.3.1 Engineering Drawings
Engineering Drawing (Bracket)
Engineering Drawing (Cover)
Figure 10(a).
Figure 10(b).
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After the fabrication of the bracket and the cover, the student was tasked to install it
onto the left compartment of the USV.
5.4 Modeling of Existing Products
The students also help to model components using SolidWorks, such as the two
screens and AC DC Converter above so that it can aid in the downstream design
Figure 11(a). Figure 11(b).
Figure 11(c).
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process. For example, with this virtual model, designers can have a better idea how
big / wide a frame / bracket has to be to hold the screen / AC DC Converter in
position.
5.5 Bow Thruster Removal Manual
The Bow Thruster Removal Manual was written to record down the procedure
required to install / remove the bow thruster. This manual is written to help users
without any prior experience, be able to remove the bow thruster by following the
simple instructions.
The Bow Thruster Removal Manual can be found under Appendix A.
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5.6 BUILDING OF MOCK-UPS
In manufacturing and design, the building of a mock up, which a scaled or full-sized
model of a component / design for the purpose of demonstration, design evaluation,
promotion etc. It is also known as a prototype that provides a part of the
functionality of a system and enables testing of a design.
During the building of the mock-up, we begin to see the structural weakness in
certain parts of the component such that we can make amendments to the design.
During this stage we can also assess whether the user / operator can use the
equipment comfortably (Ergonomics), these questions might include, “Are the
screens located too high up such that the operator needs to strain his neck?”, “Can
the operator reach the controls easily?”.
Hence, the building of mock-ups would allow us to identify the design deficiencies.
It is a useful method of assessing engineering designs.
Figure 5.6(a)
Figure 12.
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5.7 MARINE CORROSION CONTROL RESEARCH PAPER
To generate a knowledge / reference database for DBU as well as for the internship
students, the students were tasked to do a research on one of the topics below. This
project will directly, be related to our field of work.
1. Marine fouling
2. Marine corrosion
3. Shock mounts - types, applications and selection
4. Shock and vibration study
5. Aluminum and steel - types and applications
7. Plastics - types and applications
8. Design for Human Factor Engineering
9. Fastener joints - design and selection
10. Types of fastening joints and applications
11. Design considerations for Thermal Management
12. Design considerations for EMI/EMC
13. Welded joints
The student selected Marine Corrosion to do research on. The Marine Corrosion
Control Research Paper can be found under Appendix B.
This Research Paper will inform the readers on the different causes of marine
corrosion, the 8 different types of corrosion commonly form as well as the means to
retard / eliminate corrosion.
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5.8 THRUSTERS
Due to a need to keep the position of the boat exact for the recovery of the AUV,
maneuvering thrusters have to be used to keep position of boat exact. The student
was tasked to search for thrusters that can provide sufficient force to move the boat,
with the requirements that the reaction of the boat, to the water jet is reasonably fast.
The student did a research on available thrusters in the market, but costs
approximately S$10,000. As this is just to experiment how much of force is actually
needed to obtain a reasonable reaction from the boat, the student is task to find other
alternatives. The student did a research on water pumps available in the market that
can provide the same amount of thrust as the thrusters. Key considerations are that
the pump must be able to supply sufficient pressure at a depth of approximately
0.6m. Based on calculations it should supply around 50kgf at the nozzle of 45mm
diameter. This will then be installed onto the boat for testing. Before that,
Solidworks layout of the aft deck of the boat has to be done.
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CHAPTER 6 - CONCLUSION
The 22 weeks Internship Program has exposed the student to working environment
of the engineering industry. This is the experience that the student would not be able
to have in school.
It allows the student to better analyze and solve problems, including the attitude
towards problems. Without a doubt, this experience changed him not to see
problems as just obstacles, but also as learning opportunities. By learning from the
experience of the engineers within the department has not only widened the
student’s perspective but also allowed the student to exercise his innovation and
creativity in overcoming problems. Key lesson learnt as a designing engineer is that
during the design stage, we have to foresee / imagine how the product / component
will be manufactured / assembled.
The program has also provided the student with not just the design process
experience but also seeing the outcome of his design. At the same time the program
provided hands-on projects, which were far more beneficial than the theoretical
information that we learn from books, and expands his technical knowledge. This
training will put him in a good start for prospective job opportunities.
Furthermore, the student is exposed to the realities of the society, learning to handle
working relationships with colleagues, most importantly learning how to juggle
work / personal time properly. It is indeed a valuable experience.
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APPENDICES
APPENDIX A
Bow Thrusters Removal
Manual
A1
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APPENDIX A
Basic Tools Required:
1. Wrench
2. Spanner
3. Flat Head Screwdriver
4. Hydraulic Jack (Can be used to secure blanking plate to
mounting)
5. Sealant
6. Grease
A2
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APPENDIX A
Removal of Bow Thrusters
Figure 1
Figure 2
Figure 3
Bow
Bow
Rubber
Sealant
Bow Thrusters
Hull
Figure 1.
The initial configuration
prior to removal. Take
note of the orientation
of the bow thrusters.
Figure 2.
The rubber sealant
that seals the hull and
the bow thruster
interface shall be
removed.
Figure 3.
Fore Bow (Above Bow
Thrusters)
Access
Hatch
A3
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APPENDIX A
Figure 4
Figure 5
Figure 6
v
Bow
Nuts
(x3)
Figure 4. Fore deck
above bow thruster,the
nuts (x3) must be
loosened to allow
removal of bow
thrusters.
Figure 5.
Loosen the bolt using a
wrench (For both the
port and starboard bolt)
Note: It is important to
support the bow
thrusters at this point of
time.
Figure 6.
Nuts fully removed.
Lower the bow
thrusters.
Note: The larger bolt
has cables running
through it.
A4
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APPENDIX A
Figure 7
Figure 8
Figure 9
Figure 7.
Cabling
Note: Do not pull the
cables out.
Bow
Figure 8.
On fore deck, starboard
side. Remove the cover
by removing the nuts
(x4)
Cover
Figure 9.
Cover opened. Bow
thrusters cabling can be
removed by removing
the nuts.
Remove the red and
yellow cabling (Only
remove the cabling with
smaller diameter).
A5
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APPENDIX A
Figure 10
Figure 11
Figure 12
Figure 10
Cables (Red and Yellow)
of smaller diameter is
removed and then
pushed through the
deck, through the
glands.
Figure 11.
After removal of cables
Figure 12.
After cables are
unattached, the bow
thrusters can be
lowered fully.
A6
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APPENDIX A
Figure 13
Figure 14
Figure 15
Figure 13.
Mounting. Bow thrusters
removed.
Figure 14.
Apply sealant around
the profile of the
blanking plate and apply
grease around bolts to
allow ease for future
removal.
Figure 15.
Blanking plate is used
to seal the holes.
Secure the nuts to the
bolts from the fore deck.
A7
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APPENDIX B
MARINE CORROSION CONTROL
Prepared by: CHU WEI XIN
Student No: U0920905B
Institution / Organisation: NANYANG TECHNOLOGICAL UNIVERSITY
Faculty: MECHANICAL ENGINEERING
Date: 24 June 2011
B1
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APPENDIX B
1 ABSTRACT
Marine corrosion is a significant and costly problem faced by the marine industry.
Day in and day out, vessel owners have to spend time and money to install
preventive measures to reduce / prevent damage to the hull and underwater
machinery so that it can remain in seawater for extended periods of time. The cost of
repairing damages due to corrosion is directly proportional to the degree of
corrosion.
This research paper describes the mechanisms of corrosion, the different types of
corrosion faced by the marine industry, as well as the measures to control corrosion.
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APPENDIX B
2 TABLE OF CONTENTS
CHAPTER
1 ABSTRACT……………………………………………………………………….B2
2 TABLE OF CONTENTS………………………………………………………….B3
3 INTRODUCTION…………………………………………………………………B4
3.1 Definition of Corrosion…………………………………………………...B4
4 MECHANISMS OF CORROSION……………………………………………….B5
4.1 Driving Force for Corrosion………………………………………………B5
4.2 Fundamental Mechanism for Corrosion…………………………………..B5
5 FORMS OF CORROSION………………………………………………………..B7
5.1 General Corrosion………………………………………………………...B7
5.2 Galvanic Corrosion……………………………………………………….B8
5.3 Erosion / Abrasion Corrosion…………………………………………….B8
5.4 Intergranular Corrosion…………………………………………………...B9
5.5 Pitting Corrosion………………………………………………………...B10
5.6 Crevice Corrosion………………………………………………………..B11
5.7 Microbiologically Induced Corrosion……………………………….…..B12
5.8 Stress Corrosion Cracking……………………………………………….B12
6 METHODS OF PROTECTION FROM
CORROSION…………………………………………………………………….B13
6.1 Applied Coatings………………………………………………………...B13
6.2 Cathodic Protection……………………………………………………...B18
6.3 Materials Selection and Design………………………………………….B22
7 CONCLUSION…………………………………………………………………..B23
8 REFERENCES…………………………………………………………………...B24
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APPENDIX B
3 INTRODUCTION
Corrosion of marine and underwater machinery is a common and serious problem in
the marine industry. Actions carried out to control the degree of corrosion are among
one of the reasons for us to carry out maintenance on marine machinery.
Understanding the mechanisms that lead to corrosion, the different forms of
corrosion as well as corrosion control measures is vital for the effective control of
corrosion on marine machinery.
3.1 DEFINITION OF CORROSION
Corrosion is the disintegration of an engineered material into its constituent atoms
due to chemical reactions with the environment that it is in. It is simply the
electrochemical oxidation of metals in reaction with an oxidant such as oxygen. The
formation of an oxide of iron due to the oxidation of iron is often known as rusting.
In short, corrosion is the wearing away of metals due to a chemical reaction.
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APPENDIX B
4 MECHANISMS OF CORROSION
4.1 DRIVING FORCE FOR CORROSION
In nature, most metals are found in chemical combination with other elements.
These metallic ores are refined by man and formed into metals and alloys. As the
energy content of the metals and alloys is higher than that of their ores, chemical re-
combination of the metals to form ore like compounds is a natural process.
4.2 FUNDAMENTAL MECHANISM OF CORROSION
As stated in the previous section, corrosion is an Electro-Chemical Reaction.
Definition of E·lec·tro·chem·i·cal
– noun - the production of electricity by chemical changes.
- are chemical reactions in which not only may elements be added or removed from a
chemical species but at least one of the chemical species undergo a change in the
number of valence electrons.
Figure 1. An example of a corrosion cell
Electron
Path
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APPENDIX B
An Electro-Chemical Reaction can be explained as follows. A metallic surface is submerged
in an aqueous Electrolyte. An Electrolyte is simply a solution that conducts electricity. This
metallic surface will have sites for oxidation and reduction, bearing in mind that oxidation
occurs at an anode and a reduction occurs at a cathode. These sites will form a
Corrosion Cell.
At the anode, electrons are produced through the chemical activity of the metal.
Metal loss occurs in this area and migrates from the metal surface through the
environment. At the cathode, it is the site where electrons are consumed. For each
electron that is produced at the anodic site, an electron must be consumed at the
cathodic site. There will be no metal loss at sites that are cathodic.
The path taken by electrons follows through a metallic path. This occurs due to the
difference in voltage between the anode and the cathode reaction. Electrons can
move through metals and some non-metals easily.
Seawater
Seawater (NaCl) is an excellent electrolyte. Seawater (NaCl) contains large amounts
of dissolved salts, or sodium chloride, which makes it an excellent conductor.
Seawater, is especially aggressive as it would break down any natural protective
films on the surface of metals, for example titanium and stainless steels. Seawater
also contains significant amounts of oxygen for reducing water to be the cathodic
reaction in many cases.
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APPENDIX B
5 FORMS OF CORROSION
There are 8 different forms of corrosion. They are as follows:
1. General corrosion
2. Galvanic corrosion
3. Erosion/abrasion corrosion
4. Intergranular corrosion
5. Pitting corrosion
6. Crevice corrosion
7. Microbiologically induced corrosion
8. Stress corrosion cracking
5.1 GENERAL CORROSION
General corrosion is the corrosion of an entire metal surface or a large fraction of the surface.
The metal becomes thinner until it fails. This corrosion occurs uniformly. This form of
corrosion is least dangerous as it can be predicted and measured. Two typical conditions for
a metal corrosion are:
1. Metal and humidity in the same environment.
2. Chemical reaction between the metal and water that form an oxide.
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APPENDIX B
5.2 GALVANIC CORROSION
Galvanic corrosion occurs when two different metals are in electrical contact and immersed
in the same corrosive solution. Stainless steels are noble metals and therefore seldom suffer
increased corrosion rates as a result of galvanic corrosion. When a galvanic couple forms,
one of the metals in the couple becomes an anode while the other becomes the cathode. The
anode would corrode faster than it would all by itself. The cathode will corrode slower than
it would by itself. In order for a galvanic corrosion to occur, the three conditions must be
present:
1. Electrochemically dissimilar metals must be present.
2. These metals must be in electrical contact.
3. The metals must be exposed to an electrolyte.
Galvanic corrosion can be slowed down or eliminated by cathodic protection. One of the
methods is simply to attach a third metal to the metals to be protected. The most active
metal will corrode in place of the protected metal. This is called sacrificial protection. Zinc
is a common metal that is used to protect marine machinery from corrosion by seawater.
5.3 EROSION/ABRASION CORROSION
Erosion corrosion occurs due to a flow-induced mechanical removal of the
protective surface film. This would result in an increase in the subsequent corrosion
rate through either an electrochemical or chemical process. The fluid that flows
across the surface of the metal will create disruptive shear stresses or pressure
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APPENDIX B
variations. Corrosion can be enhanced when there is presence of particles, such as
solids or gas bubbles.
5.4 INTERGRANULAR CORROSION
Intergranular corrosion is a form of corrosion that occurs at the grain boundaries of
crystallites. To increase the corrosion resistance, a minimum of 12% chromium is
added. The metal in itself contains some carbon content. Noting that metals are
composed of many microscopic crystallites. The adjoining portions of the crystals
are called grain boundaries. Even in metals, diffusion will occur. Diffusion rates are
most significant along grain boundaries. Chromium carbide will be formed along the
grain boundaries, causing chromium-depleted boundaries. This will greatly reduce
the corrosion resistance of the metals along the grain boundaries. With the grain
boundaries being linked to the surface of the metal, corrosion will start within the
metal, and progress towards the surface. Hence, any solution that contacts the
surface of the metal will seep into the metal via the chromium-depleted grain
boundaries.
Grain Boundary
Metal Surface
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APPENDIX B
This problem can be countered by lowering the carbon content in the metal.
Impurities that have a greater affinity with carbon, for example titanium, can be
added to prevent the formation of chromium-carbide. This will significantly reduce
the chromium depletion along grain boundaries and metal surfaces.
5.5 PITTING CORROSION
Pitting is a localized form of corrosion. It occurs when cavities or holes are produced
in the material. This form of corrosion is considered to be more dangerous than
uniform corrosion damage because it is more difficult to detect, predict and design
against. A small narrow pit with minimum metal loss can lead to the failure of an
entire engineering system.
Pitting can be initiated by localized chemical or mechanical damage to the protective
oxide film. It can be caused by the acidity of the water, low dissolved oxygen
concentrations and high concentrations of chloride. Other causes can be due to poor
application of protective coating as well as the presence of non-uniformities in the
metal structure of the component.
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APPENDIX B
5.6 CREVICE CORROSION
Crevice corrosion occurs in spaces to which the excess of the working fluid from the
environment is limited. These spaces are called crevices. Crevices are gaps and
contact areas between contacting parts. Corrosion resistances of metals are
dependent
on the presence of the natural protective oxide layer on its surface. However it is
also possible to break down this protective oxide layer in reducing acids. The design
of the component can also affect the places where the protective oxide will break
down. For example, sharp corners with incomplete weld penetration or overlapping
surfaces. All these form crevices which promote corrosion.
Crevice corrosion usually occur in gaps a few micrometers wode. This problem can
be overcomes by paying close attention to the design of the component, in particular
avoid the formation of crevices or keep them as wide as possible. It is very similar to
pitting corrosion. Crevice corrosion can be seen as a more severe form of pitting
corrosion due to the fact that it occurs at significantly lower temperatures than
pitting. Two factors are initiates an active crevice corrosion, firstly is the chemical
composition of the electrolyte in the crevice and secondly, the potential drop into the
crevice.
Taking note of the differences with galvanic corrosion.
Galvanic Corrosion – Two connected metals in a single environment
Crevice Corrosion – One metal part in two connected environments
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APPENDIX B
5.7 MICROBIOLOGICALLY INDUCED CORROSION
Microbiologically induced corrosion, also known as bacterial corrosion, is corrosion
caused by microorganisms, in most cases, chemoautotrophs. It can occur on both
metallic and non metallic materials.
5.8 STRESS CORROSION CRACKING
Stress corrosion cracking is the sudden failure of ductile metals subjected to tensile
stress in a corrosive environment, especially under elevated temperatures in the case
of metallic materials. Stress corrosion cracking is dangerous in the sense that metal
parts with severe stress corrosion cracking can appear bright and shiny, while being
filled with microscopic cracks. This makes it even more prone for stress corrosion
cracking to go undetected prior to failure. Stress corrosion cracking progresses
rapidly and it occurs more often in alloys than in pure metal. Hence the environment
is of a crucial important and very small amounts of highly active chemicals are
needed to produce catastrophic cracking, which leads to sudden and devastating
failure. Causes can be due to stress concentration, or can be caused by the type of
assembly or residual stresses from fabrication, for example cold working. Annealing
can relieve this internal stress.
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APPENDIX B
6 METHODS OF PROTECTION FROM CORROSION
6.1 APPLIED COATINGS
There are several questions to be asked :
1. What is the type and condition of the metal to be protected?
2. What is the basic function of the coating on the metal?
3. What is the nature of the environment?
4. What are the desired properties of the coating?
6.1.1 SURFACE PREPARATION
Prior to applying protective coatings, the most important factor that affects the
success of the corrosion protection system is its surface preparation. Surface
preparation not only cleans the surface of the metal, but it also creates a suitable
surface to receive the protective coating. There are 4 grades of cleanliness for
abrasive blast cleaning.
SA1 – Light Blast Cleaning
SA2 – Thorough Blast Cleaning
SA3 – Very Thorough Blast Cleaning
SA4 – Blast Cleaning to Visually Clean Metals
The type and size of abrasive used in abrasive blast cleaning affects the profile of the
surface produced. Grit abrasives produce a coarse surface such that the protective
coating can have a ‘grip’ onto the surface.
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APPENDIX B
6.1.2 PAINT COATINGS
Protective coatings usually consist of a primer and an intermediate layer of coating.
The primer wets the surface of the metal, and provides a good adhesion between the
metal and the protective coatings. The intermediate coatings are mainly to increase
the thickness of the protective film. In simple, the thicker the coatings, the longer is
the life of the protection. These surface coatings not only provide the necessary
surface appearance, but it also protects the surface from sunlight, humidity and
weather.
There are mainly 7 types of coatings.
1. Oil Base Coatings
They are the first coatings used to protect steel from corrosion. They are used widely
today. However they are prone to failure and have limited lifespan in severe
environments. Oil based coatings are more tolerant of incomplete surface
preparation as compared to other coatings due to the fact that they wet surfaces to be
protected, better. However these coatings deteriorate rapidly in water
2. Latex Coatings
Latex Coatings are easy to apply and clean up. They are also environmentally
acceptable. The disadvantages are that they are less durable when applied to steel
and other metals. At the same time they are less resistant to chemical and solvents.
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3. Epoxy Coatings
Epoxy has the best combination of resistance to chemical, water and solvents. They
form a hard film with resistance to abrasion and durability. However epoxy coatings
are inflexible, poor resistance to weather. Epoxy coatings are used mainly for on-
shore facilities.
4. Coal Tar Epoxy Coatings
Coal Tar Epoxy Coatings have coal tar added to epoxy to increase its resistance to
water. However it becomes brittle when exposed to sunlight.
5. Urethane Coatings
Urethane coatings have a greater range of properties as compared to epoxy. They
can be rigid or elastomeric and have excellent or poor resistance to weather. They
have excellent resistance to water, solvents and chemicals. This coating is highly
toxic. Another disadvantage is that it does not bond as well to metals as epoxies,
hence it is quite oftenly, applied over
6. Zinc Rich Inorganic Coatings
Inorganic coatings are abrasion resistance and provide cathodic protection to metals.
They require the cleanest surfaces prior to application.
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7. Zinc Rich Organic Coatings
Several resins can be used to produce zinc rich organic coating. They include
epoxies and urethane coatings. They provide both surface protection and cathodic
protection to metals. They require very clean surfaces prior to application and are
easier to top coat as compared to zinc rich inorganic coatings.
6.1.3 METALLIC COATINGS
The two most common methods of metallic coatings are thermal spraying and hot-
dip galvanizing.
Thermal Spraying
Thermal spraying provides long term corrosion protection to steel structures that are
exposed to aggressive environments. The metal for coating, which can be in the
form of powder or metal wire, is sprayed through a spray gun with a heat source. A
compressed air jet blows these molten globules of metal onto the treated metal
surface. This protective coating, is porous and requires sealing after application.
Hot Dip Galvanizing
It is the process of dipping a steel component into molten zinc. This coating of zinc
provides cathodic (sacrificial) protection to any small damage areas where the steel
is exposed.
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APPENDIX B
6.1.4 REACTIVE COATINGS
These coatings form an electrical insulation or chemically impermeable coating on
exposed metal surfaces, to suppress electrochemical reactions. This makes the
component less sensitive to defects in the coating.
ANODIZATION
Aluminium alloys are often subjected to undergo a surface treatment. The treatment
involves dipping the metal into a bath, which is carefully adjusted so that uniform
pores several nanometers wide appear in the metal’s oxide film. These pores enable
the oxide film to be much thicker than passivating conditions would allow. After
which, the pores are allowed to close, which forms a even stronger and harder
surface layer. In cases where the coating is being scratched, the normal passivation
processes will take over to protect the damaged area. This process is very resistant to
weather and corrosion.
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APPENDIX B
6.2 CATHODIC PROTECTION
When two metals with different energy levels or potential are coupled together,
current will flow. The positive current will flow from the metal with the more
negative potential to another metal, which has a more positive potential. Corrosion
occurs at the point where the positive current leaves the metal. In order to prevent
corrosion, current must flow from the electrolyte to all points on the metal. Any
point that does not receive the current, corrosion will continue there.
Cathodic protection can be achieved by two means:
1. Use of galvanic anodes
2. By impressed current
It is an electrical method of impeding / preventing corrosion on metallic structures
that are submerged in electrolytes.
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APPENDIX B
Galvanic Anode System
This system employs the use of reactive metals as auxiliary anodes that are directly
electrically connected to the steel to be protected. The difference in the natural
potentials between the anode and the steel can be seen from the electrochemical
series. This will result in a positive current to flow in the electrolyte, from the anode
to the steel. The whole surface of the steel will become negatively charged and
becomes cathodic. Common metals used as anodes are aluminium, zinc and
magnesium. This system has the advantage of being easy to install , independent of
an external power source, suitable for localized protection and less liable to cause
interaction on neighboring structures.
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APPENDIX B
Impressed Current Systems
Impressed current systems use inert anodes and an external dc power to create a
current from an external anode onto the cathodic surface. Impressed current system
has the advantage of being able to supply a large current, able to provide high dc
driving voltage which enables it to be used in most electrolytes and able to provide
flexible output that may accommodate changes.
6.2.1 ADVANTAGES OF CATHODIC PROTECTION
The main advantage of cathodic protection is that it can simply be done so by
maintaining a dc circuit. This is commonly applied to a coated structure to provide
corrosion control where the coating may be damaged. This can be done so to
existing components to extend their life.
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APPENDIX B
6.2.2 LIMITATIONS OF CATHODIC PROTECTION
The presence of negative potentials can cause an acceleration in corrosion of lead
and aluminium structure because of the alkaline environment created at the cathode.
These alkaline conditions may cause a loss of adhesion of the coatings. The
generation of hydrogen at the cathode surface of high strength steel may result in
hydrogen embrittlement. This will cause a loss in the strength of the metal, thus
causing a catastrophic failure.
6.2.3 BASIC REQUIREMENTS OF CATHODIC PROTECTION
a. A galvanic system requires:
i. Sacrificial anodes
ii. Direct welding to the structure or a conductor connecting the anode
to the structure
iii. Minimum resistance between the conductor and the structure, and
between the conductor and the anode
b. A impressed current system requires:
i. Inert anodes
ii. DC power source
iii. Electrically insulated and minimum resistance and secure connectors
between the anode and power source.
iv. Secure and minimum resistance between power source and structure
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APPENDIX B
6.2.4 APPLICATION
Galvanic anodes made of aluminium, zinc or magnesium is available in block, rod or wire
forms. These alloys are cast around steel inserts to allow for the fixing of the anode and to
maintain electrical continuity and mechanical strength at the end of the anode life. The
insert may be welded or bolted onto the structure to be protected. It can also be attached to
the structure by means of an insulated lead, usually made of copper for both onshore and
offshore applications.
6.3 MATERIALS SELECTION AND DESIGN
There is no material that is resistant to all corrosive situations. Material selection is
very important to preventing failures due to corrosion. Design includes many factors
that are taken into consideration. They include materials selection, process and
construction parameters, geometry for drainage, or electrical separation of dissimilar
metals, operating lifetime, maintenance and inspection requirements.
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7 CONCLUSION
The mechanisms that encourage corrosion have been explained in this paper. This
would enable the user to eliminate / impede corrosion propagation. The 8 different
forms of corrosion has also been explained, they are namely: General Corrosion,
Galvanic Corrosion, Erosion / Abrasion Corrosion, Intergranular Corrosion, Pitting
Corrosion, Crevice Corrosion, Microbiologically Induced Corrosion and Stress
Corrosion Cracking. The various types of corrosion have different signs that can be
identified by various means. Early detection would allow the user to apply the
various protective measures. These measures include Galvanic Anode System
protection, Cathodic Protection System as well as Material Selection and Design.
These answer the issues of the cause of corrosion, the different types of corrosion as
well as how to counter them.
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8 REFERENCES
1. Naval Facilities Engineering Command (1992)
http://www.vulcanhammer.net/marine/Mo307.pdf, Corrosion Control
2. http://www.corrosionist.com/Corrosion_Fundamental.htm, Fundamental of
Corrosion Chemistry
3. D Wesley Fowler,
http://geminimarinesurvey.com/yahoo_site_admin/assets/docs/Marine_Metal_Corro
sion.325111027.pdf, Marine Metal Corrosion
4.http://www.csun.edu/~bavarian/Courses/MSE%20531/corrosion_class_notes/Coat
ings_and_Inhibitor_Ch_15.ppt, Coatings and Inhibitors
5.Wikipedia, http://en.wikipedia.org/wiki/Corrosion, Corrosion
6. Ernest B. Yeager Center for Electrochemical Sciences (YCES),
http://electrochem.cwru.edu/encycl/art-c02-corrosion.htm, Electrochemistry of Corrosion
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