IA Final Report

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



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



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



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.



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.



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



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



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.



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.



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.



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



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



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.



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.



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



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).



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


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



Concept 2


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


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



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.



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.




4.4.2 SAMPLE DETAIL CALCULATIONS





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).



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).



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(c).



5.3.1 Engineering Drawings

Engineering Drawing (Bracket)

Engineering Drawing (Cover)

Figure 10(a).

Figure 10(b).



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(c).



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.



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.



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.



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.



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.



APPENDICES

APPENDIX A

Bow Thrusters Removal

Manual

A1



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



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



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



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



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



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



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



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.

B2



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

B3



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.

B4



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

B5



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.

B6



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.

B14



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.

B15



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

B24

http://www.vulcanhammer.net/marine/Mo307.pdf

http://www.corrosionist.com/Corrosion_Fundamental.htm

http://geminimarinesurvey.com/yahoo_site_admin/assets/docs/Marine_Metal_Corrosion.325111027.pdf

http://geminimarinesurvey.com/yahoo_site_admin/assets/docs/Marine_Metal_Corrosion.325111027.pdf

http://en.wikipedia.org/wiki/Corrosion

http://electrochem.cwru.edu/

http://electrochem.cwru.edu/encycl/art-c02-corrosion.htm



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