EFFECTS OF DISSOLVED HYDROGEN ON HIGH TEMPERATURE CORROSION RESISTANCE OF

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EFFECTS OF DISSOLVED HYDROGEN ON HIGH TEMPERATURE CORROSION RESISTANCE OF

CHROMIA SCALE

BY

SYAMSUL KAMAL BIN ARIFIN

A dissertation submitted in fulfillment of the requirement for the degree of Master of Science (Materials Engineering)

Kulliyyah of Engineering

International Islamic University Malaysia

JULY 2018

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ii

ABSTRACT

Fe-Cr alloy is commonly being used as boiler tube’s material. It is subjected to prolonged exposure to water vapor oxidation. The ability to withstand high temperature corrosion can normally be attributed to the formation of a dense and slow growing Cr-rich-oxide scale known as chromia (Cr2O3) scale. This scale protects Fe- Cr from further high temperature corrosion. However, oxidation may limit the alloy’s service lifetime due to the declining of its protective capability. One of the factor to this issue is hydrogen induced cracking which paradoxically, water vapor dissociates to dissolved H2. But to date, this claim has not being fully studied systemically. Thus, these led to the need of studying the effect of dissolved H₂ on high temperature corrosion resistance of chromia scale. This work focus on the effect of dissolved H2 to Cr2O3 protectiveness and its surface bond. To observe the protectiveness capability, Cr2O3 pellet has been examined its mass change by thermo gravimetric analysis. A dense sintered Cr₂O₃ was being exposed to dry (Ar) and wet (Ar-5%H₂) environment for 172.8 ks (48 h) at 1073 K. By ratio, the mass change different between these conditions is at 1.2. It could be presumed that exposure time of 27.5 h is the critical time where Cr₂O₃ in wet condition loss its protectiveness based on thermodynamic calculation. FT-IR result confirms that dissolved H2 affect the chemical bonding of Cr2O3 and thus later promotes volatilization of protective Cr2O3 scale. Further observation has been done to determine the effect of dissolved H₂ on electrolyte (water vapor) conductivity which led to gas phase conductivity analysis. The result provides an indication to corrosiveness of Cr2O3 scale. It was found that resistivity ratio value Rwet/Rdry is around 1.4. It is substantiated that the presence of dissolved H2

contributes to 40% higher corrosivity.

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ثحبلا ةصلاخ

A

( موركويرفلا ةكيبس مدختست Fe-Cr

رابخ ةدسكأ لىإ اهضيرعت متي .ةيلاغلا بوبنأ في ةدامك ًةداع )

مامأ اىدومص ةيناكمأ امأ .ةليوط ةترفل ءالدا تلا

ّنغ قاطن نّوكت لىإ عجري ونإف ةرارلحا لياع لك آ ديسكأب

ا موركل - ومنلا ئيطبو فيثك ( ايموركب ىّمسُي -

Cr

2

O

3

) . موركويرفلا يميح قاطنلا اذى (

Fe-Cr )

للقُت انهلأ ةكيبسلا ةمدخ رمُع نم دُحتَ دق ةدسكلأا نإف كلذ عمو ،ةرارلحا ةيلاع لكآتلا ةبسن ةدايز نم ينجورديلذا نع جتانلا رسكلا وى ةلأسلدا هذى لماوع دحأ .ةياملحا ىلع اتهردق نم سكع يذلاو

كفت دهشي فولألدا ُبخ ك

لُمُ ينجورديى لىإ ءالدا را .ل

اذلذ ةلماك ةسارد يأ متت لم ،اذى انموي لىإ نكلو

نم لكشب ءاعدلاا لاا دّلوت كلذل ،مظ ت

ينجورديلذا رثأ ةساردل جايتح لللمحا

ةمواقم ىلع ذ لُكآتلا

تا

صالخا ةيلاعلا ةرارلحا ة

ته ةساردلا هذى .ايموركلا قاطنب يرثأتب اخ لكشب مت

لمحا ينجورديلذا ةردق ىلع لحل

ايموركلا (

Cr

2

O

3

.اهحطس كُساتم ىلع كلذكو ةياملحا ىلع ) ذخأ تم ،ةياملحا ىلع ةردقلا ةبقارلد

ايمورك ةنّيعك ةّيحرُك (

Cr

2

O

3

يريغت ةساردل ) يرارلحا نيزولا ليلحتلا قيرط نع ةلتكلا

( thermogravimetric analysis ضيرعت تم .)

ينتئيب لىإ ايموركلا نم ةد بلُم ةفيثك ةعطق

اهمادحإ نوجرأ ىلع يوتتَ( ةفاج

Ar و ) ر ىرخلآا ( ةبط

نوجرأ ىلع يوتتَ

Ar و 5 )ينجورديى %

ةدلد 172.8

( سنميسوليك 84

ةجردو )ةعاس 3701

،ةبسنلا صيخ اميف .ينفليك نإف

يريغت ةلاح

يى ينتئيبلا ينب ةلتكلا 3.1

بسن نأ رابتعلاا عيطتسن . رعتلا ة

ةغلابلا ض 27.5

مسالحا تقولا يى ةعاس

.يرارلحا نيزولا ليلحتلا تاباسح ىلع ًءانب اهتياحم اهيف تدقف تيلاو ةبطرلا ةلاحلل لا جئاتن تراشأ

FTIR لمحا ينجورديلذا نأ

خبت يييعت ّحَ نمو ايموركلل يئايميكلا كسامتلا ىلع رثثي لل دصر تم .اىر

رثأ نع دييلدا ينجورديلذا

ة يِليِصْوح ت ىلع لل لمحا ءارجأ لىإ ىدأ يذلاو ءالدا راخبب الخا تيلوتركللاا

( ةيليصوتلا ةيزاغلا ةلحرلدا ليلتَ

gas phase conductivity analysis )

تيلاو حئاتنلا تراشأ

لىإ ةقيقح يى ةفالجا ةئيبلل ةبطرلا ةئيبلا ةبسن نأو ،ايموركلا قاطن لكآت 3.8

، نأ لىإ يرشي اذىو

لذا لمحا ينجوردي ب ر كأ لكآت ةبسن ىطعأ لل

87

% .

BSTRACT IN ARABIC

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APPROVAL PAGE

I certify that I have supervised and read this study and that in my opinion, it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Master of Science (Materials Engineering).

………..

Mohd Hanafi bin Ani Supervisor

………..

Abd. Malek bin Abdul Hamid Co-Supervisor

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Master of Science (Materials Engineering).

………

Syed Noh bin Syed Abu Bakar Internal Examiner

………

Ahmad Zamani bin Jusoh Internal Examiner

This dissertation was submitted to the Department of Manufacturing and Materials Engineering and is accepted as a fulfillment of the requirement for the degree of Master of Science (Materials Engineering).

………..

Mohamed bin Abd. Rahman Head, Department of

Manufacturing and Materials Engineering

This dissertation was submitted to the Kulliyyah of Engineering and is accepted as a fulfillment of the requirement for the degree of Master of Science (Materials Engineering).

………..

Erry Yulian Triblas Adesta Dean, Kulliyyah of Engineering

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DECLARATION

I hereby declare that this dissertation is the result of my own investigations, except where otherwise stated. I also declare that it has not been previously or concurrently submitted as a whole for any other degrees at IIUM or other institutions.

Syamsul Kamal bin Arifin

Signature ... Date ...

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COPYRIGHT PAGE

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLARATION OF COPYRIGHT AND AFFIRMATION OF FAIR USE OF UNPUBLISHED RESEARCH

EFFECTS OF DISSOLVED HYDROGEN ON HIGH TEMPERATURE CORROSION RESISTANCE OF CHROMIA

SCALE

I declare that the copyright holders of this dissertation are jointly owned by the student and IIUM.

No part of this unpublished research may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior written permission of the copyright holder except as provided below

1. Any material contained in or derived from this unpublished research may be used by others in their writing with due acknowledgement.

2. IIUM or its library will have the right to make and transmit copies (print or electronic) for institutional and academic purposes.

3. The IIUM library will have the right to make, store in a retrieved system and supply copies of this unpublished research if requested by other universities and research libraries.

By signing this form, I acknowledged that I have read and understand the IIUM Intellectual Property Right and Commercialization policy.

Affirmed by Syamsul Kamal bin Arifin

……..……….. ………..

Signature Date

ACKNOWLEDGEMENTS

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In the name of Allah, the most Merciful and the most Compassionate.

All glory is due to Allah the Almighty, whose Grace and Mercies have been with me throughout the duration of my program. Although it has been tasking, His Mercies and Blessings on me ease the herculean task of completing this dissertation.

I am most indebted with my Supervisor, Associate Professor Dr. Mohd Hanafi Ani, whose enduring dispositions, kindness, promptitude, thoroughness and friendship have facilitated the completion of my work. Despite his commitments, he took time to listen and attend to me whenever requested. The moral support he extended to me is in no doubt a boost that helped in building and writing the draft of this research work.

I am also grateful to my Co-Supervisor Asst. Prof. Dr. Abd. Malek Abdul Hamid, whose support and co-operation contributed to the outcome of this work.

Thank you very much to all of Kulliyyah of Engineering staff especially technical staffs who always there accompanying me whenever I needed.

My gratitude also goes to my lovely parents for their prayers and understanding Arifin Taib and Allahyarhamah Siti Esah Ibrahim which she has passed away while I was still in final stage of writing this dissertation.

The thankfulness also goes to my mother-in-law Hajjah Junaidah Zainal who taught me not to be afraid to pursue a dream and ambition.

My appreciation to my siblings especially my brother Anuar Kamal Arifin whose encourages me to go further in academics and engineering.

Lastly, my gratitude goes to my lovely wife Tarita Tholpakar who has been beside me every time when I was about to surrender to many difficult situations, her understandings, support and endurance during the duration to complete this work. To my sons Rayqal and Ilyasa, I love you two from the bottom of my heart. This is for you.

Without their blessings, consent and encourage, it would be very difficult for me to finish my study

Once again, we glorify Allah for His endless Mercy on us one of which is enabling to successfully round off the efforts of writing this dissertation.

Alhamdulillah.

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CHAPTER TWO: LITERATURE REVIEW ... 8

2.1 Introduction... 8

2.1.1 Alloys in Thermal Power Plant ... 9

2.1.2 Ferritic, Austenitic and Other Improvised Steels ... 12

2.2 Fundamentals of Oxidation Kinetics ... 14

2.2.1 Linear Rate Law ... 15

2.2.2 Parabolic Rate Law ... 16

2.2.3 Logarithmic Rate Law ... 16

2.3 Solid-State Diffusion ... 17

2.4 Oxidation of Fe-Cr Alloying System ... 18

2.5 Chromia Protectiveness on Fe-Cr Alloy ... 21

2.6 Oxidation of Fe-Cr Alloy in Water Vapor Environment ... 23

2.7 Hydrogen Involvement in Fe-Cr Alloy Oxidation ... 24

2.8 Surface Bonding ... 25

CHAPTER THREE: RESEARCH METHODOLOGY ... 29

3.2 Research Process ... 29

3.3 Experimental ... 31

3.3.1 Sample Preparation ... 31

3.3.2 Mass Change Analysis ... 32

3.3.3 Surface Bonding Analysis ... 34

3.3.4 Gas Phase Conductivity on Cr2O3 Surface at 1073 K ... 35

3.3.5 Morphology ... 39

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CHAPTER FOUR: RESULTS AND DISCUSSION ... 40

4.2 Mass Change Analysis ... 40

4.3 Surface Bonding Analysis ... 43

4.4 Gas Phase Conductivity on Chromia Surface ... 47

4.5 Corrosion Model ... 51

4.6 Surface Morphology ... 53

CHAPTER FIVE: CONCLUSION AND RECOMMENDATION ... 54

5.1 Conclusion ... 54

5.2 Recommendation ... 55

REFERENCES ... 57

PUBLICATION AND AWARD ... 62

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LIST OF FIGURES

Figure 1.1 Types of Power Plant in Malaysia (Energy

Commission, 2015). 1

Figure ‎1.2 Statistical data of power generation from all TPP in

Malaysia (Energy Commission, 2016) 2

Figure ‎2.1 Line diagram of a typical thermal power plant. 10 Figure ‎2.2 CO₂ emissions (Coal Industry Advisory Board of

International Energy Agency, 2010) and estimation of energy conversion efficiency at various hot

reservoir temperatures, T_H 11

Figure ‎2.3 Boiler tube damage in thermal power plant due to

creep 12

Figure ‎2.4 Interfacial reactions and transport processes for high temperature oxidation mechanisms: (a) cation

motion and (b) anion motion 15

Figure ‎2.5 Isothermal section of Fe-Cr-O phase diagram at 1273 K 19 Figure ‎2.6 Parabolic rate constant of Fe-Cr at various temperature 21

Figure ‎3.1 Flowchart of the research. 30

Figure ‎3.2 Schematic diagram of sintered Cr2O3 pellet. 31

Figure ‎3.3 Steps of sample preparation. 32

Figure ‎3.4 Schematic diagram of the TGA system. 33

Figure ‎3.5 TGA equipment setup for mass change analysis. 34

Figure ‎3.6 FT-IR equipment used. 35

Figure ‎3.7 Sample placements for conductivity measurement. 36 Figure ‎3.8 Schematic diagrams for conductivity measurement. 37

Figure ‎3.9 Oxidation experiment setup. 37

Figure ‎3.10 Quartz oxidation chamber with Langmuir probe. 38

Figure ‎3.11 Autolab® potenstiostat. 38

Figure ‎3.12 Gold sputtered Cr2O3. 39

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Figure ‎4.1 Mass change of Cr₂O₃ (linear plot) being exposed at 1073K for

172.8 ks (48 hr) in dry and wet environment. 41

Figure ‎4.2 Oxidation kinetics (parabolic plot) kp of Cr2O3 being exposed at

1073K for 172.8 ks (48 hr) in dry and wet environment. 42 Figure ‎4.3 IR spectrum of Cr₂O₃ in dry and wet condition. 44 Figure ‎4.4 Close up view of IR spectra in the Range 1. 45 Figure ‎4.5 Close up view of IR spectra in the Range 2. 46 Figure ‎4.6 Close up view of IR spectra in the Range 3. 46 Figure ‎4.7 Close up view of IR spectra in the Range 4. 47 Figure ‎4.8 Conductivity on Cr2O3 surface in different environment at 1073 K. 48 Figure ‎4.9 Conductivity comparisons on gas phase with no presence of

Cr2O3 in wet environment at 1073 K. 50

Figure ‎4.10 Corrosion model of Cr2O3. 52

Figure ‎4.11 Surface morphology of Cr₂O₃ after 1073K for 48 hr in a) dry

and b) wet condition. 53

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LIST OF TABLES

Table ‎2.1 Coefficient of thermal expansion and thermal conductivity

comparison between ferritic and austenitic steels (Metals, 2008) 14

Table ‎2.2 A summary of studies on the interaction 26

Table ‎4.1 Measured gas phase resistance. 50

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LIST OF ABBREVIATIONS

TPP Thermal Power Plant

EC Energy Commission

FT-IR Fourier Transform Infrared

IR Infrared

FE-SEM Field Emission Scanning Electron Microscopy

TGA Thermo Gravimetric Analyzer

XPS X-Ray Photoelectron Spectroscopy CTE Coefficient of Thermal Expansion

2D Two Dimensional

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LIST OF SYMBOLS & UNIT

T_C temperature at cold reservoir TH temperature at hot reservoir

ɳ Car Carnot efficiency

kp parabolic rate

k1 linear rate

J net flux of atoms

D diffusion coefficient

x thickness

t time

I electric current

V electric potential

R electrical resistant

Fe iron

Cr chromium

H hydrogen

O oxygen

Ar argon

C carbon

Sn tin

Zn zinc

Mo molybdenum

V vanadium

W tungsten

Ni nickel

Pt platinum

Ti titanium

Nb niobium

Cu copper

Al aluminium

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xx

Co cobalt

Rh rhodium

K Kelvin

°C degree Celcius

µm micrometer

mm millimeter

cm centimeter

m meter

µg microgram

mg milligram

kg kilogram

h hour

s second

ks kilosecond

atm atmospheric pressure

W watt

kW kilowatt

MW megawatt

GW gigawatt

v volt

A ampere

Ω ohm

J joule

kJ kilojoule

mol mole

wt% weight percent

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CHAPTER ONE INTRODUCTION

1.1 BACKGROUND OF THE STUDY

Electricity is generated from various types of power plant such as hydro, thermal and renewable energy plant. In Malaysia, mostly thermal power plant (TPP) has long been used to generate electricity. Pie chart in Figure 1.1 shows the fraction of power plant types in Malaysia. It can be seen that TPP dominates the power generation by 80.23%

while hydro power plant is by 19.76%. Only slight fractions of the power generation in Malaysia are sourced from renewable energy such as solar and wind.

Figure 1.1 Types of Power Plant in Malaysia (Energy Commission, 2015).

Over the year, the demands for electrical energy are increasing due to the population growth and development of heavy industrial sectors thus urging the power plants to increase their energy output. These highly demands of electricity resulting power generation from all TPP in Malaysia to be drastically increased within these 20 years (Energy Commission, 2015). Figure 1.2 shows the statistical data of power

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generation from all TPP in Malaysia. From 1990, it shows an increasing trend until 2012. The latest statistical data by Energy Commission of Malaysia in 2016 reported a 4.3% growth of the total electricity consumption from 2013 to 2014. The highest electricity consumption recorded was by industrial sector at 45.9%, followed by commercial sector at 32.3%, residential sector at 21.2%, agriculture at 0.4% and transport at 0.2% (Energy Commission, 2016). It is expected that this trend will continue for another 20 years.

Figure 1.1.2 Statistical data of power generation from all TPP in Malaysia (Energy Commission, 2016)

Despite of increasing trend in power consumption, the efficiency of energy conversion in TPP is relatively stagnant over decades. Currently, TPP’s maximum efficiency is only 40%. In 2036, TPP is targeted to operate at efficiency of 45%.

(Viswanathan et al., 2006).

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The conversion rate from fossil fuel to electrical energy in TPP is governed by thermal exchange rate at the boiler. It is generally described by Carnot’s cycle as follows:

ηCar = 1

[ ]

^(1.1)

Where ηCar is Carnot efficiency, T_C and T_H is temperature at cold reservoir and hot reservoir of boiler, respectively. It is clear that from Equation 1.1, higher energy exchange rate can be obtained by increasing the boiler temperature at hot reservoir.

1.2 PROBLEM STATEMENT

By bringing hot reservoir temperature up to 963 K, the energy conversion efficiency could be increased to 45%. However, from the materials point of view, prolonged exposure duration at high temperature causes variety of drawbacks such as high temperature corrosion, thermal cracking, creeping, hydrogen damage, spallation and other materials failure to the boiler tubes.

This is a usual problem that yet to be solved entirely, albeit improvement strategies have been introduced in the last few decades. General shutdown to the power plant is needed and it took weeks to replace boiler tubes. This will cause a great loss to the TPP operators in term of time, money and energy shortage.

It is interesting to note that recent development of oxy-fuel combustion systems in which fossil fuels are burned in a mixture of re-circulated flue gas and oxygen, rather than in air, has caused renewed interest in the effects of water vapor and steam on alloy oxidation (Mu et al., 2013). Many researchers (Ani et al., 2009;

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Essuman et al., 2008; M. Hansel, W. J. Quadakkers, 2003; Michalik et al., 2014) clearly showed that water vapor accelerated the oxidation rate of protective oxide layer.

At temperature above than 647 K, water vapor will dissociate into dissolved hydrogen, H⁺and OH^-. Equation 1.2 is the possible chemical reaction happened for water dissociation.

H2O  H⁺ + OH^- (1.2)

Steels exposed in dry oxygen (hydrogen free environment) were having less oxidation rate as compared in a water vapor environment. Ani (2009) reported that dissociated hydrogen during high temperature oxidation increased the oxygen permeability by a factor of 1.4. Therefore, it is clear that water vapor oxidation always become a main topic or challenges in thermal power plant whereby it can greatly modify the behavior of protective layer. Dissolved hydrogen that dissociated from water vapor on the other hand, does give significant effect on the oxidation rates to the steel (Ani et al., 2009).

All alloys that are resistant to corrosion at high temperature require the formation of a protective oxide layer. In boiler tubes, ferritic Fe-Cr alloys will oxidize chromium oxide or known as chromia, Cr2O3 scale as its protective oxide layer. The lifespan and resistivity of boiler tubes towards high temperature environment greatly depends on the protectiveness of Cr₂O₃(Arifin et al., 2017).

The fundamental understanding of this high temperature corrosion has been developed over the years for exposure in pure oxygen or air. However, there is no consensus pertaining the effect of water vapor on high temperature oxidation of Fe-Cr

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alloy boiler. Fundamental study on oxidation of water vapor is still lacking. The role of dissolved hydrogen in high temperature environment has yet to be clarified. Thus, it is no clear solution to above stated problems.

1.3 RESEARCH OBJECTIVES

The effect of dissolved hydrogen on high temperature corrosion resistance of Cr2O3

which will be determined by these objectives:

1. To evaluate of the protectiveness of Cr₂O₃ using mass change method.

2. To clarify the hydrogen effect using FTIR spectroscopy of Cr2O3.

3. To verify electrical conductivity of gas phases on Cr₂O₃ surface during reaction

1.4 SCOPE OF RESEARCH AND LIMITATIONS

The experiment will be done in a controlled environment by flowing Ar, O₂ and H₂ gas to simulate a dried, hydrogen free and water vapor environment. It will be conducted in a laboratory scale under 1 atm pressure. Due to safety reason, the experiment is impossible to be executed at high pressure as exactly as in the TPP boiler. However, it is postulated that high pressure does not significantly change the chemical reaction of oxidation.

Boiler tube is exposed to high temperature oxidation around 100,000 h throughout its service time. In this study, the experimental reaction time is done at 48 h. Although the real exposure time for boiler is longer, it is considered to be sufficient since initial reaction will achieve an equilibrium state on the early stage of oxidation.

Water vapor or steam humidity is usually measured by using hygrometer which is less accurate and unsuitable technique for sintered powder sample. Instead of

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bubbling water to produce steam, synthetic water vapor is used to simulate the wet environment. The mixture of Ar-5%H2 gas was flown into the reaction chamber and react with O₂ impurity in the gas tank to form water. The amount of water vapor was measured by using Gibb’s free energy equation.

Electrical conductivity measurement was conducted only at a potential range of -4.95 to +4.95 V using potentiostat due to the constraint of the equipment which only able to read at maximum of 10 points of potential. However, it is adequate to investigate the electronic behavior of Cr₂O₃.

1.5 THESIS ORGANIZATION

This thesis consists of five chapters. Chapter 1 mainly discussed on the background of the research. It starts with the needs of increasing the efficiency of thermal power plant to cater the future demand. This is where problem occur when boiler material are facing several of material failures when subjected to prolonged exposure duration at temperature higher than 873 K.

Chapter 2 was devoted to the literature review. It consists of fundamental

information on high temperature oxidation of alloys in dried and water vapor environment. It revolves around the protective oxide scale and its formation dependency on various parameters such as temperature, duration, oxidation rate, chromium composition and gas partial pressures.

Four analysis of Cr2O3 in dry, O2 and wet condition at 1073 K was conducted which are mass change, conductivity, surface bond, surface morphology. Chapter 3 explained experiment methodology and setup. It started with apparatus design, equipment setup followed by sample preparation. Later, it described the method of oxidation for mass change and conductivity measurements. Oxidation process for

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conductivity was done in quartz chamber while mass change analysis in thermo gravimetric analyzer (TGA). Finally, the description on surface bond analysis and surface morphology was reported. Fourier transform infrared (FT-IR) spectroscopy was used for surface bond analysis while field emission scanning electron microscopy (FE-SEM) for surface morphology.

Chapter 4 presented the results, analysis and discussion on the findings of this work while Chapter 5 summarized the findings including conclusions and recommendation for further work on this subject.

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CHAPTER TWO LITERATURE REVIEW

2.1 INTRODUCTION

Most metals oxidize and corrode at high temperature. Material properties such as strength, creep resistance, fatigue and corrosion resistance defines the alloys composition at high temperature applications. Several high temperature applications like thermal power plant necessitated the development of such alloys having superior properties. Materials that are used in power plants are heavily exposed to long term high temperature environment susceptible to high temperature oxidation and corrosion attack. From boiling water, it is exposed to oxidation in steam side boiler tube while hot corrosion occurs from the burning side due to burning of fossil fuel.

High temperature oxidation also gives major problems to other field of applications. In gas turbine such as jet engine, degradation of metal is major issue due to high temperature oxidation and sulphidation. Chemical plant needs materials that can sustain high temperature due to sulphidation and carburizing issues. Furnace materials acute problem is a sudden loss of its strength because of material loss due to oxidation (A.S. Khanna, 2002).

Countermeasure stage for these problems has been taken by researchers and scientists since 50 years ago. The most substantial achievement is the development of alloying system that provides an improvement of materials properties for high temperature applications. Properties that improved including high temperature strength; high Young’s Modulus and high creep resistance capability are attained.

From the corrosion point of view there is a need to study the properties of the alloys to know rate of metal reaction with atmosphere at high temperatures, the mechanism of

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the reaction, the corrosiveness of the environment, method to protect a metal at such environment and alloy selection for such applications.

The imperative criterion in developing alloying system is based on the ability to form a protective layer against corrosion attack (C. Wagner, 1956). This layer should be capable to perform as a diffusion barrier. The electrical conductivity of the oxide layer is a measure of the diffusivity of the moving ions. A very low conductivity indicates insignificant deviation from stoichiometry and, hence, a low diffusivity, which effectively increases the oxidation resistance. A relatively high conductivity oxide indicates much faster diffusion of the diffusing species (Per Kofstad, 1972). The oxidation resistance of a metal is improved by the addition of suitable alloying elements to the base metal. The alloying element must be present in sufficient concentration to produce the desired oxide layer. The most common alloying elements added to iron for this purpose are chromium, aluminium and silicon (Per Kofstad, 1966).

2.1.1 Alloys in Thermal Power Plant

In TPP, water from cold reservoir is pumped and heated to supercritical steam in boiler. Heat energy sourced from coal or any other fossil fuels transferred to steam at the boiler which later converted to kinetic energy at the turbine. Then, the kinetic energy converted to electrical energy. Figure 2.1 shows a line diagram of a typical power plant. These temperature different is determined by the thermal conductivity of the boiler tube. TH is the temperature at hot reservoir exits the boiler and TC is the steam temperature exit the turbine and entering cold reservoir at condenser.

Kulliyyah of

EFFECTS OF DISSOLVED HYDROGEN ON HIGH TEMPERATURE CORROSION RESISTANCE OF