SOIL CORROSIVITY CONDITION INDEX FOR BURIED STEEL PIPELINE

FATIMAH AQILAH BINTI MOHAMAD NAZIM

A thesis submitted in fulfilment of the

Requirements for the award of the degree of

Master of Engineering (Structure)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

DECEMBER 2015

iii

I dedicate this to

Myself

My husband and lovely children, abang, syifa’ and zayd.

My beloved family, mama, deda, aqil, afif, atifah and eira.

My family in-law, ummi, ayah and those brothers and sisters.

My supportive supervisor and co-supervisor, Dr. Lan and Prof. Nordin.

RESArians.

My akhawats and murabbi.

My ummah.

iv

ACKNOWLEDGEMENT

Alhamdulillah, praise be to Allah, Who created everything including

knowledge as a gift to mankind and through this knowledge, goodness is defined.

May Allah bless us with His guidance and beneficial knowledge.

I offer my sincerest gratitude to my supervisor, Assoc. Prof. Dr. Norhazilan

Bin Md. Noor, who has supported me throughout my thesis with his patience and

knowledge, and gave me plenty of opportunity to improve my shortcoming. My

warmest thank also go to my co-supervisor, Prof. Dr. Nordin Bin Yahya for all the

shared knowledge and opinions on my research.

Special thanks go to all my friends especially the RESA members (Reliability

Engineering and Safety Assessment Research Group), for their excellent co-

operation, inspirations and supports throughout my research study. Many special

thanks to my akhawat, my unforgettable murabbi, ummi Nailah, ummi Anisah and

ummi Khairul Sozana for the prayers, motivation and ukhuwwah.

I acknowledge my indebtedness and sincere gratitude to my beloved family

and family in-law especially to my parents, Mohamad Nazim Bin Syed Mohamad

and Salbiah Binti Ahmad, my siblings, my lovely husband, Muhammad Thabit Bin

Zaharudin, our lovely daughter and son, Syifa’ Najla’ Binti Muhammad Thabit and

Hassan Zayd Bin Muhammad Thabit for the endless support, love, prays and

motivation throughout my life.

Thank you all.

v

ABSTRACT

External corrosion is common threat on underground pipeline structures

resulting bad impact on human, environment and financial. Researches show that the

identification of soil corrosivity level may be determined by the location conditions

and suitability of pipeline structures installation. Currently, there is no guideline to

assess the condition of site corrosivity by rank or index system for soil conditions in

Malaysia. The index system, referring to site corrosivity may provide an early

indication on the potential structural damages subjected by soil corrosion prior to

pipeline installation and to assess the possible failures of damaged pipeline. This

research focuses on the development of soil corrosivity condition index based on soil

parameters and site characteristics evaluation for pipeline structure installation and

maintenance work purposes. A total of 207 carbon steel coupons originated from X-

70 metal type were installed in site A, B, C, D and E located at peninsular Malaysia

for a period of 18 months. The buried coupons were retrieved every 3-months to

monitor the corrosion rate by metal loss product coupled with measurement of the

soil parameters including Soil Resistivity (Res), Moisture content (Mc), pH, Sulphide

(SO4), Sulphate (SO3), Chloride (Cl) and site characteristics information including

Soil Type (ST), Water Access (WA) and Disturbance Factor (DF). The results of

corrosion rates and soil parameters were analyzed by using statistical method

through normality, hypothesis and outlier’s detection test, and the corrosion rates

were classified into three categories: crmax, cravg and crmed. The site corrosivity

conditions were designed by the classification of four corrosivity percentage levels

with 0% as the worst condition and 100% as the best condition namely as “not

corrosive” for 76-100%, “mildly corrosive” for 51-75%, “corrosive” for 26-50% and

“very corrosive” for 0-25%. A number of six (6) soil parameters and three (3) site

characteristic indexes were designed within 0-10, where 0 represent the worst

condition and 10 points represent the best condition. The equation model of site

corrosivity condition percentage was finally designed along with the weighing factor

considerations. The collected data of soil parameters and site characteristics were

applied into the model equation to compare the accuracy of designed indices with the

existing corrosion rate data. Based on the comparison, the results show that the soil

corrosivity condition index proposed model is identical to crmax data and

approximately similar to cravg and crmed data for every site. The results also show that

site B and C are identified as the most corrosive sites compared to site A, D and E. In

conclusion, the proposed index system can assist pipeline operators in selecting the

most suitable sites for pipeline installation by considering the level of soil

corrosivity, hence, minimising the unnecessary corrosion protection on buried

pipeline.

vi

ABSTRAK

Kakisan luar paip merupakan salah satu ancaman terhadap struktur saluran

paip bawah tanah yang mengakibatkan kesan buruk kepada manusia, alam sekitar

dan kos kewangan. Kajian menunjukkan bahawa pengenalpastian tahap kakisan

tanah boleh ditentukan oleh keadaan lokasi dan kesesuaian pemasangan struktur

saluran paip. Sehingga kini, masih tiada garis panduan untuk menilai keadaan

pengaratan tanah di tapak melalui sistem indeks bagi keadaan tanah di Malaysia.

Sistem indeks pengaratan di tapak boleh memberi petunjuk awal terhadap potensi

kerosakan struktur tertakluk kepada kakisan tanah sebelum pemasangan saluran paip

dan menilai kemungkinan kegagalan bagi saluran paip. Kajian ini memberi tumpuan

kepada penghasilan sistem pengindeksan keadaan pengaratan tanah berdasarkan

parameter tanah dan penilaian ciri-ciri tapak untuk pemasangan struktur saluran paip

dan tujuan kerja penyelenggaraan. Sebanyak 207 kupon keluli karbon daripada jenis

logam X-70 telah dipasang di tapak A, B, C, D dan E di semenanjung Malaysia

untuk tempoh 18 bulan. Kupon keluli yang ditanam telah diambil pada setiap 3 bulan

untuk memantau kadar pengaratan melalui kehilangan produk logam beserta

pengukuran parameter tanah termasuk rintangan tanah (Res), kandungan lembapan

(Mc), pH, Sulphide (SO4), Sulphate (SO3), Klorida (Cl) dan maklumat ciri tapak

termasuk jenis tanah (ST), akses terhadap air (WA) dan faktor gangguan (DF).

Keputusan kadar pengaratan dan parameter tanah dianalisis dengan menggunakan

kaedah statistik melalui ujian normal, hipotesis dan pengecaman titik terpencil, dan

kadar kakisan telah diklasifikasikan kepada tiga kategori: crmax, cravg dan crmed.

Keadaan kakisan tapak telah dikelaskan melalui empat tahap peratusan pengaratan

dengan 0% sebagai keadaan yang paling teruk dan 100% sebagai keadaan yang

terbaik iaitu 76-100% sebagai "tidak mengkakis", 51-75% untuk "separa mengkakis",

26-50% untuk "mengkakis" dan 0-25% untuk "sangat mengkakis". Sejumlah enam

(6) parameter tanah dan tiga (3) ciri tapak telah diberikan nilai 0-10, di mana 0

mewakili keadaan yang paling teruk dan 10 mewakili keadaan yang terbaik. Model

persamaan peratusan markah indeks akhirnya direka dengan mengambil kira faktor

pemberat. Data parameter tanah dan ciri-ciri tapak yang diperolehi di tapak telah

digunakan ke dalam model persamaan untuk membandingkan ketepatan indeks yang

direka dengan kadar kakisan yang sedia ada. Berdasarkan perbandingan, ia

menunjukkan bahawa keputusan daripada model indeks keadaan pengaratan tanah

yang dicadangkan adalah sama dengan data crmax dan hampir sama dengan data cravg

dan crmed di setiap kawasan. Keputusan juga menunjukkan bahawa tapak B dan C

dikenalpasti sebagai tapak yang paling mengkakis berbanding dengan tapak A, D dan

E. Kesimpulannya, sistem indeks yang dicadangkan mampu membantu operator paip

dalam menentukan kawasan yang paling sesuai bagi pemasangan paip berdasarkan

tahap kakisan tanah. Seterusnya mampu mengurangkan perlindungan pengaratan

yang tidak perlu kepada saluran paip dalam tanah.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION

ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xii

LIST OF FIGURES xiv

LIST OF ABBREVIATIONS AND SYMBOLS xvii

LIST OF APPENDICES xx

1 INTRODUCTION 1

1.1 Overview 1

1.2 Research Background 2

1.3 Research Problem 3

1.4 Research Aim 5

1.5 Research Scopes 6

1.6 Research Significance 6

2 LITERATURE REVIEW 8

2.1 Introduction 8

2.2 Pipeline’s Basic Study 8

2.3 Underground Pipeline System 10

2.3.1 Pipeline Risk and Integrity 11

viii

2.4 Corrosion of Underground Structures 13

2.4.1 Corrosion of Buried Pipeline 13

2.4.2 Soil Corrosion 15

2.5 Soil Corrosion Factor 18

2.5.1 Soil Resistivity 19

2.5.2 Effect of pH 19

2.5.3 Moisture Content 20

2.5.4 Texture and Type of Soil 21

2.5.5 Pipe to Soil Potential 22

2.5.6 Redox potential 23

2.5.7 Chloride Content 23

2.5.8 Sulphate and sulphide content 24

2.5.9 Microbiologically- Influenced Corrosion

(MIC)

24

2.5.10 Miscellaneous Effect on Soil Corrosion 25

2.6 Soil Corrosivity Assessment 27

2.6.1 Quantitative and Qualitative Assessment 28

2.7 Corrosion Index Study 29

2.7.1 Previous Corrosion Index study 29

2.7.1.1 American Water work Association

(AWWA)

30

2.7.1.2 Metalogic N.V Method 31

2.7.2 Application of Weighting Factor 33

2.8 Conclusion 33

3 RESEARCH METHODOLOGY 35

3.1 Introduction 35

3.2 Methodology Overview 36

3.3 Experimental Work 38

3.3.1 Identification of Soil Parameter 38

3.3.2 Selection of Site and Material 39

3.3.3 Sample Preparation and Installation 40

3.3.4 Coupon Installation 46

3.4 Data Collection 49

ix

3.4.1 Coupon Retrieval 49

3.4.2 Soil Parameter Collection and Site

Observation

51

3.4.2.1 Soil Resistivity Measurement 51

3.4.2.2 Moisture Content Measurement 53

3.4.2.3 pH Measurement 53

3.4.2.4 Chloride Content Measurements 55

3.4.2.5 Sulphate Content Measurement 56

3.4.2.6 Sulphide Content Measurement 56

3.4.2.7 Miscellaneous Data by Site

Observation

57

3.4.3 Corrosion Evaluation 58

3.4.4 Corrosion Rate Determination 60

3.5 Data Analysis 61

3.5.1 Data Screening 61

3.5.2 Analysis of Qualitative Data 62

3.6 Soil Corrosivity Index Design 62

3.6.1 Soil Corrosivity Condition 63

3.6.2 Quantitative and Qualitative Index 63

3.6.3 Equation of Soil Corrosivity Condition

Index

64

3.7 Assessment Result 64

3.8 Conclusion 64

4 DATA ANALYSIS AND DEVELOPMENT OF SOIL

CORROSIVITY CONDITION INDEX

66

4.1 Introduction 66

4.2 Experimental Result 67

4.3 Data Screening 75

4.3.1 Normality Test 75

4.3.2 Hypothesis Test (Mann Whitney U – test) 77

4.3.3 Outliers Detection 79

4.4 Corrosion Growth Pattern 83

4.5 Qualitative Data Analysis 85

x

4.6 Soil Corrosivity Index Design 86

4.6.1 Corrosion Conditions Classification 87

4.6.2 Soil Parameter and Site Characteristics

Index

88

4.6.2.1 Soil Resistivity Index 88

4.6.2.2 Moisture Content Index 89

4.6.2.3 pH Index 90

4.6.2.4 Chloride Content Index 91

4.6.2.5 Sulphate Content Index 91

4.6.2.6 Sulphide Content Index 92

4.6.2.7 Mark of Soil Types 93

4.6.2.8 Mark of Water Access 93

4.6.2.9 Mark of Disturbance Factors 94

4.6.3 Soil Corrosivity Index Equation Model 95

4.6.3.1 Linear Correlation Analysis (LCA)

Test

95

4.6.3.2 Parametric Correlation Test 96

4.6.3.3 Non Parametric Correlation Test 97

4.6.4 Weighting Factor Application 97

4.7 Pipeline Assessment Simulation 99

4.8 Conclusion 105

5 DISCUSSION ON SOIL CORROSIVITY

CONDITION INDEX AND POTENTIAL

APPLICATION

107

5.1 Introduction 107

5.2 Data Screening Process 107

5.3 Corrosion Growth Pattern 109

5.4 Soil Corrosivity Condition Index Design 110

5.4.1 Soil Corrosivity Condition 110

5.4.2 Soil Parameters and Site Characteristics

Index

111

5.4.3 Model Equation of Soil Corrosivity

Condition Index

111

xi

5.4.4 Comparison of Soil Corrosivity Index

Model and Corrosion Rate Data

112

5.5 Possible Errors 113

5.6 Benchmark of the Proposed Index 114

5.7 Soil Corrosivity Index Practicability and Benefits 115

6 CONCLUSIONS AND RECOMENDATIONS 117

6.1 Introduction 117

6.2 Recommendations 119

REFFERENCES 120

APPENDIX A - D 129 - 143

xii

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1

Table of AWWA soil test evaluation (Source: Appendix A

in ANSI/AWWA C105)

30

2.2 Soil Corrsoivity of Metalogic N.V method (1998)

32

2.3 Previous studies on soil corrosivity index

32

3.1 Site Informations

39

4.1 Quantitative Data on Site A

68

4.2 Quantitative Data on Site B

68

4.3 Quantitative Data on Site C

68

4.4 Quantitative Data on Site D

69

4.5 Quantitative Data on Site E

69

4.6 Site Characteristics based on observation

71

4.7 Metal Loss (ML) and Corrosion Rate (CR) at Depth of 0.5m

73

4.8 Metal Loss (ML) and Corrosion Rate (CR) at Depth of 1.0m

74

4.9 Normality Test Result

76

4.10 Hypothesis Test Results

77

4.11 Metal Loss (ML) and Corrosion Rate (CR) data

78

4.12 Corrosion rate and soil parameters after removal outliers

data (max)

80

4.13 Corrosion rate and soil parameters after removal outliers

data (avg)

81

xiii

4.14 Corrosion rate and soil parameters after removal outliers

(med)

82

4.15 Classification of site characteristic

86

4.16 Table of corrosion conditions

87

4.17 Soil Resistivity (Res) Index

89

4.18 Moisture Content (Mc) index

90

4.19 pH (pH) Index

90

4.20 Chloride content (Cl) index

91

4.21 Sulphate content (SO3) index

92

4.22 Sulphide Content (SO4) Index

92

4.23 Soil Type Marks

93

4.24 Water Access Marks

94

4.25 Disturbance Factor Marks

94

4.26 Person’s correlation test on corrosion rate (max) with soil

parameters

96

4.27 Person’s correlation test on corrosion rate (avg) with soil

parameters

96

4.28 Person’s correlation test on corrosion rate (med) with soil

parameters

96

4.29 Spearman’s correlation test [Corrosion rate (max)]

97

4.30 Spearman’s correlation test on [Corrosion rate (avg)]

97

4.31 Spearman’s correlation test [Corrosion rate (med)]

97

4.32 Soil parameters and site characteristic correlation value

98

4.33 Site A (time exposure: 12 months)

100

4.34 Site C (time exposure: 18th

month)

100

4.35 Percentage of soil corrosivity conditions (Site A – Site E) 102

xiv

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1

Network of Peninsular Gas Utilisation (PGU) in

Peninsular Malaysia (Source: Gas Malaysia Berhad, 2015)

11

2.2 Pipeline failure primary incident (Source: Keystone XL

Project, 2009)

12

2.3 Schematic illustration of corrosion process (Source:

Ahmad, 2006)

14

2.4 Exposure of buried pipeline to the soil environment

(Source: Uhlig’s Corrosion Handbook, 2006)

17

2.5 Model of corrosion of metal by SRB (Source: Advances in

Applied Microbiology, Volume 68, 2009)

25

2.6 Basic risk assessment models (source: Muhlbaeur, 2004)

27

3.1 Flow of research strategy

36

3.2 Design Sequence

37

3.3 Pipeline cutting process

41

3.4 Pipeline section

41

3.5 Hot cut process

42

3.6 Cold cut processes

42

3.7 Sample dimension (60mm × 80mm)

43

3.8 Coating layer removal (using hand grinder)

43

3.9 Before and after coating layer removal

44

3.10 Sample cleaning process using acetone 44

xv

3.11 Sample drying process

45

3.12 Measurement of initial weights (Wo) of steel coupon

45

3.13 Sample stored in sealed plastic bag

46

3.14 Detection of existing underground pipe location

47

3.15 Drilling process by using hand auger

48

3.16 Layout of metal installation

48

3.17 Digging out process to retrieve the coupon

50

3.18 Retrieved coupon

50

3.19 Resistivity meter

51

3.20 Application of soil resistivity meter (Source: Chaker, 1981)

51

3.21 Electrode pins order

52

3.22 Moisture Content Meter

53

3.23 pH Meter

54

3.24 Soil Sample Collections

58

3.25 Mechanical Cleaning Process (Before)

59

3.26 Mechanical Cleaning Process (After)

59

3.27 Chemical Cleaning process

60

3.28 Weighed metal coupon

60

4.1 Boxplot summaries of outlier’s data

79

4.2 Graph of corrosion rate (mm/year) for site A – site E (crmax)

84

4.3 Graph of corrosion rate (mm/year) for site A – site E (cravg)

84

4.4 Graph of corrosion rate (mm/year) for site A – site E (crmed)

85

4.5 Summarization flow of Soil Corrosivity Condition Index

design

87

4.6 Effect of moisture content on soil corrosivity (Source:

Ismail and El – Shamy, 2009)

89

xvi

4.7 Graph of average marks percentage on every site

103

4.8 Graph comparisons of corrosion rate (max) and marks

percentage (%)

104

4.9 Graph comparisons of corrosion rate (avg) and marks

percentage (%)

104

4.10 Graph comparisons of corrosion rate (med) and marks

percentage (%)

105

xvii

LIST OF ABBREVIATIONS AND SYMBOLS

*

°C

Ω.cm

±

%

ρ

Σi

A

a

avg

AWWA

C

Ca2+

CP

Cl

Cl

cravg

crmed

crmax

CR

Corr.

df

DF

D

e-

emf

Fe2O3nH

Asterisk marks (Significance value)

Degree Celsius

ohm - centimetre

plus - minus

Percentage

Resistivity

Total sum

Area (in cm2)

Electrode separation (cm )

Average

American Water Work Association

Concentration of the standardized thiocyanate solution (in mol/L)

Calcium Cation

Cathodic Protection

Chloride

Chloride Content

Average corrosion rate

Median corrosion rate

Maximum corrosion rate

corrosion rate

Corrosion rate

Degree of freedom

Disturbance factor

Density (in g/cm3)

Electron

Voltage potential

Hydrated crystallized ferric oxide

xviii

Fe

g

GPS

H0

H2O

I

K

K+

LCA

LNG

m3

m4

mm

mL

Mc

Mo – Nb

max

med

ML

mm/y

mc

Mc

Mg2+

mV

MIC

m.per

n

nP

nT

Na+

O2

OH-

pH

Iron

grams

Global Positioning System

null hypothesis

water

Index

a constant (8.76 x 104mm/y)

Potassium ion

Linear Correlation Analysis

liquefied natural gas

mass of each test specimen used (g)

mass of ignited precipitate (g)

millimetre

millilitre

moisture content

Molybdenum – Niobium

maximum

median

metal loss

millimetre per year

moisture content

Moisture Content

Magnesium ion

milivolts

microbiologically influenced corrosion

marks percentage

weighting factor

weighting factor of parameter

total summation of weighting factor

Sodium ion

oxygen

hydroxide ion

pH content

xix

p value

ppm

R

Res

Sig.

SM

STATSGO

SC

SO4

SO3

ST

SPSS

SRB

SCC

SR

T

t

t

V2

V3

v

W

WA

W0

Significance value

part per million

resistance, Ω

soil resistivity

Significations

Soil Moisture

State Soil Geographic Steel corrosion

Soil Corrosivity

sulphide content

sulphate content

soil type

Statistical Package for the Social Science

Sulphate Reducing Bacteria

Soil Corrosivity Score

Soil Resistivity

Time of exposures (in hours)

exposure of time

month

volume of the silver nitrate solution added (in mL)

volume of the standardized thiocyanate solution added (in mL)

volts

Mass loss (in grams)

water excess

Initial weight

xx

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Metal Loss and Quantitative Soil Parameters Data on Sites 128

B Outliers Data for Metal Loss and Corrosion Rate 132

C Soil Corrosivity Condition Index’ Marks on Sites 135

D Soil Corrosivity Condition Index Manual 140

CHAPTER 1

INTRODUCTION

1.1 Overview

Pipelines play an important role as they transfer liquid, oil and gas from their

sources to the ultimate consumers. The structures are commonly installed

underground, under the water or at above ground. Underground pipeline structures

are commonly exposed to various types of risk, such as corrosion. The corrosion

process of underground pipeline structures may reduce the strength of the metal and

cause structural failure. Corrosion is an issue that has to be taken seriously into

consideration as it has negative impacts on the environment as well as human and

economic systems. Some of the problems that can possibly occurs due to corrosion

are pipeline leakages, plant shutdowns, waste of valuable resources, contaminated

products, efficiency reduction, high maintenance cost, expensive over-design, serious

injuries to personnel, and explosion.

Corrosion of underground pipeline structures can be categorized into two

groups: external and internal corrosion. External corrosion is caused by exposure to

soil environment, while internal corrosion is caused by the influence of material flow

in the pipeline. In order to reduce the possibility of underground external corrosion, it

is important to identify the level of soil corrosivity of the pipeline installation

location.

2

1.2 Research Background

Many cases have been reported on the pipeline structures failure due to

corrosion problems which has a devastating impact on the surrounding life and

environment. Wiese (2015) reported that the probable cause of pipeline failure on the

West Texas Gulf Pipeline System on February 2015 is due to external metal loss

caused by corrosion. For that reason, it is important to understand and recognize the

mechanism of corrosion by identifying the suitable material, design, protective

system, treatment and device for pipeline structures. Generally, underground pipeline

structures are designed to have a long life span by having protection system applied,

such as coating and cathodic protection to preserve the external integrity. Sausville

and Wu (1998) reported that metallic pipeline system has about 30 years of life

expectancy as per State regulations requirement. As reported by Kiefner and

Rosenfeld (2012), older pipelines in 1940s and 1950s seem to be more susceptible to

external corrosion because the pipelines were installed without coating and the

cathodic protection applied was lesser back then. This shows that the age pipeline

structures contribute to the corrosion threat on pipeline systems.

However, Peabody (2001) suggests that corrosion damages are still a reality

even though pipeline structure are protected by this kind of system as it is not

certainly guaranteed as a complete anti corrosion attack system. This is because

underground pipeline structures are constantly exposed to the soil environment that

contains varying types of material which can damage the protection system and

accelerate the corrosion process. The soil environment consists of complex measured

parameters and characteristics which can determine the extent of soil corrosivity. Soil

corrosivity is a multi scale process involving metal degradation reacting with soil due

to the soil behaviour itself. Soil corrosivity, when compared to that of the atmosphere

or seawater, corrosivity is often more difficult to categorise with regards to both pipe

specific parameters and surrounding soil properties (Farreira, 2006; Pritchard et al.,

2013).

Pritchard et al. (2013) states that soil influenced corrosion is a complicated

phenomenon due the complexity and heterogeneous dynamics of soil environments.

3

In this case, it is important to analyse and evaluate the soil corrosivity parameters in

order to assess the phase of soil corrosivity. By obtaining information about the soil

corrosivity phase, researches can provide useful guidance on pipeline selection,

corrosion control method and the maintenance system of pipeline structures.

1.3 Research Problem

The current practices to mitigate the external corrosion on underground

pipelines involve the combination of cathodic protection and pipeline coatings.

Cathodic Protection (CP) is a technique used to reduce corrosion rate of a metal

surface by making it the cathode of an electrochemical cell (Peabody, 2001), while

coatings normally are used to form a continuous film of an electrically insulating

material over the metallic surface to be protected (Peabody, 2001).

However, Fessler (2008) reported that cathodic protection application alone

would not be practical to protect pipelines against corrosion as the required amount

of current are highly proportional to the exposed area and will be expensive to

protect a long bare pipeline. Coatings by themselves also would not be totally

effective, because it is impossible to produce a perfect coating over an entire pipeline

(Fessler, 2008). These protection methods are actually applied during designing the

pipeline structures and after the process of pipeline installation. Hence, the methods

of protection applied are not designed based on corrosion analysis on the site prior

installation as per stated by Ismail and El-Shamy (2009) that risk of corrosion should

be estimated prior to pipeline structures installation.

Other corrosion potential assessment practiced by industries is generally

identified by examining a few variables for corrosion evidence, such as pipe-to-soil

potential due to its simplicity. However, it is difficult to quantify the characteristics

that may indicate high corrosion potential since corrosion is a function of many

parameters. For example, the soil acts as an electrolyte which reacts within specific

locations and time depending on variables such as moisture content, bacteria, ion

4

concentrations etc. which leads to difficulties in accurate estimation.

By investigating the characteristics of soil; soil engineering properties and

their chemical content of the proposed or existing pipeline installation locations,

researches can provides insight on the corrosion potential experienced by the buried

pipeline and the potential threats to structural integrity. The assessment of soil

corrosion risk may act as an initial step that enables the circumvention of the

hazardous impacts caused by pipeline corrosion. However, the study of soil corrosion

risk assessment still has a certain limit and has yet to be extensively modified.

Muhlbauer (2004) suggests that, the application of corrosion index may

reflect the potential for corrosion, which may or may not mean that corrosion is

actually happening. The ranking or index systems referring to site corrosivity are

vitally required to give an early indication on the potential of structure damage

subject to soil corrosion. It can also be used prior to installation of pipelines or to

assess possible failures of damaged pipelines qualitatively.

Distribution of pipeline infrastructure conveys that natural gas products from

Kerteh to end-user (industry) in Malaysia are buried underground. Up until now,

there are no specific guidelines that can be used and referred to in order to assess the

level of soil corrosivity of potential installation sites in Malaysia. The current

practice to identify the level of soil corrosivity in Malaysia is only through the soil

resistivity measurements and the potential of pipe to soil on site. The detailed site

conditions and information were not being studied and identified whether the site is

suitable or not for pipeline installation. These will incur higher cost in the future due

to the removal and reinstallation process of pipeline structures. Although previous

studies on soil corrosion risk have been carried out in several European countries,

there is no evidence or strong recommendation of the applicability of the findings to

assess soil corrosivity in Malaysia. In fact, Malaysia is located on the equatorial zone

and has a tropical climate.

Revie and Uhlig (2008) stated that a metal in some part of country may

5

perform satisfactorily, but may not in other countries due to the specific differences

of soil composition, pH, moisture content etc. Revie and Uhlig (2008) also stated that

groundwater in tropical climates tends to be more acidic. Based on the requirements,

soil corrosivity condition index system needs to be developed in order to facilitate

the identification process of soil corrosivity condition of pipeline installation

locations. Soil corrosion risk design in accordance to soil characteristics in Malaysia

can be very useful to the pipeline companies in Malaysia as the installation of

pipeline structures shall be more systematic and safety-ensured.

1.4 Research Aim

The aim of this research is to develop condition index of soil corrosivity

based on the evaluation of soil parameters and site characteristics for pipeline

installation and maintenance works. To achieve the stated research aim, the following

objectives must be fulfilled as follows:

i. To measure metal mass loss of corroding X70 steel coupon exposed to the

underground environment.

ii. To measure soil parameters and site characteristic data which may have

strong influence towards corrosion of the X70 steel coupon

iii. To develop index values of soil parameters and soil characteristics and an

empirical model to quantify soil corrosivity condition.

iv. To verify the validity of soil corrosivity condition index design by comparing

the results of corrosivity condition for every site with the existing corrosion

rate data.

6

1.5 Research Scopes

The research puts the focus on the study of parameters related to soil engineering

properties and chemical content affecting soil corrosiveness, such as soil resistivity,

moisture content, chlorides, sulphide, sulphate, pH and the general characteristics of

site field work. The corrosion process caused by microbial activity is not considered.

The metal loss products are obtained from the buried samples derived from the X70

steel pipeline section. Field work and laboratory experiments are carried out to

measure the weight of metal loss, an indication of the corrosion process of steel

pipelines.

The field works are carried out in five selected sites in Peninsular Malaysia,

located in three states which are Pahang, Terengganu and Johor. These sites were

selected based on the inspection data and maintenance records provided by

PETRONAS. The environment diversity, coupon installation feasibility and safety

aspect were also considered in selecting these sites. The corrosion of the steel coupon

is considered under the worst case scenario whereby the steel coupon is assumed to

experience a coating breakdown. Hence, corrosion can start to initiate immediately.

The corrosion index system is designed by considering the type of soil in east coast

only due to time and cost constraint. As the types of soil on east coast are not the

same as the type of soil on the some part of west coast, the proposed procedure may

be used on the recommended types of soil only.

1.6 Research Significance

Various efforts have been proposed to minimise corrosion problems on pipeline

structures. However, there are some surveillance methods that are considered

inefficient in terms of operational cost, such as Cathodic Protection (CP) where the

current are applied to the entire pipeline structures, and pipeline coating where the

entire pipeline structures are coated by the same amount of coating layer. Even with

all the modern pipeline construction practices, better coatings, more extensive CP

and other methods of corrosion control, the pipeline industry continues to experience

7

corrosion (external and internal) on pipelines (Norsworthy, 2014). Thus, the system

of Soil Corrosivity Condition Index is a possible solution to overcome the cost issues

and benefits the pipeline industry.

The Indexing system offers preliminary information of the selected site for

pipeline installation. This allows the pipeline industry parties to determine the site

suitability in term of soil corrosion level prior to pipeline installation. The system is

suitable to apply by the industries as it can be viewed before and after laying the

pipeline structures. As natural resources are becoming more and more valuable,

losses must be kept to the minimum as the industry strives to become perfect (which

will not happen) in its corrosion control effort (Norsworthy, 2014). By the

application of the index system, industries would be able to control the cost for the

protection of the pipeline structure by having a proper control on the amount of

protection applied. Soil corrosivity index system is specifically developed using

parameters from local sites that has the potential to be a reliable method of

controlling the corrosion on pipelines and provides the following benefits:

i. The proposed index system can be utilized by operators to detect potential

threats to the existing pipeline structural integrity due to soil-corrosion by

considering various types of environmental parameters.

ii. It can greatly assist the pipeline system operator in making accurate decisions

on what, when and where future inspection repair and maintenance resources

can be deployed.

iii. The ranking system is designed to reduce errors in selecting installation sites

with low-risk of corrosion by ranking the sites according to soil corrosivity

for future pipeline installation.

121

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