the effect of corrosion defects on burst … · between modified asme b31g and finite element...

THE EFFECT OF CORROSION DEFECTS ON BURST PRESSURE OF PIPELINES

KHAIRUL ANWAR BIN IBRAHIM

Report submitted in fulfillment of the requirements for the award of the degree of

Bachelor of Mechanical Engineering

Faculty of Mechanical Engineering

UNIVERSITI MALAYSIA PAHANG

JUNE 2012

vii

ABSTRACT

The predictions of pipeline burst pressure in the early stage are very importance in order

to provide assessment for future inspection, repair and replacement activities. The

failure of oil and gas pipelines contribute to economic implications and also constitute a

serious hazards to the environment due to leakage. This thesis deals with the study on

the effect of corrosion defect on the burst pressure of pipelines for API 5L X42 steel.

The objectives for this project are to determine the burst pressure of corroded pipelines

using Finite Element Analysis (FEA) and to compare the results with the available

pipelines design code. This project implicates analysis of the API X42 steel by using

MSC Patran 2008 r1 software as pre-processor and MSC Marc 2008 r1 software as a

solver. A quarter of pipe was simulated by fully applying the symmetrical condition.

The pipe is modeled in 3-D with outer diameter of 60 mm, wall thickness of 6 mm and

different defect parameters. In this analysis, stress modified critical strain used as failure

criterion to predict the failure of defective pipe. Result shows that the burst pressure

decreases when both defect depth and length increases. The defect depth appear as a

most influence parameter that affect the burst pressure. The circumferential extent has a

less influence on the burst pressure. The results have been compared to available design

codes for corroded pipelines such as ASME B31G, Modified ASME B31G and DNV

RP F101. Comparison with available design codes have shown that FEA burst pressure

gives higher values compare to codes. From the results, ASME B31G gives the lowest

values than other codes.

viii

ABSTRAK

Ramalan-ramalan tekanan letus saluran paip di peringkat awal adalah sangat penting

untuk menyediakan penilaian bagi pemeriksaan pada masa akan datang, aktiviti

pembaikan dan penggantian. Kegagalan saluran paip minyak dan gas menyumbang

kepada implikasi ekonomi dan juga merupakan suatu bahaya yang serius kepada alam

sekitar yang berpunca daripada kebocoran. Tesis ini berkaitan dengan kajian pada kesan

kecacatan kakisan pada tekanan pecah saluran paip untuk API 5L keluli X42. Objektif

bagi projek ini adalah untuk menentukan tekanan pecah paip berkarat yang

menggunakan Analisis Unsur Terhingga (FEA) dan membandingkan keputusan dengan

kod saluran paip reka bentuk yang ada. Projek ini aib analisis keluli API X42 dengan

menggunakan MSC Patran 2008 r1 perisian sebagai pra-pemproses dan MSC Marc

2008 perisian r1 sebagai penyelesai. Satu perempat daripada paip adalah simulasi

dengan menggunakan sepenuhnya keadaan simetri. Paip model 3-D dengan diameter

luar 60 mm, ketebalan dinding 6 mm dan parameter kecacatan yang berbeza. Dalam

analisis ini, menekankan tarikan kritikal yang diubahsuai digunakan sebagai kriteria

kegagalan untuk meramalkan kegagalan paip rosak. Keputusan menunjukkan bahawa

tekanan yang pecah berkurangan apabila kedua-dua kedalaman kecacatan dan panjang

bertambah. Kedalaman kecacatan muncul sebagai satu parameter pengaruh yang paling

yang memberi kesan kepada tekanan pecah. Sejauh lilitan mempunyai pengaruh yang

kurang pada tekanan pecah. Keputusan telah berbanding kod reka bentuk tersedia untuk

saluran paip berkarat seperti ASME B31G, Modified ASME B31G dan DNV RP F101.

Perbandingan dengan kod reka bentuk yang ada telah menunjukkan bahawa tekanan

letus FEA memberikan nilai yang lebih tinggi berbanding dengan kod. Daripada

keputusan, ASME B31G memberikan nilai yang terendah daripada kod lain.

ix

TABLE OF CONTENTS

Page

EXAMINER’S DECLARATION ii

SUPERVISOR’S DECLARATION iii

STUDENT’S DECLARATION iv

DEDICATIONS v

ACKNOWLEDGEMENTS vi

ABSTRACT vii

ABSTRAK viii

TABLE OF CONTENTS ix

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF ABBREVIATIONS xviii

CHAPTER 1 INTRODUCTION

1.1 Introduction 1

1.3 Project Background 2

1.3 Problem Statement 3

1.4 Objectives 4

1.5 Scope Of Study 4

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction 5

2.2 Oil Exploration Review in Malaysia 5

2.3 Theory of Corroded Pipeline 8

2.4 Types of Corrosion 9

2.4.1 Uniform Corrosion 9

2.4.2 Pitting Corrosion 10

2.4.3 Dealloying Corrosion 11

2.4.4 Intergranular Corrosion 12

2.4.5 Erosion-Corrosion/Impingement 13

2.4.6 Transgranular Corrosion 14

x

2.5 Submarine Pipeline Corrosion 15

2.5.1 External Corrosion 16

2.5.2 Internal Corrosion 16

2.6 Pipeline Failures 18

2.6.1 Pipeline Failure Causes 19

2.7 Corrosion Prevention Methods 22

2.8 Finite Element Analysis 23

2.8.1 Meshing 23

2.8.2 Application of the Finite Element Method 24

2.8.3 Advantages of Finite Element Method 24

2.8.4 Analytical Method 25

CHAPTER 3 METHODOLOGY

3.1 Introduction 26

3.2 Flow Chart of the Project 26

3.3 Methodology 28

3.3.1 Structural Modelling 29

3.3.2 Mesh Model 34

3.3.3 Loads / Boundary Conditions 36

3.3.4 Input Data 38

3.3.5 Materials Application 40

3.3.6 Element Properties Application 42

3.3.7 Analysis Performing For Model 43

3.4 Predicting Burst Pressure 44

CHAPTER 4 RESULTS AND DISCUSSIONS

4.1 Introduction 45

4.2 Result 46

4.2.1 Comparison of burst pressure of different defect depth

between Modified ASME B31G and Finite Element result.

46

4.2.2 Comparison of burst pressure of different defect length


48

4.2.3 Comparison of burst pressure of different defect width


51


between ASME B31G and Finite Element results.

53

xi



55



57


between DNV RP F101 and Finite Element results.

59



61



63

4.2.10 Summary of burst pressure with different defect depth,

defect length and defect width for ASME B31G, Modified

ASME B31G, DNV RP F101 And FEA

65

4.2.11 Radial displacement for different defect depth 68

4.2.12 Radial displacement for different defect length 71

4.2.13 Radial displacement for different defect width 73

4.2.14 Summary of radial displacement with different defect

depth, defect length and defect width

75

4.2.15 Comparison between deformed pipe and undeformed pipe. 77

4.2.16 Finite element analysis (FEA) defect deformation with

different length at same pressure 30 MPa.

78

4.2.17 Finite element analysis (FEA) pipe deformation with

different depth at burst pressure.

79


different length at burst pressure.

80


different width at burst pressure

81

CHAPTER 5 CONCLUSION AND RECOMMENDATIONS

5.1 Introduction 82

5.2 Conclusion 82

5.3 Recommendations for Future Research 83

REFERENCES 84

APPENDICES 86

xii

LIST OF TABLES

Table No. Title Page

2.1 Hazardous liquid pipeline accident summary 20

2.2 Natural gas transmission pipeline incident summary 21

2.3 Natural gas distribution pipeline incident summary 21

3.1 The parameter of the defects 31

3.2 Material data for API 5L - X42 steel 41

4.1 Burst pressure for different defect depth Modified ASME B31G

and FEA

46

4.2 Burst pressure for different defect length Modified ASME B31G

and FEA

49

4.3 Burst pressure for different defect width Modified ASME B31G

and FEA 51

4.4 Burst pressure for different defect depth ASME B31G and FEA 54

4.5 Burst pressure for different defect length ASME B31G and FEA 56

4.6 Burst pressure for different defect width ASME B31G and FEA 58

4.7 Burst pressure for different defect depth DNV RP F101 and FEA 60

4.8 Burst pressure for different defect length DNV RP F101 and FEA 62

4.9 Burst pressure for different defect width DNV RP F101 and FEA 64

xiii

LIST OF FIGURES

Figure No. Title Page

2.1 Malaysia oil production and consumption 7

2.2 Uniform corrosion 10

2.3 Pitting corrosion 11

2.4 Dealloying corrosion 12

2.5 Intergranular corrosion 13

2.6 Erosion-corrosion 14

2.7 Stress-corrosion cracking (SCC) 15

3.1 Overall flowchart 27

3.2 Methodology flowchart 28

3.3 A quarter model of the pipe 29

3.4 Defect dimensions 30

3.5 Corroded defect 30

3.6 Geometry bar 32

3.7 Geometry properties 32

3.8 Pipe sketch 33

3.9 Pipe surface 33

3.10 Element bar 34

3.11 Mesh seed properties bar 34

3.12 Mesh properties bar 35

xiv

3.13 Equivalence properties bar 35

3.14 Loads / Boundary conditions bar 36

3.15 Loads / Boundary conditions properties bar 37

3.16 Geometrical modelling with load, x-axis, and z-axis vector 37

3.17 Engineering stress strain curve of API 5L X42 steel 39

3.18 True stress strain curve of API 5L X42 steel 39

3. 19 Input data table 40

3. 20 Material input menu 41

3. 21 Element properties input menu 42

3.22 Creating job step analysis 43

3.23 Critical location 44

4.1 Graph burst pressure versus defect depth for Modified ASME

B31G

47

4.2 Graph burst pressure versus defect depth for FEA 47

4.3 Comparison graph burst pressure versus defect depth for

Modified ASME B31G and FEA

48

4.4 Graph burst pressure versus defect length for Modified

ASME B31G

49

4.5 Graph burst pressure versus defect length for FEA 50

4.6 Comparison graph burst pressure versus defect length for


50

4.7 Graph burst pressure versus defect width for Modified ASME

B31G 52

4.8 Graph burst pressure versus defect width for FEA 52

xv

4.9 Comparison graph burst pressure versus defect width for


53

4.10 Graph burst pressure versus defect depth for ASME B31G 54



ASME B31G and FEA

55

4.13 Graph burst pressure versus defect length for ASME B31G 56



ASME B31G and FEA

57

4.16 Graph burst pressure versus defect width for ASME B31G 58



ASME B31G and FEA

59

4.19 Graph burst pressure versus defect depth for DNV RP F101 60



DNV RP F101 and FEA

61

4.22 Graph burst pressure versus defect length for DNV RP F101 62



DNV RP F101 and FEA

63

4.25 Graph burst pressure versus defect width for DNV RP F101 64


xvi


DNV RP F101 and FEA

65

4.28 Comparison graph for burst pressure with different defect

depth

66


length

66


width

67

4.31 Graph internal pressure versus radial displacement for

3 mm defect depth

69


3.5 mm defect depth

69


4 mm defect depth

70


4.5 mm defect depth

70


30 mm defect length

71


40 mm defect length

71


50 mm defect length

72


60 mm defect length

72


4 mm defect width

73


6 mm defect width

73

xvii


10 mm defect width.

74


14 mm defect width.

74

4.43 Comparison graph for radial displacement with different

defect depth.

75


defect length.

76


defect width.

76

4.46 Undeformed pipe. 77

4.47 Deformed pipe. 78

4.48 Defect deformation with different length at 30 MPa. 79

4.49 Pipe deformation with different depth at burst pressure. 80

4.50 Pipe deformation with different length at burst pressure. 80

4.51 Pipe deformation with different width at burst pressure. 81

xviii

LIST OF ABBREVIATIONS

2-D Two Dimension

3-D Three Dimension

ASTM American Society for Testing and Materials

ASME American Society of Mechanical Engineers

API American Petroleum Institute

ANSI American National Standards Institute

DNV Det Norske Veritas

FEA Finite Element Analysis

FEM Finite Element Method

HIC Hydrogen Induced Cracking

RP Recommended Practice

SCC Stress Corrosion Cracking

SOHIC Stress-Oriented Hydrogen Induced Cracking

SSC Sulfide Stress Cracking

MSS Maximum Shear Stress

CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION

A pipeline is all parts of the physical facility where liquids or gases such as

crude oil and natural gas are transported usually over long distances between a

producing region and a local distribution system. Offshore pipeline systems are vital to

transport the raw oil products and gas from the oil platform to the onshore terminal.

Such pipelines are necessary because the locations of oil/gas production sites tend to be

far away from the refineries, processing plants and end user (Khan and Islam, 2007).

Offshore pipeline transport enormous quantities of oil and gas vital to the

economic of virtually all nations. Therefore the exploration and production of oil and

gases form adverse or hostile environments and from marginal field is becoming

increasing important to ensure a continuous and independent energy supply. Production

of oil and gas from sea bottoms,performed from stationary platform has gained wide

development. Most of the sub sea oil and gas fields that been developed,or are under

development, are marginal with a production life time between 5 and 15years

(Martinussen, E. 1995).

As a pipeline ages, it can be affected by a range of corrosion mechanisms, which

may lead to a reduction in its structural integrity and eventual failure. The economic

consequences of a reduced operating pressure, loss of production due to downtime,

repairs, or replacement can be severe and, in some cases, not affordable.

2

There are lots of methods (codes) in the engineering practice to determine the

burst pressure of corroded pipes depending on the loadings and the scopes of the

pipelines. These semi-empirical methods based on measurement data (ASME B31G,

Modified ASME B31G, DNV RP F101,) consider only the length and depth dimensions

of the simple, 3D geometrical shapes which are used to approximate the real corrosion

failures. They are based on limit analysis of defective pipelines, however, one part of

them over- or underestimate the burst pressures considering their geometrical models or

semi-empirical factors. The transmission steel pipelines are usually made from ductile

steel, but the majority of codes consider only elastic and perfectly plastic material

behaviour. A fairly severe disadvantage of them is that they consider internal loads

only. Because of these enumerated properties they can be called conservative.

1.2 PROJECT BACKGROUND

Predicting the failure of damaged oil and gas pipeline has become an essential art

for the determination of design tolerance. A pipeline may experience significant internal

and external corrosion defects by chemical and environmental effects that reduce its

strength and resistance to fatigue, local buckling, leakage and bursting. Finite Element

Modeling has become a reliable method for a prediction technique. The technique

developed recently has enabled the reliable and accurate location and sizing of pipeline

wall corrosion. The burst pressures of pipes with corrosion defects on their outer

surfaces were determined with the help of FEA, where the calculated burst pressure

values were called as ultimate pressures.

The main goal of the simulations was to determine how the depth, width, and length

of the corrosion defects influence the burst pressures. The material use for this analysis

is API 5L X42 steel. In order to determine stress triaxiality and equivalent strain, model

with different parameter defects will be simulated in finite element software. For this

purpose, MSC Patran/Marc 2008 r1 were applied. The main reasons for using MSC

Patran/Marc for failure prediction is to reduce cost by replacing physical testing with

less expensive digital simulation. True stress-strain data for API 5L X42 steel was used

as input data in the finite element analysis.

3

Throughout this project, ASME B31G, Modified ASME B31G, and DNV-RP-F101

are the standards followed in order to standardize the results obtained. The limitations

of this study are subjected to previously mentioned codes and standard. The data from

the analysis will be compared with the available design code for pipelines.

1.3 PROBLEM STATEMENT

Nowadays, the investigation of the crude oil- and natural gas transmission steel

pipelines applied in the pipeline industry has generally revealed that the primary reason

for their failure is corrosion. Wall thinning caused by corrosion failure on the inner or

outer surfaces of the pipelines will generate stress concentration on the pipe wall. The

highest stress and strain value will occur at the deepest point of the corrosion defect,

therefore the failure of the pipelines are usually expected at this location. Including

dimensions (length, width, depth) of the corrosion defects influence the stress

concentration to a different extent. (Length of the defect refers to the longitudinal, the

width of the defect refers to the circumferential directions of the pipelines.)

Integrity assessment of corroded pipeline is very vital in oil and gas industry. Better

understanding is required to reduce the conservatism involved in the current assessment

method. Previous research has found out that finite element analysis has become a

reliable engineering approach towards achieving actual results. Many Consultant

Company realize that it is difficult to have a finite element modeling of the offshore

corroded pipeline as the modeling need further understanding and detail research on

each data. In this research, finite element analysis will be implemented comparing with

the available codes as it is a higher demand in the oil and gas industry. This research

will be a start and guidance in helping industries towards achieving accurate prediction

of failure on corroded pipelines.

4

1.4 OBJECTIVES

For this project, two main objectives are listed:

i. To determine the burst pressure of corroded pipelines using Finite Element

Analysis (FEA)

ii. To compare the FE burst pressure results with available design code for

corroded pipelines.

1.5 SCOPE OF STUDY

The scope of study of this project is failure predictions which include the study

of remaining strength of corroded offshore pipeline by using finite element analysis

software. The scope of the research are :

a) API 5L X42 steel is used in this analysis.

b) MSC Patran is used as pre-processor and MSC Marc is used as solver.

c) Finite element analysis (FEA) condition:

3-D model.

Homogeneous material model.

Elastic-plastic.

Reduced integration.

Non-linear.

d) True stress-strain data for API 5L X42 steel was used as input data in the

finite element analysis.

e) Stress modified critical strain model is the failure criterion used to

predict the burst pressure.

f) Finally, finite element results will be compared with the available design

code that are ASME B31G, Modified ASME B31G, and DNV-RP-F101.

CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

This chapter will briefly explain about the properties, material , design, failure

and cause of failure in pipeline. The sources are taking from journals, articles, and

books. Besides, the information about the software that will be used also included in

this chapter. Literature review is done to provide information about previous research

and that can help to smoothly run this project. All this information is important before

furthering to the analysis and study later.

2.2 OIL EXPLORATION REVIEW IN MALAYSIA

The first oil well discovered in Malaysia was by Shell Company, in 1910 in

Miri, Sarawak. Thereafter, the same company constructed Malaysia's first refinery in

1914, which undertakes the whole manufacturing of petroleum products. At present,

Malaysia's oil company, PETRONAS undertakes the exploration and production of the

oil and gas in Malaysia whilst Shell and other oil companies operate as a contractor to

PETRONAS under Production Sharing Contracts.

6

Malaysia's oil and gas fields can be found mainly offshore of Peninsula Malaysia

as well as the east coast. At present, Malaysia has 37 producing oil fields and 11

producing gas fields whilst several others are under development. The main five oil

fields that produce high quality blends of crude can be found in the east of Peninsula

Malaysia mainly, Tapis, Labuan, Miri, Bintulu and Dulang. It has been estimated that

Malaysia has been producing 630,000 barrels of oils and five billion cubic feet of gas

per day. Such an amount produced has made Malaysia one of the niche players in the oil

and gas industry.

Malaysia has uncovered an estimated 214 gas field and most of these fields are

under some development. As at 1 January, 2000, Malaysia has about 3.4 billion barrels

of crude oil reserves and about 84.2 trillion standard cubic feet of gas reserves. This

reserve has successfully placed the country at 27th and 12th places respectively in terms

of world ranking. PETRONAS has the licensing authority for all upstream activities:

exploration, production and transportation of oil in Malaysia. Most of the country's oil

fields contain 10 low sulphur, high quality crude, with gravities in the 35-50 API range.

Over half of the country's oil production comes from the Tapis field, which contains 44

API oil with low sulphur content (EIA, 2000; PETRONAS, 1999). Esso Production

Malaysia Inc. (EPMI) is the largest crude oil producer in Peninsular Malaysia,

accounting for nearly half of Malaysia's crude oil production. EPMI operates seven

fields near the peninsular, and one-third of its production comes from the Seligi field.

(EIA, 2000).

Currently, Terengganu produce more than half of Malaysia's total oil output with

daily production totalling 380,000 barrels (EIA, 2000). Proven reserves off Terengganu

total 2.4 billion barrels from 18 oil fields. Besides PETRONAS Carigali (PCSB), five

other companies are also involved in the oil and gas exploration off Terengganu coast in

PSC agreement. They are International Petroleum Ltd, USA; Esso Production Malaysia;

Western Mining Corporation, Australia; Texaco and Penyu International Inc. The others

major oil companies operating in Sabah and Sarawak are Shell, Sarawak Shell Berhad,

Sarawak Shell/PETRONAS Carigali, and Amoco (PETRONAS, 2001). Figure 2.1

shows Malaysia`s oil production and consumption in 1990 until 2009.

7

Figure 2.1: Malaysia`s oil production and consumption

Source: Petronas (2001)

PETRONAS is concern in the area of safety regulations and enforcement.

Among the tools for ensuring pipeline integrity, one of the most successful is risk

management and RBI (Reid, 1998). PETRONAS has been successful in implementing

RBI for platform structures and for mechanical piping. Number of planned

comprehensive inspection for platform structures have been reduced from 117 to only

59 after the implementation of RBI procedure (Goh, 2000). Now, PETRONAS is

moving ahead in implementing the same procedure for offshore pipelines.

8

2.3 THEORY OF CORRODED PIPELINE

Corroded pipeline are referring to the pipeline that undergo the chemical reaction

between a metal or alloy and its environment. A pipeline may experience significant

internal and external corrosion defects that will reduce its strength and resistance to

fatigue, local buckling, leakage and bursting. Corrosion mechanisms include

electrochemical corrosion, chemical corrosion, and stress-promoted corrosion.

The strength of old pipelines declines because of a number of reasons, with

corrosion being the major one. This is especially true when the pipeline is not well

corrosion–protected. The study of increasing corrosion resistance is essential to reduce

the maintaining cost. The factors that most influence the behaviour of the stainless steel,

in rough order of importance to corrosion, are as follow:

1. Presence of oxidizing species which aids reformation of the oxide film

2. Chloride ion concentration because chloride hinders oxide film repair

3. Conductivity of the electrolyte, which affects the cathode/anode ration

4. Crevices that can initiate corrosion

5. Sediments that prevent reformation of the oxide film

6. Scales and deposits that prevent reformation of the oxide film

7. Chlorinating practice that alters the chlorine content of the environment

8. Surface condition of the stainless steel

9. pH(if below 5) that increase the cathodic reactions

10. Temperature that alters the relative rates of oxide film breakdown, corrosion

processes and oxide film reformation rate.

The reaction that occurs when steel is immersed in sea water or corrosive liquid

environment can be written as followed (Craig, 1993):

Oxidation: Fe Fe2+ + 2e- (2.1)

Reduction: O2 + 2H2O + 4e- 4OH- (2.2)

9

The overall reaction will be written as (Khan and Islam, 2007):

2Fe + 2H2O + O2 2Fe2+ + 4OH- (2.3)

Or

2Fe + 2H2O + O2 2Fe(OH)2 (2.4)

However, ferrous hydroxide (corrosion products) reacts with salt to form ferrous

chloride:

Fe(OH)2 + 2NaCl FeCl2 + 2NaOH (2.5)

In the later stage of corrosion, ferrous chloride reacts with water to form hydrochloric

acid:

FeCl2 + 2H2O Fe(OH)2 + 2HCl (2.6)

2.4 TYPES OF CORROSION

Corrosion can be categorized in various ways which are (Craig, 1993):

2.4.1 Uniform corrosion

Uniform corrosion represents the ideal case in which the metal is uniformly

corroded away at some constant rate. Figure 2.2 shows uniform corrosion of pipe. This

type of corrosion attack is the basis for most design. Corrosion often very localized and

failure occurs long before failure by general thinning of metal. This form of corrosion is

observed on metal structures exposed to the atmosphere such as offshore platforms.

10

Figure 2.2: Uniform corrosion

Source : Craig (1993)

2.4.2 Pitting corrosion

Pitting attack is one of the most frequent forms of corrosion encountered. It

shows a very localized attack in a few weeks or months while the remaining area of

metal is relatively uncorroded. The shape of pits depends on the particular pitting

environment. Once pitting is initiated, the remaining unpitted surface area becomes

cathodic to the pits. As pits progress, pH of solution in the bottom of pit is reduced often

to a pH of 1. With the reduction in pH together with anodic character of the pit, it drives

the corrosion process until the metal is perforated. During perforation of metal, some

pits will initiate and then stop growing while others propagate to various depths and

stop or continue to grow until failure. While pitting can be catastrophic and difficult to

predict, it is necessary to understand the environments which induce pitting. Figure 2.3

shows pitting corrosion of pipe.

11

Figure 2.3: Pitting corrosion

Source : Craig (1993)

2.4.3 Dealloying corrosion

Dealloying or selective leaching is the selective corrosion of one element in an

alloy. Figure 2.4 shows dealloying corrosion of pipe. Dezincification is an example of

dealloying whereby zinc is selectively attacked and removed from brass alloys, leaving

only copper behind. Another form of cast irons attack is called graphitization is

whereby the iron matrix of gray cast iron is being corroded leaving behind a layer of

graphite. For instance, gray cast-iron butterfly valves and water pumps used in

petroleum industry are most susceptible to this type of corrosion.

the effect of corrosion defects on burst … · between modified asme b31g and finite element...

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