DTIC ADA440262: Numerical Simulation of Hydrogen Assisted Cracking in Supermartensitic Stainless Steel Welds

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Numerical Simulation
of Hydrogen Assisted Cracking
in Supermartensitic Stainless Steel Welds
Vom Fachbereich Maschinenbau
der Helmut-Schmidt-Universitat
- Universitat der Bundeswehr Hamburg -
zur Erlangung des akademischen Grades
eines Doktor-Ingenieurs (Dr.-Ing.)
genehmigte
Dissertation
vorgelegt von:
Ekkarut Viyanit, M.Eng.
DISTRIBUTION STATEMENT A
Approved for Public Release
Distribution Unlimited
aus:
Ayutthaya, Thailand
Hamburg 2005
Die vorliegende Arbeit entstand an der Bundesanstalt fOr Materialforsc hung und -pnifung
(8AM).
Gutachter: Prof. Dr.-Ing. Hans Hoffmeister
Assoc. Prof. Dr.-Ing. Gobboon Lothongkum
Dr.-Ing. Thomas Bbllinghaus, VP u. Prof.
Tag der mOndlichen Pnifung: 27. Januar 2005 in Hamburg
impressurm
Numerical Simulation of Hydrogen Assisted Cracking
in Supermartensitic Stainless Steel Welds
2005
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ISSN 1613-4249
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2005 Dissertation
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Numerical Simulation of Hydrogen Assisted Cracking in Supermartensitic Stainless Steel Welds
6. AUTHOR(S)
Ekkarut Viyanit
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
REPORT NUMBER
UNIBW
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Bundesanstalt fuer Materialforschung und -pruefung
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Text in Englsih, 196 pages, ISBN 3-86509-270-5, ISSN 1613-4249.
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ABSTRACT (Maximum 200 words)
Replacement of expensive duplex stainless steel and conventional carbon steel by a new generation of supermartensitic stainless steel has
been taken into account since the last decade corresponding to the "Fitness for Purpose" concept in order to meet the technical-economical
challenge for transportation flowlines of unprocessed oil and gas products in offshore technology, in particular. Supermarlensitic stainless
steels can provide appropriate material properties such as: improved strength-to-weight ratio, enhanced useful corrosion resistance as well as
application at relatively low cost. With decreased carbon content and increased molybdenum content compared to traditional martensitic
stainless steel, hydrogen assisted stress corrosion cracking (HASCC) problems have been found during service caused by hydrogen being
taken up during from sour service environments by cathodic protection. Hydrogen assisted cold cracking in supermartensitic stainless steel
can also occur during fabrication welding with hydrogen picked up during welding, since this steel is relatively crack-susceptible by
hydrogen.
Therefore, effects of hydrogen assisted cracking (HAG), i.e. HASCC and HACC, on characteristic susceptibility of girth welds of
supermartensitic stainless steel pipelines are studied in the present thesis by numerical modelling, which is developed using a available
commercial finite element program. Firstly, numerical modelling for simulation of HASCC based on the NACE-TM 0177-96 approach is
carried out for providing a basic understanding of the crack propagation behaviour. Secondly, a two dimensional finite element according to
the gauge length cross-section of the orbitally welded pipeline is created for numerical modelling in order to calculate the time to failure of'
welded the component exposed to the NACE electrolyte solution with various H2S saturation. Externally applied loads of a series of
constant strain rates and of the load history of full scale testing are also taken into account. Finally, numerical modelling is carried out under
three specific aspects, i.e. thermal analysis, structural analysis, and hydrogen diffusion analysis, in order to simulate HACC in
supermartensitic stainless steel pipelines welded orbitally by four layers of matching filler wires with an interpass temperature of 40'C.
14, SUBJECT TERMS 15. NUMBER OF PAGES
UNIBW, Germany, Numerical modelling. Supermartensitic stainless steel, Girth welds, Pipeline, Hydrogen
assisted cracking (HAG). Hydrogen assisted stress corrosion cracking (HASCC), Hydrogen assisted cold
cracking (HACC), Hydrogen subsurface concentration, Crack propagation, Time to failure (CTF), Hydrogen
diffusion coefficient, Post weld heat treatment (PWHT), Full scale test
16. PRICE CODE
17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19, SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT
OF REPORT OF THIS PAGE OF ABSTRACT
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Prescribed by ANSI Std. 239-18
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Abstract
ABSTRACT
Replacement of expensive duplex stainless steel and conventional carbon steel by a
new generation of supermartensitic stainless steel has been taken into account since the
last decade corresponding to the "Fitness for Purpose" concept in order to meet the
technical-economical challenge for transportation flowlines of unprocessed oil and gas
products in offshore technology, in particular Supermartensitic stainless steels can provide
appropriate material properties such as: improved strength-to-weight ratio, enhanced useful
corrosion resistance as well as application at relatively low cost. With decreased carbon
content and increased molybdenum content compared to traditional martensitic stainless
steel, hydrogen assisted stress corrosion cracking (HASCC) problems have been found
during service caused by hydrogen being taken up during from sour service environments
by cathodic protection. Hydrogen assisted cold cracking in supermartensitic stainless steel
can also occur during fabrication welding with hydrogen picked up during welding, since this
steel is relatively crack-susceptible by hydrogen.
Therefore, effects of hydrogen assisted cracking (HAC), i.e. HASCC and HACC, on
characteristic susceptibility of girth welds of supermartensitic stainless steel pipelines are
studied in the present thesis by numerical modelling, which is developed using a available
commercial finite element program. Firstly, numerical modelling for simulation of HASCC
based on the NACE-TM 0177-96 approach is carried out for providing a basic
understanding of the crack propagation behaviour. Secondly, a two dimensional finite
element according to the gauge length cross-section of the orbitally welded pipeline is
created for numerical modelling in order to calculate the time to failure of welded the
component exposed to the NACE electrolyte solution with various H S saturation. Externally
2
applied loads of a series of constant strain rates and of the load history of full scale testing
are also taken into account. Finally, numerical modelling is carried out under three specific
aspects, i.e. thermal analysis, structural analysis, and hydrogen diffusion analysis, in order
to simulate HACC in supermartensitic stainless steel pipelines welded orbitally by four
layers of matching filler wires with an interpass temperature of 40'C.
By indirect coupling of numerical diffusion and numerical structural modelling, all three
stages of HASCC, i.e. crack initiation, stable crack growth and rapid rupture, are
represented for the standard specimen when appropriate interaction between local
hydrogen and local strain ahead of the crack tip takes place, so that the time to failure is
controlled by Stage I1: stable crack growth. In the case where the local strain rate is above
5.OE-05 s-1, rapid rupture of the specimen occurs by mechanical overload rather than
HASCC. As evidently represented by numerical modelling, the heat affected zone (HAZ) is
the most susceptible region to HASCC due to its kinetics of crack propagation, which is
affected by the metallurgical HAZ behaviour of HAZ and by relatively high hydrogen
subsurface concentrations in the base metal (BM) diffusing into the susceptible HAZ region
ahead of the crack tip. The life time of orbitally welded pipelines with HASCC is significantly
dependent on the HAZ crack propagation characteristic, however, this phenomenon may be
changed by the presence of a previous crack in the weld metal resulting from HACC, which
can reduce the new crack length generated by HASCC during exposure to sour service
environments. This HACC can be avoided by using a welding fabrication in which the local
hydrogen concentration picked up during welding remains below 10 ml.(lOOgFe)-. In
$
--- _/ ,,7
Abstract
addition, the short-term approach of post weld heat treatment (PWHT) may be employed to
reduce local hydrogen concentration from sensitive regions in order to minimise the risk of
failure during the spooling/pipelaying process.
Keywords: numerical modelling, supermartensitic stainless steel, girth welds, pipeline,
hydrogen assisted cracking (HAC), hydrogen assisted stress corrosion cracking (HASCC),
hydrogen assisted cold cracking (HACC), hydrogen subsurface concentration, crack
propagation, time to failure (TTF), hydrogen diffusion coefficient, post weld heat treatment
(PWHT), full scale test
IV BAM-Dissertationsreihe
Contents
CONTENTS
Page
AB S TR A CT ...................................................... ................................................................... III
CO N T E N T S ...................................... .................................................................................... V
AC KN O WL E DG E ME N T ................................................................................................. . . IX
LI S T O F S YM B O LS ........................................................................ ..................................... XI
LI S T OF TA B LE S ...................................................................................... ...... . ....... XV II
LI S T OF F IGU R ES ..................................................................................................... . . X IX
1 INT RO DU C T ION ................................................................................................... . . 1
2 LIT ER A T UR E R EV IEW S ........................................................................................ . . 5
2.1 Supermartensitic Stainless Steels ......................................... 5
2.1.1 Base Material and Weld Microstructures ........................................ 6
2.1.1.1 Martensite Formation ................................................... 10
2.1.1.2 Second Phase Precipitation .......................................... 12
2.1.1.3 Post Weld Heat Treatment ........................................... 13
2.1.1.4 Filler Materials for Supermartensitic Stainless Steels ....... 16
2.1.2 Me chanical P roperties ................................................................... 17
2.1.3 Corrosion Resistance ..................................... 19
2.2 Mechanisms of Hydrogen Assisted Cracking ........................... 20
2 .2 .1 P ressure T heo ry .......................................................................... .. 2 1
2.2.2 Decohesion Theory ...................................... 22
2.2.3 Adsorption Theory .................................. 23
2.2.4 Dislocation Interaction Theory ..................................................... 24
2.2.5 Hydride Theory ..................................... 27
2.3 Effects of Crystal Structure of Steels on Hydrogen Transport .................... 28
2.3.1 Hydrogen Evolution and Absorption ............................................ 30
2.3.1.1 Hydrogen Absorption during Corrosion Processes ........... 30
2.3.1.2 Modelling of Hydrogen Absorption during Welding ........... 33
2.3.2 Determination of Hydrogen Diffusion Coefficients ..................3 5
2.3.3 The basic principle of diffusion ............................... 37
2.3.3.1 T rapping Effect ............................................................ 39
V
Contents
2.4 C rack Propagation Ch aracteristics .................................. ........................... .43
2.4.1 Determination of Crack Propagation Kinetics .............................. 45
2.4.2 Mechanisms of Stress Corrosion Cracking ................................... 50
2.5 Failure and Fracture Mechanisms for Modelling Hydrogen Assisted
Cracking ........................................... 52
2 .5,1 F ra ctu re T h e o ry ....................................................... ................... ... 5 3
2.5.1.1 Definition of Local Strain Rate .......................................... 54
2 .6 S low S tra in R ate T est .................................................................................... .57
2.6.1 NACE Standard TM 0177-96 ................................. 59
2.6 .1.1 Test specim en ...................... .................................... .. 60
2 .6.1 .2 T est S o lutio n .............................................................. . . 60
2.6.1.3 Test P rocedure .......... .................................................. 60
2 .6 .1.4 Fa ilure De term ination ....................................................... 6 1
2.7 Hydrogen Assisted Cold Cracking in Girth Welds ........................ 62
2.7.1 Overview of Hydrogen Assisted Cold Cracking of Welded Steels ... 64
2.7.2 Hydrogen Assisted Cold Cracking Test Methods ................... 64
2. 7 .2 .1 IR C -T e st ........ ............................................................. 6 4
2.7.2.2 Com ponent Test ......................................................... 67
2.7.3 Model of Temperature Distribution in Welding Processes ............... 70
2.7.3.1 Heat Generation in Arc Welding Processes ................. 70
2.7.3.2 Heat Transfer in Me tallic Ma terials ................................... 71
2.7,4 Mo delling of Stress-Strain Distribution .................................... ........ 73
2.7.5 Modelling of Hydrogen Distribution in Welded Joints....................... 74
3 FINITE ELEMENT MODELLING DEVELOPMENT .............................................. 77
3.1 Two-Dim ensional Finite Elem ent ................................................................ 77
3.2 Finite Element Models for Modelling HAC .............................. 77
3.2.1 Geometric Parameters ................................ 77
3.2.2 Mo delling of Hydrogen Diffusion ................................................... 82
3,2.3 Numerical Modelling Concept ............................... 87
3.2.4 Sequence of the Modelling Program ................................. ........ 88
3.2.5 Specific Input Data for Modelling .............................................. 90
VI BAM-Dissertationsreihe
Contents
3.2.6 Modelling of HASCC at Pipeline Welds ........................................ 97
3.2.6.1 Description of the Test Procedure .............................. 97
3.2.6.2 Numerical Modelling Program Sequences .................... 99
3.2.7 Modelling of HACC at Pipeline Welds ............................... 100
3.2.7.1 Definition of Boundary Conditions ................................... 101
3.2.7.2 Numerical Modelling Sequences .................................... 102
4 RESULTS AND DISCUSSION .......... ......................................... 107
4.1 Modelling of HASCC based on NACE Standard Test Method ....................... 107
4.1.1 Effects of Hydrogen Subsurface Concentration ............................... 109
4.1.2 Effects of Various Hydrogen Diffusion Coefficients ......................... 112
4.1.3 Global Strain Rates and Local Strain Factors .................................. 116
4.1.4 As-Quenched Supermartensitic Stainless Steel .................. 118
4 .1. 5 C rac k T ip An g le ............................................................................... 12 2
4.2 Modelling of HASCC in Girth Welds of Pipelines ........................................... 126
4.2.1 Series of Constant Strain Rate ........................................................ 126
4.2.2 Crack propagation in BM, HAZ and WM under the Realistic Test
C o n d itio n ......................................................................................... 1 3 2
4.3 Modelling of HACC in Girth Welds of Supermartensitic Stainless Steel
P ipe lin e s ....................... ................................. ............................................... 1 3 5
4 .3 .1 T he rm a l An a lysis ............................................................... ............. 136
4 .3.2 S tructural An alysis ............................................................... .... 138
4.3.3 Hydrogen Diffusion Analysis ........................................................... 143
4.3.3.1 Effects of Initial Hydrogen Concentration on Local
Hy drogen Di stribution ..................................................... 143
4.3.3.2 HACC Initiation and Propagation .................................... 149
4.3.4 Effects of PWHT on Local Hydrogen Concentration in the Welded
C o m p o n e n t .................................................................... ................. 1 5 2
4.4 Modelling of HASCC in the Welded Component Having a Pre-Crack
Ca u se d by HA C C ................................................................................ .... 16 0
5 CONCLUSIONS AND PERSPECTIVES .................................. 165
5 .1 Co n c lu s ion s ................................................................................................ 1 6 5
5 .2 P e rs p e c tiv e s .................................................................................................. 16 8
R EF ER EN C ES ..................................................................................................... ...... . . 17 1
VII
Acknowledgement
ACKNOWLEDGEMENT
Since May 2000, the present thesis has been elaborated in the Division of Safety in
Joining Technology, Department of Materials Engineering, Federal Institute for Materials
Research and Testing (BAM), Berlin, within the framework of the Ph.D.-program.
Many people have assisted the author by giving advice, encouragement, discussion as
well as great assistance. The author would like to take this opportunity to express sincere
gratitude to all of them. First of all, sincere thanks are due to Dr.-Ing. Thomas Boellinghaus
(Vice President and Professor at BAM), the author's major advisor, for his magnanimity in
expending time and effort to guide and assist the author throughout this thesis and for
opening the door on many professional opportunities along the way. The author has never
forgotten to express his appreciation to Assoc. Prof. Dr.-Ing. Gobboon Lothongkum
(Chulalongkorn University, Bangkok, Thailand) who provided many opportunities for the
author. Additionally, the author's sincere acknowledgement must be reached to Prof. Dr.-
Ing. Hans Hoffmeister (Institute for Failure Analysis and Failure Prevention, University of the
Federal Armed Forces Hamburg) who is the thesis's major professor.
The author is very pleased to be grateful to Dr.-Ing. Thomas Kannengiesser, Acting
Head of the Division, for his great assistance as well as to Mr. Andreas Hannemann and
Mr. Andre Hofmann for their computer expertise.
Also, expressed appreciation is due to all doctoral candidates in the Division: Mr. Dirk
Seeger for providing data of hydrogen diffusion behaviour, Mr. Mathias Neuhaus and Mr.
Martin Wolf for valuable discussion on FEM-simulation and Mr. Peter Zimmer for useful
discussion on hydrogen assisted cold cracking. The author is extraordinarily gratefully to
Ms. Margit Bauer and Ms. Angelique Lasscigne (Colorado School of Mines) for their great
assistance to review the manuscript of the present thesis.
Furthermore, the author must sincerely thank for the financial support of the present
thesis by the Federal Institute for Materials Research and Testing (BAM).
Finally, the author would like to acknowledge to his parents and his near relatives as
well as his girl friend for their support and understanding even though they are living on the
other side of the world.
Ekkarut Viyanit
Berlin, October 2004
IX