Setting conditions for the avoidance of in-service crack growth in aggressive corroding environments has long been a major challenge due to the number of variables that have a significant effect on material behavior. One area where both experimental data and a validated assessment methodology are lacking is the behavior of shallow cracks. This paper describes the early results of an ongoing research program aimed at addressing the shortfall in experimental data to characterize material behavior in the shallow-crack regime, with the long-term aim of improving the understanding and assessment of the early stages of environment assisted cracking. There is an industry need for a better understanding of material behavior under these conditions and for the development of a more robust assessment methodology. API 5L X65 pipeline steel parent material was tested in a sour environment with initial flaw sizes in the range 1–2 mm. Fatigue crack growth rate tests have been performed to investigate the influence of crack depth on crack growth rate (da/dN). Initial results suggest that crack growth rates for deep flaws can increase by a factor of 5–100 compared with air depending on the applied stress intensity factor range (ΔK). Shallow cracks have been shown to grow up to 130 times faster in a sour environment than in air and up to an order of magnitude faster than deep cracks in a sour environment at the same value of ΔK. Constant load tests have also been performed to investigate the influence of crack depth on the threshold stress intensity factor for stress corrosion cracking (KISCC). Preliminary results suggest that in this case there is no crack depth dependence in the range of flaw sizes tested. While further experimental work is required, the results obtained to date highlight the potential nonconservatism associated with extrapolating deep-crack data. Guidance is therefore provided on how to generate appropriate experimental data to ensure that subsequent fitness for service assessments are conservative.

1.
Bristoll
,
P.
, and
Roeleveld
,
J.
, 1978, “
Fatigue of Offshore Structures: Effect of Seawater on Crack Propagation in Structural Steel
,”
Proceedings of the European Offshore Steels Research
, ECSC,
The Welding Institute
,
Cambridge, UK
.
2.
Webster
,
S. E.
,
Austen
,
I. M.
, and
Rudd
,
W.
, 1985, “
Fatigue, Corrosion Fatigue and Stress Corrosion of Steels for Offshore Structures
,” ECSC Report No. EUR 9460.
3.
Vosikovsky
,
O.
, and
Rivard
,
A.
, 1982, “
The Effect of Hydrogen Sulphide in Crude Oil on Fatigue Crack Growth in a Pipeline Steel
,”
Corrosion (Houston)
0010-9312,
38
(
1
), pp.
19
22
.
4.
Vosikovsky
,
O.
,
Macecek
,
M.
, and
Ross
,
D. J.
, 1983, “
Allowable Defect Sizes in a Sour Crude Oil Pipeline for Corrosion Fatigue Conditions
,”
Int. J. Pressure Vessels Piping
0308-0161,
13
, pp.
197
226
.
5.
Watanabe
,
E.
,
Yajima
,
H.
,
Ebara
,
R.
,
Matsumoto
,
S.
,
Nakano
,
Y.
, and
Sugie
,
E.
, 1994, “
Corrosion Fatigue Strength of Ship Structural Steel Plates and Their Welded Joints in Sour Crude Oil
,”
Offshore Mechanics and Arctic Engineering Conference (OMAE 1994)
,
ASME
,
New York
, Vol.
III
, pp.
151
158
.
6.
Eadie
,
R. C.
, and
Szklarz
,
K. E.
, 1999, “
Fatigue Crack Propagation and Fracture in Sour Dilute Brine
,”
Proceedings of Corrosion
,
NACE International
,
Houston, TX
, Paper No. 611.
7.
Eadie
,
R. C.
, and
Szklarz
,
K. E.
, 1999, “
Fatigue Initiation and Crack Closure of Low Alloy Steels in Sour Brine Environments
,”
Proceedings of Corrosion
,
NACE International
,
Houston, TX
, Paper No. 610.
8.
Baxter
,
D. P.
,
Maddox
,
S. J.
, and
Pargeter
,
R. J.
, 2007, “
Corrosion Fatigue Behaviour of Welded Risers and Pipelines
,”
Proceedings of OMAE2007 26th International Conference on Offshore Mechanics and Arctic Engineering
, San Diego, CA, Paper No. OMAE2007-29360.
9.
Gooch
,
T. G.
, 1982, “
Hardness and Stress Corrosion Cracking of Ferritic Steel
,”
The Welding Institute Research Bulletin
,
23
(
8
), pp.
241
246
.
10.
2005, “
BS 7910: Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures
,” British Standards Institution, London.
11.
FITNET
, 2008, “
Fitness-for-Service
,” Revision MK8, ISBN 978-3-940923-00-4, prepared by the European Fitness-for-Service Thematic Network, FITNET.
12.
2007, “
Fitness-For-Service
,”
1st ed.
, The American Petroleum Institute and The American Society of Mechanical Engineers, Washington, API 579-1/ASME FFS-1.
13.
2006, “
Assessment of the Integrity of Structures Containing Defects
,” R6 Revision 4, British Energy.
14.
Jones
,
R. H.
, and
Simonen
,
E. P.
, 1994, “
Early Stages in the Development of Stress Corrosion Cracks
,”
Mater. Sci. Eng., A
,
176
, pp.
211
218
. 0921-5093
15.
Kitagawa
,
H.
, and
Takahashi
,
S.
, 1979, “
Applicability of Fracture Mechanics to Very Small Cracks of the Cracks in the Early Stage
,”
Proceedings of the Second International Conference on Mechanical Behaviour of Materials
, pp.
627
631
.
16.
Gangloff
,
R. P.
, 1985, “
Crack Size Effects on the Chemical Driving Force for Aqueous Corrosion Fatigue
,”
Metall. Trans. A
0360-2133,
16A
, pp.
953
969
.
17.
Akid
,
R.
, 1994, “
Modelling Environment-Assisted Short Fatigue Crack Growth
,”
Advances in Fracture Resistance and Structural Integrity
,
Pergamon
,
New York
, pp.
261
269
.
18.
Murtaza
,
G.
, and
Akid
,
R.
, 1995, “
Modelling Short Fatigue Crack Growth in a Heat-Treated Low-Alloy Steel
,”
Int. J. Fatigue
0142-1123,
17
(
3
), pp.
207
214
.
19.
Turnbull
,
A.
,
McCartney
,
L. N.
, and
Zhou
,
S.
, 2006, “
Modelling of the Evolution of Stress Corrosion Cracks From Pits
,”
Scr. Mater.
,
54
, pp.
575
578
. 1359-6462
20.
Kondo
,
Y.
, 1989, “
Prediction of Fatigue Crack Initiation Life Based on Pit Growth
,”
Corros. Sci.
0010-938X,
45
(
1
), pp.
7
11
.
21.
Chen
,
G. S.
,
Wan
,
K.-C.
,
Gao
,
M.
,
Wei
,
R. P.
, and
Flournoy
,
T. H.
, 1996, “
Transition From Pitting to Fatigue Crack Growth—Modelling of Corrosion Fatigue Crack Nucleation in a 2024-T3 Aluminium Alloy
,”
Mater. Sci. Eng., A
,
219
, pp.
126
132
. 0921-5093
22.
Holtam
,
C. M.
, and
Baxter
,
D. P.
, 2007, “
Environment Assisted Cracking Assessment Methods: The Behaviour of Shallow Cracks
,”
Proceedings of the UK Forum for Engineering Structural Integrity’s Ninth International Conference on Engineering Structural Integrity Assessment (ESIA9)
,
EMAS
, pp.
862
866
.
23.
NACE
, 2005, “
MR 0177-2005: Laboratory Testing of Metals for Resistance to Sulfide Stress Cracking and Stress Corrosion Cracking in H2S Environments
,” Houston.
24.
Pargeter
,
R. J.
,
Gooch
,
T. G.
, and
Bailey
,
N.
, 1990, “
The Effect of Environment on Threshold Hardness for Hydrogen Induced Stress Corrosion Cracking of C–Mn Steel Welds
,”
Conference Proceedings on Advanced Technology in Welding, Materials, Processing and Evaluation
, Apr.,
Japan Welding Society
,
Tokyo
.
25.
Albarran
,
J. L.
,
Martinez
,
L.
, and
Lopez
,
H. F.
, 1999, “
Effect of Heat Treatment on the Stress Corrosion Resistance of a Microalloyed Pipeline Steel
,”
Corros. Sci.
,
41
, pp.
1037
1049
. 0010-938X
26.
Sponseller
,
D. L.
, 1992, “
Interlaboratory Testing of Seven Alloys for SSC Resistance by the Double Cantilever Beam Method
,”
Corrosion (Houston)
0010-9312,
48
(
2
), pp.
159
171
.
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