Cracks may occur coincident with corrosion representing a new hybrid defect in gas and oil pipelines known as crack in corrosion (CIC) that is not directly addressed in the current codes or assessment methods. Hence, there is a need to provide an assessment of CIC and evaluate the line integrity, as well as identify the requirements for defect repair or line hydrotest. An experimental investigation was undertaken to evaluate the collapse pressures of lines containing corrosion, cracks, or (CIC) defects in a typical line pipe (API 5L Grade X52, 508 mm diameter, 5.7 mm wall thickness). The mechanical properties of the pipe were measured using tensile, Charpy, and J-testing for use in applying evaluation criteria. Rupture tests were undertaken on end-capped sections containing uniform depth, finite length corrosion, cracks, or CIC defects. Failure occurred by plastic collapse and ductile tearing for the corrosion defects, cracks, and CIC geometries tested. For the corrosion defects, the corroded pipe strength (CPS) method provided the most accurate results (13% conservative on average). The API 579 (level 3 failure assessment diagram (FAD), method D) provided the least conservative collapse pressure predictions for the cracks with an average error of 20%. The CIC collapse pressures were bounded by those of a long corrosion groove (upper bound) and a long crack (lower bound), with collapse dominated by the crack when the crack depth was significant. Application of API 579 to the CIC provided collapse pressure predictions that were 18% conservative. Sixteen rupture tests were successfully completed investigating the failure behavior of longitudinally oriented corrosion, crack, and CIC. The pipe material was characterized and these properties were used to predict the collapse pressure of the defects using current methods. Existing methods for corrosion (CPS) and cracks (API 579, level 3, method D) gave conservative collapse pressure predictions. The collapse pressures for the CIC were bounded by those of a long corrosion groove and a long crack, with collapse dominated by the crack when the crack depth was significant. CIC failure behavior was determined by the crack to corrosion depth ratio, total defect depth and its profile. The results showed that the failure pressures for CIC were reduced when their equivalent depths were similar to those of corrosion and using crack evaluation techniques provided an approximate collapse pressure.

References

References
1.
American Petroleum Institute, API579
,
2000
, “
Recommended Practice for Fitness for Service
.”
2.
British Standards Institute, BS 7910
,
2000
, “
Guide on Methods for Assessing the Acceptability of Flaws in Metallic Structures
,” BSI-10.
3.
Escoe
,
A. K.
,
2006
,
Piping and Pipeline Assessment Guide
,
Elsevier
,
New York
.
4.
Hosseini
,
A.
,
2010
, “
Assessment of Crack in Corrosion Defects in Natural Gas Transmission Pipelines
,” MASc. Thesis,
University of Waterloo
, Waterloo, Ontario, Canada.
5.
CEAP, Canadian Energy Pipeline Association
,
2005
, “Stress Corrosion Cracking Recommended Practice,” 2nd Edition, 1860, 205 5-Aveniue SW, Calgary, Alberta, Canada T2P 2V7.
6.
Cronin
,
D. S.
, and
Plumtree
,
A.
,
2008
, “
Assessment of Crack in Corrosion Defects in Natural Gas Transmission Pipelines
,”
7th International Pipeline Conference
.
7.
Cronin
,
D. S.
, and
Pick
,
R. J.
,
2000
, “
Prediction of the Failure Pressure for Complex Corrosion Defects
,”
Int. J. Pressure Vessels Piping
, Vol. 79, pp.
279
287
.
8.
Cosham
,
A.
, and
Hopkins
,
P.
,
2007
, “
Best Practice for the Assessment of Defects in Pipelines-Corrosion
,”
Eng. Failure Anal.
, Vol. 14, pp.
1245
1265
.10.1016/j.engfailanal.2006.11.035
9.
CEAP, Canadian Energy Pipeline Association
,
2005
, “Stress Corrosion Cracking Recommended Practice,” 1st Edition, 1860, 205 5-Aveniue SW, Calgary, Alberta, Canada T2P 2V7.
10.
Hosseini
,
A.
,
Cronin
,
D. S.
, and
Plumtree
,
A.
,
2010
, “
Experimental Testing and Evaluation of Crack Defects in Line Pipe
,”
8th International Pipeline Conference
, Calgary, Alberta.
11.
American Society for Testing and Materials (ASTM) Standards
, ASTM E8M,
2007
.
12.
American Society for Testing and Materials (ASTM) Standards
, ASTM E23,
2007
.
13.
Bedairi
,
B.
,
2010
, “
Numerical Failure Pressure Prediction to Assess Crack in Corrosion Defects in Natural Gas Transmission Pipelines
,” MASc. Thesis,
University of Waterloo
, Waterloo, Ontario, Canada.
14.
American Society for Testing and Materials (ASTM) Standards
, ASTM E1820,
2008
.
15.
Kiefner
,
J. F.
,
Maxey
,
W. A.
,
Eiber
,
R. J.
, and
Duffy
,
A. R.
,
1973
, “
Failure Stress Levels of Flaws in Pressurized Cylinders
,”
American Society of Testing and Materials
Report No. ASTM STP 536, pp.
461
481
.
16.
Cravero
,
S.
, and
Ruggeri
,
C.
,
2006
, “
Structural Integrity Analysis of Axially Cracked Pipelines Using Conventional and Constraint-Modified Failure Assessment Diagrams
,”
Int. J. Pressure Vessels Piping
,
83
, pp.
607
617
.10.1016/j.ijpvp.2006.04.004
17.
Dowling
,
A. R.
, and
Townley
,
C. G. A.
,
1975
, “
The Effects of Defects on Structural Failure: A Two-Criterion Approach
,”
Int. J. Pressure Vessels Piping
,
3
, pp.
77
137
.10.1016/0308-0161(75)90014-9
18.
Jaske
,
C. E.
, and
Beavers
,
J. A.
,
1999
, “
Fitness-For-Service Evaluation of Pipelines With Stress-Corrosion Cracks or Local Corrosion
,”
The International Conference on Advances in Welding Technology (ICAWT)
.
19.
Tyson
,
W.
,
2000
, “
Assessment of Crack Defects
,”
Banff Pipeline Workshop
.
20.
Zerbst, U., Schodel, M., Webster, S., Ainsworth, R.
2007
. Fitness-for-Service Fracture Assessment of Structures Containing Cracks, Academic Press.
21.
Anderson
,
T. L.
,
2005
,
Fracture Mechanics Fundamental and Application
,
3rd ed.
,
Taylor & Francis
,
London
.
22.
Paris
,
P.
, and
Erdogan
,
F.
,
1963
, “
A Critical Analysis of Crack Propagation Laws
,”
J. Basic Eng.
,
85
, pp.
528
543
.10.1115/1.3656900
You do not currently have access to this content.