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PRCI PR-218-9925
- Acceptance Criteria for Mild Ripples in Pipeline Field Bends
- Report / Survey by Pipeline Research Council International, 09/16/2003
- Publisher: PRCI
$198.00$395.00
L51994e
Kiefner & Associates. Inc. and SSD, Inc.
Need: Mild ripples or wrinkles (buckles) are often unavoidable when forming cold field bends in high-D/t pipe. Construction standards contained in U.S. federal regulations require that bends have "a smooth contour and be free from buckling" while widely used industry consensus standards also require that bends "be free from buckling". These requirements are often interpreted as prohibiting even very subtle ripples. It would be desirable to establish the extent to which pipe bends with mild ripples can be treated as equivalent to bends having a smooth contour from the standpoint of structural performance. However, industry construction codes are vague about what is acceptable, in part because the available data on cold field bend performance are too sparse. Consequently, acceptance standards for such features are not explicit, leaving operators potentially exposed to inconsistency or excess conservatism in the application of inspection criteria.
Result: Shell finite element analysis was used to estimate the effect of ripple magnitude and spacing on stresses due to pressure and bending. Stress concentration effects were used with a suitable fatigue damage rule to estimate the effect of ripple parameters on service life. Results were benchmarked against the available test data. The results indicate that (1) mild or shallow ripples up to 2 percent of the pipe diameter in crest-to-trough dimension would not be expected to be harmful in gas transmission pipelines operating under conditions normally encountered in the gas transportation industry; (2) mild or shallow ripples up to 1 percent of the pipe diameter in crest-to-trough dimension would not be expected to be harmful in hazardous liquid transportation pipelines operating under conditions normally encountered in the liquid transportation industry; (3) the presence of ripples could be harmful to long-term integrity in a severe cyclic loading (pressure, thermal expansion, flow-induced vibration) environment, or where soil movement could take place.
Benefit: Recommendations are made for ASME Code criteria specifically permitting mild ripples within stated limits.
Kiefner & Associates. Inc. and SSD, Inc.
Need: Mild ripples or wrinkles (buckles) are often unavoidable when forming cold field bends in high-D/t pipe. Construction standards contained in U.S. federal regulations require that bends have "a smooth contour and be free from buckling" while widely used industry consensus standards also require that bends "be free from buckling". These requirements are often interpreted as prohibiting even very subtle ripples. It would be desirable to establish the extent to which pipe bends with mild ripples can be treated as equivalent to bends having a smooth contour from the standpoint of structural performance. However, industry construction codes are vague about what is acceptable, in part because the available data on cold field bend performance are too sparse. Consequently, acceptance standards for such features are not explicit, leaving operators potentially exposed to inconsistency or excess conservatism in the application of inspection criteria.
Result: Shell finite element analysis was used to estimate the effect of ripple magnitude and spacing on stresses due to pressure and bending. Stress concentration effects were used with a suitable fatigue damage rule to estimate the effect of ripple parameters on service life. Results were benchmarked against the available test data. The results indicate that (1) mild or shallow ripples up to 2 percent of the pipe diameter in crest-to-trough dimension would not be expected to be harmful in gas transmission pipelines operating under conditions normally encountered in the gas transportation industry; (2) mild or shallow ripples up to 1 percent of the pipe diameter in crest-to-trough dimension would not be expected to be harmful in hazardous liquid transportation pipelines operating under conditions normally encountered in the liquid transportation industry; (3) the presence of ripples could be harmful to long-term integrity in a severe cyclic loading (pressure, thermal expansion, flow-induced vibration) environment, or where soil movement could take place.
Benefit: Recommendations are made for ASME Code criteria specifically permitting mild ripples within stated limits.
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