Experimental Study of the Behavior of Wrinkled Energy Pipelines Subjected to Cyclic Pressure Loading

The development of a small wrinkle defect in a buried pipeline can be a challenging issue for pipeline operators to approach. Although extensive research has been conducted to evaluate the integrity of a pipeline showing signs of irregularities such as corrosion, pipe wall buckling, and/or rippling, limited research data or guidelines are available to assess the severity of a small wrinkle defect. If not dealt with appropriately, these small wrinkle defects can lead to further damage of the pipe wall as a result of fatigue damage caused by internal pressure cycling. A research program comprised of a full-scale two-stage experimental test setup was initiated to investigate the postwrinkling behavior of field pipelines undergoing typical pressure fluctuations. This paper presents test procedures describing both the wrinkle defect initiation stage and the subsequent cyclic pressure fatigue test stage, as well as the corresponding observations and results. The results indicate that wrinkle defects that initiate in pipelines that operate at lower pressures or are temporarily shut down are more susceptible to fatigue failure as a result of pressure fluctuations, due to internal cracks initiating at the apex of the wrinkle and propagating outward.