Cyclic Dynamic Load Test of API X42 Pipelines with Interacting Defects

A major factor in the reduction of pipeline service life is corrosion, and the resulting defects. The behaviour of interacting defects is more complex than general uniform and single defects. External conditions of the pipelines like the weight of seawater (bending effect), movement of soil seabed (lateral effect) and movement of seawater (dynamic effects) also influence the corroded subsea pipelines’ strength integrity. The cyclic loads caused by waves, currents, and wind makes the pipelines are susceptible to fatigue failure. This study aims to investigate the effect of such loads on a pipe with interacting defects, specifically the deflection and strain behaviour. To mimic the effects of these cyclic dynamic loads, a loading machine was set up to apply a cyclic load to two pipe specimens with multiple defects in different positions. It was found that circumferential distance between defects will increase the interaction between defects and reduce the strength of the pipeline under dynamic loads, compared to having longitudinal distance only between defects. For cyclic dynamic loads, longitudinally aligned defects seem to have a stronger impact on the strain behavior of the pipe sample compared to circumferentially aligned defects. The defect interaction effect becomes stronger as the defects are spaced further from each other. However, the inverse is true for circumferential defects.