Experimental Investigation of Fracture in Wrinkled Pipelines Under Monotonic Axial and Bending Deformation

Buried pipelines, used by petrochemical industries in North America for transporting oil and derivatives, are often subjected to large deformations resulting from geoenvironmental factors such as: geotechnical movements, thermal strains, and internal fluid pressure. Exceeding the critical deformation limit of these pipes initiates wrinkles and further increase may result in fracture; thus jeopardizing the safe operation of a field pipeline. A recent field fracture and failed laboratory specimens under monotonic load history addresses the necessity of conducting a full-scale test program for the better understanding of the complete post-wrinkling behaviour and failure modes of wrinkled pipes under similar loading condition inducing axial and bending deformation. Six tests with two sizes of pipe (NPS16 and NPS20), representative of those used in pipelines for transmission of hydrocarbons, were performed. Only one of the tests were found to yield the desired failure mode and hence chosen to present and discuss in this paper in detail to understand the tearing mode of failure. However, test results in general had shown that both X60-grade and X65-grade steel pipelines generally exhibited a ductile behavior after wrinkling. Eventually, these line pipes failed in a deformation mode due to excessive cross-sectional deformation and several occurrences of rupture at the wrinkle face of the bent pipe were observed.