Fracture of Wrinkled Pipes Subjected to Monotonic Deformation: An Experimental Investigation

Abstract

Buried pipelines, used by petrochemical industries in North America for transporting oil and derivatives, are often subjected to large deformations resulting from geo-environmental factors and operating conditions, 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 address the necessity of conducting a full-scale test program to better understand the complete post-wrinkling behavior and failure modes of wrinkled pipes under similar loading conditions. Six tests with two sizes of pipe (NPS16 and NPS20), which are typical of those used in the field for transmission of hydrocarbons, were tested under monotonic axial and bending deformation. Test results in general had shown that both NPS16 (pipe material grade X60) and NPS20 (pipe material grade X65) steel pipelines generally exhibited a ductile behavior after wrinkling. Eventually, these pipe specimens failed due to excessive cross-sectional deformation. Several incidents of rupture or fracture in the pipe wall were observed at the sharp fold of the wrinkle on the compression side of the deformed pipe.