Evaluation of UOE and Spiral-Welded Line Pipe for Strain Based Designs

Strain-based designs for Arctic pipelines place stringent demands on properties of the pipe body as well as the girth weld and associated heat affected zone. The pipe body must demonstrate good work hardening behavior in addition to satisfactory strength and toughness properties. Girth welds are required to overmatch the strength of the pipe body; both the weld and heat affected zone must also provide good toughness. In this study, X80 line pipe produced using the UOE and spiral welding processes were compared. The UOE process provides some degree of work hardening resulting from cold expansion. This extra hardening renders the UOE pipe more responsive than the spiral pipe to aging effects associated with pipe coating. However, the UOE pipe has an advantage in balancing LPA (longitudinal to pipe axis) and TPA (transverse to pipe axis) strengths. Greater strengths in the TPA orientation afford the capacity to meet specified minimum requirements of the pipe grade and lower strengths in the LPA orientation facilitate overmatching by girth welds. The two types of line pipe offer both advantages and disadvantages for strain-based designs. It must be emphasized that good work hardening characteristics can be maintained in the UOE pipe when the coating process involves a low temperature, which is an objective of modern coating technologies. It was also observed that aging effects did not affect toughness properties significantly.