EFFECT OF FORMING ON BEHAVIOR OF UOE PIPE MATERIAL

摘要

The worldwide share of oil&gas produced from offshore sources is constantly increasing. Accordingly, deep and ultra-deep water projects go to ever increasing depths. Large diameter pipes for this type of projects are often manufactured by the UOE process. After the cold work associated with UOE forming, mechanical properties of pipe material are different from those of the original plate. In particular, the circumferential compression behavior is markedly affected by the Baushcinger effect which develops after the last expansion step, and this is a key property for the resistance to collapse under external pressurization. Standard formulas for the assessment of the collapse pressure p_c variedly account for this effect. For instance, DNV OS-F101 penalizes the SMYS of the pipe with a fabrication factor α_(fab) that reduces the p_c rating of UOE pipes. Understanding the effect of deformation history on final material properties becomes desirable for a proper identification of processing strategies. A testing program was developed aimed at evaluating the effect of UOE forming on final transverse compression behavior, as it is relevant for collapse resistance. Work softening (i.e., the Bauschinger effect) and hardening were quantified under a variety of deformation operations.