Residual contact pressure for mechanically lined pipe hydroforming with carrier pipe plastification

Abstract

Mechanically Lined Pipe (MLP) is a rigid carbon steel pipe internally lined with a flimsy Corrosion Resistance Alloy (CRA). This bi-metal composite structure has become an economic and flexible solution to offshore Oil & Gas (O&G) transportation of highly caustic hydrocarbon fluids. The residual contact pressure that arises from the hydraulic expansion fabrication process may prevent wrinkling and interlayer detachment when the pipe is bent or axially compressed during installation and operation. Increasing the residual contact pressure thus becomes a relevant topic for maintaining MLP integrity. The traditional MLP manufacturing process retains the carrier pipe entirely elastic. Yet, a light degree of plastification of carrier pipe will enhance the mechanical adhesion. Mathematical formulations including linear and Ludwik Power Law (LPL) hardening models are here developed to describe the stress-strain behavior of partially plastified carrier pipe. The stress state analysis is performed throughout the whole fabrication process based on the Tresca criterion. Results for residual contact pressure and residual stress state are obtained analytically and numerically. It suggests that an appropriate plastification of carrier pipe favors the mechanical adhesion.