Design of mechanically lined pipe for reel-lay installation and subsea Service

Abstract

An increasing demand for subsea transport of corrosive fluids has generated interest in mechanically lined pipes (MLP), made of carbon steel (CS) pipe lined with corrosion resistance alloy (CRA). MLP offers shorter lead times and is more economical than alternative products. Reel-lay is a cost-effective method for installing pipelines up to 18'' in diameter subsea. This work examines the development of structural integrity procedures for assessment of MLPs installed by reel-lay.

The CRA liner is susceptible to wrinkling when an MLP is subjected to plastic deformation representative of reeling. This thesis discusses an approach where the liner thickness is increased to enable reel-lay of MLP using standard procedures. A framework is proposed for the numerical prediction of liner wrinkling during reeling.

In contrast to surface flaws, solutions for fracture assessment of embedded flaws in evenmatch welds subjected to reeling are overconservative. New limit load solutions are proposed. After showing that pre-strain does not degrade the toughness of undermatch welds similar to those in MLPs, a methodology for fracture assessment of undermatch welds is proposed.

Subsequently, it is demonstrated that although they include more crack initiation sites than standard pipelines, high in-service fatigue performance can be achieved with MLPs. It is proposed that fatigue assessment of MLP welds be undertaken using existing stress intensity factor solutions. Finally, it is shown that liner imperfections up to 6~mm would not compromise the in-service integrity of MLP.