Mechanically Lined Pipe MLP with Improved Fatigue Resistance

Mechanically lined pipe (MLP) has been successfully used in many applications where the fatigue load is low. The use of mechanically lined pipe in higher fatigue load applications require proof of fatigue strength and therefore, additional testing, including full scale fatigue testing, are typically performed. Petrobras has been a pioneer in this work and has developed an MLP specification designating in detail the qualification conditions for using MLP pipe in dynamic applications (see [1]). This paper describes the qualification of Cladtek MLP for dynamic applications including the results of full-scale fatigue testing and a concept, designed by Cladtek, intended to further improve fatigue performance of MLP. Cladtek has filed a patent application for this concept named: Upset-end MLP with improved fatigue resistance [3]. This document presents full-scale fatigue testing results higher than experimental data previously available but in line with the results presented by Subsea 7 in the document IBP1137_15 (see [4]). These results demonstrate that improved fabrication techniques could lead to the use of MLP in the applications with high fatigue demand where, up to now, only clad pipes were considered suitable for use. The use of MLP in high fatigue load applications results in substantial cost savings.