Qualification of Cost Effective Mechanically Lined Pipe Solutions for Reel-Lay Installation

The use of mechanically lined pipe (MLP) for both flowlines and risers installed by reel-lay is well established, giving significant cost and schedule benefits relative to conventional metallurgically clad pipe. Successful offshore installation of MLP is underpinned by comprehensive qualification testing. Evolving MLP products, including the use of thin liners and adhesively bonded MLP, i.e. GluBi®, continue to improve the competitiveness of this linepipe product. The paper will highlight the key steps for qualification, including new products, the lessons learnt captured during fabrication and installation as well as the benefit of a local spool base for the Asia Pacific region. Subsea 7 has worked in close collaboration with leading supplier Butting to perform the qualification of MLP. The latter, initially, comprises extensive non-destructive and destructive testing of the linepipe materials including the liner/ weld overlay interface. Subsequently reeling test strings are fabricated using qualified welding solutions. Internal visual inspection and dimensional measurements are carried out using laser metrology to provide a benchmark for comparison post reeling. The test strings are given a simulated reeling procedure using bending and straightening formers, representative of Subsea 7's installation vessels. The internal pressurisation technique, as per standard installation practice for MLP, is applied during the simulated reeling procedure. The need for internal pressurisation is eliminated in the case of adhesively bonded MLP. Post reeling the internal laser metrology inspection procedure is repeated to confirm the integrity of the liner and to check for the presence of any evidence of liner wrinkling or damage. Subsequently, for riser applications, full-scale fatigue testing is performed using the high- frequency resonance bending procedure with a focus on the integrity of the junction between liner and weld overlay or, as commonly termed, the triple point. Additionally, finite element analysis (FEA) is often performed to further validate the satisfactory reeling performance of the MLP. All the qualification activities are carried out and verified in alignment with DNV-RP-A203 Technology Qualification (Ref.1) To date Subsea 7 has installed several hundreds of kilometers of MLP flowlines and risers, with pipe NPS in the range 7" to 14" and including 316L, Alloy 825 and Alloy 625 liners. This thorough qualification process and experience combined with the successful set up of a regional spool base provides a robust and cost-effective alternative to the conventional metallurgically clad pipe.