Qualification of a Thermoplastic Composite Pipe for Subsea Pumping Well Intervention Systems - A Practical Implementation of DNVGL-RP-F119
Authors: Charlesworth David , Mullan Mick , Scott Anna , Priddy James , Richardson Joshua 
Published: April 2018

Subsea Pumping Well Intervention Systems (SPWISs) include a reeled fluid conduit (or riser) that connects a surface pumping spread to a subsea tree via a subsea safety module. Current pipe technologies used for fluid conduits are limited in terms of their pressure capability, volume of fluid they can supply, fatigue performance or the ease with which they can be deployed. Thermoplastic Composite Pipe (TCP) addresses many of the limitations of existing products, and therefore is attractive as an alternative.

This paper describes the qualification of a TCP as a SPWIS fluid conduit. The TCP is manufactured from carbon and S2-glass fibre, laminated with a Poly Ether Etherketone (PEEK) matrix.

The TCP was qualified following the processes recommended by DNV-RP-A203 "Qualification of New Technology" and the specific guidance given in DNVGL-RP-F119 "Recommended Practice for TCPs". The former defines a structured process for developing a qualification basis, assessing the risk of all potential product failure modes, and then mitigating those risks through the collection of qualification evidence. The latter provides a methodology based upon a testing pyramid and a linked structural model, to gather the appropriate qualification evidence for a TCP.

The results of the TCP qualification are presented in three areas, materials testing, pipe testing and structural analysis. The material testing focussed on characterising both pure PEEK, and the properties of individual carbon and S2-glass plies in the composite laminate. Testing was performed across the design temperature range (4°C to 80°C), and was used as input into the structural model of the TCP that was developed.

At a pipe scale a comprehensive set of single and combined static load cases were tested, including axial tension and compression, internal pressure, bending, and bending and internal pressure. These test results were compared against the predicted TCP performance given by the structural model, both in terms of stiffness and ultimate failure.

In addition to the static testing, long term performance of the composite laminate was also characterised. Laminate testing methods were developed for fatigue and stress rupture, and the test results used to construct life curves for both failure modes. The combination of both the materials and pipe testing, and the structural analysis, culminated in a qualification certificate being issued for the TCP by an Independent Verification Agent.

DNVGL-RP-F119 is a new recommended practice that was published in December 2015. This paper presents one of the first applications of the recommended practice to a TCP product, and therefore provides valuable insight into the practical implementation of DNVGL-RP-F119. In addition, qualification of a TCP as a SPWIS fluid conduit offers the potential to enable more frequent and effective well interventions, thereby improving the productivity and ultimately reducing the cost of subsea wells.