Abstract

Mechanically lined pipe is a cost-effective solution to produce corrosive fluids. A thin tubing made of corrosion resistant alloy is fitted into a carbon steel backing pipe. Under repeated or large bending, the liner can detach from the backing steel to form potential wrinkles. While liner detachment cannot be considered alone as a failure mode, excessive collapse of the liner inside the pipeline can jeopardize the mechanical integrity of the liner or the functional objectives of the pipeline. This specific failure mode can be reached at a load level at which the backing steel pipe is not yet jeopardized. Though several studies addressed the subject, from a testing or a numerical perspective, no clear consensus emerges for a global methodology to assess liner wrinkling limit state encompassing full life cycle approach. This paper proposes a detailed methodology to assess response and define global behavior envelop that the MLP can safely face during operational life, accounting for fabrication & installation load history.

Introduction

To produce hydrocarbon fluids from subsea wells, specific attention is paid to corrosion of flowline. Several options are used to mitigate detrimental impact of corrosive fluids on steel pipes such as injection of corrosion inhibitors, increased pipe thickness to account for corrosion or use of corrosion resistant alloy (CRA). As described by Kyriakides and Corona (2007), although seamless pipes manufacturing process is efficient, a full CRA pipe bear long lead delivery time and is expensive due to raw material cost. A thicker carbon steel pipe, including a corrosion allowance in the order of several mm, brings additional material, logistics, fabrication & installation cost. The additional thickness may also limit the depth at which the pipeline can be installed. Alternative solutions, where a CRA liner is inserted into a carbon steel pipe, were developed to reduce pipeline system overall cost. The liner is either welded to the host pipe joint at the extremities only (mechanically lined pipe, MLP) or metallurgically bonded or welded along full length of the joint (metallurgically bonded pipe, full length overlay pipe, see Barnes et al. (2018)). Since the latter is still a long and expensive manufacturing process, mechanically lined pipe is a cost-effective compromise of growing interest to reduce oilfield development costs. The seamless backing steel pipe provides structural strength while the CRA liner provides corrosion protection.

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