Probabilistic Physics of Failure Modeling of Non-metallic Pipelines in Oil and Gas Applications

Summary & ConclusionsThe use of composite pipelines has grown in recent years as an alternative to steel pipelines in the offshore oil and gas industry, due their excellent corrosion resistance and high specific strength. Among these developments, thermoplastic composite pipes have seen a recent rise in research and use due to their greater flexibility and impact resistance than traditional thermoset-matrix composites. To understand the performance of these materials in the field, studies have derived experimental, analytical, and theoretical estimates of the mechanical and thermal properties of TCP in dry conditions, but studies in wet or acidic environments are currently restricted to the empirical domain. As a part of ongoing work to predict behavior in these conditions, this study describes a method to predict the degradation of mechanical properties from one form of environmental degradation: diffusion of the transport fluid through the pipe wall. This process forms a gel layer at the interface between the pipe and fluid. The thickness of the gel layer and degree of stiffness reduction within the gel are taken as metrics for pipeline degradation. A test case of a polypropylene/E-glass fiber (PP/G) laminate pipe is presented to show the effects of this degradation on the pressure capacity of the pipe. It was found that as the gel layer thickness approaches that of the innermost ply, the internal pressure capacity is significantly reduced.