Critical Thermal, Corrosion And Material Issues Related to Flowline Pipe-in-Pipe (PIP) Systems

The common method of achieving enhanced thermal insulation performance of flowlines (U values of 1.0 W/m2K, or less) requires a ‘Pipe-In-Pipe’ (PIP) insulation system, in which the inner pipe carrying the fluid is encased within a larger outer pipe separated by an annulus insulation material. However, with all PIP systems it is important to ensure that the structural integrity is maintained for both installation and operational loads for each of the PIP components (thermal insulation, linepipe, centralisers, waterstop seals, and loadshares). The temperature of the internal contents of a PIP system can have a significant effect on the long term degradation and performance of materials. It is not uncommon for recent designs of pipelines to be considered for temperatures up to 350°F (177°C). Also it is important to ensure integrity for the entire life of the project, and that undesirable degradation of the thermal and structural performance does not occur. The effects of temperature on the PIP components are discussed within this paper. Various insulation materials are considered and these consist of mineral wools, polyurethane foam, granular or microporous materials, ceramics and Aerogels. Annulus related corrosion integrity issues including monitoring, inspection and on-going degradation and aging management are addressed. Performance of insulation in terms of thermal, heat transfer and effects of corrosion under wetting conditions and cathodic protection at the field joints will also be considered. The new technology presented in this paper is; a discussion into the critical aspects of testing PIP components for high temperature applications (centralizers, waterstops, loadshares, thermal insulation), a critical evaluation of different thermal insulation materials, mechanisms of MICC 'Microbially Influenced Crevice Corrosion' and the hidden annular 'Corrosion under Insulation' for pipelines, and inspection methods. Hence, this paper discusses key issues associated with PIP systems in terms of the structural integrity, corrosion and material integrity with regards to the PIP components. Lessons learned from recent J P Kenny / IONIK PIP projects, and key technology gaps and recommendations for the future are identified and discussed.