Abstract
In consideration of recent North Slope field experience and the potential for external corrosion on its pipelines, as well as the high costs of using tape wraps or coatings to mitigate external corrosion, several laboratory tests on polyurethane insulation were conducted by SAPC. These tests included short-term electrochemical tests, insulation density measurements, chemical analyses of the insulations and their leachants, optical microscopy and a hot water test loop in which the corrosion rate was determined under various insulation samples after six months.
The laboratory tests showed that corrosion under the polyurethane insulations used on the North Slope is a form of crevice corrosion. Most of the preformed insulations, including SAPC's System X insulation, produced corrosion rates ranging from 15 to 30 mpy or more. In the test loop, similarly high corrosion rates were obtained under wet field applied foamed-in-place insulation. However, shop applied foamed-in-place insulation produced little or no corrosion when wet. Therefore, external corrosion similar to that experienced by ARCO on the North Slope is possible on SAPC pipelines with preformed or field foamed-in-place insulation if the insulation becomes wet. The occurrence of corrosion under the shop applied, insulation appears to be unlikely.
