Abstract
Accurately predicting where high- or near-neutral pH stress corrosion cracking (SCC) of buried pipelines is possible requires a prediction of the environmental conditions at the pipe surface under the disbonded coating. This is a challenging task since traditional above-ground measurements give little information about the pipe-surface environment. If such predictions could be made, however, the success of selecting locations for direct examination as part of the direct assessment methodology or for other maintenance activities would be greatly enhanced.
The nature of the coating degradation has a significant impact on the development of environmental conditions for SCC. A series of soil box tests has been performed to determine the evolution of the trapped water environment under disbonded shielding polyethylene tape coating. The effects of soil type, moisture content and drainage, and CP level have been studied. In a second series of tests, the relative effects of current demand and coating permeability on the generation of high-pH SCC conditions under disbonded permeable coating have been studied.
The results of the tests on shielding coating have been analyzed using two computer models; a Transient ElectroChemical TRANsport model (TECTRAN) for shielding coating and the Permeable Coating Model (PCM) for permeable coatings. The aim is to use such codes to predict the pipe surface environment based only on above-ground measurements and other readily available information.
