External pipeline coatings given critical review

A summary of the factors to consider in the selection of pipeline coatings is presented. For the factors where the four coating types are judged to be equivalent, or where there are no good reasons for ranking one type before or behind the others, the mark 0 is given. In case one or more of the coating types is judged to have an advantage or a drawback compared to one or more of the others, the mark + or - respectively is given, without further attempts of differentiation. The various factors are considered to have quite varying significance, sometimes also different for the two main types of pipelines--land lines and offshore lines. The latter are presumed to have a concrete weight coating on top of the anticorrosion coating. It can be concluded that it is hardly justifiable to rule out any of the four generic-type pipeline coatings for technical reasons. Asphalt and coaltar-based coatings are still relevant and may be the best alternatives for offshore lines underneath a concrete weight coating. Epoxy powder coating may be the second best alternative, while polyethylenes are ranked third for offshore lines due, mainly, to their susceptibility to disbonding and low upper service temperature.more » For onshore lines, epoxy-powder coating would be the first choice, especially at high operating temperatures. Asphalt and coal-tar-based coatings should still be adequate if applied to a properly blast-cleaned pipe surface and handled carefully in pipelaying. Polyethylenes are relevant for onshore underground lines due to relatively low susceptibility to coating damage in pipelaying and underground service, despite disbonding and low upper temperature limit.« less