Internal coating of multiphase pipelines – requirements for the coating

Pressure drop along the pipeline is the main obstacle to transportation of unprocessed or partly processed multiphase fluids over long distances. Several parameters contribute to pressure drop in multiphase flow, e.g. liquid hold-up, precipitations, gas-liquid surface drag forces, liquid wetting of pipe wall and surface roughness. Application of coatings inside the pipeline can reduce pressure drop by preventing corrosion, preventing precipitations on the pipe wall and modify the pipe wall wetting properties. Meso scale pressure drop tests have shown that pressure drop is significantly affected by moderate corrosion, even in multiphase flow, demonstrating that application of internal coatings is beneficial. However, the coating must have the same lifetime as the pipeline. The objective with this work has been to identify the most important coating degradation mechanisms and to find relevant test methods for evaluation and qualification of coatings.