COATING APPLICATION AND EVALUATION FOR HEAVY WALL THICKNESS, TEMPERATURE, AND PRESSURE PIPELINE

A Venezuelan oil company was developing a project for high-pressure ga s injection for oil recovery. This project had a compression plant to increase the gas pressure from 1,200 psi to 9,000 psi. Because of the high gas pressure and high temperature (90 degrees C), a carbon steel API 5L-X60 with 2.5 in.-thick pipe was selected. The gas was transport ed from the compression plant to the injection well. This type of pipe line was unique in that no one had previously applied and evaluated ex ternal coatings for this combination of heavy wall thickness, pressure , and temperature. Dual fusion-bonded epoxy was selected as the main c oating, combined with high-temperature sleeves for the joints. Several parameters were considered in the selection of the coating: high temp erature, wall thickness, application condition, heat during the weldin g process, and coating performance in the lab. The evaluation of the c oating was performed with a specially designed test for high temperatu res. The laboratory results (impact resistance, degree of curing, cath odic disbonding, adhesion, and hot wafer immersion) indicated that the application condition used satisfied the specification of the project .