Tar-Polyurethane Joint Coating for the Three-Layer Polyethylene Pipeline Coating

This article describes a new joint coating system implemented by Bechtel for a major international, 48 inch diameter gas pipeline. Despite the long history of use as a pipe and valve coating, the new implementation is the industry’s first significant use of a thermoset hot spray coating applied to field weld areas of pipe, mill coated with a three layer polyethylene system. In the laboratory and in field trials, the coating demonstrated integrity, was applied much quicker than the traditional heat shrink sleeve, and eliminated several application contingencies. Laboratory investigations undertaken in Houston, Texas and Lyon, France were key steps in selecting the 100% solids tar-polyurethane coating. Additionally, the testing assisted in developing the surface preparation technique, and demonstrating the coating’s ability to adhere to the polyethylene coating as well as the steel pipe. Serious localized corrosion, and cathodic protection shielding associated with other joint coatings are less probable with the new joint coating system. Actual field cathodic protection testing indicated very low current consumption for the completed pipeline. The efficient joint coating operation contributed to setting new construction records.