Hydrothermal ageing of X65 steel specimens coated with 100% solids epoxy

• There is no standard for ageing pipeline coatings equivalent to a period in service.
• Soaking in hot water tries to age coatings, and degrades coating properties.
• After weeks of immersion in 80 °C water, hardness and adhesion of the coatings drops.
• Coating ability to exclude the hot water from the pipe drops with respect to time.
• Results are difficult to quantify, but trend in properties degradation is apparent.

In some regions of Australia, epoxy-based coatings are commonly used to isolate the outer steel surface of a buried gas pipeline from the aggressive soil environment, but the rate at which the ability of the coating to exclude the environment deteriorates is unknown. The aim of this project was to investigate the accelerated ageing of a pipeline organic coating using a hydrothermal test as a proxy of pipeline's long-term exposure in the field. API-5L-X65 pipeline steel specimens were coated with a commercial 100% solids epoxy coating and immersed into an 80 °C distilled water bath with traces of carbonate–bicarbonate salts whilst electrically connected to an aluminium sacrificial anode. A limited number of specimens were taken out at different predefined ageing times, providing data to evaluate the degradation rate of the coating. Samples aged for 28 weeks were found to have a lower Barcol hardness, greater electrical permeability, and lower dry adhesion strength than non-aged samples.