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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.

In the present work, water sorption kinetics and equilibrium in 100% solids epoxy coatings are investigated by immersion into distilled water baths from 20 to 85 °C (absorption tests) and drying in a furnace between 60 and 85 °C (desorption tests). The gravimetric liquid sorption measurements reveal a non-Fickian two-stage diffusion behaviour during both absorption and desorption. The effect of hydrothermal history was also investigated. Cycling the immersion bath temperature increases the saturation values. Alternating sorption–desorption cycles increases the speed of water movement. The hydrothermal-induced coating degradation and the sorption modes are discussed.