Failure Mechanisms of Epoxy Coatings in Pipelines

Abstract

Epoxy, a thermosetting polymer due to its attractive properties, has been widely used in many industries as a coating material such as the oil and gas industries. This study provides an insight into the corrosion behavior of epoxy looking at its adsorption properties at the epoxy steel interface and the adhesion behavior for different corrosion environments. The study was carried out using conventional weight-loss measurements and microscopic observation after immersion in Hcl of varying pHs. After 31days of exposure, the results indicate an increase in weight of the different coated steels implying that adsorption occurs in the epoxy. Different mixing ratios of base to hardener were studied with different rates of adsorption obtained and the 2:1 ratio having the highest mass increase. To test adhesion properties of epoxy on X65 low carbon steel hot water immersion test was adopted and the 3:1volume ratio recorded the highest weight gain. High osmotic pressures result in causing vapor to migrate rapidly to the coating/steel interface at areas of marginal coating adhesion. This weakens the polar bond formed between the coating and the steel surface and may crack due to hydrostatic stresses, exposing the steel to corrosive environments or may start corroding the steel underneath leading to the deterioration of the pipeline. The implication of this result is to provide a more cost effective way of testing the adhesion quality and the corrosion behavior of epoxy.