A comparative study of mechanical properties and corrosion behavior of fusion-bonded epoxy and liquid epoxy coatings and their service life in drill pipe applications

The current investigation evaluated the service life and characteristics of fusion-bonded epoxy (FBE) and liquid epoxy coatings applied on ST37 substrates to determine the optimal properties for the inner coatings of the drill pipes in the practical operating conditions. For this purpose, various mechanical tests of flexibility, hardness, adhesion resistance, impact resistance, and wear resistance along with corrosion tests of salt spray, acid immersion, and impedance tests were employed. The mechanical test results verified that FBE coating with 88 Shore D hardness and 25 MPa adhesion strength had the lowest weight loss during the wear test and provided the most desirable mechanical properties among the liquid coatings. Furthermore, the FBE sample was found to have the maximum flexibility and the highest impact resistance. The corrosion test results revealed that the FBE sample had the lowest corrosion rate, which can offer extended durability for the internal coating of the drill pipes. The results also showed that the higher compactness of the FBE coating structure, as well as the lower permeability against the penetration of aggressive agents, were the primary factors accountable for the superior service life.