Resistência à fratura de revestimentos aplicados ao aço ASTM a 516 Gr 60 para uso na área de petróleo e gás.

Abstract

In this work the fracture resistance of applied coatings in metallic substratum of type manganese steel (ASTM A 516 Gr. 60) for applications in petroleum and gas industry was evaluated. For this, traction specimens of rectangular traverse section were made (Norma ASTM AND 8M), using steel (ASTM A 516 Gr. 60) as substratum manganese. The studied coverings were: a) Nickel deposited by electrolytic process with medium thickness of 20 urn; b) Epoxy paints of type I, II and III (N-2912 - Petrobras) developed in CENPES-PETROBRAS for protection against the corrosion. With the objective of analyzing the fracture resistance of the coatings and at the same time the relationship between this resistance and surface roughness, traction specimens with three roughness profiles Ry (20, 40 and 60 urn) were made for the tests with electrolytic Nickel coating. For the coatings with epoxy paints the substratum roughness was Sa 2 Vz (average of 80 urn - dry-sand blasting). On the other hand, the coatings with epoxy paints were submitted to traction adherence tests (Norma ASTM 4541). The traction tests with the purpose to determine the fracture resistance of the coatings were accomplished at room temperature with the following loads levels: 30%, 50%, 70%, 90%, 110%, 120% and 130% of the substratum flow stress. The results showed that for the nickel coatings the cracks appeared with a load of 90% of the substratum flow stress. The coatings with the epoxy paints of the type I, II and III presented a good resistance to cracks during the loading. Only the type I paint presented cracks at the level of 110% of substratum flow stress. The epoxy paints presented a resistance of 15 MPa to traction adherence tests, a solid value for these coatings.