Stress corrosion cracking behavior of high strength casing steel in working fluids

Aiming at the stress corrosion cracking behavior of a high strength steel, the air working conditions, the annulus protection fluid and the organic salts mud were simulated under the temperature of 60 degrees C, 100 degrees C, 150 degrees C by slow strain rate tests (SSRT). Tensile strength and elongation and stress corrosion cracking susceptibility index and fracture morphology were analyzed by stress-strain curves and SEM. To determine the applicability of high strength steel under different working conditions, the extent of damage were analyzed quantitatively. The results showed that less degree of stress corrosion occurs when temperature below 100 degrees C or even lower, and severe increase of stress corrosion occurs when temperature is 150 degrees C. The high strength steel stress corrosion cracking tendency increase as the temperature grows, and so do the stress corrosion cracking susceptibility index F(sigma) and F(delta). Besides, the tendency of increase of F(sigma) is more significant than that of the F(delta). In the working conditions of the organic salt mud, the changes of mechanical properties of the high strength casing steel are more significant. The corrosion pits on the sample surface contributed to such changes as a mainly factor. The crack nucleation can occur under the action of stress concentration at the bottom of the corrosion pits, and results in crack initiation extension inside the sample along the direction perpendicular to the tensile stress. In addition, the annulus protection fluid protected the strength and toughness of the casing excellently. (C) 2016 Elsevier B.V. All rights reserved.