Sulfide Stress Cracking Fracture Toughness of 125 ksi Grade in Mild Sour Service Conditions

摘要

NACE TM0177 Method D corrosion test is very frequently used for the determination of the fracture toughness of low alloyed steels in sour environments. The use of the standard NACE Solution A environment saturated by 1 bar H_2S allows an efficient quality control of OCTG products for order release but does not provide K|SSc values for well design in fit-for-purpose conditions. This is more especially true for 125 ksi grade which is essentially used in mild sour conditions. However, the definition of the most reliable test condition is still lacking consensus, more particularly regarding the appropriate test duration and pH buffering. Consequently, an extensive DCB testing program has been performed on 125 ksi grade sour service casings and couplings in 0.07 bar H_2S gas for solving these issues and for providing meaningful K_(issc) values.