Environmentally Assisted Cracking Evaluation of a Large UNS N07725 Forging Under Cathodic Protection Conditions

An investigation to determine the stress intensity factor for environmentally assisted cracking (K-EAC) of a large UNS N07725 block forging is described. Displacement-controlled testing was conducted using 1 in thick (25.4 mm) precracked compact tension (CT) specimens machined in the LS (longitudinal-short) and SL (short-longitudinal) orientations.(1) Experiments were carried out under simulated cathodic protection conditions in ASTM D1141 artificial seawater. Test results show that the environmentally assisted cracking threshold of this UNS NO 7725 material exceeds 100 ksi root in (110 MPa root m) under an applied cathodic potential of-1.0 V vs. saturated calomel electrode (SCE), for experiments of approximately 300 h in duration. However, a hydrogen-assisted fracture mode was identified under the more severe testing conditions used.