Fatigue Crack Growth and Fracture Studies on Stainless Steel Straight Pipes Having Circumferential Surface Crack

The primary objective of this manuscript is to verify the LBB criterion, by carrying out fatigue crack growth (FCG) and fracture tests on SA 312 Type 304LN stainless steel pipes having a part-through crack in the circumferential direction. FCG tests were carried out on pipe specimens under constant amplitude loading in bending till the crack became through-wall and further reached 1/8th of the circumference of the pipe. During the FCG tests, beach marks were introduced by changing the minimum load of the cycle, keeping the maximum load as constant for clear identification of marks on the fracture surface. Subsequent to FCG tests, fracture tests were carried out on the through-wall cracked pipes under displacement control. During the fracture tests, load, load-line displacement, deflection of the pipe at critical locations, Crack Mouth Opening displacement (CMOD), surface crack length (circumferential) and angular rotation of the pipe with respect to the supports were monitored. Stress intensity factor (SIF) was determined by using API Code, RCC-MR and R6 approaches. SIF range and number of cycles predicted using the three analytical approaches are found to be very close to each other with a variation of ± 10