Abstract
Fatigue sensitive pressure containing components in the oil & gas industry requires a life cycle assessment. High Pressure High Temperature (HPHT) equipment designed using API 17TR8 and ASME Section VIII Division 3 are evaluated for cyclic fatigue crack growth per API 579/ASME FFS-1 fitness for service level 3 assessment. The level 3 assessment requires more advanced stress analysis to define the state of stress at critical locations and a defined initial flaw for cycle growth assessment. The cyclic crack growth in pressure containing equipment depends on the alternating crack tip stress intensity values for the defined load histogram. Therefore, in this paper, the stress intensity at crack tip is calculated using two approaches for 20ksi pressure equipment. The first approach is to utilize linear elastic stresses obtained from a three-dimensional finite element evaluation, where the stress profiles are used as an input to Signal FFS (fitness for service) Quest software, to calculate stress intensity at crack tip. The second approach utilizes a J-integral based on fracture mechanics analysis considering a pressure penetration on cracked surfaces. Although there is a difficulty in representing the complete production load histogram applying the J-integral solution, this paper provides evaluation of the two methods for comparison of results. It also demonstrates the feasibility of application to pressure vessel equipment.
