EXPERIMENTAL INVESTIGATION OF FAILURE ESTIMATION METHOD FOR CIRCUMFERENTIALLY CRACKED PIPES SUBJECTED TO COMBINED BENDING AND TORSION LOADS

When a crack is detected in a nuclear piping system during in-service inspections, the failure estimation method provided in codes such as the ASME Boiler and Pressure Vessel Code Section XI or JEME Rules on Fitness-for-Service for Nuclear Power Plants can be applied to evaluate the structural integrity of the cracked pipe. In the current codes, the failure estimation method for circumferentially cracked pipes includes bending moment and axial force due to pressure. Torsion moment is not considered. The Working Group on Pipe Flaw Evaluation for the ASME Boiler and Pressure Vessel Code Section XI is developing guidance for combining torsion load within the existing solutions provided in Appendix C for bending and pressure loadings on a pipe. A failure estimation method for circumferentially cracked pipes subjected to general loading conditions including bending moment, internal pressure and torsion moment with general magnitude has been proposed based on analytical investigations on the limit load for cracked pipes. In this study, experimental investigation was conducted to confirm the applicability of the proposed failure estimation method. Experiments were carried out on 8-inch diameter Schedule 80 stainless steel pipes containing a circumferential surface crack. Based on the experimental results, the proposed failure estimation method was confirmed to be applicable to cracked pipes subjected to combined bending and torsion moments.