EVALUATION OF LEAK/RUPTURE BEHAVIOR FOR AXIALLY PART-THROUGH- WALL NOTCHED HIGH-STRENGTH LINE PIPES

摘要

Concerning the fracture assessment of high strength linepipes for natural gas transportation, it is necessary to take into consideration not only the crack arrestability of running ductile fractures but also the characteristics of ductile fracture initiation from defects which can cause fracture propagation. The original leak/rupture criteria proposed by Kiefher et al. have been widely used in many industries and worked well for ordinary grade pipes. However, as pointed out by D.-J. Shim et al., recent modern line pipes have some unusual characteristics that differ from older materials. Kawaguchi et al. also revealed that the leak/rupture prediction using Charpy V-notch (CVN) absorbed energy-based equation was not applicable to pipes having CVN energy (C_v) greater than 130 J and flow stress greater than X65. To verify the leak/rupture criteria using CVN absorbed energy-based equation for high strength linepipes with higher Charpy energy, hydrostatic burst tests were conducted for API 5L XI00 linepipes with an axial part-through-wall (PTW) notch. Based on the relationship between the axial PTW notch length/depth and hoop stress, Leak-Before-Break (LBB) criteria was experimentally determined. A series of tests demonstrated that the C VN-based equation underestimates the failure stress for X100 linepipes i.e., the predicted failure stress is 0.943 times the experiment on average and the flow stress dependent equation has a tendency to overestimate the failure stress for longer notched pipes. Concerning the leak/rupture behavior, it is observed that the flow stress-dependent curve for through-wall (TW) notch overestimates the leak/rupture boundary and the toughness-dependent curve for TW notch is relatively close to the leak/rupture boundary.