Fracture mechanics evaluation of small diameter piping considering the latest experimental results

The results obtained from investigations carried out on austenitic piping o f small nominal diameter (DN80 and DN50) are introduced and discussed toget her with their assessment using fracture mechanics methods. Essential resul ts are summarised as following. The pipes with flaws (fatigue crack) down t o a depth to a(max)/t = 0.51 (DN80) as well as a(max)/t = 0.62 (DN50) and a circumferential extension of results 2 alpha = 120 degrees reached bending angles up to 26 degrees. The ASME collapse load (test collapse load) was e xceeded considerably and the experimental maximum load could not be reached . Failure due to a leakage or rupture did not occur in any test. The maximu m crack extension was 0.69 mm (DN80, a(max)/t = 0.51) resp. 0.3 min (DN50, a(max)/t = 0.62). The experimental maximum load can approximately be assess ed by the limit analysis. The fracture mechanics approximation methods GE/E PRI and LBB/NRC calculated a/t = 0.4 and 2 alpha = 120 degrees initiation l oads above the experimental maximum load for pipes containing flaws. These results confirmed the procedures for the proof of integrity of small diamet er piping by updating information on load, deformation and failure behaviou r of austenitic piping damaged with circumferential flaws. Using these resu lts may formulate a final safety concept for the proof of integrity of smal l diameter piping by completing the current concepts. (C) 2000 Elsevier Sci ence S.A. All rights reserved.