Improvement of the failure-assessment diagrams used to check the harmfulness of pipe defects

Abstract

In this paper, the principle of the failure-assessment diagram (FAD) is presented including the definitions of the failure-assessment curve and the assessment point. Classical FAD allows computing a safety factor associated with defect geometry and loading conditions. Extension to a probabilistic FAD (PFAD) is used to compute the failure probability. In order to reduce the conservatism associated with the ‘crack-like defect’ procedure, the use of notch-failure-assessment diagram (NFAD) takes advantage of the increase of fracture toughness by reducing the defect acuity. The domain-failure-assessment diagram (DFAD) are pertinent to associate the right fracture-mechanics’ tool with the failure mechanism: brittle, ductile, or plastic collapse. The fatigue-assessment diagram (fAD) use the Wohler curve as failure-assessment curve and is used to develop a maintenance policy by determining loading conditions to guarantee a life duration with a given probability.