Comparison of experimental, numerical and analytical risk assessment of oil drilling rig welded pipe based on fracture mechanics parameters

Abstract

Fracture mechanics parameters are used for experimental, numerical and analytical risk assessment of structural integrity and life of oil drilling rig welded pipe with a crack. As a simple analytical tool, the Failure Assessment Diagramme (FAD) has been applied to assess probability of pipe failure, using the ratio of linear elastic fracture mechanics parameter, K-I, and its critical value, K-I(c), in relation to the ratio of applied stress and its critical value. Alternatively, the ratio of J integral, evaluated experimentally and numerically, and its critical value, J(I)(c), has been used to estimate probability of failure. Risk was then assessed for all three approaches, in combination with the estimated consequence. Results are given in the form of risk matrix, indicating the effects of the most (analytical) and the least (experimental) conservative estimates. In the case of risk based structural life assessment, number of cycles, obtained analytically and numerically, are related to the number of cycles to the critical crack length, to assess risk due to fatigue.