Reliability Analysis of Spherical Tank by Monte Calro Simulation

Abstract

Fracture toughness, size of weld defect, fabrication error etc. which control brittle fracture of welded structure are generally thought to be probabilistically distributed factors. It is easy to evaluate deterministically whether fracture occurs or not by using fracture mechanics and the worst values of various factors. However, there exists some ambiguity in determination of the worst values.Reliability analysis of spherical tank for the model case was performed by means of fracture mechanics and Monte Calro simulation under postulation of distribution functions for various factors.The present report describes the postulated probabilistic distributions, model of simulation and formulation of analysis which are used in reliability analysis of the tank. It is recognized that Monte Calro simulation is effective method for reliability analysis of the tank.From the results of simulation, it is shown that 1) probability of failure Pf of the tank is 10-310-4 and 2) average value of δc, distribution parameter αδc, of δc, average size of retained weld defect etc. have significant effect on Pf, but angular distortion and misalignment of butt welded joint have trivial effect on Pf.It is pointed out that the following information and data accumulation are important to reliability analysis of welded structure. That is 1) probabilistic distribution parameters, especially in NDI detection probability and δc distribution function. 2) probabilistic information in what kind of microstructure the tip of weld defects exist. 3) information about difference of δc value between for natural crack and for fatigue crack.