Application of the Nonlinear Fracture Parameter J-integral to the Welded Joint of Cylindrical Tank

Abstract

In this paper, the author have developped the elastic-plastic fracture analysis code “FRACT-2D” using the finite element method for evaluating the nonlinear fracture parameter J-integral of an axi-symmetric crack problems in addition to the J-integral. Applying this code to the shell-to-bottom junction of a 113, 000kl oil storage tank, the J-integral of a crack assumed at the toe of the fillet weld was evaluated numerically under the filling and emptying operation of the tank. Then, following results were obtained;
(1) Filling the tank with liquid, the J-integral coincides well with the J-integral at the lower liquid level. Futher filling, the difference between both parameters increases gradually and the J-integral becomes lower than the J-integral by about 15% when the tank is full.
(2) Emptying the tank, the J-integral decreases along the history of the filling operation. Then, it takes a negative value due to compressive residual stresses distributed at the crack-tip when the tank is empty
(3) The J-integral has a path-independence during the filling and emptying operation of the tank.