No abstract

No abstract

No abstract

A simulation method for microscopic creep damage at grain boundaries in the fine-grain heat-affected zone of low-alloy steel welds involving high energy piping was proposed on the basis of the combination of elastic-creep FEM analysis and random fracture resistance modeling of the materials. First, the initiation and growth-driving forces of small defects were concretely determined based on microscopic observation of the damage progress at the grain boundaries of the material, taking into account dependence on stress and temperature. Then, a simulation procedure combining the stress distribution from elastic-creep FEM and the random fracture resistance model was proposed, and this procedure was applied to the simulation of the microscopic damage progress in a welded joint model test and in actual power piping. The results in terms of the simulated number density of small defects throughout the wall thickness were in good agreement with the observed results.

Creep damage analysis method of welded joint on the basis of the random fracture resistance model was proposed and was applied to the creep damage evaluation of welded joint of low alloy steel. Firstly a random fracture resistance of grain boundaries, an initiation and a growth driving forces of small defects, which were necessary in the above model, were determined considering the stress-dependent damage progress of the fine-grain HAZ material of 21/4Cr-1Mo steel. Secondly a procedure combining both the stress distribution in the welded joint and the random fracture resistance model was concretely proposed and was applied to the creep damage evaluation of the model test and the actual power piping. Experimental results of both the time history and the distribution of the number density of small defects in the welded joint were successfully reproduced by the proposed method.