Through study and analysis of failure accidents occurred on boiler tubes made from 18-8 type austenitic steel in course of long-term operation under high temperature

it is believed that the important causes resulting directly in failure of 18-8 type auste- nitic steel tube in operation under high temperature are as follows:continuous and blocked separating-out phase and needle like O phase of carbide appeared in the grain boundary;growth and peeling-off of the oxide layers;phase change of the elbow under com- plicated stress conditions;deterioration of material′s performance resulted directly from mettalographic structure ageing.The results of analysis provide with certain reference for operation supervision of said boiler tubes.