Crack Growth Under Creep Conditions in HK-40 Stainless Steel

Abstract

In a steam reformer furnace the HK-40 catalyst tubes are subjected to severe conditions of high temperature and pressure, and are vulnerable to creep-rupture failures. The resultant lost production and high cost of replacing tubes provide a strong incentive for predicting the service life of catalyst tubes. The crack growth behaviour of the HK-40 alloy under creep conditions was investigated and the results used to ascertain whether current concepts of creep-fracture mechanics were applicable to the HK-40 alloy. It was demonstrated that crack growth rates in different specimen geometries could not be correlated as a whole with either nett-section stress or the elastic stress intensity factor. The metallographic studies provided a valuable insight into the crack growth mechanisms operating in the HK-40 alloy. It was apparent that the cracks followed the continuous interdendritic chromium carbide networks; interdendritic microcracks were always observed ahead of the main cracks in the HK-40 alloy.