STRESS-RELAXATION PROPERTIES OF ALLOY HP50NB AND THEIR APPLICATION TOLIFE ASSESSMENT OF REFORMER FURNACE TUBING

Traditional life assessment techniques based on an inverse design appr oach do not explain the premature failures frequently encountered in r eformer tube applications. This is because no account is taken of the through wall stresses generated by the thermal gradient. In order to a ccount for the thermal stresses in reformer tubes, the stress relaxati on properties of alloy HP50Nb in both as-cast and in-service aged cond itions have been determined for input to a ductility exhaustion model for assessment of creep damage due to thermal cycling. The ductility e xhaustion model proposed is that used in the Nuclear Electric R5 high temperature assessment procedures. The model predicts that thermal cyc ling contributes significant levels of damage. While variations in str ess relaxation properties are significant, the overwhelming influence on predicted life is material ductility. Copyright (C) 1996 Elsevier S cience Ltd.