Section B: Lessons learned in new build-projects and O&M

Thursday, 14 September 2017, 09:00-09:30h/B01

Damage on austenitic material HR3C - root cause analysis and investigation program

Christian Ullrich, Peter Körner, VGB PowerTech e.V.; Thomas Hauke, Lausitz Energie Kraftwerke AG; Simon Heckmann, RWE Generation SE

After the commissioning phase of some highly efficient latest generation coal fired power plants, intensive cracking was observed in the hot reheat tubes all located in the area of welds. Only the austenitic material HR3C containing 25 % of chromium was affected by the cracking. The crack initiation was purely on the tubes inside in the HAZ of the weld showing always an intercrystaline propagation. As root cause of this failure intercrystalline corrosion superposed by high tensile stresses was identified. To clearly identify the media causing the corrosive effect laboratory tests were being conducted in parallel to the failure analysis confirming finally the mechanism.

Further damage which occurred after the repair also showed intercrystalline crack propagation in the area of the weld but in this case located directly at the fusion line. The specific characteristics identified during the root cause analysis revealed a different failure mechanism. Intensive study of the materials properties revealed ductility dip cracking or relaxation cracking to be the root cause. The behavior on HR3C was also compared to other 25 % Cr-steels showing similar behavior.