An Assessment of the Risk of Type Ⅳ Cracking in Welds to Header, Pipework and Turbine Components Constructed from the Advanced Ferritic 9 and 12 Chromium Steels

摘要

The susceptibilities to Type Ⅳ cracking of pipework systems constructed from P91 and P92 have been estimated from system stress levels calculated inversely from known Weld Reduction Factors and failure times of CrMoV plant. P91 and P92 pipework are predicted to be immune from Type Ⅳ cracking at 540°C for a WRF of 40% but to become increasingly susceptible with temperature. Widespread cracking is predicted at 600°C for P91 with a 40% WRF and at 625°C for P92 with a 50% WRF. Cross-weld data are currently indicating WRFs close to these values. The estimates suggest that better definition of the long term WRFs and/or programmes to determine metallurgical and design methods of avoiding the problem are needed to ensure that the reputations of the advanced alloys are maintained.