The management of weld cracking in high-temperature CrMoV pipework systems

Most power stations operated in the UK by the CEGB successor companies have 1/2CrMoV high temperature steam pipework welded with 2CrMo weld metal. The welds have historically been prone to a number of cracking mechanisms and have constituted a structural integrity risk. In National Power this risk has been successfully contained and controlled by a detailed system of inspection and repair. The National Power approach involves extensive weld inspection at planned outages with weld selection being based on cracking susceptibility. The approach relies heavily on detailed metallurgical investigation of damaged welds, by either sampling or in-situ metallography (replication) the results of which are fed back into the inspection programme. In this way the constantly evolving programme takes full account of changes in damage trends. Since the inception of National Power in 1990 this approach to the management of weld cracking has resulted in a significant reduction both in the numbers and sizes of cracks found in CrMoV steam pipework systems.