THE FIRST TWO OCCURRENCES OF EXTERNAL DAMAGE ON 600TT ALLOY TUBES IN FRANCE

摘要

During the last decade, in different countries, several occurrences of external corrosion have been identified on SG tube bundles with thermally treated 600 alloy tubes. In France, this feedback has led EDF to enhance the SG inspection program. Nevertheless, until now, no damage of this type had been reported. Recently, during in-service inspection on an SG with 600TT alloy tubes, eddy current tests have highlighted a signal that could be related to external corrosion. The tube was removed and sent to the EDF hot laboratory for destructive examinations. Various examinations were performed at different scales to characterize the causes of the NDT signal, the material properties, the environmental parameters and the residual stresses. This paper describes these examinations, their results, and our analysis of the mechanism and the potential aggravating factors. We can then compare our conclusions with similar known cases.