Cracking Causes of Leak Monitoring Tube of Nuclear-Grade Equipment Flange in a Nuclear Power Plant

During the overhaul period of a domestic nuclear power plant after 1 a operation, it was found that the flange leak monitoring tube of nuclear-grade equipment was cracked. The reasons for the cracking of leak monitoring tube were analyzed by chemical composition analysis, metallographic examination, tensile property test, scanning electron microscopy and energy spectrum analysis. The results showed that the cracking form of leak monitoring tube was stress corrosion cracking. During the installation stage, the flushing of leak monitoring tube was not complete, and caused chloride ions remaineing in the tube. Some corrosion pits first formed on the site of chloride ions aggregation. Under the combined action of stress and corrosive medium, cracks occurred there, and the crack continued to expand, eventually leading to leak monitoring tube cracked.