Failure Analysis of a Low-Temperature Carbon Steel Pipe from a Nuclear Power Station Cooling Water System

Abstract

This paper presents the results of a failure examination on an ASTM A106 carbon steel pipe from component cooling water system at a nuclear power station. The pipe was associated with a large motor air cooler. Through-wall cracking occurred after over three decades of total service and approximately one decade following a refurbishment. The pipe was filled with demineralized water and operated at a temperature <40 °C. Sections of the failed pipe along with a similar non-leaking section were examined with light optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, mass spectrometry, a gas analyzing furnace, and a microhardness indenter to provide data about the failure mechanism and the base material. The results of the study showed that the failure was the result of outside diameter initiated, intergranular stress corrosion cracking. The failure occurred in the vicinity of a weld in the heat-affected zone (HAZ) of the pipe. Other areas of non-through-wall cracking were also observed in the pipes outside of the HAZ.