Wall thinning in carbon steel pipeline carrying pure water at high temperature

Abstract

In the boilers of thermal and nuclear power plants, neutral pure water with low electric conductivity is generally used after de‐oxygenation, which is utilized to suppress the corrosiveness of the water. Nevertheless, a relatively high rate of wall thinning occurs on the inside surface of carbon steel pipes, in particular the downstream orifice meters and T‐junctions, sometimes leading to the rupture of the pipe. The generation of wall thinning has been attributed to FAC (flow accelerated corrosion), implying that the water flow must raise the corrosiveness of the boiler water. Contrary to this explanation, the macro‐cell corrosion theory, which was proposed by this author, regards this occurrence as merely localized corrosion. Under such circumstances, a case study was conducted on a burst carbon steel pipe from a high pressure steam line, and the cause was substantially proven to be water‐line corrosion. Because water‐line corrosion is a localized corrosion that can occur without water flow, the wall thinning damage that occurred in the carbon steel pipes must have been brought about by localized corrosion and not FAC.