Failure analysis of boiler leakage due to caustic corrosion on Cr-Mo steel

Abstract

In the system of steam generation, condenser and boiler are the most prone to suffer corrosion attack. It usually occurs due to the interaction between the pipe surface that made from steel with the fluid of boiler. One of the dangerous types of failure is pitting corrosion. There are several causes of pitting corrosion, such as; the oxygen content in the fluid, the amount of contaminants that may easily form a deposit on the Cr-Mo steel surface, and the use of improper concentration of inhibitors. The electrochemical process takes place during the occurrence of pitting corrosion. Failure analysis of the boiler water-wall tube is presented in this work. In order to examine the causes of failure, various techniques including visual inspection, optical microscopy, and energy dispersive spectroscopy were carried out. Tube wall thickness measurements were performed on the failed tube. The water-facing side of the tube was observed to have experienced significantly localized wall thinning. The failure mechanism is suggested as oxidation due to caustic corrosion as a result of inappropriate usage of phosphate inhibitors.