The mechanism and identification of corrosion of steel pipes in hot water supply systems

Abstract

The problem of corrosion of steel pipes in hot water supply systems is very relevant in Russia. In a number of cases, the accelerated corrosion of pipelines and fittings installed in hot water supply networks is observed. The purpose of this study is to investigate the mechanism of corrosion of steel zinc-coated and non-galvanized pipes in hot water supply systems, to analyze the causes of corrosion and to develop methods for identifying active corrosion processes occurring in water supply systems. According to literature review the microstructure and composition of the zinc coating and the methods of its application are studied. A SEM/EDS study of the structure and elemental composition of inner zinc coating on new and used steel galvanized pipes is conducted. This study shows the nonuniform distribution of zinc layer which can lead to a rapid corrosion of both the zinc layer and the metal substrate and the development of pitting corrosion. A structure and composition of corrosion sediments formed on the inner surface of pipes was studied. The different causes and factors of steel corrosion in hot water are considered and discussed. A method of corrosion identification of galvanized pipes and heat exchange equipment based on the determination of corrosion products, in particular zinc and copper, was proposed.