Pitting Corrosion on a Water Pipe of the Grade 1.4301

Abstract

Pipes made of stainless steel in the drinking water supply system showed pitting corrosion in the heat-affected zone (HAZ) of the welded joints. This was very surprising considering the chemical composition of the fresh water and the fact that no microbiologically influenced corrosion (MIC) had been found.Testing for pitting corrosion showed no increased sensitivity of the HAZ. The Electrochemical Potentiodynamic Reactivation test (EPR test), however, was positive for the tube interior and only within the HAZ. Metallographic examinations were carried out to clarify if sensitization or intergranular attack, a type of corrosion, were the cause.The holes showed an irregular propagation which can be explained by segregation lines in the steel. It is noticeable that the holes preferably propagate in the mid-thickness region of the steel sheet. The metallographic samples showed no preferred corrosive attack along the grain boundaries (intergranular attack) and also no sensitization of the steel.