Failure analysis of the industrial water piping system leakage

Abstract

The damage in the form of the leakage occurred at the end piping transporting industrial water in the press hall of the automotive plant in the specific position of 12 o'clock after twelve years of operation. The piping diameter 80 mm, wall thickness 4 mm, is made of low carbon steel produced according to the Slovak standard STN 41 1353 equivalent to the S235 according to the EU standards or ASTM A519-82 grade 1020. In order to determine the cause and course of corrosion damage to the piping there were performed the analyses of the transported industrial water (composition, properties, pH), ultrasonic measurements of piping wall thickness, piping steel material (microstructure, chemical composition) corrosion products from the entire inner surface of the piping and from the point of the leakage and pinholes (visual, EDS and X-ray). The UT measurements of wall thickness changes revealed the massive corrosion damage manifested as pinholes at the 12 o'clock position with the max. depth of the pinholes 3.6 mm. The analysis of the industrial water confirmed the quality corresponding to drinking water. The X-ray analysis of the corrosion products from the pinholes and leakage confirmed the corrosion process in the humid atmosphere with the dominance of Goethite, Akaganeite and the low CaCO3 content. The presence of Akaganeite and the direct confirmation of the Cl− presence in the corrosion products by the pinholes EDS analyses designates Cl− as the accelerator of pinholes corrosion in the humid atmosphere above the stagnant water level, propagating against the direction of gravity (12 o'clock) in the air bubble created by improper venting of the piping.