Einfluß des pH-Wertes,des Sauerstoffgehaltes und der Strömungsgeschwindigkeit von kaltem Trinkwasser auf das Korrosionsverhalten und die Schutzschichtbildung bei feuerverzinkten Stahlrohren

Influence of pH-value, oxygen content and flow velocity of cold drinking water on corrosion behaviour and surface layer forming of galvanized steel tubes During a test program of 28 months determinations of weight loss, metallographical examinations and chemical analysis data of surface layers showed clearly that in the chosen variation range mainly the pH is important for the longterm behaviour and the expected working life of galvanized steel tubes. Lower pH-values of 6.9 lead to increased rates of Zinc attack and to inhomogene, disturbed surface layers, whereas higher pH-values of 7.9 show decreased Zinc loss and favour the forming of well protecting layers. Oxygen content and flow velocity become important only in the early stage of Zinc corrosion. Additional electrochemical measurements gave a good impression of Zinc corrosion rate development, corrosion attack morphology and properties of surface layers.