Corrosion monitoring techniques used in water supply systems

Abstract

Typical Norwegian drinking water has a high content of natural organic compounds and is acidic and soft, with low alkalinity and low salt content. Such water corrodes the major materials used in potable water systems. Internal corrosion causes water quality deterioration due to release of corrosion products, and increased operational and investment costs due to pipe breakage and increased repair and maintenance requirements. Results are presented of a corrosion monitoring programme conducted for Oslo waterworks, which determined corrosion products (water quality) and corrosion rate (using the linear polarisation rate (LPR) technique and weight loss coupons). Monitoring the turbidity of tap water was shown to be an accurate method of determining the corrosion products from cast iron, steel, and ductile iron pipes, but corrosion products from dissolved metals could only be determined using specific analyses of the metal ions. Corrosion rates determined by the LPR method and weight loss coupons for copper and mild carbon steel showed relatively good agreement. The corrosion rate for copper as determined by LPR was too high, butthis method is useful in comparing water quality from various sources. Although severe pitting corrosion was detected only for iron, pitting corrosion was also observed for copper.