Book Description

The objective of this study was to assess the rate of corrosion of bare steel with and without cathodic protection, and the effectiveness of various commercially available coating systems in preventing corrosion of steel piles in seawater. Included were 25 coatings and four sacrificial anode cathodic protection systems. Twenty-nine (two piles per set) American Society for Testing and Materials (ASTM) A36 or ASTM 690 steel H-piles were exposed for 10 years. Most of the piles were coated or had cathodic protection. In 1981, the piles were pulled out and inspected visually. Performance ratings were then established for the following coatings: organic, metal-filled, organic over metal-filled, metallic, organic over metallic, and organic with cathodic protection. Based on this study, the following conclusions were drawn: (1) The corrosion rates-determined by flange thickness measurements in the immersion zone-were 7 and 6 mils (0.18 and 0.15 mm) per year respectively for bare carbon (A36) and mariner (690) steel. Sacrificial zinc or aluminum anodes effectively reduced the corrosion in the immersed zone to less than 0.1 mil (0.003 mm) per year. (Adding sacrificial anodes to a coated steel piling also protects steel in the immersed zone if the coating is damaged). (2) A polyester glass flake coating (System 29) was the top performer. Epoxies over zinc-rich primers (Systems 20, 10, and 18) and vinyl-sealed, flame-sprayed aluminum and zinc (Systems 14 and 16) coatings performed very well after 10-years' exposure. (Author).