Interim Results on the Corrosion Behavior of Engineering Alloys in Ozonated Artificial Seawater.

Abstract : Initial testing of metal alloys in ozonated vs. aerated artificial seawater has been completed for exposure times of up to 16 weeks. Five alloy groups were tested: nickel-based, stainless steel-based, titanium-based, aluminum-based, and copper-based. Three types of samples were used to evaluate corrosion behavior: weight loss, creviced and wire (electrochemical). Of the five alloy groups, titanium was the most resistant, showing little difference in the corrosion behavior between aerated and ozonated solutions. Although evidence of crevice corrosion was found on titanium crevice samples in ozonated solutions, data indicate that this is due to the breakdown of the Teflon washers used to create the crevice. Solutions containing alloys with nickel precipitated a black corrosion product which contains hydrated nickel chlorate. However, the percentage of weight lost by these nickel-containing alloys did not indicate a significant weight change. Nickel alloys behaved in a transpassive manner when exposed to ozonated solution. Nickel alloys and highly alloyed stainless steels were resistant to classical crevice corrosion in ozonated solution, however differential oxidation cell corrosion was noted between free surfaces (high ozone concentration) and slots between multiple crevice washer plateaus (low ozone concentration). Ozonation appeared to be beneficial to the corrosion of aluminum alloys, decreasing corrosion rates and the amount of crevice corrosion compared to aerated seawater. The general corrosion resistance of copper was higher in ozonated vs. aerated solutions, however, the crevice corrosion behavior was adversely affected. Although nickel is beneficial to the corrosion resistance of copper-nickel alloys in aerated seawater, alloys with higher nickel concentrations were adversely affected both in terms of both general and crevice corrosion. jg p2