Moller, G.E., International Nickel Co., Inc., Torrance, Calif.
Abstract
Austenitic stainless steels are providing excellent trouble-free service in sea water for pumps, propellers, valves. and other marine equipment. propellers, valves. and other marine equipment. Occasionally, a failure occurs as the result of deep localized pitting in a crevice. Data are given showing that austenitic, ferritic. and martensitic stainless steels suffer pitting in crevices and under deposits in quiescent sea water. Austenitic stainless steels remain free from attack in high-velocity sea water. Low-purity ferritic and the martensitic stainless steels frequently pit in high-velocity sea water. Crevice corrosion can be controlled effectively with cathodic protection from iron, zinc. aluminum or magnesium galvanic anodes or impressed current cathodic protection by polarization to -0.6 v vs Calomel. Austenitic stainless steel performs well in many situations because it is a component of a multi-alloy assembly utilizing iron or steel. Examples from field experience arc given.
Introduction
During the past decade, there has been a growing use of austenitic stainless steel in marine equipment. Most applications have been successful but an unexpected failure has been observed occasionally. It is the purpose of this paper to describe when and how to use austenitic stainless steel with success. The selection of stainless steels appears to result from the engineering requirements of new, advanced, high-speed, high-reliability commercial, pleasure, and military craft. Ocean science and pleasure, and military craft. Ocean science and engineering, offshore oil production, fishing, and ocean mining are also contributing to the selection of stainless steels for sea-water applications. The increasing use of stainless steel in the marine environment is found in work-boat propellers, pump components, bow thrusters, valves, shafting pump components, bow thrusters, valves, shafting and shaft components, through-hull fittings, parts on data-gathering buoys, fasteners, and housings of oceanographic instruments. When austenitic stainless steel has given good, corrosion-free service, it is most often found to be used as a key component in a multi component, multi-alloy assembly or system receiving the benefit of built-in cathodic protection. For example, in Fig. 1 a cast Type 304 (Alloy Casting Institute CF-4) propeller is being used on a steel seagoing tugboat with zinc anodes attached to the rudder. Fig. 2 shows a cast ACI CE-30 power-plant sea-water circulation-pump impeller free power-plant sea-water circulation-pump impeller free of any corrosion after 6 years of service that was used in combination with an austenitic cast-iron suction bell and diffuser.
SPEJ
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Surface Modification of a Nickel-Free Austenitic Stainless Steel by Low-Temperature Nitriding
