《High Strength Corrosion Resistant Alloy Solves Marine Fastener Problems》.pdf

A High Strength, Corrosion-Resistant Alloy Solves Fastener Problems in the Marine Industry by Edward L. Hibner Lewis E. Shoemaker Huntington Alloys / Special Metals Corporation Huntington, WV 25705, USA Introduction Vessels and equipment built for service in seawater and other marine environments must employ fasteners that are resistant to corrosion by the aggressive service conditions to which they are exposed. Contractors and fabricators who build ships for the U.S. Navy must recognize this requirement, as a structure is no stronger or more reliable than its weakest member. Failure of a nut or bolt can have catastrophic results. Because the fastener is generally much smaller than the components it is used to support, the fasteners generally must be more corrosion resistant to offset any effects of galvanic corrosion. Should the fastener be anodic to the remainder of the structure, the relative size effect could cause severe corrosion and degradation of the fastener in a short period of time. Thus, corrosion-resistant nickel- base fasteners have been extensively used in marine service. For example, MONEL® alloy K-500 (UNS N05500) fasteners are used with alloy steel in a seawater environment. However, the resulting galvanic coupling can induce hydrogen charging and subsequent embrittlement of the fasteners, and failures of the alloy K-500 have occurred. Consequently, more noble high strength bolting materials are needed. INCONEL® alloy 686 (UNS N06686) is a high performance nickel-base alloy that exhibits high tensile strength and fracture toughness. It offers excelle