72 Nickel And Nickel Alloy Systems

Nickel and nickel alloys have useful resistance to a wide variety of corrosive environments, typically encountered in various industrial processes such as in chemical processing, petrochemical processing, aerospace engineering, power generation and energy conversion, thermal processing and heat treatment industry, oil and gas production, pollution control and waste processing, marine engineering, pulp and paper industry, agrichemicals, industrial and domestic heating, the electronics and telecommunication industries, and others. In many instances the corrosive conditions are too severe to be handled by other commercially available materials including stainless and super stainless steels. Nickel by itself is a very versatile corrosion-resistant metal, finding many useful applications in industry. More importantly, its metallurgical compatibility over a considerable composition range with a number of other metals as alloying elements has become the basis for many binary, ternary, and other complex nickel base alloy systems, having very unique and specific corrosion-resistant and high-temperature resistant properties to handle the modern day corrosive environments. These alloys are more expensive than the standard 300 series stainless steels due to their higher alloy content and hence are only used when stainless steels are not suitable or when product purity cannot be compromised and safety considerations became very important. The subject of corrosion is highly complex and is dependent on the chemical composition, the microstructural features of the alloy, the various reactions occurring at the alloy/environment interface, and the chemical nature of the environment.

This chapter will mainly concentrate on the aqueous corrosion alloy systems, with a brief description of high-temperature alloys. The intent of this chapter is not to go into the theoretical discussion and analysis of corrosion science but to present the major nickel alloy systems, their major characteristics, the effects of alloying elements, and, most importantly, the strengths, weaknesses, and application of these alloy systems in the industry. A few words on fabrication are also included because an improper fabrication may destroy the corrosion resistance of an otherwise perfectly good nickel alloy.

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