NICKEL BASE ALLOYS: CORROSION CHALLENGES IN THE NEW MILLENNIUM

摘要

To fully appreciate the corrosion challenges of the new millenium, one has to learn from the innovations made in the nickel alloy metallurgy of the past century. In the 21 t century, as was the case in the last century, within the various industries, after carbon steel, the 300 series stainless steels will continue to be the "most widely used tonnage" material. Other corrosion mitigation technologies such as electrochemical protection, non-metallics, coatings and paints and use of inhibitor technology will also play a major role. The materials of construction for these modern chemical process, petrochemical industries and other industries not only have to resist uniform corrosion caused by various corrodents, but must also have sufficient localized corrosion and stress corrosion cracking resistance as well. These industries have to cope with both the technical and commercial challenges of rigid environmental regulations, the need to increase production efficiency by utilizing higher temperatures and pressures, and more corrosive catalysts, and at the same time possess the necessary versatility to handle varied feed stock and upset conditions. Even though nickel as an element was discovered about 250 years ago, the first major nickel alloy introduced to the industry, about 100 years ago, was a Ni-Cu alloy 400. This alloy is still being widely used in a variety of industries and will continue to be used in this current century. Over the past 100 years, specially in the last 50 years, improvements in alloy metallurgy, melting technology, and thermo-mechanical processing, along with a better fundamental understanding of the role of various alloying elements has led to new nickel alloys. These have not only extended the range of usefulness of existing alloys by overcoming their limitations, but are reliable and cost-effective and have opened new areas of applications. This paper briefly describes the various nickel alloy systems developed and in use during the last 100 years with comments as to what the future holds for the newer alloys developed in the last 20 years and the competition faced by these alloys in the new millennium.