Alloy design, high-temperature corrosion

High-temperature corrosion and wear is encountered in various industries such as waste incineration, fossil energy, pulp and paper, petroleum refining, chemical and petrochemical, mining and smelting operations. One of the methods to combat corrosion and wear and its control is to select suitable material, i.e., an alloy, for the plant design and maintenance. The selection of proper material for plant design and fabrication is followed... 

In designing alloys for use at elevated temperatures, the alloys must not only be as resistant as possible to the effects produced by reaction with oxygen, but resistance to attack by other oxidants in the environment is also necessary. In addihon, the environment is not always only a gas since, in practice, the deposihon of ash on the alloys is not uncommon. It is, therefore, more realishc in these cases to speak of the high-temperature corrosion resistance of materials rather than their oxidation resistance. 

Tras CHAPTER HIGHLIGHTS the coiTOsion resistance of nickel and its alloys and identifies relevant ASTM standards associated with their evaluation. The test technique selected ultimately will depend upon the specific alloy involved, the type of corrosion in question, or the end application, or a combination thereof. The following discussions will deal primarily with aqueous corrosion and the nickel-base (greater than about 30 % nickel) alloys designed for aqueous corrosion resistance. High-temperature gaseous corrosion will be addressed in other sections. 

This section presents a brief discussion of the establishment and maintenance of protective oxide scales, with particular relevance to the design of oxidation-resistant intermetallics. The reader is referred to the reference books by Kubaschewski and Hopkins (1962), Birks and Meier (1983), and Kofstad (1988a), and to the chapters Fundamentals of High-Temperature Corrosion by Schiitze and High-Temperature Corrosion of Metallic Alloys and Coatings by Gleeson in this volume for a more detailed discussion of the fundamentals of oxidation. 

Alloys designed to resist high-temperature corrosion are basically oxidation-resistant materials because all forms of attack at elevated temperatures are... 

Alloys that retain high strength at high temperatures (>1000°C in some cases) are known as superalloys. Some of these materials are also highly resistant to corrosion (oxidation). These alloys are difficult to make, contain metals that are not readily available, and are expensive. They are used in situations where the conditions of service make them essential, such as in aircraft engines, where certain designs require as much as 50% by weight of some of these special alloys. 

The pilot plant is designed for temperatures and pressures up to 300 °C and 300 bar. Because of the highly corrosive enviromnent inside the plant, only Ni alloy steels are used. Special fittings and instruments had to be developed to ensure high reliability of the pilot plant. 

---