ABSTRACT
A metal in a gaseous environment constitutes a very complex chemical system. In most situations an interpretation of the reaction behavior can be achieved only with great difficulty. The terms metal oxidation, tarnishing, and scaling are used in literature whenever oxidizing gases such as oxygen, sulfur vapor, the halogens, water vapor, colt etc., attack a metal or an alloy at low, intermediate, or high temperatures. In general, the oxidation processes at high temperatures leading to the formation of thick oxide layers are referred to as the scaling process, whereas at lower temperatures the phenomena of thin oxide film formation are termed the tarnishing process. Oxidative attack on metals can take place under widely varied conditions from the "mild" oxidizing one that prevails in air at room temperature to the extremely "severe" conditions of mixed environments at elevated temperatures encountered by high-temperature components such as superheater and reheater tubes, gas turbine blades and vanes, alloy components in fuel conversion and power-generating units, reformer tubes, heat exchanger tubes, and the like, which are often subjected to thermal fluctuations and thermal cyclings under actual service conditions. The severity of the operating condition can be inflated due to thermal fluctuations and sudden high-temperature excursion.
