TABLE OF CONTENTS Many different materials are used in the construction of a steam generating system. They range from mild carbon steel for condensate/feedwater piping and boiler waterwall tubes, to high-alloy steels for high-temperature superheater components, to copper alloys or other non-ferrous metals for many tube-in-shell heat exchangers.
This chapter outlines the most common materials that make up the steam-generating portion of power production or industrial plants. Certain groups of materials, such as the austenitic stainless steels, have members whose compositions are similar to but might vary slightly in one or two alloying elements. We will examine some of the basic properties of the materials and how alloying elements influence metal behavior.
Humans have used iron for more than 4,500 years. Its chief benefits include strength, hardness, integrity at high temperatures, malleability when combined with other elements, and natural abundance. Iron has a very strong affinity for oxygen, which is why many natural iron deposits exist in combination with oxygen or oxygen-bearing compounds. This also explains why unprotected iron structures rust so easily. A little bit of moisture, and "voila!" the material reacts with atmospheric oxygen and degrades into a pile of flakes. For many years, mankind's efforts have focused on production of iron-based alloys the steels that resist corrosion but maintain the desired properties of strength and hardness.
The basic definition of steel is an alloy of iron and carbon. The addition of a wide variety of other elements to steel (principally metals but also some non-metals) imparts special properties.
