Materials Selection – Cost
The objective is to select the most economical material that will reliably satisfy the design life of the vessel. This is often achieved by selecting carbon or low alloy steels in preference to stainless and highly alloyed materials and by specifying conservative corrosion allowances. See the discussion of design life below.
When stainless steel or a more highly alloyed material is required, it is often preferable to use a carbon or low alloy steel clad with a thin layer of the high alloy material. Clad plate is usually less expensive than solid alloy plate unless the thickness of the vessel is less than 3/8 to 1/2 inch. Clad plate is also preferred because it is less likely to develop through-wall stress corrosion cracks than solid alloy. Some of the commonly used cladding materials, such as Types 405 and 410 stainless steel, are not practical to fabricate for solid wall construction because of the difficulty in making reliable welds.
For some aqueous services, up to about 200°F, nonmetallic thin film coatings can be applied to reduce corrosion rates and the need for alloy material.
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