Introduction to Materials Selection

From a purely technical standpoint, an obvious answer to corrosion problems would be to use more resistant materials. In many cases, this approach is an economical alternative to other corrosion control methods. Corrosion resistance is not the only property to be considered in making materials selection but it is of major importance in the chemical process industries.

The choice of a material is the result of several compromises. For example, the technical appraisal of an alloy will generally be a compromise between corrosion resistance and some other properties such as strength and weldability. And the final selection will be a compromise between technical competence and economic factors. In specifying a material, the task usually requires three stages:

The materials selection process is also influenced by the fact that the materials are either considered for the construction of a new system, or for the modification or repairs in an existing facility. For the construction of new equipment, the selection procedure should begin as soon as possible and before the design is finalized.

The optimum design for corrosion resistance will often vary with the material used. In a repair application, there is usually less opportunity for redesign, and the principal decision factors will be centered on delivery time and ease of fabrication in the field. It is also advisable to estimate the remaining life of the equipment so that the repair is not over-designed in terms of the corrosion allowance.