Procedure for Material Selection

The first step in material selection is a thorough review of the corrosive environment, process parameters, and equipment operating conditions, including temperature, pressure, flow rates, liquid versus gaseous phase, aqueous verses anhydrous phase, continuous verses intermittent operation, media used for cooling or heating, etc. 

In the second step, the corrosion rate (CR) should be predicted and the corrosion allowances (CA) determined for the service life of the equipment and its various components in carbon steel. 

For the third step, if the determined total wall thickness (mechanical + CA) is not acceptable, great effort should be exercised to select and evaluate a suitable corrosion prevention measure to lower the required corrosion allowance. Some of these measures cannot withstand the process conditions, e.g. temperatures too high for polymer lining, no facilities for chemical injection, no continuous electrolyte for cathodic protection, and so on. 

In the fourth step, if the preventive measures cannot reduce the corrosion rates of carbon steel to an acceptable level, then a more corrosion-resistant material should be considered. Many materials can be immediately excluded because of service conditions. 

The fifth step, if required, is to conduct standard test methods to evaluate the nominated materials in a simulated environment. These tests give assurance to the right selection. 

---

This section will discuss problems that can complicate the selection procedure. Such problems include the variability of materials selection criteria, conflicting project objectives such as minimizing capital cost, and mandatory criteria such as those in governing engineering codes. Other topics discussed include organization of the information needed for the materials selection process, a procedure for materials selection, and the use of a materials selection diagram. 

Though material selection is based upon material properties, it is advisable to follow international standards, which provide a systematic procedure for material selection [2,3] ... 

---