Materials of construction selection

A compromise among properties, cost, and manufacturing process generally determines the material of construction. Selecting a plastic is very similar to selecting a metal. Even within one class, plastics differ because of varying formulations, just as steel compositions vary (tool steel, stainless steel, etc.). There are, of course, products for which no plastics is satisfactory, and the interests of the producer and consumer alike are best served by using some other material. 

Materials of construction selected should be compatible with control measures such as sanitizing, cleaning, and passivation. Materials selected should be able to handle elevated operating, sanitization temperature, and chemicals or additives to be used to clean, control, or sanitize the system. 

After completion of the research phase, it is usually found that further demonstration of the viability of the process and more design data is needed, but under conditions that will more closely resemble the final plant. It may also be required to obtain some product for market research. In this case, the development engineer will plan the development program and design the pilot plant. Whenever possible the equipment selected will be smaller versions of the plant size equipment, using the same materials of construction selected for the plant. 

Rupture disk devices installed on compressed gas cylinders may either be an integral part of the cylinder valve assembly or may be installed on the cylinder as an independent attachment. To minimize corrosion, the materials of construction selected must be compatible with the contents of the cylinder, as well as the cylinder valve materials with which the rupture disk device comes in contact. 

To obtain an estimate of the capital cost of a chemical plant, the costs associated with major plant equipment must be known. For the presentation in this chapter, it is assumed that a PFD for the process is available. This PFD is similar to the one discussed in detail in Chapter 1, which included material and energy balances with each major piece of equipment identified, materials of construction selected, and the size/capacity roughly estimated from conditions on the PFD. Additional PFDs and equipment summary tables are given for several processes in Appendix B. 

The design objectives for a vacuum-insulated transfer line are similar to those for a conventional vacuum-insulated dewar. A vacuum-insulated line consists of an inner pipe which carries the cryogenic fluid and an outer concentric pipe which contains the vacuum. The inner line should be made as thin as possible to minimize cooldown losses, and the material of construction selected should be compatible with the cryogen. The outer piping, which may enclose an evacuated powder, MLI, or simply high vacuum, must resist the compression due to atmospheric pressure. The ASA Code for Pressure Piping provides design equations for both the inner and outer lines. The thickness of the inner line is determined by... 

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