Materials of construction in the fatty acid industry

The basic material of construction for the tankage and reactors that are used in the fatty chemical industry is one or another variant of the 300 series stainless steels. The use of these alloys essentially eliminates the possibility of iron and other metal contaminations which may either degrade the product or catalyze undesirable oxidation and other side reactions. With certain exceptions, it has been found that Type 304 stainless steel may be used in fatty chemical processing at temperatures up to 150 C and Type 316 stainless steel for tanks and vessels designed for use above that temperature. Where welding is involved in the fabrication of equipment designed for high temperature usage, it has been found necessary to use either a special low carbon stainless steel or an alloy which contains an extra ingredient that will inhibit carbide precipitation in the weld area since such precipitation usually results in a point of corrosion and ultimate failure. in the fabrication of pressure vessels, it is normal practice to use carbon steel plates of suitable thickness that have a minimal amount of the desired alloy bonded to the surface rather than fabricate of solid alloy. This not only reduces the cost of the vessel but adds greatly to the strength of the sheet since most high alloys lose tensile strength rapidly as temperatures are increased while carbon steel retains strength until very high temperatures are reached. In addition to the 300 series stainless steels, certain highly specialized alloys such as Inconel 825, Carpenter 20 Cb, or Monel are frequently used for extreme acid conditions. The lower cost of aluminum as compared to a high alloy makes it attractive for storage tanks but it can be used only when materials contain no moisture, since even traces of water accelerate the rate of corrosion and rapidly render the tank unusable. New materials on the scene are fiberglass-polyester tankage and applied linings of the phenolic or the epon-epoxy type. These materials do not have a wide application, but where their use is possible, it is a lower cost answer to the problem of iron contamination.