The optimum gasket material would have the following characteristics. It would have the chemical resistance of PTFE, the heat resistance of graphite, the strength of steel, require zero seating stress such as soft rubber and be inexpensive. Obviously there is no known gasket material that has all these characteristics and each material has certain limitations that restrict its use. It is possible to overcome limitations partially by several methods such as including the use of reinforcing inserts, combining it with other matrials, varying the construction or density, or by designing the joint itself to overcome some of the limitations. Obviously, mechanical factors are important in the design of the joint but the primary selection of a gasket material is influenced by three factors.
1. the temperature of the fluid or gas to be contained
2. the pressure of the fluid or gas to be contained
3. the corrosive characteristics of the fluid or gas to be contained.
Some of the factors that can influence the corrosion resistance of a particular material at operating conditions are:
1. Concentration of the corrosive agent. (Full strength solutions are not necessarily more corrosive than those of dilute proportions and, of course, the reverse is also true.)
2. The purity of the corrosive agent. For example, dissolved oxygen in otherwise pure water may cause rapid oxidation of steam generation equipment at high temperatures.
3. The temperature of the corrosive agent. In general, higher temperatures of corrosive agents will accelerate corrosive attack.
As a consequence, it is often necessary to “field-test” materials for resistance to corrosion under normal operating conditions to determine if the material selected will have the required resistance to corrosion.
