A gasket has one basic function - to create a positive seal between two relatively stationary parts. The thinnest gasket that will create this seal is the most efficient and will last the longest. It is also the most economical. To achieve a "tight joint" that will survive the rigors of service, these nine criteria must be met:
The gasket must be impervious to the substance handled in the system.
The gasket must have sufficient chemical resistance, both at its inner and outer areas in contact with the substance, to prevent impairment of its physical properties.
The gasket must not contaminate the substance being handled by the system.
The gasket must not promote corrosion of the flanges with which it comes in contact.
The gasket must be capable of withstanding the required bolt pressure without crushing or undergoing excessive plastic flow.
The gasket must be sufficiently deformable, without resorting to excessive thickness, to distribute the applied pressure evenly over the surfaces, compensating for normal irregularities.
Gasket material must be elastic enough to maintain an adequate portion of the applied load when joint movements are not fully eliminated by the joint design.
The gasket must develop sufficient friction in contact with the flange surface to resist excessive creep or extrusion.
The gasket must lend itself to easy installation and separation for ultimate removal.
Selecting the Right Gasket Material
Every gasket material available to the industry has certain inherent advantages that should be utilized to extend its range of applications. Limitations in a material can frequently be partly or wholly eliminated by using reinforcing inserts, combining with other materials, and varying the construction or type of joint the material must seal. Although mechanical factors are important to the design of the complete joint, primary selection of a gasket material is greatly influenced by two factors: temperature and type of substance to be contained.