Selection of Gasket
Proper selection of gasket depends upon following factors.
- Compatibility of the gasket material with the fluid.
- Ability to withstand the pressure-temperature of the system.
- The service life of the gasket
It is important to understand the requirements of particular applications before making gasket selection. Gaskets must maintain a seal for an acceptable period against all the operational forces involved. There are eight important properties which any gasket must possess to achieve this –
- Impermeability– The gasket should not be porous to the fluid being sealed.
- Compressibility– The gasket should compress into the imperfections on the flange sealing faces to create the initial seal.
- Stress relaxation (creep resistance)– The gasket should not show significant flow (creep) when subjected to load and temperature. Such flow will allow the bolts to relax, reduce gasket surface stress and cause leakage.
- Resilience– Although normally stable, flanges do in fact move slightly relative to one another under the influence of cycling temperature and pressure. The gasket should be capable of compensating for such movements.
- Chemical resistance – The gasket should withstand chemical attack from the process medium being handled. Likewise, the gasket material itself must not contaminate the process medium.
- Temperature resistance– The gasket should be able to withstand the effects of the maximum and minimum temperatures within the process and the external atmospheric temperatures.
- Anti-stick– The gasket has to be easily removable after use.
Anti-corrosion– The gasket must not cause corrosion of the flange faces.
Types of Gaskets
There are three types of gaskets used in process piping.
Metallic – Ring Gasket
Compressed Non-Asbestos Fibre Gasket (CNAF)
Oval Ring Gasket
Spiral Wound Gaskets
Octagonal Ring Gasket
Metal Jacketed Gasket