What influences the behavior of the flanged joints?

Gaskets are basic elements for flanged joints, with the purpose to create and maintain a static seal between two imperfect surfaces of a mechanical system, designed to contain a wide range of liquids and gases in different operating conditions, with varied pressure and temperature ratings.

The gasket material must fill the imperfections of the flange faces and the gap between them and guarantee tightness under operating conditions including extremes of temperature and pressure.  In most cases, the gasket provides tightness by external forces deforming the gasket material.  Gasket performance is influenced by many factors, each of them influencing gasket choice.

• The internal pressure: Once the internal pressure occurs, the initial gasket compression is reduced by the occurrence of the blowout pressure acting against the gasket and the hydrostatic end force tending to depart the flanges. This is why an additional preload should be considered.
• The flange load represents the compression force of the gasket creating the seal, the effective pressure resulting from the bolt loading.
• Temperature is a key factor and must be carefully considered as it affects all joint components – including bolt elongation, creep relaxation of the gasket material or thermal degradation. Both the ambient temperature and the process temperature must be taken into account.  The higher the operating temperature, the more problems that may arise and more critical.  Pay attention to the different expansion coefficients of the joint elements, as it can lead to the appearance of forces that affect the optimal operation of the gasket.
• Fluid: The media being sealed is usually a liquid or a gas, the gas being harder to seal than a liquid. The effect of the temperature on many fluids causes them to become more aggressive.  Therefore, a fluid that can be sealed at ambient temperature, may adversely affect the gasket at a higher temperature.  The gasket material must be resistant to corrosive attack from the fluid.
• General characteristics: flange type, sealing surface type, flange surfaces, flange material, fastener material, the number of bolts, etc.
• Gasket type has, also, an extremely important role. Choosing the wrong type may result in joint failure once the system has started.  The steps to be followed and the factors taken into account in choosing the correct gasket have been detailed in a previous article.  Always follow the manufacturer recommendations!
• Gasket parameters and the assembly procedure. Both gasket parameters and the assembly procedure play a crucial role in the proper functioning of the joint.  Due to the great importance and the fact that for many users these concepts are relatively new, the gasket parameters and the assembly procedure will be analyzed in detail in the following articles.