July 2015

Dealing with Expansion and Contraction of Flange Gaskets

A gasketed joint is rarely static. Changes in temperature can cause mating flanges to move apart or closer together, creating a variable gap that the gasket has to fill. That’s why understanding the influence of temperature helps when selecting the gasket material for flange gaskets.

Flanged joint dynamics

In service a gasket is compressed between two flanges. Sufficient load must then be applied to hold the joint closed, regardless of how conditions change.

Fluid moving through the pipe creates hydrostatic end thrust that opens up the joint. Internal pressure also creates side loading on the gasket, trying to extrude it out between the flanges. And changes in temperature result in expansion and contraction of both the piping and the fastening bolts.

Temperature influences

Temperature changes have two sources: the temperature of the fluid being transported, and the environment through which the pipe runs. In a continuous process media temperature may vary very little, but a pipe exposed to hot desert sun could experience a range of 80 deg F or more over a twelve hour period.

The influence of media temperature changes, (perhaps at start-up or shut-down,) will depend on the details of the pipework installation. However, most likely higher temps will act to close the gap between mating flanges.

Higher temperatures will make the flange bolts grow, so reducing the clamping force. Tightening to recommended torque levels creates some elongation that compensates for expansion, which is why proper jointing procedures should always be followed.

Of lesser importance, gasket materials and piping usually have different coefficients of thermal expansion. This may cause differential movement between flange and gasket which could, in marginal situations, open up a leak path.

Material selection impact

The ideal gasket possesses both good compressibility and good recovery or resilience, enabling it to maintain a seal as the gap between flanges changes and the compressive load varies. Natural rubber is one of the most effective materials, but is not always suitable.

The prudent approach is to discuss the application with the gasket vendor, being sure to make them aware of the various temperatures to which the joint will be exposed.  Contact Hennig Gasket & Seals today to discuss your flange gasket application.