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Piping Flange Fundamentals
10 = 20 / 2
The relationship between pressure, force, and area, can be briefly summarised:
Decreasing the sealing face area leads to a decrease in the force required to create a given amount of pressure.
Increasing the sealing face area leads to an increase in the force required to create a given amount of pressure.
The amount of force that can be applied to a flange assembly is limited because of problems relating to physical strength
(nuts are often hand-tightened), gasket blow-out4, and stripping5 of the flange bolt threads; but these problems can be
overcome if the size of the sealing face is reduced. The type and size of the sealing face used will be dictated by relevant
piping standards once the temperature and pressure rating of the flange is known.
Based on what has been discussed in this section, it can be determined that flanges required to seal at higher pressures,
have smaller sealing faces. It is possible for a viewer to guess the pressure at which a system operates by visually inspecting
the flange sealing faces e.g. large flange sealing faces indicate low pressure systems.
4 Refers to the expulsion of the gasket from the sealing face due to pressure; this usually occurs due to overtightening of the flange during assembly.
5 Refers to the removing of the threads from the stud or bolt; the result is a spherical piece with no screw threads.