In brief
A flat gasket is a flat, static seal that is compressed between two flat surfaces, such as pipe flanges or housing covers.
Contents
What is Flat gasket?
Flat gaskets seal stationary joints in which the components do not move relative to each other during operation. The bolt force compresses the gasket so strongly that it fills irregularities in the sealing surfaces and the medium cannot pass through. The main applications are pipe flanges, pump and valve housings, vessel covers and gearbox housings.
Depending on pressure, temperature and medium, bonded fibre materials, expanded graphite, PTFE, elastomers or semi-metallic gaskets such as kammprofile and spiral wound gaskets are used. For non-metallic flat gaskets on PN-designated flanges, EN 1514-1 specifies the dimensions. Key parameters are inside and outside diameter, thickness, bolt pattern, material, permissible surface pressure and temperature and media resistance.
Leaks are usually caused by insufficient or uneven surface pressure, gasket relaxation, reused gaskets, damaged sealing surfaces or a material unsuitable for the medium and temperature. Flange gaskets are therefore replaced every time the joint is dismantled. For joints with higher requirements, assembly is often carried out and documented with a defined tightening torque and a specified tightening sequence so that the gasket is compressed evenly.
In practice: maintenance and procurement
For flange gaskets, nominal size, nominal pressure, gasket type and material are usually sufficient; for special shapes, a drawing or template with all dimensions is required. Medium, pressure and temperature should always be stated so that the material can be checked; the bolt tightening torque belongs in the assembly instructions.
Synonyms and abbreviations: flange gasket · sealing washer · static seal
Frequently asked questions
What information is needed for a flange gasket?
For standard flanges, the nominal size, nominal pressure or pressure class, flange type and gasket material are sufficient, for example DN 100 PN 16 with a ring or full-face gasket. For special parts, the inside and outside diameter, thickness, pitch circle and the number and diameter of the holes are needed. Medium, pressure and temperature should also be stated.
Can a flat gasket be reused?
As a rule, no. A flat gasket is permanently deformed when tightened and adapts to the sealing surfaces. Once loosened, it lacks the recovery needed to seal again when retightened. A new gasket is therefore fitted every time the joint is dismantled, even if the old one still looks undamaged.
What is the difference between a ring gasket and a full-face gasket?
A ring gasket lies only inside the bolt circle between the flange faces, with the bolts running outside it. A full-face gasket covers the entire flange face and has holes for the bolts. Which type is needed depends on the flange design and the construction; the two must not be interchanged without checking.
Which material is suitable for flat gaskets at high temperatures?
At high temperatures, graphite gaskets, mica materials or semi-metallic gaskets such as kammprofile and spiral wound gaskets are often used. Which variant is suitable also depends on pressure, medium and flange design. The limit values are specific to the material and manufacturer and should be checked against the data sheets.