How to specify a gasket
A five-step routine for turning a flange and a service condition into a complete, orderable gasket specification — and avoiding the omissions that cause leaks.
Define the flange and standard
Start with the flange standard, size and pressure class — for example ASME B16.5 Class 300, DIN/EN PN40, or a custom heat-exchanger face. This fixes the gasket's outside and inside diameter, bolt circle and the available seating area. Note the flange facing (raised face, flat face, ring-type joint) because it dictates the gasket family you can use.
Establish the service conditions
Record the design and operating temperature and pressure, including transients and upset cases, plus the media and its concentration. The worst-case combination — not the normal duty — drives material selection. Flag cyclic service: thermal cycling and pressure pulsation favour recovery-rich constructions such as spiral wound or kammprofile over plain sheet.
Select the material and construction
Use the material selection matrix to shortlist by temperature, pressure and media, then match the construction to the joint: spiral wound or metallic for critical high-class joints, CNAF or PTFE sheet for general duty, and full-PTFE for aggressive chemistry. Confirm chemical compatibility against the specific media rather than a family name.
Confirm dimensions, thickness and finish
Specify the gasket dimensions and thickness — thinner gaskets generally leak less and creep less, so use the thinnest that the flange finish and flatness allow. Check the flange surface finish; spiral-wound and graphite gaskets want a defined serrated finish, while soft-cut gaskets tolerate rougher faces. For RTJ joints, specify the ring number and material hardness.
Specify quantity, marking and documentation
State quantity, any marking or colour-coding for plant identification, and the documentation you need — material certificates, compliance statements (PED, FDA, fire-safe) and a recommended bolt torque sequence. Capturing this on the order avoids re-work and gives the assembly crew everything they need to make the joint up correctly.
Take it from reference to recommendation.
Send your service conditions — media, temperature, pressure and motion — and our engineers will specify the exact seal, material and construction for the duty.