Pick the flange class
Use the B16.5 pressure-temperature rating table for the material group (1.1, 2.1, etc.). The selected class must envelope the design pressure at design temperature, including upset and relief cases.
Pick the facing
- Raised Face (RF): default for most hydrocarbon and utility service
- Ring Type Joint (RTJ): high pressure, high temperature, sour service (typ. ≥ Class 900)
- Flat Face (FF): mating to cast-iron equipment to avoid bending the flange
Pick the gasket
- Spiral wound with inner+outer ring (CGI): general process duty
- Kammprofile: tight sealing with low bolt load, good for thermal cycling
- Soft-cut sheet: low pressure utility only — never on hydrocarbons
- Octagonal RTJ: matches RTJ flanges, oval is legacy only
Bolting note
Stud and nut grade must match flange class and service temperature (e.g. ASTM A193 B7 / A194 2H standard, B7M for sour). Confirm with project piping spec.
Key references
- · ASME B16.5
- · ASME B16.20
- · ASME PCC-1
Use of this content
This page is a decision-support and training reference. It is not a substitute for the governing code, the project specification, or the judgement of a responsible engineer. Always validate against the current edition of the applicable standard before use on live engineering work.