Overview
A raised face flange has a gasket seating area raised above the surrounding bolting plane. This geometry concentrates the bolting load on a defined gasket contact area. The facing dimensions, surface finish, gasket type, material, rating, and mating component must be selected as one joint system.
Why It Matters for Pipe Components
A flange can meet outside dimensions and still be unsuitable if its facing does not match the gasket or mating flange. Facing damage, coating, wrong gasket dimensions, and incorrect bolt loading can cause leakage.
Raised face is a geometric description, not a complete specification. The inquiry must still state the dimensional standard, size, class or PN, material, and required surface finish.
Methods, Parameters, or Process
Control the joint through these parameters.
| Parameter | Selection question |
|---|---|
| Standard | Which document defines the facing dimensions? |
| Rating | What pressure class or PN is approved? |
| Facing height and diameter | Are they correct for the size and rating? |
| Surface finish | What finish range or machining pattern does the project require? |
| Gasket | Is it dimensionally and chemically compatible? |
| Bolting | Does the material and tightening procedure suit the joint? |
| Mating face | Is it also approved for the same gasket arrangement? |
ASME B16.20 addresses several metallic gasket types dimensionally suitable for referenced flange standards. ASME B16.21 addresses nonmetallic flat gaskets. Gasket selection still depends on service conditions and the engineering specification.
Verification note: never copy a facing dimension or finish value from an unrelated size, class, standard, or old drawing. Verify the project-required edition.
Supplier and Inspection Checklist
- Verify facing type on the purchase order, drawing, and product marking.
- Measure raised-face diameter and height when required by the inspection plan.
- Inspect the seating area under suitable lighting.
- Reject or repair only under an approved procedure when scratches, dents, chatter, corrosion, or coating exceed acceptance criteria.
- Confirm gasket dimensions and material.
- Check flange flatness and parallelism where specified.
- Keep protective covers in place until assembly.
- Use the approved bolting and tightening procedure.
Application to Pipe Fittings, Valves, and Flanges
Raised face flanges are common on piping, valves, pumps, heat exchangers, and pressure equipment. They may be supplied as weld neck, slip-on, blind, socket weld, threaded, or other flange types.
For cast equipment or flat-face connections, do not assume an RF-to-FF joint is acceptable. The equipment manufacturer and piping engineer should review the joint arrangement, gasket, and bolting loads.
FAQ
Is RF the same as a pressure class?
No. RF describes the facing. Class or PN describes the rating system. Both must be stated.
Can two raised face flanges use any gasket?
No. Gasket dimensions, construction, material, pressure-temperature capability, and surface-finish compatibility must be checked.
Should the raised face be painted?
The gasket seating surface is normally protected rather than coated with a finish that interferes with sealing. Follow the project coating specification.
Can a raised face flange mate with a flat face flange?
Only after an engineering review confirms the arrangement. Similar bolt patterns do not establish joint suitability.
Next Steps
Provide the complete flange type, standard, size, class or PN, material, RF requirement, surface-finish requirement, gasket basis, and inspection level. Ask for close-up facing photographs when remote inspection is used.
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