The facing is the part of the flange that seals against the gasket. Two flanges of the same size and class will not seal if their facings, finishes or gaskets do not match. This page explains the three common facings — raised face, ring type joint and flat face — and the details procurement should confirm on every flange order.
The Three Common Facings at a Glance
| Facing | What it is | Typical gasket | Typical use |
|---|---|---|---|
| Raised face (RF) | A raised ring around the bore that concentrates gasket stress | Spiral wound (ASME B16.20) or sheet gasket (ASME B16.21) | The most common facing for process piping in Class 150–2500 |
| Ring type joint (RTJ) | A machined groove that holds a solid metal ring gasket | Metal ring gasket — R, RX or BX type (ASME B16.20 / API 6A) | High pressure and high temperature service, often Class 600 and above |
| Flat face (FF) | The gasket surface is level across the full flange face | Full-face sheet gasket covering the bolt circle | Low-pressure service and mating with cast iron, plastic or FRP flanges |
Raised Face (RF): Height and Finish
In ASME B16.5, the raised face height is 1.6 mm (1/16") for Class 150 and 300 and 6.4 mm (1/4") for Class 400 and above. Check how the flange thickness on the drawing or datasheet is quoted, because the two cases are treated differently in the dimensional tables. The gasket surface normally has a serrated (phonographic) finish; state the required roughness range if your gasket supplier or piping specification calls for one.
Ring Type Joint (RTJ): Groove and Ring
- Ring number: the groove dimensions and ring number depend on size and pressure class; quote the ring number from the standard, not just "RTJ".
- Ring type: oval or octagonal R-type, pressure-energised RX, or BX for API 6A flanges.
- Hardness: the ring should be softer than the groove so that the ring deforms, not the flange. Confirm the ring material and hardness against the flange material.
- Groove finish: the groove surface is smooth-machined and must be protected in transit.
Flat Face (FF): When It Is Required
Flat face flanges are used where the mating flange is cast iron, ductile iron, plastic or FRP. Bolting a raised face flange to one of these concentrates the load inside the bolt circle and can crack or distort the weaker flange. The usual rule is to mate a flat face with a flat face and use a full-face gasket. If a steel valve or nozzle with a raised face must connect to an FF flange, the raised face is often machined off — confirm this with the engineer before ordering.
Other Facings
Tongue-and-groove and male-and-female facings are used where the gasket must be confined, for example on some heat exchangers. They are ordered as matched pairs, so the RFQ must state which half (tongue or groove, male or female) is required for each flange.
What to Confirm on the Order
- Facing type: RF, RTJ, FF, or tongue/groove or male/female with the half specified
- Facing finish requirement, if different from the standard
- For RTJ: ring number, ring type and ring material / hardness
- The facing of the mating flange, valve or equipment nozzle
- Gasket type and standard, so facing and gasket are compatible
- Face protection for transport
For the full list of flange order details, see our flange RFQ worked example, or browse our flanges by material.
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