Flanged joints allow pipe connections to be taken apart. To stop the joint from leaking, a gasket is always clamped between the surfaces of the two mating flanges. Some flanges are flat across the sealing surface while others have a raised annular region around the bore.
This blog discusses the advantages of raised face flanges and what this means for the gasket material. We’ll also cover some pros and cons of the two flange types.
Sealing Flanges
A gasket always goes between two flanges to prevent leaks. Tightening the bolts closes the gap between the flanges and compresses the gasket material. With a flat face flange, the gasket is the same size as the flange and has holes for the bolts to pass through.
Raised Face Flanges
When two raised face flanges are brought together, the raised areas meet first, leaving a gap between the flanges at the periphery. Accordingly, the gasket should have the same inner and outer diameter as the raised face.
The raised face has a smaller area than the full surface of the flange. If the same fastening torque is applied, the load per unit area is much higher with the raised face design.
Higher unit load means more gasket material compression. This allows the use of harder gaskets that are better able to resist internal pipe pressure.
Applications for Raised Face Flanges
This design is used in higher-pressure applications and where it’s vital to prevent any trace of a leak. Chemical processing and oil and gas are two industries where raised face flanges are very common.
Pros and Cons of Raised Faces
- Ensure sealing against high pressure
- Require less gasket material
- Hard to position gasket without intruding on the fluid flow – gaskets for flat flanges are located by the bolts
- Overtorquing bolts can bend the flange and open up the joint
Gasket Material Implications
Use softer material with flat flanges. On raised flanges the gasket must be harder to resist higher loads. Contact us for advice on the best gasket material for your application.
