Flange sealing surfaces play a critical role in ensuring leak-proof connections in pipelines, pressure vessels, and industrial equipment. Selecting the right sealing surface type is essential for maintaining system integrity under varying pressures, temperatures, and corrosive conditions.Common standards such as ASME B16.5 and EN 1092-1 define various types of sealing surfaces, each suited for specific applications and pressure classes.This article mainly introduces the type of flange sealing surfaces and their applicable environments to help you make a better choice.
Flange sealing surfaces are mainly divided into five types, including flat face (FF), raised face (RF), ring joint face (RTJ), male-female face (MFM), and tongue-groove face (TG).
Flat Face (FF)
A flat face flange has a smooth sealing surface and is typically used with full-face gaskets. It is suitable for low-pressure applications (Class 150 or PN10/PN16) and is often found in cast iron or fiberglass piping systems.
Advantages and Disadvantages
| Advantages | Disadvantages |
| Simple manufacturing and cost-effective. | Poor performance under high pressure. |
| Suitable for soft gaskets (e.g., rubber, PTFE). | Gaskets may extrude under excessive bolt load. |
Applications
•Water treatment systems.
•Low-pressure HVAC pipelines.
•Non-toxic, non-hazardous fluids.
Raised Face (RF)
The raised face flange is the most common type, featuring a small raised area where the gasket is placed. This design concentrates the bolt load over a smaller area, improving gasket sealing efficiency.
Advantages and Disadvantages
| Advantages | Disadvantages |
| Compatible with various gaskets (spiral wound, metal jacketed). | Gasket blowout risk under extreme pressure cycling. |
| Preload is concentrated on a smaller area, improving sealing performance. | Performance depends on maintaining the correct surface roughness. |
Applications
•Petrochemical plants.
•Power generation (steam, water, oil pipelines).
•General industrial fluid transfer.
Ring Joint Face(RTJ):
RTJ flanges feature a machined groove into which a metal ring gasket is fitted. This type is used for high-pressure and high-temperature services. The metal-to-metal seal ensures excellent performance under extreme conditions.
Advantages and Disadvantages：
| Advantages | Disadvantages |
| Provides excellent sealing for Class 600–2500 flanges. | Requires precision-machined grooves and metal ring gaskets. |
| Ensures sealing integrity even when gasket material degrades. | Only compatible with specific ring-type gaskets. |
Applications：
•Oil & gas wellheads.
•Hydroprocessing units (500+°C, 100+ bar).
Tongue-Groove (TG)
In this design, one flange face has a raised ring (tongue) and the other has a matching recess (groove). The gasket fits into the groove, providing precise alignment and preventing gasket blowout. This type is common in heat exchangers and specialty piping.
Advantages and Disadvantages
| Advantages | Disadvantages |
| Accurate gasket positioning and easy installation. | Must be used in pairs, cannot be mixed. |
| Reliable sealing to prevent gasket blowout. | High processing precision, increased cost. |
Applications
•Pump and valve interfaces
•Chemical pipeline systems
•Oil and gas pipelines
Male-Female Face(MFM)
Similar to tongue – groove, male and female faces have matching raised and recessed areas, but the dimensions are different. They allow the use of composite gaskets and provide better sealing in certain high-integrity joints.
Advantages and Disadvantages
| Advantages | Disadvantages |
| Secure sealing to prevent leakage. | Must be used in pairs; cannot be mixed and matched. |
| Composite gasket for stronger sealing. | High processing costs; complicated repairs after damage. |
Applications
•Chemical and petrochemical pipelines
•High-pressure water and steam lines
•Heat exchangers and pressure vessels
Conclusion
The types of flange sealing surface are directly related to the safety and reliability of piping systems. In practical engineering applications, it is essential to select the most appropriate sealing surface type based on operating conditions including medium properties, working pressure, and temperature.
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