[Valve knowledge] 7 types of commonly used flange sealing surfaces

There are basically seven types of flange sealing surfaces: full plane FF, raised surface RF, concave surface FM, convex surface M, tenon surface T, groove surface G, ring connection surface RTJ (RJ), etc., according to the working conditions, medium, pressure, and specifications. Due to different conditions such as temperature and temperature, the types selected are also different. Let’s get to know these commonly used types of flange sealing surfaces!

1. FF-full flat sealing surface

Flat Face Full Face type sealing surface is completely flat, suitable for situations where the pressure is not high and the medium is non-toxic.

2. RF-raised sealing surface

The Raised Face type sealing surface is the most widely used among several types. It is the most commonly used one. International standards, European systems and domestic standards are all fixed heights. However, in American standard flanges, it should be noted that the height of high pressure will increase the sealing surface. Depending on the height, there are many types of gaskets used.

Gaskets suitable for raised-face sealing surface flanges include various non-metallic flat gaskets, coated gaskets; metal-coated gaskets; wound gaskets (including with outer rings or with inner and outer rings), etc.

3. M/FM-concave and convex sealing surfaces

The two types of sealing surfaces, Male Face and Female Face, are a pair, one female and one male, and must be used together. They facilitate centering during installation and prevent the gasket from being extruded. Suitable for high pressure situations.

The sealing gaskets suitable for concave and convex sealing surfaces include: various non-metallic flat gaskets, coated gaskets; metal-coated gaskets; basic type or inner ring-type winding sheets, etc.

4. T/G-tongue and groove connection sealing surface

Tongue Face and Groove Face are similar to concave and convex surfaces. They are also a male and a female matching sealing surface type, and they are also used in pairs. The gasket is located in the annular groove and is limited by the metal walls on both sides, which can prevent the gasket from being squeezed into the pipe due to pressure deformation. Since the gasket is not in direct contact with the fluid medium in the pipe, it is less susceptible to erosion or corrosion by the fluid medium, so it can be used in situations with strict sealing requirements such as high pressure, flammable and explosive media, and toxic media. This kind of sealing surface gasket has good installation and neutrality, but it is difficult to process the sealing surface. It is easy to damage the sealing surface when replacing the gasket. Moreover, the flange must be separated axially during installation and disassembly, so this should be taken into consideration when designing the pipeline. It is possible to separate the flange axially.

Gaskets suitable for tongue and groove sealing surfaces include: various metal and non-metal flat gaskets, metal-clad gaskets and basic spiral wound gaskets.

5. RTJ (RJ)-ring connection sealing surface

The ring joint face flange is also a narrow-face flange, and a ring-shaped trapezoidal groove is opened on the protruding surface of the flange as the flange sealing surface. This method is the same as the tongue-and-groove surface flange. The flange must be separated axially during installation and disassembly. Therefore, the possibility of axially separating the flange must be taken into consideration when designing the pipeline.

This sealing surface is specially designed to cooperate with a solid metal gasket processed from metal material into an octagonal or oval shape to achieve a sealed connection. Since the metal ring gasket can be based on the inherent characteristics of various metals, this sealing surface has good sealing performance and is not too strict in installation requirements. It is suitable for high temperature and high pressure working conditions, but the processing accuracy of the sealing surface is high.