Typical Types of Flanges Sealing Surfaces

The flange is a standard component extensively utilized in industrial pipe installations. Flanges are typically employed in pairs and feature three common sealing surface configurations: flat, concave-convex, and tongue-and-groove surfaces. Each type serves distinct purposes, which we'll explore together.

Flat flange

The sealing surface of this flange is a smooth plane, sometimes exhibiting a water line on its surface. Gaskets suitable for flat flanges include various non-metallic flat gaskets, clad gaskets, metal-clad gaskets, and spiral wound gaskets. Due to its straightforward structure and ease of processing, it's ideal for constructing anti-corrosion linings, making it suitable for low nominal pressure and temperature environments. However, because of the extensive contact area between this sealing surface and the gasket, a substantial pressing force is required, and the gasket should not be shifted during installation. After pre-tightening, the gasket may easily stretch or move sideways. For instance, gaskets with a low friction coefficient, such as polytetrafluoroethylene, should be avoided. Additionally, no water line is present on the sealing surface when using a spiral wound gasket for gasket reuse.

Concave-convex face flange.

The flange sealing surface consists of a concave and convex surface, with the gasket positioned on the concave surface. Various applicable gaskets include non-metallic flat gaskets, clad gaskets, metal-clad gaskets, spiral wound gaskets, metal corrugated gaskets, metal flat gaskets, and metal-toothed gaskets. Compared to a flat flange, gaskets in concave and convex flanges are less prone to extrusion, facilitating alignment during assembly. This flange type has a broader working pressure range and is suitable for applications with stringent sealing requirements. However, gasket extrusion may still occur with this sealing surface for equipment operating at high temperatures and with large sealing diameters, compromising the required sealing pressure between the gasket and the flange surface. Consequently, replacing the gasket material or using a tongue and groove face flange, along with a concave and convex face flange featuring two notches, may be necessary to address this issue.

Mortise and groove face flange.

The flange sealing surface features a tongue and groove surface, with the gasket positioned within the groove. Applicable gaskets include metal and non-metal flat, metal-wrapped, and wound gaskets. Like concave and convex face flanges, tongue and groove face flanges prevent gasket extrusion within the groove, ensuring even stress distribution across the gasket's smallest pressing area. The gasket is shielded from direct contact with the medium, so its susceptibility to medium corrosion and pressure penetration is minimal. This makes it suitable for use in environments with high pressure and those involving flammable, explosive, and toxic media, where stringent sealing requirements are essential. During installation, the sealing surface gasket provides excellent alignment, and replacing the gasket can be challenging due to the complexity of processing the sealing surface.

Flanges with other sealing surface types

Besides the three sealing surface types, trapezoidal groove sealing surfaces and specialized sealing surface configurations are available, particularly when incorporating O-rings and lens gaskets.

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