SELECTION OF SEALING SURFACE AND GASKET MATERIAL OF FLANGE

Sealing surface and gasket material are very important for flanges. The sealing performance of flange connection is directly related to the type of sealing surface, so the shape of sealing surface should be reasonably chosen. Gasket is an important component of seal. Proper deformation and resilience of gasket are the necessary conditions for forming seal. The choice of gasket material should be decided by temperature, pressure and corrosion of medium. In the following, the specific selection methods will be introduced.

1. Type of Sealing Surface of Flange

Raised Surface

The surface is a smooth plane, and it can also be made into dense waterlines. The sealing surface has the advantages of simple structure, convenient processing and anti-corrosion lining. However, the contact area of the gasket on the sealing surface is large. Additionally, the gasket is easy to squeeze to both sides and not easy to compress when preparing for tightening.

Male and Female Surface

The sealing surface is composed of a convex surface and a concave surface. Placing gaskets on the concave surface can prevent the gaskets from being extruded, so it can be used in high pressure situations.

Tenon Groove Surface

The sealing surface is composed of tenons and grooves. The gasket is placed in the groove and will not be squeezed. The gasket can be narrower, so the bolt force required to press the gasket is correspondingly smaller. The bolt size should not be too large even when used at high pressure. Therefore, it is easier to obtain good sealing effect than the above two kinds of sealing surfaces. The disadvantage of the sealing surface is that its structure and manufacture are complex, and it is difficult to replace the gasket squeezed in the groove. In addition, tenon parts are easy to be damaged. Attention should be paid to them in the process of disassembly, assembly and transportation. Tenon groove sealing surface is suitable for inflammable, explosive and toxic media and high pressure occasions. When the pressure is not high, even if the diameter is large, it can be well sealed.

Full Plane and Ring Joint Surface

Full plane seals are suitable for low pressure situations. （PN≤1.6MPa）

The ring joint surface is mainly used for the long weld neck flange and lap joint flange, and the applicable pressure range is 6.3MPa≤PN≤25.0MPa.

Other Types

For the sealing of high pressure vessel and high pressure pipeline, conical sealing surface or trapezoidal groove sealing surface can be used. They are matched with spherical metal gaskets and elliptical or octagonal metal gaskets respectively. Sealing surface can be applied to high pressure occasions. However, it needs high dimensional accuracy and surface finish, and it is not easy to process.

 

2. Selection of Gasket Material of Flange

Medium Pressure Rubber Asbestos Board

There are two types. For one of these types, the sealing surface is smooth or concave-convex. The pressure range is ≤2.5MPa. The temperature range is ≤150℃. The applicable mediums include compressed air, inert gas and ammonia. For another type, the sealing surface is smooth. The pressure range is ≤1.6MPa. The temperature range is ≤300℃. The applicable mediums include steam and water.

Polytetrafluoroethylene Chloride

The sealing surface is smooth or concave-convex. The pressure range is ≤1.6MPa. The temperature range is ≤200℃. The applicable mediums include various oil and gas, solvents, petrochemical raw materials and products.

Oil-resistant Rubber Asbestos Board

There are two types. For both of them, the sealing surface is smooth or concave-convex. For one of these types, the suitable pressure is 2.5MPa. The temperature range is ≤200℃. The applicable mediums include various oil and gas, solvents, petrochemical raw materials and products. For another type, the pressure range is ≤1.6MPa. The temperature range is ≤50℃. The applicable medium is liquefied petroleum gas.

Metal Wound Gasket

Its materials include steel strip of 0Cr13 and special asbestos. There are three types. For the first one, the sealing surface is concave-convex. The pressure range is 4.0~6.4MPa. The temperature range is ≤60℃. The applicable medium is inert gas. For the second one, the sealing surface is smooth or concave-convex. The suitable pressure range is 2.5MPa. The temperature range is ≤450℃. The applicable mediums include various oil and gas, solvents, petrochemical raw materials and products. For the third one, the sealing surface is concave-convex. The suitable pressure range is 4.0 or 6.4MPa. The temperature range is ≤450℃. The applicable mediums include hydrogen vapor and mixture vapor of hydrogen and petroleum.

Metal Jacketed Gasket

Its materials include iron or aluminium sheet and special asbestos, or steel strip of 0Cr13 and special asbestos. There are three types. For all of them, the temperature range is ≤450℃ and the applicable mediums include hydrogen vapor and mixture vapor of hydrogen and petroleum. For the first one, the sealing surface is smooth or concave-convex. The suitable pressure is 2.5MPa. For the second one, the sealing surface is concave-convex. The suitable pressure is 4.0MPa. For the third one, the sealing surface is concave-convex. The suitable pressure is 6.4MPa.

Flexible Graphite Mixed Pad

Its materials include graphite and metal framework. There are three types. For all of them, the temperature range is ≤450℃. For the first one, the sealing surface is smooth or concave-convex. The suitable pressure is 2.5MPa. The applicable mediums include various oil and gas, solvents, petrochemical raw materials and products. For the second one, the sealing surface is concave-convex. The suitable pressure is 4.0MPa. The applicable mediums include hydrogen vapor and mixture vapor of hydrogen and petroleum. For the third one, the sealing surface is concave-convex. The suitable pressure is 6.4MPa. The applicable mediums include hydrogen vapor and mixture vapor of hydrogen and petroleum.

l Metal Ring Pad

Its materials include steel strip of 10, 0Cr13 and 0Cr19Ni9. The sealing surface is dovetail groove. The suitable pressure is 6.4MPa. The temperature range is ≤450℃. The applicable mediums include hydrogen vapor and mixture vapor of hydrogen and petroleum.