Sealing surface form and connection method of special-shaped flange

Posted by BAOWI STEEL MANUFACTURING CO.,LTD on May 9th, 2024

Special-shaped flange connection method

Special-shaped flange is a part that connects pipes to each other and is connected to the pipe end. There are holes in the flange, and the bolts tightly connect the two flanges. The flanges are sealed with gaskets. Flanged pipe fittings refer to pipe fittings with flanges (flanges or plates). It can be made of casting (picture is missing), or it can be made of threaded connection or welding. Special-shaped flanges are generally processed through special processing, such as drilling blind flanges or using lathes to make them according to flange standards. At present, in chemical piping, reducers are usually used for diameter reduction, which is simple, economical and convenient.

Large flanges are widely used as sealing and fastening connectors in large vessels in aerospace, petroleum, chemical and other fields. Although the issue of processing capacity is not taken into consideration, for large flanges, due to their large size and transportation reasons alone, it is impossible to process large flanges as a whole and must be processed in pieces. Normally, the large flange is always divided into several arc segments for processing. First, the rough edges are forged into square ones, and then cold-bent into arc segments. After annealing and stress-relieving heat treatment, they are formed into full circles and processed on a vertical lathe to the designed shape and size. Finally, they are transported to the construction site, and several arc segments are Welded together to form a complete flange and assembled with the pressure vessel.

The sealing surface form of special-shaped flange has the following aspects:

a. Concave-convex type

It consists of a concave surface and a convex surface. The gasket is placed in the concave surface.

Advantages: Easy to center and can prevent gasket extrusion.

Available in P<6.4Mpa, DN<800mm

b. Tongue and groove type

It consists of one tenon and one groove sealing surface. It has the advantages of good neutrality, low sealing preload pressure, the gasket is not easy to squeeze out, and is not washed away by the medium. It is used in places with high requirements for flammable and explosive sealing. The disadvantage is that it is difficult to replace and easy to damage.

c. Flat pressing surface

The surface of the pressing surface is flat or grooved.

Advantages: simple structure and convenient processing.

Disadvantages: The contact area is large, the required preload specific pressure is large, and the bolt load is large, so the flange and other parts are required to be high and heavy, the gasket is easy to squeeze out, and the sealing performance is poor. Operating pressure P<2.5Mpa, it cannot be used in toxic, flammable or explosive media.

d. Trapezoidal groove pressing surface

The bottom of the groove does not have a sealing effect. The inner and outer conical surfaces of the groove contact the gasket to form a trapezoidal seal, which is matched with a metal gasket with an elliptical or octagonal cross-section.

Special-shaped flanges are widely used in water conservancy, electricity, power stations, pipe fittings, industry, pressure vessels, etc.

e. Tapered pressing surface

Usually used for high-pressure sealing, its disadvantage is that it requires high dimensional accuracy and surface roughness. It must be matched with the lens gasket and is often used in high-pressure pipelines.

For the special-shaped flanges connected to the heads used on some large pressure vessels, in order to ensure the flatness and processing accuracy of the flange sealing surface, the above-mentioned flange processing technology is adopted to complete the flange body processing, and the flange and seal are After the heads are welded together, the flange sealing surface should be finished on a large vertical lathe.