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Types of Flanges and Selection of Flange Fasteners

Jun. 08, 2020



What is a flange?

The flange is the benchmark for determining the nominal pressure rating of the pipeline. There are many types of flanges. Different types of flanges have different sealing performances and different application occasions.

Flanges, gaskets, and bolts form a detachable connection structure in the pipeline, and the application in the pressure pipeline is very common and is also a very important form of connection. Usually, flange, bolt, and gasket together form a sealing pair, and the three work together to complement each other to ensure a good seal of the joint. Blind plates, 8-shaped blind plates, restrictive orifice plates, mixed orifice plates, etc. are closely related to Carbon Steel Blind Flange, gaskets and bolts, and are often used in conjunction with them.

What are the types of flanges and sealing surfaces?

Structure type: Pipe flange is divided into the following six basic types according to the connection method with the pipe: flat welding, butt welding method, socket welding, loose sleeve, threaded flange, and integral flange.

Flange structure

Sealing surface type:?Flange sealing surface has five types: flat surface, protrusion (boss) surface, concave and convex surface, tongue and groove surface, ring groove (ring connection) surface.

Flange sealing surface form

Selection of flange structure:

1) Flat welded flange: mostly used in the case of relatively mild media conditions, such as low-pressure non-purified compressed air and low-pressure circulating water, its advantage is that the price is cheaper;

2) Butt welding flange: the most commonly used one, it is connected to the pipe by butt welding, the quality of the welded joint is relatively good, and the neck of the flange uses a tapered transition to withstand harsh conditions;

3) Socket welding flange: commonly used in pipelines with PN≤10.0MPa and DN≤40;

4) Loose flange: It is often used when the medium temperature and pressure are not high and the medium is corrosive. When the medium is highly corrosive, the part of the flange that contacts the medium (flanging short section) is a high-grade material that is resistant to corrosion, such as stainless steel, and the outside is clamped by a flange ring of low-grade material, such as carbon steel. To achieve sealing;

5) Threaded flange: Threaded flange is a widely used flange structure in engineering design. It has the advantages of easy installation on-site and no need for welding. Threaded flanges are only suitable for inch pipe size series.

6) Integral flange: The flange is often integrated with equipment, pipes, fittings, valves, etc. This type is commonly used in equipment and valves.

Selection of flange sealing surface type:

1) All-plane sealing surface: It is often matched with the flat welding type to be suitable for the mild operating conditions (PNg1.0); it is often used in cast iron flanges or steel flanges connected with cast iron;

2) Boss surface sealing surface: It is the most widely used type. It is often used in conjunction with butt welding and socket welding. In the "American flange", it is commonly used in PN2.0, PN5.0, and some PN10. 0MPa pressure level; in "European flange" it is commonly used in PN1.6, PN2. 5MPa pressure level;

3) Concavo-convex sealing surface: It is often used in conjunction with butt welding and socket type. It is not commonly used in "American-style flanges", and is commonly used in "European-style flanges" in the PN4.0 and PN6.4 MPa grades. But it does not Easy to replace the gasket;

4) The sealing surface of the tongue and groove surface: the usage is the same as the concave and convex flange;

5) Ring groove sealing surface: often used with butt welding connection type (not with socket welding), mainly used in high temperature, high pressure, or both high working conditions. In "American flange", it is commonly used in PN10.0 (part), PN15.0, PN25.0, PN42.0MPa. Pressure rating. In "European flange", it is commonly used in PN10.0, PN16.0, PN25.0, PN32.0, PN42.0.

Selection of Carbon Steel Plate Flange

Flange fasteners refer to bolts, nuts, and washers connecting flanges. Half of the tightness of the flange during use depends on the tightening force of the bolt, so it is very important to choose the appropriate bolt. Let's learn some knowledge about the bolt.

Flange bolts are divided into thick bolts, semi-refined bolts, and fine bolts according to the manufacturing method. The thick bolts are not processed except for the threaded part, and the tensile strength of the bolts that can withstand is not high is "bolt diameter x bolt Length" means.

1) Single-sided bolt: When the tightening force is large, it is easy to break at the connection between the screw and the screw head, and cannot be used on medium and high-pressure flanges.

2) Double-sided bolts can be used for medium and high-pressure flanges to facilitate tightening from both sides.

The nuts used for flange bolts are generally hexagonal, which are divided into two types of AB. The surface of the A-shaped nut in contact with the connected parts is flat, and the round is only guided on the other side of the hexagon, and the two sides of the B-shaped nut All are round.

Key points for selection of flange bolts:

When selecting bolts for flange connection, the type, size, number and material grade of bolts should be determined.

1. The type, material, quantity, and size of bolts used in the flange mainly depend on the nominal diameter, nominal pressure and working temperature of the flange, and can be selected according to the corresponding flange technical standard.

2. The number of bolts is usually a multiple of 4, which is convenient for tightening by the cross method.

3. The length of the screw should be about 5mm after the flange is tightened, and no less than 2 screws.

4. The hardness of the nut should not exceed the hardness of the bolt.

5. Generally, no washer is provided. When the thread length on the screw is too short to tighten, a flat washer can be added, and the washer must not be superimposed. We are Carbon Steel Plate Flange Supplier, if you are interested in our products, please feel free to contact us.