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Flange type introduction and flange connection design

Types of flanges

(1) flange of pressure vessel is divided into general flange and reverse flange according to overall structure.
(2) according to the layout of gaskets, it can be divided into two categories: narrow flange and wide flange.

  1. A) Narrow flange refers to the gasket contact surface located in the flange bolt hole around the circumference of the flange, is the most widely used flange.
  2. B) wide flange is the flange on the two sides of the center of the flange. Generally only for low pressure occasions.

(3) According to the integrity of each part of the flange, it can be divided into loose flange, integral flange and arbitrary flange. Its characteristics are:

  • A) loose flange: flange that fails to effectively connect the container or nozzle. In the calculation, it is considered that the cylinder does not bear the action of flange moment with the flange ring, and the flange moment is completely borne by the flange ring itself.
  • B) integral flange: finger ring, neck and cylinder three can be effectively connected into a whole flange. The three part bears the role of flange torque.
  • C) arbitrary flange: flange with the overall degree between them. Although the cylinder and the flange ring can not form a whole structure, but as a structural element, they can bear the effect of flange torque together. Flat welding flange belongs to such flange.

(4) According to the connection between flange and cylinder, it is divided into looper flange, thread connection flange, socket welding flange, flat welding flange and butt welding flange.
(5) The pressure vessel flange standard divides the flange into three kinds: A-type flat welding flange, B-type flat welding flange and long neck butt welding flange.

Flange connection design

Flange design refers to the design of flange connection, including three parts: gasket design, bolt (stud) design and flange body design. The most important method of flange design is the famous Waters method, GB 150. The design points are as follows:

  • (1) Gasket design

This is the basis of flange connection design, according to the design conditions and the use of media, should select the appropriate gasket type, material, determine the size of gasket (inner diameter, outer diameter, thickness), and then calculate the gasket in the pre-tightening state and operating state of the pressure.

  • (2) Bolt / stud design

According to the design conditions, the bolt area needed to meet the pre-tightening and operating conditions of the gasket is calculated. The actual bolt area should not be less than the calculated area.
The principle of bolt design is to determine the smaller central diameter of bolts. It is possible to meet the requirements by selecting the appropriate bolt specifications and quantities.

  • (3) Flange design

Flange design is divided into two parts: internal pressure and external pressure. Flanges subjected to external pressure can be designed according to the calculation method of flanges subjected to internal pressure, but the calculation of flange operating torque is slightly different.
The calculation method of narrow flange is divided into two types: loose flange calculation and integral flange calculation. Arbitrary flange is usually calculated by integral flange, which can be simplified to loose flange under certain conditions.
Loose flange calculation is relatively simple, flange thickness can be calculated at one time. The design of the whole flange should be completed by assuming that the structural size of each part is calculated repeatedly.
For the whole flange, first, according to the structural conditions of the equipment, suppose the dimensions of the flange cone neck and the flange ring. The torque and stress generated by the flange are calculated. When the difference between each stress and the corresponding allowable stress is large, the original size of the flange should be adjusted, and the above calculation should be repeated until all the stresses are less than their allowable stress and the difference is not too big.
The calculation of wide flange is irrespective of form, and is calculated according to the simplified model of “simply supported beam”.
Source: China Flanges Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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