Type A flat welding flange is directly welded to the vessel. The welding size is small or welding is not grooved. It cannot guarantee that the flange and the container are stressed at the same time. The strength calculation refers to the loose flange; the B flat welding flange usually has a thick section. The short cylinder. The welding quality of the flange and the short cylinder is reliable, and it can ensure that the flange and the container are stressed at the same time. The strength calculation can be considered according to the integral flange. The B-type flat welding flange is widely used for the connection of medium and low pressure containers and pipelines.
The advantages and disadvantages of the two: Type B flange has a short cylinder, so the rigidity is better than that of Type A flange, and it can be used in occasions with higher pressure and larger diameter. Type B is a U-shaped groove, and Type A is a V-shaped groove. Therefore, Type B is easier to penetrate, so its strength and rigidity are higher.
The factors affecting the sealing of pressure vessel flanges are as follows:
1. Bolt pre-tightening force
Appropriate pre-tightening force can ensure that the gasket can maintain a certain specific sealing pressure when working. If the pre-tightening force is too large, the gasket will be crushed or squeezed out, thereby breaking the seal. The distribution of the pre-tightening force on the gasket also affects the sealing performance. The method to ensure the uniform distribution of the pre-tightening force is to increase the number of bolts under the condition that the space required for bolt tightening and disassembly is satisfied.
2. Gasket sealing performance
Gasket is an important part of the seal. When working, the distance between the flange sealing surfaces is enlarged. The gasket material should have sufficient resilience to make the gasket surface and the flange surface closely contact to continue to maintain a good seal. Performance, a suitable gasket material should reflect that the gasket can not only produce the necessary elastic deformation under the action of an appropriate pre-tightening force, but also will not be crushed or squeezed out.
3. Flange sealing surface characteristics
The form and surface properties of the flange sealing surface play an important role in the sealing effect. When working conditions are stricter, concave and convex surfaces and tongue and groove surfaces should be used. The surface roughness of the flange sealing surface should be compatible with the requirements of the gasket. Radial knife marks or scratches on the surface are not allowed, let alone surface cracks. The flatness of the flange sealing surface, the sealing surface and the flange center The line and perpendicularity directly affect the uniformity of the gasket force and the good contact between the gasket and the flange.
4. Flange stiffness
Insufficient stiffness will cause excessive flange deformation and warp deformation, resulting in seal failure. There are many factors that affect flange rigidity. Increasing flange thickness and flange outer diameter can increase flange rigidity and reduce deformation. The bolt force can be evenly transmitted to the gasket to obtain a uniform and sufficient sealing pressure, and at the same time improve the sealing performance. Reducing the bolt arm can reduce the bending moment of the flange, which is conducive to sealing.
5. Operating conditions
The operating temperature, pressure and the chemical and physical properties of the medium also affect the reliability of the flange connection. The higher the temperature, the smaller the viscosity of the medium, and the greater the tendency to leak. High temperature can also cause creep of the bolts, flanges and gaskets. And stress relaxation, high temperature increases the chemical and physical activity of the medium, causing corrosion and dissolution of gaskets and flanges.
