Influential Factors of Flange Sealing
1. Bolt pretightening force
Bolt pretightening force is an important factor affecting flange
sealing. Pretightening force is used to press gaskets so as to meet initial sealing requirement. The force is passed on gasket though flange sealing surface. For the purpose of achieving good sealing, the force should be evenly imposed on gasket. Hence, when the force for flanges are definite, it is favorable for good sealing to reduce bolt diameter and increase bolt number.
2. Gasket performance
Gasket is an important component of sealing structure. Its deformability and resilience are the indispensible requirements for forming sealing. Gasket deformation includes elastic deformation and plastic deformation. Gaskets with plastic deformation have high resilience and can be applied in the condition with great fluctuation of operating pressure and temperature, so such gaskets have relatively good sealing property. However, deformability and resilience of gaskets are related to bolt pretightening force as well as gasket materials and structure. When used in high-temperature, high-pressure or corrosive condition, gaskets for sealing are usually made from alloy materials with octagon or oval shaped cross section. Octagon or oval shaped gasket is a kind of self-tight sealing in static seal categories. Octagon or oval shaped metal ring gasket can be inserted in trapezoid groove on flange surface, forming the structure favorable for sealing by automatic increasing pressing force between sealing gasket, flanges and tube ends due to increasing pressure.
3. Sealing surface
Sealing surfaces directly contact with gaskets and pass bolting force to deform gaskets. In order to achieve expected sealing effect, shape and roughness of sealing surface should be in conformity with gaskets. As for sealing surface used with hard metal gaskets, the requirement of dimensional accuracy is high, while, as for sealing surface used with soft metal gaskets, the requirement is not high. But radial tool marks or scratch marks are not allowed on sealing surfaces.
4. Flange rigidity
Warping deformation, caused by insufficient rigidity of flanges, is often the reason why sealing effect fails. Flanges with high rigidity have small deformation, helping to uniformly pass bolting force to gaskets and thus improving sealing property. Flange rigidity is affected by many factors. Bending rigidity of flanges can be improved by increasing their thickness and outer diameter. But more rigid flanges are heavier in weight, resulting in more cost.
5. Operating conditions
Operating conditions refer to influential factors like pressure, temperature and medium of flange sealing. Only pressure or medium will not cause severe consequences. But if pressure or medium coexist with temperature, severe consequences may occur.