Principle of Flange Sealing
Factors that affect flange sealing are various. Mainly include: bolt preload; sealing surface; flange gasket performance; stiffness;operating conditions.
For decades, the ANSI flange, which designed by the American National Standards Institute, has provided a suitable sealing technology for the oil and gas industry and gained fruitful results. However, due to the demand for oil and gas industry has changed, ANSI flange’s defects continue to expose. Cost benefit principle, the environment protection and the best guarantee of health and safety are three major issues for the 21st century operators and contractors. Therefore, people began to consider new flange sealing method.
Flange sealing principle is very simple: The two sealing surface of the bolt extrude flange gasket mutually and form a seal. But it also leads to the sealing damage. In order to keep the sealing, people have to maintain a huge bolt force. To this end, the bolt will do even greater. And the greater bolt must match the larger nut. This means that larger diameter bolts are needed to create conditions for tightening the nut. As everyone knows, the greater the diameter of the bolt, the flange will become more curved, the only way is to increase the thickness of the flange part of the wall. The whole device will require a large size and weight, which became a special issue in the offshore environment, because in this case the weight is always the main problem that people have to pay attention to. And, fundamentally speaking, the ANSI flange is an invalid seal, which needs to be 50% of the bolt load for the compression gasket, while the load used to maintain the pressure left only 50%.
However, the main drawback of the ANSI flange design is that it can't guarantee no leakage. This is the defect of its design: the connection is dynamic, and thermal expansion and the ups and downs of the periodic load will cause the movement between the flange surface, and affectthe function of flange, so that the integrity of the flange damaged, and leaked.
The latest new flange developed by the Vector Company overcame the shortcomings of the ANSI flange. The compact flange has the advantages in various aspects: the standard flange not only saves space, reduces the weight, the more important is to ensure that the joint site will not leak. The reason for the reduction of the compact flange in size is that the diameter of the seal is reduced, which will reduce the cross section of the sealing surface. Secondly, the flange gasket has been replaced by the sealing ring to ensure that the sealing face matching face. In this way, it requires only small stress to compress the sealing surface. With the reduction of required pressure, the size of the bolt and the required number can be reduced accordingly. In the end, a new product which has a small volume and light weight (70% to 80% less than the weight of the traditional ANSI flange) was designed.