There are many factors affecting flange sealing. The main features are: bolt preloading force; sealing surface type; gasket performance; flange stiffness; operating conditions. 

 For decades, the ANSI flange designed by the National Standards Institute of the United States has provided a suitable sealing technology for the oil and gas industry, and has been effective. However, as the demand of the oil and gas industry has changed, the defects of ANSI flanges have been exposed. The principle of cost-effectiveness, environmental protection and the best health and safety assurance are the three major issues facing operators and contractors in the 21st century. Therefore, people have begun to consider new flange sealing methods. 

 The sealing principle of ANSI flange is extremely simple: the two sealing surfaces of the bolt squeeze the flange gaskets with each other and form a seal. But this also leads to the destruction of the seal. In order to maintain the seal, it is to maintain a huge bolt force. To do this, the bolts should be made bigger. Larger bolts need to be matched with larger nuts, which means that larger diameter bolts are needed to create conditions for tightening nuts. However, the larger the diameter of the bolt, the more curved the applicable flange will be. The only way is to increase the wall thickness of the flange part. The whole device will require great size and weight, which has become a special problem in the offshore environment, because in this case, weight is always the main problem that people must pay attention to. Moreover, fundamentally speaking, ANSI flange is an ineffective seal. It needs to use 50% of the bolt load on the extrusion gasket, while only 50% of the load to maintain pressure is left. 

 However, the main design disadvantage of ANSI flange is that it cannot guarantee no leakage. This is the disadvantage of its design: the connection is dynamic, and periodic loads such as thermal expansion and upsating will cause movement between flange surfaces, affecting the function of the flange, thus damaging the integrity of the flange and eventually leading to leakage. 

 The new flange developed by Vector overcomes the shortcomings of ANSI flanges. Compact flanges have advantages in all aspects: standard flanges not only save space and reduce weight, but more importantly, ensure that the joints do not leak. The reduction of the compact flange size is due to the reduction of the diameter of the seal, which will reduce the cross-section of the sealing surface. Secondly, the flange gasket has been replaced by the sealing ring to ensure the matching of the sealing surface. In this way, only a small amount of pressure is needed to compress the cover tightly. As the required pressure decreases, the size and number of bolts can be reduced accordingly. Finally, a new product with small size and light weight (70% to 80% less than the weight of the traditional ANSI flange) was designed. 

 Flange leakage seal treatment method 

 I. The leakage site and condition of the connecting flange bolts on both sides of the DN150 valve body leak. Because the flange connection gap is extremely small, it is impossible to eliminate the leakage by injecting a sealant through the gap. The leakage medium is steam, the leakage system temperature is 400~500℃, and the system pressure is 4MPA. 

 Two. The sealing construction method is based on the on-site survey of the leakage site. In order to achieve limited sealing, the fixed fixture method is used to form a sealing cavity to accommodate the leakage point and inject the sealant to eliminate leakage. 

 1. Fixture design 

 (1) Determination of fixture structure 

 1 Embrace the leakage point and establish a sealing cavity between the valve body flange and the pipeline flange connecting the short flange. In order to prevent further leakage at the potential leakage between the valve body and the flange due to pressure, a circular cavity injection is set up where the fixture matches the outer edge of the flange of the valve body. 

 2 In the process of different diameter flange injection, the displacement occurs on the flange side of the easy-to-diameter flange of the fixture, so the limiting measures of tooth-shaped contact clamping are adopted. 

 2. Sealant selection and dosage estimation 

 (1) The sealant is selected according to the temperature of the leakage system and the characteristics of the leakage site. The sealant has excellent temperature resistance, medium resistance and injection process performance. It is easy to establish a uniform and dense sealing structure, and the seal can maintain long-term stability. 

 (2) 4.5KG of sealant is needed to estimate the single-sided leakage point. 

 3. Construction operation 

 (1) Fixture installation. Due to the contact of the tooth shape, the inner diameter of the tooth tip is small. When installing, it is necessary to hit the outer wall of the fixture to deform the end of the tooth and tighten the limit. 

 (2) After the injection operation is completed, the fixture and the valve body and flange ring cavity are injected into the sealing cavity, and then the intermediate cavity is injected. The injection process should be balanced and pressure should be applied, and attention should be paid to the pressure to prevent stress relaxation. 

 (3) After the sealant is cured, after the effect is observed, local filling and pressing is carried out to prevent stress relaxation, and then the injection hole is closed.