Leakages of Steam Flange Sealing

In the ironmaking process, steam is mainly used to replace the gas inside the blast furnace body, gravity dust collector and hot blast stove, so that maintenance personnel can inspect and repair the equipment. At the same time, steam is also used for heat preservation of some equipment in the ironmaking process to ensure the stable and efficient operation of the equipment. In addition, steam is also the main energy medium for blast furnace blast humidification. By adding a certain amount of steam to blast furnace blast, the thermal state of the furnace can be effectively kept stable.
 
The reasons for the leakage of flange seals in the steam system are more complicated. At the same time, the leakage of steam flange seals will directly or indirectly cause the maintenance of the blast furnace to be out of schedule and the furnace condition to be unstable. Therefore, there are strict requirements for the leakage of the blast furnace steam flange seals. To ensure the sealing effect of the steam flange, a treatment method for the leakage of the steam flange seal is proposed, which includes sealing gaskets, adding high-temperature sealing grease between flanges and adding disc springs to flange bolts. Combined with the treatment of flange leakage of the No. 2 blast furnace blast steam humidification control valve by the ironmaking operation department in China, the treatment method and implementation effect of steam flange leakage are expounded.
 
Flange sealing
A flange connection is generally composed of three parts, that is, flanges, gaskets, bolts and nuts. Usually by tightening the bolts, the flange sealing surface is pressed against the gasket; the gasket produces elastic-plastic deformation, and the gap formed on the flange sealing surface due to microscopic unevenness such as processing roughness is filled to achieve sealing. Although the flange has the advantages of simple structure, repeated disassembly and use, if the flange, gasket, bolts and nuts are not selected properly, or the installation is incorrect, it will cause serious leakage at the flange, resulting in sealing failure, as shown in Figure 1, the structure diagram of the flange seal.
 
Leakages
There are two leakages: one is the leakage along the contact surface between the flange and the gasket, which is called interface leakage. The interface leakage is caused by the gap between the flange sealing surface and the gasket sealing surface due to the roughness and unevenness, resulting in the gap between the two contact surfaces. Relying on tightening bolts to reduce the clearance of the contact interface is one of the beneficial methods to reduce leakage. The second is the leakage of non-metallic gaskets made of fibers through tiny gaps between fibers, which is called penetration leakage. Penetration leakage can be regarded as a capillary phenomenon, and the amount of leakage is related to the tightness of the material. Add some fillers to fiber materials, such as adding asbestos to rubber. Fibrous materials and metal materials form combined gaskets, such as stainless steel graphite wound gaskets, metal-clad gaskets, which can avoid leakages. Generally speaking, most of the leakage of high-temperature medium flange seals belongs to interface leakage and causes much greater harm than penetration leakage.