信阳Brief description of corrosion of gas holder

The gas holder is mainly used to store city gas, feed gas in chemical production, semi-water gas, coke oven gas, etc. It plays a role in balancing the system load and buffering in production, and also has a role in purification and dust removal of process gas. Due to its large volume and large consumption of steel, it is very important to do a good job in corrosion protection of the gas holder to extend the service life of the gas holder. The most severely corroded parts of the gas holder are near the water line of the bell cover and the water seal wall plate, the lower cup ring of the water seal and the bottom of the sink.
1. Corrosion mechanism
The cause of corrosion is electrochemical corrosion. It mainly includes gas corrosion, water corrosion, H2S stress corrosion cracking, atmospheric corrosion and bacterial corrosion.
1.1 Corrosion of gas
Gas generally contains corrosive media such as H2S, CO 2, O2, HCN, NH3 and other organic sulfur, and is often saturated by water vapor. The following table shows the composition of several common gas.
Generally, wet gas will continue to be cooled after entering the gas holder, especially in winter or on the negative side of the gas holder. Saturated gas will precipitate condensate containing corrosive media such as H2S, CO2, O2 on the cold wall (this is an electrolyte solution), which will form a liquid film and hang on the wall, causing "liquid film" electrochemical corrosion of H2S-CO2-O2-H2O. H2S is the main corrosion component, and CO2 and O2 play a role in accelerating the H2S corrosion under certain conditions. In the corrosion of H2S to carbon steel, the "liquid film" corrosion is many times greater than that in the liquid phase, and greater than that in the gas phase. According to relevant data, the annual corrosion rate of carbon steel obtained from the hanging test in semi-water gas is 0.041 mm in liquid phase and 0.144 mm in gas-liquid phase. In production, the actual annual corrosion rate of the inner wall of the wall panel can reach about 0.5mm. The main forms of corrosion are uniform and spot corrosion. Stress corrosion cracks often occur in places with large internal stress.