The chemical industry is a diverse basic industry, and in order to meet the various needs of chemical production, there are many types of chemical equipment and the operating conditions of the equipment are also relatively complex. According to operating pressure, there are vacuum, atmospheric pressure, low pressure, medium pressure, high pressure, and ultra-high pressure; according to operating temperature, there are low temperature, normal temperature, medium temperature, and high temperature; Most of the processed media are corrosive, or flammable, explosive, toxic, and highly toxic. Sometimes for a specific equipment, there are both temperature and pressure requirements as well as corrosion resistance requirements, and these requirements are sometimes mutually restrictive, and sometimes certain conditions often change