A21H type applies to equipment or pipelines with water, air, steam, and other media whose operating temperature is no more than 200;
A27Y applies to equipment or pipelines with corrosive medium whose operating temperature is no more than 200, as overpressure protection device. A28H (Y) is applicable to equipment or pipelines with air, steam, water, nitrogen and hydrogen gas mixture, and other media whose operating temperature is A28Y-P / R apply to equipment or pipelines with corrosive media whose operating temperature is no more 200, as overpressure protection device.