A61-160, A61-320 type are used for the equipment and pipeline of the air, ammonia,petr-oleum gas etc.medium what theworking temperature are less than 200 , A61Y-160P , A61Y-320P type are used for the equipment and pi- peline of the quality with corrode gas and liquidmedium what the working temperature are lessthan 200 . Take for extra pressureprotection devices.