Technical Articles
Cryogenic and Non-corrosive Conditions of Valves
Posted: 07/05/2017 09:33:59  Hits: 26
The valve operating temperature is one of the problems which must be considered when valves are designed and selected. In order to standardize the appropriate operating temperature of valves' main materials and facilitate the valves' design, production, manufacture and inspection, the explicit stipulation has been made on the main materials' operating temperature of valves used in various industries, including petrochemical, chemical, power and metallurgical industries. In addition, from the views of technical management, production management, material procurement and other considerations, steel with good comprehensive performance is supposed to be selected and too many types of steel and grades of alloy should be avoided to prevent confusion.

Cryogenic conditions
The main material of the super-cryogenic valve must be austenitic stainless steel with face-centered cubic lattice, copper alloy or aluminum alloy and the low temperature mechanical properties, especially low temperature impact toughness of the main material must meet the standard's requirements after heat treatment.

Manufacturing and testing of cryogenic valves
There are stringent manufacturing process requirements, special equipment and strict quality control of parts' process during the production of cryogenic valves. With special cryogenic treatment, placing the rough parts in cooling media for several hours, usually about two to six hours, the stress will be released to ensure that the cryogenic performance of materials as well as the accuracy of process. This kind of cryogenic treatment is to prevent the leakage of valves due to deformation which is caused by the variation of temperature under cryogenic conditions. The assembly of cryogenic valves is also different from ordinary valves'. All the parts of cryogenic valves must be rigorously cleaned and oil must be removed completely to ensure the operating performance.

Non-corrosive conditions
Valves used under non-corrosive conditions which contain media such as water, steam, air, oil and other non-corrosive substances are generally made of carbon steel. Carbon steel used for valves refers to WCB cast steel, WCC cast steel and ASTM A105 forged steel in ASTM A216 standard. The suitable working temperature of carbon steel used for valves is between -29℃ and 425℃. However, for the sake of safety, that the operating temperature of media may fluctuate must be considered. Therefore, the general operating temperature of carbon steel should not be higher than 400℃.