In the previous passage, we made a brief on the cryogenic valve
. In this article, we are going to introduce the special requirements of cryogenic valves
in a further step.
A cryogenic valve
has severe requirements for its working conditions since the medium delivered by the valve are flammable, explosive, poisonous and high-permeable. The minimum operating temperature of the cryogenic valve
is as low as -269℃ while its maximum working pressure is up to 250MPa. Therefore, the design, manufacture and inspection of the cryogenic valve
have great differences from the other normal valve products.
In the following passage, we are going to introduce some special requirements of cryogenic valves' designs, structures and materials.
Requirements of cryogenic valves' designs and structures
1. Long working life
With the low temperature medium and under the low temperature, a cryogenic valve and its components are supposed to work for long periods of time. The working life of a cryogenic valve
is required to be not less than ten years or to be opened not less than 3500 to 5000 times.
2. Cold and thermal insulation performance
External heat not only enables the thermal effects of the cryogenic valve
to be reduced, but also causes internal fluids to evaporate rapidly, increasing its operation cost. Thus, in order to prevent the loss of medium temperature, the insulation material is generally used for the coating of the part below the bonnet neck of the cryogenic valve
3. Structure for abnormal increase of pressure
For cryogenic valve
sealed with double seats, there are residual cryogenic liquids in the cavity of the valve as the valve is closed.
The liquids absorb heat in the air and then turn into the gas, whose volume expands approximately 600 times of the previous one, increasing valve temperature abnormally. In such case, the abnormal increase of valve pressure can threaten the operating of valves, pipelines and facilities. For instance, LNG (Liquefied Natural Gas) exists as a liquid at -162℃ (pressure between 0.2 and 0.4Mpa) and the valve pressure is increased to 29.3Mpa at 20℃. Therefore, several measures are supposed to be adopted to the structure of the cryogenic valve generally in order to prevent the abnormal increase of pressure in the valve cavity.