Ordinary steel (such as WCB cast steel) in -30 ℃ below will be directly 'frozen brittle', a slight shock like glass crack, and professional low-temperature steel (such as LCB, LCC) even in -100 ℃ can still maintain the toughness. But some manufacturers in order to save costs, will use ordinary steel posing as low-temperature steel - such as the valve nameplate is not marked ASTM A352 LCB / LCC and other low-temperature steel standards, but instead of writing WCB or simply do not mark the temperature level, this kind of 'fishing in troubled waters' of the valve! Once used in low-temperature scenarios, burst open just a matter of time.
If the casting process is not strictly controlled, the valve will be hidden inside the air holes (like a big hole in the bread), slag (similar to the cake mixed into the eggshell fragments), shrinkage (such as not baked wet core) and other issues. These defects are usually hidden inside the metal is not easy to detect, but the low temperature environment will make the metal contraction, defects, like winter road cracks, will be the stress of the larger the pull - especially the flange and the valve body connections such as the concentration of stress location. With a strong flashlight oblique illumination of the valve body wall, if you find black spots, pits or fine cracks, you have to be vigilant; with a brass rod to tap the valve body, if the sound is muffled like cracking a tin can, the probability of the existence of internal air holes or shrinkage of the low-temperature pressure is very likely to be blown away directly from the defects.
Formal low-temperature valve casting must be experienced in -196 ° C in liquid nitrogen for deep cold treatment, release the internal stress; after the impact test, the sample is placed in the -100 ° C environment with a hammer, do not break to be considered qualified. Safety has nothing to do with size, must pay more attention to cast iron gate valve, cast iron check valve, cast iron butterfly valve and other valve castings must be picked regular.