Cryogenic Valves
It generally is accepted in the oil and gas industry that the cryogenic temperature range starts at -238° F (-150° C). In addition to this temperature range, certain gases are considered “cryogenic” because they take more than just an increase in pressure to compress their volume. Anything warmer than the cryogenic range up to 37° F (3° C) is called “refrigeration.”
Understanding where cryogenic temperatures start is very important to valve selection. There are a number of things to understand about cold temperatures when considering how to select a valve that will work over a long period of time.
“The valve industry is conservative,” Nathaniel Paxton, product manager for TBV ball valves, said. “A general rule is that continuous temperatures less than -100° F (-73° C) are considered cryogenic service and warrant specific valve preparation.”
Problems With Transporting Cryogenic Media
Cryogen leakage is not only dangerous, but also very expensive, especially when one considers the cost to make a gas into a cryogen in the first place.
“As it pertains to the valve, it has been said many times that thermal swings can be the Achilles heel for any valve, and severe temperature variations of a cryogenic nature take this to a new level,” Paxton said.
The components of any valve (body, bonnet, stem, stem seals, ball, seats, etc.) will contract and expand at different rates because of different material composition or the amount of time exposed to the cryogen.
Heat gains from the environment are a constant battle when dealing with cryogens, hence the reason for valve and piping insulation. One has to remember that, during gas processing, we are dealing with the physical properties of gases, such as liquefied natural gas (LNG), nitrogen, oxygen, argon, and helium. “These ‘liquids’ do not want to be liquids at atmospheric pressure and, if allowed, can violently transform to gases in a heartbeat,” Paxton said.
In the normal processing of cryogens, there always is the buildup of pressure because of this heat gain from the environment and the subsequent vapor formation. There needs to be special consideration in designing the valve/piping system to allow for this pressure build up.
Other big problems with cryogenic services include seat leakage potential. The linear and radial growth of the stem in relation to the body often can be underestimated. Selecting the correct valve can help avoid the problems mentioned above.
Selecting a Valve for Cryogenic Service
While there are not strict guidelines for valve type in cryogenic service, there is a trend to select quarter-turn ball valves for their tight shut-off capabilities. This quarter-turn motion is also found in high-performance and triple offset butterfly valves. For larger valve sizes, gate valves often are utilized over ball valves, because ball valves can be more costly. However, with a ball valve, you pay more up front,” but will save more later on in terms of valve performance over time. As for the type of piping connections, flange and welded configurations are used mostly for cryogenic service, although customer preference typically determines which type is used.
Valves intended for cryogenic service should be assembled in a clean room and be lubricant free, or utilize lubricants compatible with cold service. The valves should not have machine oils, grease, dirt, or any foreign material in the valve for the clean service. Any unnecessary matter can inhibit the valve performance at cryogenic temperatures meaning, if something gets in between the ball and seat sealing, problems can occur.
“When buying a valve for cryogenic service, you should insist to see documented procedures for cleaning and verify the procedures are being followed during the assembly process,” Paxton advised.
We are willing to rigorously prepare valve components for clean room assembly and take the precautions to keep components contaminant free to the standards required by the industry. Our TBV line of ball valves has been a recognized leader for cryogenic service since 1978. In addition, our in-house clean room, quality processes, and testing help ensure that TBV valves will perform when you need them to. With numerous stem seal designs, soft or metal seats, and two-piece and three-piece body construction, TBV valves offer a range of options for a variety of cryogenic applications.
