Safe transportation of LNG with cryogenic valves
When choosing a valve, two critical things to consider are quality and safety. In a technical paper that was recently issued by family-run company AS-Schneider, the limelight is put on cryogenic valves and how these can be utilized for safe transport and storage. Standard valves contract and expand when exposed to extreme temperatures, cryogenic valves however –providing the right materials are chosen – can withstand pressure at cryogenic temperatures.
^ The Testing of cryogenic valves down to -196°Celsius. AS-Schneider tests its cryogenic valves in liquid nitrogen | Picture by: Armaturenfabrik Franz Schneider GmbH + Co. KG
Article by Jolanda Heunen
Cryogenic valves are used in the production of liquefied gases and operators also use the valves for the transport and storage of these gases. By liquefying natural gas, the volume for transport is kept as small as possible. But how to ensure safe transportation? With highly flammable gas, the valve has to perform well in the case of a fire. There needs to be a special consideration in designing the valve/piping system to allow for pressure buildup. These and more challenges are discussed in Schneider’s paper.
Valve selection for cryogenic service
When choosing a valve for cryogenic applications a few things need to be taken into account. Considering the conditions aboard ships and in plants can be quite complicated for buyers. The specific nature of low-temperature cryogenic fluids demands specific valve performance. Proper selection ensures plant reliability, protection of equipment, and operational safety. The global LNG market uses two main valve designs: triple offset rotary tight isolation valves and single and dual flapper check valves.
Triple offset rotary tight isolation valves
These offsets allow the valve to operate open and closed, with minimal rubbing and friction in their operation. It also uses stem torque to make the valve more sealable. Trapped cavities are one of the challenges of LNG storage. In these cavities, the liquid can expand over 600 times explosively. The triple rotary tight isolation valve eliminates this challenge.
Single and dual flapper check valves
These valves are critical components in liquefaction plants. They prevent damage from flow reversal.
Material and sizing are essential considerations because cryogenic valves are expensive. The results of an incorrect valve can be detrimental.
How can the tightness of cryogenic valves be ensured? When contemplating the cost of making a gas into a cryogen in the first place, leakage is both costly and dangerous. A huge challenge with cryogenics is the potential for seat leakage. Buyers often underestimate the radial and linear growth of the stem as it relates to the body. If buyers select the correct valve, they can avoid the problems mentioned above. Schneider recommends the use of cryogenic valves made of stainless-steel material. This material copes well with the temperature gradient during operation with liquefied gases. The cryogenic valves should have the right sealing materials for a high tightness up to 100 bars.
Testing and cleaning of cryogenic valves
Suppliers test cryogenic valves down to -196°Celsius; these tests are in keeping with specific international standards. AS-Schneider tests its cryogenic valves in liquid nitrogen. They use helium as the test medium. The cleanliness of the valve is essential in the cryogenic application. Grease or lubricants get very hard at low temperatures. Schneider try to prevent particles from getting into sealing areas. For example, if they get between the ball and the seats of a ball valve, there is no flat contact and sealant gets leaky. Thus, the manufacturer has to clean and degrease the valve before use. The buyers also have a responsibility for the cleanliness of the valve. They have to ensure that the installers assemble the valve with clean tools. All connections and piping parts should also be free of pollution of any kind.
The family-run company, AS-Schneider, was founded in 1875 and with over 350 employees, is one of the leading manufacturers of Instrumentation Valves and Manifolds worldwide. In the market segment for Large-Bore Diesel Engine Valves such as those used in marine propulsion and the generation of electricity, AS-Schneider is even the world market leader. With their own subsidiaries in Romania, Singapore, Dubai (UAE) and Houston (USA) and professional partners in over twenty countries worldwide, the company is always located near its customers.