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premature failure. Simply using harder materials does not go
far enough to address the problem and can introduce
unnecessary expense. It is more effective to address the
problem at source with applied engineering skill.
Severn primarily uses specially designed trims, such as
its own multi-labyrinth trim (MLT), to address some of the
most arduous challenges surrounding velocity and pressure
in cryogenic valves. With an MLT, the incoming flow medium
is segmented into smaller streams, each of which follows a
tortuous path of multiple flow turns which achieve
reductions in pressure and velocity. This technique removes
kinetic energy and lowers pressure in a controlled manner.
The number and nature of the turns is precisely calculated,
based on the expected fluid velocity at the inlet and the
optimum velocity at the outlet. In this way, flow speed can
be carefully controlled in each flow passage within the
valve, ensuring operation is managed purposefully across its
entire service range.
MLTs are especially well suited to compressor anti-surge
valves where performance is greatly enhanced through
well-controlled velocity of the cryogenic fluid. This solution
can reduce the vibration and noise typically associated with
LNG compressors, as well as improve reliability and extend
valve life.
Retrofitting cryogenic valves
It is not just new LNG projects that can benefit from
customised trims for cryogenic valves. When production
volumes increase at existing plants, the cryogenic valves
originally installed may no longer be fit for purpose.
Replacing them with new products is costly and often
takes too long, but strategic retrofit solutions offer an
Figure 2.
Thorough cryogenic testing reduces the risk of
problems during startup.