Severe Service Control Valves

MASCOT are a market leader in Severe Service control valve technology. We manufacture and market a range of specialized valve trims and devices to control or eliminate various problems encountered in process plants such as noise, cavitation, flashing, erosion and corrosion.

Control valve manufacturers are given great freedom in the way that they interpret severe service control valve specifications. Many manufacturers utilize hard trim materials, the size of the valve exit or the size and schedule of the downstream pipe to substantiate their claims that their valve / trim design won’t be damaged by cavitation in liquid service or won’t be noisy in gas service without a solid engineering basis. Valve selections are made on the basis of lowest cost with little consideration to the longer term effects which could potentially jeopardize plant safety and operation in the longer term.

Industry, through the ISA, has recognized that control valves with severe service trims and associated process piping systems can fail through erosion and fatigue caused by excessively high trim velocity head and control valve induced vibration. As a result the ISA has incorporated a Vibration and Erosion Limits clause into its Control Valve Technical Specification. This clause is of particular importance when specifying severe service control valves.

In Liquid service it limits the trim exit Velocity to 23 m/sec (75 ft/sec) for cavitating, flashing or erosive service.

In Gas service it limits the trim exit Velocity Head to below 480 kPa (70 psia) through each pressure reduction stage of the trim, where Velocity Head (Vh) is a measure of Kinetic Energy such that: Vh = Kinetic Energy = ρV2/(2g)

Limiting the trim exit Velocity Head to below 480 kPa (70 psia) ensures that amount of energy being dissipated through each pressure reduction stage of the trim is considered so as to avoid fatigue and failure of the valve and process pipe work caused by control valve induced vibration.