Understanding Outgassing in Control Valves
Outgassing is a severe service phenomenon in which dissolved gas in a process liquid is released as pressure decreases. Process liquid enters the control valve as a liquid, and exits the control valve as a liquid and a gas. This two-phase flow produces excessive gas and typically causes two types of damage, cavitation and erosion. Excessive vibration and noise may occur as well.
Principles of Outgassing
How to Identify
Outgassing is one of several severe service phenomena that are encountered in refining, petrochemical, and oil and gas applications involving control valves. The ability to identify an outgassing application is important because it is handled very differently than any other application.
Outgassing occurs in many combinations of liquids and gases. So how can you tell if your application may have an outgassing problem? Listed below are some good indicators that outgassing is occurring:
- Application Indicator – The control valve is providing liquid-level control for a phase separation process. The tag may have an LC, LCV, or sometimes LV to represent that it is a level control valve.
- Molecular Weights – Outgassing may be occurring in a control valve if the liquid and gas exiting it have different molecular weights.
