In short: online set-pressure testing checks the pressure at which a pressure safety valve (PSV) opens while the valve stays installed and the plant keeps running. An external force is applied to assist the process pressure in lifting the valve, and the opening point is measured electronically.
Why the set pressure matters
A PSV protects equipment from over-pressure by opening at a set pressure. If it opens too late, equipment can be over-pressured; if it opens too early, product is lost and the process is disturbed. Periodic testing confirms the valve still opens where it should.
Bench testing and online testing
Bench testing removes the valve and tests it on a test bench. It allows full inspection and repair, but needs the valve to be isolated or the unit shut down. Online testing leaves the valve in place, so it can be done between shutdowns and gives the set pressure under operating conditions.
When online testing is used
- To check PSVs between planned shutdowns
- To confirm set pressure under actual operating temperature and pressure
- To decide which valves need removal and bench overhaul at the next shutdown
Online testing complements bench testing; it does not replace inspection and overhaul when a valve needs repair.
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