Partial Stroke Testing
Increase Safety Instrumented System reliability by automatically checking the condition of the valve with each partial stroke test.
Increase Safety Instrumented System reliability by automatically checking the condition of the valve with each partial stroke test.
SIS standards dictate proof test frequency for the final element in a safety system. Operators usually perform an offline full stroke test during a scheduled shutdown because it impacts the process. But when a safety integrity function requires more frequent testing, users perform a partial stroke test while the valve is online without impacting the process.
During the partial stroke test, the valve is stroked a portion of its total travel to verify it is not stuck and to uncover other dangerous failures. It exercises the shutdown valve to verify it will operate and move to its safe position in the case of a safety demand.
A partial stroke test safely extends the time between full stroke tests. It eliminates the need for expensive test panels and skilled personnel for testing.
A digital valve controller can be used as a partial stroke device. The instrument performs a partial stroke test by slowly moving the valve a portion of its total travel and then returns to the normal state. This exercises the mechanical components of the safety shutdown valve with minimal disruption to the process.
The digital valve controller has the ability to diagnose potential issues and communicate test results. It can provide documentation of any emergency event that can be used as proof test documentation. The instrument also calculates stroke time that can be compared to the required stroke time / response time.
Although partial stroke testing does not eliminate the need for full stroke testing (full stroke testing is required to check valve seating, etc.) it does reduce the required full stroke testing frequency to the point where it can most likely be tested during a plant shutdown.
