Partial Stroke Testing (PST)

PST solution by Val Controls

What partial stroke testing (PST)?

The purpose of partial stroke testing is to exercise, and test shut down valves without disturbing the production. The valve will typically be closed 20% for a short time and fully opened again. The test will ensure the valve function is tested and working as required. When PST is successfully implemented it offers serval production benefits including an extension between compulsory plant shutdowns and insight in potential valve failures.

PST is most often used on high integrity emergency shutdown valves (ESDVs) in applications where closing the valve will have high-cost burden yet proving the integrity of the valve is essential to maintaining a safe facility.

 

BENEFITS OF PST

Safety benefits

If Partial Stroke Testing is successfully implemented the site will receive a higher safety integrity level (SIL). With Val Controls solution the site will typically receive a SIL score of 3, however the IDC24 unit is certified up to SIL4. The higher safety integrity level is rewarded because the probability of failure on demand is reduced. During a PST, the valve will get exercised reducing the risk of stiction, ultimately reducing the risk of malfunction.

Production benefits

One of the main production benefits of PST, is that the time between compulsory plant shutdowns is extended because the valve can be tested during operations. Furthermore, the PST will collect data of the test - which can be compared to previous tests - enabling the staff to predict when certain parts need replacement. This method of predictive maintenance allows any upkeep or repairs to be forecasted and scheduled, making procurement and overall plant operation to run more smoothly and efficient.

 

VAL CONTROLS PST SOLUTION

Val Controls PST solution can be used for pneumatic and hydraulic systems and is performed by the IDC24 controller. The IDC24 controller can be used in any environment as well as existing or new installations. Typically, the IDC24 can be added to the system without any need for new cables, extra software etc. making it very easy to install. The Partial Stroke test can be started locally or remote and be customized for the end-user's specifics needs.

The SOV-based solution for PST, which Val Controls provides can test the complete valve system - including the SOV. Furthermore, it can collect valuable diagnostics information to be used for troubleshooting. The solution is more reliable than the traditional positioner-based solution because it bypasses the supply pressure.

The software provided by Val Controls, allows the end-user to monitor the PST reaction time enabling you to project at which time the different parts need replacement. This method of predictive maintenance reduces the number of unplanned shutdowns and increases the overall site safety.

Image: Val Controls SOV based layout for PST

SOV based PST

The SOV-based solution is a less complex and more reliable solution compared to the positioner-based solution. This is because the SOV-based solution bypasses the supply pressure and therefore eliminates the need for extra tubing and wiring. The SOV-based solution minimizes the amount of mechanical failure points because it is placed directly on the actuator, this means that there is no need to add any further fittings or tubing.

Because the SOV-based IDC24 controller is installed directly on the actuator there are no limitations in relation to flow, air quality or temperature. The flow restriction is only determined by the capacity of the SOV. Overall, this solution simplifies the PST setup making it more reliable and less prone to mechanical failure compared to the positioner-based solution.

Summary: Benefits of SOV-based PST

No flow restrictions

No extra fittings or tubings needed

No air quality restrictions because the supply is only passing through ESD SOV

Auto-calibration

Spring return (SR type) compatible

Double acting (DA type) compatible

SOV test available

Control panel test available

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