Triconex: Keeping PST Simple

Tuesday, October 23, 2012 @ 06:10 AM gHale

By Gregory Hale
Joe Pittman knows partial stroke testing does not have to be complicated.

He also knows partial stroke testing is an important safety feature users have to practice often to ensure valves are able to open and close properly, the team leader for safety instrumented systems and automation integrity at Chevron said during his Monday talk at the 2012 Americas Triconex Technical Conference in Galveston, TX.

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Partial stroke testing (PST) checks the function of the safe position of emergency shutdown valves. The partial valve stroke prevents unexpected failure of the safety function by breaking down solid masses or the onset of corrosion. A successfully executed partial stroke shows certain unresolved errors that would otherwise go undetected are not present. The end result is the user has a better idea of predictive maintenance.

“There are three ways to do a partial stroke test: Manual, semi automatic and automatic,” Pittman said. “At first, operations does not want to do automatic, but after they keep getting reminders from the system they go to automatic.”

Pittman said it is easy to get complicated in conducting partial stroke testing, that is why he wants to keep it simple. He said every valve has the same design and a HART-based digital controller all using 4-20 mA.

Again, in the mode of keeping it simple, there are only three messages coming out from the PST manager, pass, warning, which means something will need replacement, and failure, Pittman said.

He talked about the features of a successful partial stroke testing program where you have to “ensure operators what is happening. You also have to establish the link between the PST device and positions currently installed.”

One of the most important factors, though, is to “keep it simple and use hardware and software designed for the implementation of partial stroke testing,” he said.

In what seems obvious, but does not always occur is after conducting the partial stroke testing, users then have to gather the information and understand the results.

“You have to utilize the information during the testing,” Pittman said.

To take advantage of the data, users should:
• Designate a PST owner
• Train those working with PST to understand the data
• Develop a work practice when a PST is done to learn what is a fault or failure

Another key factor when conducting partial stroke testing is to test often.

“When testing is prescheduled and connected automatically, frequent testing does not mean more manpower,” Pittman said.

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