To close or not to close?

[CostasV]

I work in the gas distribution and transmission for 7 years. I have learned that continuous supply to the customers is one of the major requirments of the job. In this sense, we always try to minimise any possibility of stopping the supply to the customer. As a result, for example, we avoid to open/close valves except if it is neccessary, thinking that if you can avoid to close a valve, it is better to leave it open.

My question: What are the records regarding valves (any type of valve, sizes from 10in to 36in or more) that have been closed and after that the valves would not open?

Our records say that in 7 years, NOT one valve from the approx. 400 valves between 10 and 36in has shown a failure to open. Network pressure: 16 bar for medium pressure and 40 to 55 bar for high pressure. Periodic maintenance (including open/close manouvring): every 6 months.

I suppose we could have two categories of failure to open. First, pure valve-blocking and second, transmission-failure (including all automatisms, gears etc).

Any input/comment would be appreciated.

Costas

 

[jsummerfield]

Most actuator manufacturers recommend excercising the actuator fequently. As a contractor, we contacted Bettis Bettis about stroking valves that were assembled but would sit a long time before installation. Bettis suggested that an actuator sitting on the shelf should be stroked about every 120 days and to stroke it about three-times when we excercise the valve.

Many companies are interested in partial stroke testing for shutdown valves. I am not a big advocate of this. The most likely problem is that the valve does not provide bubble-tight closure. Partial stroking will not verify that the valve closes.

Pressure does not fall off quickly in a lengthy, large diameter high-pressure gas line if the valve is closed briefly. Consider testing automated shutdown valves at least annually. I would be less concerned about the actuator than the valve. Assure that everything is well lubricated before stroking a valve that has remained open for seven years. Consider having a manufacturers representative evaluate such situations before beginning a regular testing program.

John