On board FPSO, the gas injection commissioning phase is ongoing. We have a PCV installed here to control high pressure gas injection up to 290 bar.

the control valve was calibrated and function checked ok when there is no pressure on the line. The valve is an 8" globe type with spring diaphragm Fisher type 667 actuator and fisher body type EHT-1.
The problem is that when there is a high pressure 245 bar upstream and downstream of the PCV in manual control mode, the valve is not controlling correctly and not even going to 0 % position, sticking at bet. 4 to 10 % @ 4 mA signal from CCR.

Fail-close action of the valve was proven well under no pressure condition.

Somebody suggested to adjust bench set of the actuator and we tried but not done and difficult with 245 bar on the line.

This is my first time to seek help from the web and I hope I got the best site and answers from the experts online. Thank you very much

 

You have two separate issues to deal with, one is critical and the other is merely serious.

In regards to the critical issue: Fail-safe not closing the valve under all operating conditions. This must be solved first. Fail-safe operations must always work. Bring the problem back to your control valve vendor and get his recommendations. You may very well find that replacing the fail-safe spring with a larger spring will be sufficient. This will result in a larger area actuator head.

In regards to the serious issue: The valve not controlling when in high pressure. The force on the valve stem due to the high flow through the valve is not being overcome by the actuator. Again, bring this problem back to your control valve vendor and get his recommendations. You may find that the solution which fixes your first problem (a larger spring and larger actuator) will also fix this problem. Your actuator must be able to easily overcome any loads produced on the valve stem due to flow and/or pressure.

 

I have seen this before when the valve was installed backwards. The upstream pressure should help close valve, so when installed backwards the upstream pressure pushes up on the plug. When there is no pressure in the line it will work fine.

There should be an arrow on the valve so it is easy to check. Otherwise bench set should be checked with actuator uncoupled.

 

Thank you Bruce. It feels good reading reply from you mentioning first about the valve operational safety status.

As we began investigating this PCV issues, after all the maintenance checks on the valve were done, we also concluded that the control valve actuator might be wrongly sized for its application. We checked the instrument data sheet and noted that everything there shall meet the design requirements but actually is not.

We are also trying to reach the valve vendor for support but cannot find the right person because all the equipment used here are supplier package and got other party involved.

In the meantime,we just want to find a quick solution for the problem if there is but we appreciate any reply could be helpful.

Have a nice day.

 

The valve is installed correctly following arrow direction. We here in our maintenance department had also the discussion of uncoupling the valve actuator and adjust the bench set but majority's decision is not to do it. Either it's no effect or little effect, last option to do and to do it will take time and hard works.

Well, we got one vote to do it and we appreciated. Thanks for the reply post. Have a nice day!

 

From the sounds of it the inlet is under the plug pushing it open.
i.e. 245 bar under the seat. Just figure it out, an 8" valve has quite a cross section.

Compensating for this is called Bench Set, any good Instrument Tech should be able to do that for you.

Roy

 

Hi,

You may check the actuator sizing and just to ensure that the shutoff pressure used for the actuator sizing is correct. Otherwise, it may cause insufficient thrust to sit the plug.

As far as i know, Fisher has their own local business partner for technical support.