Control Valve Fail Open convert to Fail Close 2

[elaineabc]

I have an old control valve Fisher with 4160 Controller and 657 Actuator Fail Open type. I would like to install this Control Valve to a similar application required Fail Close type.

My supervisor indicated to Fail Close would require Actuator 667 Model to be able to switch the valve to Fail Close to protect our N/G Pipeline MAOP 720 psi. Could anyone provide valuable advise that help me to better understand HOW DO WE CHANGE FROM FAIL-OPEN to FAIL-CLOSE requirement. Thank you.

Elaine
There are admirable potentialities in every human being. Believe in your strength and your youth. Learn to repeat endlessly to yourself, 'It all depends on me.'

 

[JLSeagull]

Your supervisor is probably correct that the actuator must change. An exception could exist if you have an old Fisher "A" body. Those have not been marketed for 35 years.

The Fisher diaphragm actuators either permit air to push down on the diaphragm or push up on the diaphragm in opposition to spring force. The spring mounting installation is different for those two actuators.

Other valve patterns and actuator arrangements better accommodate directional changes.

So, back to the "A" body to address the unlikely exception. These were flanged on top and bottom. The body plug and stem could be reversed. You could make the trim drop out the bottom instead of top. In this way the actuator that used to push down to close could push down to open. My money is that you will not find this opportunity and will buy another actuator.

You can also reverse the accessories such as the positioner etc. and perhaps accommodate a different failure direction for the 4-20 mA signal than the pneumatic. Don't bother.

 

[elaineabc]

Thanks for a very comprehensive reply. I would like to further explore an opportunity to learn from you.

Let's said MAOP of the system is 720 psi, what pressure setting do we need to set? I set it at 1000 psi. Now, if the coming pressure is more than 1000 psi, it will require to FAIL CLOSE, valve will open, is that mean the valve will open and dump more pressure to the line? That will go against the purpose of us protecting over pressure of the line. I don't understand the logic of it. Could you read my analogy and explain to me so I could understand this? Thanks.

 

[JLSeagull]

We need to know how the valve is controlled and more. A system could have a pressure controller looking at the inlet to the valve or the outlet from the valve. What is the valve trying to do?

If it is an inlet to the 720 psi system from a high pressure system, measure the pressure in the lower 720 psi system and close the inlet valve on higher pressure. I would assume fail closed in this case. As the pressure increases the reverse action of the controller would reduce the output.

Let's assume the same 720 psi system with a valve that vents the pressure instead of closes the inlet. Both valves could be good things to have. The failure position of the vent valve could be controversial (more later). With increasing pressure the controller would need to open the valve. With a fail closed valve you would decrease the output. With a fail open valve you would decrease the output on increasing pressure.

As you would want a pressure safety valve to open automatically, why might there be a controversy for the control valve? Perhaps the vent relieves the pressure to a flare header but the flare system is at capacity. Perhaps one would not want a pneumatic or electric signal problem on a control valve to dump the system to the flare - instead relying on the relief valve in the event of an instrument failure. Other reasons could exist.

 

[BigInch]

If I can interject, I think this is the answer elaineabc might be looking for.

To protect a downstream low pressure pipeline system, a typical pressure control station might use something like this,


HI Press PL>===PCV===ESD======PSV==|.|====>LO Press PL

|.| Break point between, a Hi (say 1440 psig) and a Lo (say,720 psig) piping design specifications.

PCV Pressure Control Valve, set to 720 downstream Pcontrol
ESD Emergency Shut-Down Block Valve, Close at 750
PSV Pressure Set Valve (Relief Valve), set at 720+10% = 792
For your particular set pressures, see your assigned piping design spec or relavent design code.
ESD required because FCVs are never considered positive shut-off. ESD Might not be required, if the relief capacity is guaranteed and able to accomodate the entire flow until the high pressure system dumping in can be shut down or otherwise locked off. I'd put one in anyway, because SAUDI ARAMCO requires it.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[JLSeagull]

Halas.

If Saudi ARAMCO requires it, then let's do it.

 

[BigInch]

Don't matter. I learned to do it first at Northern Natural, think its the same (or was) in API RP 14E, Then at Transco, Texas Eastern... SA was only the last place I used it. Most of their specs and practices came from Exxon, Mobil, Chevron, Gulf Oil, Texaco...

Do you have a problem with that arrangement?

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[BigInch]

DNV just approved, not two days ago, that very addition I made to a 3rd party design of a facility that had no protection between one Hi and Lo P spec change.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[JLSeagull]

Slap my hand. However, my observation of one oil company was that you use their standards whether or not they work. If the application does not work but followed the standard then the project guys were OK. Do something new and have trouble then their employement could be a bust. Regardless of this observation from about 13 years ago, their money spends well.

 

[BigInch]

Consider it slapped.

I have never used a standard that would not work and have found that there are procedures for getting them changed even at the most rigidly standardized company, at least in specific application where you can demonstrate the standard is a poor remedy for the situation at hand. At SAramco it may take a couple of extra months going through SAES (or 3 to 6) to do it, but that's the way it is. Different clock there.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com