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irprocess (Chemical) (OP)
24 Aug 10 8:53
I want to know a brief description for shut off pressure of control valve which is located on pipeline in inlet of plant.

I found two description from other members,please let me know which of them is correct:

1-Line hydrotest pressure is 1.5 times design pressure. For cases like tube rupture we take credit of hydrotest pressure of low pressure side.

I would prefer to size control valve in such a case for 1.5 times design pressure so that I can close the valve in event of tube rupture.

2- In the oil and gas industry, the maximum shutoff pressure is taken as the maximum ANSI class pressure. So, on a 300# system, the shutoff pressure (actually, it is a differential since we also assume atmospheric on the other side) is 740 psi.

tanx
sshep (Chemical)
24 Aug 10 9:20
Hey irprocess

This is what I think for the definition:

Shutoff pressure is the maximum pressure drop across the control valve under the worst case of high supply pressure and lowest downstream pressure. This data is given to size the actuator so that it can work the valve under any condition which may occure. Shutoff pressure has nothing directly to do with the pipe design pressure except that the pipe design pressure is set using similar process criteria (some margin above maximum process pressure).

best wishes,
sshep
irprocess (Chemical) (OP)
24 Aug 10 10:05
for your information,FCV is located after chock valve and ESDV .

Stream condition in upstream and downstream of FCV is as follows:

upstream (P=74.6 bara . T= 63 oC and rating is 2500#)
downstream (P=71.5 bara . T= 54.2 oC and rating is 600#)

wellhead condition (P=185.8 bara . T= 86 oC)

let us know your suggestion for shutoff pressure.

Regards
irprocess
sshep (Chemical)
24 Aug 10 10:49
Sounds like the shutoff pressure should be at least 185.8 bar-d, reasoning that the valve may see the entire well head as static pressure at start-up with no downstream pressure, but this is only based on my experience working in chemical plants.

best wishes,
sshep
JLSeagull (Electrical)
24 Aug 10 11:59
Piping/process normally assign a design pressure for downstream and midstream projects.  Unless required by a client specification consider using the design pressure and avoid the full ASME line class pressure (100 deg F) for the shutoff pressure.  The design pressure normally includes some allowance above the normal operating range and is often the same as the process safety relief valve setting.  Using the design pressure for shutoff assumes no downstream pressure.  This may not seem conservative.  However the actuator selected would normally be larger than required just because of the limited number of actuator sizes and some pressure normally exists downstream.

Some wellhead piping line lists lack a design pressure.  If this is the case consider the full ASME or API line class pressure.

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