7 replies to this topic

[irprocess]

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

Edited by irprocess, 24 August 2010 - 07:26 AM.

[ankur2061]

irprocess,

I think you are complicating things. The approach could be as simple as below:

1. The pipeline has a source (upstream of the control valve). Assuming liquid flow (you fail to mention the fluid), the shut-off pressure of the control valve would be pump shut-off (again I am assuming that there is a pump upstream) minus the static head (again assuming that the control valve is located above the pump discharge nozzle). If the control valve is at a height below the pump discharge nozzle then add the static head.

or

2. Consider the pound rating of the connected pipe and use the pressure rating of the pipe against the design temperature as per the tables given in ASME B16.5 for the different material classes to specify the shut-off pressure. You would require to know the material class of the pipe for this. This would be a more conservative approach.

Regards,
Ankur.

[irprocess]

Dear Ankur,

I forgot to mention that the upstream of FCV is a wellhead and downstream is a header that collected the two phase streams from another wellhead.

Tanx again

[ankur2061]

irprocess,

Now that you have mentioned that it is a wellhead piping. For one of the companies which we are consultants to, the practice is to use pipe spool pieces of standard lengths of 12, 18 and 24 m upstream of the choke valve. The choke valve shut-off is based on the shut-in pressure of the well and the connected piping pound rating is also based on the same (generally 600# or above).

Hope this helps.

Regards,
Ankur.

[irprocess]

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)

Regards
irprocess

Edited by irprocess, 24 August 2010 - 08:53 AM.

[ankur2061]

irprocess,

Your pipeline is fully rated which means that the line downstream of choke valve is also rated for the well shut-in pressure. This is a very expensive design and it also means that you neither require nor do you have a relief device or a HIPPS system for overpressure protection downstream of the choke valve.

Considering the information you have given, this is how I would proceed to provide the shut-off pressure of the FCV:

Design Temperature: 86 deg C

Material Class: 1.1 as per ASME B16.5 (assumed)

Connected Upstream Piping Design Pressure or Allowable Pressure: 392.9 bara (calculated based on the ASME B16.5 table for Material class 1.1, 2500# rating and temperature 86 deg C)

This would be unreasonably high to be considered as shut-off pressure for the control valve.

I would simply take the shut-in pressure of the well (I presume 185.8 bara is the shut-in pressure) and provide this as the shut-off pressure for the FCV.

Hope this helps.

Regards,
Ankur.

[irprocess]

please be informed that this pipeline is existing and client wants to change in project only for FCV .

As you see the rating of pipeline is inconsistency with wellhead pressure,please let us know your suggested shut-off pressure.

Tanx again

[ankur2061]

irprocess,

You didn't read my post carefully. The shut-off pressure for the FCV is simply the shut-in pressure of the well. The shut-in pressure of the well needs to be known and I presume that it is 185.8 bara as mentioned in your post. If not, then this needs to be found out from the initial well data report prepared when the well was first commissioned or from the de-rated well data after reservoir pressure depletion.

Hope this helps.

Regards,
Ankur.

Edited by ankur2061, 24 August 2010 - 12:33 PM.