Pipeline Vent connection and support

[Joe AUS]

Hi,

Sorry for this simple question but some guidance will be of help.

I have a DN 300 SCH 40 Pipe carrying Natural gas at 32 Bar . This pipeline is connected with a vent line of 20mmm which includes a Gate valve and ball valve of 20mm size and the vent pipe is of SCH 80 and it is if 600mm long .

The vent line is currently supported by an externally installed support having its on concrete foundation. The concrete foundation need to be removed and we are trying to see other support options. SO the questions are

1) Do we really need a support here ? How to check or calculate that ? Which document or standard shall I refer ?
2) If a support is required , can we consider it in such a way that the pipe is supported to the pipe itself . ie pipe support connected to the main pipe of DN300 . What all should I consider if this option is opted.

Thanks in advance for any valuable advice or recommendation.

Joe

 

[1503-44]

Vents can at times be extremely problematic. Vent vortex oscillations of the riser can easily initiate and amplify when venting. They can facilitate snapping off the vent. Any vents should generally be minimum of 2" sch 80. In the case of the valve being smaller, I make the riser 2" sch 80 and put a reducer just before the valve. Your riser being only 600mm long might be OK as is, depending on the max pressure. If low pressure, maybe no additional support is required. If high pressure, you might want to consider a clamp bolting to an additional support. As you say, there was a support there before. Also plug valves are preferred for vents. Much better flow control. Balls sometime come flying out of the valves and both balls and gate valves have poor flow control capability. They both should be used for on/off service only. If you want finer control of vent flow, rather than on/off, a plug valve is much better.

You might also consider a brace from the riser back to the 300mm pipe. At least some additional stability is provided.

Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

 

[saplanti]

Check the following post;

https://www.eng-tips.com/viewthread.cfm?qid=470184

 

[saplanti]

I am sorry that I missed the vent size in the OP’s post. It is really interesting that the vent size is that small. Is that for releasing the air during the hydrotest? Or anything to do with natural gas? If related to the natural gas there might be a safety concern there.

You need to provide a sketch with some dimensions to be able to get better answers.[pre][/pre]

 

[LittleInch]

saplanti - there is an edit button on any post you write which is active for a few days and allows you to correct errors or typos in your posts.

Joe Aus, A drawing, sketch or photo helps hugely in understanding your issue. A dead straight say vertical teed is different to one with bends or the end vent line pointing somewhere else.

Is it flanged, welded, any reducers, elbows etc etc ??

I would question first what is the purpose of this vent and how often is it used? It seems quite odd that a 12" 32 bar gas line has a permanently installed 20mm vent line.

"1) Do we really need a support here ? How to check or calculate that ? Which document or standard shall I refer ?"
a) - Don't know - Not enough information, but if it was only there for testing then you could delete it and plug it off
b) You chack for forces and stress analysis in your design code. Often the issue is the stress at the tee or weldolet that carries all the forces onto the main pipe
c) Your design code

2) If a support is required , can we consider it in such a way that the pipe is supported to the pipe itself . ie pipe support connected to the main pipe of DN300 . What all should I consider if this option is opted.
a) Yes - That is a common support brace to a flange from the main pipe
b) Welding of a support or clamp to the main pipe in operation can be difficult. Also check thermal movement of the main pipe. Weight of all the fittings and thrust force from the venting operaton are all needed to be included.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Latexman]

Could it be a high point vent for the hydrotest, and, hopefully, it'll never be used again.

Good Luck,
Latexman

 

[saplanti]

Thank you LittleInch for the tip.

 

[1503-44]

Not hydrotest. Vent for pipe "carrying natural gas at 32 barg"

 

[georgeverghese]

Most likely, prolonged depressurisation through this vent line will bring metal temps below -20degC, so check that the throttle gate valve and downstream piping is Charpy impact tested CS.
In most oil/gas OpCos', manual venting is done by trained operators, so you may rely on operating procedures to assume this vent line wont be overloaded (from a flow perspective). An RO on this line to restrict flow wont be necessary in any case, since line size is only DN20. Avoid using socket weld connection for this DN20 branch off the DN300 line.