3 replies to this topic

[ehsank1358]

my question is about pigging operation in gas pipeline,but before anything let me explain the system:

System:
multiphase pipeline (gas+condensate) comes from platform to onshore facilities.distance between platform and onshore plant is around 100 km.a 4" MEG injection line is mounted to pipeline to inject MEG in offshore start point of pipeline for hydrate inhibition.MEG is provided from onshore.

a pig launcher has been installed in offshore and relevant pig receiver exists in onshore.

normally pigging operation is done from offshore to onshore by driving force of gas.

my question is about possibility of pig running from onshore to offshore.

indeed objective of this type of pigging is intelligent pigging to inspect a short length of pipeline(around 500 meters of pipeline near to onshore plant).

Method:
pipeline will be depressurized from onshore side.
pig will be launch from pig receiver (located in onshore) with an external gas source (e.g. nearby plant) and pig will move from onshore to around 500 meters of pipeline ,then operation will be stopped and with gas coming from offshore pig will come back to pig receiver.

My Questions:
i want to know whether it is possible to use pig receiver (located in onshore) for launching pig with a external gas source (e.g. nearby plant) or not?
is this method applicable?
what are limitations?
what is the rule of condensate holdup.as you know max holdup is near onshore.
is it possible to do this method without depressurizing of pipeline?
thanks

[jprocess]

Hi,
I doubt this operation be possible using pig receiver because as I know pig launchers have positive slope against connected pipeline and pig receivers have negative slope.
If your operation is temporary you can replce receiver and launcher together and this is whatever that we did in one of our projects.

[Art Montemayor]

Yes, you can launch a pig from whatever source you want. However, you need sufficient driving force and if you want to pig an idle pipeline – as you infer – then you will need a receptacle to catch all the muck, liquids, and gases that will be emitted at the outlet. I have never heard this done from an on-shore facility to an off-shore facility for the simple reason that there is no space or economic manner to install a receptacle tank and receiver on the off-shore platform. This just doesn’t make common sense nor economic sense. You would need a tank to contain the line pack of a 100 km long, 4" pipeline. How big is that? - and don't forget about the associated gas!

I still don’t understand what you mean by “pig will move from onshore to around 500 meters of pipeline ,then operation will be stopped and with gas coming from offshore pig will come back to pig receiver”. Do you mean “pig will travel from the onshore to within 500 meters of the pipeline origin”? Please explain with clear English. One doesn’t move to a position “of pipleline”. You must specify WHERE in the pipeline the pig will stop.

How can you possibly pig an idle pipeline without evacuating it? This clearly doesn’t make sense and you don’t seem to understand how a pigging operation works or operates. Have you ever operated - or seen operated – a pigging operation? You must have a driving force and you must displace the pipeline contents - that is one of the primary aims of the operation.

The slope of the launcher or receiver has little or nothing to do with the ability to do the operation. It helps and is recommended – but for other reasons. I recommend you research and study the methods and practice of pigging a pipeline and what are the limitations.

[ehsank1358]

i am sorry if i did not explain the problem clearly.
the welding and laying of first 500 of pipeline(near onshore) is doubtful. so the best method for recognizing whether pipeline is in good manner or not is using intelligent pig.

as i told before the pipeline will be pressurized(evacuated) from onshore and pressure will be decrease to a little more than sea water static pressure due to depth of sea.


your understanding from my explanation is right and pig will travel from the onshore to within 500 meters of the pipeline origin by an external gas source feed from onshore. to return pig from pipeline,the pressure from offshore can be provided.