Pigging system

[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

 

[dcasto]

why don't pig from the platform. If it is a long line, they can put the pig to sleep and have it start recording near the end.

I believe there would be a problem running the pig backwards, with all the driving cups.

 

[ehsank1358]

actually the problem is with first 500 meters of pipeline located near onshore.so intelligent pigging is required.
managers think if this method is applicable then it will be less expensive and less time consuming rather pigging from offshore.

 

[dcasto]

You need to be talking with the vendors about running a pig backwards then. You can go to their web sites and they will give you the dimensions of their pigs and you can then see if your reciever is large eough to be a launcher. You can always rent a launcher or make your own modifications.

 

[zdas04]

The major problem I've had with using a receiver for a launcher is the location of the bypass line (called a "kicker" on the launcher). People tend to put this line very close to the reducer and that can allow the kicker-flow to bypass the pig without launching it. If yours is this way and there is a vent closer to the closure, I've had good luck connecting a gas source into the vent to launch the pig without the risk of bypassing.

It is less frequent (but still fairly common) for people to foolishly (in my opinion) build receivers significantly shorter than launchers. I've never understood the reasoning behind this choice, but then again I've never been asked to understand it, there may be valid reasons beyond saving a couple feet of pipe. If you have that problem, you can fabricate a temporary extension to your launcher by adapting a spool piece to mate with the closure. Except in very large sizes (say above 20 inch), you can build the spool piece to just be an elongated cap (i.e., load the pig with the end sticking out and slide the spool piece over it until the connections can be made up--this lets you terminate the spool with a weld cap instead of an expensive closure).

Some smart pigs have been absolutely uni-directional in the past, but the ones I see most often today are fine with being run backwards (some will record in both directions, others are freewheeling). Like dcasto says, check with your supplier.

Good luck with this.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

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