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Participant

Join Date: Jul 2011
Posts: 2

Magnitude of Pipeline Pig Trap Forces on Closure

07/04/2011 4:43 AM

Hi,

I am currently performing stress analysis of a pipeling facility containing a pig trap.

Client specifications require us to consider all safety scenarios when investigating facilities. As such a scenario may occur where the valve on the bypass line to the pig trap is closed too soon, be it from a false signal from the pig indicators or otherwise. This would mean that the pig will not slow down as it enters the pig receiver.

This is a 42" pipeline carrying a 5tonne pig at a operational speed of approximately 5m/s. If faulty the pig may travel up to 9m/s I'm told.

In previous facilities have taken a conservative route my assuming a simply Impulse type equation where the mass will come to rest in 0.1 seconds, this would result in a worst case force of 450kN. This has been fine previously as a lot of the force is transfered to directly to an underground anchor block upstream of buried induction bend. When applied to this facility model where no such mitigation is present, movement of the pig receiver on its sliding supports is too great resulting in very high nozzle loads on the kicker line nozzle.

Rather than redesigning the inlet to the facility, which may turn out to be a costly exercise, and may not be possible due to space, I was wondering what best practice is in design is when considering such scenarios, whether it is actually considered at all?

Are there any references around covering pig impacts into closure and methods of calculating the resulting force.

Cheers,

James

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Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 21001
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#1

Re: Magnitude of pipeline pig trap forces on closure

07/04/2011 5:09 AM

This is a really good question, but I am getting too sleepy right now to consider all angles. One idea that comes to mind is to slow down the flow rate while the pig transits the line, thereby minimizing any impacts that might occur. I don't know if that is feasible, though. I'll try to get back.

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Participant

Join Date: Jul 2011
Posts: 2
#2
In reply to #1

Re: Magnitude of pipeline pig trap forces on closure

07/04/2011 6:18 PM

Thanks Tornado,

Looking forward to hearing your other thoughts.

At the moment before playing around with facility redesign or operational controls (which I have a feelign won't go done well) we are trying to determine a way to more accurately quantify the impact force rather than just simply assuming that it decelerates in 0.1 seconds. OR discover whatever 'best practice' is when considering these events.

Playing around with the model, if we can accurately predict that the force will not exceed around 200kN, receiver slide becomes acceptable and nozzle loads are decreased also to acceptable levels.

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Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 21001
Good Answers: 781
#3
In reply to #2

Re: Magnitude of pipeline pig trap forces on closure

07/04/2011 11:11 PM

I'm no expert on this, so here is just an idea: Put a big sponge or other type of shock absorber in the end-of-line receiver, thereby spreading out the deceleration of the pig.

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