Pigging Forces
Pigging Forces
(OP)
What are the forces, if any, applied to the piping system during the pigging process.
Any information will be appreciated.
Any information will be appreciated.
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RE: Pigging Forces
RE: Pigging Forces
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Pigging Forces
Those are very big numbers. An 80 lbm, 16-inch turbo pig will move with less than 1 psi dP (1 lbf applied over 201-in^2 is about 200 lbf). Putting 400 psi across the same pig is 80,000 lbf which would move Volkswagons let alone 80 lbm pigs.
I generally see about 5 psi dP plus the weight of water on the longest uphill on 6-inch and smaller pigs (i.e., if you have 100 ft uphill elevation change your dP available needs to be 5+100*0.44=49 psig).
The coeffecient of sliding friction is a pretty small number when you're pushing liquid so you really only have to provide enough dP to shift the mass plus a small amount.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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RE: Pigging Forces
If you have some direct observations I'd appreciate as much detail as you can spare.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Pigging Forces
Once I put a Barton pressure chart on a launcher and the biggest dP I saw (about a 5 psi spike in a 20-inch line) was when the pig was trying to get out of the launcher dry. After it started moving, you could tell where it was by the pressure reading (it was pretty cool data). The pressure at the end of the line never varied from 100.0 psig during the run (I had people stationed at the Compressor Station to make darn sure of that) and the pressure at the launcher was about 1 psi higher than that on the flat, up to 50 psi higher on the up hill and up to 20 psig lower on the down hill (I'm assuming that was from the water running away from the pig and pulling it along). The annotated chart was in a file that I left in my old office when I retired, its probably been discarded on a records-retention binge like most of my other paper.
David
RE: Pigging Forces
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Pigging Forces
David
RE: Pigging Forces
For liquids lines, cleaning pigs normally run at 10 ft/sec or less, and instrumented pigs need to be run at 5 ft/sec or less. Therefore there is generally no significant inertial pig forces created at bends at these velocities in liquids lines.
RE: Pigging Forces
Interesting combination of units there. Just so that everyone doesn't need to get out a calculator, 200 km/hr is about 82 ft/sec which is a high but not outrageous gas velocity in a low pressure flow line. I've seen pigs run a lot faster than that, and yes, it can get exciting.
When you calculate the forces that these chunks of liquid and pig apply to the lines you rarely reach a significant fraction of SMYS--steel pipe has considerable elasticiity.
David
RE: Pigging Forces
As long as the forces remain axial, axial stresses won't be much, however going around a 90 may be another story when some rather large displacements can be developed with that elasticity.
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Pigging Forces
Most of the pigs I am familiar with ride in the process fluid and flow with the flow as it were. I would have thought it wouldn't really impose much more pressure/stress to anything beyond what the process fluid already does.
Then again, I am no expert - just my thoughts.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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