Poly-pig Trap

[ucfmech]

My company has recently started using poly-pigs in order to remove the thermofluid inside. We've been using them by inserting them into one end of the coil and blowing them through with 40 psi of compressed air. I'm assuming that the fluid being pushed out by the pig is also undergoing the same 40 psi of pressure, as if it was a regular flow. Is that correct? Also, I've been tasked with designing a trap in order to catch the pig and allow the removed fluid to flow out. I've basically designed a box that attaches to the coil and has a drainage pipe on the bottom. My question is that when the box fills up with fluid and is going through the drainage pipe, will it still be under that same 40 psi? Thank you in advance for any help.

 

[PetroSynergy]

I believe your assumtions are wrong. Alot of that pressure energy used to move the pig is converted to heat energy via friction. The actual fluid pressure on the dowstream side of the pic will be <40psi.

 

[zdas04]

You didn't say what size line you are pigging. If it is less than 8-inch then I'd look at something like the Argus Pigging valve instead of designing a new trap.

David

 

[tr1ntx]

There are commercially available pig traps, but I can't remember any names. M-Co, I think is one of the small co's. A bunch of oil pipeline fabricators make them. Aceco makes pigging valves if you would rather go that route (acecovalves.com).

Most pipeline pig traps are just a straight run of slightly larger pipe, continuing past a "T" where the pipeline turns away at 90 deg. The far end of pig trap is connected downstream ("vented" back to the pipeline) so there is flow/pressure to push the pigs into it. Valves are installed to allow you to open & close the system.

-----T--X-- pig catching chamber ---) closure
| valve |
| | vent line
| X valve
|_____main pipe_______________|____________