Pipeline Pig Stuck
Pipeline Pig Stuck
(OP)
I work in an older refinery 1950's. We have old u/g piping. Inspection methods have been limited to LRUT. We have just started a pigging program to get a better handle of what our current risks are. The lines have never been pigged before from our records. We have researched the lines and given the ILI contractor all the data we have. We agreed to run foam cleaning pig, then gauge pig, then def, then a multi-data set tool with go/no-go's between each run depending on information gathered after each run. When the contractor got to site he was leary of running the foam pig given we only run at 150psi. After much discussion we ran the gauge pig first. After successfully running the gauge pig, we had a go by the contractor and stuck the deformation tool. We were prepared for the situation but ended up cutting out the section of line to remove the pig. An investigation is underway. The tool passed through back to back 45's and then 10 feet later ended up stuck in a 1.5 D 90 degree elbow. It had passed through 3 similar 90's without trouble. After the cut out it was observed that the drive cups were inverted but the tool couldn't be pulled from the elbow using significant force. it was jammed. The elbow had to be cut apart and it looks like the "finger" portion was jammed up against the elbow. The contractor is baffled and we don't have a lot of experience with pigging. Is sticking a pig a common occurrence ?? Why would it pass through several elbows then get stuck in one? We are leary of continuing with this contractor until we find out what went wrong and why.





RE: Pipeline Pig Stuck
Just a smidgen too little. Or the butt weld had a glob of weld metal inside.
You have an idea. But run a "too little" AND "too short" pig FIRST through every pipe. When it passes through, then run a "just a little longer" pig at the same "too small dia". Then, after both have passed through, then run a "minimum dia" full-length pig to measure the wall thicknesses. It might get through most of the pipes.
That is, you are now trying to run a "gage pig" through an unknown system that has been running 60 years. Is every pipe and every elbow and every weld joint "perfect" and "in spec"?
No. And you don't know which ones are just a little too small. yet.
RE: Pipeline Pig Stuck
What did the guage plate look like when it came out?
I assume by a deformation pig you mean a caliper pig? I'm a little surprised you seem to running a uni-directional pig ("cups inverted") which doesn't allow some reversal.
Although it is not cheap, a crawler camera unit may be what you need to make sure that there are no unexpected changes in diameter, valves not aligned, excessive weld metal etc. Also a towed unit able to be pulled back and forth may be better than trying to flow - what is the fluid by the way - gas or liquid or 2 phase?
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pipeline Pig Stuck
RE: Pipeline Pig Stuck
RE: Pipeline Pig Stuck
Though very much belated reply but may be helpful;
at times there exist minor dents in the piping, even in some fittings(e.g. ell's etc.)
accordingly cups inversion could have been due to this and final outcome appearing as few inverted cups& a finger stuck at the specific spot.
Also the cups inversion and axially off-centering may have been caused from such dents.
We long time back (early 80's) suffered similar episode; as an intelligent pig got stuck mid way of my ex-employer's 18.6 Kilometer 6 inches diameter U-G pipeline& we resorted to pipe cut for gadget removal.
Also a thorough survey of 'design' vs 'as built' drawing was conducted;few identified short radius bends(as against the intelligent pig's requirement) were replaced before further inspection/pigging.
I understand this will prove helpful.
Best Regards
Qalander(Chem)
RE: Pipeline Pig Stuck
RE: Pipeline Pig Stuck
RE: Pipeline Pig Stuck
what sort of sizes are you looking at here? The smaller you get, the worse it tends to get. Pigging 1.5 D bends / elbows is a bit of a lottery and each system there will be some learning about what is and isn't possible. Back to back bends is a known issue which causes problems so those lines may need to be looked at differently or removed prior to inspection of the rest of the line. All depends on how long your lines are and how critical it is to inspect rather than just replace them.
I would suggest you look critically at all the runs and start to grade them in terms of risk where multiple elbows in a short distance or simply the total number of elbows in a run starts to exceed a certain number. Your issue is elbows so there is a cumulative risk of a stuck pig as the number increases.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Pipeline Pig Stuck