Two Stuck Scrapers!!!!
Two Stuck Scrapers!!!!
(OP)
Hello all
Here is the situation:
Pipeline Diameter 36", lenth of 16 km. Sour gas service 300psig MAOP.
Shutdown in order to replace a 12meter joint with a crack and the reciever valve. Scrapable but haven't been scraped in a while because the reciever valve was changed a couple of years back with a valve which turned out to be not full bore (32").
After shutdown, it was deprussrized to 0psig. a scraper was sent using N2(disks, Bi-directional) status unknown. Another scraper same type was sent after it, missing inside the pipe. N2 is received at the end of the pipeline.
There is a mainline valve and a bypass, close to 2/3 the pipeline length stuck while trying to close it at 60%, after the scrapers were sent. An xray was done on it to see if something is hendring it, but nothing was found. The pipejoint to be replaced is around 2km before the mainline valve.
What are my options now? Please list everything because I came in after the fact and I am not sure what has been done to resolve the situation.
Here is the situation:
Pipeline Diameter 36", lenth of 16 km. Sour gas service 300psig MAOP.
Shutdown in order to replace a 12meter joint with a crack and the reciever valve. Scrapable but haven't been scraped in a while because the reciever valve was changed a couple of years back with a valve which turned out to be not full bore (32").
After shutdown, it was deprussrized to 0psig. a scraper was sent using N2(disks, Bi-directional) status unknown. Another scraper same type was sent after it, missing inside the pipe. N2 is received at the end of the pipeline.
There is a mainline valve and a bypass, close to 2/3 the pipeline length stuck while trying to close it at 60%, after the scrapers were sent. An xray was done on it to see if something is hendring it, but nothing was found. The pipejoint to be replaced is around 2km before the mainline valve.
What are my options now? Please list everything because I came in after the fact and I am not sure what has been done to resolve the situation.





RE: Two Stuck Scrapers!!!!
Anyway, you're not in a good place. First off you need to try and find out where your missing pigs are. Do you have flow when you put Nitrogen on the launcher side? Fit pressure gauges in as many locations on the pipeline as you can and see if you can plot pressure versus length to see where the pressure drop across the stuck pigs is, or at least some idea of where it might be.
If you haven't tried reverse flow it's always worth a shot, but if you have two pigs stuck then they are not likely to move.
If you can open your main line valve, try sending a tracker pig down fitted with a radio or magnetic sender and track it at locations not exceeding 500m. One more stuck pig won't make much of a difference but at least you'll find it.
Then get the cutting torches out.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Two Stuck Scrapers!!!!
What we are going to try now is pressurize the line (From launcher) with N2 (High flow rate). Pigs might move and also we ll be able to check pressure along the pipe. (Pipeline is underground so will be difficult)
Sending another scraper while the mainline valve is still not fully open is not an option, still working on that but seems like a dead end so far.
RE: Two Stuck Scrapers!!!!
Long shot I am sure.
Regard
Brad Stone
RE: Two Stuck Scrapers!!!!
You need to recognise that you're in a bad place right now and all this will do is elongate the time taken to get your line back in service.
You should start now to mobilise some crews and hot tap gear to install 2" taps every km to monitor what is happening. You might need to go for 8" or 12" taps if that doesn't work and send a pig WITH TRACKING DEVICE, venting at each of your taps in turn until it stops.
what tends to happen with stuck pigs is that everyone goes round at high speed trying all sorts of brutal options without any real idea of where the pig is or why it is stuck. If you start planning now and do it properly, you'll have a much better outcome in a shorter time. Doing all this is a complete b:tch, but it's where you are so start doing it properly. You will need to fix your mid point valve though and don't listen to whoever sent two pigs down a line without tracking equipment. One maybe, but not the second...
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Two Stuck Scrapers!!!!
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: Two Stuck Scrapers!!!!
I hate Windowz 8!!!!
RE: Two Stuck Scrapers!!!!
RE: Two Stuck Scrapers!!!!
You hear about this kind of crap periodically and I don't think there is any way to stop it.
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: Two Stuck Scrapers!!!!
is it really that bad with with about 30gal/min and 50 psig? About 1-2 m/s speed and open drain at the end of the pipe.
I am actually against that approach but can't win the argument with the idea of cutting the pipe to get the pigs out.
There is a vaporizer so it is gas nitrogen and don't think it ll pressurize high enough to liquidify (plz correct me if am wrong)
And like I said, we are trying on the mainline valve, once it opens we can send a tracker.
And I too wish ppl follow procedures correctly.
RE: Two Stuck Scrapers!!!!
A vapouriser is exactly that - it just vaporises the liquid - the key point is what is the temperature. You can get, as zdas04 says, very cold gas coming from the nitrogen provider. If your inlet line freezes - it is quite possibly too low...
I agree that a lot of people run around trying not to do, or at least plan for, what is often required - i.e. find it then cut the thing out. One pig you might just get out by huffing and puffing, but two is very difficult. Everyone just tries to do this on the cheap, without realising that what you have here is a train wreck.
Good luck and keep us informed.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Two Stuck Scrapers!!!!
RE: Two Stuck Scrapers!!!!
RE: Two Stuck Scrapers!!!!
We found the 2nd pig under the main line valve, its a gate valve and the pig was a grotesque inside lol. Almost cut in half.
Work is resumed and we will find the 1st pig no doubt..