It isn't a silly question at all. The way I design pig traps, the launcher and receiver are identical in their major components. I do this so that if Marketing finds a new delivery point that requires reversing flow in a line (as they've done to me on 5 different occasions), then I want to be able to say "OK", not "I've got to rebuild the pig traps".
On a launcher I want the Pig Sig to tell me that the pig has passed the barrel-isolation valve on the way out. On the receiver I want the Pig Sig to tell me that the pig is home (i.e., has passed the barrel isolation valve on the way in). To do this I put the specialized Pig Sig boss on either side of the barrel isolation valve on both launchers and receivers. On launchers I cap the barrel side. On receivers I cap the pipeline side. When marketing says to reverse the flow in a line, I just reverse it and the next time we're scheduled to blow the line down I shift the Pig Sigs.
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
Other than magnetic ones you normally find they don't work after a few years / a few operations. I think they were invented / decided by process engineers who had never seen the amount of dirt and gunk a pig can bring in or stood next to one which hasn't operated despite the pig trap shaking whne the pig comes in....
Just my opinion, but I normally remove them from a design if I have half an opportunity as you somply can't rely on them and if they start leaking on a pressure point (pipelie side of the main pig trap valve), you have to shut down, de-presusirise or clear the entire line and for what - a signal that you don't need.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
You really shouldn't buy them on e-bay. Seriously, the TDW bi-directioal units I call out work well. One that I installed in 1997 has had a dozen operations a week for 16 years with flawless performance. The magnetic ones I've used all have had screens that you can't read after a few months in the sun.
I would nearly agree that you don't need them on launchers with the "pressure launch" design, but I had a launcher with a leaking barrel isolation valve and when we jammed the pig into the throat on the launcher and closed up the barrel, the stupid thing would pop out of the throat. When we closed the side valve the pig was far enough out of the throat that full flow could bypass it and it never launched. The pig sig saved us a lot of pointless waiting at the other end.
For receivers, if your receiver is attended on receipt then you may not need them. I had a 20-inch pig once that ran faster than the operator could get to the receiver (the line was cross country and the road took a bit longer route), so if he drove up and the flag was up he was able to retrieve the pig and return to normal operations. If the flag is down then he knows that he's going to get an ocean when it does come in. Without the pig sig we would have to have a second guy at the receiver.
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
I know they have some uses and a few work well, but far too many don't. As for receving pigs without someone there, well let's just agree to dffer on that one. My point is that it is very difficult to rely on them and without regualr maintenece or regualr operation, many, in my experience, don't work after a few years of not moving if you only pig once in a blue moon.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
I agree that pig sigs that are not exercised rarely work. If a line is going to be infrequently pigged I use pigging valves (no pig sig) instead of pig traps. For lines bigger than you can buy pigging valves, they need to be pigged pretty often.
The most effective (by far) field development organizational model in unconventional gas is to have the same guys that operate the wells operate the gathering system up to the first compressor station. This organizational model puts people with a gas-production motive in operational charge of the tools of production (the "mid-stream model" puts people with a cost-control motive in charge and turns the gathering system from being a tool of production to being a sales tool). But it also spreads staff geographically thin. It is common under this model for a guy to set up a receiver in "receive" mode (which is why I use pretty large bypass and kicker lines) and drive over and launch the pig, then drive back and receive it. I had one line that the pig would sit in the receiver for a couple of hours before the operator got there to remove it. Worked fine.
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
I also like to use virtually full size kicker lines, especially for small sizes (<12") and in those cases non attended receipts can work well. My favourite (and only) is the portable magnetic detectors which sit on the top of the pipe and flash when the pig goes past.
Like I said - I hate installed in situ pig sigs.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
I knew this would kick up a hornet's nest.
Do you build those with a 5[°] bi-directional adjustable slope. Sloping down into the pipeline for launching, and down, away from the pipeline for receiving? Do you put two kicker lines, one for launching, one for receiving, even though it's only one way? Do you use two launcher valves? I prefer one pigsig, one kicker, one launching valve and a horizontal (0[°] sloped) barrel ... and they work ... great.
No I don't use the adjustable slope ones, first to me the purpose of a pig sig is to indicate you are clear of the barrel isolation valve so a pig sig placed for launching is in the wrong place for receiving and vice versa; and second they seem too delicate for field use.
My launcher design is identical to my receiver design. A single bypass/kicker line that both come in pretty close to the closure in either case. I've attached a picture of the design I've evolved to. Notice the flange near the closure-that lets you insert a spool piece for long pigs (nothing is connected between the flange and the closure so you can just unbolt it).
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
Surely somebody's going to comment about that flange.
What about eccentric reducers, flat side down for launchers, flat side up for receivers
Thanks for the drawing.
LittleInch,
e-mail me (my e-mail address is on my web page) and I'll send it to you.
I've seen a couple of other people's receivers with the flat side up, and it doesn't make sense to me. The infinitesimal value of creating a sump is far outweighed by the receiver never being able to launch a pig (bigger inch pigs are heavy and there is no way that you could get a 12-inch or bigger mandrel pig into the throat with the flat side up).
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
FS Up would be a receiver only. Believe it or not, I've seen it, but would never do it that way without a .45 held to my head. The 5{°] slope thing is pretty common, but I think pretty much just another example of how logic can be extended past its useful limits.
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
