Dual Purpose Pig Receiver - doable? 4

[sollapalooza]

Hello Eng-tips!

Recently our client requested to design the offshore pig receiver to be dual purpose (can both receive and launch). Is this doable? The receiver shall have some slop to assist in pigging, I'd assume is difficult to load a pig in there. We need larger flowrate of gas to move it inside the pipeline.

 

[zdas04]

Every launcher/receiver I build can be either a launcher or a receiver. There are some examples on my web page.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[LittleInch]

Is is doable - Yes, so long as the trap is flat. The only usual difference in launchers and receivers is the length of the mionr barrel, the position of the kicker line(s) and sometimes you see slopes (up for launcher, down for receiver. I prefer flat for both regardless. Otherwise they should be identical.

Your other points need more information - "The receiver shall have some slop to assist in pigging" - Please explain what you mean

"We need larger flowrate of gas to move it inside the pipeline" - again please explain. Launching pigs is a bit of an art, but you need to make sure the pig is very firmly in the neck and make sure you equalise the pressures before you open the main trap valve so that it doesn't push the pig backwards.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[zdas04]

LittleInch,
You were ok until the end. The procedure that TDW recommends is the one I've used for 30 years:
[ol 1]
[li]Seat the pig in the throat[/li]
[li]Shut the closure[/li]
[li]Purge the barrel using gas from the kicker valve then shut the vent[/li]
[li]Open the kicker valve[/li]
[li]Open the barrel isolation valve[/li]
[li]Begin shutting the side valve (the pig will launch when the side valve is about 50% open[/li]
[li]Open the side valve, shut the barrel isolation valve, shut the kicker, blow the launcher down[/li]
[/ol]
That procedure works every time with zero drama. If the pig is not properly seated, flow past it will re-seat it and then the dP will launch it (as long as the reducer was eccentric with the flat side down, I've seen people put the flat side up to facilitate drainage, but that is counter productive).

A lot of people use sloped pipe to "help" the pig fall into the line. This is anthropomorphic nonsense. It doesn't have any measurable impact on the effectiveness of the either the launch or the receive. It does successfully make the process uni-directional.

Also the position of the kicker/bypass is largely immaterial. I've seen them located at the reducer. I've seen them at the closure. No measurable difference in performance. I put them at the closure (on both launchers and receivers) because people feel more comfortable with that even though it doesn't matter.


David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[LittleInch]

Dave,

Your procedure is a more detailed version of what I was talking about - it's when step 5 is done before step 4 that I was referring to, which is a mistake as the pig can move far enough back that even at full flow, it just won't launch.

I tend to put the kicker in the middle just so it avoids the "this is a launcher you can't use it as a receiver" nonsense, but I agree, it makes no discernible difference.

I agree with all your comments, especially the sloped pig trap. Best one I ever saw was when someone mis read a 1.5 degree slope as 15 degree and built it with the end closure 4m in the air...

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[zdas04]

If there is zero dP across the barrel isolation valve, it won't make the pig move. I tell the guys that they should wait to start opening it until they can't hear flow.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat