Reducer in Scraper Launcher / Receiver

Dear all,
In Scraper Launcher & Receiver which reducer (Conc. or ECC) to be used and why? Is there is any change in type of Reducer, if scraper is bi-directional or not, If Intelligent Pigging facility required or not, If scraper is manufactured for Gas pipeline or Liquid pipeline.

If anyone have idea, please share.

When designing a launcher & receiver we normally use eccentric reducers (bottom flat) for the launcher. If you’ll think it, it’s pretty simple why; when you load a pig with any length to it you need to shove it down into the launcher, so if you used a concentric reduce you would have to fight the “up hill bump” caused by this reducer to be able to get pig loaded (it’s easier even on the shorter pig to make the transition into the pipeline too). Probably not an issue with foam or poly-pigs, but smart pigs are like a satellite with all the feelers, electronic packages, and they’ll have some weight to them, making it difficult to load. Using and eccentric reducer makes this a far easier job.
Receivers are the reverse of this, they catch the pig, and using an eccentric reducer here would not be an issue either! It would allow the pig to move easily into the receiver with no problems (many companies that fabricate receiver use eccentric reducers!) …However using a pig (of any type) the diameter of the pig is close to the I.D. of the pipe, so when the force of the commodity in the line is use to push the pig down the line. This does one other thing besides move the pig (and is the main function of a normal pigs), if there is any debris or built-up in the line the pig scraps this off and accumulates it, pushing it ahead of the pig and down the line to end up in the receiver. Using a concentric reducer here acts as a “sump” to catch and hold this debris until it can be dealt with by the maintenance crew. Use of an eccentric reduce at this location “could” allow this debris to be back washed back into to the line. Obviously if one of your goal is to have a bi-directional pipeline it would seem to be a better idea to use an eccentric reducer on the receiver in this location.
FYI - …IF this is bi-directional operation is not a routine operation I advocate the use of a concentric reduced on the receiver! This is a personal conviction I have after talking with afew maintenance crews that performs this pigging operation and has to deal with the mess. …Again, my $0.02!

I do have a similar experiece as 11echo, I have seen both the horizontal type pig launcher & receivers with ECC reducers however in case of vertical pig launchers (seen it in offshore facility) CON reducers worked just fine.

Never given a thought on using Concentric Reducers on both the Launcher and Receivers but I think there might be few pros/cons with that kind of arrangement. need to research.

Thanks all of you for sharing your knowledge n experiece. Unfortunately I couldn't get complete answer.