Pigging System Issue

[cheme13]

Hello,
We currently have an HPS Pigging System installed in our plant for our cold blend soup line. The pig is being pushed perfectly in the forward direction at 50 psi, however when the pig is returning back to its homing station, it gets stuck at the metal detector crimp we have installed (at this place we have a decrease ID). We are also returning it back with 50 psi of pressure. Does anyone happen have a solution or direction on where we can go in resolving this issue? We think we might have an issue with the seal or one of the valves not being opening properly but we are unsure.

 

[zdas04]

What kind of pigs are you running?

David Simpson, PE
MuleShoe Engineering

"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.

 

[MiketheEngineer]

Squeally!!!

 

[Latexman]

Have you tried turning the pig before sending it back? Does it get stuck then? Just trying to distinguish if the problem is the swine or the line.

Good luck,
Latexman

 

[vpl]

A followup question to zdas04's and Latexman's -- Are you just pushing the pig back and forth up and down the line?

Patricia Lougheed

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[bimr]

Have you run this issue past HPS?

Would expect that a reduced pipe size such as the metal detector crimp ID would trap the pig. There is probably more air energy would the pig is moving forward.

Is it possible to install a line size metal detector?

 

[cheme13]

The pig is symmetric so it doesnt matter if I turn the pig around. Yes the metal detector crimp decrease ID. I have talked to HPS and they have given me the run around and the engineers their don't even know how to solve the issue. I talked to a vendor who said it could be that the dump valve or surge tank valves are not opening properly. Another vendor said it could be a seal issue. Would you think if I changed the metal detector piping to something thinner it would work?

 

[Latexman]

If it's brand new, it probably is symmetrical. If not, it probably isn't.

Good luck,
Latexman

 

[1gibson]

50 psi pressure on one side of the pig is half the information. What is the pressure on the other side when going forward and back? Forward it is probably pretty low. Back, maybe a check valve or othsomething else is building up pressure on the backside of the pig. Can you measure that?

Even if pressure is the same forward and back, is the metal detector near any sharp turns? Maybe forward there is enough straight pipe and pig momentum to jump the metal detector, backwards if it slows at a turn shortly before it gets to the metal detector, it hangs up.

 

[Thealanator]

This is wild speculation:

The distance (and volume) from station A to the crimp is much less than that from the crimp to station B. The charging bottle volume is not large compared to the B side volume. As volume (behind the traveling pig)expands pressure drops to the point where it will not push the pig past the crimp.

Can you increase pressure or enlarge the charging bottle?

 

[MiketheEngineer]

If the ID decreases - is the pig seeing a "jump" in the surface. Maybe it is hanging up on that due to gravity pulling it down into the crimp?? Can you smooth the jump or even "bang" the piggy so it jumps up back into place??

 

[bimr]

There has been a lot of speculation on here. The problem most likely is that the energy on the return side is less or that there is a bend immediately upstream of the crimp.

Without seeing further details of the system, the only sure fix is to install a line size metal detector.

 

[cheme13]

Well to clarify any points made:
[ul]
[li]Yes, the pig is being pushed forward at 50 psi and being pushed backwards at 50 psi (someone at a parent plant that my company owns is pushing at 50 psi and returning back with 65 psi to overcome the crimp issue)[/li]
[li]The metal detector is not near sharp turns BUT their is one 45 degree elbow as well as two 90 degree elbows in the process line[/li]
[li]The crimp has been smoothed/polished and it still hasn't worked[/li]
[li]I talked with a vendor and he says that a valve (surge tank or dump) may not be opening properly or the PLC programming is intermittently opening and closing the valves causing back pressure.[/li]
[/ul]