Good engineering practice for sizing kicker line for scraper traps? 4

[gbratis]

Sorry for my ignorance folks,but is a 4" kicker line of a 22"x18" scraper trap of 1400 c.m/hr flow rate adequate?
Is there a good engineering practice for sizing kicker line for scraper traps(launching/recieving)?
Thanks in advance.

 

[BigInch]

That's not the flowrate through the kicker and trap, right??? Is this liquid or gas? That's slightly fast for a liquid pipeline.

Something like mainline diameter/4.

You might target a flow velocity in the kicker line for about 1/2 the volumetric rate of the mainline flowing at a veloity of 1 m/s

Actually a 6" sounds better.


BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[zdas04]

I size them based on gas velocity. For an 18" gas line at 50 psig my program picks a 6-inch kicker. For 20-inch it picks an 8-inch at 50 psig. If your pressure is substantially higher then you can probably get by with a smaller kicker/bypass but then you might have problems if the line ever gets converted to lower pressure.

The kicker/bypass line is such a small portion of the total price of the launcher/receiver that I'm not sure why someone would undersize the kicker/bypass but I see it all the time.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[gbratis]

Dear ZDAS,
Thank you for your valuable post. If the medium is gasoline what does your program picks?

 

[gbratis]

Dear Biginch,
The kicker line in our example is a branch from the main pipeline. The most logic thing is that the flow rate is the same as the pipeline's, that is 1400 cm/hr.Do we need to throttle the flow first? As for the medium, it is either gasoil or gasoline.

 

[zdas04]

I've never worked in gasoline flows (or any commercial liquid) and you'll have to look elsewhere for help with sizing liquid-flow equipment.

David

 

[BigInch]

No, do not divert all flow from the mainline into the kicker line. The bulk of the mainline flow will continue through the launcher/receiver bypass. You slowly open the kicker valve just to fill the launcher as you vent air. When the launcher is full, close the vent and start opening the launcher's injection valve, while at the same time begin pinching down on the bypass, only enough until your pig gets going. When the pig passes the injection valve and enters the mainline, close the injection valve and the kicker valve and you're off to the races.

In your case I would think a 6" ball or gate valve, when fully open, would provide more than enough flow to fill a launcher or drain a receiver.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[zdas04]

BigInch,
I'm a real stickler for nomneclature on pigging equipment, if you're not then you'll often find people not understanding and making mistakes. On both launchers and receivers, the normal flow path is through a "side valve" and the barrel is shut of with a "barrel isolation valve". The line that allows fluids to push the pig out of a launcher barrel is a "kicker" and the line that allows the pig to enter a receiver barrel is a "bypass".

When I've seen people use your launching technique the pig regularly gets tubmled in the barrel-isolation valve and really loses effeciency. The way that Girard recommends (and I've used for years with really good success) is:
1. Purge and fill the receiver barrel through the bypass
2. Open the receiver barrel-isolation valve
3. Shut the receiver sde valve
4. Blow down the launcher barrel and load the pig
5. Shut the barrel closure then purge the barrel using the kicker valve and the vent
6. Shut the vents and fill the launcher barrel through the kicker
7. Fully open the kicker valve
8. Fully open the barrel isolation valve
9. Slowly shut the side valve until the pig is launched
10. Fully open the side valve
11. Shut the barrel isolation valve
12. Shut the kicker valve
13. Blow the barrel down and leave it vented
14. When the pig comes into the receiver open the side valve, shut the barrel isolation valve, shut the bypass, blow the barrel down, and remove the pig.

This procedure works very well every time without any special jiggery pokery that can result in a damaged pig. Using this technique you have considerable time with the full flow going through the recievier bypass and really never have full flow through the kicker. I still build them the same size because you just never know when you'll need to reverse the direction of flow in a line.

David

 

[BigInch]

David, I like it.

We make it so.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[acedude]

A "Rule of Thumb" is that kicker/bypass lines are sized to be 1/4 to 1/3 the main line diameter. Most Operating Companies specify their criteria for kicker/bypass lines, and generally fall within this range.

Kicker (launcher) or bypass (receiver) lines are only operated periodically, and as a result, product (gas or liquid) erosional velocity threshold concerns are not necessarily applicable. Therefore, liquid velocities in excess of 15 ft/sec and gas velocities in excess of 60 ft/sec can be tolerated from a design standpoint, especially for "clean" products (i.e. white fuels, stabilized crude, natural gas, etc.).