Pipeline Pigging 1

[echo4bravo]

Hello everyone,
I am seeking advice/cautions/tips on launch and retrieval methods for pushing (via air) a "pig" through a closed piping system, for cleaning purposes. This is a new process for us, the manufacture of SMC. This system carries one of the ingredients for making the paste. This material has a viscosity of 56,000 cps. The piping run is about 150 ft. of 6 in standard pipe with several 90's from tank to pump. I'm still learning the finer points of the art of piping, and would appreciate all advice.

Thanks

 

[pennpiper]

Just my thoughts.

Do not push a pig with air!!!!!

Do push the pig with water or a solvent compatable with your product

 

[echo4bravo]

Thanks for your reply. What problems are associated with using air?

 

[pennpiper]

Think BOMB

 

[zdas04]

pennpiper,
I was wondering why you were so adamant about using air? Do you know that the paste being pushed is volitile (I'm not familiar with "SMC" and don't know if it is or not)?

If it is volitile and can create an explosive mixture then avoiding completing the fire triangle is a good practice.

If it is non-flamable (like a cement slurry for example) then air is probably a good choice for pushing the pig since it is easy to remove after the pig run. Even with a highly volitile substance I'd rather push it with some non-reactive gas (maybe N2, I don't know the process) than water or solvent--cleaning up contaminated water is just too much of a pain, we're having to treat hydrotest water as hazardous waste these days.

I just know that there are many occsions where I've pushed pigs with air without blowing anything up, maybe I've just been lucky for the last 30 years.


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

 

[stanier]

IF SMC has such a visocity then the fluid is likely to be Non Newtonian. You will need to mdel the pipeline with full to empty contents and obtain the friction values as the pig is pushed through the line.

Again do not use air as the process medium to drive the pig. Liquids are far safer and you can control the pressure/volume far more easily.

If they are standard 90 LREs then a sphere is the best you could hope to get through the line. There are some "gel" pigs on the market but for such a short line it would not be economic.

DO a risk analysis of the process of pigging. What are modes of ailure and l;ikelihood. What is the consequence of each event? Read Pipeline Risk by Kent Muhlbauer

Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng

http://www.waterhammer.bigblog.com.au

 

[DesignerMike]

As stamier mentioned, a high viscosity product will take higher pressures to push the fluid down the pipe, so the pig may require 100 psi (or more) to get it to move at all. As the pig travels through the pipe, the pressure required to move it will quickly drop. BUT you have a significant section of pipe filled with compressed air that was required to get it moving in the first place. What will happen is that the pig will quickly accelerate (exponentially I believe) as it gets closer to the end of the pipe. Now you have a pig "rocket" that you are going to need to stop. I have a customer that shot a polyurethane pig right though the catcher, it looked like you droped it into a bread slicer...lucky no-one got hurt.

If you have a way to control the flow of product from the end of the pipe, you would have a chance to keep the velocity in check BUT you need to BEWARE of the issues before you send a pig down the line. It is very difficult to control the air side of the equation.

 

[echo4bravo]

Thanks for the advice everyone.
Since I posted my plea for help, I have become aware that one of our competitors is currently using regulated air to push pigs through their lines. My plan is to introduce the pig just after the supply, using a lateral. On the other end, I can remove it just before the mixer by the same method. I'll add a "cage" to trap the pig and some method of catching the waste on the discharge end With valves in the right places, I can drive it where I need to.
Thanks again.