Distance between pigs during commissioning of a new pipelin 1

[nouanda]

Hi all,

My company will start a new oil pipeline. The builder will deliver it just after removal of the water used for hydrotest, so the pipe will be wet and full of air at atmospheric pressure.

We decided to send a train of 3 pigs (nitrogen + nitrogen + oil) to clean and dry the pipeline.

My question is: what is the minimum distance between pigs?

The pressure will be between 7 and 10 barg (the first step will be to fill the pipeline with air at this pressure), the pigs should run at about 0.8 m/s.

Thanks.

 

[00100wsts]

I want to know this topic too ,anyone can tell us ?

 

[dcasto]

none, think about what would happen if 1 of the pigs leaked, they could both come in together any way.

 

[zdas04]

Or, you can guess how much water would be bypassed by the first pig (e.g., assume an even film on the entire pipe wall) and put enough N2 behind the first pig for that volume to be saturated to 80% RH. Follow that with another pig and the same amount of N2. Finding the 100% RH water content of Nitrogen at 7 barg (and some unstated temperature) will be a challenge, but the data is out there.

Then run pig with the oil.

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.

"Life is nature's way of preserving meat" The Master on Dr. Who

 

[MortenA]

Or you could run a pig mith MEG inbetween insteady of N2?

Best regards
Morten

 

[BigInch]

Why did you "decide" to dry it? Its crude not gas transmission. Crude is wet anyway and water will settle out of all tanks.

If you just have to do it, assume air at 100% humidity, for which @ 70 F has 1253 lbs of water (150 gal) per 1,000,000 cubic feet. Clean with superdry air, do as Morten suggests and run a batch of MEG, or N2. Those are the 3 cheapest methods, usually in that order.

Before starting ANY drying be sure to clean the line with wire brush pigs followed by soft foam pigs. Weigh pigs before and after. When they are about the same weight, you've got all the water you're going to get with the foam pigs. Then start the drying opeation.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[nouanda]

dear all,

thank you for your guidance.

Biginch > actually, it's not crude oil, but stabilized oil (so it's dry). thanks for the info about the cleaning sequence for cleaning (with brush pigs and soft foam pigs, I’ll keep it in mind for the future). Unfortunately, I don't decide of these subjects, I just have to write the procedure...

In that project, recovery/disposal of any product is not an easy part (and moreover, it has not been taken into consideration in the budget...), so MEG is not suitable. N2 has been chosen because, well, you know, it's just vented at atm...

So I think I'll go on with the calculation. Thanks for water content of saturated air.

 

[BigInch]

I don't think stabilized means "dry". At least it does not in my opinion, it means not "live" oil. Its only degassed, free from associated well gas, perhaps with some water allowed to settle out, but that's all it means.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[nouanda]

Sure it's not perfectly dry, but it's enough to require a dry pipeline (for this project, max BSW are 0.1%vol).

 

[BigInch]

If you say so. I assumed you meant crude oil.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/