33 replies to this topic

[VikingUK]

Hello Viking,

No liquids expected during pigging? OK...

Can you elaborate on the purpose of this proposed pig run. I had assumed it was a cleaning run with the intent of removing liquid hold up and debris.

Is it a pipeline inspection with an intelligent pig?? In any case, if you can send us a brief sketch/schematic incl properties, conditions, linelength etc , maybe we can help you better.

Thx

It is indeed an intelligent pigging run (mag flux) temp/press of gas is 25 C and 60 barg
basically a straight run of 150 mm pipe 7400 metres long.pig goes in one end and is driven by gas pressure
and other end is open to flare

can I put this problem a different way ??

Imagine I have a pipe an inch diameter and 100 feet long
I put a table tennis ball (negligible mass) just slightly under an inch diameter in the pipe and apply 10 psi pressure

How can I calculate the time it will take to reach the other end ?

Pls see attached file.

Request someone to check the basis and calculation.

VikingUK please give me your feedback.

7.44 seconds for a mag flux pig to travel 7400 metres ???? I think there is something seriously wrong with that spreadsheet...!!!!

Yeah thats what i thought initially, but i verified the calculation using Campbell solved example (In the theory section).Come to think of it, if you had 60 barg pressure at inlet....you completly open the inlet valve, and no pressure at the downsteam of the 6" line you actually would have some serious velocity.

That is why you would have to crack open the inlet valve to the pig reciever pressurize it to maybe 0.5 barg and then the pig would probabely take 10-15 minutes @ an acceptable velocity of 10 m/s to travel the 7.4 km distance.

If you suddenly open the well at 60 barg after loading the pig,i think the pig wont be a pig anymore..it would be "Superpig", travelling faster than a bullet, shattering the sound barrier.

PLEASE CONFIRM YOUR DOWNSTREAM PRESSURE..as you know, flow and velocity depend almost entirely on the pressure differential.

Wait for someone to give 2nd opinion.

just ran the spreadsheet based on 50 barg P1 and 40 barg P2.. still shows a pig travelling 5 miles in less than 14 seconds !!!

[VikingUK]

Hello Viking,

No liquids expected during pigging? OK...

Can you elaborate on the purpose of this proposed pig run. I had assumed it was a cleaning run with the intent of removing liquid hold up and debris.

Is it a pipeline inspection with an intelligent pig?? In any case, if you can send us a brief sketch/schematic incl properties, conditions, linelength etc , maybe we can help you better.

Thx

It is indeed an intelligent pigging run (mag flux) temp/press of gas is 25 C and 60 barg
basically a straight run of 150 mm pipe 7400 metres long.pig goes in one end and is driven by gas pressure
and other end is open to flare

can I put this problem a different way ??

Imagine I have a pipe an inch diameter and 100 feet long
I put a table tennis ball (negligible mass) just slightly under an inch diameter in the pipe and apply 10 psi pressure

How can I calculate the time it will take to reach the other end ?

Pls see attached file.

Request someone to check the basis and calculation.

VikingUK please give me your feedback.

7.44 seconds for a mag flux pig to travel 7400 metres ???? I think there is something seriously wrong with that spreadsheet...!!!!

Yeah thats what i thought initially, but i verified the calculation using Campbell solved example (In the theory section).Come to think of it, if you had 60 barg pressure at inlet....you completly open the inlet valve, and no pressure at the downsteam of the 6" line you actually would have some serious velocity.

That is why you would have to crack open the inlet valve to the pig reciever pressurize it to maybe 0.5 barg and then the pig would probabely take 10-15 minutes @ an acceptable velocity of 10 m/s to travel the 7.4 km distance.

If you suddenly open the well at 60 barg after loading the pig,i think the pig wont be a pig anymore..it would be "Superpig", travelling faster than a bullet, shattering the sound barrier.

PLEASE CONFIRM YOUR DOWNSTREAM PRESSURE..as you know, flow and velocity depend almost entirely on the pressure differential.

Wait for someone to give 2nd opinion.

just ran the spreadsheet based on 50 barg P1 and 40 barg P2.. still shows a pig travelling 5 miles in less than 14 seconds !!!

Your calculations are correct for velocity based on the calculated flow rates you use plus the known diameter...but Qsc is wrong..and basically this was the original question I asked.. HOW DO I CALCULATE FLOWRATE FROM PRESSURE DROP

[latexman]

7.44 seconds for a mag flux pig to travel 7400 metres ???? I think there is something seriously wrong with that spreadsheet...!!!!

1000 m/s is about Mach 2.3, which is impossible in a pipeline with no converging-diverging nozzle. I think the limits of the method have been far exceeded.

[VikingUK]

7.44 seconds for a mag flux pig to travel 7400 metres ???? I think there is something seriously wrong with that spreadsheet...!!!!

1000 m/s is about Mach 2.3, which is impossible in a pipeline with no converging-diverging nozzle. I think the limits of the method have been far exceeded.

I think so too..there is nothing wrong with Ashetty's maths, I have checked the spreadsheet a dozen times.
Can you suggest a different method to calculate flow rate from pressure drop based on the parameters previously mentioned ?

[latexman]

The classic solution for a long pipeline is isothermal, frictional, compressible flow. Every fluid flow text I've seen has the derivation and equation. Crane's TP 410 has the equation. So does Perry's Handbook. I believe there are spreadsheets with this equation on this site. Just search for them.

The pig vendor can give you pressure drop vs. velocity of a new pig. You'll have to incorporate that into the solution.

Edited by latexman, 14 October 2009 - 11:17 AM.

[VikingUK]

The classic solution for a long pipeline is isothermal, frictional, compressible flow. Every fluid flow text I've seen has the derivation and equation. Crane's TP 410 has the equation. So does Perry's Handbook. I believe there are spreadsheets with this equation on this site. Just search for them.

The pig vendor can give you pressure drop vs. velocity of a new pig. You'll have to incorporate that into the solution.

Actually I have just looked again at the equation Ashetty used in the spreadsheet he posted here.
The reason for the supersonic velocity is simply that the solution is given in STANDARD form ie @ 101 Kpa and 282 degrees K.
If you use ideal gas laws to convert to actual pressure the model works fine.

[ashetty]

The classic solution for a long pipeline is isothermal, frictional, compressible flow. Every fluid flow text I've seen has the derivation and equation. Crane's TP 410 has the equation. So does Perry's Handbook. I believe there are spreadsheets with this equation on this site. Just search for them.

The pig vendor can give you pressure drop vs. velocity of a new pig. You'll have to incorporate that into the solution.

Actually I have just looked again at the equation Ashetty used in the spreadsheet he posted here.
The reason for the supersonic velocity is simply that the solution is given in STANDARD form ie @ 101 Kpa and 282 degrees K.
If you use ideal gas laws to convert to actual pressure the model works fine.

I dont know how i didnt even think of that.Revised speadsheet attached.

We still get the pig velocity as 17 m/s which is way too high.If the pig travels too fast during intelligent pigging it will not be able to gather accurate data about the pipeline and you would have to conduct the pigging again.Ask vendor what the optimum velocity should be.The lower the better, i think 3 m/s would be great.
Some gas would bypass the pig and there would be some pressure on the downstream.

Results from the isothermal & panhandle method are nearly the same and the GPSA does not endorse any particular method...so i think this calc is ok now.Just need think about other factors that might come in play & also your pigging procedure.

Attached Files

•  PIG VELOCITY.xls   183.5KB   65 downloads

[VikingUK]

pigging company (GE) quote 1.5-2.3 m/sec as ideal velocity.
Pig run completed today and velocity (calculated from actual time to arrive/pipe length) was in that spec.

Im guessing the gas velocity was as you say about 17 m/sec but a lot of it was flying past the pig sides and not been used to propel it (pig is on wheels so not a tight fit in pipe)

[VikingUK]

I thought that was some very good problem solving and advice..can't believe I have been given 2 negative points on my reputation....!!! Come on...!!