Procedure for Vacuum Drying of a Long Pipeline
Procedure for Vacuum Drying of a Long Pipeline
(OP)
Dear Sirs/Madams
We are working on a 26" sub-sea pipeline and its length is 75 Km .
We hydro-tested the line and now we are going to dry it and prepare it to nitrogen purging stage.
The service of pipeline at this stage is sweet natural gas.
We tried injecting dry air and propelling foam pigs to drying of pipeline but this method takes long time , so we decided to use a vacuum pump for this matter.
We are buying a vacuum pump and we are going to be ready to do this but owners asks us to submit a procedure for this work. We now general steps of this job but we do not have any procedure for it.
Pipeline specification are as follows :
size: 26"
Length: 75 Km
Sub-Sea
Temp: 34 C
Thk: 12.7mm
des press: 70 Bar
Vacuum pump capacity: 500 M^3/Hr
Vacuum pump type: Oil sealing
Best Regards
Siavash
We are working on a 26" sub-sea pipeline and its length is 75 Km .
We hydro-tested the line and now we are going to dry it and prepare it to nitrogen purging stage.
The service of pipeline at this stage is sweet natural gas.
We tried injecting dry air and propelling foam pigs to drying of pipeline but this method takes long time , so we decided to use a vacuum pump for this matter.
We are buying a vacuum pump and we are going to be ready to do this but owners asks us to submit a procedure for this work. We now general steps of this job but we do not have any procedure for it.
Pipeline specification are as follows :
size: 26"
Length: 75 Km
Sub-Sea
Temp: 34 C
Thk: 12.7mm
des press: 70 Bar
Vacuum pump capacity: 500 M^3/Hr
Vacuum pump type: Oil sealing
Best Regards
Siavash





RE: Procedure for Vacuum Drying of a Long Pipeline
This is not my field of expertise but I don't think the solution is as simple as it appears, the following might help.
http://hy
RE: Procedure for Vacuum Drying of a Long Pipeline
You hit the nail straight on the head.
If I presume that the temperature in the pipe is 30C, corresponding saturation pressure is 0.042 bara. This is about 30 Torr.
With a 500 cu.mtr/hr pump, it takes,
3.142x(0.66^2)x75000xln(760/30)/(4x500) = 165.88 hours. Then the water traces start vaporising.
RE: Procedure for Vacuum Drying of a Long Pipeline
The question I always ask at this point is "how dry do you have to get the line?". I'll assume that the pipeline is carrying field gas that is saturated with water vapor. When it cools off, some will condense and re-wet the line. This can be expected to start within seconds of turning the line on. So how much value did you get from sucking on this pipe for 6 days with a high-cost compressor?
On the other hand, assume that it is dehydrated. You always shoot for some amount of dew-point depression, so any water left behind by the pigs will evaporate within a few days. Either way, no harm, no foul.
Run turbo pigs after the foam pigs. Run them with an air compressor with the after cooler bypassed. Call it good.
David
RE: Procedure for Vacuum Drying of a Long Pipeline
Be careful you don't colapse it.
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
http://www.youtube.com/watch?v=hpiIWMWWVco
"Being GREEN isn't easy." Kermit
http://virtualpipeline.spaces.live.com
RE: Procedure for Vacuum Drying of a Long Pipeline
RE: Procedure for Vacuum Drying of a Long Pipeline
To handle this application it is important to get the right vacuum system design, along with the right size. Evacuation time is certainly one of the criteria you need to consider, but also an estimate of the amount of water remaining in the piping. The temperature of the piping will be a starting point on the vacuum you need to pull. Lastly an estimate on air leakage (all systems under vacuum will leak to some degree, and at higher vacuum levels this is critical). Lastly the vacuum pump design needs to be able to handle the water vapor without becoming contaminated by the water.
Paul Winter
Wintek Corporation
www.wintek-corp.com
RE: Procedure for Vacuum Drying of a Long Pipeline