Nitrogen velocity through steel pipe (500 psig) 3

[fnunez]

I'm designing a Nitrogen distribution system that is going to fill a pressure tank (500 Psig), so I need to know the recommended/allowed velocities that I should consider through the steel pipe and if you can refer a Standard or book that talks about it.


Thanks in advance.

Fernando

 

[austsa]

http://www.eng-tips.com/viewthread.cfm?qid=30500

 

[fnunez]

I've read the article, but I don't find the answer it's refered more for liquids.

I want to design a nitrogen pipeline (-astm a312_), also I've read Crane the chapter about principles of compressible flow and said that the maximum possible velocity in the pipe is sonic velocity.

So in order to choose my pipe diameter I will have two limits, the first that I've estimated about the thickness/diameters of piping with ASME b31.3 at this pressure (500 psig), but I need the velocity value to select which Diameter is the most suitable.

I found in a paper that someone consider the velocity of Nitrogen transport like Natural Gas (15-25 m/s). Could I use the same criteria?

And finally, do I have to consider laminar flow?.

Thanks a lot.

 

[StoneCold]

Fnunez
Most of the time the velocity would be set based on an allowable pressure drop per 100 ft. This is usually determined by the designer based on how much pressure he has available. Lacking that criteria I would start with 100 ft/sec as the design velocity.
Standard you might want to look at is API RP 14E.

Regards
StoneCold

 

[BigInch]

100 fps a bit on the high side for me, if it's not a vent to atmosphere. I'd limit to 40-60 fps for short distances, but I doubt you'd want, or need it that high, since you are only filling a distribution tank to 500 psig with N2, probably pretty clean and not even much water if any. 14E - Offshore Piping Design, has a whole different set of success criteria.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[katmar]

Sometimes fluid velocities are specified for particular process circumstances such as avoiding noise, erosion, static electricity or salting out of solids (in that case a minimum velocity). And sometimes velocities are proposed purely as a rule of thumb to avoid doing the hydraulic calculations. Unless you know why someone is proposing a particular velocity range it is difficult to comment on it.

In your case noise is about the only reason to limit the velocity. Norsok P-001 gives good guidance on this, but even then it depends on how often this operation is carried out, what other noise is in the area, are there workers close by etc etc.

The rules of thumb ranges are based on velocities that would give pressure drops that result in "economic" pipe diameters. But these are based on all sorts of assumptions regarding the cost of power, piping supply and maintenance costs. These assumptions should be tested where the answer is not obvious. If the nitrogen is coming from a pressurised source then the cost of compression is a sunk cost and irrelevant to the pipe sizing calculation. It does not matter whether you lose the pressure over a valve or through the pipe, so you might as well use up the pressure in the pipe and save money by using a smaller pipe with a higher velocity (subject to noise constraints).

On the other hand, if you are compressing it specifically for this duty then the delivery pressure of the compressor is extremely important and specifying too high a velocity could result in a higher delivery pressure and increase the capital cost of the compressor (as well as the cost of running it).

In general, the velocity should be result of your calculations rather than an input.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[austsa]

With available info, I suggest you keep under 20m/s.

 

[fnunez]

Thanks for the answers,

API RP 14E have information like Crane but the difference that API rP 14E works with Qg gas flow rate expressed at 14.7 psig and 60° F; not sure why, but I guess that if I work with one of this expressions at the last I will have to convert this Qg to operation conditions (from P(V)=(m)RT)in order to get the velocity at operation conditions, is it right?

This line will be short I think that 15-30 meters average, no compressors because N2 will be supplied from cylinders with manifold and pressure regulator.

So which equation will be more suitable to get the velocity for this conditions.