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Liquid Velocity In Pipe

Liquid Velocity In Pipe

Liquid Velocity In Pipe

(OP)
Fluid Velocity In Pipe
I am trying to determine if we need an additional pipe installed. Is our six inch pipe adequate to handle increased flow? At a cryo gas plant the NGL products are run to metering through a six inch pipe with inside diameter of 5.76 inches. This pipe only runs about 1000ft and then swedges to 8". Upgrades are proposed that would increase the flow through this line to 46,000 barrels per day.
Pressure: 1150psig
Temperature: 95F
I can give composition if someone requests; density: 30.8lb/ft^3. I ran simulation in HYSYS. I found that the velocity would be around 16ft/s.
The pressure drop over the 1000ft of pipe was around 25psi.
The pipe is rated to 1440psi.
Based on this, I told my boss we are fine-we don't need to replace. He said he thought 16ft/s was too high.
He asked me to look into the erosion problems we may encounter since there is a couple 90 and 45 elbows on the way to metering.
I tried to use HYSYS under the flow assurance tab-erosion; but I don't understand the chart. It lists a bulk density, then a bulk velocity, and lists zero for all erosion velocity, no matter how high I change the flow. I ended up using erosion velocity= 100/density^.5 this gave me an erosion velocity of 18ft/s.

So, does this mean that my operating velocity of 16 ft/s is "too close" to the 18ft/s. 89% of erosional velocity.
Considering the cryogenic NGL products are very "clean", I would think that erosion would be minimal.

Also, on a side note. I do not know how to model a pipe TEE. I have two pipes converging in a TEE that goes to metering. One flowing 28,000 bbl/day, converging with a line flowing 18,000 bbl/day. This is what give me the 46,000. HYSYS did not seem very helpful for modeling this TEE and the turbulence/fluid dynamics associated with it.

Let me know if I left any pertinent information out. I am a recent graduate.

Any experience or help would be appreciated.
Thank you for taking the time to post,

RE: Liquid Velocity In Pipe

(OP)
Sorry about that,
I also posted this yesterday in the wrong area, and I believe it was deleted after a couple of responses were posted.
So I never got to see the responses.

Thanks for the help.

RE: Liquid Velocity In Pipe

Jacob B

This is a question to which there are no clear cut answers

16ft/sec (4.9 m/sec) is quite high, but this is normally just a process / pressure drop issue. Also surge pressure can be quite high at that velocity so that needs checking.

Erosion in clean liquids is very difficult to calculate and various studies have shown that the classic erosion calc in API 14E is very conservative. Also look at the DNV RP referenced in the report below.

See the attached which can be downloaded officially for free from the UK HSE website. http://www.hse.gov.uk/research/rrhtm/rr115.htm

Please only ask one question per post - there is also a forum for HYSYS which might answer your question. I didn't know HYSYS looked at turbulence issues.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Liquid Velocity In Pipe

(OP)
OK. Thank you.

RE: Liquid Velocity In Pipe

I agree that 16 ft/s does not seem high. Is there a concern with the shear in the medium at this velocity?

In a totally different industry, with high abrasive medium, we used the rule of thumb that wear increases with the 4th power of the velocity increase . . . (V2/V1)^4
From there, I would look at your current maintenance interval and see if the increase in maintenance frequency is tolerable.

I used to count sand. Now I don't count at all.

RE: Liquid Velocity In Pipe

In indoor hydraulic systems, 16 ft/s would be a little above the onset of flow noise.
In a setting where nobody gives a crap about noise, something else will govern.

Mike Halloran
Pembroke Pines, FL, USA

RE: Liquid Velocity In Pipe

(OP)
Thanks for the input.

SandCounter-
Would the concern for shear come from the viscosity?
What would be a concern regarding high shear?
The viscosity = .09019cP = 6.06*10^-5 lb/s*ft.

I am currently looking into the pressure surge that Little Inch stated. I assume the first step is to see if I have a fast closing valve in the line. If not, no worry about surge/water hammer?

Since I am not on site, it has been difficult to get all the information I need including engineering docs and P&ID's.

Thanks for the help.

RE: Liquid Velocity In Pipe

0.1CcP?? That's slippery stuff....

fast closing valves is one issue, but sudden stop of the pump upstream can also cause issues as the liquid column doesn't stop and creates a vacuum which then collapses when the fluid flow reverses and can cause very large shock waves / pressure.

The absolute key for erosion is the presence or otherwise of hard particles. No particles at all - not many problems. Some particles - big problems.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Liquid Velocity In Pipe

(OP)
Thank you.
Very helpful.

RE: Liquid Velocity In Pipe

NGLs usually dont develop too much surge pressures as the NGL de
nsities are relatively low.

Reaction to change doesn't stop it smile

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