Crude oil velocity in pipelines for various API grades

[mrspcs]

Does anybody know if there are recommended values (list, table etc) for maximum velocities of crude oil in pipelines depending on crude API and type (e.g. waxy, asphaltenic etc) ??

Thanks and regards,

MRS

 

[TD2K]

Maximum velocity for what? Erosion, sizing the pipeline, etc?

For erosion, I've typically seen the Vmax = 100 / (rho)^0.5 used or the 100 replaced with 150 in some cases. For clean oils, I would be willing to go higher (sand or solid particles is what you are concerned about) if necessary though your pressure drop over a long run will be high.

I've not familar with any more detailed numbers getting into the oil density (other than above) or the type of oil.

 

[BigInch]

Usually the rule of thumb for pipelines is 3 to 10 ft/sec, coupled with a maximum erosion velocity limit, if any. 3-10 ft/sec is generally acceptable to keep the lines free of deposits from accumulating at low spots and also (usually) give acceptable total pressure drops in long flat pipelines.

 

[monaco8774]

You might want to get hold of a copy of API 14e which gives methods for calculating maximum recommended velocities and includes factors for sand and multiphase flow situations

 

[mrspcs]

Thank you all for the replies. Each one contributes to the answer in a different way and all together pretty much add up to what I was looking for.

TD2K: could you please indicate what is "rho" ??

BigInch: 3-10 is a good approx. taking into considereation the sand-dirt issue (absence of it).

Monaco: also a good ref. (API specific rule), will check it.

The situation actually encompasses a preliminary evaluation / audit of a production facility. So, there is a portion of multiphase flow from fields to flow stations, then separated oil ("clean") from production tankfarms to refining and/or shipping (various pipelines). API is from 7 to 14 (maybe 19) depending on the flow point (well, field-to-flow station or production tanks to shipping or refining). The API difference is due to diluent added all along the production chain.

Thanks and regards,

MS

 

[TD2K]

Sorry, should have done that. rho is density, lb/ft3. Vmax is the erosional velocity, ft/sec.

 

[BigInch]

You didn't say that this was for a gathering system and production treating station. For gathering lines you should use higher velocity allowables, since pipelines are short you can usually deal with higher pressure drops/ft, they are full of sand and grit, the lifetime of the short lines need not be longer than the lifetime of the well, say 5 to 10 years maximum, the lines are often full of reactive compounds, CO2, SOn, HS, water and acid producing bacteria, not to mention waxes, hydrates and other good stuff. Erosion can be accepted in gathering wells, because of the short life, so you can add some wall thickness. There is an optimum wall thickness addition you can find by evaluating steel cost vs erosion rate for 5 years or so. You usually should keep velocities towards the higher sides to try to help keep the gathering lines cleaner. Higher velocities also help to keep corrosion treatment chemicals coated on the pipe, rather than running down along the bottom only. Higher gross flowrates will also tend to avoid problematic slugging flow regimes if operating in two phase flow.

 

[Hookem]

Industry standards are 3 fps minimum, 10 fps average, 15 fps maximum. Use lower values in suction piping to pumps.

 

[BigInch]

Lower than what valuee,10, 15?

IMO, and if you have the NPSHA to spare, there is no need to keep flow velocities before pumps lower than 15 fps. This is proven by the fact that pipe diameter usually change at the pump inlet nozzle, when they actually reduce diameter by one size. That is because you can theoretically get NPSHA credit for the V^2/2/g term, although to be a little conservative, this term is usually ignored in NPSHA calculations. The real reason you generally want to limit velocities over very short runs of small diameter piping in pump stations is to try to ensure you are not losing too much of NPSHA, which is generally in short supply at pump suctions, but if that's no problem, you can raise velocities higher than even 15 ft/sec.