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Pressure Drop Formula 6

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Meksen

Meksen

Mechanical
Dec 28, 2002
1
Dear All,
Is there anybody knows that pressure drop formula(largely used) for oil/petroleum as liquid in pipeline?

thanks.

 
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For oil & gas - single or 2-phase - I suggest you purchase API Recommended Practice 14E, "Recommend practice for Design and Installation of Offshore Production Platform Piping Systems". Don't let the phrase "Offshore Production Platform" throw you; it works for both shore and offshore. It's simple, direct, and straightforward. I've developed gathering and production line sizing spreadsheets using this and Serghides' equation and they work very well and very accurately.

For long distance pipeline work and single-phase liquids, then I use Darcy's equation and also Serghides. When you get involved in fluid flow and resistance, be sure you own and dominate all that is written between both orange covers of Crane's Tech Paper No. 410. If you don't, you're in for a lot of Excedrin Headaches.

 
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Excellent advice, BigIncher. No serious engineer should accept a "calculator" result on the internet without thoroughly checking it out and demanding credible and acceptable documentation as references.

Allow me to give you an example (this is meant for all younger engineers who may think they are getting something for nothing) of what happens when you go to sites such as the one mentioned. It just so happens that I've been there and done that and the following was an email that has gone unanswered for exactly one year to date (isn't that a coincidence?):

"To: webmaster@engineeringpage.com
From: artmontemayor37@hotsheet.com
Subject: Your Fluid Flow Calculation Webpage
Date: Oct 31, 2005; 5:08 PM


Sirs:

I visited your webpage after finding out about in one of the Engineering Forums. I like the way you've organized the method of resolving a piping system's pressure drop calculation. I also admire the way you've presented the results.

You say you use the Hooper 2-K calculation method and this provoked me to test your algorithm. I found something wrong in the results when I tried to find the pressure drop for 1,000 gpm of water flowing in 500 feet of 10", sch 40 pipe at a density of 62.5 lb/ft3.

Your results show a pressure drop of 3.54 psi for the straight pipe while I consistently get 1 to 1.25 psi with 5 other programs and this checks with the Hydraulic Institute's pipe tables for clean water.

I consider the 3.5 psi as a very high figure and wonder if others have noted this to you as well. I believe I'm correct and would like to verify this with you since I consider your product as very well organized. There may be a bug in your equations or algorithm and perhaps you can share this possibility with me.

Thank you for your attention to this. I'm an experienced, registered engineer with 45 years of field experience and I'm at a loss to explain the difference.

Art Montemayor
Spring, TX"

I'm still waiting for a response. Great webpages with beautiful colors and great artistic splendor don't seem to contribute too much to engineering demands on accuracy and documented proofs.



 
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Good work!

I'm not too surprized you found problems. I didn't expect to see it included surge, but since it is so very easy to include elevation differences in such a program, and such an annoyance when they arn't, it indicated to me that it was a pretty lazy programmer that wrote that one up. From what you say, it may have been much more than laziness. Now that you mention it I also believe it has not been fixed yet.

And yes, back in the "old days"... we would spend a great deal of time throughly testing all software products we purchased to validate the results before they were allowed to be used on the floor. I still see "real" professional engineering companies doing this, where the use of such programs for project work is banned. Applets are allowed to be used ONLY to get preliminary non-design use numbers (WAG), but no such results can form any part of officially documented work to be handed over to a client. Only approved programs can be used, and, in fact, all engineers are not permitted to write any personally written spreadsheets, without preapproval to do so. Most clients I've worked with have also had lists of programs that were approved for use on their projects as well, and if you didn't have those programs in-house, you didn't need to waste your time bidding for their work.

Well, all in all I guess I shouldn't compain. It might just mean more business for me next year fixing those engineering BOT designs. How do I love this internet? Let me count the ways.

BigInch[worm]-born in the trenches.
 
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Meksen, I would like to second Art's recommendation of getting a copy of the Crane 410 manual. It is a great starting point, and a resource that you will refer to again and again throughout your career. It has a very good balance of theory and practice.

Art, it seems that EngineeringPage have taken your comments to heart and fixed whatever was wrong. I just plugged in your data and got a pressure drop of 1.09 psi. It is very disconcerting when a program gets a simple calc like this wrong.

I am very surprised that they have not written back to you thanking you for your help. As a software author myself, I know how difficult it is to test for every eventuality and I am always very grateful when users write back to me to point out problems.

BigInch, as I am sure you have experienced, in addition to using only approved software large contractors check all critical calcs by independent means. Even the best software carries a disclaimer and it is up to the engineer to interpret its output. I find that these little applets are useful for the independent checks because I cannot afford to purchase all the serious software. Unfortunately Art's experience is not unusual and many of them have wrinkles in them. And as a final check many engineers will pull out their copy of Crane and use the relevant chart to ensure they are in the right ballpark.



Katmar Software
Engineering & Risk Analysis Software
 
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Ungrateful and illeducated in manners.

I thought I just got what was a high dP for 100 m3h in 100 m of 6". ... maybe not. Anyway, still no elevation diff.


I usually have my own programs of one kind or another to use for checking, so I don't often have to revert to applets.

In addition to that, I never did my first design on any particular item, without having someone with tons of experience reviewing my work. Afterwards, still had a super looking over my shoulder and answering any questions I had. From the looks of many questions that get posted on all of these forums, there's a lot of people today that either do not have qualified managers they can turn to, or they do not feel comfortable asking them questions; either one of which is a travesty to the field.

Oh by the way, thanks for your unit converter. I haven't found a useful unit you've left out of it yet and it does have pleanty of the good ones. Best engineering unit converter I've seen anywhere. Really a good creation there.

BigInch[worm]-born in the trenches.
 
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BigInch, I am sorry that my manners offend you ;-) but thanks for the kind words on the unit converter :~/ Glad you like it.

Like you, I was very fortunate to start my career under some very competent engineers who had a great way of pointing out errors without laying blame. I still feel an obligation to pay this back to the engineering fraternity and I help youngsters where I can. Unfortunately South Africa is just like the rest of the world where there are fewer and fewer mentorship opportunities.

This is one of the factors that makes Eng-Tips such a useful resource and is why I try to help where I believe the posters are making a genuine effort to better themselves. That sounds rather arrogant - I still learn more here than I teach, but it is one of the very few avenues where we can put back something in return for the benefits we enjoyed.

Harvey

Katmar Software
Engineering & Risk Analysis Software
 
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About 10 years ago I got a copy of MathCAD and started a "notebook" of useful equations that I had stumbled across. The file is now over 12 MB and I add 3-4 equationa a year to it. With the "areas" capability that came out about release 8, I can collapse all the calculations and just show the titles, makes it pretty easy to find a specific bit of arithmetic.

Consequently I never have to take a black-box program on faith. I can just open my notebook and quickly verify the answers with equations that I trust. If the black box is significantly different from my notebook then I don't bother with it any more (I just don't write those, "I think you may have screwed up" e-mails).

David
 
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Montemayor (Chemical)
How about the below post which has recieved only one response?
sailoday28 (Mechanical)2 replies20 Oct 06 (18 Oct 06)
isothermal choked flow of perfect gas

Regards
 
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Regarding the pressure drop calculator I mentioned, I had checked it against theory before recommending it.
 
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Harvy,

NO, no no! I was referring to the webmaster, the addressee of Monte's letter, that never bothered to respond with a simple thanks. I can only say [cheers] to you.

Right, I believe the only bad questions are the ones that go un-asked. I also try to help by returning what I can back into the profession, although it is pretty hard to match the typical quality of responses found on these forums, I try anyway. In the meantime I soak up all the great conglomeration of experience that manages to make its way here.

wfn, Thanks for being conscientious and responsible!

I still say they need to add the elevation difference to make it really useful, but maybe we should let zdas write that letter. :)







BigInch[worm]-born in the trenches.
 
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I used Hazen Williams with moody friction factor in an excel spreadsheet on supercriticle ethylene and beat the contractors calculated pressure drop. The contractor was using an un-named expensive program. As I projected, we had to loop the line.
 
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No I had a look up table for density at the different segements that I integrated along the rout, about every 10 miles. The contractor was trying to use Panhandle B.

 
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I even I can see how HW would be better than Panhandle B, but can I ask why you chose HW instead of another formula? According to the conventional wisdom (on this forum), chemical engineers use Darcy and only civil types use HW.

I guess if the line was eventually looped, you didn't win that battle for quite awhile after initial construction?

BigInch[worm]-born in the trenches.
 
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dcasto, I would be very interested to know how you incorporated the Moody friction factor into Hazen Williams, and how you modified the formula to take the density into account. Rather than doing all this modifying I suspect it might have been easier just to use the Darcy Weisbach formula and be done with it.

Katmar Software
Engineering & Risk Analysis Software
 
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i put the friction factor equation in and ran it twice since it is iterative. The density was found in a look up table I created from the API equation of state "ETHYL". I assumed iso thermal line conditions, but I left the temperature as a variable. I looked at the viscosity tables and there isn't much change in viscosity, but I allowed it to be a variable too. I actually wrote a macro where the spread sheet would promt be for actual data from the SCADA system and the spreadsheet would solve for roughness. Then I could change rates, pressures and and predict how the system would look with different deliveries and reciepts. I even used it to do natural gas replacing the lookup table with a non iterative solution for find zfactor. The key to accurracy is in the iteration steps to compensate for changing density. The more steps you can take the better. With a spread sheet you can replicate the line where the calculations take place a 1000 times and make each segement 1000 feet if you desire.
 
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