Hi all, I'm quite new to piping engineering, and I've been tasked to determine the sizing/diameter of a branch pipe for a reducing tee junction. Are there any equations that I can use to compute this? I've seen some of the ASME B31.3/31.4 and I am not sure as how it is governed. for example, the use of the header-branch diameter ratio. Thanks all in advance.
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(Petroleum)
26 Apr 12 03:36Theoretically you should start with a required flowrate and the available pressure drop to work with to get the branch diameter, or it becomes a purely mechanical exercise in which you could pick virtually any smaller, or even equal, diameter as the mainline. Generally you can use a stock T for diameters down to 1/3 the mainline diameter. Below that, probably branching from a weld-o-let would be more suitable.
What would you be doing, if you knew that you could not fail?
(Civil/Environmental)
(OP)
26 Apr 12 03:39do you have any idea for reference that i could use to obtain the flowrate/pressure drop process?
(Petroleum)
26 Apr 12 03:47Probably a million on a slow day.Gas or liquid line?Google the D'arcy or Darcy equation, or the Churchill equation to get the pressure drop in a pipe running full. Churchill is easiest, no iterations needed to determine friction factor.
What would you be doing, if you knew that you could not fail?
(Civil/Environmental)
(OP)
26 Apr 12 04:00ok i managed to go to the library and dig out a book "Flow of fluids through valve,fittings and pipe".
They gave the an equation for flow of fluid through nozzle and orifices. There is a diameter term inside, so I'll just use it to compute?
(Petroleum)
26 Apr 12 05:23No, that's for flow out of a tank nozzle, across an orifice, or something. You will find that you lack certain information for some of those variables and you won't be able to solve directly. You have a pipe with a pressure drop that will establish the flow rate for a given diameter.
What would you be doing, if you knew that you could not fail?
(Civil/Environmental)
(OP)
26 Apr 12 05:26oh, so u mean i need to compute the pressure drop first? how do i find the pressure drop for a reducing tee?
(Petroleum)
26 Apr 12 05:31you need the pressure difference between 1) the pressure in the mainline at the point where you will place the tee and 2) the pressure at the end of the new branch at wherever it will tie in.
What would you be doing, if you knew that you could not fail?
(Civil/Environmental)
(OP)
26 Apr 12 05:33i see, so using the pressure difference, i can find the diameter of the branch pipe
(Petroleum)
26 Apr 12 08:20YES! If you know what flowrate you want. Otherwise you can assume a diameter and see what flowrate that diameter gives you with your given pressure drop.
What would you be doing, if you knew that you could not fail?
(Mechanical)
26 Apr 12 19:56PantheraXYou could download the freeware from this site and model the branches with different flow rates and compare the losses.If you get to engineer systems of greater complexity you could invest in AFTs athom for steady state Impulse for dynamic analysis. The PSIM software is a cut down version of Fathom
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His Holiness the Dalai Lama.
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(Mechanical)
26 Apr 12 20:11PantheraXIn PSIM sotware the complex tee cannot be defined directly. However the pipes that are conencted to a tee can have a tee's losses defined.Once drawn select the pipe and go to Fittings and Losses. Then select "Others" go to tees in the drop down menu. There you can add a tees loss, whether straight through or branch, to the pipe losses.You could draw a system then copy and paste so two ssytems are on the workspace. One could be with losses and one without and you can see the differences.Pipes could be kept short so losses in fittings mean more than straight pipe.
Want more information on building branch pipe fittings? Feel free to contact us.
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
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(Petroleum)
27 Apr 12 00:44Please let him learn how to do it a little bit before you change him from an engineer into a software operator.
What would you be doing, if you knew that you could not fail?
(Civil/Environmental)
(OP)
27 Apr 12 00:59thank you so much BigInch and stanier!
will do the manual calculations for this first and attempt the software in awhile!
thanks again guys.
(Petroleum)
27 Apr 12 11:25Good plan. I think you have to at least get enough experience to be sure you can spot a garbage in - garbage out problem before you go pushing the buttons.
What would you be doing, if you knew that you could not fail?
(Mechanical)
27 Apr 12 21:03This reference may be of help.
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
http://waterhammer.hopout.com.au/
(Civil/Environmental)
(OP)
29 Apr 12 22:09hi guys, i've been trying the manual calculations and could i ask, in the equation of headloss (HL) = K(v^2)/2g, where does this headloss represent? between the start of the run pipe to the end of the run pipe? how do i then find the head loss between the section of the branch pipe?
(Civil/Environmental)
(OP)
29 Apr 12 22:10hi guys, i've been trying the manual calculations and could i ask, in the equation of headloss (HL) = K(v^2)/2g, where does this headloss represent? between the start of the run pipe to the end of the run pipe? how do i then find the head loss between the section of the branch pipe?
and also, for the division of flow for tee fitting, could i just use the ratio of areas to compute?
(Civil/Environmental)
(OP)
29 Apr 12 22:46let me try to answer my own question, correct me if im wrong guys.
1) the headloss equation for fittings, HL = K(v^2)/2g is for the head loss through the section of the branch pipe.
2) Division of flow for tee fitting, i'm supposed to use ratio of pressure drops. I've read that for reducing tee, flow split ratio may not be equal to ratio of areas.
(Petroleum)
30 Apr 12 02:08K(v^2)/2g is not the D'arcy (or Darcy) equation, or the Churchill equation
What would you be doing, if you knew that you could not fail?
(Civil/Environmental)
(OP)
30 Apr 12 02:19hmm, but i came across it in some piping articles that suggested using the K (obtainable from Miller chart) instead of f(L/d) to obtained additional losses due to fittings such as that of tees. Am I not supposed to do that?
Also, your emphasis on knowing the flow rate for my design is that the velocity would be required, is that right?
(Petroleum)
30 Apr 12 05:55Don't do that. K values are for calculating pressure drops at relatively short valves and fittings.Three primary variables are,FlowInlet pressureOutlet pressureknowing 2 of those, you can calculate the one missing variable.Flow divided by pipe area = velocity
What would you be doing, if you knew that you could not fail?
(Civil/Environmental)
(OP)
30 Apr 12 06:08ok i understand, since K is just a modification of the f(L/D) term. Better to go back to basics.
But now i'm stuck with a problem, how do I calculate pressure of a point in a flowing pipeline?
It has static and dynamic pressure components?
Say, for an underground buried pipe?
(Petroleum)
30 Apr 12 13:02That is derived beginning with the Bernoulli equation, include a head loss coefficient (based on D'arcy's method, or some other one) for friction due to the flow between any two points. With Bernoulli, if you know the energy at one point, you should be able to calculate the energy at another point.Since two of the three variables I gave you above are pressure and you must know two of the three, at least one known variable must be a pressure.If you know the upstream pressure, you can calculate downstream pressure, or visa versa. If you know both pressures, calculate the flow.
What would you be doing, if you knew that you could not fail?
(Civil/Environmental)
(OP)
1 May 12 09:35ok. I understand it now.
Thank you so much BigInch. I felt i have gained a lot from your comments. Thanks stanier as well.
(Petroleum)
1 May 12 12:49Good. You're off on the right track then.Come back when you have more questions.
What would you be doing, if you knew that you could not fail?
(Civil/Environmental)
(OP)
1 May 12 22:51Ok, I have managed to create an Excel template to help me compute.
BigInch, do you know of any pressure drop limits for large diameter pipelines? It seems like my pressure drop value is quite small though.
(Petroleum)
1 May 12 23:32What's your pipeline diameter, length and the product inside? Gas or liquid? Some pipelines can have flow friction losses of up to 10 psi/mile, especially if pump power costs are low. Once an initial pipeline diameter has been found, usually based on liquid velocities of 3 to 10 fps, a potential increase in that diameter can be seen worthwhile if pumping costs drop at least as much as the cost of the larger pipe diameter plus the supposed construction cost increment. Most of my pipelines seem to fall into 50 to 100 mile distances between pump stations, depending on products, water, diesel, gasoline, kerosene, natural gas, etc. and, if a liquid product on the topography of the pipeline (elevation profile). Pumping over hills or a mountain range will roughly shorten the distance between stations by the static pressure of the change in elevation / psi per mile pressure loss.
What would you be doing, if you knew that you could not fail?
(Civil/Environmental)
(OP)
1 May 12 23:50my pipeline diameter (run diameter) is about 7ft, run length about 5ft , branch diameter is 4ft with the branch length of 2ft and it carries water (liquid). My initial pressure at inlet is 230psi and a relatively slow flow of 1.6 fps.
Based on what I calculated, it seems the pressure loss over the length of branch pipe is around 0.07psi.
I'm not quite sure if such a small value of pressure loss would be practical as I have no dealt with such pressure loss calculations thus far.
Would your experience justify such a value for the above mentioned dimensions?
(Petroleum)
2 May 12 05:39It's probably correct for the pipe. The pressure drop with normal flowrates for pipes that short would be less than the pressure loss of fluid exiting the Tee fitting where they start. The Tee losses are probably 15-20 x the loss of a foot of branch piping.If you have a 1.6 fps velocity the size is OK. The trick may be holding enough backpressure in the downstream connection to keep the branch pressure near the 229.93 something psi that you will need to keep your actually developed flowrate hanging around that calculated value. Without sufficient backpressure at the branch outlet in the downstream pipeline, flow in the branch will tend to accelerate. You need to verify that the downstream pipe pressure at that point is nearly 230 psig, or try to live with the increased flowrate, if it is lower, or for that matter, the decreased flowrate, or backflow, if it should be higher. If it's backflow, put in a check valve to stop backflow when the pressure is high. If the downstream pipe has a very low pressure, you will need to install a backpressure control valve on the branch to keep the flow from increasing.
What would you be doing, if you knew that you could not fail?
(Nuclear)
2 May 12 12:21"my pipeline diameter (run diameter) is about 7ft, run length about 5ft , branch diameter is 4ft with the branch length of 2ft and it carries water (liquid). My initial pressure at inlet is 230psi and a relatively slow flow of 1.6 fps."
7 ft diameter x 5 ft run, branch = 4 ft dia x 2 ft run?
That describes a single Tee fitting, not a pipeline. What are the lengths of the whole assembled run?
(Mechanical)
2 May 12 16:56If your objective is to treat the fitting in isolation and assume that the delivery pressure at the end of the branch pipeline is the same as the delivery pressure at the end of the main run pipeline (thus equating the dP in the run and branch downstream of the tee), then I think your flow split will end up being:
(Qb/Qr) = [(Lr/Lb)*(Db/Dr)^5]^0.5
I apologize if I got that wrong and made myself look like a fool.
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