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Natural Gas Piping

Natural Gas Piping

Natural Gas Piping

I am installing a new gas meter in a 6" poly line DR11.  During this installation I have to take this out of service.  Problem:  The bypass for this line is only a 2" Polyline DR11.  I have tried numerous equations and have come up with different answers everytime.  Here is the information I have.  I need about 40,000 KCF/hr.  I have an input pressure of 30# guage and can allow this pressure to drop to 10# before I have to relight all 900 houses.  Will it work?  Can you suggest a good book so when I encounter this again I can find the answer?

RE: Natural Gas Piping

This is how Crane would have done it (Compressible flow manual p. 6-9)

You need to determine k (Cp/Cv) and temperature of the gas Tt0

Assume soic velocity in pipe exit: M2=1.0 and calcuate exit pressure. If the exit pressure is less than ambient (exit pressure) then Ps2=ambient and the exit mach no. is subsonic

I did a quick check with a program called flowmaster this implies that your way over the top your pressuredrop with a 20 psig exit pressure would be around 15000 psi when simulating the bypass as a sharp orifice - but there  is to little info

What do you mean by KCF (standard?) are you sure its 40000 K (not 40 K or 40000 "no-K")? Because thats a lot of gas (266 kg/sec if molweight is about 20)

whats the molweight (or composition) whats the gas temp

RE: Natural Gas Piping

    You were correct when you asked was it standard cubic feet it was.  The quantity was 40k not 40000K and the gas should be at ground temperature which is about 60F.  The molecular weight will be slightly over that of methane as it is natural gas.   

RE: Natural Gas Piping

If you pick your time, shouldn't you be able to schedule this on a warm day? If you also aim for, say 9 or 10 AM during the week, even the domestic hot water use should be pretty much non-existant. If you can time this right, you should only need to feed enough gas through the bypass to keep the pilots lit.

RE: Natural Gas Piping

I agree TBP this should be the way it works, but if the contractor has problems on site the nearest poly fitting supplier is 3 hrs away.  I could have to go through a night on the bypass.  I am thinking worst case here.  Just as soon as I cut the line.  I am nervous until the project is done.  It should take only 2 hours to fuse the 2 couplings to the line.

RE: Natural Gas Piping

I took a look at this using Crane as Morten suggested.  Assuming the ID of the 2" bypass line is actually 2" (not sure if these following the same dimensions as piping, have seen some stuff that plastic piping ID = nominal).

To get 40,000 scf/hr through the bypass line, assuming an equivalent length for the bypass valve and fittings of 30 feet and including the inlet/outlet loss, I estimate you only need a couple of psi to get the necessary flow through this line.

RE: Natural Gas Piping

I checked this using a few different formulae (Weymouth, Moody, Panhandle, AGA - man don't ya just love Pipephase for little jobs like this...  took me about 5 minuntes to do this calc even with changing the correlations...)  and it looks like TD2K has the right answer (as usual   - was that gratuitous?)  Looks like it'll work to me.


RE: Natural Gas Piping

rechecked with the 40000 (not 40000K) and got a nice low figure (about 1 PSI if simplified to just an orifice).

Best Regards


RE: Natural Gas Piping

If you are using NG for stove and hot water, I would estimate the usage at 1800 CF/H at min, and 9000 CF/H at max.  You could get better numbers by dividing up a monthly total usage by number of hours in a month (from same month last year).  If you are heating the houses, I really cant guess cause I work in Hawaii and don't know much about that.  Supply systems tend to be way oversized from my experience.

What does it cost you to relight 900 houses, include the irritation factor? Swag the probability of having to do so, keeping in mind that it takes alot of atta boys to wipe out an oh shit.   What does it cost to get a complete backup set of parts ahead of time?  

Let me know how you like this totally non scientific approach.


RE: Natural Gas Piping

Pacific Steve
It takes about 30 minutes to bleed the air out of the lines and relit the furnace and water heater.  The stove is on an electronic ignitor.  The "we've got a problem factor"  was more than enough to pay for the bypass.  I have enough extra parts on hand so that if there is a mistake it can be corrected.  I would have to get the parts replaced by the contractor.  Thanks to all who have written.  Where can I get this Crane manual?  
Bron Howard
Altus OK

RE: Natural Gas Piping

Go to:  http://www.cranevalve.com/tech.htm
 This is really a "must-have" book for anyone doing any fluids work and it's relatively cheap ($33 american)

Patricia Lougheed

RE: Natural Gas Piping


Just FYI, did you know that one of the top energy guys in America is located at Oklahoma State University, Stillwater, OK.  Dr. Wayne C. Turner.  He is the editor for the American Energy Engineers monthly periodical, as well as having lots of practical and technical experience.  Could be a great resource to assist in your overall energy planning.  Not his phone number, but he can be tracked down by calling 770-447-5083 AEE.


RE: Natural Gas Piping

Hi All:  
Sorry I'm late to the party.
In the Gas Industry (Natural Gas, that is) we have used a nice little program called GasCalc, by Bradley B. Bean.  Call him at 800-391-9391.  The program has all kinds of features that help you design natural gas systems, including pipe flow, line pack, orifice flow, etc.  Has all the equations to choose from (high pressure, low pressure, distribution pressure, e.g. Panhandle, Spitzglass,Weymouth, etc.) and is inexpensive.  You might even be able to get it over the web.

If you are responsible for a n.g. system this one of the tools I would get - Crane Tech 410 is the authority, and I would get it also, but Gas Calc is much easier on a daily basis to use.

One question - are you (hopefully ) transitioning to steel before installing the meter?  Have you checked wtih the manufacturers specs for installation?  Is it above or below ground?  Just curious.

RE: Natural Gas Piping

I am using anodeless risers that are coming off of a 6" poly line, necked down to 4" steel as it goes through the meterset with bypass.  I had DMD Dresser size and design the meterset for me.  The meterset is a little over 36" above ground.  I will have a concrete pad and rail installed around the meterset to protect if from damage.  Hopefully it will be installed by the end of the month.  Thanks for the information.  

Bron Howard  

RE: Natural Gas Piping

Bron - I tried to respond to the email you sent me but it was returned, said you exceeded your storage capacity?  Don't ya just hate when that happens?  


RE: Natural Gas Piping

Why not add a second (or third) bypass?  At my company when we cut out sections of PE (damage, new in-line tee, etc.) if we are concerned about a single 2" branch saddle bypass (2 - 6" x 2" branch saddles with a 2" PE interconnect, then squeeze between the two saddles to cut out the section you are working on) we will add a second or third bypass.  We also time the work for low flow periods.  Sometimes we utilize our 70,000 cf equivalent "tube" trailer of CNG to tide us over until the work is done.  Lots of options.  I don't like tons of branch connections unless you absolutely need them but re-lights are hard.

By the way, have you been happy with DMD Dresser's meterset design?  I was never very impressed by them.  Very large and kind of pricey for what you get.  Of course, I'm on the West Coast and they manufacture in Erie, PA.

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