Standard pipe dimensions
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  1. #1
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    Default Standard pipe dimensions

    I have often been curious where the weird pipe dimensions come from. Half inch is never half inch etc. in the plumbing world. I found this chart thinking it might help someone other then me.


    pipes.jpg

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    The inside is the important dimension - what can pipe FLOW. Even at the Schedule 80 wall thickness, 1/2" pipe is still larger than 1/2" bore - .546

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    Where those dimensions come from has always baffled me too--certainly no logic behind them. Still, they
    are what they are. Learn the numbers and work with them...

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    John has it correct but.. Over the centuries wall thickness has been reduced as metal working has improved. So what started out as 1/2" bore has stayed the same on the outside but the inner bore has gradually been increased. For high pressure use the inner bore has been reduced since wall thickness had to be increased to hold back thousands of pound of pressure.
    Tubing is normally measured by outside diameter, including PEX tubing. Thus 1/2 water pipe is the same as 3/4" PEX as far as inner bore.
    Bill D

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    Indeed. Our standards were initially written for wrought iron pipe, and named as such, which should give some idea what strength material they were written for. 1/2 inch pipe was originally a nominal half inch I.D. As the material got stronger the walls got thinner and the I.D. bigger but the threaded connections still work.
    Dennis

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    Quote Originally Posted by crossthread View Post
    I have often been curious where the weird pipe dimensions come from. Half inch is never half inch etc. in the plumbing world. I found this chart thinking it might help someone other then me.


    pipes.jpg
    No, but 24" is 24". You just need to work bigger pipe!

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    Amazing effort by someone
    Attached Thumbnails Attached Thumbnails pipe-data.jpg  

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    Damn John. Again someone has made me feel somewhat inadequate. However I will try to stick with my puny little chart.

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    The logic behind pipe dimensions depends on two factors. First, the inside diameter is used as the nominal pipe size because that determines how large the flow rate can be. And second, the threads on the fittings for each nominal pipe size need to fit the threads on all weights (Schedule #s) of pipe in that nominal size. So it is the ODs (outer diameters) that must be constant so that the same threads can be cut.

    The problem or mystery arises when you see that different weights (Schedule) pipes will have different wall thicknesses. So, for a 1" nominal pipe size the OD will be a constant 1.315" for all Schedule sizes. But a 1", Schedule 5 pipe will have walls that are only 0.065" thick and the actual inside diameter will be 1.185". That's quite a bit larger then the nominal 1". But a 1", Schedule 80 pipe will have walls that are 0.179" and an ID of 0.957" which is a bit under the 1" nominal size.

    The Schedule 80 pipe IDs seem to match the nominal sizes best, but they are usually a bit under that nominal size. This may be due to changes in materials used or in other specifications, such as pressure ratings over time.

    The train of thought goes like this:

    1. Specify a nominal size.
    2. Add twice the wall thickness of the HEAVIEST schedule pipe made in that size.
    3. That gives you the nominal OD for ALL schedules of pipe in that nominal size so the threads are compatible.
    4. The actual ID is the nominal OD for that size minus twice the wall thickness for the schedule that you are using.

    Thus the ID varies greatly over the range of different schedule sizes.

    Nominal Pipe Size - Wikipedia

    Many other internet references on this.

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    Quote Originally Posted by johnoder View Post
    Amazing effort by someone
    I'd LOVE to have this in a high-res scan! Could I talk you into that? I'll send it to drafting and have it plotted for my office.

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    Quote Originally Posted by Cole2534 View Post
    I'd LOVE to have this in a high-res scan! Could I talk you into that? I'll send it to drafting and have it plotted for my office.
    PM an email address (with PIPE in the subject line) - its a little over 1Mb

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    Some people had me make a bunch of fittings that are a fixed orifice determined by the particular application. I make them with only a pilot hole in the closed end and bore them to size as requested. The ODs and bores were all odd dimensions that made no sense until the told me they were substituted for adjustable valves with standard pipe connections.

    And so it goes.

    bill

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    Come into my world of the oilfield. We don't use schedule for pipe. IT's based on weight in pounds per foot on threaded and coupled pipe in either 30 foot for tubing and 40 foot for casing. One size I use a lot in designing equipment is 5-1/2" OD x 20 pound/foot casing. It can be as much as 5.550" on the OD and the I.D. can vary as much as 4.653" minimum to as much as 4.868" maximum. So if your head is not spinning now, it will be. Ken

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    We work with HDPE IPS SDR pipe. IPS is iron pipe size so standard Sch pipe Od. SDR is standard diameter ratio. SDR11 has a wall thickness of 1/11 the OD. Sounds weird, but makes perfect sense. All sizes of SDR11 pipe have the exact same pressure rating and hoop stress.

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    standard "black iron" plumbing pipe, usually schedule 40, is used and sold all over the world. In INCH sizes, even if everything else in the country is metric. But, some places the threads are tapered, and, in some countries, the threads are straight cut, and you have to use oakum to get a non-leaking connection. Dont ask me how I know this, but it involves mops, buckets, multiple disassemblies and reassemblies, and multiple trips to the plumbing supply store.

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    Quote Originally Posted by EPAIII View Post

    The train of thought goes like this:

    1. Specify a nominal size.
    2. Add twice the wall thickness of the HEAVIEST schedule pipe made in that size.
    3. That gives you the nominal OD for ALL schedules of pipe in that nominal size so the threads are compatible.
    No, sorry. The HEAVIEST schedule is commonly going to be 160, or XXS, and that formula isn’t even close to correct for those. Look ‘em up.

    What is so hard about looking up a schedule dimension or chart?

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    Nothing in this whole mess is perfect. You can't just apply formulae to the nominal sizes. I am totally aware of Schedule 160 and XXH which is even heavier. But the system appears to be based on the APPROXIMATE sizes of the Schedule 80 pipe. From there it appears that there have been a lot of compromises and probably changes as the system evolved.

    I also suspect that pipe sizes heaver than Schedule 80 were added after the other Schedules were already in use. Anybody know for sure?

    One thing that all the pipe size charts do show is that the OD is constant for all the Schedule sizes, all the way from Schedule 5 up to Schedule 160 and even for the XXH size. It would be quite difficult to start with the Schedule 160 or the XXH at the nominal inside diameter, add the needed wall thickness, and then use the resulting number for the OD. That would make the OD of XXH, 1" pipe 1.716" instead of 1.315" which would be another 0.4". And, to keep the threads the same size, all the other Schedules, even Schedule 5, would have to be that big. That would be absurd.

    If you have a better explanation, I await.



    Quote Originally Posted by cyanidekid View Post
    No, sorry. The HEAVIEST schedule is commonly going to be 160, or XXS, and that formula isn’t even close to correct for those. Look ‘em up.

    What is so hard about looking up a schedule dimension or chart?


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