# Pipe dimension

I was looking up dimensions of steel pipe. I found a few tables with figures. Here is what puzzles me: Take a 3/4 pipe: ID mm. OD&.7 mm. This is the same for about five
different pipes listed. Yet each pipe *had different wall thickness*. How is this possible? Another Tardis principle?
--
Michael Koblic,
(confused of) Campbell River, BC
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Pipe sizes were defined in the 'old days' when everything was threaded connections and you needed to be able to flow a certain amount of gas or liquid.
Pipe has a defined OD so all the different pipe fittings can be be attached. The ID is sized so that "normal" wall thickness (designated 'Schedule 40')will give an ID that is equal to or larger than the nominal dimension. After that, there are Schedule 5, 10, 20, 40, 80, and 160 to handle different pressures which give you all the different wall thicknesses. Confused yet?
Michael Koblic wrote:

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I think the ID of Schedule 80 pipe is closest to the Nominal Size. At least it is for 3/4" as I recently made a bunch of spacers for 3/4" bolts from 3/4" Schedule 80 pipe after checking the size tables.
I recently acquired a large manual of Society of Automotive Engineers (SAE) standards for 1957 and I noticed it has lengthy standards for many things, such as for windshield wiper hose in two sizes. It includes requirements and testing for such things as pressure, vacuum, and radius of bend!!!
Don Young
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OK, if I understand you right the nominal size refers to the ID but it is the *OD* that is held constant and the ID varies with the schedule and the wall thickness. Why, that makes perfect sense!
Not surprising I feel like Alice in wonderland...
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Correct on both counts!!!! :)
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You got it!!
Don Young
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Because the threads are on the OD.
Steel pipe isn't precise in size and definitely isn't guaranteed to be round, as you'll find out when you try turning it in a lathe. Brass pipe is much closer. The pipe I've bought recently from HD and Lowes does machine and weld nicely.
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Steel pipe isn't precise in size and definitely isn't guaranteed to be round, as you'll find out when you try turning it in a lathe. Brass pipe is much closer. The pipe I've bought recently from HD and Lowes does machine and weld nicely.
***Yes. My RedNeck lathe v3.0 has not done a good job so far I am sad to say :-) BTW do not ask - one day I might muster sufficient courage to tell. I have got a pair of superb little 1" pillow blocks cheap. I found a 9" pulley to match from scrap - cleaned up nicely. However, taking 1mm off the pipe diameter - priceless.
Still, I have solved minor intellectual puzzles (which I am sure you guys would have done on a sub-tentorial basis), such as finding a centre on a mounted endcap (sadly, the bolt through the centre will not turn the pipe in a true concentric fashion even with a liberal use of hammer). On the other end of the pipe I fashioned a decent red neck 4-jaw chuck with four 10-32 screws. Much better result.
I was thinking of a floor flange in lieu of a face plate, however the way they fit together with the pipe I would have to take a whopping 3 mm off the flange thickness to make it run true.
I might cut a 1"-8 thread in one end of the pipe instead - that would have all sorts of other benefits.
BTW the local machine shop quoted me \$45 for the job...
--
Michael Koblic,
Campbell River, BC
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On Mon, 27 Oct 2008 19:33:21 -0700, the infamous "Michael Koblic"

So, Mikey, who holds your beer while you're using it?
-- Some days, it's not even worth chewing through the restraints.
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That's what the hard-hat with two duct-taped cans and a hose is for!
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On Tue, 28 Oct 2008 18:07:54 -0700, the infamous "Michael Koblic"

OK, got it. So where's the video?
-- Change is the process by which the future invades our lives. -- Alvin Toffler
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Repo man got the camcorder...
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Yup, been there. I wanted to make an extended support column for my cheapie bench drill press, found a suitable piece of pipe in the drop bin at the local hardware store. Just a bit oversize, no lathe big enough and no pipe center anyway. I used a belt grinder to do the deed. Found out the stuff was square when I started grinding it down. So, round and round for several hours on a piece that was maybe 3" in diameter and 3' long. Used the table support for gauging and a Magnum-sized magic marker for finding high spots. Got it within .005" from end to end, close enough for the table support to lock tightly from top to bottom. Needed the extended column for fitting a tubing fish-mouthing jig. Works great and I'm pretty sure I wouldn't have gotten as good a finish on a lathe, had I had one handy. Belt grinder has proven indispensable for a lot of things since then, that was the first real project I used it on.
Stan
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Yup, been there. I wanted to make an extended support column for my cheapie bench drill press, found a suitable piece of pipe in the drop bin at the local hardware store. Just a bit oversize, no lathe big enough and no pipe center anyway. I used a belt grinder to do the deed. Found out the stuff was square when I started grinding it down. So, round and round for several hours on a piece that was maybe 3" in diameter and 3' long. Used the table support for gauging and a Magnum-sized magic marker for finding high spots. Got it within .005" from end to end, close enough for the table support to lock tightly from top to bottom. Needed the extended column for fitting a tubing fish-mouthing jig. Works great and I'm pretty sure I wouldn't have gotten as good a finish on a lathe, had I had one handy. Belt grinder has proven indispensable for a lot of things since then, that was the first real project I used it on.
***LOL! Belt sander is my best friend. I tried spinning the pipe on a sort of mandrel. Hours of fun! Not enough patience. P.ss-poor result. But I am working on an alternative...
--
Michael Koblic,
Campbell River, BC
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My understanding is that pipe had an ID that was the nominal dimension and the OD was such that the strength was good for normal water pressures. When the steel used for pipe improved, the OD stayed the same so threaded fittings still worked. But with the improved steel the ID could and was made bigger. So now steel pipe has an ID that is somewhat bigger than the nominal size.
Dan