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miniature copper pipe

advice sought

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Anthony Knights10/05/2021 11:29:07
509 forum posts
209 photos

I have now got to the stage with my latest build where plumbing the steam ( or in my case, air) is involved. I do have some small copper pipe but am unsure of the actual size. The OD is 3.192 mm, which is just a bit over 1/8th of an inch. The bore was checked using drill shanks and is between 1.9mm (go) and 2mm (no-go). This is about 5/64 of an inch.

I always understood that imperial copper pipes were specified by their bore. Does this change when the smaller sizes are involved?

 

pipe.jpg

Is my pipe an actual "proper" size? I can't remember where it came from because I've had it for so long. The item I'm building does specify 1/8" pipe and the related holes are 3mm so it's close.

Finally, what type of fittings are available for this sized pipe and could someone point me towards a source, even if I have to buy correctly dimensioned pipe. Thank you in advance gentlemen.

Anthony

 

Edited By Anthony Knights on 10/05/2021 11:32:08

Paul Lousick10/05/2021 12:11:22
1755 forum posts
637 photos

British Standard Pipe (BSP) is specified by a nominal diameter and a schedule (wall thickness). While the wall thickness varies, the outside diameter remains the same so it is compatable with all screwed fittings for that size pipe.

Your example is more likety to be 1/8" copper tube which is specified by its OD and a wall thickness.

Lots fo brass fittings available for tube. Solder on, Clamp with an olive or flared ends.  Adaptors to BSP threads, Tees, Elbows, etc.   Do a search for capillary fittings or Brass tube fittings, etc.

Paul

Edited By Paul Lousick on 10/05/2021 12:19:45

Martin Connelly10/05/2021 12:37:54
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Paul, I think you are mixing up the American ANSI Nominal Pipe size system with BSP. Wall thickness schedule is not usually used with British Standard Pipe which had a standard wall thickness for each nominal size. BSP is generally no longer used for pipes but BSP threads are still in general use. At work we still had a lot of drawings with BSP pipe on them but it was all mild steel and we went away from both mild steel and BSP to stainless 321 and later 316L in ANSI sizes. We still had the company standards for BSP pipe being maintained when I left in 2019. When a spares request came through for a spare and the drawing called up mild steel BSP we raised a concession to replace it with stainless nominal pipe sizes. BSP was close to the ANSI size in sch40, this was the minimum wall thickness required for threading but with ANSI sizes we used sch5 due to weight reduction and material costs being lower.

I think you are correct that this is 1/8" outside diameter and is probably 14swg wall (0.08", 2.03mm).

Anthony, what fittings do you require, I think it may be a case of make your own.

Martin C

Jim Nic10/05/2021 15:39:10
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335 forum posts
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Macc Models sells 1/8 dia copper tube and associated fittings including complete unions, pipe ends and nuts or olives.

I use some fittings bought from Macc, some fittings I make and incorporate Macc olives and/or pipe ends and nuts and some I make entirely from round or hexagonal bar stock. The choice usually depends on what materials I have to hand.

Jim

Anthony Knights11/05/2021 09:25:07
509 forum posts
209 photos

Thank you all.

I have looked on the Macc Models site and that is the type of stuff I'm looking for, although not much in 1/8" sizes. I now know what I'm looking for, so I can search else where. If all else fails I can order a 1/8" tap and die, some brass hex bar and make the fittings myself. Both 1/8" whit and ME are 40tpi while 1/8" BSP is shown as 28tpi. Personally, I think the finer thread would look better so I'll go for that. Just got to trawl the internet to find the correct AF size for the hex bar.

Mike Hurley11/05/2021 09:46:11
135 forum posts
64 photos

Be careful! 1/8" BSP is NOT the same as 1/8" BSW (not just tpi!). Do a quick Google on BSP and you'll see what I mean

regards Mike

Jim Nic11/05/2021 10:07:11
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335 forum posts
197 photos

Anthony

+1 for be careful.

I think you will find that your 1/8" OD pipe will fit in a 1/8" ID nipple which will require a nut with a 1/4" x 40 TPI ME thread.

Jim

Anthony Knights11/05/2021 10:34:04
509 forum posts
209 photos

Thanks guys. If you see my first post, you will see I was already aware of the discrepancy with the BSP specification and the size of pipe (1/8" ) OD which I have. This was one reason for asking the original question. I have been on the internet for ages, looked at loads of different sites, but nowhere can I find the AF size of the nuts used on the 1/8" fittings. The threads seem to be either 7/32" or 1/4" x 40 tpi. Jim has mentioned 1/4" x40tpi so that must be it. Still don't know what size hex bar to order. I may have to order some nuts and measure them.

Anthony

Stupid smiley thing deleted

Edited By Anthony Knights on 11/05/2021 10:35:14

Hopper11/05/2021 10:34:31
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I have never seen copper tubing threaded. It usually slides into a brass compression fitting or the like where a 1/8" ID brass nipple is slipped over the 1/8"OD tubing and held captive by a brass nut against the main fitting, using a taper to compress the nipple and hold the pipe. Otherwise the copper tubing is soldered into a brass fitting. This often looks tidier on models as the standard compression fittings look too big to be true scale fittings.

And 1/8 BSP is a whole different size again. The thread is much larger diameter, made to fit the outside of a steel pipe with a nominal 1/8" hole up the middle.

Rule of thumb is pipe is measured by nominal ID while tube is measured by the nominal OD. Thus 1/8" pipe is much bigger diameter than 1/8" tube. (And what you have is nominal 1/8" tube. 3.192mm is half a thou over 1/8". Manufacturing tolerances are a lot looser than that so you have done well.)

Edited By Hopper on 11/05/2021 10:37:36

Hopper11/05/2021 10:42:08
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5505 forum posts
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OOps simultaneous post on the last one. Disregard any repetition of what was already said.

Size of hex may depend on what fittings you are making. If you are going to use a 1/4" thread the hex will need to be the next biggest size available, giving the wall thickness required for what you want to do. I suppose 5/16? Hard to say without seeing a pic or drawing of the fitting you want to make.

Paul Lousick11/05/2021 10:43:15
1755 forum posts
637 photos

Martin,

The BSP system does not have a standard wall thickness for each size but is available in different thicknesses as shown in this link: **LINK**

If your work is using the ANSI standards for pipe (American National Standards Institute) it may be because of the availability of obtaining stainless steel pipe. S/S pipe is not as common as MS pipe and galvanised MS pipe used for plumbing, etc.

Paul

Anthony Knights11/05/2021 11:05:15
509 forum posts
209 photos

Hi Hopper. I was aware that BSP is specified by bore, but I wasn't aware of the difference between "tube" and "pipe". To me they both had holes down the middle. The old Imperial system defined size by bore but when we went metric, just to be awkward, they changed it to OD. Thus the difference between 1/2" pipe OD and 15mm is so small that you can join them with a 15mm compression fitting, provided you use a slightly differently size olive for the 1/2" end.

If it turns out that the actual 1/8" fittings look too cumbersome and out of scale, I may just solder the ends and use some suitable sized hex bar to make dummy nuts.

Anthony

Paul Lousick11/05/2021 12:19:23
1755 forum posts
637 photos

When BSP pipe sizes changed to metric they did not change the bore size to an OD in metric but specified it as an approximate mm size of the nominal bore diameter. The OD of a 1/2" pipe is 21.3mm, not 15mm.

The link above for 1/2" BSP pipe has the wall thickness for the available schedules. (From 0.065"- 0.294"). The wall thickness varies but the OD has to remain constant to be compatable with screwed fittings. The ID is important for calculating the volume of liquid that can pass thru the pipe and is given a nominal size (average size) for the bore.

Pipe tends to have thicker walls and have screwed connections. Tube is thinner and uses flared or clamp type fittings using an olive or are soldered.

Paul

bsp schedule.jpg

 

Edited By Paul Lousick on 11/05/2021 12:35:28

Martin Connelly11/05/2021 13:49:43
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1757 forum posts
189 photos

Paul, it doesn't say BSP pipe it says Nominal Pipe. You are repeating the same mistake again. British standard pipe was not supplied to a schedule, it had standard (imperial) gauge size wall and was a close match to ANSI but not the same.

Martin C

p1150783.jpg

Edited By Martin Connelly on 11/05/2021 13:53:53

Edited By Martin Connelly on 11/05/2021 13:57:53

Jim Nic11/05/2021 14:33:26
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335 forum posts
197 photos

Here is a picture of a set of bought in components.

pipe fittings.jpg

The pipe is 1/8" OD, the union thread is 1/4" x 40 TPI ME and the nut is 8mm across the flats.

HTH

Jim

 

Edited By Jim Nic on 11/05/2021 14:34:06

Edited By Jim Nic on 11/05/2021 14:34:41

Anthony Knights11/05/2021 16:59:27
509 forum posts
209 photos

A picture is worth a thousand words. Thanks Jim

Anthony

Paul Lousick11/05/2021 23:52:43
1755 forum posts
637 photos

Hi Martin,

Is not the Standard pipe size in your table the same as Schedule 40 pipe which is the common size used for plumbing ?  It is even listed next to the Schedule 40 in the table above and is only one of the sizes available

Paul.

Edited By Paul Lousick on 11/05/2021 23:58:03

Anthony Knights12/05/2021 08:03:21
509 forum posts
209 photos

That's me sorted. It's confirmed that my tube is the correct size and thanks to Jim, I now know what fittings to order, should I decide to use them. I must also remember, that should I do any more plumbing work in my house, I will be working with copper TUBE, not PIPE!

Thank you all who contributed.

Anthony

Martin Connelly12/05/2021 08:18:03
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1757 forum posts
189 photos

If you look at the tolerances of the ANSI standard and the BSP standard you will find that the ANSI standard is much looser. So while the nominal sizes of both look close but are not quite the same the actual sizes delivered under the two standards can be very different. Additionally the wall thickness in BSP is defined with upper and lower limits, the wall thickness with ANSI schedule pipe is a minimum with no maximum. The limitation on wall thickness with ANSI pipe is only limited by the pipe standard defining a maximum weight per unit of length. This means the wall thickness with ANSI pipe can be at the minimum for some distance then be a lot thicker for a short stretch before returning to the minimum and still be within spec. European manufacturers started to supply ANSI standard pipe defined by a metric defined OD and wall thickness that kept it within the ANSI standard but was made to a much better tolerance, more like an OD tube with ±0.005" tolerance on OD. This was important for people who needed accurate sizes for bending machines with costly outside dies and internal mandrels. Where I worked we often had ANSI pipe that we had to put aside labelled as for straight lengths only as it was either too large or too small a diameter for the clamp and bend dies to grip correctly or had a bore that was too small for any of the mandrels we had to go down smoothly (or occasionally was too hard and snapped rather than bent).

The wall thickness issue showed up when looking at elbows, tees and reducers and pipes from different batches. In order to do  a satisfactory weld that was going to be X-rayed you needed to have matched bores and this often required that the thicker walled part had the internal wall reduced and blended out at a smooth and shallow angle to match the thinner walled part. Scoring that would show up on X-rays were unacceptable and the result was that a lot of time was spent manually blending parts for welding which put up the cost of pipes that required radiographic testing.

The wall thickness issue with ANSI fittings also caused issues when the designers had assumed that ANSI pipe bores were what they calculated from the basic tables and had not looked fully into the tolerance issues. With smaller sizes such as 1" or 3/4" nominal bore you could have elbows with the actual bore as much as 50% less than the maximum. It plays havoc with flow calculations.

Martin C

p1150784.jpg

 

Edited By Martin Connelly on 12/05/2021 08:33:10

Martin Connelly12/05/2021 08:42:16
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1757 forum posts
189 photos

This is the page of ASTM tolerances applied to ANSI general purpose pipes. Using this information you can calculate the maximum and minimum diameters of a 2" ANSI pipe and compare it to the BSP 2" pipe from the earlier post to see how different they can be. It also shows there is a minimum wall but there is no mention of a maximum and you have to delve fully into the standards to find the limiting factor on wall thickness is purely by weight. This means that the maximum wall on a pipe at the maximum allowed diameter is different from the maximum wall on a minimum allowed diameter pipe. An example of a very poorly written standard in my opinion.

p1150785.jpg

Martin C

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