Copper tube for boiler

I need a 12 inch & 3 inch length of 4 inch diam copper tube for a boiler on a PYRTE traction engine. The cost from most model suppliers seems excessive, especially as I have never tried silver soldering such an item & it may end up in the bin

I can obtain a 1.5 metre length of table "Y" copper which is 108 diam with 2.5 Th wall for a much more reasonable price ( per metre that is) & gives me a chance to make a mistake as there is some spare to boot.

So what i want to know please - Is it the same grade of copper that is being sold by the model suppliers & will I be making a mistake buying it? I do not intend to get any test certs. It is for my own pleasure only. Working pressure is 45 PSI. Will the burners have a negative effect on the copper etc etc

Thanks

Edited By Sam Longley 1 on 17/10/2020 07:59:20

Hello Sam

Table Y seems to list a number of different grades of copper. Ideally you should get BS EN 12449 (C106) Phosphorus de-oxidised copper, which is probably what ME suppliers will sell you.

https://www.wolseley.co.uk/wcsstore7.00.1066.925/ExtendedSitesCatalogAssetStore/images/products/AssetPush/DTP_AssetPushHighRes/std.lang.all/ui/de/Lawton_Technical%20Guide.pdf

The wall thickness of a traction engine boiler is more a function of its strength as a stressed chassis; having the machine run over unexpected holes or kerbs when you're driving about is likely to put far more stress on the boiler than its internal pressure. You need a really good throatplate to barrel joint!

2,5mm wall would be about right for pressure purposes at 80psi, but regardless of the working pressure I think I'd want 3mm wall for a road vehicle.

Good luck with it; you'll need plenty of heat when you come to make it. Practice your silver-soldering first on some bits of steel or something so you get the feel for it without it costing you too much in materials. Don't just start on the boiler if you've no experience. There's plenty of literature about (especially old ME articles) on boilermaking.

You could try Noggin end metals, they are listing 4" 10swg approx 3.25mm (i think) but limited stock. Also look at M-Metals both do C106

David

Have a look at this posting of mine. It is the first boiler I have soldered it needs a good blowtorch a good hearth to contain the heat and corect flux and solder.

https://www.model-engineer.co.uk/forums/postings.asp?th=161241

Silver soldering boiler.

Ask for help.

David

Edited By David George 1 on 17/10/2020 13:35:20

Thanks for the replies. The drawings call for 1.5 Th wall but I just felt that as I was buying spare I would go for 2.5 th. Suppliers like Noggin end at £10-00 per inch are just too expensive. So far I have found 300 mm lengths at £38-00 each

As an example, I can buy a 1.5 metre length of 1.5 th walled copper for £78-00.+VAT delivered

However, I will go for table "Y" with 2.5 Th wall ( obviously much dearer) which will do me for now. I was just concerned about the effect of a concentrated heat from a burner on the copper, albeit with water inside.

But I will research C106 as suggested by Nigel

Hi Sam,

You have said that you do not intend to get any test certs. Why not build it to a code and approved design ? You may want to display it in public or at a club in the future. Or to family and friends.

A 12" long x 4" dia boiler operating at 45psi is a dangerous toy. It contains approx.2 litres of water at 135 deg C which could cause serious injury if something goes wrong.

Paul.

As far as I can tell from the specifications almost any copper tube will do for a model boiler provided the wall is thick enough.

Although copper tube comes in bewildering variety, for drinking water, drainage, brake-line, chemical, refrigeration, electrical and medical purposes, the differences in terms of heat resistance and physical strength as needed for a small low-pressure boiler are minimal.

Some problems with different coppers cancel out. Water pipes come hard or semi-hard whilst brake-line and medical tube are both annealed (soft). I don't believe it matters. After brazing, water pipe becomes at least partly annealed, but it's still as strong as before and pressurising the boiler will tend to re-harden it. Annealed copper, though soft at the outset is still strong, and it too work-hardens on the job.

I suggest the main thing to avoid is thin-walled tube and buying specials like medical or refrigerator tube new. Not because they're mechanically inferior but because they're expensive. Buying medical grade copper tube is a waste of money.

Sam mentions a concern about concentrated heat on the tube even with water inside. Shouldn't be a problem. Water cools metal faster than a flame can heat it, which is why the bottom of a sauce-pan on a gas ring only rises to 100°C, not flame temperature. It's even possible to boil water in a paper bag over an open fire. Always exceptions, but a properly designed and maintained boiler should keep itself cool. (About 150°C at 50psi) Fault conditions can fire damage a boiler, for example by turning the protective layer of water into steam, or by allowing scale to build up, or by running the boiler dry. Don't use oxy-acetylene to raise steam quickly!

I've never tried to silver-solder a boiler but experience suggests the main problem is getting enough heat on to the joint quickly enough. Too low a temperature and the solder won't flow properly, take too long getting up to temperature and the flux fails. As a thick-walled copper tube will absorb more heat than a thin one, I suggest 10g tube will be harder to solder than 3mm, which is more difficult than 2.5mm, which is distinctly trickier than 1.5mm. My advice, practice on smaller jobs first and move up step by step because the beginner is doomed to fail on a big job if his torch, hearth and technique can't deal with smaller diameter thin tube.

Trying to save money is asking for trouble. Skimping on a small torch and an ad-hoc hearth, then not practising with real copper and silver-solder because they're costly is likely to be a false economy. Owning a big torch, 50 quids worth of insulating firebricks, and a giant gas cylinder make it all much easier!

Dave

Hi Sam,

Neil offers sound advice. Practice using steel tube. If you can produce sound joints, copper will present no problems.

But use C101 or C106 grade to avoid the pitfalls associated with cheaper grades.

Carry out your brazing procedure using the principle of capillary flow.

Follow the guidelines in

BS EN 14324 available from BSI at £254.

Alternatively see PM

Keith

paul

I am following the instruction set that I purchased from the designer, so there should be no problem. Making the copper thicker than the detailed 1.5mm should not be detrimental to the construction.I am sure that I can do a pressure test myself, following all the info one can get online .

As for using a club just to get a test cert is, in my view, wrong. If one joins a club one should do it to become an active member; not someone who turns up just to get a test cert & then disappears. That is something that I cannot do as I am already member of an RC flying club & I am a very active member of my local sailing club.

I believe that the nearest club, 20 miles away in Chelmsford, is more interested in locomotives anyway

Increasing the diameter from the original design though slight may be detrimental to the end plates and the single central stay, have you done any calculations to check?

You don't have to be in a club to get your boiler tested, many traction engine builders prefer to go to an independent boiler inspector.

What is a PYRTE traction engine as it dosnt come up on search.

David

Could this be the model in question

https://www.youtube.com/watch?v=sGf5pFK0OXc

This is the  link

PYRTE

If you have not seen it you do not know what you have been missing

Edited By Sam Longley 1 on 18/10/2020 12:02:22

Jason

I always thought that inspectors operated from clubs & club membership was normally a condition of them doing the work. Clearly I was wrong.

I have an email that suggested that you put an email querying the source of tube

May I suggest this link. I have not contacted them, but there are others.

Copper pipe prices

Edit previous comment re design

I know the size is 108mm but on checking the manual it says that originally the design allowed for 4.5 inch diameter but the drawing size was reduced to 4 inch due to non availability of 4.5 inch. That tells me that 108 mm diam is perfectly Ok.

Edited By Sam Longley 1 on 18/10/2020 12:34:36

Edited By Sam Longley 1 on 18/10/2020 12:34:53

Yes I saw that price after posting but it does not say which thickness they are selling at that price?

Did not know if anything else had been changed on the boiler when the tube size was changed

The cheapest way for many is via the club inspector and the clubs insurance but you can go the independant route of a professional inspector and tailored insurance

Emailed them this afternoon ( sunday) & received a reply immediately from their MD. Pipe is 1.5mm th & they can obtain 2.5 th if I wish. i have ordered 1.5 as that is what is required on the drawing. i now need to get the copper for the end plates which is considerably thicker