Copper for boilers

[ed miles]

What grade of copper sheet, and what thickness do you use. Boiler (vertical) dimensions of the unit that I have the drawings for does not state this. They only show the outside diameter of 6 1/8" and the length is 12". The drawing is essentialy to scale and the wall scales out at 1/8" thick. Is that realistic, or should it be heavier. Is this material mostly a purchased item from a metals house or can it be found in other places if you want to spend the time to look.

Ed

 

[compound driver]

hello Ed

I build boilers partly for a living. Contact me off site and il email you all you need to know on boiler copper. What ever you do DO NOT USE PLUMBING copper it contains traces of Pb. You need and must have a grade of copper thats recognised by boiler inspectors and the authorities.


From the OD of the boiler tube you then need to work out the hoop stress to find the gauge of copper to use. its a simple formula as follows.

P= Dx W.P. x F
__________
Sx2xRxCxT

Where P = plate thicknes (barrel) in inches
S = Ultimate tensile strength in PSI (copper 25,000 PSI Steel 60,000 PSI)
F = Factor of safety from 6-10 as a rule 8
R = riveting allowance (.8 for welded brazed or silver soldered)
D = Diameter of barrel in inches
C = corrosion allowance (for steel only .25 inch and bellow .5 to .8)
temperature allowance (copper at 400F =.7 200F = .87)
W.P. = working pressure

All flat surfaces should be atleast 1/3 thicker than the boiler barrel. Stays should not exceed a pitch = to

tx800
_____
W.P.

t = thicknes of inner firebox wrapper

Firebox stays should be twice the thicknes of the inner firebox wrapper.


Cheers kevin

 

[sidecar_jon]

. What ever you do DO NOT USE PLUMBING copper it contains traces of Pb. You need and must have a grade of copper thats recognised by boiler inspectors and the authorities.

kevin

That's interesting, i've noticed a difference between older copper pipes and new ones, the older are smoother and easier to heat treat (to soften for bowl making) Has the composition changed in the last 20 years?

 

[compound driver]

HI
I know what your saying I have noticed copper works different now. I had put it down to my arms and hands getting older.

I am assured by my boiler inspector and metal stockist that copper compositions are much the same just being pulled into line with europe (what ever that gets us).

Theres a very interesting article on the CUP aloys website abut copper and soldering copper it explains it very well il dig up the link if I can find it

http://www.cupalloys.com/content.php

Couldnt find the direct link but have a look and im sure you will find it.

Cheers kevin

 

[Mcgyver]

What ever you do DO NOT USE PLUMBING copper it contains traces of Pb. You need and must have a grade of copper thats recognised by boiler inspectors and the authorities.

Kevin, i'd tucked that one away with a note to self to better understand at some point. I'd piad a small fortune ages ago for a length of 4" copper pipe with the intent of building the electric benchtop boiler described in live steam (or HSM) years ago.

I see the above post and me thinks, hmmm, is that expensive piece of copper unsuitable? do i have to roll my own?

than I see your terrific post on making a boiler (thank you for the huge amount of work you put into that). You're using a piece of copper that looks identical to what i have. I'm speculating a bit here, but do they make 4" copper pipe for uses other than plumbing? in other words isn't it plumbing copper and subject to the traces of lead concern? ....or do they use different alloys for the larger dia?

since it was before i joined, i might not have noticed the boilder piece except for it being locked today ....what's with all the locking of threads? I was going to post a compliment to that thread.

 

[PTsideshow]

Here is the deal on the copper, Here in the US and Canada the standards for electrical wiring are such due to the need for it to carry known electrical properties etc. It can be only made form virgin copper.

I'm sure that it is the same in the countries on the other side of the pond. No recycled copper bits even old wire can be used. This is so there is no chance of unknown scrap getting in the material stream. All the copper recycled is used for plumbing fixture, fittings and piping and refrigeration tubing etc.

In other words all no electrical related products, which makes sense. As other metals in the mix change the properties of the material.

Like the magnetic brass cast do dads from India etc. Some of the current plumbing fitting and pipe can vary in the soldering or cleaning of it from store to store or batch to batch.

 

[Lakc]

At the risk of thread necromancy, I have to bring this back up.

Copper water pipe in the US should be alloy C122, which lists .0002ppm lead and is actually slightly stronger 31,300 then the usual 25,000 psi thumb spec.

And with all the big box copper plumbing going into schools, government, and millitary installations, I can hardly expect any lead would escape without notice?

Given proper parameters for use, shouldn't this be ok for boiler work?

 

[SandyC]

Hi Guys,

For copper boilers which are silver soldered/brazed the copper grade most specified and acceptable to the boiler inspectors is: -

C106 Copper

Phosphorus deoxidised copper is the grade of copper where oxygen is removed by the controlled addition of phosphorus during the melting cycle. A slight excess of phosphorus ensures complete removal of oxide. The residual phosphorus remains alloyed with the copper within the specified range 0.013-0.050%. The copper content is 99.85% minimum and the grade conforms to the compositional requirements of British Standard alloy designation C106.
C106 is superior to the electrolytic tough pitch copper electrical grade (C101) and should be specified for all non-electrical applications, especially those involving assembly by welding or brazing. Phosphorus deoxidised copper is not susceptible to hydrogen embrittlement which is a serious risk with non-deoxidised grades.

Related Specifications

BS2871.
Cu-DHP.
DIN 1787.

It will be acceptable in every country I know of, without question as the best grade for model boilers.
It is available in Solid drawn Tube , Solid extruded bar and rolled sheet forms.


The formulae generally accepted by Inspectors for EU and UK, Aus.

Are : -
For boiler shell calculations the applied safety factor is generally accepted a being 8, which results in an accepted tensile strength of: -

25,000/8 = 3,125psi = Tensile strength (t)

1. The formula for plate/wall thickness is given as: -

T = P x D / 2t


2. And for Pressure as: -

P = 2T x t / D


Where D = Internal dia
t = Tensile strength
T = Thickness
And P = Working pressure

These apply for Solid Drawn (seamless Tube) only... If the shell is rolled from sheet material then an additional allowance/reduction must be made for the resulting joint/seam as per Kevins formulae above.


Hope this helps.


Best regards.


SandyC.

 

[kvom]

Best alloys are 101 and 106.

Copper pipe is hard to find i n short lengths, so it's like you'd need to roll from a sheet.

 

[Charles Lamont]

Just as an interesting factoid, C107 arsenical copper is used in full-size locomotive fireboxes, for its higher strength at raised temperature, for its corrosion resistance, and its weldability.

 

[Lakc]

Thanks for the responses folks.
After much searching and technical reading, I understand the hydrogen embrittlement issue.
The good news, is according to all sources I have found, including this site http://www.copper-key.org/index.php?lang=english English C106 copper is the same as US C122.
Which, to us folks on this side of the pond, means copper pipe at any big box home improvement store.

 

[GWRdriver]

Thanks for the responses folks. The good news, is according to all sources I have found, [smip] English C106 copper is the same as US C122.
Which, to us folks on this side of the pond, means copper pipe at any big box home improvement store.

Bingo! After all this dust & smoke you have it right. USA C122 for tubes, C110 for plates. Simple as that. What you need to be mindful of the is the "Type" (which implies wall thickness or gauge.) - in the USA Types K, L, M, and DVW.

Type DWV is for non-pressurized waste and should never be used for any part of a boiler.
Type K has the thickest wall and is almost invariably overkill, and that is costly! You can used it, but you gain nothing in effective strength but plenty in cost. Because of the cost of keeping it on hand, Type K is also the most difficult to find in stock locally. I always use Type K for flues (for longer life) and I always have to order the material.
Type L is also usually a bit over-thick but that dimensional stability comes in handy when fabricating and is the Type I always use. It is usually available locally, in ODs of 4" or less..
Type M has a thinner wall than Type L, and while it can usually meet the minumum wall thickness requirements for some boilers at some operating pressures, you need to run the formula to see exactly what is required. Local availability is about the same as Type L.

 

[modeng2000]

Thanks for the info on boiler tube calculations. What are the factors to take account of for flat end plates?

John

 

[nevadablue]

So, in summary, if I may... Standard plumbing pipe IS acceptable? Of course assuming proper gauge and size and the calculations have been done and show the proper safety factor?

 

[Lakc]

If by standard you mean US drinking water spec pipe, then apparently so.