Author Topic: Copper for boilers  (Read 16362 times)

Offline tangler

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Re: Copper for boilers
« Reply #15 on: January 05, 2017, 11:23:09 PM »
I'll re-ask part of Rods post: reworded: Is silver brazing going to result in an oxygen problem the same as welding would??? Brazing doesn't melt the base metal....

Pete

I'm no expert on copper alloys.  This may be of help: https://www.copper.org/publications/pub_list/pdf/a1050.pdf.  An excerpt from page 7 is appended:

Rod

Offline 10KPete

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Re: Copper for boilers
« Reply #16 on: January 06, 2017, 01:49:39 AM »
Thanks for that, Rod!!

I've done a ton of welding and been exposed to a ton a metalurgy and everything I've learned says that for the feared embrittlement to  occur the temperature must be at or very near melting. But I'm no expert so I always seek the advice of those more learned than I.

I will continue to silver braze with no fear of compromising the material, what ever the alloy!!!!!

Pete
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Offline SandCam

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Re: Copper for boilers
« Reply #17 on: January 06, 2017, 12:50:44 AM »
Hi Pete,

I would suggest you review this excerpt from the same publication.


"Page 38

Brazing Copper

Oxygen-bearing coppers are susceptible to oxide migration and Hydrogen embrittlement at elevated temperatures. These Coppers should be furnace brazed in an inert atmosphere or torch brazed with a neutral or slightly oxidising flame."

If you can't provide the correct atmospheric conditions then you could well be in trouble.
Best bet is to use de-oxidised Copper and not worry about it.



Rod,
As for the regulations and the Green Book etc... I don't propose to get into a heated discussion on this other than to say that whilst a lot of the PSSR 2000 stuff is not applicable a great deal of the PER regulations are and have been since 2002... with amendements in 2013.

The argument that things have been done a certain way for the last 50 years has led to a huge number of different interpretations of the rules with many clubs and organisations doing their own thing so to speak, which just resulted in a great deal of confusion and the whole purpose of the Green Book was, in conjunction with the HSE, the various model engineering organisations and the insurers of our models, to establish a common testing and certification method, based on the salient points from both official regulations, which satisfied all concerned, be they commercial builder or amateurs.

I don't think people/clubs etc should put their own interpretations on it's content... to do so just creates unnecessary confusion.

Rich and Julian,

There is no foolproof way that I know of, other than a full metallurgical analysis test, to distinguish between different grades of copper such as C101 or C106.
Any supplier worth his salt will provide a traceable certificate of authenticity, not just a piece of paper with his say so on it... if he can't or won't then go elsewhere... Providing a customer with a Phoney one could lead to his prosecution.

Keep Happy guy's and gal's

Best regards.

Sandy. :)

Online Jasonb

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Re: Copper for boilers
« Reply #18 on: January 06, 2017, 09:41:25 AM »
Hi Pete,

I would suggest you review this excerpt from the same publication.


"Page 38

Brazing Copper

Oxygen-bearing coppers are susceptible to oxide migration and Hydrogen embrittlement at elevated temperatures. These Coppers should be furnace brazed in an inert atmosphere or torch brazed with a neutral or slightly oxidising flame."


Sandy By Braze are they talking of the higher temp brazing as we know it in the UK where the Oxy-acc torch will be getting the copper very close to melting point, the description of the flame type suggests oxy-acc not propane.  Or do they include the lower temperature silver soldering?


Best Advice to Rich and Julian is to talk to whoever will be inspecting the boiler as it is there interpretation of the rules that will ultimately be the deciding factor if their boilers get passed or not.

J

Edit, answered it myself and it does include silver solder as a brazing material.
« Last Edit: January 06, 2017, 09:51:41 AM by Jasonb »

Offline 10KPete

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Re: Copper for boilers
« Reply #19 on: January 06, 2017, 10:54:35 AM »
This is where I have always received my definitions:

"Brazing - The American Welding Society (AWS ), defines brazing as a group of joining processes that produce coalescence of materials by heating them to the brazing temperature and by using a filler metal (solder) having a liquidus above 840°F (450°C), and below the solidus of the base metals."

"The basic difference between soldering and brazing is the temperature necessary to melt the filler metal. That temperature is defined to be 842ºF/450ºC by the American Welding Society (AWS) but is often rounded to 840ºF. If the filler metal melts below 840ºF the process being performed is soldering."

I don't know how the rest of the world defines these things but I suspect it is similar.

Just trying to clarify....

Pete
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Online steamer

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Re: Copper for boilers
« Reply #20 on: January 06, 2017, 12:13:17 PM »
This is where I have always received my definitions:

"Brazing - The American Welding Society (AWS ), defines brazing as a group of joining processes that produce coalescence of materials by heating them to the brazing temperature and by using a filler metal (solder) having a liquidus above 840°F (450°C), and below the solidus of the base metals."

"The basic difference between soldering and brazing is the temperature necessary to melt the filler metal. That temperature is defined to be 842ºF/450ºC by the American Welding Society (AWS) but is often rounded to 840ºF. If the filler metal melts below 840ºF the process being performed is soldering."

I don't know how the rest of the world defines these things but I suspect it is similar.

Just trying to clarify....

Pete


Yes this has been a debate for as long as I can remember, I'm sure a better definition can be found by specifying the "spelter" liquidius point on the boiler documentation...but then again....I'm not digging that one up.....

Dave
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Offline SandCam

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Re: Copper for boilers
« Reply #21 on: January 06, 2017, 02:29:37 PM »
This is where I have always received my definitions:

"Brazing - The American Welding Society (AWS ), defines brazing as a group of joining processes that produce coalescence of materials by heating them to the brazing temperature and by using a filler metal (solder) having a liquidus above 840°F (450°C), and below the solidus of the base metals."

"The basic difference between soldering and brazing is the temperature necessary to melt the filler metal. That temperature is defined to be 842ºF/450ºC by the American Welding Society (AWS) but is often rounded to 840ºF. If the filler metal melts below 840ºF the process being performed is soldering."

I don't know how the rest of the world defines these things but I suspect it is similar.

Just trying to clarify....

Pete

Hi Pete,

As Dave states below, this has been a frequently debated topic for many years with no real resolution.

To help clarify things regarding the temperature ranges involved when using Silver Solders (the correct term being Silver Brazing) on Copper boilers... the 2 most generally used alloy types here in the UK  for boiler work are: -

Johnson and Matthey 'Silver-flo 452' which contains 45% Silver and has a liquidus range between 640 - 680deg C. (This replaced the older Easyflo and Easyflo 2 grades which contained Cadmium)

and their 'Silver-flo 252'  which contains 25% Silver and has a liquidus range between 680 - 760deg C.

These latest alloys are both Cadmium free.

The USA and other countries have direct, or very close, equivalents for these grades which will have much the same liquidus temperatures.

So these fall well above the minimum 450deg C specified by the AWS as Brazing Temperatures.

There are some high temperature Silver loaded soft solders which are often used by the Plumbing/heating trade but these generally have a melting point around 300deg C... 'Comsol' being one of these.

A quite common problem being seen more frequently is that a beginner mistakenly uses this type for his/her boiler construction as it is often sold, and described, only as Silver Solder... unfortunately it is not an easy solution to remedy, since you cannot use the correct Silver Braze material without first totally removing the soft type first.

Jason,

Oxy- Acetylene is not the only gas mix which can melt Copper... MAP and/or Propane torches are just as capable of doing so.
There is always the Oxy-Propane variety as well, which can almost equal oxy-acetylene and is becoming more popular now since the annual costs of hiring oxy-acetylene bottles has risen very sharply, both here in the UK and also in the USA, so a lot of users are making the change over.
There are now places where you can buy an Oxygen tank and a Propane tank for a one of fee and you then just exchange them for new ones when empty, just paying for the gasses... there is no annual hire fee since you own the bottles.
All of these types of torch are very capable of producing a non-neutral flame, the straight gas types are more likely to produce a carburising one rather than Neutral, let alone an oxidising one and a long way from an inert atmosphere... they are therefore very likely to provide the means for producing Hydrogen Embrittlement in Silver Brazed joints in Copper containing Oxygen.

And Yes I agree that having a talk with your local boiler inspector is the best way to go since he/she will, or should, be able to advise the appropriate construction materials where these are not specified... generally the inspector will also wish to examine progress at several stages of the construction process and well before testing time comes.

I trust this helps.

Best regards.

Sandy. :)
« Last Edit: January 06, 2017, 02:47:55 PM by SandCam »

Offline 10KPete

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Re: Copper for boilers
« Reply #22 on: January 06, 2017, 06:04:03 PM »
The debate issue is why I posted the AWS definitions. If you read the definitions, by AWS and other authorities, there is no debate!! Brazing is brazing and soldering is soldering.

The confusion is primarily in Model Engineering!! Primarily in Britian it seems where silver brazing is almost always referred to a silver soldering. Both the process and the products!! Until I looked in to Model Engineering I never found contradictory terms.

Having observed the issue for some decades now it is obvious that the issue is so well entrenched among the 'established set' in ME that a change will be difficult. But I also believe that correct usage by those so willing can seriously reduce the usage error and perhaps even cause some new to ME to take up the proper terms. I include the periodical literature.

By the way, "spelter" is a term for brass used as filler in brazing and does not apply to silver alloys.

Pete
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Offline Jo

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Re: Copper for boilers
« Reply #23 on: January 06, 2017, 04:23:10 PM »
Any metal alloy designed to melt and join metal together is called a "solder,".

You can blame Holtzaffel for the term silver soldering, he was caught using it back in 1846  :facepalm:

Jo
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Offline 10KPete

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Re: Copper for boilers
« Reply #24 on: January 06, 2017, 07:13:38 PM »
That's right, Jo. And when it melts above 840*F it's then a braze. So 60% silver alloy is silver brazing alloy. :happyreader:

Warm up the Time Machine, boys. And bring the pitchforks and ropes.    :lolb:

Pete @ off to slibber slobber some oxy-Cu with some oxy-acet in my 1/2" superheater. :ShakeHead:
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Offline Johno

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Re: Copper for boilers
« Reply #25 on: January 06, 2017, 09:19:23 PM »
Hi to you all,

It’s been some time since I have posted, due to other distractions.

I have been following his thread with some interest as I am looking to obtain a small boiler to run my Stuart Engines. Do I buy an off-the-self one at some cost, but with limited satisfaction or do I construct one, less cost, but greater satisfaction?

If I choose the self-build route, I not only need to decide upon a design, I also need to obtain suitable materials, hence the relevance to me of this thread.

It would appear that some would say that the precise grade of copper (either C101 or C106) is not that important given that the joining method is ‘Silver soldering’.

Others are adamant that using the correct grade (C106) is crucial in order to avoid the very real possibility of hydrogen embrittlement.
Then there is the question of is it;  ‘silver soldering, silver brazing or just brazing? I see this is more of a question of common usage, I vacuum the carpets but my good lady ‘hoovers’ them, although we have a Dyson!

To add to the debate, I refer to references I found following a web search.

One is from the relevant data sheets with respect to grades of copper from a UK Material Company: Holme Dodworth Ltd. http://www.holmedodsworth.com/materials/copper/copper-specifications
 
“C101 / CW004A is the normal grade for general electrical use as busbar, motor and transformer components, windings and many other current carrying applications. It is also very popular with architects for applications where the corrosion resistance is required for building applications. Over time the C101 will also develop the weathered copper, green patina, appearance that offers additional corrosion resistance and a desirable look. The use of this alloy in elevated temperature environments can be limited due to oxygen being present in the form a serious risk with non-deoxidised grades. Oxygen being present in the form of CU O. This can cause the alloy to be susceptible to hydrogen embrittlement in reducing gasses or when welding or brazing using an oxy-fuel gas flame.”

“The copper content of C106 is 99.85% minimum. This is the preferred grade for non-electrical purposes such as fasteners, roofing sheet, plumbing tube and other general engineering and constructional applications. The alloy comes into its own where the manufacture of the component or plant involves welding or brazing. This grade of copper is not susceptible to hydrogen embrittlement which can be serious risk with non-deoxidised grades. “

And the other from: CuP Alloys Ltd a supplier of Silver solder/brazing materials
http://www.cupalloys.co.uk/best-practice/: -

“Copper is available in many grades. Tough pitch copper should be avoided. It contains dissolved oxygen. If the reducing (blue zone) of the flame heats the copper, the oxygen is converted into steam. This steam penetrates the grain boundaries of the copper causing cracks to form. This phenomenon is called "hydrogen embrittlement". Catastrophic failure can occur without significant deformation or obvious deterioration of the component.
Use oxygen free copper C101 and C106.”

At the moment still very confused and sitting on the fence, although currently my legs are daggling on Sandy's (SanyCams) side.  There must be a definitive answer to this one, or least some clear guidance depending on specific circumstances.

Cheers
Ian

Online crueby

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Re: Copper for boilers
« Reply #26 on: January 06, 2017, 10:14:11 PM »
Another question in all this - does it matter if the boiler is going to be coal-fired or butane fired when complete? I have seen some references in the past to additional issues with alloys on coal-fired boilers.

Hope this does not generate another round of historically different standards/opinions based on different countries rules and regulations, but it probably will...   

 :old:

Offline Johno

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Re: Copper for boilers
« Reply #27 on: January 06, 2017, 11:06:02 PM »
Hi,

I agree, although i would suggest that it's not an issue of local regulations, more of engineering principles, engineering is a based physics after all.

In full size practice the method of combustion, or more importantly the products of combustion that it produces has great bearing on the modes of deterioration of the various boiler components. When boilers were converted from coal to oil, then to gas, whole teams of engineers would spend many hours exploring the consequences.

the same may be true in model engineering field.

Cheers

Ian

Offline 10KPete

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Re: Copper for boilers
« Reply #28 on: January 06, 2017, 11:07:28 PM »
 :ShakeHead:
 :facepalm:


Pete
« Last Edit: January 06, 2017, 11:19:13 PM by 10KPete »
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Online Jasonb

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Re: Copper for boilers
« Reply #29 on: January 07, 2017, 07:57:24 AM »
Another question in all this - does it matter if the boiler is going to be coal-fired or butane fired when complete? I have seen some references in the past to additional issues with alloys on coal-fired boiler

The sulphur in the coal gasses will attack filler alloys containing phosphor

 

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