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[Solitary Sailor]

Further to the above, it has always been my intention to have the finished boiler tested and certified, by an independent 'Certified' authority,  as I also wish to know whether it is safe to operate. 

[Solitary Sailor]

We seem to be drawing numbers out of the air here and then using a 'suck-it-and-see' process to test them.

The reason for the quoted testing pressures, is that I wish to go above and beyond the normally accepted requirements, to be absolutely sure that what I am building is indeed safe to operate. Just testing to twice the operating pressure, would only require a test pressure of 160 psi.  Double that figure, and I think we can all agree allows for a greater safety margin.

It has been my experience over many years of work that pressure failures in closed systems are due to small pinhole leaks occurring due to poor brazing of joints, long term vibration of the affected pipe,  or small ruptures of heavily corroded pipe (after many years exposure to saltwater air conditions prevalent in the areas where I ply my trade). These leaks DO NOT suddenly expand into some great explosion as the high pressurized gas seeks to escape.

I recognize that boilers do operate under high pressure conditions coupled with high heat. Hence the reason for using the brazing technique, since getting the solder to melt and flow around the joint requires a much hotter flame than a normal propane torch, therefore the heat stresses would not affect the soldered joint ... ie. the heat from a propane torch (or boiler's gas burner), is insufficient to melt the solder on the joints. Yes, there may be conditions where this rule fails, but by that time, any joint soldered under the normal process of 'silver solder', done with a propane torch, will have long since melted away.

It has also been my experience, when faults occur in the operation of equipment which I deal with on a daily basis, that conditions can occur where pressures within a closed refrigerant circuit can exceed 450 psi, with no structural breakdown of the copper tubing / brazed joints involved, they simply continue to hold pressure, until such time as someone comes to correct the fault. Yes, this is in a different environment than a boiler, but as Nick says, providing I follow AS1167.1, I should have no problem. In short, experience has taught me that refrigeration copper can and will withstand high tolerances for structural integrity when put under these sort of pressures.

[around]

Solitary Sailor,

Our experiences tend to shape our world view and I think that is happening here. 

I would imagine that refrigeration systems tend to operate at low temperatures (no pun intended) when compared to boilers.  This would mean that the integrity of the joint is the primary operational concern and that the material properties of the copper tubing used would be relatively static.  Failure modes would not be due to the tubing exceeding yield strength but to other causes.  This would lead to a focus on the joint material and the joining process.   A pressure test of the "cold" system would provide a comfort level that everything is great.

The difference in the boiler world is that when we add heat, the material properties of the copper change considerably.  Now the joint is not the only failure mode.  The tube material itself has becomes a potential failure point.  All industrial codes and the boiler formula that are used for model boilers "de-rate" the mechanical properties of copper to account for the change in strength due to heating.
 
What you are hearing from the members here is that the design of a model boiler needs to take into account many factors, not just the joint method.  A safe boiler starts with a structured design approach including setting the design goals for the boiler, running calculations to determine acceptable shell thickness, looking at stay requirements for end shells, etc.   Then build and test to confirm the design.

Cheers,

Adrian

[MONAHAN STEAM MODELS]

Solitary Sailor,

I think it's great that you have decided to build your own boiler. I'm all about finding new and improved ways of doing things especially if these new ways increase safety. The way to find these new and improved ways of doing things is to first have a firm understanding of why certain materials and welding practices for building boilers and certain testing methods for them have been done they way they have in the past.

It sounds like you are drawing on the years of experience that you have gained working in a certain field of expertise to help you construct this boiler. I can respect that. Although refrigeration equipment and model boilers both share similar materials in their basic construction the two are not the same and need to be engineered and constructed to withstand the operating conditions specific to their nature.

As I mentioned before, Silver Solder is the standard joining material most copper boiler builders use. This is not your standard garden variety Silver Solder either. This is typically a high temp high silver content welding material. Welding with this type of Silver Solder can not be done with a propane torch. It requires an oxy/acetylene torch to successfully weld a joint. Typical melting temperature can range from 1150F to 1300F+ . Standard accepted joint designs in standard boiler building practice were designed for and depend on the capillary nature of silver solder to make a strong joint capable of withstanding the shearing force that they will be exposed too. Also these joints are designed to work with the limitations of strength copper tubing has when heated during use. Silver solder can be expensive when compared to other welding materials but, considering the fact that you are only building one boiler, you may not want to rule out its use completely.

As I stated on here before, Bronze brazing is an accepted method of creating welds on copper pressure vessels but it must be carried out by someone who knows what their doing and the Filler material must comply with AS1167.1 - 1993 Welding and Brazing - Filler Metals. Alloy RCuZnA Tobin Bronze.

In my opinion there can be no substitute for hydro testing a boiler.

Using high pressure air or inert gases to test welded joints is a very bad idea. The amount of energy that will be release if a failure does occur during the use of this testing method can potentially cause severe damage and injury. Copper becomes annealed when exposed to high heat during the welding process. It will deform much easier and will tear or burst much more effectively.

Although I personally use an industrial certified hydro testing pump for testing my boilers this is not necessarily needed by the home model boiler builder. I own one of these testing rigs because I regularly use it to test our full sized boilers. I'm sure you have seen the small hand force model water pumps advertised on the net produced by companies like Stuart, Cheddar, PM Research, Main Steam Models and so on. You can use one of these small hand pumps in conjunction with a certified pressure gauge to build your own hydro testing rig for a very reasonable cost. When Cheddar Models was still producing their range they offered a hydro testing rig build from these components for model steam clubs to purchase for testing their club members boilers. It's worth investing in this equipment especially if you plan to build more than one boiler for yourself.

I hope you will continue building your boiler and enjoy the experience that you will gain by doing so. I also hope that you will soak up the knowledge being expressed by other forum members here and employ their thoughtful suggestions and advice during your construction of your boiler. We are just all looking out for one another safety.

nick

[Solitary Sailor]

Thanks Adrian

You are correct, I am indeed drawing upon years of experience within my own field of work. Your assumption regarding the low temperatures and pressures found in the field of refrigeration is only partially correct; for while the evaporative process removes heat from the medium being cooled (air), that heat needs to be dissipated into the ambient air of the great outdoors. This means that while we do indeed have a cold environment at the working end, the evaporator, we also have a warm, often hot environment at the disposal  end, the condenser; that heat that you are extracting has to go somewhere. This is where temperatures can get hot and pressures get quite high ... under normal operating conditions (speaking of air conditioning in the typical South Florida environment), the high side pressure would be in the range of 190 - 250 psi dependent upon system design and outdoor ambient temperature, maybe even a little higher in some circumstances. However, when things go wrong, as they sometimes do, those conditions can change, quite dramatically, hence the references above to experiencing conditions where the pressures could be found in the 450 psi range. The potential exists for the pressure to go higher, however, the safety features built into the systems will cause a shut down, and so relieve all pressure build up, restoring the system to a static pressure, subject only to the expansion forces caused by surrounding ambient air temperatures. With R-22 having a boiling point of - 41*F at atmospheric pressure, and with the action of the compressor turning the vaporous gas into a liquid state, laden with recovered heat, the temperatures in the condenser can become very hot.

Sorry to be so long winded about it, but it is an aspect which is overlooked by the layman, and in the context of this debate, it does have some, but by no means all characteristics pertinent to this subject.

As I said before, I am on a learning curve.

Again, thanks for your comment, especially the reference to the material changes in the base metal itself when placed under heat

[Solitary Sailor]

Hi Nick

Many thanks for your input. Further to your previous comment and in association with one from Gerald ... I had indeed used a 'silphos' type solder with a silver content of 5 %. Given Gerald's comment about a deterioration found in the brazed joints using this type of solder when used in boilers, I may have to discard the first attempt at a fire tube 

After a cursory look on the net, I was unable to find much about AS1167.1 Welding and brazing. That of course may be me, looking in all the wrong places. Yes, I did find my way to the 'Australian Miniature Boiler Safety Committee',  part 1, but only an offer to buy the complete 56 page book. So I am still none the wiser regarding AS1167.1

After a visit to a local welding supply house, where much discussion ensued by all parties ... with little knowledge of the practices involved. It was determined that the higher silver content, the more likely a strong joint would be obtained, although all  The less likely for  deterioration of the brazed joint over time would likely transpire.  Such brazing processes required the use of oxy/acty with temperatures ranging in the 1200 to 1300 *F  area, so at least there I am on the same page as you. With this in mind, I purchased an ounce of 'Harris' Safety-silv 35, having a silver content of 35%. We shall have to try it and see what results I get.

I am also stuck with the fact that there appears to be no model engineering group in the Florida area, who could assist me in the certification process.

As to your suggestion, I will look into the possibility of obtaining some equipment for me to be able to hydro-statically test my own work. An expense I had hoped to avoid  , but with all comments pushing towards that direction, I will, out of common sense, proceed on that course.

[ooyah/2]

Hi Sailor,
I think that you are looking at a solder that is way above the requirements for building a boiler.
You are working on very high temperatures and so is Nick.
In the U.K. most model engineering society members use Johnson, Matthey silver solder 'Easy-Flow which has a melting point of 620-630 deg for boiler making.
I have tried to find them on the net but can't get any info on their Silver Solder.
I use a Company called C.U.P.Alloys and their solder that I use is 42% silver. you can get them at (  www.cupalloy.co.uk  ) with some data on their Silver Solder Rods.
I don't find them exceptionally expensive, Last time I bought 50 rods it was about £2 per 600 mm long rod.
I have made many boilers using a 1" dia burner head with a .018 "jet ( all home made ) using straight Butane from a 4.5kg bottle and all my boilers are Hydraulic tested as I progress with the build.
When I asked about the Vacuum test I realized that you would use a vacuum gauge but I couldn't see how you could detect the leak, B.B. has explained it adequately.

I fail to see that you are Cavalier with your experiments as with your work experience you know what you are doing, however Hydraulic testing every time.
B.B. might have been a bit more diplomatic and left out his first line and then pointed out that Vacuum testing is not on as far as the U.K. is concerned.
Please don't be put of.
Regards
George.

[Solitary Sailor]

Thanks for the words of encouragement George.

Anyone have an address where I can purchase some equipment for hydrostatic testing purposes?

[gondolier88]

Mainsteam models pump is very good quality- just type 'mainsteam models' into google, theirs is the first site that comes up.

Then you just need some cheap hosing from a tub to the pump, then copper pipe from the pump to the boiler, the pump has an integral check valve- but just to make sure I would purchase one to go on the boiler- preferably from steamfittings.co.uk, they are VERY good check valves and give no blowback at all.

Then you will need a callibrated pressure gauge (I would think in your line of work you can get one quite easily), make a threaded adaptor to go from the pressure gauge straight onto the boiler- safety valve connection is the usual place.

Fill the boiler right up with water, then pump until you have the required test pressure, leave for 30 mins for thermal balancing, then re-pump to test pressure again if it has dropped, this is the true test- a new boiler should NEVER have a drop on it (as soon as you steam it it's not classed as new however...!).

Leave at test pressure for a further 30 mins.

If it's succesful then slowly get it ready to steam.

Greg

[MONAHAN STEAM MODELS]

You are working on very high temperatures and so is Nick.
In the U.K. most model engineering society members use Johnson, Matthey silver solder 'Easy-Flow which has a melting point of 620-630 deg for boiler making.

Are you referring to 620-630 Degrees Centigrade or Fahrenheit ?

Yes, I do openly admit to using a higher temp Silver solder on my boilers than what most other people commonly use but remember I was building boilers with the Village idiot in mind. I personally use Cadmium free Harris brand Safety Silver 45. It's expensive stuff to use especially considering the large number of boilers that I was producing but I found that it's stronger and takes more punishment than what other Silver Solders would take. Another reason I chose to use this Silver Solder opposed to the lower temp stuff was that I was considering boilers that are run dry by accident by beginners. I didn't mind spending the extra money. I looked at it as cheap insurance for the end user.

nick

[Solitary Sailor]

Hi Greg

Yes I went to the Mainsteam site, it was one of the first places I looked, but other than the little boiler feed pumps, or the weir pump, I can't find what; maybe I just need to ferret around so more. As you say, the gauge will be no problem, and piping is in the bag. Just the actual pump. 

[Solitary Sailor]

Hi Nick

Well it looks like I found the right solder, even if a little less of a silver content, 35% as opposed to the 45% you use. I shall just have to learn to be a little economical with my brazing technique 

[ooyah/2]

Hi Nick,

Temps quoted are in Deg "C"
Don't blame you for using high melting point solder, as a commercial venture you must protect your self, however I have only made boilers for myself and friends
and 42% silver solder is more than acceptable and doesn't require the heat that amateure boiler makers require.
George.

[Solitary Sailor]

Hi George

What would be the lowest silver content you would recommend. The type which I just purchased is from the same manufacturer and same cadmium free 'Safety Silv'  as that used by Nick, but with a lower silver content. So if 35% is too low, I'd better find out now, before I do another fire tube.

[steamboatmodel]

.............
I am also stuck with the fact that there appears to be no model engineering group in the Florida area, who could assist me in the certification process.
..........

There should be lots of groups in Florida! Check for the ride on size Model Trains.
I did find a reference to a state Boiler Code at;
http://www.homemodelenginemachinist.com/index.php?topic=8846.0
The code is at;
 http://www.myfloridacfo.com/SFM/pdf/FAC_69A-51_03_1118.pdf
Regards,
Gerald.

[Solitary Sailor]

Gerald. Fantastic, thanks. I did get in touch with the treasurer of the Australian Miniature Boiler Safety Committee, asking for a copy of the code. We will see what he comes up with.

I am not saying a model engineering society does not exist in South Florida, just that I have been unable to locate one, and I have made some extensive inquires. There is not much support here in general for the model making fraternity.

[Bunkerbarge]

You might find it interesting to have a read through the following:

http://www.ntet.co.uk/pdf/miniatures_exam_and_test_code_nov_08.pdf

This booklet is the agreed document that the four model engineering societies quoted follow but is not supported by the Model Power Boat Association in the UK.

Obviously this is not relevent to where you are in Florida however it does provide interesting reading and guidance no matter where you are.

This is the test rig we use at my club to calibrate pressure gauges and hydraulicaly test boilers.  The pump cost about £60.00, $90.00 US and the gauge is a calibrated and certificated gauge and cost about £30.00, $45.0 US.  I'm sure that you could find a similar piece of kit in Florida, probably considerably cheaper as well!!

[ooyah/2]

Hi George

What would be the lowest silver content you would recommend. The type which I just purchased is from the same manufacturer and same cadmium free 'Safety Silv'  as that used by Nick, but with a lower silver content. So if 35% is too low, I'd better find out now, before I do another fire tube.

Hi Sailor.
I have always used C.U.P. Alloys at 42% silver as it flows very easily, I don't think that there would be much difference.
I would mail them and speak to Kieth, he will let you know the difference.
Tell him that George From Glasgow recommended him, nice guy.
If you P.M. me I will give you a tip on hydraulic testing at a very low cost.
George.

[Solitary Sailor]

Hi Bunkerbarge

Thanks for the link, have copied it to my files for future reading and to ensure I don't lose the information in my travels.

In the photo of the test station ... what is the second small gauge for.

I also have found a lead to obtaining a small, hand operated water pump.

[steamboatmodel]

Gerald. Fantastic, thanks. I did get in touch with the treasurer of the Australian Miniature Boiler Safety Committee, asking for a copy of the code. We will see what he comes up with.

I am not saying a model engineering society does not exist in South Florida, just that I have been unable to locate one, and I have made some extensive inquires. There is not much support here in general for the model making fraternity.

Here is there web site where you can order the codes
http://www.ameng.com.au/ame_retail_dvds_boiler_codes_and_miscellaneous.htm
I ordered A.M.B.S.C. Sub-Miniature Boiler Code part 3, paid for it on line and received it in one week ( I have had letters take longer just coming from the other side of the city).
Regards,
Gerald.
PS IN the photo it looks like they are testing the model gauge and calibrating it to the master certified gauge.

[Bunkerbarge]

Hi Bunkerbarge

Thanks for the link, have copied it to my files for future reading and to ensure I don't lose the information in my travels.

In the photo of the test station ... what is the second small gauge for.

I also have found a lead to obtaining a small, hand operated water pump.

As Gerald rightly points out the small gauge is a boiler pressure gauge which is being calibrated against a certified gauge.  If you are doing this for your own home purposes however you could simply leave the original pressure rig gauge on and either don't bother with the expense of a calibrated and certificated gause or 'borrow' one from work!

A little rig like this is very easy to use, very portable and can be used for all sorts of pressure tests.  You'll wonder how you managed without one.

[gondolier88]

BB, I'm looking for one of these test rigs myself at the moment- I can't afford the huge prices of the Rothenberger ones, but £60 is quite reasonable- where did you get yours from?

Greg

[Bunkerbarge]

Hi Gerald,

I'm afraid it's gone up a bit since I bought ours but it is still a lot more reasonable than a Rothenburger and it is a very useful investment for home and club use.

http://www.online-pumpshop.com/xcart/product.php?productid=318&cat=0&page=1

[Solitary Sailor]

Well, took the plunge and purchased the test rig Bunkerbarge  recommends... you don't have shares in the company do you BB   

The price was great, the shipping though was something else ...OOWwwwww.

Anyway, thanks for the link Bunkerbarge. At least I will know everything is ok each step of the way.

Might have been cheaper to just buy the boiler from Mike at Maccsteam  , still, not quite the challenge.

[Bunkerbarge]

The thing is though you should get good service from it for many years to come and it will give you a peace of mind when you put your boilers into operation.

Glad I could help, sadly no shares in the company but maybe I should approach them to go on commission!!!