boiler explosion. what not to do.

[kcmillin]

Hey guys, thought I would share a bad experience with you.
I was making a boiler for use with some small steam engines I had. I used an old propane bottle and some copper tube. I had a pressure guage and steam dome on top with two water tubes made out of copper on the bottom. With a homemade burner I was making steam in no time. NOW, here is the bad part, I used electric solder to peice everything together. I pressure tested it to 140 psi, and held it for a half hour. So I though I was good to steam it to 60 psi. Well I was wrong, It pressured up and with out any warning BOOOOOOM there goes the steam dome and pressure gauge accross the shop and boiliing hot steam went shooting out the top, and there I am standin not but two feet from the thing and did not even get a drop of water. needless to say I have not pressured the boiler up again and am verry apprehensive to ever do it again. I was lucky but i might not be next time.

the morel,
DONT USE ELECTRICLE SOLDER TO MAKE BOILERS

kel

 

[Jasonb]

And fit a safety valve!!!!

Jason

 

[GWRdriver]

I'm glad you had the courage to report this to the forum. More people who are thinking of building a little boiler, and who have no prior experience, need to know about and learn from your experience. My immediate advice would be to take what's left of your boiler (less the pressure gauge) and a big hammer, find the nearest flat rock, and bash it until there is not one single molecule of it left that is recognizable as a boiler. Then come on back here, or to any one of several online live steam resources, and me or someone else will gladly walk you through the basics of how to make yourself a miniature boiler that is safe. It shouldn't be a stretch to bring your boilermaking up to the level of your engine making.

The technicality you stumbled upon is this . . steam at 60psi is around 300degF and after about 175degF the tensile strength curve of soft solder drops off steeply. Once the solder reaches the temperature of 60psi steam there is virtually no tensile strength left in the solder joints at all, and Booom. Now for some finger shaking, which I am compelled to do, . . . there is more miniature steam technology in print and online and more competent resources available free to learning builders than at any time in history so there is no excuse for anyone not being able to find out how to do it right.

 

[kcmillin]

to defend myself, I did not have the internet at the time of the explosion. I was aware of the risks, I even had quite a few succesful 30 psi runs, but i will NEVER throw caution to the wind again.

I have been looking at boilers from this forum and other places on the net and I will most definatly build my next boiler with advice along the way. ;D

 

[GWRdriver]

I'll be glad to help in any way I can.

 

[tel]

As will I, tho' I don't have Harry's level of expertise.

 

[Maryak]

Kel,

Thank you for your post, as Harry said many would not be so open about their blunder. :bow:

I am glad you, (nor anyone else), were not hurt by your experience.

I have no experience with model boilers but have spent a large portion of my life with 1:1 boilers of many shapes, sizes and types. They all have one thing in common - they demand the utmost respect from their operators and maintainers and are totally unforgiving if one slacks off on maintenance or takes operating short cuts.

Follow your countries boiler/model boiler code to the letter and all will be well. There are several members here who can guide you and help you and are more than willing to do so.

Best Regards
Bob

 

[tmuir]

Toy steam boilers are soft soldered but by law the safety valve must lift at 1 atmosphere (14.7 psi).

I certainly wouldn't run a commercially made soft soldered boiler over 20PSI and agree when I finally get around to making myself a boiler from scratch it will be silver soldered.

This video has done the rounds a few times before but is worth putting up again.
This is why you need to know what you are doing even with small model boilers.

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Thanks for sharing your story

 

[kcmillin]

Oh man, I'me getting flashbacks from that video.
Do you know what broke exactly. I would like to know where the weekest link of that boiler was? It would seem that the end caps would have the most strain on them, because of the surface area.

Can copper be welded or brazed?

 

[GWRdriver]

Kel,
It can be both welded (tig) and brazed, but for small copper boilers the preferred method is silver solder, which of course is a form of brazing. I'm not a welder but I know of a couple of people who have successfully (so far) tig welding some boiler assemblies, but not a whole boiler. My understanding is that tigging copper requires pre- and post-welding treatment to prevent cracking and warpage. There's more to it than simply putting the wire to it.

PS - IIRC there is now a commercial model boiler maker in the UK whose boilers are now all-welded.

 

[Paul_C]

I've been working around low pressure (15psi) boilers for about 8 years. I was told 15 psi steam was the limit for plumbing solder. At the shop we use Harris #15 silver solder for all repairs.

I recently completed the PM Research BLR-1. Although many have been built with the "silver solder" that came with the kit I thought it was too soft for the threaded bushings. Since all the other fittings are riveted or swagged I wasn't worried about the solder becoming plastic there. It flowed rather well into the joints. But for the brass threaded bushings I used the Harris silver solder and flux. Learning curve if you want to solder them in that way. Insert a pipe plug finger tight into the bushing before soldering to prevent the threads from rolling over. I hydro tested the vessel to 160 psi, the relief valve is set at 60. I feel safe that some stress on the threaded bushings is not going to pop them out at full pressure.

 

[steamboatmodel]

Anyone who is thinking of building a model boiler should have read and reread Model Boilers & Boilermaking by K. N. Harris.
Regards,
Gerald.

 

[Majorstrain]

This is the best I could get to see where it opened up. I don't ever want to see this happen in real life.
Dam lucky.

Elvis is leaving the building!!

 

[Bluecat]

As I'm on the road of building a boiler, I should ask this right now. If I completely rivet a boiler together and solder the seams with soft solder, it should be fine, right?
At the moment I do not have enough heat to properly solder a boiler of such size (3x7,8 inch, if I remember correctly). It's going to be fired with wood or charcoal, whatever I can get for a run.

The bushings could go pop though. Should I invest in another blowtorch and silver solder it or will soft solder do? I'm hoping to go up to 2 bar/29,4 PSI pressure with this boiler.

 

[arnoldb]

Bluecat, Thanks for asking first before doing

I'd strongly advise you not to make a boiler with soft solder for any of it's joints.

Soft solder weakens very quickly with higher temperature, and the safety of bushings, stays and tube joints will be dubious. I don't know where in the world you are, but there is a good possibility that you have some form of local boiler code. If you do, try and get a hold of it and build your boiler safely.

Rather spend the money, get as big an additional blowtorch as you can, and silver solder the entire boiler. It's more work, and slightly more difficult, but definitely worth the peace of mind.

A good read through the threads in the "Boilers" section is definitely worthwhile, especially FireBird's Build

I'm also in the process of designing a boiler, and will most likely start working on it this weekend. I just had to close my eyes and open my wallet for one of these:

On a previous boiler build I quickly realized I needed a bigger torch - and that boiler was tiny for an O gauge locomotive.

Regards, Arnold

 

[Bluecat]

Thank You, Arnold. Actually I'm not new to the world of boilers and their design, I did build some boilers this summer. However, most of them failed. ;D Soft-soldered, of course. I had one success as well - a steam turbine plant, which runs to this day, although there's a bad leak in the boiler. It runs well though, as it ignores the leak.
I have some questions about building a boiler this big, but I'll put them in a new thread perhaps - I think I'm wandering a bit off topic here.

 

[steamboatmodel]

Bluecat,
Check into a Welding Supply they usually carry Silver Solder. If not its available on line.
Regards,
Gerald.

 

[Ken I]

I long ago learned not to trust "soft" solders for any mechanical duty.

But like most lessons we sometimes choose to forget.

I needed to do some TIG welding but my regulator was elsewhere - I had a spare but no fitting for the bottle - I had one fitting for the bottle but it did not fit the regulator and another that fit the regulator but not the bottle.

So a bit of drilling and turning and I soft soldered the two parts together - I thought 10mm diameter by 10mm long "wetted" area would be sufficient (for 2000 psi ????).

It wasn't.

It worked for a couple of hours and then "BANG" ! - the regulator flew across the shop with alarming force.

No harm done other than jangled nerves - still an'all a stupid thing to do. Potentially very dangerous.

I thought that maybe I had done a bad soldering job, but no the entire area had been wetted and failed.

Lesson - you can't trust soft solders for stressfull duty.

 

[Bentwings]

Oh my gosh! I don’t remember when I learned about soft solder joints. Some time before machine shop apprentice. I never soft solder anything but electrical wire. I clean very well use proper flux and make the repair. I see the ac guys using soft solder on ac copper tubing lot. Even in auto school we could not use soft solder anywhere near ac stuff. It was quality hose with proper fittings. Not even push loc fittings. AN OR HYDRAULIC ONLY. I’ve seen some model steam boilers built on the internet with soft solder. Some with nice work but time bombs. I got to mak military lithium batteries out of stainless steel laser welded or tig welded. Not nay did these have very high pressures they contained some of the msodt corrosive reactive chemically materials known to man. He’s were flammable under the right conditions to th point of being explosive. The battery cases were hydraulically tested to failure as a rule. For each lot. T was said the battery was as good as the ordinance as far as destructive capability. So I learned to be extremely careful around pressure vessels.

im building a boiler for my new steamer but I’ve already gone through every calculation I could find in my roars boo which has calculations for about any situation known.ere are plenty of helpful math test on the internet. I’ve got pages of notes. Even made some hangers based on knowledge gained here. Boilers are supposed te tested to 8 times working pressure I think.have a set model that I’ll un to failure just to prove my piece. I wanted to do a video but that’s just too far down those. I may do some pictures eventually. This is a completely new hobby for me ss I’m limited in what I can do see and hear. . We’ll be safe every one. Steam can be very dangerous.
byron

 

[abby]

Bentwings , I think you need to check some of your facts re boiler pressure testing .
Model boilers should pass a hydraulic test at TWICE the working pressure which should hold steady for 10 minutes.
A steam test should follow at one and a half times the intended maximum working oressure .
Soft solder is quite good enough for low pressure boilers , Mamod have been soft soldering their boilers for at least 50 years.
Dan.