Recommissioning a small vertical boiler

[Mark Salzedo 1Participant @marksalzedo1]

I bought a small 3″ diameter silver-soldered copper coal-fired vertical boiler a few months ago. I am in the process of recommissioning it. Whilst cleaning the boiler, I noticed two bulges on the inner underside. I have made a short video here

Do you think it is worth spending the time (and money) making up blanking plugs to pressure test the boiler. It certainly has been steamed in the past, it is coated with soot deposits. Does it look like it has been over-stressed at some point? I bought it to steam a small Stuart 10V steam engine, so a working pressure of about 40 psi (max. 60 psi) should be adequate. It would be used ‘privately’ and not in a public setting. But it still needs to be safe to use.

It is obviously a non-commercial boiler and it didn’t come with a certificate. Most of the fittings are serviceable but need a good clean. It has an old ‘Bonds’ pressure gauge, which probably dates it. I bought it quite cheaply, around £80 I think. It would be a shame to just throw it away. I suppose I should press ahead make the blanking plugs and pressure test it. Anyway, any suggestions and advice from those who are more experienced with boilers will be appreciated.

Happy Christmas and New Year.

Many thanks.

[Clive Brown 1Participant @clivebrown1]

I would pressure test, perhaps to a lowish value, with a view to using it. Difficult to be certain from video, but it seems to me that the lower tube-plate was formed that way. The general scantlings, as far as can be seen, look reasonable

40psi is masses to run a little Stuart off-load. 20psi WP would be plenty.

[noel shelleyParticipant @noelshelley55608]

Hi Mark, for the bulge to have occurred on the inside of a curved surface is likely to have been from one of two reasons:- One SERIOUS over pressurisation or two the boiler ran dry and the copper became soft. The former does NOT have to have been steam pressure, it could have been caused by over enthusiastic  pumping for a hydraulic pressure test but now distorted it’s strength is much reduced. If you are a member of a club then talk to the boiler inspector. If you have the knowledge and understanding of what you are doing examine the boiler VERY carefully ! It may be possible to by VERY careful work force the inner firebox back into a circular shape, by pressing a round object into the firebox, greased to lubricate. If all still looks OK then conduct a hydraulic test to 1.5 X working pressure, in this case 60PSI. If there are ANY leaks then it is not fit for service or REPAIR.

For private use the above could be considered OK but I would urge you to get a proper boiler test at a club.

By all means make the bungs and try.  Good luck. Noel.

PS If you can get your hands on a domestic pressure cooker, replace the rubber mounted T valve with a brass fitting and pipe to your engine, or just drill a hole for the fitting – it works, gives 15 PSI, I tested a Stuart No 1 this way.

[Mark Salzedo 1Participant @marksalzedo1]

Thanks Noel and Clive for the advice and suggestions. The bulges in the first video aren’t all that clear, so I have uploaded another here They appear where the copper shows through, the dirt and grime have been removed. The largest bulge is on the right-hand side and the smaller one to the left.

I don’t belong to a club (at the moment) nor am I conversant with the intricate construction of boilers but the bulges did raise flags. It will be a shame if it has to be binned but I am reluctant to spend too much money on it at this stage if it is all in vain. It may be that 20 – 30 psi would be quite sufficient for the Stuart 10V. So, it is a difficult call. Thanks again.

[noel shelleyParticipant @noelshelley55608]

Hi Mark, looking at the pictures again, there appears to be some slight distortion on the firebox tube plate that makes me think it has been caused by hydraulic pressure – far to much of it. This is very easy to do by accident, and in industry it’s called hydroforming.

Some would think that 300PSI is a high pressure. A small hydraulic car jack may well go up to 10,000PSI.

Good luck. Noel.

[Clive Brown 1Participant @clivebrown1]

The 2nd. video does show up the bulges more. I’d definitely keep any pressure on the low side but I still think that it could run a small engine for demo. purposes.From your post it seems that you might not have facilities for making blanking plugs so perhaps that reduces your wish to test the boiler.

[Dave HalfordParticipant @davehalford22513]

Was there a safety valve on it? It would be interesting to know what pressure it vents at.

If there wasn’t one, or isn’t a spare fitting for one then the boiler was likely built to power a wobbler engine. The spring holding the cylinder to the valve block acts as the safety on these and the pressure is low.

[noel shelleyParticipant @noelshelley55608]

You mention the costs. Do you have the ability to measure the threads used, both dia and TPI ? Can you make them ? Noel.

[Mark Salzedo 1Participant @marksalzedo1]

Thank you for the feedback. I do have a small lathe to make the fittings, a thread gauge, and some taps and dies which I am sorting out at the moment. I want to keep the recommissioning of the boiler on a tight budget, just in case the boiler is not sound. So, I would rather not have to spend money on more taps and dies and/or buy expensive steam fittings. We’ve recently moved and somewhere I had a small bag of spare steam fittings, unions, and cones etc. but as is normally the case I can’t find it now.

There is a safety valve on the top side of the boiler, along with a blower valve, check valve, water gauge, pressure gauge (Bonds), and steam regulator.

Thanks again for the comments.

[Paul KempParticipant @paulkemp46892]

Mark,

Difficult to comment from your videos as the iPad only seems to play around 10 seconds of either before the picture turns into a revolving wheel!

As mentioned above if it were mine I would first make up a fitting to allow testing on the safety valve on air and note the pressure it lifts at.  That will give you a rough indication of working pressure the boiler was previously run at.  I take it there is no “red line” on the pressure gauge?

Also as Noel mentioned the distortion in the firebox may have been due to overheating (running out of water) but there is another possibility.  From what I can see the water space between the inner firebox and boiler shell looks quite small, maybe 1/4”?  If the boiler was steamed on hard water there may be a build up of scale in the water leg that has insulated the inner firebox causing local over heating and softening of the material.  I would have a poke around inside with an endoscope to see if there is any evidence of scale / the water leg is clear.  You can get some small diameter scopes these days quite cheaply on the “shopping” sites that plug into a mobile phone.  You don’t need anything fancy, just something that gives a reasonable picture (and a scope is always handy to have, every man needs one, right?).

The thickness of the outer shell and inner firebox looks quite thin, can you measure them at the foundation ring?  Anything less than 16g is unlikely to be suitable for pressures much over 40psi at a very rough guess.  Very difficult to say with certainty from a picture!

If the inner firebox is still reasonably malleable as Noel suggested you could possibly gently dress it back roughly into shape if you are going to use it at low pressure.

Paul.

[Mark Salzedo 1Participant @marksalzedo1]

Thanks for the suggestions Paul. The IF and OS are about 1.3mm in thickness. Once all the fittings are made, I can carry out a hydraulic test of the boiler. As both you and Noel suggest I might try dressing the two affected areas back into shape. I’ll have to think through how to do this. There is no red line on the pressure gauge. Thanks again.

[Paul KempParticipant @paulkemp46892]

Mark, that is probably 18g sheet or tube (@1.26mm) it was made from which is a bit “skinny” for any significant pressure.  You would have to do some calcs for a SWP really, my guess it will come out around 40psi for copper with a reasonable safety margin.  What is the max reading on the pressure gauge that was fitted to it?

As you say it is a Bonds gauge it might be worth a trawl through old catalogues if you can find them on line – could be it was commercially made.

Best regards,

Paul.

[noel shelleyParticipant @noelshelley55608]

Hi Mark, It’s Sunday morn and I’m having a coffee ! Whilst I did think that 18G was may be a bit thin I’ve done the sums ! Using the published formula of NAMES is :-   0.048″ X 25,000 X 2

3″ X 8                = 100psi

or 18G X tensile strength X 2   over     Boiler OD   X   Safety factor of 8.

Since the shell is seamless tube there is no riveting allowance, also as the pressure is below 60PSI no temperature allowance !

Well there it is, so at SWP 40PSI you have ample margin. Good Luck and a Happy Christmas. Noel.

[SillyOldDufferModerator @sillyoldduffer]

I like to approach these questions by considering risk and impact.

The risk is that persons or property might be injured if a suspicious boiler fails catastrophically.  Two different cases:

• If a faulty boiler injures a member of the public, the impact is severe. Think prosecutions and civil lawsuits.  Therefore clubs insure against sky-high financial damages and appoint inspectors to stop dodgy boilers being fired up on club premises.  Very sensible: although the risk is low, the impact is serious.  The club is responsible and can’t be gung-ho .
• If a faulty boiler goes bang on private property and only the owner gets hurt, he can take much bigger risks, and mitigate them, for example, by running the boiler behind a screen.  He can’t sue himself, and the law doesn’t consider private individuals doing their own thing to be as accountable as an organisation.

If I were Mark, I’d steam the boiler in private.  BUT!  I’d assume it was dangerous, and mitigate the risk.  Put it in an  enclosure, wear googles, maybe ear-defenders and take other simple precautions like not getting too close!

When considering impact, what happens when a risk comes to pass, small copper boilers aren’t particularly dangerous even if they do let go.   You don’t need a nuclear bunker:

• The amount of energy stored in a litre or so of boiling water isn’t that high.
• Copper boilers with soft soldered or brazed joints tend to release steam slowly by tearing open rather than exploding violently with a shower of shrapnel.  They go phut rather than bang.   A 100 litre steel welded domestic boiler is far more dangerous, and a faulty full-size locomotive or industrial boiler is in a different league entirely!

I base my small copper boilers “aren’t particularly dangerous” comment on four observations:

• Officialdom isn’t worried about them.  That strongly suggests small boilers don’t put many people into A&E.
• Almost no incidents involving hobby boilers are reported by clubs or hobbyists.
• One of my old ME’s has an account written by one of the clubs who deliberately exploded three or four failed inspection boilers.   Sealed shut and fired until they failed.   If I recall correctly they all went phut harmlessly apart from one.  It failed dangerously by blowing an end off and rocketing about 50 yards.  Wouldn’t have happened if the boiler were fixed to a loco, though it might have blinded the driver by blowing the firebox contents into his face.   I hope drivers wear safety glasses.
• Small boilers up to a few hundred PSI are low energy and explode slowly compared with a domestic firework, let alone a hand-grenade!  More like a push than a shocking hammer blow.

Though small boilers have to be treated with respect and the operator has to think about what that means in practice, it is possible to mitigate the risk.  But only in private!

Dave

[Dave HalfordParticipant @davehalford22513]

I’m waiting for this Minnie one to appear on here.

It’s the scariest one I’ve seen yet

[Paul KempParticipant @paulkemp46892]

Not scary as such, I very much doubt it would hold water let alone build up any pressure if you lit a fire in it!  It’s difficult to burst a colander!  The most difficult bit would be explaining to the ‘proud’ owner when it is presented for a test that the kindest thing to do is weigh it in 😉

Paul.

[noel shelley]

On noel shelley Said:

Hi Mark, It’s Sunday morn and I’m having a coffee ! Whilst I did think that 18G was may be a bit thin I’ve done the sums ! Using the published formula of NAMES is :-   0.048″ X 25,000 X 2

3″ X 8                = 100psi

or 18G X tensile strength X 2   over     Boiler OD   X   Safety factor of 8.

Since the shell is seamless tube there is no riveting allowance, also as the pressure is below 60PSI no temperature allowance !

Well there it is, so at SWP 40PSI you have ample margin. Good Luck and a Happy Christmas. Noel.

The inner firebox has failed by collapsing, somewhat like that Titanic submarine recently, although less catastrophically. Noel’s calc does not cover this, but it must have taken a pretty high pressure,as the tube is supported by the foundation ring one end and the tube plate at the other.

Rather than trying to hammer it back into shape, I’d be tempted to make up 2 part circular pieces with a jacking screw between and try to jack it back into shape. Make sure the gap isn’t full of scale first. Even better would be to try and return it for a refund, unless the bulge was pointed out by the seller.

[Mark Salzedo 1Participant @marksalzedo1]

Thank you to you all for your thoughtful analyses and observations. I appreciate your time. I’ll make the blanks when I have the time to hydraulic test the boiler and possibly (before the test) reshape the inner shell. Unfortunately the boiler was bought some time ago and probably not eligible for a refund. It has been stored in a box ready to be looked at when my workshop was up and running, which it now is – sort of.

The max. pressure on the gauge is 80 psi. The gauge is marked ‘Bonds’. I think they traded in London and probably closed down sometime in the 70s. So, it is likely that the boiler is around 50 years old at least. I bought the boiler for £80 hoping that it would steam my 10V. It may still do yet though! I’ll let you know how I get on with the hydraulic test. Season’s greetings to you all.

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