Assessment of an old copper boiler

I have acquired an old scotch marine type boiler that appears to have been well conceived and made. It is from copper seamless tube, 5” for the shell, 2” for the main furnace tube, 6x 5/8” smoke tubes. Three stays (copper). The end plates are flanged and riveted both to the shell and furnace tube. All ? caulked with what i reckon is soft solder.

The builder is unknown and the provenance is from a deceased estate.

My initial thought on deciding that it was probably soft solder rather than silver solder was that it was too risky to consider seeing if it could be brought into service, but on the other hand i’m loathe to scrap it when my impression is that it is well made. Material sizes, numbers of rivets etc would seem to comply with KN Harris when he discusses this type of construction (and then gives examples st 100psi!! I would aim at 50 or 60- running a D10 or 10V)

I imagine that the way to proceed is a series of hydro tests? Is there a benefit to moderately heating the whole construction (all ports open) in an oven (200C or so) then allowing to cool between hydro tests?

On the other hand, if there was universal opinion that it was too risky ever to steam, then the effort in setting it up for testing can be avoided.

Final point- private risk only- never to be steamed in public

I am not a boiler tester but I know it won't hurt to do a hydraulic test as long as you get all the air out so why wouldn't you give it a go.

If you hit it with a hot air gun you should soon see if its soft solder or silver solder.

And finally you say never to be steamed in public, that is until someone picks it up from your estate and they might have a different idea. Just my thoughts.

But that situation wouldn't be any different to the OP's current position - no paperwork would have been created, so the new owner would need to have it certified if they wanted to steam it in public.

Rob

If as you say the boiler is riveted together in accordance with KN Harris specs, then caulked with soft solder, it could be ok for home use. I would hydrostatic test it first though, at least at 1.5 times the planned working pressure, and then set your safety valves for that working pressure.

If the rivets are up to the job, what is the worst that could happen? It could spring a leak around a tube end etc. Not the end of the world. Just don't hold your face next to it when firing it the first few times.

I can't think of any benefit to heating it in the oven between hydro tests.

What is its volume and working pressure?

regards Martin

I don't see any significant risk at all, provided it passes a hydraulic test satisfactorily and it's soundly constructed from adequate materials.. There's nothing inherently wrong with soft solder caulking. Very many boilers have been so constructed in the past and provide years of good service. My Simplex boiler for example at >100psi WP.

For small Stuart engines, 20 - 30 psi would be ample for demonstration purposed.

Edited By Buffer on 21/03/2023 09:49:34

I would go along with Clive ! Noel.

To my mind the whole boiler problem is one of risk management. When a boiler is operated in public, the risk is that the operator will be held responsible for any and all damage resulting from and accident. As the cost of an accident can be off-the-scale expensive, it pays to insure against it. Necessary because the cost of life changing injuries to a child can easily run into millions and if it's your fault they will come after your house and assets.

Running in private is a game changer to my mind. Excluding others is a good way of avoiding the risk of heavy damages after an accident. If the worst happens the only person with a claim against the operator is the operator. If he ends up maiming himself, that's his problem (mostly). A whole bunch of legal and financial liabilities disappear when the operator and victim are the same person.

The risk of personal injury in home workshops is widely accepted by Model Engineers. The risk is moderate - people occasionally end up in hospital - but our workshop accidents are extremely unlikely to affect innocent passers-by. UK government accept the risks of DIY, which is far more dangerous than Model Engineering, by not charging for NHS treatment.

So if I were Russell, operating in private, I'd take the precautions needed to ensure my personal safety and not attempt to meet the higher standards needed to run in public. Not a boiler expert, so I'd take advice but I'd:

• Assume the boiler is untrustworthy - approach pessimistically, wear safety glasses, and screen it
• Keep the working pressure low, and control it with
• A trustworthy pressure gauge and a tested safety valve (or two), ideally the 'pop' type because they dump excess pressure quickly
• Fit a trustworthy water gauge, and make sure the firebox is never allowed to run dry.
• Before firing up the first do a 2x working pressure hydraulic test. Red alert if it fails for any reason, ask for advice.
• Inspect carefully before and after each run.
• Don't mess with experimental firing methods or force the fire.
• Do regular deep maintenance (look inside) including 1.5x pressure tests. How often would depend on how often and for how long the boiler was run.
• Never assume it's safe if all goes well for years on end! Christen it 'The Widow-Maker' and don't forget it's never been properly assessed by a 'competent person'.

If it were me, I'd be a little more formal, and improve the to-do list by writing a 'Risk Assessment'. Not complicated - it's a table summarising 'What could possibly go wrong', with 'How bad is the impact it does go wrong?', 'What can sensibly be done to stop it happening?, and 'What will I need to do if it does happen?" Then ask someone else to comment! Risk Assessments are only as long and complicated as needed. A Model Boiler feels like a couple of A4 pages maximum.

For private steaming only, I wouldn't worry too much about soft-solder provided the boiler passes the hydraulic tests and I guarantee to avoid overheating by supervising the boiler at all times. Silver-solder is better because it's stronger and has a higher melting point, but many boilers were soft-soldered in the good old days without causing obvious mayhem.

Nor would I worry unduly about Buffer's next owner concern. No-one buying a second-hand boiler should ever assume it's safe without doing their own due diligence. As boilers are expensive, it's not unknown for naughty folk to forge certificates. This one, I'd put a label on it - "Warning Uncertified Pressure Vessel, Might Explode".

Dave

A suprisingly realistic set of comments?

One further comment I would add, and this from reading 19thC books on boiler safety, is look at the riveting. Are all the rivets in straight lines, all equally distant from the plate edges, if you can see the back then are all the heads well formed. Also the flanging, is it even all around the flange, is it tight against the plate, is it reasonably smooth with no thin sections. Again with rivetting, is it damaged from the rivetting. They are copper rivets, not brass!

If the rivets look like a dog's hind leg then what about the distance from plate edge to rivet, In the old days boiler failure was frequently caused by gouging, the appearance of cracks in plates along rivet holes, in Tee and angle iron in the corner, in the middle of plates due to temperature stress with hot steam and cold air or water.

It only takes on weak rivet to cause a leak, and that is what the 2X hydraulic test is for.

There must be multiple thousands of old boilers, before 2000 with the CE marking etc. Foolish to throw them away, even at £5/kg scrap price. Just be careful.

Many thanks for all this advice

Encouraging enough to do the hydro test

Russell,

The 'soft solder' in this case would be Comsol or similar which melts at around 100C hotter than electrical solder. Don't mix them.

Not likely I’m afraid - tinman’s or plumber’s solder was recommended right up to the 1970’s in published designs and it was suggested by LBSC more than once that silver solder on threaded stays (unlike copper rivets) could crack.

I personally doubt it, but it is there in print.

Edited By Nick Clarke 3 on 21/03/2023 14:47:25

One thing you might do is pump it up to a couple of pounds with a bike pump or such like and dunk it in a bucket of water. If it leaks like a sieve then you have a lot more work to do than just convincing yourself it’s safe. You may decide at that point it’s not worth the effort.

regards Martin