As an ex coded welder and boiler maker I have made a few with tig. The main advantage is that there is no phlanging required. Its a lot easier to set up and a lot cheaper to build. There are no downsides other than they look different. On the other hand the welder is very expensive – think minimum 500 amp water cooled industrial – nothing that you can buy at machine mart! You also know that every joint has the penetration you have put into it.

Fizzy –

I believe the copper has to be a "de-oxidised" grade for welding, could you confirm / explain / correct. please?

Most copper sheet/tube on sale to model engineers will be C106, which is claimed to be OK for welding

Cool

What's the best way to preheat a big copper boiler without oxidising it as a gas torch would ? An oven?

By that I assume you don't back purge by filling the barrel with gas?

Not wishing to stir up a hornet's nest, but I think anyone contemplating welding their own copper boiler should speak to their club's boiler inspector first. The SFED rules on testing say

An Inspector acting as a competent person who carries out an examination under the Written Scheme of Examination shall have such sound practical and theoretical knowledge and actual experience of the type of system which is to be examined as will enable defects or weaknesses to be detected which is the purpose of the examination to discover and their importance in relation to the integrity and safety of the system to be assessed

which implies that the inspector should know about copper welding and possible defects. Not all will. Don't get me wrong, welded boilers are fine as long as stuck together by someone who knows what he is doing.

Agreed, if you turn up with a commercially built boiler and a proper welder cert for the bloke who built it there should be no problem, time for some SFED guidance. If it's commercially built then whatever has replaced CE mark will require welder certs, so there should be no issue. It only costs pennies to photocopy the cert. Problem comes with home built.

The big railways used to weld repair copper fireboxes with oxy acetylene. That must have been heroic. I believe they had one bloke inside and another outside to get a balanced setup. Bags I be the outside man!

I have very little respect for certifications and markings. Exceptional designers and builders very seldom make good bureaucrats and I have yet to meet a bureaucrat that can do anything other than talk.

We had a CE UK professionally built Romulus boiler that one of our members imported with all the necessary paperwork. I had a look at it and wasn’t impressed with the welds; as a general rule you don’t TIG weld hot rolled boiler plate without the correct prep-work. It lasted a few runs and failed (quite badly) in the firebox. The supplier was of course very distresses, sorry and would fix it free of charge as long as shipping was covered by the buyer, and another two years waiting; the normal BS (bureaucrats speech). I made the comment that if they couldn’t do it with clean plate there was no chance of them fixing a steamed boiler. He eventually decided to have one of our builder’s fix it and it’s been running ever since (think it cost a good bottle of something nice!).

Lucky for us our boiler inspector is a qualified engineer who has designed and built a few boilers and between him and the other members (who have built locos) any new members are guided through the design and construction of their boiler. In the end each boiler has walked a careful path and the data book is kept with the boiler inspector with the welding samples etc.

I think the O/P questioned Tig welded COPPER boilers so Hot rolled boiler plate hardly qualifies. Fizzy has given the simple answer as although Ex, at least he was coded and advised that Mickey Mouse welders and welding equipment is a no no. No doubt the O/P will be checking on the qualifications of the supplier? and yes, horror stories abound of some suppliers disasters. A mate ordered a Simplex boiler from a noted supplier in OZ and was surprised to find water coming out as fast as he could put it into it DESPITE the test certificate stating it had been pressure tested to 150psi. Although taking a bit longer and costing a bit more due to overseas postage, the company set up by a young lady in the UK supplied the excellent new one.

Regards Ian

Further to Noel's comment about the destructive capacity of a pressure vessel failure:

A colleague at work lost two fingers when a compressed air tank exploded.

In a book on US trains, there is a picture of the after effects of a 1953 explosion on a 1942 manufactured 400 ton articulated steam locomotive. It killed three enginemen, tore the boiler from the frames and severly damaged the track.

A steam boiler can be a very dangerous item. Not only does it contain a lot of pressure energy, but the steam contained under pressure is at high temperature, and so contains a LOT of heat energy.

At atmospheric pressure water boils at 100'C and it takes 536 calories to turn one gramme of water into steam.

So there is a lot of heat energy released when the steam condenses. Think of a domestic kettle!

At 70 psi the steam will be about 170'C so again, there is a lot of heat energy available.

In short DON'T take any chances with any pressure vessel, even a small one. Ensure that it is well made, and the materials used are traceable..

Model Engineering Clubs test boilers every year to maintain their insurance.

Howard

Hi, your original question: "How do TIG welded copper boilers compare with traditional silver soldered boilers? What are the advantages and disadvantages?"

My opinion:

Welded boilers – properly made and certified – will perform and last as long as silver soldered boilers.

Because of the controlled manufacture and certification required, they both meet the "same" standards – in the result that means you have a boiler powering your loco. I should not expect you to experience any difference when using your loco, even in 50 year's time. Abuse will destroy anything quickly, but treated with appropriate care (no difference between a welded or silver soldered copper boiler) they should both outlast many of us.

However, a steel welded boiler is a different animal. It NEEDS water treatment and more cars due to the normal corrosion of the steel.

Boiler testing and certification is basically the same, whatever you have on your loco. But the inspector may be trained to certify silver soldered copper boilers, but not other types, so won't do those. Check your local club, to be sure.

K