Boiler Construction

Soft Solder vs Bronze Welding

by L.B.S.C.

The Live Steamer, May-June 1950

Question: Is a boiler safe to use if it is sweated at the joints, tubes and stays with soft solder?

Answer: Whilst a boiler can be safe to use with riveted and soldered joints, it rapidly deteriorates and eventaully leaks. The reason is that the solder gets hard, just like the whitemetal in the big ends of an automobile engine, and presently cracks under the stresses of continued expansion and contraction. Also, a riveted boiler can never be as strong as a brazed or bronze-welded one, for this reason: The perforations where the rivets go thru weaken the plates just like the performations in a sheet of postage stamps; and given sufficient stress, the plate would tear along the line of holes, just like you can tear the sheet of stamps. This was the cause of several boiler explosions in the early days of steam locomotives.

It is many years ago that I abandoned riveting, except for just a few needed to hold the parts of a boiler together while bronze-welding. In my experience, the most satisfactory construction is all bronze-welded seams, and silver-soldered flues. Thinner metal can be used, with a greater factor of safety, than if the joints are riveted and sweated.

Smaller Loco, Lower Pressure

Karl Friedrick

2039 5th Ave

Pittsburgh 19, PA

The North American Live Steamer, Volume 1 Number 4

Just a few words about steam pressures in small engines. That is, engines with boilers 5 inches or less in diameter. In my opinion, a lot of the fellows are using pressures entirely too high. 100 to 125 pounds is much more than can be used efficiently on the average small locomotive. Most of these little fellows can get along quite nicely on 60 to 75 pounds, and even less if superheated. In my experience and observation, I have come to the conclusion that a superheated job at 60 pounds will do about as well and maybe better than a wet steamer at 90 or 100. Also, the 100+ pressures are liable to cause many little leaks to develop around glands and fittings. The only thing to be gained by higher pressures is that they tend to cancel out defects in workmanship, etc., by sheer brute force.

External Links

• Australian Boiler Codes
• "Steel firebox forming", Chaski.org
• Welding Rod Selection for Boilers, Chaski.org
• "Airco welding of locomotive fireboxes, 1919"
• "Soldering flue tubes", Chaski.org
• "Wagon top boilers", Chaski.org
• "Home Built Code Boiler?", Chaski.org