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 eventually 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 perforations 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.

Tube Sheet
From "Reaming vs. Drilling Holes In Tube Sheets", Chaski.org:


 * Question: I am working on building a steel boiler with copper tubes. The tubes will be 1/2 inch type K copper, with an O.D. of 0.625 inch. If I use a 16 mm drill for the tube sheets (16mm = 0.6299 inch) this would yield about 0.005 inch oversize on the holes. Some clearance is a good thing, although I recognize that a drill is not as precise as a reamer. A drill would also give a somewhat rougher finish than a reamer, which may (or may not) be desirable to key in the tubes after rolling (?) I would appreciate any comments on this.


 * Answer: Welding of the tube sheet is likely to distort the drilled holes in proximity of the weld(s). Also, drills have a nasty habit of cutting less than round holes, which may or may not be straight, or on size. While reamers, too, can yield similar errors, they're reduced drastically, so the end result would be more reliable, plus any distortion of hole diameter due to welding would be eliminated.


 * If you must drill and not ream, don't drill the hole with the target diameter drill. Drill undersized, then open the hole with the proper sized drill after the boiler has been welded. That's not as good as reaming (or boring), but it will yield more consistent hole size, and likely a better surface finish.

Boiling mechanics
There are three types of boiling.


 * Nucleate boiling
 * Transition boiling
 * Film boiling

Read more here:


 * "Basic Steam Engineering"
 * "The Effects of Nucleate Boiling Versus Film Boiling on Heat Transfer in Power Boiler Tubes"
 * "An Overview of Surface Roughness Effects on Nucleate Boiling Heat Transfer"

Magazine Articles

 * "Boiler Q & A (Boilers)", Marty Knox, Live Steam & Outdoor Railroading, January-February 2000
 * "Introducing Marty Knox - Making Steam (Boilers)", Marty Knox, Live Steam & Outdoor Railroading, January-February 2000
 * "Laying Out Firebox Stays - Making Steam (Boilers)", Marty Knox, Live Steam & Outdoor Railroading, November-December 2000
 * "Making MORE Steam - Making Steam (Boilers)", Marty Knox, Live Steam & Outdoor Railroading, July-August 2001
 * "Making Steam (Boilers)", Marty Knox, Live Steam & Outdoor Railroading, July-August 1999
 * "Making Steam (Boilers)", Marty Knox, Live Steam & Outdoor Railroading, November-December 1999
 * "Making Steam (Boilers)", Marty Knox, Live Steam & Outdoor Railroading, September-October 1999
 * "Making Steam: Some Thoughts on Welding (Boilers)", Marty Knox, Live Steam & Outdoor Railroading, May-June 2002
 * "Marshall Black's Boiler Feedwater Treatment Revisited - Making Steam (Boilers)", Marty Knox, Live Steam & Outdoor Railroading, September-October 2000
 * "Response to Marty Knox's Comments on the Filer & Stowell Boiler", Jesse Livingston, Live Steam & Outdoor Railroading, July-August 1999
 * "Stayed and Unstayed Boilers - Making Steam (Boilers)", Marty Knox, Live Steam & Outdoor Railroading, July-August 2000
 * "Time for a Boiler Wash? (Boilers)", Marty Knox, Live Steam & Outdoor Railroading, March-April 1995