Boiler Design & Fabrication

The Boiler ! The heart and soul of any portable or traction engine. When built right and maintain properly it will give years of service. When approaching the design of a model boiler it is very important to remember that water, steam and

 thermodynamics do not scale down. There is a series of engineering calculations one must go through to determine the parameters that the boiler must be built too. Maryland has a very good section in their Boiler Codes pertaining to model boilers.

Here is the link: http://www.dsd.state.md.us/comar/09/09.12.01.33.htm This will give you an excellent over view of what is entailed in designing a model boiler.

I must say that boiler design and construction should be left to those who are experienced and have the proper welding credentials. “Pressure Vessel Quality” (PVQ) materials must be bought and used through out the boiler construction. The weld joints must be properly prepared and welded in a special manner to obtain full pentration. Bob Oliver of Oliver’s Boiler and Jonas Stutzman of Middlefield, Ohio would be excellent starting points to have a professionally build boiler made for your scale steam project.

Knowing all that I still decided to pursue building my own boiler based on my 45 years of machining and welding experience. I had already jumped through most of the hoops when I fabricated the boiler for my ¼ scale CASE.

The original boiler design for the 1/3 CASE was based on a flanged and riveted boiler. These boilers are a thing of the past and North Carolina Board of Labor would not begin to work with me on such a construction or even approve its operation. So a new boiler had to be designed for my project. I had a piece of 10” seamless pressure tested schedule 40 pipe of the right materials just begging to be used as a boiler. So with that piece of pipe and the engineering calculations I started to develop a design for my 1/3 scale CASE. I discussed my design with the NC Board of Labor Boiler Division Bureau Chief; several professional boiler makers and Bill Bondie, a federal boiler inspector, of Iron Horse Water Treatment, Inc. Bill was most helpful in the layout and sizing of the cleanout plugs. His comments and suggestions about operation and maintenance should provide a long life for my new boiler. (I will share those comments in another posting.) What I am suggesting is too gather as much information as you can so you can have a well-conceived and sound design. I purchased the necessary PVQ materials and cutting, drilling and weld joint preparation began. I used the TIG (tungsten inert gas) method for all my weld joints. There is no weld spatter to clean up and you can control the heat of the weld very precisely. After completing the boiler, my son and nephew helped me to do an initial hydro test. The initial hydro test must be twice the calculated maximum operating pressure. My maximum operating pressure will be 150 pounds. Several pin hole leaks showed up as we kept elevating the pressure but we finally got the boiler to hold the required 300 pounds for a prolong period of time. Prior to this hydro test, I did contact our area boiler inspector to see if he wanted to be involved with the process. He said,” call me when you are ready to fire for the first time and I will check it out then”. If all goes well, he will issue a North Carolina “Special” boiler permit. 

The bottom left photo shows the boiler shell sitting in a special fixture mounted to my Kearney & Trecker horizontal milling machine. The bottom right picture up shows a pointed shaft I used to find the centers of the various points of penetration of the boiler shell. The top left picture up is my father and grandson inspecting my work. Note the bar welded across the end of the boiler shell. I used this bar for locating my verticle and horizontal planes as I would rotate the boiler shell for the various machining operations. The top right picture shows the boiler shell and some of the flat plate sections being welded together.