[Steam-engine] lap seam boiler pressure

[Lawrence Swanz]

Ken,

You stated, "Also I have issues with the Minnesota safety factor. They state they use 5 for code or 6 for non code and they clearly use a SF of 4 on the stayed surfaces. That almost got us in trouble when the inspectors were confiring a couple years ago...."; You may have a problem with Minnesota using a factor of safety of 4 for stayed surfaces, or a hard number of 13,800.  But this is a number, that until late, A.S.M.E. used in the formula for figuring design for stayed surfaces.  A few years ago however, A.S.M.E. changed this to 15,800 or roughly a factor of safety of 3.5.  So, for those who are building new boilers, the boiler industry is and will be using the current A.S.M.E. formulas.  With this in mind, a boiler designed for 150 lbs., assuming they lightened the boiler plate to its thinnest material instead of the standard .375" thickness that we hobbyist like to see; then it is possible for a brand new boiler to automatically have a reduced pressure by the assumption that we should be using a factor of 5 for code boilers.  This is why I believe Minnesota uses the 13,800 or factor 4 in its formula.  By the way, does anyone know when the last boiler in Minnesota ruptured as a result of thinning due to over pressurizing by utilizing this methodology in its stayed surface formula? or any boiler in Minnesota for that matter?  I believe in operating these relics safely, but I also believe in that if the metal is there, then let it run, and if it isn't repair or replace.  But don't over precaution, let's be realistic about it.

Lawrence