[Steam-engine] lap seam boiler pressure

HISTMACHRY at aol.com HISTMACHRY at aol.com
Fri Jul 8 07:17:11 PDT 2005


Chas,

55,000 is the general default tensile strength when no plate documentation 
exists. The charts to determine rivet size are accepted, so you can use that 
info. A chart I have from Michigan gives the same value as Lawrence indicated. 
There is a direct relationship between the thickness of the plate and the rivet 
size, to give the best compromise joint design, so that is why the charts 
work, unless the boiler mfg did something different! To determine the rivet size, 
the ASME has acceptable rivet sizes, so by knowing the type of head, the 
diameter, and height we can determine or verify the rivet diameter, usually. I have 
had to x-ray some seams to determine the diameters, in these cases the 
efficiency of the individual seams are calculated.


To determine the condition of the boiler a detailed UT of the entire boiler 
must be done. The ultra sonic thickness measurement is one of the best tools 
for evaluating a boiler. You indicate that there are no pits, which could be 
true where you can see. But what along the mudring, is grooving present? There 
could also be general overall corrosion and wastage of the sheets, this is not 
all ways visible. The inspector will not kill the boiler, although some are 
really stupid, the boilers condition will speak for itself. Just because you did 
a hydro and nothing leaked doesn't mean anything, other than the boiler will 
hold water. It is truly amazing how thin plate can be, and I mean paper 
thin-literally, and the boiler will still not leak. The UT is the best tool. In the 
ASME world of new boilers there are some who would like to eliminate the need 
to hydro a boiler. You did a hydro at 200 psi, with an assumed operatin 
pressure of 100 psi; that could ruin the boiler right there. You have placed a 
greater stress on the boiler than it was designed for. Hydros are 1.25 or 1.5 times 
the working pressure, not twice the pressure!

Also, you have a lap seam boiler, this makes many people and jurisdictions 
very uneasy. Usually boilers with lap seams are usually required to be operated 
at a very reduced pressure, something else to consider.

Where are you located, I'm near Birmingham, AL.

Robert 



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