[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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