It would require 1406 lbs. per square inch to burst this shell if it
were solid, that is if it had no seam, a single seam affords 62 per cent
of the strength of shell, 1406 x .62 = 871 lbs. to burst the seam if
single riveted; add 20 per cent if double riveted.
To determine the safe working pressure divide the bursting pressure of
the weakest place by the factor of safety. The United States Government
use a factor of 6 for single riveted and add 20 per cent for double
riveted, 871 / 6 = 145 lbs. the safe working pressure of this particular
boiler, if single riveted and 145 + 20 per cent=174 double riveted.
Now suppose you take a boiler the same length and of the same material,
but 80 inches in diameter. The bursting pressure would be 3,240,000 /
(80 x 72) = 560 lbs., and the safe working pressure would be 560 / 6 =
93 lbs.
You will see by this that the diameter has much to do with the safe
working pressure, also the diameter and different lengths makes a
difference in working pressure.
Now all of this is nice for you to know, and it may start you on a
higher course, it will not make you handle your engine any better, but
it may convince you that there is something to learn.
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