Okay - without obtaining and reading the new standard thoroughly, I
can get a sense of what the formula is describing, but without
knowing how it was derived, I am unable to source errors. Taking a
stab in the dark, I did notice that if you change the exponent to
0.054 instead of 0.54, you get a value of 2.894 for c, which is
close to the limit test of 2.8.
-Sean
On 01/11/2010 10:31 AM, Jon Wallace wrote:
Sean,
Context is "maximum plus/minus deviation from true circular form"
measured radially either inside or outside the shell. The formula
is used to determine the chord length for the template used to
perform the measurement. The PVHO document states that this
section is a replacement of UG-80(b)(2).
Lc = 2R sin (pi/2n)
c = 2.28(R/t)^0.54 is-less-than-or-equal-to 2.80
Sorry can't do subscripts and stuff with this mailer. The "^"
character in "c" formula is "raised to power".
Hugh,
The only way I was able to get a number less than 2.8 was to use
"1" as the radius and ".9" as the thickness. For any reasonable
dimensions of a manned vessel, R/t will never equate to a number
smaller than or equal to 2.8.
Jon
On 11/1/2010 1:26 AM, Hugh Fulton wrote:
Hi
Jon,
I
think that we should have the Q.A. part tied up for P-subs
as well so that the home builders appreciate the
requirement for roundness. I am afraid I am lacking in
the understanding and math behind getting the answers and
I think that Cliff, Sean, and you would come to some
agreement as to a formula.
I
cant believe that it is a misprint in ASME. I am missing
something somewhere but I don’t know what. Chs, Hugh
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