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As far as I'm aware, ABS doesn't deal with crush depth only
maximum working pressure which incorporates usage factors (n), in
this case of n=.67. If n=1 could be considered "crush depth",
then the calculator shows crush occurring at 2287 psi with 1.5
inch thick hemisphere and max working depth of 1532 psi with a
usage factor of n=.67 which is right in the parameters that he is
looking for. The problem with using n=1 as an indicator of crush
depth, I believe, is that there's no way to guarantee it's an
accurate representation of when the hull will fail because actual
fabrication variables resulting in less than ideal geometric
structures can lower the calculated result. When using ABS/ASME
we should always be solving for max working pressure, not crush
depth.<br>
<br>
So your observation is correct, and solving for a working depth of
~3000 feet results in a much thinner hemisphere. I didn't know
what Scott was using for a safety factor so just plugged the
numbers to get 2578 psi from the ABS calculator, but that
obviously is over-built for what Scott's intended use is. Using a
thickness of 1.25 inches, ABS is showing max working pressure of
1268 psi or 2849 feet, just slightly less than his 3000 foot
requirement.<br>
<br>
Jon<br>
<br>
<br>
On 4/9/2014 10:08 PM, Alan James wrote:<br>
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<blockquote
cite="mid:1397095738.19217.YahooMailNeo@web120903.mail.ne1.yahoo.com"
type="cite">
<div style="color:#000; background-color:#fff;
font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial,
Lucida Grande, sans-serif;font-size:14pt">
<div><span>I'm a bit confused Jon,</span></div>
<div style="color: rgb(0, 0, 0); font-size: 18.88888931274414px;
font-family: HelveticaNeue, 'Helvetica Neue', Helvetica,
Arial, 'Lucida Grande', sans-serif; background-color:
transparent; font-style: normal;"><span>Scott was asking for
the thickness for a crush depth of </span><span
style="font-size: 12pt;"> </span><span style="font-size:
12pt;">5709 feet (2543 psi).</span></div>
<div style="color: rgb(0, 0, 0); font-size: 12pt; font-family:
HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, 'Lucida
Grande', sans-serif; background-color: transparent;
font-style: normal;"><span style="font-size: 12pt;">You are
saying 2.5 for a maximum working pressure of 2578 psi. The
working pressure</span></div>
<div style="color: rgb(0, 0, 0); font-size: 12pt; font-family:
HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, 'Lucida
Grande', sans-serif; background-color: transparent;
font-style: normal;"><span style="font-size: 12pt;">I thought
was the design depth or maximum operating depth.</span></div>
<div style="color: rgb(0, 0, 0); font-size: 12pt; font-family:
HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, 'Lucida
Grande', sans-serif; background-color: transparent;
font-style: normal;"><span style="font-size: 12pt;">Alan</span></div>
<br>
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</blockquote>
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