Re: [PSUBS-MAILIST] Hull Penetration and Reinforcement

[Jon Wallace <jonw@psubs.org>]

After considerable time looking at ABS and ASME standards for hull 
openings and reinforcement, I've completed an online calculator for hull 
penetrations (Radial to hull, and circular).  This is separate from 
Hugh's spreadsheet calculator which I hope to use for cross-referencing 
and comparison before publishing either of them on the website.  What I 
thought would be a simple matter of converting some algebraic formulas 
into computer code turned out to be much more than that, primarily 
because the formulas in isolation are not enough to explain the nuances 
and theory that must be considered for hull penetration, and because, my 
strategy was to use the known specifications of the K250 (certified by 
ABS in 1970) and K350 (certified by Lloyds in 1980) to check the results 
of the calculator.

Unfortunately, neither the K250 nor K350 conning tower reinforcement 
specifications match results I am getting from ABS/ASME formulas.  
Kittredge plans call for an 23 ID insert of .75 inch thickness to 
transition from the hull to the conning tower.  However, the ASME 
formulas are showing a required thickness of 1.248 inches.  With 
Kittredge gone now I can only assume that either the formulas and 
requirements have changed since he his plans were certified back in 1970 
and 1980, or he received a waiver to use thinner material.  There is 
some evidence to support an argument that ASME formulas are excessively 
conservative in some cases.  In 2000, a paper called "A Proposed Method 
for Finding Stress and Allowable Pressure in Cylinders with Radial 
Nozzles" was written regarding this issue.  It is interesting reading 
but apparently was never incorporated into ASME rules.

There are many nuances and peripheral considerations required to 
understand openings and reinforcement in general.  Radial, hill-side, 
inclined, and tangential openings are possible.  And that 
blasted-bloody-{insert-adjective-here} "F" correction factor that caused 
me so much aggravation trying to understand what it was, and what to do 
with it.  If you don't know what these terms mean relative to the 
geometry of hull openings you'll need to brush up on the terminology and 
application.  Fortunately there are some good references on the web that 
make most of this understandable while also illustrating the complexity 
involved with the mere act of cutting a hole in your pressure vessel 
hull.  Probably the best document I found was at 
http://www.pdhonline.org/courses/m205/m205content.pdf which does a great 
job of illustrating most of the terms you will read about in the 
ABS/ASME specs.  At least in my case, a picture is worth a thousand 
words and this document has lots of illustrations that do a great job 
explaining things.

Other references I've found that are helpful:
http://www.pveng.com/documents/content_157.pdf
http://www.absa.ca/IBIndex/ib05-005.pdf
http://www.gowelding.com/pv/asme8-nozzle.pdf

I have created a table of results from a few calculations using both the 
K350 and some hypothetical subs designed for 1000 and 2000 foot depths 
which can be accessed at http://www.psubs.org/design/pvho/ and includes 
some notes regarding those calculations.  I would like to see some 
independent verification of these results before making the calculator 
public on the website, especially considering that I can't verify 
against the K-sub specifications.  The more people we can get to look at 
the results and do an independent calculation, the better.

The calculator has the following restrictions:
1) Penetration Radial (perpendicular) to the Hull
2) Nozzle is unstiffened
3) Both nozzle and hull opening are circular
4) All reinforcement is integral to the nozzle
5) Hull thickness and required hull thickness are identical






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