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May I chime in?
The ABS calculations work for hulls that do not have ring stiffeners and are geared toward finding the most efficient combination of all the variables. In the case of no ring stiffeners, (along with the case of having ring stiffeners), the heads on either end of the hull (or pipe) act like stiffeners. There is a picture of this on page 78 in the ABS rules. The center to center spacing becomes the distance between the heads at a distance of 0.4 times the inside head height. For example, ¼ thick heads that are 10 inches in diameter have an inside head height of 3.88 inches with a 1.5 inch flange. The center of the head stiffener is located 3.052 inches from the face of the head (0.4*3.88) +1.5. If the center to center spacing of the stiffeners is 60 inches, the actual hull (pipe) length will be around 54 inches. The abs rules cover three failure modes, one of which says that a long un-stiffened cylinder is a bad idea, unless it ok to be thick and heavy.
Adam
-----Original Message-----
Hi Doug,
I think we need Cliff Redus to comment.
I checked your spreadsheet and compared it to mine, and the difference was the center to center spacing of stiffeners. I left mine at the default value of 10 inches and you had changed yours to the length of the pipe (I assume) which is 60 inches. The output doesn't make sense to me either since I assumed a .0001 stiffener and web was essentially equal to not having a stiffener. The center to center spacing of stiffeners shouldn't be a factor in that case. I'm guessing there are some assumptions built into the formula's behind the spreadsheet geared towards a reasonably sized hull and it may not be applicable to pre-manufactured small diameter pipes without stiffeners.
Hopefully Cliff will see this message and take a look himself.
Jon
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