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Hi Les, I'm afraid I cannot adequately explain failure lobes and so I won't even try. In layman terms they refer to the number of "dents" created when a cylinder fails by general instability (I think). However I do not understand why a particular cylinder of specific dimensions would fail with two lobes instead of three, four, five, or six lobes. The following video link shows a good series of illustrations of failure lobes. At 3:01 they show what appears to be a one lobe failure. At 3:06 it shows what they describe as "A near perfect 6 lobe failure". So these will at least show you what a failure lobe looks like. http://www.dailymotion.com/video/x86dsc_collapse-of-model-submarine-pressur_tech The following link also does a good job of illustrating local buckling and general instability. Scroll down about two-thirds and look for Figures 11.1, 11.2, 11.3, etc. In Figure 11.2 you can see that the cylinder appears to have failed with two lobes. Be careful with this link...you might need to piece it together carefully if it gets split into separate lines by the mailing list mailer. http://books.google.com/books?id=rv0QXKI0HvMC&pg=PA289&lpg=PA289&dq=buckling+vs+general+instability&source=bl&ots=WYPwdqGZU6&sig=mtT5QVjTCj8_sLX4o9CZakPsUL8&hl=en&ei=zc8KTc3TKYGBlAea5J2tDA&sa=X&oi=book_result&ct=result&resnum=2&ved=0CCEQ6AEwAQ#v=onepage&q&f=false The multiple references to "maximum allowable working pressure" are specific to the kind of failure being calculated. Cylinder failure can be by general instability, buckling, inter-stiffener strength, etc. From previous discussion about this, the goal is to adjust your cylinder specifications so that all the "maximum allowable working pressure" results are as close as possible to each other. You won't ever get any of them exactly the same, but extreme differences are not preferable. The usage factor is essentially a safety margin. Use the defaults and you will end up with the ABS recommended "Design Depth" or maximum operating depth. Ok, Alan, Jim, and Sean, did I get that right this time??? :) Jon On 12/16/2010 9:27 PM, Les & Anna wrote:
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