Re: [PSUBS-MAILIST] Design depth

[Jon Wallace <jonw@psubs.org>]

Hi Alan,

The only safety margin I've seen in ABS documents is the hydrostatic 
test to 1.25x the design pressure of the vessel.  This implies that max 
operational depth is equal to design depth.  If you rely entirely upon 
an in-water pressure test you are correct that the maximum operating 
depth becomes a factor of the rated depth, not design depth.  In that 
case, two identical subs could easily have different rated/operating depths.

Jon


On 12/10/2010 3:24 AM, Alan James wrote:
> Jon,
> The missing link seems to be; what sort of margin do you have between 
> your test depth or rated depth
> and your crush depth. For instance, if a submarine should fail in 
> theory at 1000ft one person might test
> it to 900ft, divide that by 1.25 & say it's rated to 720ft; whereas 
> someone else with the same design
> may test it to 500ft & say it's rated for 400ft.
> I'm not familiar with ABS or ASME but wouldn't there be some sort of 
> regulation that stipulates a margin of error, & if your boiler for 
> instance will blow up at 1000 psi then it's only rated to 400psi 
> despite any testing.
> Maybe some of the engineers could wade in on this & advise us of a 
> general margin of safety that is applied
> steel design in engineering applications where life is at risk. Or 
> advise some nominal % figure in relation to how
> close to the theoretical crush depth the pressure test should be taken.
> Regards Alan




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