[PSUBS-MAILIST] External Stiffeners

[Sean T. Stevenson via Personal_Submersibles]

They are both permissible, provided that the stiffener section is
symmetrical, and the web to hull weld is full penetration.  Vance refers
to a "doubler plate" which is typically a reinforcement joined by
perimeter welding only, which would be prohibited.  Any partial
penetration weld joint creates an artificial crack at the interface
which can precipitate a failure.  All of your pressure boundary welds
must be full-penetration and 100% NDT inspected for defects.  With a
thick section like the posted example against the hull, you can see how
the acceptable technique would be difficult to accomplish, both to first
create the fully fused full-penetration weld and then to do your
subsequent 100% NDT inspection.  The amount of heat you would drive into
the hull cylinder when welding the thick version is also apt to cause
more warpage / shrinkage of the joint than welding the narrow version.
Additionally, the purpose of the stiffener at all is to increase the
area moment of inertia of the combined hull / stiffener section, which
the version with the flange / outstand AWAY from the hull does more
effectively (more efficiently for the same weight of material), in
addition to being simpler to properly fabricate and inspect.

Sean



On 2014-04-26 15:02, Pete Niedermayr via Personal_Submersibles wrote:
> I have been looking at external stiffeners and I see that the figures in the ABS Hull Calculator shows them as (see Hull B pdf ) where as some subs (Curasub and Aquarius) seem to have them as (see Hull B pdf). Are they both correct ?
>
> Thanks Pete