Re: [PSUBS-MAILIST] Lengthwise internal supports

[Carsten Standfuss <Merlinsub@t-online.de>]

A good picture of the I-Frames. The closed field between the two aft
frames is a diesel tank. 

http://www.prismnet.com/~moki/20050731.133903/IMG_1763.JPG

regards Carsten

Sean T. Stevenson schrieb:
> 
> Carsten - if I understand you correctly, you rolled I-beam sections into
> circular form, and then welded these in place by means of fillet welds at the
> edges of the flange in contact with the pressure hull?
> 
> An interesting idea, but I am concerned about the fatigue sensitivity of that
> detail, since by creating a partial penetration fillet weld you essentially
> introduce an artificial crack in the joint.
> 
> Every project I have worked on (mostly ROVs and heavy mining machinery) has
> entailed the application of full penetration welds where a prepared joint (V-
> chamfer or similar) is welded from one side, then the weld is backgouged from
> the opposite side into the root pass from the first weld, then the weld is
> completed from that side, ensuring full penetration with no voids.  Further
> refinement can include profile grinding to a smooth fillet, which eliminates
> surface stress concentrations and inclusions at the bead surface, and finally
> whole-assembly stress relief.
> 
> Granted, the mining machinery is subjected to higher loads and more cyclic
> loading than a sub will ever see, but I wonder if it would be prudent to
> design for full penetration welding of any joint directly connected to the
> main pressure hull?  Does ABS have any guidelines regarding this?  PVHO?
> 
> In your specific case, I think that a crack in that weld would probably just
> lead to separation of the stiffening ring from the pressure hull surface,
> which is probably not a big deal since the ring is loaded in compression.  If
> there is, however, any chance of such a crack propagating into the main
> pressure hull, then this issue needs to be considered.
> 
> Is fatigue analysis a necessary part of PSUB design, or are PSUBS generally
> subject to so few loading cycles in their lifetime that it is sufficient to
> consider strength only?
> 
> I don't know, I am just thinking out loud (in print?).
> 
> -Sean
> 
> Quoting Carsten Standfuss <Merlinsub@t-online.de>:
> 
> > Hi Cliff,
> >
> > as some test has shown the lengthwise internal supports will not work
> > properly.
> >
> > But you can use rolled H-Profile instead of T -Frames. H-Profiles are
> > much easier to roll than T-Frames and there is no need to weld them
> > together. U-Frames will also work this way.
> >
> > http://www.prismnet.com/~moki/20030115.120916/113-1333a.JPG
> >
> > Regards Carsten
> 
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