[PSUBS-MAILIST] External Stiffeners

Sat Apr 26 21:47:49 EDT 2014

I think that GL may allow it as I noticed that Carsten's sub used I section
stiffeners and his explanation is that with a full seal weld the oxygen will
form a light rust initially but then the available oxygen is all used up and
no further rusting will take place.  Pressure vessels often have a breather
hole in doubler plates possibly to eliminate pressure from the heat of
welding.  I don't know if they are supposed to be welded up after the seal
weld. 

Hugh

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org]
On Behalf Of via Personal_Submersibles
Sent: Sunday, 27 April 2014 12:58 p.m.
To: personal_submersibles at psubs.org
Subject: Re: [PSUBS-MAILIST] External Stiffeners

Sean, 

Thanks for that. It just never occurred to me that you could actually get
enough penetration (without excessive warpage) to qualify. And it seems not.
My doubler plate analogy notwithstanding, of course. I was thinking back to
the old days when Perry used doublers. ABS put the kibosh on that, and it
was a big change to install doubled thicknesses (for lift pads, for
instance). We ground a few old doublers down on a couple of bells and found
(surprise, surprise) rust.

Vance

-----Original Message-----
From: Sean T. Stevenson via Personal_Submersibles
<personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion
<personal_submersibles at psubs.org>
Sent: Sat, Apr 26, 2014 8:42 pm
Subject: Re: [PSUBS-MAILIST] External Stiffeners

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
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