<html><head></head><body><p dir="ltr">I used to see doubler plates used all the time on mining machinery, despite the fact that these details are extremely sensitive to fatigue. Fatigue seems to be overlooked by a lot of junior designers. Failure after failure, and every time the same solution: cut it out, and replace with a casting which accomplishes the same thing but with only full penetration welding, and of course the casting allows for generous radii and mitigation of stress concentrations that you can't achieve with plate fabrication. Full penetration is required on hull welds. I would employ it everywhere I couldn't afford a failure.</p>
<p dir="ltr">Sean</p>
<br><br><div class="gmail_quote">On April 26, 2014 6:58:12 PM MDT, via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<font color="black" size="3" face="Arial, Helvetica, sans-serif"><font class="Apple-style-span" size="3">Sean,</font>
</font><div><font color="black" size="3" face="Arial, Helvetica, sans-serif"><font class="Apple-style-span" size="3"><br />
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<div><font class="Apple-style-span" size="3">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.</font></div>
<div><font class="Apple-style-span" size="3"><br />
</font></div>
<div><font class="Apple-style-span" size="3">Vance<br />
</font><br />
<br />
<div style="font-family: helvetica, arial; font-size: 10pt; color: black; ">-----Original Message-----<br />
From: Sean T. Stevenson via Personal_Submersibles <personal_submersibles@psubs.org><br />
To: Personal Submersibles General Discussion <personal_submersibles@psubs.org><br />
Sent: Sat, Apr 26, 2014 8:42 pm<br />
Subject: Re: [PSUBS-MAILIST] External Stiffeners<br />
<br />
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<pre style="font-size: 9pt;"><tt>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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