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RE: [PSUBS-MAILIST] warning for smyth
Alec,
I believe that the reason that some people feel that a dressed weld is
inferior to an undressed weld is the small abrasions (scratches) in the
surface. These are viewed as crack initiators where stresses are set
up. It could probably be related to notch toughness on a very small scale
as these scratches are tiny.
The problem with an undressed weld can come where there is a natural V
in the metal between passes or else between the upper or lower pass and the
hull. When the metal has a bending torque the V becomes a notch and a
notch that is much deeper than the scratches of a grinder. Stress can set
up at this point yielding a weaker scenario than a rounded ground weld. I
believe one of the URLs I posted was trying to debunk the "myth" that a
ground weld is better than an unground weld!!
One other thing to say about grinding; when I welded my sail section
to the hull, I ground almost every weld placed. I welded with 7018 low
hydrogen rods and after each pass, I ground anything that looked as though
it might not fully enter the melt on the next pass. 7018's are not known
for their penetration, more so for their strength. In this process, I
noticed at least once that I had gas inclusions in the weld at the end of
the bead. This porosity was from not lifting the rod quick enough. These
were well ground out before proceeding.
Perhaps at the end of this... We are all more "Well-ground-ed."
Gary Boucher
At 01:02 PM 9/25/2002, you wrote:
>Aha, there might be some worthwhile discussion here after all. The
>certified pressure vessel welder who did the hull said the following with
>respect to dressing the surface of the weld: It is not a problem so long
>as you go no deeper than the plate surface on either side. The reasoning
>is that if its a full penetration weld done with the right material, it
>essentially becomes one piece of metal.
>
>So yes, the welds are dressed. I would not see any reason to do this on a
>conventional sub, by the way. But its significant given the very specific
>intent of this design. I've done things like countersink the heads of
>screws, and make teardrop fairings around hull appendages.
>
>In any case, the welds are going to be ultrasound examined and the entire
>sub tested unmanned. And I doubt very much I'll ever be able to test to
>anywhere near its design crush depth, which is 3,000 feet.
>
>BTW I don't take offense in the slightest at this sort of post. I'm pretty
>sure in one way or another several people on the list have saved my skin
>already.
>
>thanks,
>
>Alec
>
> -----Original Message-----
> From: Carsten Standfuss [mailto:MerlinSub@t-online.de]
> Sent: Wed 9/25/2002 2:44 PM
> To: personal_submersibles@psubs.org
> Cc:
> Subject: Re: [PSUBS-MAILIST] warning for smyth
>
>
>
> Great America - submarines was welded there in early 1920 ies.. :-))
> .. and maybe it was in a freeflooding area..
> Carsten
>
> Michael B Holt schrieb:
> >
> > True story of a submarine welding problem:
> >
> > In the early 20s, on an O-class boat in a U.S. shipyard...
> >
> > A reporter was assigned to cover the launching of the
> boat. He arrived
> > early, met the important folk and sat back to wait. After a
> while, the
> > launching was postponed for an hour or so. The reporter
> decided to
> > look around.
> >
> > Security wasn't what it is today, so he was able to get on the deck
> > of the sub. He also got to walk alongside the hull. He
> started looking
> > at the hull closely, and he noted a pitting in a weld at the
> stern of the
> >
> > boat, at about the waterline. He scratched at it, wondering
> what it
> > was. Finally he looked around for something with which he could
> > scrape at the place. He found a couple of feet of stiff wire,
> and he
> > poked for a bit.
> >
> > Suddenly the wire broke through the weld. It went all the way
> into the
> > pressure hull. The reporter left the wire in the hole and
> ran for the
> > nearest foreman. Breathlessly, he told the man of his find.
> >
> > The foreman just grinned cheerfully and said, "It's OK. We'll
> just
> > cover it up with grease after we launch her."
> >
> > I think this was on Arch Whitehouse's book on submarine
> > warfare. Right now I can't find it because I re-arranged all
> > the books at midnight while I was looking for a copy of Sir
> > Thomas More's "Utopia."
> >
> > Mike H.
> >
> > ________________________________________________________________
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