Hi all,
I've just run into a good example of the practical
differences between design and construction. I know there's a bunch of you out
there with more practical experience than myself, so really look forward to
suggestions.
I'm building a hatch which is comprised of a
"dished-only" head in 516 grade 70 and a stainless ring half an inch thick.
"Dished-only" means the head has no flange, so it meets the SS ring at an
acute angle. This is similar to a K-350 hatch, though my dimensions are a
little different.
The head was beveled from the outside, which
allowed me to make a full penetration outside TIG weld. I should probably have
left it at that. But I had an opened box of SS electrodes going to waste, so I
decided to weld it on the inside as a little extra. Initially I thought it was
virtually impossible to do that inside weld, because one had to make the weld
blind. But with the help of a little mirror and by bending the electrodes into
the right shape, I was actually able to do it. I took the inside weld the
whole way to the inside edge of the SS ring, which is now nicely faired into
the head. This inside weld is, due to the difficulties of the position, surely
full of flaws. But again, it's just supposed to be bonus safety margin on top
of the high-quality outside weld.
Now for the problem?
I expected the inside weld might pull the ring
inwards a little, but I never expected HOW MUCH it would do so. The half inch
SS ring is deflecting inwards a quarter inch. My next step was going to be
putting the hatch on a lathe to true the SS ring surface and cut the O-ring
groove. There's still enough material to do that. But what worries me is that
the pull of the inside weld must be putting enormous tension on the critical
outside weld. This tension is in the same direction as the tension that will
be produced by water pressure at depth. So instead of bracing the outside
weld, I have the impression I'm actually adding to the tension that will be
stressing it when submerged.
So what do people think should be done about
this?
1) Nothing, machine it as planned.
2) Is possible to relieve the tension with a heat
treatment?
3) Grind away the whole inside weld? (oh no, please
no!!!)
4) Use a cutoff wheel between the inside weld and
the SS ring to let the ring pop flat again, then just fill the gap with an
additional weld pass?
I like the idea of #4 because it would relieve the
tension while still providing the bracing I was after originally. I'd need to
be careful about the depth of the cut, I don't want to go anywhere near the
outside TIG weld. But again, I'm just wondering what more experienced builders
might suggest!
Thanks,
Alec
The contents of this e-mail are intended for the named
addressee only. It contains information that may be confidential. Unless you
are the named addressee or an authorized designee, you may not copy or use it,
or disclose it to anyone else. If you received it in error please notify us
immediately and then destroy
it.