Re: [PSUBS-MAILIST] Ultra-sound NDT [was: two man sub on ebay (or buying used submarines)]

[David Hahn <delta531@yahoo.com>]

Hi Dave,
That is really a good point.  At my plant we have a
really big steam header that has bad welding on the
brackets that hold it up.  It is about 80 feet long,
36 inches in diameter, and about 7 inches thick. 
Normally it is operated at about 1000 deg F and at
2400-2600 psi.  The welds on the brackets should have
been full penetration welds, but due to poor fit up
really consist of two really big fillet welds with
about 1/2" gap between them.  The gap has slag in it,
as it wasn't back gouged/back ground and cracks
develop and travel along the interface between the
root of the weld and the header surface.  In addtion
to the weight that of the header that is being held by
these big brackets, the header itself also is a
suspension point for long and heavy steam tubing
loops.  We didn't want to just cut a bracket off, and
re-weld it and hope to get all the load balanced
again. So we ended up grinding out one side of the
weld, cleaning out the old root and rewelding it. 
Then we would go to the other side, remove that old
weld, grind or gouge any slag that remained from the
new weld on the other side, and then re-weld the
second side.  We have done this on more than a dozen
of these brackets and it seems to be working well.  I
think the same technique could be used to repair bad
welds in a submersible.  You wouldn't have to remove
the weld holding the heads on, just a foot or two, and
then reweld it on both sides, grinding out any slag
and porosity. That would prevent any of the parts from
getting misaligned.

TIG is great but a little slow.  We like to TIG the
roots of our steam tube welds because we can't get
into the back of the weld to clean it up.

Ian, I don't know about UT cables.  We usually have an
NDT company come in with their equipment.  How good
you get will probably depend on how much you read and
practice.  I am thinking that 1/4" is probably about
as thin as you can get and use shearwave UT reliably. 
We ususally use it on big mongo steam piping and
headers -  2-7" thick.

Rick, Yeah, that is a devils advocate question!  And I
am totally unqualified to give anything but an
opinion.  I like Dave's suggestion best.  If you have
a bad weld, or section of weld, grind it out and
reweld it.  I do think that you won't really know what
you have as far as weld quality goes until the paint
has been removed.  It is possible that no filler was
used at all, and that the welds are fine.  After it is
blasted you will be able to see pretty easily if they
ground off the gobs and filled in the holes with
putty.  If you have a nice, neat weld with out pits,
cracks, porosity, or cold lap areas  you are probably
OK as far as welding goes.

So... here is my question:  How do you test something
like this?  In steam and pressure vessel construction
they are pressure tested or hydro-ed.  Would the plan
be to remotely sink this machine to four or five
atmostphers to see if the welds and the seals can take
the pressure?  Just curious.  That seems like it would
be a prudent precaution, and one that would win the
support of your wife and insurance carrier.  :)

One more question: Does the tower have a repad?  A
reinforcing pad is needed where an attachment is made
in a pressure vessel to strengthen and re-inforce the
hole that has been made.  Calculations will have to be
made concerning the width and thickness of the pad and
that will depend on the planed operating pressure,
tower size (dia) and main vessel size.

Also, does it have re-inforcing rings running
circumferencially?  This would be a really good
feature.  I guess I had better read up on the design
features of the K series.  

Well, the day is about done, hope it was a good one. 
Good night all,

Dave
--- No Periscope <noperiscope@yahoo.com> wrote:

> A big part of welding a submarine together is the
> fit of all the parts before the welding
> begins..Welding the boat together is in some
> respects the easy part...the hard work has already
> been done..a good welder will know if he or she has
> done a good job and if it is welded with the TIG
> method,,, then all the welds will be very good if
> the person knows what they are doing.  If some one
> is thinking about buying this sub on E Bay and is
> concerned with the safety of the welds,, then it
> would be simple to grind out the welds and have a
> pro re weld the boat.  It would take me about a week
> to grind out all the welds and re weld the boat.
> This would eliminate any concerns...
>  Any one interested in this can e mail me. Dave from
> Advanced Welding in Marathon Florida 
> 
> Ian Roxborough <irox@ix.netcom.com> wrote: 
> 
> Welcome Dave. Thanks for sharing some of your NDT
> experience, feel
> free to go a longer if you like.
> 
> A while back I started collecting NDT testing
> components with the
> intent of being able to do my own ultra-sound
> testing. I've just
> been buying things that I could afford (i.e. when
> they where cheap).
> 
> I've been wondering about the cables used for
> connecting the tranducers
> to the signal generator and O-scope. Is there
> anything special about
> these cables? Could I make them myself? Cables and
> an Oscope are
> the only bits I've left to collect before I can
> start practicing.
> 
> I have a friend who has worked on Ultra-sound NDT
> robots (the type
> that inspect pipelines, etc.), he's able to give
> some pointers
> and keep in the right directions (gives me hints on
> what to buy).
> What are your thoughts on the DIY ultra-sound NDT? I
> figure even
> if I suck at it, the worse that can happen is I redo
> a weld that
> was good. Given that most ksubs/psubs are lowered to
> X feet deeper
> than operating depth for a certain length of time as
> the main form
> of materials testing, I don't think I'm introducing
> any additional
> danger by attempting my own NDT).
> 
> Anyway, a big WELCOME ABOARD, great first post!
> 
> Thanks,
> Ian.
> 
> 
> 
> On Thu, 25 Nov 2004 08:06:22 -0800 (PST)
> David Hahn wrote:
> 
> > Hi,
> > First post from a newbie, but thought I might
> comment
> > on the welding issues. I work at a powerplant,
> have
> > some NDT certs (mag and PT), and am a CWI, as well
> as
> > a boiler inspector, so have gotten to be a little
> > familiar with some of these issues.
> > 
> > I am not sure where you are, or if there are any
> NDT
> > companies near you but if you can find a good
> > ultrasound man you can find out a lot more about
> your
> > welds then you can with xray. X-rays will show
> slag
> > and porosity pretty well, and if you have a crack
> or
> > delamination that runs the same direction as the
> beam
> > it shows up pretty well, but we have had trouble
> with
> > cracks that are 90 degs to the beam. A lot of both
> > the UT (shearwave) and X-ray are in the
> > interpetation, so the operator is really
> important.
> > 
> > Actually, you could probably find out a lot about
> the
> > welds if you had just a simple ultrasound d-meter.
> 
> > These are just depth meters and catch a sound
> bounce
> > off of the back wall of the weld or piece of
> steel.
> > Really uneven readings would indicate slag.
> > 
> > But that would be sort of a half measure. In an
> > industrial settting we would sandblast all the
> welds -
> > interiour and exterior. A visual inspection would
> > tell you if they back gouged the welds and made a
> good
> > full penetration weld, or of they just gooped it
> over
> > and (horrors) puttied it to make is smooth. A dye
> > penetrant test would reveal pits, porosity, cracks
> > etc, and a dye penetrant setup is cheap to buy and
> > pretty much fool proof. It won't tell you what is
> > inside a weld, but when you are talking about 1/4"
> to
> > 3/8" thicknesses you can see most of the problems
> > looking from either side. Pressure vessel
> > manufacturing code would require x-rays on the
> > longitudinal welds as well as the cirumferential
> > welds. Some of that is probably for insurance
> > purposes, and some for thicker-walled vessels.
> > 
> > Sorry, I didn't mean to run on so long, and maybe
> > everyone already is familiar with welding and NDE
> -
> > don't mean to be a know-it-all (because I am a
> real
> > newbie when pressure comes from the outside) but
> if I
> > was going to climb into a sub that someone else
> had
> > welded and I didn't know anything about it, I
> would
> > sandblast it and run a dye penetrant test on all
> > welds, inside and out. Bad spots would get ground
> > out, retested to make sure that the defect was
> gone
> > and carefully rewelded. These would be the minimum
> > steps that I would take to ensure that the welding
> was
> > done right, and that it wasn't likely to unzip. 
> > 
> > Best of luck, 
> > 
> > Dave
> > 
> > 
> > --- "Dan H." wrote:
> > 
> > > Ian,
> > > I hate to put a damper on your enthusiasm but!
> > > I looked at the larger pic you sent and first
> off
> > > the view ports don't look
> > > right.
> > > 
> > > The sub looks like a take off of a K design all
> > > right but the builder took
> > > many liberties. After reading Gene's look-see
> and
> > > what I see in the larger
> > > pic, you may not want it unless your only diving
> in
> > > the shallows. The
> > > trailer and tire issue you can deal with but not
> > > being sure of the weld is a
> > > bigger matter. You can have it X-rayed and
> repair
> > > if needed but that's not
> > > cheep.
> > > 
> > > The bigger problem is with the view ports. From
> > > what I see in the pic,
> > > there isn't enough steel in the viewport
> housings. 
> > > They are thin and don't
> > > have nearly enough surface to back up the
> lenses. 
> > > They look to be about a
> > > eight inch lens size and need about an inch and
> a
> > > half of back up all they
> > > around the interior side of the lens. The hole
> on
> > > the interior side of the
> > > housing should be about six inches. You'd have
> to
> > > change all of them to
> > > ever take it to 250 feet.
> > > 
> > > If you get it cheep enough, it may be good buy
> for
> > > materials but already to
> > > high priced for what you'd be getting.
> > > 
> > > Sorrrry, Dan H.
> > > ----- Original Message ----- 
> 
=== message truncated ===



	
		
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