Ok Bill - wrong example but the QE2 and many other ships of equal size didn't.
BTW I did see that prog last year and remember the reinforcement belt.

The truth still stands that the heat generated when welding can and does weaken
the surrounding metal.  Generally if you look at a broken "welded" joint you
will invariably see the weld intact and the metal around it has broken showing
the weakness.

Obviously we must have watched different episodes.

Wave lengths vary at sea as does the angle of incidence of the ship, so
inevitably every ship will experience waves that will resonate with the ship
at some time in their lives.

The real reason Liberty ships sank is as follows: -

1. Material
   The steel was cheap and of poor quality, but the particular problem was
that the relatively high carbon content meant that the steel became brittle
at low temperatures, such as those experienced in the north Atlantic in
winter.

2. Welded without stress relief
   An all welded ship was a new idea, and it was not realised that once
started a crack could propagate through the entire structure.  In particular
the deck hatches were rectangular with right angle corners and this provided
a point of high stress for cracks to start from.

3. Amateur Welding (well not quite)
   Workers building the ships were relatively inexperienced (most
experienced ship builders had been drafted) in ship building in general and
welding in particular.  Tight schedules (like building a ship in three days)
meant that there was little quality assurance and welds were often weak or
defective and / or liable to corrosion.  Poor technique also weakened the
steel near the weld.

4. Poor loading
   In the fog of war the ships were simply loaded willy nilly, resulting in
increased stresses in the hull.

The net result was that cracks would start in the corners of the hatches and
propagate right around the hull and the ship would split in two.  The are
plenty of pictures of half liberty ships, and one allegedly split
immediately after launch.

That said, after relatively light remedial work (around the hatches) many
liberty ships spent decades plying in the tropics (as well as vulnerability
to cold they usually also lacked heating for the crew), and IIRC the last
one only retired in the 90's.

Early Comet aeroplanes also suffered in this way.

Dave - I didn't say that.  there is welding and "WELDING" one is done by divi
Jones the work experience school leaver and the other is done by educated
professionals with years of experience.

It only need a bit of oxygen to reach the molten metal and the weld is flawed.
GAS,  MIG & ARC have always been the favorites of crash body shops and gas is
the main culprit of porous welds with ARC coming a very close second. MIG is
generally better in the hands of a skilled operator but only if there is enough
gas pressure and flow rate.

BTW 99.9% of all airplanes are riveted and they are pretty strong they only seem
to break up when they hit the ground at speeds over 300 MPH as your car would -
don't know many ships that go that fast except space-ships.