Underwater-welding, one of the best examples
of adapting a well known process to the harsh and dangerous environment of the sea, demonstrates
what necessity, ingenuity and continuing efforts could accomplish, mostly to save huge
investments in offshore structures that were damaged and needed repair.
What is there,
deep in the water? Does it pay?
The advantages are of economical nature,
because Underwater-welding for marine maintenance and repair jobs bypasses the
need to pull the structure out of the sea and saves much valuable time. If one
thinks of Underwater-welding the hull of a ship or of a partially submerged oil
drilling tower, one understands that the alternative may be extremely
expensive, if at all possible.
The limitations of Underwater-welding concern
the inevitable bulky and expensive setup to provide the welder with all the support needed,
for respiration, for protection from cold, for special welding equipment, for
remote surveillance camera, for special non destructive testing.
Is it risky?
The main risks for the welder performing
Underwater-welding are the potential for electric shock, the
possibility of producing in the arc mixtures of hydrogen and oxygen in pockets,
which might set up an explosion, and the common danger sustained by divers, of
having nitrogen diffuse in the blood in dangerous proportions. Curiously the
risk of drowning is not listed with the hazards of Underwater-welding.
First there were no demands for quality.
Underwater-welding was just applied to weld a patch until a more thorough repair could be
performed. But as soon as more experience was gained, ambitious individuals and
companies joined forces to improve results and to establish achievable
specifications.
Let us
continue...
... with some more details on
Underwater-welding. There are three main ways to perform Underwater-welding.
One is to build an enclosure, a pit, around the place of repair and to pump away
all the water: that amounts to prepare the conditions for normal welding in
air, although the place may be deep under sea level.
Another method of Underwater-welding consists
in preparing an enclosure to be filled with gas (helium) under high pressure (hyperbaric)
to push water back, and have the welder, fitted with breathing mask and other
protective equipment, weld quite normally out of water but under pressure.
The third is the wet Underwater-welding
method, where no attempts are made to dry up the location of welding. Instead
the power of the arc generates
a bubble of a mixture of gases which lets metal melting and joining occur more
or less normally, using specially covered electrodes to avoid that too much
hydrogen be absorbed in the weld. The skilled welder must also be a diver,
equipped for Underwater-welding, with all the extra equipment and protection a
welder must use.
There is also a less used method of
Underwater-welding which features a special torch which sprays a cone of high
pressure water, within which protective gas under pressure insulates the weld
location from the water during welding.
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