Civil Engineering Reference
In-Depth Information
pressures affect the gas, slag and metal reactions for all welding processes,
and the high-density gas enhances the rate of heat loss from the weld. Hyper-
baric welding research is mainly concerned with ensuring that, for any spe-
cific environmental pressure and composition, welding parameters can be
specified that will ensure the production of welded joints with properties
acceptable to the project specification and the supervisor who is responsible
for the structure that will use this type of weld. Given that the welding pro-
cess has to be specially optimized for hyperbaric conditions, the number of
techniques used has been limited. The great majority of hyperbaric welding
is carried out using GTAW and SMAW techniques, with small amounts of
FCAW and GMAW.
A variety of habitats have been used, depending on such factors as the
extent of welding required, the complexity of the repair-site geometry, depth
of repair, welding process and ancillary equipment and environmental condi-
tions. Generally, designs of dry hyperbaric habitat fall into one of the following
four groups:
Lightweight steel habitats: These have stiffened plate construction and are
fabricated in two or more sections to allow their placement around jacket
members. They may have an open grate floor with an access hole, or they
may be fitted with a closed floor and access shaft. The latter is used in shallow
depths where the shaft acts as a surge tube, thereby reducing the volume and
pressure changes in the habitat that otherwise could affect diver physiology.
●
Inflatable flexible habitats: Where the differential pressures are expected to
be low, flexible habitats of sufficient strength are practicable and have been
used. The skin of the inflatable habitat takes a shape dictated by the skin
membrane stresses and the depth-dependent differential pressure, and it is
the same shape that would be obtained onshore by turning the habitat upside
down and filling it with water.
●
Mini habitats: These habitats are small, with just enough room for the arms
and sometimes the head of the welder/diver. In essence, mini habitats pro-
tect only the welding head and a small area around the weld.
●
Portable dry spot habitats: These protect only the welding head and a small
area around the weld. A clear plastic box, fitted with sponge or flexible rub-
ber seals, moves with the head. These devices have not undergone as much
development as either large habitat welding or wet welding.
●
In general, the hyperbaric welding conditions require that the welding be
specially optimized for the elevated pressure and for the fact that the high-density
gas enhances the rate of heat loss from the weld.
A hyperbaric welding operation requires the following equipment and tools:
Purpose-built habitat
●
Saturation diving support
●
Environmental control equipment
●
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