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Spencer Gulf crossing towers
Port August to Whyalla 275V transmission line protected
by duplex coating system
 Current Australian and overseas experience
demonstrates that in some environments, steel transmission
line towers will be well protected against corrosion
for seventy years by hot dip galvanizing. Only a few
of the steel lattice structures in Australia are this
old but overall the performance of galvanized coatings
in Australia has been excellent where good maintenance
practice has been followed.
The Electricity Trust of South Australia
recently completed the construction of a new 70km line
to reinforce supply to Whyalla (110km north west of Adelaide
across Spencer Gulf) and the far west of South Australia.
Given the corrosion performance of other transmission
towers in the area and the load capacity of the line,
the new line structures could have a viable life of 100
years.
However, two of the towers are located on piles in the
waters of Spencer Gulf, which provides a much more corrosive
environment. These towers are 110 metres in height, 17
metres wide at the base and each weight 60 tonnes. Their
size and location make both access and the work environment
for future maintenance very difficult.
 Graham Brown, Transmission Structures Engineer with ETSA
says " The extremely high cost of maintenance and
replacement of these towers encouraged ETSA engineers to
work closely with GAA to identify a method of enhancing
the performance of the standard zinc coating." Since
an increase in life expectancy would be beneficial, a duplex
system comprising galvanizing plus a two-coat epoxy paint
system was recommended by GAA to provide the required additional
maintenance-free life.
Painting was carried out away from the site to minimise
contamination of the galvanized steel surface by airborne
salts, and any damage to paint coatings during transport
was repaired on site before erection. The selected paint
colour matches the colour of weathered zinc, so few people
would be aware of the extra protection provided.
Close co-operation between all those involved in providing
the duplex system at the construction stage has provided
benefits expected to be far greater than later maintenance
painting over hard-to-clean corroded steel.
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