New Zealand’s transmission and distribution system relies heavily on line and substation
support structures constructed using millions of tonnes of hot dipped galvanized steel. It
collectively represents an industry investment worth billions of dollars. All this investment
has a finite life before rusting sets in. With the average asset age now exceeding 40 years and
some structures over 80 years old, zinc protection applied decades ago is now heavily
depleted in many locations.
Every day hundreds of kilograms of galvanising corrodes away (Note 1) and is not replaced.
Obviously this cannot continue forever and eventually these assets will have to be maintained
or, they will have to be replaced. Either way, maintenance is set to become a growing and
costly issue for the industry and a ramping up of maintenance and/or capital replacement
budgets to cope is already inevitable unless reliability is to decline.
In considering the maintenance of galvanised structures, the industry has essentially three
choices: It can maintain proactively, it can maintain reactively or it can replace. Depending
on the circumstances of particular assets, each option has its proper place. The challenge
facing the industry is to ensure that its asset management selects the correct choice for each
situation. Unfortunately this rarely happens and the outcome is usually higher long term
costs; much higher in many cases.
The objective of this paper is to show that for most assets, the proactive maintenance option
produces by far the lowest long term cost; yet this is the least adopted option. This paper will
ask why that is and should the industry be adopting a more coordinated approach given the
very large and growing sums involved.
-Mike Boardman and Wal Marshall
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