Engineers need to use plain English to explain the costs and benefits of having an effective protection plan for infrastructure assets, a recent corrosion seminar was told
One example could be a galvanized boat trailer to demonstrate the benefits of maintenance washing, Dr Jonathan Morris of Opus International Consultants told the Australasian Corrosion Association’s New Zealand branch, citing the increased life of the trailer when it’s regularly and thoroughly washed.
Liam Coleman of the Auckland Motorway Alliance shared his experiences of managing older bridges in the UK and Ireland and rail links across the world, and how careful monitoring of the asset can manage risk until funds are available to fully repair or replace it.
Many participants agreed that a design life of, say, 50 years (as is the case with residential builds including apartments) or 100 years (for major infrastructure) is often expected to perform considerably beyond that.
Many road and rail bridges built in the late 19th century are still operational and expected to carry increasingly large loads.
One such structure in Auckland is the old Mangere Bridge spanning the upper Manukau Harbour.
At the moment, it is used for pedestrian traffic only and serves as a recreational asset linking the Mangere and Onehunga communities.
However, the structure is significantly corroded and will continue to deteriorate.
A replacement pedestrian bridge is in the consenting process, but could still be up to three years away.
The existing bridge therefore needs to safely remain open until that time if possible.
The most deteriorated spans have been fenced off, and physical bracing has been installed to manage the risk and increase safety factors.
Real-time monitoring in the form of 100 sensors is in place, alerting engineers immediately if stresses exceed the agreed stringent levels.
With the decrease in “hazardous” anti-fouling coatings, microbial-induced corrosion (MIC) is increasing in ports throughout the world.
It’s now also being seen in fresh water, such as in the corroding sheet pile diversion wall in Lake Rotoiti.
This wall must divert the inflow from Lake Rotorua into the Kaituna River until 2057, so options delivered to the client included structural strengthening, use of an impermeable polymeric screen, or complete removal and replacement of the wall with vinyl sheet piles.
ACANZ President Raed El Sarraf from Opus was able to discuss the various advantages and disadvantages of each system with the client, who could then make an informed decision on the risks of each balanced against its relevant cost and maintenance requirements.
Leading materials and corrosion consultant Les Boulton believes that the leaky buildings issue will continue for at least another 20 years as a result of the design fashion begun approximately 20 years ago of building “Mediterranean-look” housing where claddings were fixed directly to timber framing using metal fixings.
No air gaps or damp proof courses meant water was able to reach insulation and interior wall linings, allowing dangerous mould to grow and rot to develop.
While such designs met the NZ Building Code and gained certificates of code compliance, the serious corrosion issues they engendered have meant repairing the resultant damage can cost up to twice the original purchase price.
Dr Patricia Shaw spoke of BRANZ’s work in updating the New Zealand Corrosivity Map, which rates exposure risk to structures based on long term field testing of a range of materials.
Early indications suggest that more sites and finer measurements delivered by the current research are changing the risk profile for many geographic areas.
BRANZ has also found that many materials display “unusual” corrosion behaviour within geothermal environments.
The best protective coating is often more expensive to apply but will also extend the “time to first maintenance” period, and appropriate maintenance after that will ensure the asset’s integrity.
Matthew Vercoe of Metal Spray Suppliers explained how a good specification can help contractors apply the coating correctly, as well as help owners to understand the benefits of spending a little more initially.
Regular inspection and testing of the protection ensures the underlying material is able to maintain its integrity at least until the end of its design life.
Phill Dravitski is qualified to inspect the state of protective coatings in New Zealand and he does a lot of work with Transpower NZ, climbing the transmission towers to physically check their surface coatings.
He points out that protective treatments change depending on the site, the previous coating used, how long ago it was applied, and the skill of the coating applicator.
It’s important that an independent third party physically inspects all of a tower by climbing and examining it for signs of corrosion as drones will miss too much, in his opinion.
And despite a check plan, he finds that personal perception of compliance when re-applying a protective coating isn’t necessarily the same as true compliance.
Representing seminar sponsor Carboline, Neil Adamson discussed the effects of concrete degradation and subsequent rebar corrosion, especially as demonstrated in wastewater treatment plants and chemical bunds.
Sub-surface defects in concrete finishes can affect the performance of protective coatings, he explained, and with the increase in unvented hydrogen sulphide, MIC levels are also increasing in enclosed systems such as wastewater pipes and tanks.
Just 30ppm of H2S will cause severe concrete corrosion, and anecdotally this has increased to over 100ppm in some systems internationally.
Asset managers cannot vent H2S from treatment plants today because nearby residents don’t want the smell, consequently trapping more sulphides than ever and placing more demand upon protective coatings.
