Simon Norton, International Zinc Association04.21.20
South Africa has a coastline of more than 2,850 kilometres and an extensive, complex and vastly expensive infrastructure has developed along the coast over the past 100 years.
This ranges from luxury houses at coastal holiday resorts and quaint villages, to rail and industrial infrastructure in the form of warehouses, cranes, electrical pylons and structural steel. The bulk of this hugely costly infrastructure is concentrated up the west coast at Saldanha Bay, around Cape Town, along the Garden Route, at smaller cities such Port Elizabeth and East London, around the Durban metropolis and at the Richards Bay coal terminal.
Billions of Rands have been invested at the coast over the past 50 years in structural steel, power line masts, roofing, water treatment plants, wastewater process units, cladding of factory structures, luxurious housing with architecturally designed features and expensive roof sheeting. Can these assets and investments actually stay the course and last long enough to ensure a good return on investment for home and business owners and municipalities?
In truth, South Africa’s coastal infrastructure is a mix of good and bad design and in some cases poor steel protection. Consulting engineers and designers seem to need intensive education on the important role that zinc hot dip galvanised steel can play in ensuring a long life (30+ years ) for exposed structural steel and other steel fixtures.
In South Africa with our long and very corrosive coastline, it is absolutely vital that civil engineers, consulting engineers and architects utilise hot dip galvanized steel structures and even galvanized reinforcing steel in concrete structures exposed to coast salt spray and sea spray.
It’s the chlorides in sea spray and sea mist that corrode steel the most and put South Africa’s coastal infrastructure most at risk and we have to inform and impress on design engineers how critical it is to use galvanized steel as well as aluzinc and galvanised roof sheeting to keep the chlorides out.
There is no need for coastal steel infrastructure to be damaged by chloride corrosion and seawater corrosion if the right tools are used to design structures, roofing or steel items. The South African Bureau of Standards (SABS) offers a range of very useful standards for working with hot-dip galvanizing of steel.
The most effective way to protect coastal infrastructure is to use what we call a DUPLEX COATING SYSTEM, where the steel is first hot-dip galvanized to SANS 121 and then overcoated with multiple layers of organic paint. This not only offers effective corrosion protection in highly corrosive coastal environments but also offers the designer the choice to choose an aesthetically attractive paint color.
It is very difficult to quantify the risk that South African coastal infrastructure faces and to highlight the magnitude of the risk.
However, the fall in the quantity of zinc imported into South Africa between 2015 and 2018, by nearly 54,000 metric tons, speaks volumes.
While part of that drop is down to the state of the South African economy, it may also be evidence that some are skimping on galvanizing in favour of organic paints. While these paints have their role in a Duplex System, they are not sufficient to ward off sea spray on their own. Over time, coastal steel that’s only been painted will fail and rust far sooner than a hot-dip galvanized and painted steel structure.
The infrastructure around the South African coast is subjected to differing corrosion regimes due to localised meteorological conditions which result in different rates of corrosion of steel and zinc.
Much of the coastal environment within 2-3 kilometres of the sea up the West Coast is highly corrosive, as are parts of the Cape Peninsula and around the Durban Harbour area. Things aren’t much better in Port Elizabeth, East London and Richards Bay and the risk is thus high that coastal infrastructure in these locations will rapidly corrode and become seriously damaged.
Not only is structural steel at risk, but also roof sheeting, cladding and bolts used to secure roof sheeting and steel structures.
I cannot emphasise enough how vital it is for designers and consulting engineers to specify hot-dip galvanised bolts with 60+ microns of zinc coating as opposed to electroplated bolts with 12 microns of zinc coating for all South African coastal installations.
When it comes to roof sheeting, meanwhile, civil engineers and consultants must select coated continuously galvanized roof sheet or cladding with special coating systems designed for the highly corrosive environments, such as aluzinc or galvalume with tough UV (ultraviolet) resistant and corrosion resistant organic coating systems over the zinc or aluminium-zinc layer applied to the steel sheet.
There are concerns that with the current severe economic downturn in South Africa, new project clients and clients looking for building upgrades or refurbishment may be tempted to seek a cheap solution and go for just a painted steel structure. The use of zinc hot-dip galvanized steel, or the correct grade of continuously galvanized steel topped over with a resilient organic coating, or coated aluzinc sheeting will all lower the risk to coastal infrastructure.
It’s therefore vital that civil engineers, consulting engineers and architects specify zinc hot-dip galvanized steel and bolts according to SANS 121, to specify duplex coating systems and to choose suitable continuously galvanized roof sheeting capable of withstanding highly corrosive environments near the sea.
All of these tools are designed to lower the corrosion risk to coastal infrastructure, prolong the life of steel near the sea, and ensure a good return on investment.
