Abstract
The first atmospheric corrosion map of South Africa, produced by Callaghan in 1991, has become outdated, because it primarily focuses on the corrosivity of coastal environments, with little differentiation given concerning South Africa’s inland locations. To address this problem, a study was undertaken to develop a new corrosion map of the country, with the emphasis placed on providing greater detail concerning South Africa’s inland regions. Here we present this new corrosion map of South Africa’s macro atmosphere, based on 12-month corrosion rates of mild steel at more than 100 sites throughout the country. Assimilations and statistical analyses of the data (published, unpublished and new) show that the variability in the corrosion rate of mild steel decreases significantly moving inland. Accordingly, the average first-year corrosion rate of mild steel at the inland sites (at all corrosion monitoring spots located more than 30 km away from the ocean) measured 21±12 μm/a [95% CI: 18–23 μm/a]. The minimum inland figure was about 1.3 μm/a (recorded at Droërivier in the Central Karoo) and the maxima were approximately 51 μm/a and 50 μm/a in the industrial hearts of Germiston (Gauteng) and Sasolburg (Free State), respectively. The variability in the corrosion rate of mild steel also decreased by as much as 80% between 150 m and 1000 m from the coastline. Moreover, the impact of changing altitude on the corrosivity of the environment was confirmed, particularly along the coastal regions.
 Significance:
 
 A new corrosion map of South Africa’s inland and coastal regions is presented.
 The map facilitates the identification of South Africa’s least to most corrosive environments; enabling the selection of more appropriate corrosion protection solutions for general, business, mining and industrial installations.
 In identifying South Africa’s least corrosive areas, the use of more environmentally friendly corrosion protection procedures is potentially encouraged.
Highlights
The first atmospheric corrosion map of South Africa was published 28 years ago.[1]. This map (Figure 1), referred to as the Callaghan map, was developed based on the atmospheric corrosion monitoring results of studies conducted during the 1970s to 1990s, at 11 sites, of which 60% were situated along the South African and Namibian coastlines
A similar study was conducted in South Africa in 1986.13 During the South African study – which covered the mining, power generation, shipping and transportation sectors – corrosion protection preventative measures, metal losses and replacement costs were estimated at ZAR1 250 million/ annum or USD625 million/annum.[13]
Assimilations, statistical analyses and interpolations of the 12-month corrosion rates of mild steel for South Africa and the Highveld region, based on the historical published, unpublished and new data, revealed that the average first-year corrosion rate of mild steel at the inland sites was about 21±12 μm/a [95% CI: 18–23 μm/a]
Summary
The first atmospheric corrosion map of South Africa was published 28 years ago.[1]. This map (Figure 1), referred to as the Callaghan map, was developed based on the atmospheric corrosion monitoring results of studies conducted during the 1970s to 1990s, at 11 sites, of which 60% were situated along the South African and Namibian coastlines. Since its publication in 1991, the Callaghan map has undergone only minor adaptations.[2,3,4,5,6,7] due to the lack of differentiation of inland locations, overstatement of the corrosivity of environments, changes in international standards regarding the measurement of corrosive atmospheres, increased industrialisation of South Africa’s large metropolitan areas, global climate change effects, and improved mapping techniques,[8] this chart has become outdated
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