IntroductionThe effects of corrosion are well known and range from the obvious, the rust we see on motor vehicles and its effect on steel constructions such as the Sydney Harbour Bridge, to the lesser known economic costs to the community such as the short lifespan of farm fencing experienced in some parts of Australia. In the battle against corrosion, which costs Australia about 2% of GDP annually, scientists from CSIRO in collaboration with the Industrial Galvanisers Corporation (IGC) have developed a new online tool that pinpoints corrosion hot spots and offers industry a more accurate prediction of the effects of corrosion on steel and galvanised products.
Corrosion Mapping SystemThe corrosion mapping system (CMS) is based on the corrosion map of Australia developed by CSIRO, which estimates the corrosion rate in every locality of the country, including all 14,700 towns and suburbs, together with case history data of performance information about coatings collated by IGC during the past 25 years. “CMS incorporates a large amount of this data with the corrosion maps to provide an exciting new tool for predicting the corrosion rates of steel, galvanised and zinc coated products used in Australia,” says John Robinson, Group Development Manager for IGC.
Geographic Information SystemsUsing geographic information systems (GIS), a corrosion model based on both statistical and process simulation was developed at CSIRO Built Environment in collaboration with its Infrastructure Systems Engineering and Sustainable Materials Engineering teams. “The map incorporates a corrosion model based on climatic conditions such as moisture, prevailing winds, salinity and pollution developed during many years of research by CSIRO,” says Stephen Pahos, Business Development Manager for CSIRO Infrastructure Systems Engineering (CISE). The model makes the following simple assumptions:
· Corrosion is influenced by two basic factors, salinity and moisture (time of wetness or TOW)
· If industrial pollution is neglected, then distance from the coast, topography, prevailing winds and the type of coast (surf or bay) will influence salinity levels
· Moisture is basically influenced by climatic parameters such as relative humidity and temperature.
The TOW, or the time a metal surface is assumed to be wet, is calculated from relative humidity and temperature records in 136 Bureau of Meteorology sites using a method suggested by the International Standards Organisation. An Australian-wide surface model of TOW is constructed from the 136 values using a geo-statistical technique called 'Kriging.' Figure 1 illustrates the resulting surface model for TOW.
Estimating Corrosion RateThe corrosion rate in each of more than 14,700 localities, including towns and suburbs in Australia, is then estimated by:
· Representing each locality as a point defined by a pair of co-ordinates (longitude and latitude)
· TOW at each locality is estimated from the surface model shown in figure 1
· The amount of salt transported to each locality from the coast is simulated, figure 2
· A surface model of corrosion rate is derived from the corrosion estimates in the 14,700+ localities, figure 3.
Using CSIRO's existing Building Information Exchange (BIEX) internet portal, and the integrated corrosion information system, corrosion maps and models can be accessed online easily and in a cost effective manner. Using the internet, users can ‘click’ on to a region in Australia from a master map and have the degradation profile for various materials reported back in microns of material lost per year. It is also possible to add value to these models and maps by coupling them with service life estimation and material selection applications.
Materials Design for LocationThis information is important to ensure that the correct materials are being used for each application. For example, it could be possible to order a steel section coated with ‘x microns’ of coating to get a given life expectancy in a particular region of the nation. This type of approach to material selection will see materials being designed for use, saving on raw materials consumption, pollution and costs associated with premature degradation of assets.
Other Uses for the Corrosion Mapping SystemThe CMS is currently being used by IGC to manage its coating guarantee programmes for its galvanised coatings and galvanised steel products. IGC offers comprehensive durability guarantees for specific projects in which its coating guarantees range from 15 to 50 years, depending on the project environment and client requirements.
“The expanding demand for performance guarantees on our products means CSIRO’s CMS is very attractive,” says Robinson. “It will help IGC manage its own coating guarantee projects and provide design professionals with real time corrosion data.”
Robinson also believes there are environmental and community benefits arising from this development. “It will give the specifying community access to environmental sustainability materials and construction information, including the greenhouse contribution of various construction materials,” he says.
Materials SpecificationsIn conjunction with the corrosion mapping programme, IGC is involved, though its industry association, the Galvanisers Association of Australia, in the development of a durability branding programme for steel products, particularly those used in construction.
Many steel construction products and builders hardware are not adequately protected from corrosion and do not give acceptable life in service. “This (the durability branding) will allow end users and specifiers to quickly identify the durability of a coated steel product through a certified ‘star rating’ system,” says Robinson.
As the demand for reliable, long term durability for steel construction products increases, and designers become more accountable for material durability performance, using the durability branding in conjunction with corrosion mapping will allow both consumers and designers to determine maintenance-free life in real time, in any environment with a high degree of confidence.
Application to Other CountriesThe system can be applied to any country, assuming the data is available. CSIRO are currently working with IGC in South East Asia providing technical support for construction durability programmes in Vietnam, the Philippines, Indonesia and Thailand. The corrosion mapping technology is expected to be expanded into these areas to assist in improving the durability of infrastructure and construction, where in the past, quality standards have led to short economic infrastructure life.
Availability of the CMS SystemThe CMS for IGC will be made available through its website, which is currently hosting a demonstration version of the CMS programme in the technical section of the site. In addition to the durability information, additional modules will provide information about inground corrosion of steel and environmental sustainability data for a range of construction materials.
The cost to industry will be relatively small. CSIRO is planning to create a web service to deliver the accumulated knowledge of its databases. During the next few years it will broaden its service with more and more data being delivered as people want it through the internet. CSIRO intends to offer its service on a subscription basis in which consumers can access the information after paying an annual fee.
Concluding RemarksWhile there are internet based databases that will provide some corrosion data, CSIRO believes its CMS is the first online corrosion mapping system in the world. “The cost of the battle against corrosion in Australia is significant. It is a battle that is wearing away the infrastructure of our economy,” says Pahos. “Applying this type of technology to help reduce the effects of corrosion will significantly boost Australia’s competitiveness in the world.”
The benefits to the Australian economy have been focused on environmental and cost issues and CSIRO believes there is no reason to assume that the same benefits could not be realised in UK and European environments.