As part of its anchor installer training service, construction industry service and technology provider Hilti South Africa offers consulting on the implications of using different grades of stainless steel as fasteners for anchoring purposes in the construction industry.
“We all know stainless steel is significantly more expensive than any other fasteners, the two most well-known stainless steel grades are: A2 and A4 stainless steel. The A4 grade is more expensive, therefore, there is a need for us to train personnel . . . when deciding on whether to use galvanised or hot dipped galvanised anchor as opposed to a 316 stainless steel anchor,” explains Hilti South Africa engineering head Christiaan Davel.
The anchor installer training service offers advice to clients, contractors and engineers with regard to identifying what the corrosive environment should be, then linking it to the correct product for the suitable anchor application.
The anchor installer training is based on empowering contractors to enable them to select suitable products for the corrosive environment when doing anchor installations. A grade of stainless steel that is stable and does not show any corrosion in the particular environment in which it will be used needs to be selected.
Davel says the resistance of stainless steel against pitting corrosion can be roughly estimated using the pitting resistance equivalent number, or PREN. The PREN is based on the chemical composition of steel, taking into account the amount of chromium molybdenum and nitrogen.
Another severe form of corrosion relevant for stainless steel is stress corrosion cracking. “Austenitic stainless steel can be prone to this form of corrosion in specific and highly aggressive environments such as indoor swimming pools. In such cases, a highly corrosion resistant grade of stainless steel must be used for some applications, for example, grades with a molybdenum content of more than 6%.”
Stainless steel is stable in humidity and water when no corrosive contaminants are present. The breakdown of the passive layer by substances like chlorides, however, has to be taken into account because it limits the use of certain grades of stainless steel, Hilti Coastal division engineering head Jandre van Zyl explains.
Unlike zinc, the influence of pure humidity without other contaminants is negligible for the corrosion of stainless steel. For stainless steel, it is important to consider the effect of chlorides, pollutants and corrosive substances and the washing effect caused by rain. In many applications, the effect of this washing renders the use of weaker grades of stainless steel possible. For applications like roofs and the facades of buildings, this can be an option; however, in typical applications where fasteners and installation products are used, there can be areas that are sheltered from the rain.
He states that most contractors are not aware of the implications of incorrectly determining the fastener required for the specific environment, so the service aims to empower contractors to better understand the relationship between fasteners and the corrosive environment, Van Zyl mentions.
Moreover, the training service is available to all construction professionals who want to improve their knowledge or need code requirement for certification. It is designed to verify that certified individuals have the necessary skills and knowledge to properly install anchors in concrete.
The training service can be done within four-and-a-half hours, comprising one-and-a-half hours of theory and two-and-a-half hours of practical work.
Davel adds that the training is very interactive. Product samples are used to explain the working principles of anchors and the corrosion resistance of different materials to practically illustrate the different factors that need to be considered when installing anchors.