Coil Coating

Corrosion properties of coil-coated products

In building industry, coil-coated materials provide numerous advantages to non-painted steel sheets. The costly and environmentally unfriendly on-site surface treatment and painting can be avoided. Because of a strict process control in production lines, quality and thus durability of coil-coated materials is generally superior. It allows producers to provide as long guarantees as tens of years, even for applications in aggressive conditions.

The membership programme involves 14 companies, including most of prominent international steel makers and surface treatment and paint suppliers. Besides providing a unique platform for regular meetings, exchange of knowledge and experience and discussions, the committee sponsors several research programmes. Themes for the supported studies are defined in collaboration between all committee members. Currently, the major research activities are:

• Understanding the mechanism of blister formation on coil-coated materials. In particular, an optimal testing procedure for evaluation of the tendency to blistering and the relationship of blistering and properties of the primer and topcoat in terms of their water permeability, residual stress, and stress formed during temperature and humidity cycling are sought.
• Study of the composition of corrosion products formed under natural weathering conditions on pre-painted hot-dip galvanized steel and Zn-Al(-Mg) alloy coatings. Knowledge about the composition of the corrosion products is necessary to determine the corrosion mechanism and is also useful to indicate if the corrosion mechanism is similar in the accelerated corrosion test and the field exposure.
• Investigation into the effect of the metallic coating thickness on paint delamination at cut edges. It is believed that the thickness of 20 µm recommended in current building standards can be reduced without affecting durability of final products due to improved air quality in Europe.
• Understanding reasons behind storage corrosion problems encountered in certain regions of Europe. If feasible, a test for evaluation of the tendency to storage corrosion will be proposed.
• Study aiming at the role of the length and geometry of coil-coated panels on cut edge corrosion and degradation in lapped and joined areas.
• Looking into connection between backside and front side paint degradation

The committee supports organization of regular symposiums on corrosion properties of coil-coated materials. They attract over 60 participants from all over the world.

Activities

Besides projects shortly reviewed above, several cost-shared projects financed by members of the committee and selected invited companies are in progress. Large efforts are invested into understanding the corrosion mechanism of newly developed Zn-Mg and Zn-Al-Mg alloy coatings. A devoted project aims at long-term stability of these materials in field conditions as a function of chloride load. We try to find a proper application window where the alloy coating products provide clear advantage compared to traditional hot-dip galvanized steel.

Several projects are aimed at the performance of coil-coated and bare materials in varying natural conditions. In total, over 20 exposure sites in Europe, America, Asia and Australia managed directly by us or provided by partner institutes are included in these programmes. Our goal is to arrive to dose-response functions allowing for rapid prediction of material degradation in terms of uniform corrosion, paint delamination and easy to clean properties from climatic and pollution data. We are strong in development of new test procedures better correlating to the extent and nature of corrosion degradation observed in service life.

We also work with the industry on a consultancy basis were we run accelerated laboratory tests and tests in natural environments to investigate their materials. The results are indeed confidential and owned by the ordering company. 

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