Test method and device for evaluation of volatile corrosion inhibitors

Volatile corrosion inhibitors (VCI), which are incorporated in packaging materials like films, papers, plastic racks etc., are a suitable means for temporary corrosion protection during transport and storage of metallic products. For the evaluation of the corrosion protection effect of VCI-containing products, numerous tests are established. In most cases, principally, a metallic sample is exposed to a climatic stress in presence of a VCI-containing product and the protection effect of the VCI is evaluated afterwards by visually assessing the occurrence/absence of corrosion products at the sample surface. In a newly proposed test method and a dedicated device, the evaluation of the VCI-containing product is based on electrochemical measurements at the interface between the metallic sample and a film of condensed water. The water film is precipitated during the test by actively cooling the metallic sample below the dew point, which imposes a corrosive stress on the sample surface. With a simple direct current potentiostat for polarization resistance measurement, the state of the metallic surface (corrosion-active, passive) is registered objectively during the test and thus the corrosion protection effect of the VCI is evaluated. In the present paper, the test method and the dedicated device are disclosed in detail. On the basis of a statistical analysis of a sample of independently repeated tests, limit values are established for the quality assessment of VCI products. Different commercially available VCI films are evaluated and the results are compared to the state-of-the-art jar test procedure based on German TL 8135. In conclusion, the proposed test reproducibly provides objective and quantitative information on the corrosion protection effect of VCI-containing products.