Light steel thin-walled structures (LSTS), in particular, thermoprofiles are widely used in construction of building frames. According to the latest amendments in the documentary standards, zinc coated thermoprofiles without additional paint coating may be used as load-bearing structures only in non-aggressive conditions. Applying paint coating in addition to a zinc one entails extra expenses, while efficiency of this measure may not correspond to the costs. Resolving this issue requires special researches. The purpose of this article is to analyze conditions of corrosion processes and to develop methods of testing thin-walled steel products, taking into account the features of their service in walling.