###### Abstract  
Corrosion processes of the most common steel grades in various environments are the subject of numerous studies. At the same time, the corrosion of welded joints hidden in concrete thickness has not yet been studied. The authors set themselves the task of investigating this process. For this purpose, the corrosion resistance of several metals (grade St.3, U7 and their weld joints) was studied in standard test solutions, simulating a concrete pore liquid, containing sodium carbonates and hydrocarbons, and sodium chlorides. Data on comparative corrosion resistance in saline media for specified materials were obtained. It was shown that the corrosion rate depends on the ease of CO\({}_{2}\) ingress into the solution, and, to a lesser degree, on the metal microstructure. The surface character of the metal samples and the composition of corrosion products were investigated by scanning electron microscopy and an X-ray diffraction analysis. Chemical forms of surface compounds were determined. For the first time, it is clearly shown that the electrode coating flowing during welding does not always protect the weld from corrosion, as was previously believed. The corrosion rate, in this case, is just the same as at the surface of the metal plate of a similar composition. In the conclusion of this work, it is emphasized that in the case of alkaline and chloride-containing media, the protective coating falling from the electrode to the weld does not protect it sufficiently from corrosion. corrosion resistance; welding unit; concrete; concrete pore liquid; carbon dioxide; scanning electron microscopy; X-ray diffraction analysis; gravimetry; weight loss kinetics; surface defects +
Footnote †: journal: Applied  
1
Footnote 1: _Applied_  
22 February 2022  
**Published:** 28 February 2022  
Currently, research is continuing in the field of corrosion of bimetallic metal compounds, a good example of which are the works [12; 13]. A number of works are related to the general problems of assessing the mechanical strength of materials, including those of welds [14; 15] and practical methods of control [16; 17]. The modern technique of corrosion control is also discussed in papers [18; 19]. Various mathematical models, in particular the graph theory, have been used to describe the corrosion process [20]. Paper [21] deals with the corrosion protection of steel pipes in petrochemical production. [PERSON] et al. paid much attention to improving the quality of the further processing of welded products [22; 23; 24; 25]. Paper [26] is devoted to corrosion investigations in the atmosphere. Currently, conducted research mostly affects the phenomena of atmospheric corrosion, a good example of this is the extensive and scrupulous work in [7]. As experience in the operation of precast concrete buildings shows, over time, various difficult-to-remove defects occur in concrete, which cause the corrosion of the reinforcement [8]. The problem of corrosion is substantive, where one or another fabricated metal part that is inaccessible for visual and instrument inspection corrodes. In particular, this applies to the assembly process of buildings and structures of precast concrete. The total output of fabricating yards is under production regulations and under the strict control of factory laboratories. In the overwhelming majority of cases, the fabricating yards produce products by autoclaving, during which the concrete setting occurs under an elevated temperature (191 \({}^{\circ}\)C) and pressure, exceeding the atmosphere's pressure by 10% [9]. However, the assembly occurs outdoors, whereby a strict quality control of joint sealing between the mating structures, or cement grout or concrete drying temperature is impossible [10; 11]. These determine the comparatively inferior quality of concrete quality in joints. To join two precast structure elements, electric welding is generally used. The characteristic feature of electric welding is fast metal heating and cooling, resulting in the formation of micro-cracks near the weld joint.