Issue 50

Ch. Apostolopoulos et alii, Frattura ed Integrità Strutturale, 50 (2019) 548-559; DOI: 10.3221/IGF-ESIS.50.46 550 C ORROSION TESTS - SALT SPRAY CHAMBER or the corrosion process all the specimens were placed in a salt spray chamber (Fig.2). The corrosion tests were organized in accordance to ASTM B117-94 specification (directly exposed to the corrosive medium). The ASTM B117 [9] specification covers every aspect of the apparatus configuration, procedure and conditions required to create and maintain a salt spray (fog) testing environment. The selection of such a procedure for corroding the specimens, relies on the fact that the salt spray environment lies qualitatively closer to the natural coastal (rich in chlorides) conditions than any other accelerate laboratory corrosion test. In principle, the testing apparatus consists of a closed chamber in which a salted solution atomized by means of a nozzle, produces a corrosive environment of dense saline fog. In this particular study a special apparatus, model SF 450 (mode by Cand W. Specialist Equipment Ltd) was used. The salt solution was prepared by dissolving 5 parts by mass of sodium chloride (NaCl) into 95 parts of distilled water (pH range 6.5-7.2). The temperature inside the salt spray chamber was maintained at 35°C (+1.1-1.7°C). Figure 2: Salt spray fog chamber. Additionally, in the present study, a severe exposure environment of wetting/drying (chloride ponding) was organized in order to achieve a better approach to the environmental conditions and to simulate the chloride exposures of marine struc- tures under splash and tidal zones. Hence, it is widely known that that in reality, structures are subjected to wet and dry periods, rather than a constant relative humidity [10]. Chloride ponding application is in agreement with the simulating corrosion methods used in existing studies as well [11-13] and ensures conditions which are qualitatively closer to the natural. This is because during wetting, chloride solution penetrates a layer of the material; during the drying stage the evaporation front moves inwards and takes some of the chloride with it [10]. It is deducted in theory that atmospheric corrosion rate of metals can be accelerated by increasing the frequency of wet-dry cycling [12]. Consequently, the ponding cycles organized consisted of alternating 1.5 hour of exposure to wet conditions and 1.5 hour of dry conditions. Eight ponding cycles of wet/dry conditions were scheduled per day. By the end of each exposure time, specimens were removed from the corrosive environment, washed with clean running water, to remove ant salt deposits from their surfaces and air dried. The corrosion products were removed from the surface of the specimen by means of a brittle brush, according to ASTM G1 specification [14]. The specimens were then weighted and the mass loss due to corrosion exposure was calculated as: c p m m x % m   0 0 100 (1) Where m 0 is the mass of uncorroded specimens and m c the reduced mass of the corroded specimens. M ECHANICAL TESTS fter the completion of the corrosion process the mechanical tests were organized. In Table 1 is given in detail the number of the specimens used in each case. According to Table 1, a total of 18 tensile tests and 134 Low Cycle Fatigue Tests was conducted for the goals of the present study. The differentiated number of the LCF tests, per strain, per steel category is owed to the fact that there were some additional tests that were invalid, the results of which are not included in the present paper. F A