# A Novel Accelerated Corrosion Test for Supporting Devices in a Floating Photovoltaic System
## 3 Results and Discussion
### Alzin Xp Screws/Bolts/Nuts  
ALZIN XP screws, bolts, and nuts were all covered with a zinc-tin alloy coating layer from Kwik-coat in Australia. The zinc-tin alloy with 20-30% zinc in the coating layer had the best corrosion resistance ability, and its corrosion rate was only one-tenth that of general galvanized zinc steel. In addition, the XP zinc-tin alloy coated steel screws, bolts, and nuts had an excellent machinability and weldability. Because of the strong coating layer structure with a high hardness and great adhesion between the coating layer and inner steel screw, it was not easy to wear or peel the coating layer significantly when one touched the substrate. Moreover, when the zinc-tin alloy was in contact with magnesium, aluminum, or zinc, it was less likely to cause heterogeneous metal corrosion because of the smaller difference in the reduction potential between the heterogeneous metals. With the goal of excluding the wearing or peeling of the coating layer and heterogeneous metal corrosion, we undertook a test by hanging brand-new unfastened XP zinc-tin alloy coated steel screws, bolts, and nuts directly using a fishing line. Figures 7 and 8 show the results of XP zinc-tin alloy coated steel screws, bolts, and nuts before the test (0 h) and after the eight-day (192 h) test, respectively. Samples without any rust showed metallic luster before the test. After the eight-day CASS test, yellow  
Figure 6: The appearance of screws after the eight-day CASS test (192 h): (**a**) type 304 SS screw, (**b**) type 410 SS screw, (**c**) XP zinc–tin alloy coated steel screw, (**d**) galvanized steel screw capped with a type 316 SS nut, and (**e**) chromate-passivated galvanized steel screw. protection layers were produced at both the heads and tails of the XP zinc-tin alloy coated steel screws, and only fine dot-like red rust was found instead of the more apparent red rust. On the other hand, yellow protection layers, as well as larger dot-like red rust, were produced at the heads of the bolts, and red rust was generated at the tails of bolts as well. Likewise, red rust was produced on the outer layer of the XP zinc-tin alloy coated steel nuts. We inferred from the results in the previous paragraph that the zinc-tin alloy coating layer would initially be dissolved in order to generate the yellow protection layer to suppress corrosion. If corrosion happened continuously, a lot of red rust would be produced due to a depletion in the zinc-tin alloy coating layer, leading to further corrosion of the inner steel. Furthermore, the results of the eight-day CASS test in the method of hanging the XP zinc-tin alloy coated steel screws by a fishing line appeared to be more significant than for the method of fastening XP zinc-tin alloy coated steel screws on the Zn-Al-Mg-Si coated steel. Not only were yellow protection layers produced at the tails of the screws, but yellow protection layers and dot-like red rust were produced at the heads of the screws as well. Because the unfastened XP zinc-tin alloy coated steel screws hung by a fishing line were brand-new, factors of wearing and peeling of coating layers or heterogeneous metal corrosion could be excluded. A possible explanation for this is that the zinc-tin coating layer had a worse acidic corrosion resistance. Although the CASS test was performed for only eight days (equivalent to 64-day NSS test according to empirical formulas), more significant consequences of corrosion were observed compared with the 136-day NSS test, as observed in Figure 9. Many papers have discussed about the comparison of corrosion behavior between NSS and field exposure test. The results showed that the extent of corrosion in the NSS test is more severe than for the field exposure test [28,29]. Therefore, the CASS test is certainly a faster and more efficient accelerated corrosion method than the NSS and field exposure tests.