PSI - Issue 42

A. Laureys et al. / Procedia Structural Integrity 42 (2022) 1458–1466 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1461

4

temperature the corrosion rate of the materials was found to increase significantly, which is due to the transition of the passive material to its active state. As a result, the materials become more vulnerable to aggressive ions. A corrosion rate of 0.15 mm/y is reached at different temperatures for the various materials; 316L, 316Ti, Sanicro35 and Hastelloy G30 reach this rate when exceeding 100 °C, while this is 110 °C for Sanicro28, and at temperatures over 120 °C for Hastelloy G35. The results also illustrate that materials which show the highest corrosion resistance at lower temperatures do not necessarily do the same at higher temperatures. The corrosion resistance ranking order of the materials changes with increasing temperatures. Hastelloy G30 clearly illustrates this point, as the corrosion rate of the material reaches a constant value between temperatures of 120 and 160 °C. So, even though Hastelloy G30 exceeds the maximum set corrosion rate at temperatures around 100 °C, it shows the best corrosion resistance at 160 °C.

10 12 14 16

316L 316Ti sanicro28 Hastelloy G35 sanicro35 Hastelloy G30

0 2 4 6 8

CPR (mm/y)

80

100

120

140

160

180

(a)

Temperature (°C)

(b)

Figure 1. Corrosion rates after testing for 48 h in FGPA for different materials. (a) Complete temperature range taken into consideration, (b) focus on lower temperatures and corrosion rates in the proximity of 0.15 mm/y. 3.2. Surface characterization Fig. 1 shows that the corrosion rate of 316L and 316Ti rises sharply beyond 100 °C. At 100 °C limited pitting and uniform corrosion of the materials is observed (Fig. 2 and 3). The materials show a high corrosion resistance up to 100 °C, while higher temperatures cause breakthrough of the passive layer followed by high corrosion rates of the materials (Lizlovs (1969)). The corrosion behavior of both materials differed. 316L corroded by localized breakdown (e.g. 120 °C), while this was clearly not the case for 316Ti. TiN precipitates were found on the 316Ti sample surface and these could influence the corrosion behavior of the material. Additional research is required to confirm this statement.