PSI - Issue 71

P.K. Sharma et al. / Procedia Structural Integrity 71 (2025) 126–133

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temperature. Similar observation was seen for different exposure time where the maximum and average defect size increases with the increase in exposure duration. Surface defects caused by corrosion act as stress concentrators reducing the effective load-bearing cross-section and initiating early crack formation during tensile loading. Hence, it can be inferred that the depth of attack depends on the stress levels, exposure duration and the test temperature of the specimen. Higher the exposure time, stress level and temperature, more will be depth of attack by the molten glass. Due to higher defect size, the degradation in mechanical properties will increase subsequently.

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Fig. 7: Depth of corrosion defect after exposure to molten glass environment for specimen tested at (a) stress level of 30 MPa, temperature - 800 °C and 95 hrs exposure duration; (b) stress level of 20 MPa, temperature - 900 °C and 95 hrs exposure duration. 5. Results and discussions The histogram of defect size depth is obtained for all the tested specimens. The statistical distribution of the defect size is determined and it was observed that the defect size follows lognormal distribution. The defect size distribution is shown in Fig. 8(a) and 8(b) for test conducted in air and molten glass environment. The distribution of defect size is left skewed that mainly depends on two parameters i.e., location parameter (μ) and the scale parameter (σ). The location parameter determines the mean of the distribution while the scale parameter gives the value of standard deviation. It was observed from Fig. 8 that the mean defect size and maximum defect size increases from 3.14μm to 11.12 μm and from 8 μm to 75 μm respectively for specimen tested in air environment and molten glass environment at 800 °C. The comparison of defect size distribution at different exposure duration is shown in Fig. 8(c). It was seen that the frequency i.e., the number of defects increases with increase in exposure duration with corresponding shift of distribution towards the right side. It indicates the increase in mean defect size as the exposure time is increased from 24 hrs to 95 hrs. Due to this increase in mean defect size and maximum defect size, the degradation in mechanical properties is higher for higher exposure duration.

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Fig. 8: Statistical distribution of defect size in (a) air environment at 800 ˚C, (b) molten glass environment at 800 °C and 95 hrs exposure duration, (c) effect of exposure duration on statistical distribution of defect size at 900 ˚C. 6. Conclusions Different tests are conducted at 800˚C and 900˚C to determine the effect of temperature, stress level and exposure duration on the mechanical properties of alloy690 material. Following conclusions can be inferred from this study.