PSI - Issue 60

Rishi K Sharma et al. / Procedia Structural Integrity 60 (2024) 264–276 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Figure 2: Schematic of hydrogen re-orientation and burst test setup at R&D center, Tarapur

A pressurized accumulator, filled with high-pressure nitrogen at 50% of its volume, is integrated into the setup, which ensures a constant pressure throughout the stress reorientation process. The pressurized accumulator also ensures load controlled condition during the pressure tube burst test studies. The primary principle for generating radial hydrides in the pressure tube relies on the applied hoop stresses exceeding the threshold value required for radial hydride formation in the material. The following steps (illustrated in Figure 3) were followed to induce radial hydride formation in the pressure tube spool: 1. The pressure tube spool was heated upto the solutionizing temperature with additional sub-cooling margin, which in turn depend on the hydrogen content i.e. 430 °C for 200 ppm hydrogen and 350 °C for 60 ppm hydrogen. It was allowed to soak for 30 minutes. 2. The spool was then cooled to the reorientation temperature (depends on the hydrogen content) and allowed to soak for 30 minutes. 3. Subsequently, the required pressure depending on the hydrogen content was applied (15 MPa for the 200 ppm spool, corresponding to a hoop stress of 168 MPa in the tube, and 20 MPa for the 60 ppm spool, corresponding to a hoop stress of 224 MPa) inside the PT spool, and was soaked for an additional 30 minutes. 4. The spool was then gradually cooled at a rate of ~ 1 °C/min to 150 °C while maintaining the constant pressure established in Step 3. 5. At 150 °C, the pressure was brought to atmospheric pressure and the spool was cooled to room temperature.