PSI - Issue 60

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

267

4

oil diffusion pump to prevent re-oxidation, which could block hydrogen ingress. The system was heated to ~360 °C before exposing it to high-purity hydrogen gas. The amount of hydrogen charged was determined by the difference between initial and final hydrogen partial pressures in the control volume. The pressure tube spool piece had inner diameter of ~83 mm, wall thickness of 3.5 mm, and length of 475 mm, and was charged with varying hydrogen content.

Figure 1: Schematic of gaseous Hydrogen charging setup to charge pressure tube spool

To verify the hydrogen content and its distribution in the charged pressure tube spool, small pieces of the hydrogen charged samples were manually sliced using a slow-speed cut-off wheel. These samples were then analyzed for their hydrogen content using the Inert Gas Fusion (IGF) technique. In this method, the cut and polished samples were cleaned with acetone to remove any contaminants, melted in a graphite crucible within an inert nitrogen atmosphere, and then analyzed for hydrogen content by measuring the change in resistance in a Wheatstone bridge compared to reference. The instrument was regularly calibrated using metallic samples with known hydrogen amounts. The results of the hydrogen analysis from gaseous-charged pressure tube spools showed slightly lower hydrogen content at the leading end (towards the furnace opening) due to minor temperature variations inside the Sievert’s apparatus. To homogenize the hydrogen content, the spools were exposed to 400 °C for 48 hours, and subsequent analysis confirmed the homogeneity of hydrogen content within an acceptable range. 3.2. Setup for Stress re-orientation of Hydrides and Burst Test Studies An experimental setup was developed & utilized for stress re-orientation of hydrides and burst test studies of Zr 2.5%Nb alloy pressure tube spools. These studies were carried at the NPCIL R&D Centre, Tarapur. Figure 2 illustrates a schematic of this experimental setup. The setup has PT spool whose both the ends were attached to end-fitting flanges through roll joining. These, in turn, were connected to the setup via flanges. A concentric Calandria tube spool was also installed around the pressure tube spool to provide specific environment. The setup can be used to generate temperatures up to 450 °C, while simultaneously applying internal pressure upto 25 MPa using water to the pressure tube spool. A minimal flow of water was maintained by natural convection to ensure uniform temperature across the length and circumference of the pressure tube.