PSI - Issue 60

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

274

11

Axial Crack Extention (mm)

250

200

150

100

50

0

As received

Circumferential hydrides (80 wppm)

Radial hydrides (80 wppm)

Mixed hydrides (200 wppm)

Figure 9: Pressure tube axial crack extension for burst tests at R&D centre, Tarapur

A5. Burst test of pressure tube spool with 200 wppm radial hydrides and crack initiation Pressure tube spool was introduced with 200 ppm of radial hydrides to achieve brittle material properties even at higher temperatures. The first such experiment was carried out at R&D center, Tarapur. In this experiment, the initial notches were sharpened using sharp knife and were subjected to aggressive corrosive environment by using air bubbling through HCl on OD surface of pressure tube to form nodules. Nodular corrosion on pressure tube OD surface can initiate some micro-cracks, which, can further grow by Delayed Hydrogen Cracking (DHC) mechanism. The pressure and temperature of the system was maintained at 10 MPa and 240 °C respectively. With these changes, and by maintaining pressure and temperature at these values for ~5 days, failure of pressure tube spool at multiple locations was observed. The experiment was repeated with the same operating parameters, multiple opening of the cracks were observed even during the repeat experiment. Another set of experiment was carried out at R&D center, Tarapur to confirm the effect of sharpening on the crack behavior under aggressive corrosive environment. In this experiment also, multiple opening of the cracks were observed. In all the tests with radial hydrides and crack initiation by localized nodular corrosion, multiple burst opening of the pre-existing notches/cracks were observed. 5. Summary and Conclusions Series of burst test experiments were conducted to understand the burst behaviour of pressure tube spools under varying hydride morphology. The tests were conducted with PT spool having four number of OD notches or initial cracks. Initial set of experiments were conducted with these PT spools having different hydrogen content and morphology. It was observed that the burst pressure and extension of initial notch are function of the hydrogen content and morphology. However, in these experiments only single notch got opened up and remaining three notches were found unaffected. Crack initiation was not observed at any of the notches. Experiments at normal operating pressure and temperature condition were repeated with creation of micro-cracks at the notch locations in a brittle pressure tube material. This was done by charging the spool with more than 200 ppm