PSI - Issue 60

Varsha Florist et al. / Procedia Structural Integrity 60 (2024) 614–630 8 Varsha Florist, Santhoshkumar R, A. Vamsi, Sajju V, Sarath Mohan, Sanjeev Kumar, Dhanoop A, Venukuttan C, M.K. Sundaresan, SVS Narayana Murty / Structural Integrity Procedia 00 (2024) 000 – 000

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4.1. Qualification Test of 15-5 PH Full scale tank With the confidence derived from the subscale tank, full scale tank was realized and burst pressure tested. The strain gauge instrumentation plan for burst test is shown in Fig. 7. Specification of MEOP, proof and ultimate pressure for 15-5 PH tank is 8.63 MPa, 10.79 MPa and 12.94 MPa, respectively. The test cycle followed consists of: • 0 - 10 - 0 with hold at 0.98 MPa for 2 min. for carrying out leak checks • 0 - MEOP, in steps of 0.98 MPa and hold for 5 min. at MEOP • 0 -proof pressure in steps of 0.98 MPa and hold for 10 min. at proof pressure • Repeat step 2 for 11 more cycles and repeat step 3 for 3 more cycles • 0 – proof pressure in steps of 0.98 MPa, 10.79 MPa – ultimate pressure in steps of 0.5 MPa and hold for 1 min. at ultimate pressure and bring down the pressure to 0 MPa • 0-8.63-10.79-12.94, hold at each pressure for 1 min and proceed till burst. 4.2 Evaluation of Mechanical Properties For preforms, 3 specimens each in both longitudinal and transverse directions were extracted 120º apart for performing tensile tests. For first article inspection at 10 mm thickness level, 3 nos. of specimens in longitudinal direction were tested and at 4.2 mm thickness level 3 nos. each in both longitudinal and transverse direction were tested. Specimens were collected from various thickness regions at 120º apart circumferentially from first article batch as well as from production batch. Hence, the properties achieved can be considered to represent the entire shell. At 4.2 mm thickness level, 3 nos. of specimens each in L and T directions were tested for all production batch shells. For weld properties, three parent and six welded tensile specimens were tested against the qualification tank realized.

Fig. 7. Strain gauge instrumentation plan

4.3 Fractographic and Microscopic Analysis Specimens collected from different locations of the burst tested tank were identified and observed in a Field Emission Scanning Electron Microscope (FESEM) for observing the fracture surface Abhay K. Jha (2010). Further, samples in both circumferential and longitudinal fracture edge directions were sectioned and polished with different grades of silicon carbide abrasive papers. Final polishing was conducted with alumina suspension and one micron diamond lapping compound. The specimens were etched with 25 ml HCl+ 13 ml HNO 3 +0.5gm CuCl 2 + 75 ml H 2 O to reveal the microstructure. After etching, the microstructural observations were made using Carl Zeiss optical