PSI - Issue 60

4

Rahul Mittal et al. / Procedia Structural Integrity 60 (2024) 604–613

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Rahul Mittal/ Structural Integrity Procedia 00 (2019) 000 – 000 Detailed stress classification as per ASME Section III Div-1 Sub-Section NB requirement has been carried out to derive Primary membrane ‘Pm’ Primary local membrane ‘PL’ Primary bending ‘Pb’ Secondary stress ‘Q’ and Peak stress ’F’ etc. at different section called Stress Classification Lines (SCL), defined at critical locations in the component. These stress values on each SCL are then compared with different allowable value as per ASME section III Sub-Section NB[1]. Cross section for stress linearization has been selected at various locations across the component as per guideline given in ASME Sec. III Div-1 Sub-Section NB viz. location of material discontinuity, head to shell junction, nozzle to shell junctions, junctions between shell of different diameters or thicknesses and other critical locations. These calculated stresses are then compared with code allowable stress intensity limits. The allowable stress limits for vessel qualification as per ASME Section III Div-1 Sub-Section NB[1] for various design and service load conditions including test condition are given in Table-4. During the finalization of the methodology for structural integrity check of FWN, detailed literature survey was carried out referring [2] to [10] comprises of FE analysis (including CFD, FSI and structural) of the nozzles subjected to thermal stratification, cold water injection thermal transients, failure of the nozzles under accidental loading conditions. Additionally, studies were carried out for aspects related to the fatigue evaluations and impact of corner flaws in the nozzle evaluated using FEA tools.

Fig. 2. Schematic diagram of Steam generator