PSI - Issue 60

Rosy Sarkar et al. / Procedia Structural Integrity 60 (2024) 75–92 Rosy Sarkar/ Structural Integrity Procedia 00 (2019) 000 – 000

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The secondary stress parameter (Y) is calculated as per equation (2). = ( ) (2) Where (Q R ) max is the maximum range of the secondary stress intensity during the cycle being considered and S y is the average of the S y values at the maximum and minimum wall averaged temperatures during the cycle.

Figure 10 Odonnel Porowski Diagram indicating initiation of ratcheting at room temperature Elastic analysis has been carried out at various values of pressure ranging from 7 bars to 30 bars at room temperature and high temperature of 600 ℃ . Various values of displacements ranging from 0 mm to 60 mm have been applied at each value of pressure considered. The primary stress intensity is taken as the maximum stress range at 0 mm displacement for the pressure considered-the reason for considering it as primary stress is that there is no secondary load applied. The X and Y parameters have been calculated as per equations 1 and 2 and are plotted in Figure 10 and Figure 11 at room temperature and 600 ℃ ǡ respectively. The red line in Figure 10 and Figure 11, i.e., XY=1, limits ratcheting. The points beyond this line are the loading conditions at which ratcheting is expected. It is inferred from the elastic analysis that at room temperature, ratcheting is expected to take place at 25 bars pressure and 34 mm displacement. At 600 ℃ , ratcheting is expected at 10 bars pressure and 22 mm displacement. It is also inferred that at the design pressure (7 bars) of SGDHR piping system, the ratcheting is not significant as per OPD.