PSI - Issue 60

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

84 10

Figure 11 Odonnel Porowski Diagram indicating initiation of ratcheting at 600 ℃ temperature As per the ASME design standard guidelines, the maximum linear strain (elastic + plastic + creep) across the pipe thickness is limited to 2% [ASME (2013)]. The total strain is estimated using isochronous curve. The effective creep stress parameter (Z) is calculated using X and Y paramete rs, and the core stress is determined as σ c =Z*average yield stress. The core stress is used to find the creep ratcheting strain using isochronous curve (Figure NH-T-1800-B-7) [ASME (2013)]. The creep hold time is taken as 0 hours; hence hot tensile curve in the isochronous curve is used. The stress causing 2 % strain is found to be 181 MPa. All the parameters are estimated at each pressure, and the displacement corresponding to the core stress value of 181 MPa is identified as the condition at which ratcheting will initiate. The values are shown in Table 2. Table 2 Initiation of ratcheting at 600 ℃ as per ASME ratcheting strain limits Pressure (bars) Displacement (mm) X Y Z Core Stress (σc) = Z*Sy 7 45 0.175 7.66 1.34 181.6 10 31 0.25 5.41 1.35 183.3 12 25 0.3 4.43 1.33 179.6 15 20 0.37 3.64 1.36 184.6