PSI - Issue 60

R.P. Pandey et al. / Procedia Structural Integrity 60 (2024) 324–334 R.P. Pandey/ StructuralIntegrity Procedia 00 (2023) 000 – 000

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(a) (b) Fig. 9: (a) A typicalcontour ofvonMises stress (in MPa) developed in the pressure tube and the end-fitting after completion of the rolling process (before withdrawal of rollers); (b) cut-section view.

-1000 -750 -500 -250 0 250 500 750 1000

220-MWe PHWR PT-EF Rolled Joint, Interference Fit

298 K 373 K 473 K 573K 673 K 773 K 873 K 973 K 1073 K 1173 K 1273 K

Residual Hoop Stress (MPa)

(a)

1 2 3

0 20 40 60 80 100 120 140 160 180

Distance along PT axis (mm)

Fig. 10: Variation of hoop residual stress with distance along the pressure tube after rolling at 298 K and its relaxation in high tem perature environment.

The magnitude of stresses in pressure tube is very high compared to the end-fitting. After the retrieval of the roller, the stresses in the pressure tubes becomes compressive and the end-fitting, it becomes tensile. This can be understood from the simple logic that by applying rolling pressure, the rollers move outward. These in turn expand the end-fitting which houses the pressure tube. Hence, the hoop stresses during the rolling process in tube and the tube-sheet (i.e., end-fitting) is tensile. After the retrieval of the roller, the end-fitting contracts as there is no roller pressure. However, the pressure tube has deformed permanently due to plastic deformation and hence, it prevents the diametrical contraction of the end-fitting. This creates residual tensile stresses in the end-fitting and residual compressive stresses in the pressure tube. It may be noted that the rolling is carried out at room temperature. However, when the joint is heated, the thermal expansion of the pressure tube and end-fiiting takes place. It is known that the coefficient of thermal expansion