Residual Stress in U-Bending Deformations and Expansion Joints of Heat Exchanger Tubes

Residual stress induced in U-bending and tube-to-tubesheet joint processes of PWR's row-1 heat exchanger tube was measured by X-ray method and Hole-Drilling Method(HDM). Compressive residual stresses(-) at the extrados surface were induced in U-bending, and its maximum value reached -319 MPa in axial direction at the position of = . Tensile residual stresses(+) of = 45 MPa and = 25 MPa were introduced in the intrados surface at the position of = . Maximum tensile residual stress of 170 MPa was measured at the flank side at the position of = , i.e., at apex region. It was observed that higher stress gradient was generated at the irregular transition regions (ITR). The trend of residual stress induced by U bending process of the tubes was found to be related with the change of ovality. The residual stress induced by the explosive joint method was found to be lower than that by the mechanical roll method. The gradient of residual stress along the expanded tube was highest at the transition region (TR), and the residual stress in circumferential direction was found to be higher than the residual stress in axial direction.