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Geometric variations and surface residual stresses in U-bending processes of an UNS N06690 row-1 heat exchanger tubes
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 Title & Authors
Geometric variations and surface residual stresses in U-bending processes of an UNS N06690 row-1 heat exchanger tubes
Kim, Woo-Gon; Jang, Jin-Sung; Kuk, Il-Hiun; Joo, Jin-Won; Kim, Sung-Chung;
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 Abstract
Surface residual stresses as well as wall thickness and ovality changes after U-bending process on UNS N06690 row-1 heat exchanger tubes, were estimated. Surface residual stresses were measured by Hole Drilling Method(HDM), calculating the stresses from relieved strains of 3 rosette strain gages. After bending of the tubes, dimensional tolerances for wall thickness and ovality were satisfied with ASTM requirements. Residual stresses at the extrados were introduced with compressive stress(-) by bending operations, and its maximum value reached-319 MPa in axial direction at in position. Tensile residual stresses(+) of MPa, MPa were introduced in the intrados surface at position of Maximum tensile residual stress of 170 MPa was detected on the flank side at position of ,i.e., at apex region. It appeared that higher stress gradients were generated at the irregular transition regions. In the trend of residual stress changes with U-bend position, the extrados is related with the changes of ovality and the intrados is related with the changes of wall thickness.
 Keywords
U-Bending Process;Residual Stress;Hole Drilling Method;Relieved Strain;Rosette Strain Gages;Tube Wall Thickness;Ovality;
 Language
Korean
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