PREDICTION OF AXIS SHIFT DISTORTION DURING CIRCUMFERENTIAL WELDING OFTHIN PIPES USING THE FINITE-ELEMENT METHOD

Axis shift distortion is one type of distortion encountered during the circumferential welding of large, thin pipes. The result of this is t he loss of coaxiality of the pipes. This type of distortion is caused by the time lag in the solidification of various segments of weld meta l around the circumference. The development of shrinkage forces in the weld metal especially in the axial direction is nonuniform due to the time lag, and this causes axis shift for the pipes. The development o f a mathematical model using the finite element method for prediction of axis shift distortion in thin pipes is described in this work. Ther mal analysis and subsequent elastic-plastic stress analysis for the pi pe are performed using four-noded, bilinear degenerated shell elements . In addition to axis shift distortion, axial and circumferential stre ss distributions in the pipe are also determined by the model. The mod el is validated by conducting partial welding on the circumference of a thin pipe and measuring the transient thermal history and root openi ng at the bottom. Details of thermal and elastic-plastic analyses, wel ding trials, thermal and displacement results and axial and circumfere ntial stress results are presented in this paper.