1986 Volume 4 Issue 1 Pages 143-147
A new measuring method for axisymmetrical residual stress distribution which is uniform neither in radial nor in axial direction, is proposed for butt welded thick pipe.
The formulas to estimate residual stresses are first introduced following a maeasuring method that has already been conducted for axisymmetrical residual stress field in a thick plate. This method requires several numbers of thin arch-specimens normal to the pipe axis to be cut out along with a z-specimen parallel to the axis. In this case, the strain change in circumferential direction, that is, Δεθ in an arch-specimen has great influence upon the accuracy of the estimated stresses. Therefore, its distribution along radial direction is next analyzed based on the elasticity, followed by the analytical investigation by finite element method using inherent strain distributions that may approximate residual stress distributions measured on a butt welded thick pipe.
As a result, it is clarified that the distribution of Δεθ in radial direction may be approximated with a good accuracy by a function of A+B/r2 where A and B are so determined as to pass through both measurements on inner and outer surfaces of each arch-specimen.
The final investigation on the accuracy for estimated residual stresses using the same inherent strain distribution concludes that the circumferential residual stress σθ can be estimated with a good accuracy by the first approximation although the relieved stress in radial direction in cutting a z-specimen, Δσr is ignored and at the same time the strain change in axial direction Δεz is approximated by a straight line joining both measurements on inner and outer surfaces of z-specimen. Axial and radial residual stresses, however, should be estimated just to the second approximation to ensure the accuracy where the distributions of Δσr, and Δεz, along radial direction calculated by making use of approximated σθ are utilized.