QUESTION OF RESIDUAL STRESS IN EXPANSION CASING

In order to find the magnitude and the cause of residual stress after the casing radial expansion and its effect to the casing performance, we conduct the casing expansion test. The hoop residual stress of the expansion is measured and analyzed by loop cutting method. We find that the hoop shrinkage residual stress is high, and the residual stress can weaken the casing collapsing strength. The reason that casing has quite high residual stress after expansion is analyzed, and indicates that non-uniform deformation is the main reason. The section form variation coefficient which is the judgment of non-uniform deformation degree index of casing is introduced. And the application of the index is examined by the test data. Finally, we provide the measurement that can weaken the residual stress by both manufacture and expansion technology.