Effects on plasticity and structural integrity of tube expansion

This paper presents an investigation of the effects of cold expansion on plasticity and structural integrity of expandable tubulars. Down-hole tubular expansion has proven itself to be a vital technology in oil well applications. One of the challenges faced by researchers and field engineers in implementing and making down-hole tubular expansion technology cost effective is to conserve the structural integrity of tubular after the expansion process. Cold expansion affects the mechanical properties and induces residual stresses in the tubular, which could reduce its collapse, burst and fatigue ratings. Hence, a knowledge of variation of properties is required in correctly predicting the life span of tubular under given operational conditions. Cold expansion of tubulars under down-hole conditions is simulated at different strain rates using finite element method. The strain rates are varied by changing the velocity of mandrel used to expand the tubular. It is found that there are variations in contact pressure at tubular-mandrel interface, effective stress, equivalent plastic strain and thickness reduction during expansion process. These variations ultimately influence post-expansion properties of the tubular particularly the collapse and burst strengths, and hence its structural integrity. However, length shortening and surplus deformation have negligible effect on post-expansion properties of tubular.