NUMERICAL MODELING OF STRAIN RATE EFFECTS ON THE POST EXPANSION PROPERTIES OF EXPANDABLE TUBULAR

The paper presents numerical modeling of tubular expansion for predicting the strain rate effects on post expansion tubular properties. The down-hole expandable tubular has proven itself to be a vital technology in oil well applications. However, there are several challenges faced by researchers and field engineers in implementing and making the technology cost effective while conserving the structural integrity of tubular in post expansion applications. The cold expansion greatly affects the mechanical properties and induces residual stresses in the tubular, which may harm the collapse, burst, and fatigue ratings. Hence, a comprehensive knowledge of tubular’s properties variation is needed in correctly predicting the life span under given operational conditions. Moreover, the expansion rate of full length (3 – 4 m ~ 10 - 13 ft) tubular is also a prime parameter at the field to control the cost of expansion. As required, the rate of expansion must be as high as possible. However, this may greatly affect the material and geometrical properties. Therefore, an exhaustive analysis is required to investigate the effects of strain rate on post expansion tubular properties. In the current work, numerical model is developed of tubular-mandrel system by considering the Johnson-Cook strain rate dependent material model of tubular. The hardening parameters of this are obtained through regression analysis of the uniaxial tensile test data of standard specimen of tubular material. The tension tests are performed at different strain rates vary from 0.05 s^-1 to 0.3 s^-1. In numerical simulations, the rate of expansion varies by changing the velocity of mandrel from 5 mm/s to 25 mm/s or 5 in/s – 1 in/s. The numerical results are validated and found to be in good agreement with the experimental observations. Finally, further simulations are executed to estimate the variation of contact pressure at tubular-mandrel interface, effective stress, equivalent plastic strain, thickness reduction, and length shortening during expansion process.