Numerical simulation of the double pits stress concentration in a curved casing inner surface

Abstract

Sour or sweet oil fields development is common in recent years. Casing and tubing are usually subjected to pitting corrosion because of exposure to the strong corrosion species, such as CO 2 , H 2 S, and saline water. When the corrosion pits formed in the casing inner surface, localized stress concentration will occur and the casing strength will be degraded. Thus, it is essential to evaluate the degree of stress concentration factor accurately. This article performed a numerical simulation on double pits stress concentration factor in a curved inner surface using the finite element software ABAQUS. The results show that the stress concentration factor of double pits mainly depends on the ratio of two pits distance to the pit radius (L/R). It should not be only assessed by the absolute distance between the two pits. When the two pits are close and tangent, the maximum stress concentration factor will appear on the inner tangential edges. Stress concentration increased by double pits in a curved casing inner surface is more serious than that in a flat surface. A correction factor of 1.9 was recommended in the curved inner surface double pits stress concentration factor predict model.

Ultrasonic and Conventional Fatigue Endurance of Aeronautical Aluminum Alloy 7075-T6, with Artificial and Induced Pre-Corrosion

“…Comparing Figures 12-14, the stress concentration factor is: 358/220 = 1.63 for two pits in transverse direction and 320/220 = 1.45 for the two pits in longitudinal direction. Stress concentration factors was obtained by numeric simulation in different materials and conditions [24][25][26]. Numeric analysis in Figures 12-14 was obtained with the Ansys software (Version R19, Ansys Inc., Canonsburg, PA, USA), SOLID187 element type and 36,039 and 35,945 elements, respectively.…”