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 CO2, H2S, 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.
Highlights
Corrosion failure caused by H2S or H2S/CO2 containing multiphase flow has affected the normal operation of the oil field, some production wells have to be shut down in a severe corrosion case
The results show that the stress concentration at the outer edges of double pits is less affected by the center distance
Stress concentration increased by double pits in a curved casing inner surface is studied using the finite element analysis (FEA) software ABAQUS
Summary
Corrosion failure caused by H2S or H2S/CO2 containing multiphase flow has affected the normal operation of the oil field, some production wells have to be shut down in a severe corrosion case. One is considered as a semiinfinite body having a hemispherical pit located on the plane’s surface. This problem was first studied by Eubanks,[7] and he presented the analytical solution, but the calculate process was very complicated and few applications appear in later research documentation. Another model is an infinite diameter cylinder with a spherical cavity; at the weakest section (excluding the spherical cavity), Timoshenko and Gere[8] theory can be used to calculate the SCF. According to the theory of elasticity, the infinite boundary problem (b!N), in x–y plane except defect, axial load sz can be calculated as following
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