几何缺陷对套管抗挤强度影响的有限元分析

FINITE ELEMENT ANALYSIS ABOUT EFFECT OF GEOMETRIC IMPERFECTION ON CASING COLLAPSE RESISTANCE

随着不圆度和壁厚不均度的增加 ,套管的临界挤毁压力逐渐减少 ,并且不圆度对套管抗挤强度影响较大。一般情况下 ,石油套管同时存在着不圆度和壁厚不均度等初始几何缺陷 ,这些制造缺陷的存在势必降低套管的抗挤毁性能。APIBul 5C3给出了抗挤强度的计算公式 ,但仅仅提供了管材屈服强度、管径、壁厚等基本输入参量 ,而未考虑管体不圆度和壁厚不均度等初始几何缺陷的影响。实践证明 ,不圆度和壁厚不均度对套管抗挤强度的影响是相当可观的。文章运用有限元法详细研究了初始不圆度和壁厚不均度对套管抗挤强度的影响规律 。

Generally,casings have geometric imperfections such as ovality and eccentricity,which decrease the casing collapse resistance. API Bulletin 5C 3 gives the calculating equation of the collapse-pressure. But it only provides primary inputs such as minimum yield strength,pipe diameter and wall thickness,etc. It doesn′t consider the effect of the initial geometric imperfections such as ovality and eccentricity,etc. Practice shows that both ovality and eccentricity affect the casing collapse resistance obviously. With the finite element method,the article studies the effect of the initial ovality and eccentricity on the casing collapse resistance in detail. And some technical measures are proposed to decrease and control the initial geometric imperfections.