基于四阶B-样条最小二乘法的油气管道凹痕缺陷应变计算方法

Calculation method of strain for dent defect on oil and gas pipelines based on fourth-order B-spline least square method

针对油气管道上的凹痕缺陷,ASME B31.8提出采用基于应变的评价方法,但在内检测数据到应变求解的过程中,缺少噪声消除和轮廓拟合的相关方法。提出了采用四阶B-样条最小二乘拟合算法将检测数据进行噪声消除和轮廓拟合,实现从含有噪声的检测数据到应变求解的应变评价方法。采用文中所提方法和有限元方法,详细计算了几种典型凹痕的轴向弯曲应变、环向弯曲应变及其总应变。对比结果表明,该方法不仅能够较为精确的计算出弯曲应变值,还能得到较准确的弯曲应变分布情况。环向弯曲应变受在线检测工具精度的限制存在一定误差。计算发现,现有标准中忽略了环向薄膜应变分量,这使得总应变的计算结果不够准确。

Aiming at the dent defect on oil and gas pipelines, ASME B31. 8 recommends a strain-based criterion for the assessment of dents. But in the process from internal detection data to quantitative calculation of strain, there is lacking of relative methods on noise cancellation and profile fitting. A strain evaluation method by applying fourth-order least-square B-spline least square fitting algorithm to conduct noise cancellation and profile fitting on detection data was put forward, which achieved strain calculation from detection data with noise. Both the proposed method and the finite element method were used to calculate axial bending strains, circumferential bending strains and com-bined strains of some typical dents. The results showed that the method can not only calculate the bending strains quite well, but also get a reasonable understanding of the bending strains distribution. There are some errors in the circumferential bending strains due to the restriction by resolution of online detection tools. What＇s more, the exist-ing standard neglects the effect of circumferential membrane strain in determining the effective strain, which leads to inaccuracy results of combined strain.