国内天然气管道强度设计系数的评估研究

采用管道单一强度设计系数方法无法科学地反映管材性能、管道施工和管道运行维护水平。为了克服上述方法的不足并评估和改进现行《输气管道工程设计规范》(GB 50251—2015)中规定的天然气管道强度设计系数,采用基于可靠性的天然气管道设计方法,针对国内近4×10~4 km已建天然气管道,根据管道压力、管径、管材钢级等划分了258种计算工况;在满足天然气管道目标可靠度的前提下,应用国内的管材、焊接情况、腐蚀情况和运行维护情况等统计数据,经过大量迭代计算得到了天然气管道的临界壁厚,并反推得到了不同工况下的天然气管道等效设计系数。研究结果表明:①从一级地区到四级地区,由可靠性方法反推得到的天然气管道强度设计系数均随管道管径的增大而逐渐增大;②小管径工况的天然气管道强度设计系数一般小于国家标准规定值;③大管径工况的天然气管道强度设计系数则大于国家标准规定值。进而分别对不同地区等级的小管径管道(管径不大于508 mm)、中等管径管道(管径介于508~711 mm)和大管径管道(管径介于711~1 219 mm)的强度设计系数进行了细化和调整,增强了其合理性。

Evaluation on strength design coefficients of domestic natural gas pipelines

When a single pipeline strength design coefficient method is used, the performance, construction, operation and maintenance of pipelines can't be reflected actually. In this paper, a reliability-based gas pipeline design method was used to overcome the defects of this method and improve and evaluate the current gas pipeline strength design coefficient stipulated in the Gas Pipeline Engineering DesignSpecifications (GB 50251-2015). Domestic existing natural gas pipelines of 4×104 km long was divided into 258 calculation working conditions based on pipeline pressure, diameter and steel grade. While the target reliability of natural gas pipelines was satisfied, the criticalwall thickness of natural gas pipelines was obtained by performing abundant iterative computation on the statistical data of materials, welding, corrosion, operation and maintenance of domestic pipelines. Then, the equivalent design coefficient of natural gas pipelines in different working conditions was calculated by the inverse method. It is shown that the gas pipeline strength design coefficient derived from the reliability-based method increases with the increase of pipe diameter in the areas of Class 1 to Class 4. Besides, the strength design coefficients of pipelines with small diameters are generally lower than those stipulated in the national standard, and those of large diameters are higher than those in the national standard. Finally, the strength design coefficient was refined and adjusted specifically for small diameter pipelines (D≤508 mm), medium diameter pipelines (508 mm＜D＜711 mm), and large diameter pipelines (711 mm≤ D≤1 219 mm) in different classes of areas. Consequently, its rationality is improved.