高钢级管道环焊缝主要特征及安全性评价

Main characteristics and safety assessment of girth welds in high grade steel pipelines

环焊缝是长输管道的重要组成部分,其失效是载荷、缺陷、局部断裂韧性、强度匹配、焊缝几何结构及残余应力等因素相互作用所致,且高钢级管道因焊接技术难度增大,也增加了环焊缝失效的可能性。基于此,分析了环焊缝的载荷、缺陷及强度匹配特征,揭示了低匹配环焊缝或热影响区软化环焊缝的应变集中机理,阐释了环焊缝的脆性断裂、屈服前净截面垮塌、屈服后净截面垮塌及母材颈缩4种失效模式,比较了GB/T 19624-2019、BS 7910-2015、API 579-1/ASME FFS-1-2016、API 1104-2013等国内外标准对环焊缝安全性评价的适用性,提出了基于应变的环焊缝安全性评价方法,讨论了裂纹尺寸、强度匹配系数等因素对环焊缝裂纹驱动力的影响。研究指出:明确环焊缝的载荷或位移是其安全性评价的前提,提高环焊缝的应变能力可以增强高钢级管道对于不良地质条件的适应性,建议开展环焊缝裂纹缺陷产生和扩展机制研究,并发展基于应变的断裂理论,优化环焊缝的强度匹配,定量环焊缝的应变能力与焊缝几何特性及力学性能参数的关系。(图9,表2,参33)

Girth weld is an indispensable part of long-distance pipelines.Girth weld failure is caused by the interaction of load,defects,local fracture toughness,strength matching,weld geometry and residual stress,and the welding for high steel grade pipelines is particularly difficult which increases the failure possibility of girth welds.In this case,the load,defect and strength matching characteristics of girth weld were analyzed,the strain concentration mechanism of low matching girth welds or softening girth welds in heat affected zone was revealed,and four failure modes including brittle fracture,net section collapse before yield,net section collapse after yield and base metal necking of girth weld were explained.Based on the comparison of the applicability of girth weld safety assessment in GB/T 19624—2019、BS 7910-2015、API 579-1/ASME FFS-1-2016、API 1104-2013 and other domestic and foreign standards,the strain-based girth weld safety assessment method was proposed,and the influence of crack size,strength matching coefficient and other factors on girth weld crack driving force was discussed.The research demonstrates that the load or displacement of the girth weld should be the premise of the safety assessment,and improving the strain capacity of the girth weld can enhance the adaptability of high grade steel pipelines to adverse geological conditions.It is suggested to carry out the research on the initiation and growth mechanism of the girth weld crack defects,develop the strain-based fracture theory,optimize the strength matching of the girth weld,and quantify the relation between the strain capacity of the girth weld and the geometric and mechanical performance parameters of the weld.(9 Figures,2 Tables,33 References)