Abstract: Polyethylene (PE) and its composite pipes have been widely used in the transportation of energy, such as natural gas and petroleum.Pipe welding joints have been proven to be a weak link of the whole pipeline.This means that non-destructive testing (NDT) and safety assessment of these joints are key technologies to guarantee safety of pipeline.In this paper, the theory and method of NDT technology on welding joint of PE pipes, inspection technique of cold welding and safety assessment of welding joints containing defects are introduced.Ultrasonic phased array and coupling focusing technology are applied in the inspection of electrofusion and butt-fusion joints of PE pipes respectively.Figures with inspecting image and cross section of practical joint are given.A cold welding inspection method based on ultrasonic phased array technology was invented, which has clear physics concept and is convenient in application.The defects in the electrofusion joints of PE pipe are classified into four categories:poor fusion interface, over welding, voids and structural deformity.Mechanical tests of joints with different kind of defects show that there are three main failure modes of EF joint under inner pressure, that is, cracking through the fusion interface, cracking through the fitting, and cracking through copper wire interface.A safety assessment method was proposed based on the experimental and analytical results.The proposed method can greatly improve intrinsical safety of such pipeline.

Key words: polyethylene pipe, composite pipe, welding joint, non-destructive testing, safety assessment

摘要： 聚乙烯及其复合管道广泛应用于油气输送、城市燃气等能源领域,其安全性至关重要。焊接接头的安全检测及评价是聚乙烯及其复合管道系统安全的关键技术。介绍了聚乙烯管道焊接接头的无损检测原理及方法、冷焊检测技术以及缺陷分类与失效模式三方面内容。对电熔和热熔焊接接头分别采用超声相控阵和耦合聚焦技术进行超声检测,并给出了缺陷剖切与检测结果的对比图。提出了物理概念清晰、工程应用方便的冷焊超声检测方法。将电熔接头中的缺陷分为熔合面缺陷、孔洞、结构畸变和过焊。分别对含不同类型和大小缺陷的电熔接头进行力学性能测试,发现电熔接头存在三种典型的失效模式,即沿电熔套筒壁贯穿裂纹失效、熔合面失效以及沿电阻丝所在平面贯穿裂纹失效。根据试验测试与理论分析结果,提出了相应的安全评定方法。所提出的方法,填补了国内外在聚乙烯管道安全检测与评价方法方面的技术空白,提高了燃气管道的本质安全性。

关键词: 聚乙烯管, 复合管, 焊接接头, 无损检测, 安全评定