焊接层数对长输管道组合自动焊接头裂纹尖端张开位移不均匀性的影响

Effect of welding layers on crack tip opening displacement in combination automatic welded joints of long-distance pipelines

  • 摘要:
    目的 随着高钢级长输管道建设中全自动焊接技术的推广和应用,主管线焊接已普及使用了该技术,其中主管线的连接处也已使用组合自动焊作业,即根焊(采用手工氩弧焊GTAW或其他手工根焊工艺)+填充焊/盖面焊(采用气保护药芯焊丝上向自动焊FCAW-G工艺)。因坡口形式为V形,所以焊接时热输入大,在当下管道行业内裂纹尖端张开位移(Crack tip opening displacement, CTOD)值作为验收值的情况下,层道数是影响CTOD值的关键因素,因此,该文针对不同焊接层数下X80M直管与L555M热煨弯管自动焊接对接接头,研究焊接层数对CTOD值的影响。
    方法 采用单边缺口三点弯曲试样进行CTOD试验,采用ISO 15653:2018标准进行CTOD值计算,并通过光学显微镜对接头的显微组织及断口进行观察。
    结果 焊接层数为8和9条件下,接头试样CTOD值离散性较大且均存在试样低于标准值,该值分别为0.229 mm,0.113 mm和0.179 mm;焊接层数为10条件下,所有试样在ISO 15653: 2018标准下计算得到的CTOD值均满足标准要求,焊接接头的断裂韧性更优。在相同的焊接层数条件下的焊接接头,熔合区试样CTOD值较焊缝试样更高,在试样中CTOD的最大值均出现在熔合区。
    结论 熔合区的断裂韧性优于焊缝,但CTOD值较为分散,断裂韧性分布不均匀;不同焊接层数下的焊接接头,焊缝与熔合区的CTOD值均随着焊接层数的增大而增大,CTOD值满足评定标准时,试样处的裂纹扩展区较为平缓。

     

    Abstract: Objective With the promotion and application of fully automatic welding technology in the construction of high-steel-grade long-distance pipelines, this technology has been popularized in welding of main line. Combination automatic welding operations has also been used in welded joints of main line, that is root welding (using manual argon arc welding or other manual root welding process) + filling/cover welding (gas-shielded flux-cored wire upward automatic welding process). Because groove form is V-shaped, heat input is large during welding. In the case that CTOD value is regarded as the acceptance value in current pipeline industry, number of layers is the key factor affecting CTOD value. Therefore, in this paper, for the automatic welded butt joints of X80M straight pipes and L555M hot simmering bends with different numbers of welding layers, effect of number of welding layers on CTOD value is studies. Methods CTOD test is conducted with one-sided notched three-point bending samples. CTOD value is calculated according to ISO 15653: 2018, and microstructure and fracture of welded joints are observed by optical microscope. Results Under the condition of number 8 and 9 of welding layers, CTOD values of welded joints are more discrete and lower than standard values, which are 0.113 mm, 0.229 mm and 0.179 mm, respectively. Under the condition of number 10 of welding layers, CTOD values of all samples calculated under ISO 15653: 2018 meet the standard’s requirements, and fracture toughness of welded joints is better. For welded joints under the same number of welding layers, CTOD values of fusion zone are higher than those of weld, and the maximum CTOD value all appears in fusion zone of samples. Conclusion Fracture toughness of fusion zone is better than that of weld, but CTOD value is more dispersed and distribution of fracture toughness is uneven. For welded joints under different welding layers, CTOD values of weld and fusion zone increase with the increase number of welding layers. When CTOD values meet evaluation standard, crack growth zone is relatively gentle.

     

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