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根据英国标准BS7448,对UOE直缝埋弧焊管不同钢级管线钢焊接接头进行裂纹尖端张开位移(CTOD)断裂韧度测试。结合加拿大标准CSA Z662-07及挪威船级社规范NDV-OS-F101,在试样形式选择、缺口取样方向、后期金相检验等方面对断裂韧性评定方法加以完善。试验结果表明X70、X65级管线钢均具有良好韧性,符合规范NDV-OS-F101的要求。X70级管线钢焊接接头各区域韧性分布规律为:母材性能最好,焊缝次之,热影响区(HAZ)相对较差。X65级管线钢其HAZ的韧性优于母材和焊缝。其原因是:X65 级钢母材含有一定气孔、夹杂,断口出现分层裂纹,导致CTOD结果分散性大。另外,X65焊缝组织为混晶组织分布不均,含有大量M-A脆性组织物,导致韧性下降。该评定结果为海底管线钢制造工艺改进提供了依据,也为海洋工程结构安全性评估奠定了基础。
According to the British standard BS7448, the fracture tip toughness (CTOD) fracture toughness of welded joint of pipeline steel with different grade of UOE LSAW was tested. Combined with Canadian Standard CSA Z662-07 and Det Norske Veritas NDV-OS-F101, the methods for assessing fracture toughness are improved in the aspects of sample form selection, notch sampling direction and post-metallographic examination. The test results show that X70, X65 grade pipeline steel has good toughness, in line with the requirements of the specification NDV-OS-F101. The toughness distribution of X70 pipeline welded joints in each region is as follows: the best performance of the parent material, followed by the weld, the relatively low heat affected zone (HAZ). X65 grade pipeline HAZ toughness better than the base metal and weld. The reason is: X65-class steel base metal contains a certain stomatal, inclusions, fracture cracks appear layered, resulting in CTOD dispersion results. In addition, X65 weld microstructure is uneven distribution of mixed crystal, containing a large number of M-A brittle tissue, resulting in decreased toughness. The result of the assessment provided the basis for the improvement of the manufacturing process of subsea pipeline steel and laid the foundation for the safety assessment of offshore engineering structures.