某天然气机组二级入口分离器筒体外壁上用于安装液位计的短管存在裂纹,裂纹位于管母材区域,为环向开裂。采用宏观观察、化学成分分析、金相检验、扫描电镜分析、受力情况分析等方法对短管开裂原因进行了综合分析。结果表明:在短管配合区的前1~2个螺纹的根部存在静止且含有腐蚀性介质的积液;该区域在交变载荷的长期作用,以及拉应力与硫离子的耦合作用下萌生裂纹;液位计与短管的配合尺寸不够、管壁受力面积较小、应力增大及腐蚀性介质等促进了裂纹的进一步扩展。

There were cracks in the short tube used for installing the liquid level meter on the outer wall of the secondary inlet separator cylinder of a natural gas unit. The cracks were located in the pipe base material area, which were circumferential cracks. Macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscope analysis and stress analysis were used to comprehensively analyze the causes of short tube cracking. The results show that there was still liquid accumulation with corrosive medium at the root of the first to second threads in the pipe fitting zone. This region initiated cracks under the long-term action of alternating load and the coupling effect of tensile stress and sulfur ions; the insufficient matching size of the level gauge and the short tube, the small stress area of the pipe wall, the increase of stress and the corrosive medium promoted the further expansion of the crack.