Abstract:

Elbow mainly controls medium flow direction in pipelines, and is one of the most commonly used pipeline components in oil and gas transportation. Corrosion-induced failure was studied on return pipeline elbow of regeneration tower in LPG desulfurization unit. From both macroscopic and microscopic viewpoint, distribution of corrosion pore diameters and reduction of wall thickness of failed elbow were surveyed. Physicochemical analysis was further performed by X-ray diffraction (XRD)and scanning electron microscope-energy dispersive spectrometer (SEM-EDS). The results show that corrosion is gradually intensified along fluid flow direction and a complete destruction zone is formed in the middle and outlet of the elbow. The main mechanism of elbow corrosion failure was that fluid scour destroyed protective film formed by electrochemical corrosion and weakened its protective effect on substrate, resulting in continuous corrosion of inner wall. Also, the presence of heat-stable salts aggravated elbow corrosion.

Key words: LPG desulfurization, return tower pipeline elbow, failure mechanism analysis, measurement, corrosion, electrochemistry

摘要：

弯头在管路系统中主要起到改变介质流动方向的作用，是油气输送中最常用的管道部件之一。重点研究了液化气脱硫装置再生塔返塔管线弯头的腐蚀失效机制。从宏观和微观两个角度入手，研究了失效弯头部位的腐蚀孔孔径分布、减薄规律，进而利用X射线衍射（XRD）和扫描电镜-能谱仪（SEM-EDS）对样品进行了系统的理化分析。结果表明：沿流体流动方向，腐蚀逐渐加剧，在弯头的中部和出口形成完全破坏区；流体冲刷会破坏电化学腐蚀形成的产物保护膜，减弱产物膜对基体的保护作用，导致内壁不断被腐蚀，这是弯头腐蚀失效的主要原因。此外，热稳定性盐（HSS）的存在也加剧了弯头的腐蚀。

关键词: 液化气脱硫, 再生塔返塔管线弯头, 失效分析, 测量, 腐蚀, 电化学