含砂流对弯管段冲蚀的机理分析

管道的弯管段、闸阀等处常常面临含砂流动的冲蚀磨损而导致管壁减薄或泄漏。为研究弯管段冲蚀磨损的主要机制,进行了加入5%石英砂的固液两相管流循环试验。试验按砂粒粒径分组,主要观测布置在弯管段的一组碳钢贴片在2~3小时后的壁面冲蚀特征。用失重法计算各贴片的冲蚀速率,基于扫描电镜(SEM)研究了贴片表面的损伤形貌。冲蚀后的贴片表面既有犁沟、挤压凹坑及划痕,亦有圆形蚀坑。能谱分析(EDS)显示有一定量的铁氧化物,且不同位置处的贴片失重率有正有负,由此可见导致贴片表面破坏的机制既包括切削、挤压和二次冲击等含沙流流动的机械作用,也伴随着腐蚀作用。这两种机制在弯管各区有不同的体现,且受砂粒粒径的影响。用数值模拟的两相流冲蚀弯管段流场压力和颗粒分布特征做了验证。结果表明弯管段的壁面损伤机制在外拱壁面以颗粒冲击和切削为主,在内拱璧面则以氧化腐蚀为主。

Erosion Mechanism Analysis of Sand Flow Passing through the Elbow Segment

Elbow and Valve and so on in pipeline are often subjected to sand fluid erosion inducing tube wall thinning even leaking.In order to study the main mechanism of elbow erosion wear,a solid-liquid two-phase flow pipe circulation experiment was conducted by using liquid added 5％ quartz sand.Experiment was divided into different groups according to the sand particle size,and was focused on observing the erosion and wear characteristics of a set of carbon steel pasters mounted on pipe elbow after 2～3 hours circulation.The erosion rate of each paster was calculated by weight loss method.Then,the paster surface damage morphology was investigated based on scanning electron microscopy (SEM).Furrows,indentation,scratch even circle etch pits are found on paster surface after eroding.Energy dispersive spectrum analysis (EDS) shows the existence of a certain amount of iron oxides.It is obvious that the damage mechanism of paster surface includes not only the mechanical actions such as cutting,extrusion and second impact due to fluid passing through elbow segment,but also the coexisted erosion action.Both mechanisms have different manifestations in elbow segment and are affected by particle size.Numerical simulation verifies the flow field pressure and particle distribution characteristics of two-phase flow erosion.Results show that damage mechanism on the outer arch wall of elbow is controlled by particle impaction,while corrosion is dominant on the inner arch wall of elbow.