Abstract

The piping systems used for the transportation of liquids and gases in power stations, petroleum petrochemical facilities, and chemical plants are significantly impacted by corrosive processes. One of the most destructive forms of corrosion is pitting corrosion, which produces holes on piping metal surfaces. Monitoring pit depth is necessary in order to prevent leakage in the piping system, especially during operation. However, measuring pit depth as a part of periodical inspections is complicated since the pit depth on the outside wall of a pipe may vary. Non-destructive testing (NDT) methods such as ultrasonic, liquid penetrants, and magnetic particles are used to detect defects in industrial components; however, they first require the removal of insulation and the shutdown of the pipe system. Another alternative NDT technique, tangential radiography technique (TRT), offers a solution to this problem as tests can be conducted without removing piping insulation, allowing testing while the piping system is online. In this study, we tested TRT using an X-ray radiation source, which has good controllability (i.e., intensity and exposure time) and a lower impact on the human body than do γ-ray sources. We focused on the comparison of film density measurements using a density meter and a light meter. The magnification of pit diameter was used to obtain an equation for small-diameter pipes (i.e., diameter of less than 50 mm). The working voltage was varied (200, 230, and 260 kV) in order to generate appropriate X-ray energies to measure various pit depth (20, 40, and 60%, receptively) of a stepped steel pipe specimen. Film density measurements using the density and light meters showed similar results; however, the film density result using the density meter was more accurate. All tangential side edges of the specimen burned off for film densities above 3.5. Degrees of magnification (1.0123, 1.0254, and 1.0379) varied as a function of distance from the midpoint of the X-ray target (30, 60, or 90 mm, respectively). Using the results, a linear equation with three variables was obtained to determine the actual diameter of pitting: 0.000385436a + 0.038350128b + 0.000467083c = d; where the actual diameter = film diameter/d. High working voltage produced low film contrast, high film definition, and low scatter. Low working voltage produced high film contrast, low film definition, and high scatter. Based on our results, a working voltage of 260 kV is most appropriate for effective analysis.

中文翻译：

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切线X射线摄影技术用于绝缘钢管外壁的点蚀几何分析

摘要

电站，石油石化设施和化工厂中用于输送液体和气体的管道系统会受到腐蚀过程的严重影响。点蚀是破坏性最大的腐蚀形式之一，点蚀会在管道金属表面上产生孔。为了防止管道系统泄漏，尤其是在运行期间，必须监测井深。但是，作为定期检查的一部分，测量凹坑深度很复杂，因为管道外壁上的凹坑深度可能会发生变化。超声波，液体渗透剂和磁性颗粒等无损检测（NDT）方法用于检测工业组件中的缺陷；但是，它们首先需要去除绝缘层并关闭管道系统。另一种NDT替代技术 切线射线照相技术（TRT）为该问题提供了解决方案，因为可以在不去除管道绝缘层的情况下进行测试，从而可以在管道系统在线时进行测试。在这项研究中，我们使用X射线辐射源测试了TRT，该射线源具有比γ射线源更好的可控制性（即强度和曝光时间），并且对人体的影响较小。我们专注于使用密度计和照度计的胶片密度测量的比较。坑直径的放大率用于获得小直径管道的方程（即，直径小于50毫米）。改变工作电压（200、230和260 kV），以生成适当的X射线能量，以测量阶梯式钢管样品的各种凹坑深度（接受度分别为20％，40％和60％）。使用密度计和照度计进行的薄膜密度测量显示出相似的结果；但是，使用密度计测得的薄膜密度结果更为准确。对于高于3.5的薄膜密度，样品的所有切向侧边都会烧掉。放大程度（1.0123、1.0254和1.0379）随距X射线目标中点（分别为30、60或90 mm）的距离而变化。使用结果，获得具有三个变量的线性方程以确定点蚀的实际直径：0.000385436 分别）。使用结果，获得具有三个变量的线性方程以确定点蚀的实际直径：0.000385436 分别）。使用结果，获得具有三个变量的线性方程以确定点蚀的实际直径：0.000385436a + 0.038350128 b + 0.000467083 c = d ; 实际直径=薄膜直径/ d。高工作电压产生较低的胶片对比度，较高的胶片清晰度和较低的散射。低工作电压产生高的胶片对比度，低的胶片清晰度和高散射。根据我们的结果，最适合进行有效分析的工作电压为260 kV。