Accelerated corrosion of low carbon steel by oscillatory acidic streams generated with a bio-inspired claw device

A mechanical device inspired by the pistol shrimp snapper claw was developed. This technology features a claw characterized by a periodic opening/closing motion, at a controlled frequency, capable of producing oscillating flows at transitional Reynolds numbers. An innovative method was also proposed for determining the corrosion rate of carbon steel samples under oscillating acidic streams (aqueous solution of HCl). By employing very-thin carbon steel specimens, with one side coated with Zn and not exposed to the stream, it became possible to electrochemically sense the Zn surface once the steel sample was perforated, thus providing the average dissolution rate into the most relevant pit on the steel surface. Furthermore, a laser light positioned beneath the metallic sample, along with a camera programmed to periodically capture images of the steel surface, facilitated the accurate counting of the number of newly formed pits. The system consisting of the thin steel sample and the Zn coating can be seen as a type of corrosion sensor. Furthermore, the proposed laser illumination method allows corroborating the electrochemical detection of pits and also establishing their location. The techniques crafted in this study pave the way for developing alternative corrosion sensors that boast appealing attributes: affordability, compactness, and acceptable accuracy to detect in time and space localized damage. Experimental data on claw motion were obtained by processing videos taken with a high-speed camera (1000 frames per second). The Excel file "Angular_motion.xlsx" contains the displacement and velocity data developed by the claw. Also attached is the Wolfram Mathematica file "Velocity_pincer.nb" with which the flow velocity plots developed by the device were created (Figure 2 of the paper and Figure S1A in the appendix). Image analysis to identify and count the pits was performed using two Python programs (Program 1.py; Program 2.py). Program 1: This program performs IMAGE segmentation using the thresholding method. Moreover, multiplies grayscale IMAGE by a manually created MASK for each exposure time. The use of a separate mask for each exposure time is necessary to compensate for mechanical device vibrations that prevent the creation of a standard mask. Consequently, a manual creation of a mask using Paint software is required for each image. The output image of this program will feed into program 2. Program 2: This program detects discontinuities in the segmented image (white pixels) and surrounds them with lines while counting them (which corresponds to the laser dots that indicate local dissolutions). The Excel program "Image processing parameters.xlsx" contains the results of image analysis such as the number and size of pits located. These data were used to construct Figures 8 and 9 of the manuscript. The Excel program "Corrosion rate.xlsx" contains the calculations for estimating the corrosion velocity of steel samples.本研究开发了一种仿手枪虾螯钳结构的机械装置。该装置的螯钳具备可控频率的周期性开合运动，可在过渡雷诺数条件下产生振荡流场。此外，本研究提出了一种创新方法，用于测定振荡酸性流场（HCl水溶液）中碳钢试样的腐蚀速率。 本研究采用单侧镀锌且不与流场接触的超薄碳钢试样，当试样被穿孔后，可通过电化学方法检测锌层表面，从而获取钢表面最显著蚀坑处的平均溶解速率。此外，通过在金属试样下方布置激光光源，并使用经编程可周期性采集钢表面图像的相机，可精准计数新生蚀坑的数量。 该超薄碳钢试样与锌镀层组成的系统可作为一类腐蚀传感器。此外，本研究提出的激光照明方法可验证蚀坑的电化学检测结果，并确定蚀坑的具体位置。 本研究开发的相关技术为开发兼具高性价比、结构紧凑且精度达标，可实现时空域局部损伤实时检测的新型腐蚀传感器奠定了基础。 通过对高速相机（1000帧/秒）采集的视频进行处理，获取了螯钳运动的实验数据。Excel文件"Angular_motion.xlsx"中存储了该螯钳的位移与速度数据。此外，附件中还包含Wolfram Mathematica文件"Velocity_pincer.nb"，利用该文件可绘制本装置产生的流场速度分布图（对应论文中的图2及附录中的图S1A）。 本研究通过两段Python程序（Program 1.py; Program 2.py）完成蚀坑识别与计数的图像分析工作。 程序1：该程序采用阈值法实现图像分割，并将灰度图像与针对各曝光时长手动生成的掩膜（MASK）相乘。由于机械装置的振动无法生成统一标准掩膜，因此需为每张图像单独通过Paint软件手动生成掩膜。本程序的输出图像将作为程序2的输入。 程序2：该程序可检测分割后图像中的不连续区域（白色像素），用线条标记这些区域并完成计数，此处计数结果对应表征局部溶解的激光光斑。 Excel文件"Image processing parameters.xlsx"中存储了图像分析结果，包括蚀坑的数量与尺寸等参数，这些数据用于绘制论文中的图8与图9。 Excel文件"Corrosion rate.xlsx"中存储了碳钢试样腐蚀速率估算的相关计算结果。