Ultrasonic guided waves data for structural health monitoring of pipelines

Structural Health Monitoring (SHM) techniques are intended to assess the integrity of structures, such as pipelines. They aim at detecting the initiation of damage (i.e. at early stages) to perform thereafter the maintenance of the damaged area of the structure, without any delay. Ultrasonic guided waves (UGW) technique is one among them. It relies on the use of permanently installed sensors on the structure being monitored. These sensors emit and receive signals which propagate through the medium and interact with defects. The comparison between the signal from the healthy state and the actual signal helps to determine whether the structure is damaged or not. However, the variation of the environmental and operational conditions (EOCs) where the structure operates could have a strong impact on the acquired data. Consequently, it will be very difficult to ascertain whether the changes in the received signal are due to the presence of structural defect or just caused by the variation of the EOCs. Therefore, the aim of constructing this database was to develop a damage detection method which is sensitive to damage but robust to the variation of EOCs. The specimen used to build the database consists of a steel tube with 6.4 m length. It was placed in laboratory conditions where temperature fluctuates between 19°C and 26°C during the monitoring period. This variation is due to the weather changes. A 1 m portion of the tube was wrapped by a composite reparation, deposited by Prokem company with multiple number of layers. The data were collected using Wavemaker G4 system, which is commercialized by Guided Ultrasonic Ltd company and is intended for pipeline testing. This acquisition system is linked to a probe, which acts as an emitter and a receiver at the same time. This probe consists of two lines of circumferentially equidistant ultrasonic transducers, in order to master the direction of propagation of the UGW. In tubular structures, three types of propagation modes of UGW can coexist: Longitudinal, Torsional and Flexural. Each mode propagates with a specific phase and group velocities. These velocities are generally dependant of the frequency, which confer to the UGW the nature of being dispersive. The used probe allows operating with two separate guided waves modes, which are Torsional (non-dispersive mode) and Flexural (dispersive mode). A corrosion-like defect was machined by removing material from the inside of the pipe-wall in the half-axial length of the composite reparation. The distance between the probe and the created damage is 2.6 m.

结构健康监测（Structural Health Monitoring, SHM）技术旨在评估各类结构的完整性，例如管道。其核心目标是在损伤萌生的早期阶段完成检测，以便后续及时对结构的受损区域开展维护作业，无任何延迟。超声导波（Ultrasonic guided waves, UGW）技术便是此类方法之一，该技术依托永久安装在被监测结构上的传感器实现：传感器发射并接收在介质中传播、且会与缺陷发生相互作用的信号，通过对比结构健康状态下的基准信号与当前采集到的实际信号，即可判断结构是否存在损伤。

然而，结构运行所处的环境与运行条件（Environmental and Operational Conditions, EOCs）的变化会对采集到的数据产生显著影响，这使得难以区分接收信号的变化究竟源于结构缺陷的出现，还是仅由EOCs的波动所导致。因此，构建本数据库的目的在于开发一种对损伤敏感、同时对EOCs变化具备鲁棒性的损伤检测方法。

用于构建本数据库的试样为一根长度6.4米的钢管，实验期间将其置于实验室环境中，环境温度随天气变化在19℃至26℃之间波动。该钢管的1米区段被Prokem公司通过多层工艺制备的复合材料修复层包裹。数据采集采用由导波超声有限公司（Guided Ultrasonic Ltd）商业化推出的Wavemaker G4系统，该系统专为管道检测设计，与兼具发射与接收功能的探头相连。该探头包含两组周向等距排布的超声换能器，以此实现对超声导波传播方向的精准控制。

在管状结构中，超声导波可同时存在三种传播模式：纵向模式、扭转模式与弯曲模式。每种模式均以特定的相速度与群速度传播，而这些速度通常随频率变化，使得超声导波具备频散特性。本研究所用探头支持两种独立的导波模式工作：扭转模式（非频散模式）与弯曲模式（频散模式）。

在复合材料修复层的半轴向长度范围内，通过去除管壁内部材料加工出类腐蚀缺陷，探头与该人工缺陷之间的距离为2.6米。