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.
Steps to reproduce
The database was collected from a pipe segment which has been monitored during a period of almost three months. The monitoring duration is divided in two periods: the specimens were being healthy firstly, and then the defects were machined in various steps. They were increased in 6 steps. Five repetitive acquisitions of UGW signals were achieved multiple times in a week and at the morning and at the evening each time in order to capture temperature changes during the day, and to investigate a posteriori its effects on the collected signals. Each acquisition (represented by an excel file) is characterized by five frequencies which are 14, 18, 24, 30 and 37 kHz. Each frequency is represented in a excel sheet and it contains four columns. The first one is the distance traveled by UGW. It must be noted here that the distance can be negative depending on the direction of propagation of UGW. The two other columns correspond to the two propagation modes: torsional and flexural. The last column is the pure DAC (Distance Amplitude Correction) curve which is the exponential decay of amplitude due to damping. This latter should be removed from the database as it is only useful in NDT context and not in SHM. At the end of the monitoring period, a total of 236 signals were collected where 207 (from acquisition number#1622 to number#1901) ones were collected from the undamaged pipe and 29 signals were acquired from the damaged pipe (from acquisition number#1902 to number#1930).