​The active methods used in structural health monitoring (SHM) consist of emitting a wave, and then studying the modifications to the wave when it encounters a defect. Passive methods are different in that they do not require the emission of a wave prior to taking measurements. Researchers at List, a CEA Tech institute, recently developed a method to measure and analyze the waves generated by the flow of a fluid inside a pipe to detect any defects in the pipe.

The solution developed is based on pairs of fiber Bragg grating rings that serve as elastic wave receivers, and offer the advantage of being more robust under extreme conditions (high temperature, radiation, etc.) than the piezoelectric sensors conventionally employed in active SHM methods. The information from the pairs of sensors is processed by a purpose-developed tomography algorithm to reconstruct the pipe-wall thickness profile. The resulting profile can be used to detect, identify, locate, and measure any defects present.

The method was tested and validated on artificial defects and its performance was compared to that of a traditional active method. It was a success! List is now partnering with French electric utility EDF to investigate how the method can be used in industrial environments. Other applications, such as in aeronautics, are also possible.