Ultrasonic monitoring of pipe wall interior surface temperature

Abstract

Accurate temperature measurement is a crucial aspect of structural health monitoring and prognosis. Conventional temperature measurement devices are either incapable of measuring subsurface temperatures in solids or need to be invasively installed. This study investigates the use of an ultrasonic technique for non-invasive measurement of subsurface temperatures in steel components; the temperature of a point on an inaccessible surface is inferred using a time-of-flight measurement from a transducer placed on an opposing accessible surface. Two different inversion approaches are presented, one named the assumed distribution method and the other named the inverse thermal modelling method. The robustness and accuracy of the two ultrasonic temperature inversion methods are quantitatively assessed via simulations and controlled experiments. It was found that both the assumed distribution and inverse thermal modelling methods demonstrate short thermal response times and are able to track the temperature evolution of inaccessible surfaces. A series of experimental studies show that in the presence of a 15°C difference between the accessible and inaccessible surfaces, the inaccessible surface temperature is typically measured to within better than 2°C with respect to a resistance temperature detector reference measurement. Additionally, the article compares the measurement performance achieved using a deployable electromagnetic acoustic transducer and a permanently installed piezo-electric PZT transducer. The time-of-flight measurements taken using the electromagnetic acoustic transducer system had higher random noise than the PZT system (standard deviations of 0.42 and 0.016 ns, respectively), subsequently leading to higher random noise in the temperature estimates.

Co-located dual-wave ultrasonics for component thickness and temperature distribution monitoring

“…[8][9][10][11][12] The authors have previously compared two ultrasound-based methods for predicting subsurface temperature distributions in solid media. 13 However, to the best knowledge of the authors, all of the previously proposed methods assume that the thickness of the component (i.e. the length of the wave path) are known and remain constant.…”

“…This is known as the inverse-thermal-modelling (ITM) approach of ultrasonic temperature inversion, which is described in more detail in our previous work. 13 In addition, since the ITM approach is a physics-based inversion method, it can be applied to either longitudinal or shear wave measurements to obtain two independent temperature predictions, T s (x, t) and T l (x, t). If the longitudinal and shear ultrasonic waves propagate through the same system with identical thickness and temperature profile, these two predictions should be identical.…”

“…This is known as the inverse-thermal-modelling (ITM) approach of ultrasonic temperature inversion, which is described in more detail in our previous work. 13…”

“…An energy balance approach 14 is used to define the convective heat transfer at Interface-A and -B while the temporal variations of the temperature distribution of the solid system are modelled by using an explicit finite difference scheme to solve the 1D heat diffusion equation. The detailed implementation of the thermal-modelling is presented in Zhang et al 13 Once the internal temperature distribution is known, the velocity-temperature relations of Equations (2) and (3) can be used to determine the ultrasonic velocity profile along the wave path. In this case, Equation (8) is used to calculate the values of ToF for shear and longitudinal waves along a discretised 1D wave pathwhere Δ x is the grid size and the subscript i for i = 1 to M represent the spatial location of the discretised nodes in x.…”

“…This is an extension of our previous work on temperature reconstruction only. 13 Here, we seek to apply the information that is gained from the subsurface temperature distribution to improve the accuracy and robustness of conventional ultrasonic thickness gauging systems, and at the same time address the inherent limitation of the temperature sensing method.…”