Proposal of the pipe diagnosis method using in-plane bending vibration of cylindrical shell

Abstract

In this paper, deterioration diagnosis for distribution main pipe was studied using the uniform cylindrical shell approximation and in-plane bending mode. The in-plane bending mode is expected to have high accuracy in detection of deterioration, because the eigen frecuency of the mode is proportional to pipe thickness. First, using the finite element method, the characteristics of in-plane bending mode are investigated. It is confirmed that in-plane bending mode has little small dependence on the pipe length and the boundary conditions at the pipe ends, it appears in the audio frequency bands, and it has linear dependence on the pipe thickness. In addition, formula with two dimensional ring approximation is derived. Moreover, the average thickness and the uniform-cylindrical shell approximation are introduced for deal with the deteriorated pipe. Using the thinning pipe thickness of previous study, validity of the average thickness and the uniform-cylindrical shell approximation were confirmed. On the other hand, actual pipeline has the sub-structure, for example, valve, hydrant, and so on. In order to deal with the coupled vibration between the cylindrical shell and the sub-structure, eigenvalue analysis are conducted using the Semi-Analytical Receptance Method (SARM). The experimental consideration were conducted in case of that the sub-structure non-attached case. The in-plane bending mode is observed experimentally on the actual pipe system and its resonant frequency shows good match with the theoretical values.

Evaluation of Pipe Thickness by Magnetic Hammer Test with a Tunnel Magnetoresistive Sensor

“…The experimental setup for investigating the applicability of MHT to inspection of piping was located outside a magnetically shielded room exposed to a geomagnetic field. This investigation targeted carbon steel widely used for oil and gas piping or water pipes, namely, Japanese Industrial Standards (JIS) STPG370 (370 N/mm 2 grade steel) [ 28 ], which is characterized by its sufficient toughness for use as gas and oil piping (Young’s modulus, (E) 205 GPa; density ( ), 7850 kg/m 3 ; and Poisson’s ratio ( ), 0.3) [ 24 ]. The reference specimen is a pipe with 1000 mm length (L), 60 mm diameter (D), and 5.66 mm thickness (h).…”

“…Circumferential frequency is mainly determined by pipe thickness, and these parameters are proportional. In the case of pipes longer than 3 m, pipe length does not depend on the natural frequency, which is the same as that of a circular ring [ 24 ]. In addition, circumferential vibration is excited by turbulence and is especially pronounced when the wall is thinner and less stiff [ 33 ].…”

“…Accuracy for the reference pipe (5.66 mm thick) was 4 Hz aboveground and 23 Hz underwater. From Equation (24), the minimum resolution for the reference pipe was calculated to be 4.4 ± 0.7 µm aboveground and 23.6 ± 2.6 µm underwater.…”

“…In our previous work, we used a TMR sensor to observe magnetic oscillations in steel plates, and we were able to estimate the millimeter-order thickness of the steel plates from their vibration frequency [ 18 ]. In addition, Takata et al found a proportional relationship between pipe-wall thickness and the vibration frequency of pipes [ 24 ]. These results demonstrate that the thickness of pipes made of steel can be easily measured from their natural frequencies.…”

Integrity assessment of turbine generator rotor wedges based on their resonance characteristics

“…Hasebe et al [26] evaluated the soundness of the amount of adhesive material from the resonant frequency shift of anchor bolts driven by EMATs. Takata et al [27] diagnosed the aging of piping from the resonant frequency shift of the in-plane bending deformation vibration of cylindrical shells attributed to the stiffness change.…”