Range Ultrasonic Testing Research Articles

Investigation of failure mechanisms and remaining life prediction of firewater pipelines used in industrial applications

Firewater (FW) pipelines network maintenance and monitoring are of utmost importance since they are not easily accessible for inspection. Failure and corrosion of carbon steel FW pipes, particularly localized corrosion, can propagate leaks and bursts of pipelines, which leads to expensive repairs or replacement, or even uncontrolled situations during an emergency. Therefore, being aware of the pipeline conditions, predicting their failure mechanisms, their remaining life, planning to manage emergencies, and evaluating their conditions are essential. In this study, visual inspection, metallurgical examinations using optical microscopy in combination with scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and corrosion test using a three-electrode system were employed to determine the cause of failure. Also, the water samples were subjected to various chemical and bacterial analyses. Corrosion and scale-forming potential, Physico-chemical properties, sulfate-reducing bacteria, Iron-reducingbacteria, and total bacterial count were investigated on water samples to evaluate the corrosion conditions of FW pipes. Furthermore, the remaining life prediction and monitoring of the pipelines have been studied based on laboratory simulation experiments and advanced non-destructive tests (NDT) by using Long Range Ultrasonic Testing (LRUT) and Phased Array Ultrasonic Testing (PAUT). The results indicate that the oxygen corrosion attack especially the accumulation of air bubbles (dissolved oxygen), forming tubercles, and aggressive anions (Cl- and SO42-) that are the root causes of the pipeline's failure. It can happen in general and localized forms such as localized pitting corrosion, tuberculation, top-of-the water line corrosion (TWLC), and cavitation damage. Also, by comparing NDT tests and laboratory experiments results, the remaining life results in state 2 are in good agreement. Thus, the laboratory simulation experiments are verified and can be used as a desirable indicator for the remaining life of FW pipelines and strategies for improved durability design and maintenance.

Mode matching in axisymmetric fluid-filled pipes: Scattering by a flange.

Long range ultrasonic testing of pipelines sends an ultrasonic wave along a pipe wall and then detects scattering from defects present. It is well known that scattering by pipe fixtures and fittings, such as a flange, can cause distortion and interfere with the ability to identify defects. This article develops a theoretical model to investigate scattering from a flange in a fluid-filled pipe with elastic walls. Mode matching is used as this is a computationally efficient way to examine long lengths of pipe and for enforcing the appropriate axial continuity conditions over area discontinuities. A recent article presented a mode matching approach for a similar problem, and it is demonstrated here that a re-casting of the equations is necessary to ensure all of the appropriate matching conditions are enforced. Mode matching predictions are also compared with an alternative point collocation approach in order to provide an independent benchmark. Excellent agreement between mode matching and point collocation is demonstrated, and reflection and transmission coefficients are generated in order to show the resonant behaviour of a flange and illustrate that its influence is significant and strongly frequency dependent.

Modeling the scattering of elastic waves from defects in buried pipes

Long Range Ultrasonic Testing (LRUT) is a popular non-destructive evaluation technique for identifying defects in pipelines. The method sends an elastic wave down the walls of a pipe and then monitors echoes that arise if the wave is scattered by a defect. The technical challenge of LRUT lies in separating out, and interpreting from coherent and random background noise, those signals that belong to a defect. This becomes particularly challenging when a pipe is buried, because energy in an elastic wave is known to leak out of the pipe walls when it is surrounded by materials such as soil, concrete, or sand. To address this problem it is necessary to develop a better understanding of how elastic waves propagate in buried structures, and so, a finite element based model is introduced here that seeks to analyze the scattering from a defect in a buried pipe in both the frequency and time domain. Results from the implementation of this numerical model for the torsional T(0,1) mode are presented, and the effects of the burying material on the LRUT time domain response are discussed.

A one dimensional numerical approach for computing the eigenmodes of elastic waves in buried pipelines

Ultrasonic guided waves are often used in the detection of defects in oil and gas pipelines. It is common for these pipelines to be buried underground and this may restrict the length of the pipe that can be successfully tested. This is because acoustic energy travelling along the pipe walls may radiate out into the surrounding medium. Accordingly, it is important to develop a better understanding of the way in which elastic waves propagate along the walls of buried pipes, and so in this article a numerical model is developed that is suitable for computing the eigenmodes for uncoated and coated buried pipes. This is achieved by combining a one dimensional eigensolution based on the semi-analytic finite element (SAFE) method, with a perfectly matched layer (PML) for the infinite medium surrounding the pipe. This article also explores an alternative exponential complex coordinate stretching function for the PML in order to improve solution convergence. It is shown for buried pipelines that accurate solutions may be obtained over the entire frequency range typically used in long range ultrasonic testing (LRUT) using a PML layer with a thickness equal to the pipe wall thickness. This delivers a fast and computationally efficient method and it is shown for pipes buried in sand or soil that relevant eigenmodes can be computed and sorted in less than one second using relatively modest computer hardware. The method is also used to find eigenmodes for a buried pipe coated with the viscoelastic material bitumen. It was recently observed in the literature that a viscoelastic coating may effectively isolate particular eigenmodes so that energy does not radiate from these modes into the surrounding [elastic] medium. A similar effect is also observed in this article and it is shown that this occurs even for a relatively thin layer of bitumen, and when the shear impedance of the coating material is larger than that of the surrounding medium.

Split-Spectrum Signal Processing for Reduction of the Effect of Dispersive Wave Modes in Long-range Ultrasonic Testing

This paper presents a Split-Spectrum Signal Processing (SSP) with applications to Long Range Ultrasonic Testing (LRUT). The problem of coherent noise due to Dispersive Wave Modes (DWM) in the context of ultrasonic scattering is addressed and a novel solution by utilizing the SSP technique is proposed for reduction of the effects of DWM in the received signal. The proposed technique investigates the sensitivity of SSP performance to the filter bank parameter values such as processing/filter bandwidth, and filter overlap. Therefore, as a result the optimum values are introduced that improve the signal to noise ratio (SNR) significantly. The proposed method has been compared with conventional approaches for synthesized signals for a 6 inch pipe by applying the different recombination SSP techniques. The Polarity Thresholding (PT) and PT with Minimization (PTM) methods were found to give the best result and substantially improve the SNR performance by an average of 10dB.

119 超音波を用いたタンク底部鋼板の非開放検査(音響・構造のモデル化・最適化技術)

We have developed inspection method to diagnose tank bottom plate by ultrasonic testing (UT) without tank opening. This paper describes a part of our result of study which is the screening method to identify corrosion area by long range UT. The applicability to diagnose tank bottom plate without tank opening by long range UT was revealed in some examinations. Jig of ultrasonic probe was developed in order to keep constant distance between ultrasonic probe and side plate of tank. It was demonstrated that the method is appropriate to detect wave reflected form corrosion area by conducting an experiment using specimen which is cut from actual bottom plate. We consider that the proposed method can be applied to the screening by creation of further database.

Time-Frequency Analysis of Long Range Ultrasonic Signals

Long range ultrasonic testing (LRUT) is a relatively new development within the non-destructive testing sector. Traditionally, conventional ultrasonic testing (UT) is performed at high frequencies, in the MHz range, and is capable of detecting small flaws within a range of millimetres; whereas long range ultrasonic inspection is carried out at lower frequencies, typically between 20 and 100kHz, and is capable of highlighting structural detail and discontinuities tens of metres from a test position. Conventional ultrasonic testing relies on the transmission of bulk waves, the velocities of which are independent of frequency and can usually be predicted easily if the elastic properties of the material under test are known. The dynamics of guided waves, however, are dependent upon frequency making the analysis of received data from a specimen complex. This paper will serve as an introduction to time-frequency representation and may allow a clearer understanding of the non-stationary raw signals produced by this inspection process. Currently, LRUT data are assessed in the time or distance domain using the amplitude vs. time 'A-Scan', therefore structural features and potential flaws are highlighted on a time-of-flight basis. However, as the data obtained are dynamic in time and frequency (non-stationary), time-frequency distributions could provide a mode identification or de-noising process to deal with the problem of coherent noise.

On the scattering of torsional elastic waves from axisymmetric defects in coated pipes

Long range ultrasonic testing is now a well established method for examining in-service degradation in pipelines. In order to protect pipelines from the surrounding environment it is common for viscoelastic coatings to be applied to the outer surface. These coatings are, however, known to impact on the ability of long range ultrasonic techniques to locate degradation, or defects, within a coated pipe. The coating dissipates sound energy travelling along the pipe, attenuating both the incident and reflected signals making responses from defects difficult to detect. This article aims to investigate the influence of a viscoelastic coating on the ability of long range ultrasonic testing to detect a defect in an axisymmetric pipe. The article focuses on understanding the behaviour of the fundamental torsional mode and quantifying the effect of bitumen coatings on reflection coefficients generated by axisymmetric defects. Reflection coefficients are measured experimentally for coated and uncoated pipes and compared to theoretical predictions generated using numerical mode matching and a hybrid finite element technique. Good agreement between prediction and measurement is observed for uncoated pipes, and it is shown that the theoretical methods presented here are fast and efficient making them suitable for studying long pipe runs. However, when studying coated pipes agreement between theory and prediction is observed to be poor for predictions based on those bulk acoustic properties currently reported in the literature for bitumen. Good agreement is observed only after conducting a parametric study to identify more appropriate values for the bulk acoustic properties. Furthermore, the reflection coefficients obtained for the fundamental torsional mode in a coated pipe show that significant sound attenuation is present over relatively short lengths of coating, thus quantifying those problems commonly encountered with the use of long range ultrasonic testing on coated pipes in the field.

Analysis on Characteristic Features of L-Mode Guided Wave in Tube Testing

Applications of long range ultrasonic testing are on cylindrical products(pipes and tubes) and planar products(plates and sheets).Guided wave testing using circumferential and longitudinal modes are getting more and more importance as there are huge requirements for testing pipes and tubes in power generators, Chemical plants, steam generators etc.. There will be infinite number of modes with charectestic propagation and wave structure. This propagation characteristic and wave structure plays a major role in deciding its suitability for use in specific application. It is highly essential to use mode control and to understand the generated modes and its characteristics based on which only testing adequacy can be evaluated. In this paper the characteristic features of L-mode generated using a source design parameter for tube testing are explained. The dispersion characteristic of L-mode are discussed using constructed Dispersion Curves, phase and group velocity, its multiple defect detection capability, pulse shape and amplitude dynamics with propagation range and inclination. The details of controlled experiment conducted and the observations are discussed. The derived inferences are explained based on the applicable particle displacement equations and dispersion characteristic equations.