Detection of multiple defects based on structural health monitoring of pipeline using guided waves technique

Monitoring and inspecting the health condition and state of the pipelines are significant processes for an early detection of any leaking or damages for avoiding disasters. Although most Non Destructive Test (NDT) techniques are able to detect and locate damage during the maintenance intervals, interrupted services could result in high cost and lots of time consumed. In addition, most NDTs are utilized to detect and locate single damage such as axial crack, circular crack, or vertical crack only. Unfortunately, these NDTs are unable to detect or localize multi-type of damages, simultaneously. In this research, the proposed method utilizes the Structural Health Monitoring (SHM) based on guided wave techniques for monitoring steel pipeline continuously in detecting and locating multi-damages. These multi damages include the circumference, hole and slopping cracks. A physical experimental works as well as numerical simulation using ANSYS were conducted to achieve the research objectives. The experimental work was performed to validate the numerical simulation. An artificial neural network was used to classify the damages into ten classes for each type of damage including circumference, hole and sloping cracks. The obtained results showed that the numerical simulation was in agreement with the experimental work with relative error of less than 1.5%. In addition, the neural network demonstrated a feasible method for classifying the damages into classes with the accuracy ranged from 75% to 82%. These results are important to provide substantial information for active condition monitoring activities

Monitoring system for long-distance pipelines subject to destructive attack

In an era of terrorism, it is important to protect critical pipeline infrastructure, especially in countries where life is strongly dependent on water and the economy on oil and gas. Structural health monitoring (SHM) using acoustic waves is one of the common solutions. However, considerable prior work has shown that pipes are cylindrical acoustic waveguides that support many dispersive, lossy modes; only the torsional T(0, 1) mode has zero dispersion. Although suitable transducers have been developed, these typically excite several modes, and even if they do not, bends and supports induce mode conversion. Moreover, the high-power transducers that could in principle be used to overcome noise and attenuation in long distance pipes present an obvious safety hazard with volatile products, making it difficult to distinguish signals and extract pipeline status information. The problem worsens as the pipe diameter increases or as the frequency rises (due to the increasing number of modes), if the pipe is buried (due to rising attenuation), or if the pipe carries a flowing product (because of additional acoustic noise). Any system is therefore likely to be short-range. This research proposes the use of distributed active sensor network to monitor long-range pipelines, by verifying continuity and sensing small disturbances. A 4-element cuboid Electromagnetic Acoustic Transducer (EMAT) is used to excite the longitudinal L(0,1) mode. Although the EMAT also excites other slower modes, long distance propagation allows their effects to be separated. Correlation detection is exploited to enhance signal-to-noise ratio (SNR), and code division multiplexing access (CDMA) is used to distinguish between nodes in a multi-node system. An extensive numerical search for multiphase quasi-orthogonal codes for different user numbers is conducted. The results suggest that side lobes degrade performance even with the highest possible discrimination factor. Golay complementary pairs (which can eliminate the side lobes completely, albeit at the price of a considerable reduction in speed) are therefore investigated as an alternative. Pipeline systems are first reviewed. Acoustic wave propagation is described using standard theory and a freeware modeling package. EMAT modeling is carried out by numerical calculation of electromagnetic fields. Signal propagation is investigated theoretically using a full system simulator that allows frequency-domain description of transducers, dispersion, multi-mode propagation, mode conversion and multiple reflections. Known codes for multiplexing are constructed using standard algorithms, and novel codes are discovered by an efficient directed search. Propagation of these codes in a dispersive system is simulated. Experiments are carried out using small, unburied air-filled copper pipes in a frequency range where the number of modes is small, and the attenuation and noise are low. Excellent agreement is obtained between theory and experiment. The propagation of pulses and multiplexed codes over distances up to 200 m are successfully demonstrated, and status changes introduced by removable reflectors are detected.Open Acces

Guided waves for power plant applications

This study explores the possibility of using the guided wave non-destructive testing technique for power plant applications. Guided waves are already used extensively in the petrochemical industry, however the nature of pipework in a power station has meant that guided waves have not been studied for use in this environment. Power station pipework is more challenging to inspect than petrochemical pipework using guided waves because the pipelines tend to be shorter, and the feature density is much higher, with welds, hangers, supports and bends all contributing to make analysis of results more difficult. A particular focus of the study was detecting axially aligned defects in pipes, a problem that emerged in the UK coal power station fleet in 2006. Guided waves provided a desirable inspection technique because large volumes of pipework can be screened quickly, this being particularly advantageous due to the high volume of pipework that requires inspection. Two guided wave approaches to detecting axial cracks in pipes were pursued. Long- range guided waves were initially examined as they are able to examine large quantities of pipework in a short amount of time. Unfortunately, long-range guided waves are sensitive to the change in cross-sectional-area of a pipe, and axially aligned defects produce only a very small change in cross-section. Therefore long-range guided waves were not sensitive enough to detect a critically sized axial crack. The sensitivity of long- range guided waves was improved using a synthetic focusing algorithm, although this was still insufficient to detect a critically sized defect. The second guided wave approach was to utilise circumferential guided waves to detect axial cracks in pipes. Although many of the advantages of long-range guided waves are lost, using circumferential guided waves is much faster than an alternative manual ultrasonic inspection. The results of circumferential guided wave experiments suggest that they would be capable of detecting a critically sized axial crack in a pipe. Besides attempting to detect axial cracks guided waves have been tested on a small number of other power station pipework systems. These systems were tested as a way to examine the viability of using guided waves as a general inspection tool at a power station. Although guided waves are not suitable for every application, there are a good number of potential applications due to the wide variety of pipework systems at a power station

Ultrasonic thickness structural health monitoring of steel pipe for internal corrosion

The naphthenic acid corrosion that can occur in oil refinery process plants at high temperature (400ÃÂðC) due to the corrosive nature of certain crude oils during the refining process can be difficult to predict. Therefore, the development of online ultrasonic thickness (UT) structural health monitoring (SHM) technology for high temperature internal pitting corrosion of steel pipe is of interest. A sensor produced by the sol-gel ceramic fabrication process has the potential to be deployed to monitor such pitting corrosion, and to help investigate the mechanisms causing such corrosion. This thick-film transducer is first characterized using an electric circuit model. The propagating elastic waves generated by the transducer are then experimentally characterized using the dynamic photoelastic visualization method and images of the wave-field are compared with semi-analytical modeling results. Next, the classic elastic wave scattering theory for an embedded spherical cavity is reviewed, results are compared with a newer scattering theory from the seismology community, that has been applied to a hemispherical pit geometry. This hemispherical pit theory is extended so as to describe ultrasonic Non-Destructive Evaluation (NDE) applications, for pitting corrosion, with the derivation of a far-field scattering amplitude term. Data from this new scattering theory is compared with experimental results by applying principals from the Thompson-Gray measurement model. The initial model validation provides the basis for a possible new hemispherical pit geometric reference standard for ultrasonic NDE corrosion applications. Next, UT SHM measurement accuracy, precision, and reliability are described with a new weighted censored relative likelihood methodology to consider the propagation of asymmetric uncertainty in quantifying thickness measurement error. This new statistical method is experimentally demonstrated and applied to thickness measurement data obtained in pulse-echo and pitch-catch configurations for various time-of-flight thickness calculation methods. Finally, the plastic behavior of a corroded steel pipe is modeled with analytical and finite element methods to generate prognosis information