共查询到20条相似文献,搜索用时 140 毫秒
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There is an increasing interest in high frequency short range guided waves to screen or monitor for corrosion. This contrasts with long range guided waves (LRGWs) which screen pipes for large patches of corrosion and have been successfully used in corrosion management for the past twenty years. The fundamental setup described in this paper uses circumferential guided waves, which are excited at a single location on a pipe and travel around the pipe wall and are detected at the same location. The study uses a finite element model assisted method to evaluate the detection capability of two short range circumferential guided wave setups which use both the reflected and transmitted signals. The setups themselves consist of either an axial array of transducers, for monitoring, or a single transducer which axially scans a pipe. Both setups have an array or scan pitch between either adjacent transducers or measurements. The detection capability of the fundamental Lamb wave modes (A0 and S0) in both reflection and transmission have been compared, as well as a hybrid shear horizontal wave setup, which uses the SH0 mode in reflection and the SH1 mode in transmission. A sensitivity analysis was conducted using two separate methods to determine the probability of detection (POD) for either the reflection or transmission signals. Both methods determine a POD for a specific defect, noise level, and array or scan pitch. Probability images are produced which map the POD for a range of defect sizes. For the parameters investigated in this study, it was found that in transmission large diameter defects have a higher detectability, whereas deep, narrow diameter defects are more detectable in reflection. A generalised overview of the sensitivity of short range guided waves is presented by combining both the reflection and transmission PODs. The data fused sensitivity of the S0 and SH hybrid modes are given as 0.6% and 0.75% cross sectional area (CSA) respectively, allowing for the comparison with LRGWs. The A0 mode was excluded from the POD analysis because it was much less sensitive than the other two modes. 相似文献
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The use of guided waves is now widespread in industrial NDT for locating metal loss in pipelines, that manifests as pitting, corrosion and general wall thinning. In this paper, a screening technique is assessed in terms of defect detection and defect sizing capability. Shear Horizontal (SH) guided waves propagate circumferentially around the pipe whilst the scanner is moved axially along the length. This type of tool is preferable to other methods, being applied to the exterior of the pipe, without requiring full circumferential access, and is able to operate through thin coatings (up to 1 mm thick). It is designed to provide a pipe screening tool for petrochemical pipelines both topside and subsea, particularly for detecting defects at pipe support areas. The system's efficacy in terms of detection and sizing of defects is considered via experimental measurements on artificially induced defects and in service corrosion patches, with results compared to finite element modelling of the interaction of the guided waves with artificial defects. Finite element modelling has been used to better understand the behaviour of different wave modes when they interact with defects, focusing on the mode conversions and reflections that occur. 相似文献
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Routine inspection of oil and gas pipes for time dependent degradation is essential. Pipelines are most commonly inspected using In-Line Inspection (ILI), however restrictions from pipe geometry, features or flow rate can prevent its use. Facility pipework rarely facilitates ILI, and external inspection often warrants the undesirable removal of the pipe insulation and cladding. This work investigates the applicability of a current deflection non-destructive evaluation technique for both the detection and growth monitoring of defects, particularly focusing on corrosion. Magnetic sensors are used to monitor variations in the spatial distribution of the induced magnetic flux density outside a pipe that arise from deflection of an injected electric current around inner or outer wall defects. An array of orthogonal magnetoresistive sensors has been used to measure the magnetic flux density surrounding six-inch schedule 40 seamless and welded carbon steel and austenitic steel pipes. The measurements were stable and repeatable to the order of 100 pT which suggests that the defect detection or growth monitoring of corrosion-type defects may be possible with a few amps of injected current when measurements are taken at around 50 mm lift-off. The sensitivity of the technique is dependent on factors including defect geometry, sensor lift-off, bends, variations in nominal pipe geometry or material properties, and the presence of ferromagnetic objects, each of which were investigated using either experiment or a validated finite element model. 相似文献
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Circumferential higher order guided wave modes for the detection and sizing of cracks and pinholes in pipe support regions 总被引:2,自引:0,他引:2
L. Satyarnarayan J. Chandrasekaran Bruce Maxfield Krishnan Balasubramaniam 《NDT & E International》2008,41(1):32-43
The non-dispersive propagation of ultrasonic guided wave higher order modes cluster (HOMC) traveling along the circumferential direction in a hollow cylinder and its interaction with defects in pipe support regions is reported. These circumferential guided waves were generated in mild steel (MS) pipe specimens containing artificially created axial notches (simulating axial cracks) and pinholes (simulating pinhole-like defects) of different sizes in order to simulate conditions such as cracking and corrosion under pipe supports. The characteristics of these guided waves were also studied as a function of parameters related to how they were generated; namely, using: (a) 2.25 MHz linear phased array transducer, (b) 2.25 MHz conventional circular transducer and (c) 1 MHz conventional circular transducer. These higher frequency modes were explored for their ability to detect and size defects. Because of access limitations to the pipe support region in actual field testing, the transducer was always placed at a fixed circumferential position and moved axially along the length of the pipe. The defect position along the circumference was ascertained from the time of flight while the defect size was estimated using the amplitude data. The signals obtained for all three transducer configurations are compared for their ability to locate, detect and size the above-mentioned defects. It was shown that at these relatively higher frequencies, the guided wave modes exhibit small dispersion and have the ability to provide improved imaging of small size defects throughout the cross-section of the pipe. 相似文献
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The utility of guided ultrasonic waves for increasing the efficiency and sensitivity of nuclear steam generator tubing evaluation by nondestructive means is explored. The basic theoretical background of guided waves in tubes is presented, with major emphasis placed on those results with direct relevance to NDE applications. The possibility of increasing the inspection range of the guided wave modes as well as their sensitivity to defects by proper choice of mode and frequency is also discussed. 相似文献
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The magnetic flux leakage (MFL) method has very good defect detection and location capabilities, but defect sizing capabilities, especially for sub-surface defect characterisation, are limited. The pulsed magnetic flux leakage (PMFL) technique has recently been introduced and shown to have great potential for automated defect sizing for surface-breaking defects using time-frequency signal processing techniques, but sizing of sub-surface defects has proved problematic. In this paper, pulsed magnetic reluctance (PMR), a new electromagnetic (EM) non-destructive evaluation (NDE) technique, is introduced and incorporated into a dual PMFL/PMR probe for the characterisation of surface and sub-surface defects in ferromagnetic materials. Experimental results from a comparison study of the two techniques using variety of defects analysed using time-frequency analysis show that the techniques offer complementary information, with PMFL providing defect location data and data for the characterisation of surface defects and PMR offering sub-surface defect characterisation capabilities. The work concludes that integration of these inspection techniques in the new pulsed EM probe can provide enhanced defect characterisation capabilities for flux leakage-based inspection systems using relatively simple time-frequency signal processing techniques. 相似文献
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The reflection of guided waves from notches in pipes: a guide for interpreting corrosion measurements 总被引:7,自引:0,他引:7
A. Demma P. Cawley M. Lowe A. G. Roosenbrand B. Pavlakovic 《NDT & E International》2004,37(3):167-180
Ultrasonic guided waves are used for the rapid screening of pipelines in service and simple, standard testing procedures are already defined. The implementation of the method enables the localization of the defects along the length of the pipe and offers a rough estimate of defect size. In this article we present a systematic analysis of the effect of pipe size, defect size, guided wave mode and frequency on the reflection from notches. The maximum and minimum value of the reflection coefficient at varying axial extent are identified and used for the purpose of defect sizing. Maps of reflection coefficient as a function of the circumferential extent and depth of the defect are presented for a 3 in. schedule 40 steel pipe. An approximate formula, which allows these results to be extrapolated to other pipe sizes, is proposed and evaluated. 相似文献
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Henry Scholz CGNPC Inspection Technology Company ChinaCITEC Jinhong Liu Peter Bieder 《无损检测》2010,(9):691-699,703
许多管道和管道系统从外部仅为部分可达甚至完全不可达,如独立管道、水下管道或埋地管道。因此,如果不解决独立问题或去除管道覆盖物,就无法实现管道裂纹或腐蚀的检测,然而解决可达问题或去除覆盖物时需要花费不菲的费用甚至根本不能实现。由此对长距离检测系统产生了需求。对于光杆和管的局部腐蚀检测,业界已经研制成功了基于超声的检测系统[1-3]。然而,目前由于外形尺寸以及费用等,这些系统并不适用于以SHM为目的的检测。为了完成用大量探头单元涵盖一个完整的产业厂房的检测,有必要研发新型的检测硬件、探头技术以及数据评估技术。 相似文献
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Recently, a magnetostrictive patch transducer (MPT) by means of the highly magnetostrictive (such as nickel or iron–cobalt alloy) patch attached on the specimen has been applied in nondestructive ultrasonic testing in waveguides. In the study, we proposed a new MPTs array employing a multi-splitting meander coil (MSMC) for generating and receiving longitudinal guided waves in pipes. In the suggested configuration, the directions of the static magnetic field produced by the permanent magnets and the dynamic magnetic field produced by the MSMC are in the axial direction of the pipe. Two finite element models were established to simulate the distribution of the static and dynamic magnetic fields in the patch, respectively. The proposed MSMC was made of flexible printed circuit (FPC), so it could be easily installed on pipe surface. The performance of the proposed MPTs array was experimentally studied. Firstly, it was experimentally verified that the axisymmetric longitudinal guided wave mode, L(0,2), could be effectively generated and received in pipes with the developed MSMC-MPTs array. Secondly, the frequency response characteristics of the developed MSMC-MPTs array were related to D (the distance between adjacent belts of the MSMC). Thirdly, we demonstrated the ability of the developed MSMC-MPTs array for the identification and location of a crack defect in pipes. Finally, we compared the performances of the MSMC-MPTs array and conventional meander coil-MPTs and proved that the signals of the longitudinal guided wave mode could be enhanced by using the developed MSMC-MPTs array. 相似文献
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Due to the large number of pipe supports over a piping run, a rapid reliable NDT system is needed to identify hidden corrosion defects at a pipe-support interface. To accomplish this, a system using Periodic Permanent Magnet (PPM) Electromagnetic Acoustic Transducers (EMAT׳s) to generate dispersive SH1 guided waves is implemented. For this study, both the effect of the support contact and a corrosion type defect are evaluated independently through finite element models and experiments utilizing a flat plate approximation. It was found that utilizing the SH1 plate wave near the inflection point or ‘knee’ of the dispersion curve yields a high sensitivity to gradual wall loss defects while experiencing a minimal effect from the support contact. 相似文献
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Corrosion inspection on pipelines with shearography Pipelines can be inspected quickly and reliably on inner corrosion by means of laser shearography. During pressure change in the pipe shearography measures all strain concentrations on the surface of the pipe. As corrosion leads to local wall thinnings inside the pipes these areas will expand more than non corroded areas and thus be indicated by shearography from the outside of the pipe. In this paper important features and conditions are described for application of this technique for inspection in power plants. It is reported about experience on practical inspection tasks. Latest developments enable numerical data processing and graphical and coloured data presentation for easier defect recognition. 相似文献
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To Kang Dong-Hoon Lee Sung-Jin Song Hak-Joon Kim Young-Do Jo Hyun-Joon Cho 《NDT & E International》2011,44(2):178-187
Ultrasonic guided waves have been widely utilized for long range inspection of structures such as oil and petrochemical pipes. However, weldments, support, insulation, and attenuation make it difficult to examine pipe-like structures. In order to overcome such difficulties, it is desired to focus ultrasonic guided wave at the area under interrogation. In this paper, we discuss two focusing techniques: angular profile tuning and signal based focusing. The angular profile tuning approach relies on a theoretical prediction of pressure field of ultrasonic guided wave produced by an ultrasonic transducer mounted on the pipe. And, the signal based focusing is focusing ultrasonic guided waves using cross-correlation analysis. To compare the performance of these two techniques, non-axisymmetric guided waves are focused to abnormalities such as a through-wall hole and a circumferential notch, using an ultrasonic guided wave array system that has been specially fabricated for this purpose. The advantages and limitations of these two focusing techniques are addressed. 相似文献
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In this work, we propose a crossed-coil magnetostrictive sensor consisting of a solenoid coil, a toroidal coil, and a ferromagnetic patch for generating and detecting torsional waves for pipe inspection. We show that the direction of the magnetic field of the ferromagnetic patch can be controlled by adjusting the input current to the toroidal coil. In addition, it is found that the amplitudes of the signals reflected from the pipe end using a crossed-coil sensor are much larger than those using pre-magnetization techniques, and excitation energies are used to generate the torsional waves only. From results on pipes with multiple circumferential notches, any defects larger in diameter than three times the pipe thickness were detected using the crossed-coil magnetostrictive sensor. 相似文献