Detection of internal crack growth in polyethylene pipe using guided wave ultrasonic testing

Despite the success of guided wave ultrasonic inspection for internal defect detection in steel pipes,its application on polyethylene(PE)pipe remains relatively unexplored.The growth of internal cracks in PE pipe severely affects its pressure-holding capacity,hence the early detection of internal cracks is crucial for effective pipeline maintenance strategies.This study extends the scope of guided wave-based ultrasonic testing to detect the growth of internal cracks in a natural gas distribution PE pipe.Laboratory experiments and a finite element model were planned to study the wave-crack interaction at different stages of axially oriented internal crack growth with a piezoceramic transducer-based setup arranged in a pitch-catch configuration.Mode dispersion analysis supplemented with preliminary experiments was performed to isolate the optimal inspection frequency,leading to the selection of the T(0,1)mode at 50-kHz for the investigation.A transmission index based on the energy of the T(0,1)mode was developed to trace the extent of simulated crack growth.The findings revealed an inverse linear correlation between the transmission index and the crack depth for crack growth beyond 20%crack depth.

Defects detection in typical positions of bend pipes using low-frequency ultrasonic guided wave

In order to analyze the possibility of detecting defects in bend pipe using low-frequency ultrasonic guided wave, the propagation of T(0,1) mode and L(0,2) mode through straight-curved-straight pipe sections was studied. FE(finite element) models of bend pipe without defects and those with defects were introduced to analyze energy distribution, mode transition and defect detection of ultrasonic guided wave. FE simulation results were validated by experiments of four different bend pipes with circumferential defects in different positions. It is shown that most energy of T(0,1) mode or L(0,2) mode focuses on extrados of bend but little passes through intrados of bend, and T(0,1) mode or L(0,2) mode is converted to other possible non-axisymmetric modes when propagating through the bend and the defect after bend respectively. Furthermore, L(0,2) mode is more sensitive to circumferential notch than T(0,1) mode. The results of this work are beneficial for practical testing of pipes.

Axial power flow distributions of ultrasonic guided waves in viscous liquid-filled pipes

The axial power flow (APF) magnitude and attenuation distributions of ultrasonic longitudinal guided waves in viscous liquid-filled elastic pipes are investigated. The optimal location, optimal mode and its frequency-thickness product (fd) for the test of pipes filled with viscous liquid are chosen according to APF and attenuation distributions. The results show that the APF magnitude distribution is an important parameter in choosing the modes and parameters. A particular mode has weak dispersion in ranges of fd values with large group velocity, while other modes with smaller group velocity in the same fd ranges have stronger dispersion. It has been observed that, within these ranges, the chosen mode has a larger APF on the (pipe’s) wall. Therefore, in the region of fd values where a particular mode has a large group velocity, this mode will be effective to be used in testing elastic pipes filled with viscous liquid. The results obtained from both the APF analysis and attenuation distribution are consistent.

Guided Waves Mode Discrimination in Pipes NDT Based on the Matching Pursuit Method

Ultrasonic guided wave have the multi-modes and dispersive characteristics, and its modes are easy to be converted at boundary or when running into defects in pipes, which makes the discrimination of different guided waves modes of the reflection signals in pipes NDT very hard. In this work, firstly, the experiments are carried out to test two kinds of stainless steel pipes by applying guided waves NDT, one is integrated pipe and another is non-integrated pipe with a small hole defect, and the detected guided waves echo signals are respectively obtained. Secondly, the measured signals are processed by matching pursuit method and the Chirplet matching atom parameters are calculated. By calculating the time-frequency distributions spectrum of detected guided waves echo signals, torsional, flexural and longitudinal guided waves modes are identified from the intact pipe, and the two wave-packets with torsional and flexural guided waves modes are also identified from the pipe with hole defect. The results showed that the matching pursuit method has a tremendous advantage to identify different guided waves modes in pipes nondestructive testing.

Pipe Inspection System by Guide Wave Using a Long Distance Waveguide

In the industrial fields, many high temperature structures that require a non-destructive inspection exist. However, there are currently few sensors that can carry out non-destructive testing in a high temperature environment. In particular, the ultrasonic sensor is normally not used at over 50 degrees Celsius. Also, a special sensor for high temperature is currently available, but there are various constraints;it has not yet reached a level that is useful in industry. Therefore, we have been developing a new sensor system using a long waveguide which can transmit an ultrasonic wave from a long distance. Especially, this study focuses on applying the developed technique to a pipe which is used in a nuclear power plant. Therefore, the best rectangular-shaped waveguide was studied and attempted to be wound around a pipe to be driven by an acoustic source of a guide wave. Finally, the L (0, 2) and T (0, 1)-mode guide waves were successfully detected by optimizing the shape of the opposite edge of the rectangular-shaped waveguide that could detect the reflected signal from an artificial defect machined into a test pipe.

A New Guide Wave Inspection System Using Three Polarized Transverse Wave EMATs without Any Couplant

A guide wave is provided with the characteristic of long range propagation in the axis direction of a pipe, so it is possible to detect many defects over a large pipe area at once. At present, there is a technique to generate a guide wave using a piezoelectric element (PZT). However, the transverse wave-transducer using PZT needs to require a high viscosity couplant because the transverse wave cannot travel into typical liquid like water or oil. A guide wave inspection system that uses an electromagnetic ultrasonic transducer (EMAT) which does not require any couplant has then been developed to solve this trouble. First, a guide wave into a pipe, L, T and F-mode, can be transmitted and received by a polarized shear horizontal transverse wave propagating to the thickness direction when the vibration direction has been adjusted to the best direction. At next stage, the three EMATs for L, T and F-mode with different polarized vibration directions were piled up to improve the performance at the same position under the permanent magnet to inspect the pipe at the same condition. Next, the system with the EMATs can be confirmed to be able to detect three guide wave modes signal with enough intensity. Finally, the detection performance using the test pipes with any artificial defects has been done by the developed pipe inspection system, and any drilled holes and any notches can be detected. It is indicated that the developed system could be useful in real industrial field.

Study of an Ultrasonic Probe Installed into a Small Diameter-Pipe Using an Electromagnetic Acoustic Transducer

Metal pipes having an inner diameter of about 25 mm or less are frequently used as heat exchangers for power plants, gas pipes, and water pipes. However, erosion and corrosion due to long-term use may cause serious accidents, such as steam leaks, resulting in economic loss and environmental pollution. Therefore, inspection of the entire length and thickness before shipping or monitoring during operation are important technologies. However, no inspection technology including the inside of the wall thickness has been developed. The purpose was to develop an ultrasonic probe that can inspect the inner and outer surfaces from the inside of the pipe at the same time. The developed ultrasonic probe is based on an electromagnetic ultrasonic transducer (EMAT) that does not require a couplant and is then easy to install in a pipe. The EMAT for the longitudinal and for the transverse vibration mode guided wave are connected in series in order to take into account the variety of defects. First, the EMAT was successfully developed for each mode. That is, it was conducted by using the magnetostrictive effect for the longitudinal mode type and by using the Lorentz force for the transverse mode type, and evaluated to improve the performance. The reflected signal from a notch defect was then evaluated in the state that each EMAT was connected in series using any artificial defects and found to be able to detect any notches with about 10% depth or about 15% circumferential length.

超声导波波包宽度与管材内径-壁厚比的关系

在自由管材的情况下,在各传播距离、各频厚积和各激发脉冲周数上,分析了内径-壁厚比和管材中较低阶纵向导波模式波包宽度的关系.分析结果表明:当内径-壁厚比较小时,内径-壁厚比的变化对各导波模式的波包宽度有较大影响,但随内径-壁厚比的增加,这种影响将减小;内径-壁厚比对导波波包宽度的影响随导波模式阶次的增加而减小.另一方面,对于不同内径-壁厚比的管材,检测中应当用不同的导波模式,所用的激发脉冲周数和频厚积也应当不同.

铝合金化学镀Ni-P/Ni-B双层复合镀层及其性能研究

基于雷达波导管内表面电镀银层工作时极易被臭氧(O3)氧化腐蚀,从而影响到使用可靠性。为了解决雷达波导管内表面既具有优良导电性能又耐臭氧腐蚀的技术要求,对铝合金化学镀Ni-P/Ni-B双层复合合金镀层的操作方法、工艺条件及主要性能进行了研究,结果表明,若用Ni-P/Ni-B化学镀层替代电镀银层,导电性能有所降低,而耐臭氧腐蚀性能明显增强。

厚壁管道轴向裂纹对C-SH_(0)模态反射特性的影响

采用有限元方法分析了激励信号的中心频率、轴向裂纹长度、缺陷深度和缺陷位置对周向超声导波反射的影响。利用时域反射系数R评价了轴向裂纹反射回波强度随缺陷尺寸和中心频率的变化趋势。对于一定尺寸的非贯通轴向裂纹,当中心频率从55kHz增加到110kHz时,周向水平剪切模态(C-SH_(0))的R略有增加。在给定的中心频率下,随着裂纹长度的增加,R先增大后减小,再进入振荡区,最后趋于稳定。因此,得出C-SH_(0)模态对内部缺陷和外部缺陷具有相同的敏感性的结论。最后确定了不同轴向范围内R的最大值和最小值,可用于缺陷尺寸的定量分析。

DETECTION OF LONGITUDINAL DEFECT IN PIPES USING TORSIONAL MODES

The multi-modes and disperse characteristics of torsional modes in pipes are investigated theoretically and experimentally. At all frequencies, both phase velocity and group velocity of the lowest torsional mode T（0,1） are constant and equal to shear wave velocity. T（0,1） mode at all frequencies is the fastest torsional mode. In the experiments, T（0,1） mode is excited and received in pipes using 9 thickness shear vibration mode piezoelectric ceramic elements. Furthermore, an artificial longitudinal defect of a 4 m long pipe is detected using T（0,1） mode at 50 kHz. Experimental results show that it is feasible for longitudinal defect detection in pipes using T（0,1） mode of ultrasonic guided waves.

Applications of Ultrasonic Techniques in Oil and Gas Pipeline Industries: A Review

The diversity of ultrasound techniques used in oil and gas pipeline plants provides us with a wealth of information on how to exploit this technology when combined with other techniques, in order to improve the quality of analysis. The fundamental theory of ultrasonic nondestructive evaluation (NDE) technology is offered, along with practical limitations as related to two factors (wave types and transducers). The focus is limited to the two main techniques used in pipe plants: First, straight beam evaluation and second, angle beam evaluation. The depth of defect (DD) is calculated using straight beam ultrasonic in six different materials according to their relative longitudinal wave (LW) velocities. The materials and respective velocities of LW are: rolled aluminum (6420 m/s), mild steel (5960 m/s), stainless steel-347 (5790 m/s), rolled copper (5010 m/s), annealed copper (4760 m/s), and brass (4700 m/s). In each material eight defects are modeled;the first represents l00% of the material thickness (D), 50.8 mm. The other seven cases represent the DD, as 87.5% of the material thickness, 75%, 62.5%, 50%, 37.5%, 25%, and 12.5%, respectively. Using angle beam evaluation, several parameters are calculated for six different reflection angles (βR) (45°, 50°, 55°, 60°, 65° and 70°). The surface distance (SD), ½skip distance (SKD), full SKD, and 1½SKD,½sound path (SP) length, full SP, and 1½SP are calculated for each βR. The relationship of SKD and SP to the βR is graphed. A chief limitation is noted that ultrasound testing is heavily dependent on the expertise of the operator, and because the reading of the outcome is subjective, precision may be hard to achieve. This review also clarifies and discusses the options used in solving the industrial engineering problem, with a comprehensive historical summary of the information available in the literature. Merging various NDE inspection techniques into the testing of objects is discussed. Eventually, it is hoped to find a suitable technique combined with ultrasonic inspection to deliver highly effective remote testing.

低频导波检测技术在输油场站应用的效果分析

本文主要是对低频导波检测技术原理和应用进行分析,进而选取本次最优开挖验证点,通过MsS长距离超声导波检测仪在姬塬外输总站管网腐蚀检测过程中的应用效果分析,判断其应用效果具有哪些局限性和优缺点,为后续输油场站常规检测工作提供参考依据。

含初应力各向异性层合管纵向导波频散特性分析

基于勒让德级数法,联立增量变形理论,分析了含初应力各向异性层合管中纵向导波的频散特性,探讨了初应力场下导波传播的过程。相较传统级数展开法,通过利用正交完备性与递推特性,可有效地避免冗余的积分运算。基于所提联合理论方法,将其与不含应力的单层复合材料空心圆管纵向导波频散曲线进行对比,验证了所提理论方法的有效性。随后,数值计算了不同堆叠顺序下单向纤维层合管的导波频散曲线,揭示了中间层纤维角度对纵向导波频散特征的影响规律。最后,计算了不同初应力状态下的单向纤维层合管的纵向导波频散曲线,并讨论了初应力对各向异性层合管的纵向导波传播特性的影响规律。通过对比分析,为含初应力的各向异性层合管的无损检测与评估提供了理论支持。

管道中激发L(0,2)导波的EMAT结构设计及优化

超声导波在管道中传播时具有多模态特性,导致超声导波检测的回波信号复杂难以分辨。依据EMAT激发机理和纵向超声导波的波结构特性,设计一种周期性永磁铁组以增大洛伦兹力轴向分量、减小径向分量,激励纯净的L(0,2)模态导波。研究永磁铁宽度对L(0,1)模态抑制效果的影响规律,得到控制效果较好的永磁铁宽度。结果表明:相比传统EMAT,新型EMAT对L(0,1)模态抑制效果显著,L(0,2)模态与L(0,1)模态峰值之比是传统EMAT的7.62倍。

基于频域合成孔径聚焦的输电线路钢管杆超声导波成像检测

输电线路钢管杆结构是一种带有拔梢斜度的大口径薄壁管,超声导波周向B扫描检测传感器激发的超声导波在钢管杆传播过程中存在波束扩散现象。为了解决钢管杆超声导波检测过程中波束扩散导致周向检测分辨率降低的问题,提出了一种钢管杆超声导波频域合成孔径聚焦方法(Synthetic Aperture Focusing Technique,SAFT)。采用文中构建的超声导波合成孔径成像检测装置对直径为608 mm的钢管杆进行超声导波扫查,可获得周向B扫描图像和频域合成孔径聚焦图像。对比钢管杆周向B扫描图像和频域合成孔径聚焦图像,频域合成孔径聚焦图像中散射体和通孔的周向检测分辨率明显优于B扫描图像,文章提出的钢管杆超声导波频域合成孔径聚焦方法能够显著改善超声导波周向检测分辨率。

基于超声导波的钢管杆件损伤探测模拟

为研究网架结构中钢管杆件损伤缺陷检测的问题,选择在杆端施加位移的方式进行有限元分析。考虑超声导波需要具有在特定频率范围内不发生频散的特征,选择L(0,2)模态超声导波开展无损检测。分析了适用于钢管无损检测的导波信号频率和信号周期特征,利用L(0,2)模态超声导波进行了不同圆周夹角的周向缺陷和不同长度轴向缺陷的导波检测。有限元分析结果表明,考虑多模态叠加和最大反射率的影响,频率为70 kHz周期为10的Hanning正弦信号激励的超声导波适用于钢管杆件的缺陷检测;当钢管缺陷宽度与深度不变时,周向损伤占圆周的比值与信号平均反射率成线性正比关系。对于杆件的轴向裂纹检测,可以利用信号反射率与裂纹宽度的关系进行对比判断。

采用矩阵束方法的复合材料圆管周向导波频散数据获取

基于矩阵束算法,提出了一种从弧形阵列采集数据中获取复合材料圆管多模态周向导波频散数据的方法。首先根据留数定理,给出了频率域导波响应信号的多模态周向导波叠加公式,构建了阵列导波信号的Hankel矩阵;然后通过求解Hankel矩阵的广义特征值获取了导波的频散数据,给出了综合利用正向和反向接收弧形阵列处理结果降低频散数据中噪声的方法;最后,设计了碳纤维复合材料圆管中周向传播导波信号的测量实验,利用矩阵束方法获取了圆管周向导波的频散数据,并与采用半解析有限元方法模拟的理论频散曲线进行了对比分析。理论频散曲线与实验数据吻合良好,表明该方法具有很强的鲁棒性,即使采用空气耦合换能器作为发射接收阵列,也可以有效地从弧形阵列波形信号中获取周向导波的频散数据。

水载压力对管道超声导波信号的影响研究

为了研究水载压力对管道超声导波信号的影响,利用半解析有限元的方法分析了管道导波的频散曲线和波结构,选择L(0,2)模态导波用于实验验证。设计了一个可承受30 MPa压力的防水卡箍,对管道上的压电传感器进行封装。将安装了防水耐压卡箍的管道放入压力舱中进行打压循环测试,压力在0~30 MPa之间变化。打压过程中采集无损伤及5%损伤的管道超声导波信号,分析水载压力对导波信号的影响。实验结果表明,该防水卡箍具有良好的防水和耐压性能,水载压力对L(0,2)模态导波信号幅值没有显著影响。

单向L(0,2)超声导波EMAT结构设计

超声导波在管道中传播时双向传播的特性以及端面反射回波的影响导致检测回波信号复杂难以分辨。依据电磁声换能器(EMAT)激发机理和纵向超声导波的波结构特性,设计了一种周期性永磁铁增强径向偏置磁场,从而增大洛伦兹力轴向分量、减小径向分量来控制激发单一L(0,2)导波;同时依据波叠加原理,通过控制相邻线圈线间距、激励电流方向和延迟时间等来选择纵向超声导波的激发方向。研究结果表明:当相邻激励线圈电流相反、线间距为λ/4,且延迟时间为T/4时,采用优化设计的周期性永磁铁可以实现管道中超声导波的方向控制,使得回波信号容易分辨,提高了管道的检测效率。