内螺纹钢管的漏磁检测方法与缺陷识别

轧制无缝钢管时芯棒与管体之间以相对进动的方式高速旋转 ,易在钢管内壁形成内螺纹。内螺纹槽超深的钢管不符合相关质量标准 ,但生产厂却难以检测出内螺纹超深的钢管。用漏磁高速检测技术结合计算机智能识别软件构成的检测方法和系统 ,可探测和识别这些内螺纹 ,能标记超深螺纹位置和持续范围。将检测信息反馈到轧制工艺中 ,可明显提高合格钢管产量。检测结果符合相关标准 YB40 83和 GB/ T1 2 60 6要求     

Variation of the stress dependent magnetic flux leakage signal with defect depth and flux density

The effects of uniaxial stress on the normal (radial) component of the magnetic flux leakage (MFL) signal induced by blind-hole defects for depths of 25%, 50% and 75% of the thickness of the pipe wall were investigated with a pipe wall flux density of 1.24 T. These three defects were on the same surface as the magnetizer and sensor for the MFL signal (near side). A fourth 50% defect was on the pipe wall surface opposite the sensor (far side). Changes of as much as 47% in the MFL signal due to stresses of up to 300 MPa were observed. Increased changes in the stress dependent MFL signal were observed with increasing defect depth. Comparison of the near side and far side 50% defects indicated similar changes in the MFL_pp signal as a function of stress, although the shape of the MFL signals was qualitatively different. The stress dependent MFL signal was also investigated for the near side 50% defect for pipe wall flux densities between 0.65 T and 1.24 T. A linear increase in the effects of stress on the MFL signal with increasing flux density was observed. Results demonstrated that the variation of the MFL signal with stress is primarily a bulk stress effect, although the effect of defect-induced stress concentrations upon the various MFL signals investigated could also be observed.     

高速漏磁检测方法的发展

漏磁检测法已成功应用于各类铁磁性材料的检测中,但当代生产技术的革新和新应用领域的出现对漏磁检测法的检测速度提出了新的挑战.高速漏磁检测的信号出现畸变,制约着检测速度的进一步提高.对此,众多研究人员对信号畸变的机理进行研究,发现磁化滞后效应是影响高速漏磁检测信号的主要因素.当高速运动的钢管通过磁化线圈时,涡流使得管壁内的...     

Wavelet-based permeability compensation technique for characterizing magnetic flux leakage images

The magnetic flux leakage method, used for nondestructive evaluation of ferromagnetic objects, generates greyscale images that are representative of the integrity of the specimen. Defective areas typically appear as bright regions in the image. Unfortunately, the task of defect characterization becomes more challenging due to the effects of variations in the test parameters associated with the experiment. One such test parameter is the permeability of the test object. Conventional invariant pattern recognition algorithms are not capable of performing invariance transformations to compensate for such variations. This paper describes a novel technique that uses wavelet basis functions to provide selective invariant features and eliminate image intensity variations from undesirable changes in operational variables. The performance of the invariance transformation is demonstrated by applying the method to magnetic flux leakage images obtained using a finite element simulation of in-line inspection of natural gas transmission pipelines.     

GCr15钢滚珠丝杠感应淬火漏磁控制及耐磨性

通过涂覆导磁体对GCr15钢滚珠丝杠表面感应淬火进行漏磁控制,对比分析了漏磁控制前后试样淬火组织、硬度、深度及耐磨性.研究表明:GCr15淬火后的组织为马氏体+残留奥氏体,控制漏磁淬火工艺显著增加丝杠滚道处的磁力线密度,提高整个丝杠表面的温度和加热深度,增加淬火硬化层的深度,也减小硬度曲线的梯度,从而显著提高了耐磨性,相对于未淬火试样耐磨性提高了2.5 ～4倍.感应淬火试样的磨损主要是磨粒磨损和剥层磨损,未涂覆导磁体时,剥层厚且是脆性和塑性断口混杂的粗糙形貌,而涂覆导磁体后,因为组织和硬度均匀,硬化层深度大,磨削片层薄且表面光整,耐磨性好.     

Magnetic flux leakage by adjacent parallel surface slots

This paper clarifies the relation between the magnetic flux leakage signals caused by two adjacent parallel slots on a metal surface and the distance between the two. The depth of smaller slot can be evaluated by considering an effect that the amplitude of leakage flux decreases as the depth ratio of two slots and the slot-to-slot distance increase. A new method is proposed as an alternative to analysing the waveform: it is based on the analysis of locus of the vector consisting of tangential and normal components of the magnetic flux leakage signals.     

Experiment and simulation study of 3D magnetic field sensing for magnetic flux leakage defect characterisation

Magnetic flux leakage (MFL) testing is widely used to detect and characterise defects in pipelines, rail tracks and other structures. The measurement of the two field components perpendicular to the test surface and parallel to the applied field in MFL systems is well established. However, it is rarely effective when the shapes of the specimens and defects with respect to the applied field are arbitrary. In order to overcome the pitfalls of traditional MFL measurement, measurement of the three-dimensional (3D) magnetic field is proposed. The study is undertaken using extensive finite element analysis (FEA) focussing on the 3D distribution of magnetic fields for defect characterisation and employing a high sensitivity 3-axis magnetic field sensor in experimental study. Several MFL tests were undertaken on steel samples, including a section of rail track. The experimental and FEA test results show that data from not only the x- and z-axes but also y-axis can give comprehensive positional information about defects in terms of shape and orientation, being especially advantageous where the defect is aligned close to parallel to the applied field. The work concludes that 3D magnetic field sensing could be used to improve the defect characterisation capabilities of existing MFL systems, especially where defects have irregular geometries.     

Mechanical damage detection using magnetic flux leakage tools: modeling the effect of dent geometry and stresses

We have used three-dimensional (3D) magnetic finite element analysis (FEA) to simulate the MFL signal from a circular dent geometry with associated residual stresses. Strain distribution information around the dent was obtained from an earlier work using finite element structural modeling. In the magnetic FEA dent model, the localized residual stresses were simulated by assigning appropriate values of magnetic anisotropy to the relevant magnetic regions. The simulated flux leakage patterns were found to be in good agreement with the experimentally observed MFL patterns associated with dent shape as well as with the stress effects from the dent.     

The influence of modeled B–H curve on the density of the magnetic leakage flux due to a flaw using yoke-magnetization

Factors which influence magnetic leakage flux density due to a flaw in magnetic leakage flux testing are the shape and dimensions of the flaw, the B–H curves, the magnetizing conditions, lift-off, etc. The influence of B–H curves which were approximated by two lines was already reported and it was documented that both initial permeability and the magnetic flux density in the saturation state are the influence parameters. In the study we discuss here, we will document that the phenomenon of magnetic saturation—observed near the bottom of the flaw—is an essential effect when we concentrate on the influences of two parameters, i.e. the average magnetic flux density in a specimen and the intensity of magnetic field, both producing changes of the magnetic leakage flux density by using B–H curves modeled according to a two lines approach.     

Imaging defects with reduced space inversion of magnetic flux leakage fields

Magnetic flux leakage technique is being used for detection of defects inside a magnetically permeable bar by measuring the leakage fields outside the bar. Defects in magnetically permeable bar have been modeled as localized anti-dipoles whose moments and locations have to be determined. Generalized inverse or pseudo-inverse technique has been used to image the defects using least-square minimum-norm solution. An initial estimate of the defects is obtained by utilizing the generalized inverse of the lead matrix over the entire region of the sample space using the measured magnetic field data including random noise. By defining a suitable threshold, and ignoring the defect locations where the moment inferred in the initial estimate was below the chosen threshold, the image of the defect is again obtained by repeating the calculation in this reduced space for the lead matrix. The leakage fields from both a line defect and a deeply buried defect were simulated and utilized for inversion using this approach. It has been possible to image the defects and quantify the strengths of the moments with the correlation coefficient approaching unity for low-noise case and attain significant improvement in the correlation coefficient for data with reasonable levels of noise.     

Defect localization by orthogonally projected multiple signal classification approach for magnetic flux leakage fields

Magnetic flux leakage technique is used for defect detection inside a magnetically permeable bar by measuring the leakage fields outside the bar. Defects of varying sizes in a magnetically permeable bar have been modelled as localized anti-dipoles with different moments. These defect locations and moments have to be determined based on the measurement of the leakage fields in the presence of random noise. Multiple Signal Classification (MUSIC) approach has been used to identify the defect locations and the moments of these defects. After finding the location of the first dipole representing the larger defect, using orthogonal projection of the measured magnetic field data away from the first defect location, location of the next dipole is identified by MUSIC. This process is continued until all the defects are exhausted. The leakage fields from three deeply buried defects were simulated by direct forward calculation and the resulting data were utilized for inversion using this approach. It has been possible to identify the number of defects and their locations by this approach even in the presence of reasonable levels of additive noise.     

Corrosion of galvanised steel cord reinforcement in HDPE composite pipes in petroleum production

In this work, corrosion of galvanised steel cord reinforcement in high density polyethylene (HDPE) composite pipes was studied in electrolytes that developed on the cord surface due to permeation of corrosive species through HDPE liner or damage of the liner in petroleum production. Parametric effects, including solution pH, temperature and concentration of chloride ions, were investigated by electrochemical corrosion measurements. A model was developed to illustrate the mechanism of corrosion of the cord. Corrosion of the galvanised steel cord includes anodic dissolution of Zn coating and the steel substrate. A deposit layer of zinc carbonate and iron carbonate forms on the cord surface to provide protection to further corrosion in the environment. Corrosive ions can diffuse into holes or crevices of the cord assembly to cause corrosion of galvanised steel wires in inner layers. The unique geometry of the cord assembly results in an accelerating localised corrosion at the crevices and holes. Generally, corrosion of the cord is accelerated by increased chloride concentration, reduced solution pH, and elevated temperature.     

纳米铝热体系制备陶瓷复合钢管组织及性能

采用纳米铝热体系制备了陶瓷复合钢管,研究了纳米铝热剂中添加4%Na2B4O7+2%、4%、6%、8%(质量分数)纳米SiO2对其组织性能的影响。XRD分析结果表明,陶瓷层主相为α-Al2O3和FeAl2O4,杂相为Al2SiO5和B2O3;金相显微镜和SEM观察表明,α-Al2O3枝晶较细,排布密集,FeAl2O4呈晶间分布;测试结果表明陶瓷致密度可达95%,压溃强度和压剪强度分别可达499 MPa、22.6 MPa。     

NDT flaw mapping of steel surfaces by continuous magnetic Barkhausen noise: Volumetric flaw detection case

This paper reports the use of a non-destructive, continuous magnetic Barkhausen noise (CMBN) technique to investigate the size and thickness of volumetric defects, in a 1070 steel. The magnetic behavior of the used probe was analyzed by numerical simulation, using the finite element method (FEM). Results indicated that the presence of a ferrite coil core in the probe favors MBN emissions. The samples were scanned with different speeds and probe configurations to determine the effect of the flaw on the CMBN signal amplitude. A moving smooth window, based on a second-order statistical moment, was used for analyzing the time signal. The results show the technique's good repeatability, and high capacity for detection of this type of defect.     

Advanced signal processing of magnetic flux leakage data obtained from seamless gas pipeline

Natural gas is normally transported through a vast network of pipelines. A major segment of this network employs seamless pipes. The manufacturing processes associated with the production of seamless pipes contribute to a helical variation in the grain properties of the pipe. This introduces an artifact, known as the seamless pipe noise (SPN), in the data obtained from magnetic flux leakage (MFL) inspection of these pipelines. SPN can overwhelm the signals generated by defects and other elements in pipelines, and can therefore, mask their indications in the MFL data. This paper presents a new technique for detecting signals in MFL data obtained from seamless pipes. The overall approach employs an adaptive filter and a wavelet based de-noising technique. The algorithm is computationally efficient and data independent. Results from application of the approach to data from field tests are presented.     

一种改进的支持向量回归三轴管道漏磁缺陷量化方法

为了提高管道漏磁内检测缺陷量化技术的精度,基于三轴漏磁内检测器采集到的缺陷漏磁数据,设计了一系列针对管道轴向、径向以及周向的特征提取方法,为后续进行缺陷的高精度量化提供了数据基础.针对缺陷不同尺寸量化任务下特征冗余的问题,基于近邻成分分析提出一种特征选择方法,该方法能够有效地剔除原始特征集中的无关特征.在基于支持向量回...     

Residual magnetic field variation induced by applied magnetic field and cyclic tensile stress

Magnetic memory testing (MMT) method is a novel non-destructive testing technique due to its unique advantages of stress concentration identification and early damage detection for ferromagnetic materials. However, a thorough understanding of the impact of exciting magnetic source and cyclic stress on the residual magnetic field variation has not been clearly addressed. The surface magnetic memory signal H_p(y) induced by applied magnetic field and cyclic tensile stress was measured throughout the fatigue process. The correlation of H_p(y) and its gradient K changes with loading cycles and applied magnetic field intensity H reported. The results show that applied magnetic field can only change the magnitude of MMT signal instead of changing the H_p(y) curve׳s profile. The H_p(y) value increases with the increase of the H, and the K value is approximately linear to the H. The maximum gradient K_max indicating the degree of stress concentration increases with the increase of either stress cycles or H. The phenomenon was also discussed from the view of the magnetic dipole in a ferromagnet.     

不锈钢活性激光焊工艺研究

以不锈钢SUS304作为试验对象,分别研究了焊接速度、散焦离焦量、激光功率和保护气体等工艺参数以及活性剂和活性元素硫对不锈钢YAG激光焊焊缝成形的影响.试验结果表明,各焊缝表面成形良好,焊接速度和激光功率能明显影响焊缝成形,散焦离焦量和保护气体种类对YAG激光焊焊缝成形的影响较小.与硫含量较低的情况相比,活性剂和活性元素硫含量较高的情况下均能使得焊缝熔宽发生明显收缩,随着热输入量增加,活性剂增加熔深的效果也越明显,表明活性剂对熔深的影响效果与焊接过程的热输入量有密切联系.     

在役钢丝绳漏磁检测信号波形分析与应用

在钢丝绳定量无损检测中,检测信号经过放大、滤波等处理后由计算机采集和判别,但计算机自动判别的结果有时和钢丝绳实际情况有一定的出入,如何减小探伤差异、对检测仪检测出的波形进行具体的分析、甄别和判断尤为重要,本文从应用的角度给予了详细分析。     

结构钢用气体保护药芯焊丝的发展趋势

以日本神钢、林肯电气集团、液化空气焊接集团、伊萨集团的产品为例,介绍了结构钢用气体保护药芯焊丝中的金红石型（T一1型）、碱性（T一5型）和金属粉型的发展趋势。金红石型药芯焊丝具有优良的焊接工艺性能和适当的力学性能,仍然是结构钢药芯焊丝中应用最普遍的品种;碱性药芯焊丝焊接工艺性能较差,品种在减少,这种药芯焊丝具有优良的冲击性能和抗裂性;金属粉型药芯焊丝由于其较高的熔敷速度和少量的渣正在得到更广泛的应用,其市场份额的提升很可能会压缩金红石型药芯焊丝的市场占有率。