A method of probabilistic analysis for steel pipeline with correlated corrosion defects

A method of probabilistic analysis is presented to consider effect of correlation of corrosion defects on steel pipeline failure. Failure probability of pipeline with correlated corrosion defects is modeled and compared with results from conventional method. The results showed that assumption of independent corrosion defects will lead to conservative results. The calculated results are within Ditlevsen bimodal bounds. This indicates the validity and feasibility of the proposed method. The combined effect of both the model sensitivity of prediction to variables and the uncertainty of variables should be taken into account in sensitivity analysis.     

Metal defects sizing and detection under thick coating using microwave NDT

An experimental study to evaluate shapes and sizes of defect under thick coating by microwaves NDT is demonstrated. Specially fabricated thick fire protect coated steel panels with embedded defects are inspected using an X-band (8.2–12.4 GHz) open-ended rectangular waveguide. The fundamental idea behind using this probe is presented along with several experimental results to validate this method for defect detection under coating. The reflected signal related to the phase and magnitude of the reflection coefficient at the waveguide aperture is used to create images of these coated samples under test. These images indicate the ability of microwaves for identifying and sizing defects under thick coating layer. Linear sweep technique is used here to obtain multiple frequency spectrum variances. Principle Component Analysis (PCA) algorithms have been employed to enhance the resolution of our proposed method. A series of performance comparison with PCA algorithms are also provided to extract the defect features from thick coating layer influence. To evaluate the proposed technique, steel with known defect and five coated steel plates with unknown defect under different coating thickness are measured. Results indicate that the defect detection capability has been enhanced with the suitable use of signal processing methods.     

Leaky Lamb waves for the detection and sizing of defects in bonded aluminium lap joints

The possibility of using ultrasonic leaky Lamb waves in a pitch and catch configuration for detecting and sizing defects in bonded aluminium lap joints is presented in this paper. Based in Transfer Matrix method the dispersion curves and the propagation modes behaviour are obtained. First the experimental scattering effects of circular holes with different dimensions on the fundamental symmetric mode S₀ are analysed and compared with the results obtained by analytical model. Very good agreement with the analytical model used is found. After, using the same methodology, scattering effects produced by artificial defects located in the bond line of lap joints are measured and the results show that the previous model could be used when an estimation of defect dimensions is needed. Finally an empirical relation between an experimental parameter and the defect dimensions is established revealing a high linear correlation meaning. So, this parameter could be used for more accurate defect dimensions evaluation.     

海底用耐腐蚀管线钢X60MOS的开发

随着油气行业的发展,亟需研发一种成本低、海底用、抗酸、综合性能优良的管线钢。参照API SPEC 5L标准,结合抗酸管线钢和海底管线钢的具体指标要求,以热模拟试验为指导,在管线钢生产基础上,通过采用低C、低Mn、低S的化学成分设计;采用连铸凝固末端压下技术;借助X60MOS钢高温应力应变曲线及CCT曲线,制定了合理的加热、轧制及冷却工艺制度,开发出晶粒细小、组织均匀,强韧性匹配优异、综合性能优良的海底用耐腐蚀管线钢X60MOS。     

Development of a magnetic corrosion probe for nondestructive evaluation of concrete against corrosion of reinforcing bar

A new magnetic corrosion probe has been developed for nondestructive evaluation of concrete against corrosion of reinforcing bar. Two types of probes, a thin iron wire (probe A) and an iron-plated copper bar (probe B) were tested whether their changes in residual magnetization with progress of corrosion of iron could be detected using a superconducting interference device (SQUID) magnetometer. The preliminary tests carried out under an atmospheric condition showed that the residual magnetization became less intensive with progress of corrosion for both probes. Then the two types of probes were embedded in mortar for an accelerated corrosion test. The results showed that probe A scarcely corroded in mortar despite that reinforcing bar suffered from corrosion under the identical condition. The probe B corroded as reinforcing bar did, resulting in a sharp decrease in the residual magnetization. Thus, the probe of type B embedded in mortar can give a magnetic warning against degradation of surroundings regarding the corrosion of reinforcing bar.     

长输天然气管道完整性管理与管道腐蚀检测技术

由于天然气管道输送距离较长,管道中途经过的环境具有复杂性,各方面的因素都可能对管道运输产生影响,威胁管道安全,对国家和人民的生命财产安全带来隐患.对天然气管道完整性的管理是对天然气管道进行全方位、系统化的管理,对安全隐患进行排查,避免安全事故的发生.管道在使用过程中,会发生不同程度的腐蚀损坏,工作人员需要对管道内外壁进...     

金属管道未焊透缺陷定量检测方法

为了解决金属压力管道焊接接头中的未焊透缺陷定量检测技术的工程应用问题,选择了数字射线成像技术和相控阵超声技术,对碳钢和不锈钢2种材质焊接试件中的预制未焊透缺陷进行检测,并对缺陷的深度、宽度进行了定量,验证了2种方法在金属管道未焊透缺陷定量检测应用的可行性。结果表明,数字射线技术和相控阵超声技术在金属管道未焊透缺陷特征尺寸的定量检测方面,对于缺陷宽度和深度定量的准确度均可以满足在用含缺陷压力管道焊接接头安全评价的工程需要,数字射线技术在判定缺陷性质方面较有优势;相控阵超声技术检测效率高、无辐射且定量准确。在实际应用中检验人员应综合两种技术的优缺点和应用特点综合选择检测方法。创新点： 将数字射线技术和相控阵超声技术用于金属管道未焊透缺陷定量检测,并对2种技术的精度和可靠性进行了验证,解决了金属压力管道未焊透缺陷定量检测的工程应用问题。     

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...     

Probing the nonuniform corrosion of pipeline weldments under stepwise increasing solution temperature using a coupled multielement electrical resistance sensor

A coupled multielement electrical resistance sensor (MERS) was designed to probe the nonuniform corrosion of an X65 pipeline weldment under a stepwise increasing solution temperature. In conjunction with electrochemical impedance spectroscopy (EIS) measurements, the initiation and propagation of the nonuniform corrosion on different welding areas, that is, base metal (BM), heat-affected zone (HAZ), and welding metal (WM) were well understood. The results show that the contributions of galvanic current (current flowing across the three different welding areas) and internal current (current flowing in a certain welding area) for the steel loss of BM, HAZ, and WM were significantly different under each solution temperature. The main contributor to the steel loss of HAZ gradually transformed from internal current to galvanic current with the solution temperature increasing. The WM would change from anodes to cathodes due to the preprecipitation of the FeCO₃ crystals on WM when the solution temperature increased over 40°C. The BM would transform from cathodes to anodes at 40°C and the steel loss of BM was mainly induced by the internal current in BM over the whole test duration.     

Stochastic process corrosion growth models for pipeline reliability

Linear random variable corrosion models are extensively employed in reliability analysis of pipelines. However, linear models grossly neglect well-known characteristics of the corrosion process. Herein, a non-linear model is proposed, where corrosion rate is represented as a Poisson square wave process. The resulting model represents inherent time-variability of corrosion growth, produces continuous growth and leads to mean growth at less-than-one power of time. Different corrosion models are adjusted to the same set of actual corrosion data for two inspections. The proposed non-linear random process corrosion growth model leads to the best fit to the data, while better representing problem physics.     

Corrosion in artificial defects. I: Development of corrosion

Artificial defects (slots) were milled through a polyurethane topcoat and chromate-inhibited epoxy polyamide primer to the underlying aluminium alloy 2024-T3. The slots were then exposed to neutral salt spray (NSS) for up to 16 days. Prior to and after exposure, the slots were examined using scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDS) and Raman spectroscopy. The milling process generated features on the surface not seen on polished surfaces, including smearing of the matrix alloy and fragmentation of Cu-Fe-Mn-Al intermetallic particles. It was found that the smears and S-phase particles acted as sites for the initiation of corrosion, which eventually developed more generally across the surface.     

音频大地电磁磁场传感器的研制

感应式磁场传感器一直是我国电磁法仪器发展的瓶颈,国外大地电磁法中测量大地磁场主要采用感应式磁场传感器。为此,根据音频大地电磁场源的特点,从感应式磁场传感器的基本原理出发,设计传感器的磁芯和线圈绕组结构以及线圈的谐振频率;另外,采用了磁通负反馈技术和频率补偿的方法,扩展了传感器的频带,得到了在1 Hz～9.8 kHz频带范围内平坦度为±1.5 dB的灵敏度曲线,满足音频大地电磁探测的需要。     

Enhancement of ultrasonic images for sizing of defects by time-of-flight diffraction

A signal processing technique is presented for significantly sharpening the resolution of ultrasonic images, similar to those acquired in the nondestructive evaluation of girth welds in oil/gas pipelines. This enhancement allows a much improved estimate of the exact size of any detected anomaly in the weld, such that fracture mechanics can be used to gauge the probability of weld failure. The algorithm is based on the synthetic aperture focusing technique (SAFT), combined with a variation of Wiener filtering and autoregressive spectral extrapolation. An analytical model of the transducer is used to construct an appropriate reference spectrum for the deconvolution operation, and accounts for the dependence of a beam's frequency spectrum on the position of a flaw relative to the transmitter. Experimental results are used to provide an estimate of the improvement in flaw sizing accuracy.     

Corrosion failure of sensor wire in leak detection system of thermally insulated underground pipeline

Abstract

The leak detection system of a thermally insulated pipeline has frequently malfunctioned due to sensor wire failures. The failures are attributed to the applied sensing current when the insulation becomes wet. Pits were generated by the sensing current and acted as stress concentration sites.     

Feasibility of under-lagging corrosion detection in steel pipe using the magnetostrictive sensor technique

The feasibility of inspecting under-lagging steel pipes without lagging removal using the magnetostrictive sensor (MsS) technique is described. With the MsS technique, elastic waves are launched along the length of a pipe, and reflected echoes from defects such as cracks or corroded areas are detected using noncontacting sensors. Experimental results obtained from 6-m long, 3.8-cm diameter steel pipe samples before and after inducing simulated defects in the pipewall are presented, and the potential capabilities of the MsS technique are discussed.     

On the suitability of induction coils for crack detection and sizing in metals by the surface magnetic field measurement technique

The surface magnetic field measurement (SMFM) technique has proved to be an accurate means for crack detection and sizing cracks in ferrous metals. The technique involves the use of two U-shaped current-carrying wires of sufficiently high frequency while measuring the discontinuity in the resultant magnetic field at the crack edge with an appropriate magnetic field sensor. In this work, we describe a mathematical algorithm to obtain the crack signal from the output of an induction coil used in a SMFM probe. We also discuss the measurement errors due to the coil size and shape. To reduce the measurement errors, we present an algorithm in which the crack signal is recovered by appropriate deconvolution of the coil output signal and its spatial transfer function. The algorithm is then used to recover crack signals for various coil shapes and sizes. The study of the results demonstrates the effectiveness of the algorithm in the case of large coils.     

A damage model for assessing pipeline safety in corrosion environments

Considering such practical pipeline service conditions in the petroleum transportation field as corrosion from harmful media (H₂S, CO₂ etc.) and load from the pressure of flowing petroleum as key factors, the degradation of the mechanical properties of pipeline steels and the corresponding variations in stress states are studied. A damage variable is introduced to reflect the degradation in the mechanical properties of the pipeline due to corrosion. A diluted solution approach is proposed to model the corrosion process of harmful media within the pipeline and the distribution of the damage variable along the radial direction of the pipeline is derived. An approach to the safety evaluation of damaged pipeline is proposed by comparing the instant properties of pipeline steels with servicing conditions.     

Nondestructive sizing and localization of internal microcracks in fatigue samples

A large number of fatigue experiments on standardized samples is required for the development of databases of the fatigue properties of specific material systems. To facilitate such studies, different visual monitoring methods for surface fatigue cracks have been used; however, the problem of monitoring internal fatigue crack initiating during cold dwell fatigue of Ti is much more complicated. This paper describes the development and integration of several nondestructive evaluation methods for monitoring and sizing microcracks in titanium fatigue samples. For in situ monitoring of crack initiation and evolution ultrasonic Lamb wave signals are excited and acquired in the sample continuously during fatigue tests at different levels of fatigue load using a high-speed data acquisition system. Localization of the secondary cracks is done by both the in situ ultrasonic method and an ultrasonic immersion scanning method here referred to as “vertical C-scan” (VC-scan). The VC-scan is developed for imaging small cracks aligned normal to the fatigue sample axis. Microradiography has been performed on fatigue samples to confirm the localization and sizing of the detected cracks with other ultrasonic NDE techniques. The fusion of data from different NDE techniques provides useful information on the initiation, location, shape, size and growth history of fatigue cracks.     

长输管道环焊缝缺陷返修

随着长输管道钢级的提高、壁厚减薄,管材的可焊性越来越低,对管道工程建设质量的要求也越来越高。返修作为管道焊接的最后一道工序,也是最主要的工序,返修质量直接决定着焊接工程的综合效率。详细分析长输管道缺陷的形成和返修工艺,以及操作者需要注意的事项。剖析典型案例,针对不同类型的缺陷,返修时操作手法和工艺也不同。为管道焊道的返修提供一定的参考和借鉴。     

X70级管线钢抗硫化物应力腐蚀开裂实验研究

用三点弯曲方法及SEM?TEM等手段研究了不同组织类型的X70级管线钢硫化物应力腐蚀开裂(SSCC)行为?结果表明,显微组织以均匀细小的针状铁素体为主的管线钢具有优良的抗SSCC性能;这主要是源于针状铁素体内高密度缠结的位错和碳氮化物在位错网络上的沉淀析出起到了强烈的氢陷阱作用?