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.

Lateral compression and energy absorption of foamed concrete-filled polyethylene circular pipe as yielding layer for high geo-stress soft rock tunnels

Foamed concrete as energy absorption material for high geo-stress soft rock tunnels has been proven to be feasible due to its high compressibility and lightweight.However,the lengthy curing and defoaming problems caused by the cast-in-place method of large-volume foamed concrete remain unsolved.In this study,we propose a novel energy absorber composed of foamed concrete-filled polyethylene(FC-PE)pipe and analyze its deformation and energy absorption capacity via quasi-static lateral compression experiments.Results show that FC-PE pipes exhibit typical three-stage deformation characteristics,comprising the elastic stage,the plastic plateau,and the densification stage.Furthermore,the plateau stress,energy absorption,and specific energy absorption of the specimens are 0.81–1.91 MPa,164–533 J,and 1.4–3.6 J/g,respectively.As the density of the foamed concrete increases,the plateau stress and energy absorption increase significantly.Conversely,the length of the plastic plateau and energy absorption efficiency decrease.Moreover,based on the vertical slice method,progressive compression of core material,and the 6 plastic hinges deformation mechanism of the pipe wall,a theoretical calculation method for effective energy absorption is established and achieves good agreement with experimental results,which is beneficial to the optimization of the composite structure.

MORPHOLOGY AND PROPERTIES OF LINEAR LOW-DENSITY POLYETHYLENE HIGHLY LOADED WITH ALUMINUM HYDROXIDE

An experimental study was carried out to investigate the effects of isopropoxy tri(dioctyl pyrophosphoryl) titanate coupling agent on the mechanical performance, rheological property and microstructures of polyethylene highly loaded with aluminum hydroxide (Al(OH)(3)) composite, It was found that the addition of coupling agent results in reduced tensile strength and increased percentage elongation of the filled systems. Silane crosslinkable polyethylene substituting for polyethylene as matrix improves the tensile strength of the composite, while the percentage elongation of the composite still remains at a desired level. Melt viscosity of the composite will be improved by addition of titanate coupling agent. Microstructures of the composites were also studied by means of the scanning electron microscopy (SEM) technique. SEM micrographs reveal that finer dispersion of Al(OH)(3) will be obtained upon treatment of titanate and a transition from brittle to tough fracture takes place before and after silane crosslinking structure is introduced into polyethylene highly filled with Al(OH)(3) composite.

Study on fracture characteristic of welded high-density polyethylene pipe

Crack opening displacement(COD) was applied to characterize the fracture initiation of the tough high density polyethylene. Normal single side notched three point bend specimens and silica rubber replica techniques were used to study the characteristic COD of high density polyethylene pipe and its butt fusion joints including the weld fusion zone and heat affected zone at different temperature from -78 ℃ to 20 ℃ . Testing results show that the characteristic COD appears to depend on the structural features that are determined by welding process and the testing temperature. As the temperature is lowered, the characteristic COD of all zones studied decreases. Because the welding process significantly changes some structural feature of the material, characteristic COD of the weld fusion zone is the smallest one among those of the three zones. The results can be used for the engineering design and failure analysis of HDPE pipe.

Formability of AA5052/polyethylene/AA5052 sandwich sheets

The formability of AA5052/polyethylene/AA5052 sandwich sheets was experimentally studied. Three kinds of AA5052/polyethylene/AA5052 sandwich specimens with different thicknesses of core materials were prepared by the hot pressing adhesive method. Then, the uniaxial tensile tests were conducted to investigate the mechanical properties of AA5052/polyethylene/ AA5052 sandwich sheets, and the stretching tests were carried out to investigate the influences of polymer core thickness on the limit dome height of the sandwich sheet. The forming limit curves for three kinds of sandwich sheets were obtained. The experimental results show that the forming limit of the AA5052/polyethylene/AA5052 sandwich sheet is higher than that of the monolithic AA5052 sheet, and it increases with increasing the thickness of polyethylene core.

Study and Evaluation of Advanced TOFD Method for Inspection of Polyethylene Pipes but Welding

Polyethylene material has some specification that makes very difficult any kind of inspection based on ultrasonic. The acoustic impedance and sound velocity in this kind of material are near to the materials commonly used in ultrasonic wedges. Also this kind of materials are highly attenuative materials for ultrasound. To inspection of polyethylene circumferential but welds and overcome to all the problems mentioned, the especial technique of TOFD （Time of Flight Diffraction） method which employs low frequency probe and concentrate on the inspection area that longitudinal waves turn into transverse waves has been used. The purpose of inspection is determining the exact location of surface and internal welding defects. For this purpose, two separate polyethylene pipes with 10 inch in diameter, 15 mm thickness and also 25 inch diameter, 28 mm thickness, were selected. In total 40 artificial defects which involve 28 side drill holes in deferent depths and 12 surface and sub-surface notches were created. All artificially created defects were detected with very good accuracy. Unlike the conventional TOFD method which have 2 to 3 mm dead zone, by using the above method even surface notch with 0.5 mm has been detected.

The Interlayer Stress Analysis of Polyethylene-steel Composite Pipes

Polyethylene-steel Composite Pipes is widely used in conveying corrosive media occasions,but the pipe may lose effectiveness in the process of transporting hot and cold media,so the research of stress distribution and variation in polyethylene-steel composite pipes is very necessary.This article first assume that a thin adhesive layer is in between the polyethylene and steel,the adhesive layer along the axial shear stress is the major cause of the polyethylene layer and the steel pipe off sticky.Secondly,we use a method of finite element to computer simulation by ANSYS,and verify initial assumptions.Finally,based on simulation data,we analyse the adhesive layer stress distribution and the variation with different parameters to change.Through the above research,preliminarily summarize the variation and distribution of interlaminar stress,and provide technical support for future design and process improvement of polyethylenesteel pipe.

A review of nondestructive examination technology for polyethylene pipe in nuclear power plant

Polyethylene （PE） pipe, particularly high- density polyethylene （HDPE） pipe, has been successfully utilized to transport cooling water for both non-safety- and safety-related applications in nuclear power plant （NPP）. Though ASME Code Case N755, which is the first code case related to NPP HDPE pipe, requires a thorough nondestructive examination （NDE） of HDPE joints. However, no executable regulations presently exist because of the lack of a feasible NDE technique for HDPE pipe in NPP. This work presents a review of current developments in NDE technology for both HDPE pipe in NPP with a diameter of less than 400 mm and that of a larger size. For the former category, phased array ultrasonic technique is proven effective for inspecting typical defects in HDPE pipe, and is thus used in Chinese national standards GB/T 29460 and GB/T 29461. A defect- recognition technique is developed based on pattern recognition, and a safety assessment principle is summa- rized from the database of destructive testing. On the other hand, recent research and practical studies reveal that in current ultrasonic-inspection technology, the absence of effective ultrasonic inspection for large size was lack of consideration of the viscoelasticity effect of PE on acoustic wave propagation in current ultrasonic inspection technology. Furthermore, main technical problems were analyzed in the paper to achieve an effective ultrasonic test method in accordance to the safety and efficiency requirements of related regulations and standards. Finally, the development trend and challenges of NDE test technology for HDPE in NPP are discussed.

Compression Molded Ultra High Molecular Weight Polyethylene-Hydroxyapatite-Aluminum Oxide-Carbon Nanotube Hybrid Composites for Hard Tissue Replacement

Ultra high molecular weight polyethylene （UHMWPE） is widely used for articulating surfaces in total hip and knee replacements. In the present work, UHMWPE based polymer composites were synthesized by synergistic reinforcing of bioactive hydroxyapatite （HA）, bioinert aluminum oxide （Al2O3）, and carbon nanotubes （CNTs） using compression molding. Phase and microstructural analysis suggests retention of UHMWPE and reinforcing phases in the compression molded composites. Microstructural analysis elicited variation in densification due to the size effect of the reinforcing particles. The hybrid composites exhibited hardness, elastic modulus and toughness comparable to that of UHMWPE. The interfacial effect of reinforcement phases has evinced the effectiveness of Al2O3 over HA and CNT reinforcements, depicting synergistic enhancement in hardness and elastic modulus. Weak interfacial bonding of polymer matrix with HA and CNT requires utilization of coupling agents to achieve enhanced mechanical properties without deteriorating cytocompatible properties.

Application of the finite element method for evaluating the stress distribution in buried damaged polyethylene gas pipes

During the loading process,buried gas pipes can experience severe stresses due to soil-structure interaction,the presence of traffic load,the soil’s column weight,daily and/or seasonal temperature changes and uniform internal pressure.In this research,the finite element method is employed to evaluate the behavior of buried Medium Density Polyethylene(MDPE)pipes which have been subjected to damage at the pipe crown.The modeled pipe damage ranges from a very small circular hole to a large circular hole and elliptic holes with various minor to major diameter ratios,a/b,to simulate circular to crack-shaped defects.The computer simulation and stress analyses were performed using the ANSYS software finite element package.The stress distribution around the defect was determined under the aforementioned mechanical and thermal loading conditions.Then,the maximum values of Von Mises stresses in the damaged buried PE pipes,which were evaluated by finite element solution,were compared with their corresponding reduced strength for safe operation with a life expectancy of fifty years.Based on the results,the maximum Von Mises stress values in the defective buried polyethylene gas pipeline are significantly above the pipe strength limit at 35℃.The previously mentioned stress values increase with the following factors:temperature increase,increase in circular hole diameter and decrease in elliptic hole diameter ratio(a/b).The maximum stress in the damaged PE pipe is due to the simultaneous loading effects of soil column weight,internal pressure,vehicle wheel load and pipe temperature increase.Additionally,the novel finite element models and stress plots for the buried damaged pipe and the pipe material allowable strength will be used to investigate the correct repair method for the damaged gas pipeline and to choose the best patch arrangement which will assure a safe repair.

高强箍筋增强SRPE套管约束混凝土短柱轴压力学性能研究

针对东部沿海及西部盐渍土地区桥梁墩柱的钢筋混凝土腐蚀等问题,提出一种新型组合结构——高强箍筋增强钢骨架聚乙烯塑料复合管(SRPE)套管约束混凝土柱。设计制作了11根试件进行轴心受压试验,对其破坏形态、极限承载力和荷载-纵向变形曲线进行了研究,分析了箍筋屈服强度、SRPE套管压力等级和体积配箍率等对其轴压性能的影响规律,并给出轴心受压承载力计算方法。结果表明:在SRPE套管和高强箍筋的双重约束下,试件的承载力、延性和纵向变形得到显著提高;试件的极限承载力随SRPE套管压力等级、箍筋屈服强度和体积配箍率的提高而增大;箍筋屈服强度越高,极限承载力越大,但荷载-纵向变形曲线的下降段更陡峭。所建立的轴压承载力计算方法可为相关工程实践提供参考。

改进YOLOv5的高密度聚乙烯管热熔接头3D全聚焦成像缺陷识别分析

为保障聚乙烯管热熔接头缺陷识别效率和准确性,该文提出一种基于改进YOLOv5的高密度聚乙烯管热熔接头3D全聚焦成像缺陷识别方法。首先,在YOLOv5模型的特征提取网络中加入SE注意力机制模块,提高不明显缺陷的边缘特征提取,在预测网络中,将原始YOLOv5的损失函数改为SIoU损失函数,提高模型回归效率和收敛速度,更有利于模型的优化;其次,对高密度聚乙烯试块典型缺陷(ϕ1 mm、ϕ2 mm、ϕ3 mm)进行3D全聚焦成像检测实验,采集原始的3D全聚焦缺陷图谱,完成图像增广并建立数据集;最后,采用迁移学习策略对改进模型进行训练,获取最优模型并进行评价。结果表明:该方法与传统YOLOv5相比,其准确率提升了2.4%,召回率提升了3.1%,较好解决检测人员错检、漏检等情况,提高检测效率。

聚乙烯管道切口试验应力和变形分析

对聚乙烯管道在1~4 mm切口深度下水压试验中的应力和变形分布进行数值模拟和分析。研究得到,聚乙烯管道应力强度和变形量随着切口深度的增加而升高,聚乙烯管道变形量较大的区域对应的应力强度相对较低。切口深度为1 mm时,管道内表面应力和变形分布较为均匀,没有明显的变化梯度;而在切口深度为2~4 mm时,管道内表面应力和变形分布已经出现明显的变化梯度。

某采油厂柔性复合输送管泄漏失效原因分析

柔性复合输送管是由高分子复合材料制成的具有一定高强度、高压力、耐腐蚀、耐结垢、摩阻系数小、保温性好、柔性好、寿命长的一种石油天然气工业用管件。然而,其在使用过程中由于工况、环境及人为因素等原因会出现泄漏失效,这对输油系统的安全性和可靠性构成了威胁。以交联聚乙烯内衬层的复合管泄漏失效为研究对象,分析了管道破损部位的特征,并进行技术检测,探讨了泄漏失效原因,最后提出防范措施和生产管理建议,为进一步做好管线输油提供参考。

Mechanical Properties Study of Reinforced Thermoplastic Pipes Under A Tensile Load

This paper presents a study on the tensile properties of reinforced thermoplastic pipes(RTPs). A mechanical model of RTPs with an arbitrary number of reinforced layers under tensile action is constructed by combining the constitutive relationship of elastoplastic materials with the continuous displacement condition. On this basis, the effects of various parameters such as the winding angle, the number of structurally reinforced layers, and the inner polyethylene(PE) liner thickness on the tensile properties of the RTPs were analyzed, and a tensile test was carried out for validation. The results showed that the winding angle of the structurally reinforced layers was the main factor affecting an RTP's tensile performance— decreases in the winding angle significantly improved its tensile ability,especially the longitudinal strength. With ±45° as the demarcation point, the winding angle smaller than ±45° will result in higher strength in longitudinal direction, and the lifting effect on RTP's mechanical properties of the increasing number of reinforcement layers was better than that of the increasing thickness of the lining layer;when the winding angle was larger than ±45°, the opposite results were obtained. The fibre load was more sensitive to the winding angle than the PE load.

利用时域叠加的声学成像法定位埋地PE管道

针对现有埋地管道探测技术难以确定聚乙烯(PE)管道埋深且通常对管线走向的探测误差较大的问题,提出了优化的时域叠加声学成像法。利用该方法对仿真信号进行直达波与表面波消除、反射波提取和成像定位处理,验证了方法的可行性。最后,对埋深0.4 m和1.0 m的PE管进行定位测试实验,最大管线平面定位误差分别为0.179 m和0.240 m,说明该方法基本满足较好埋地条件PE管道探测的需求。

高压XLPE电缆缓冲层缺陷研究现状综述

高压交联聚乙烯电缆因缓冲层缺陷引发的故障频发,已严重威胁到电力系统的安全运行。本文首先介绍了缓冲层的基本结构和作用,并在此基础上梳理了目前国内外对于缓冲层失效的相关研究;其次从缓冲层的材料特征和内部结构等角度结合电场仿真来分析缺陷发生的主要原因;之后对缓冲层缺陷中出现的白色粉末绝缘性能和理化特征进行总结,并提出其形成机理;最后对缓冲层缺陷的检测手段进行汇总,提出使用计算机断层成像技术对电缆缓冲层缺陷进行检测以弥补现有检测手段的不足,并建议对铝护套及缓冲层的材料或结构进行优化,以预防缓冲层缺陷的生成。

聚乙烯管焊接接头相控阵超声检测的优化设计

在管道工程应用中,由于良好的耐腐蚀性和韧性,聚乙烯(PE)管与其他材料相比具有显着优势,已广泛地应用在核电、油气输送领域;PE管焊接过程中,焊接参数、人员操作和环境等因素会影响聚乙烯管道的焊接情况,可能致使焊接接头内部形成缺陷,影响管道安全运行,而相控阵超声检测技术能够实现聚乙烯管道焊接接头内部结构的无损检测及评估;因此开展PE管焊接接头的相控阵超声实际检测工作,研究了聚乙烯材料的声衰减规律及声频散效应,优化了焊接接头的超声相控阵检测工艺,基于CIVA仿真软件实现了聚乙烯管道相控阵超声检测的声场模拟和缺陷仿真,通过研究检测参数及声学参量变化对检测结果的影响,获得了PE管焊接接头的最优检测工艺;通过加工带有典型缺陷的聚乙烯热熔对接接头试样,对前期基于仿真结果设计的检测工艺以及针对焊接接头相控阵检测研发的楔形耦合组件进行可靠性测试和工艺试验;研究结果为PE管接头缺陷的超声相控阵检测提供了工艺设计的理论支持和可靠的研究方法。

埋地燃气PE管道在地面沉降作用下的应力分析

为了研究在地面沉降作用下PE燃气管道的受力特性及失效原因,借助ANSYS软件,探究了在地面沉降作用下PE100、管径DN110、e=10的燃气PE管道的应力-应变响应情况,分析了管道失效影响因素以及失效原因,并得出管道的失效危险点、管道极限沉降位移及极限截面变化率。结果表明:在地面沉降作用下管道的失效危险点出现在沉降区与非沉降区交接处的管道内表面;且在地面沉降作用下,管道产生的压缩变形是导致管道失效的主要原因,管道弯曲变形的存在会使管道的压缩变形更加严重。这为防治埋地燃气聚乙烯管道在地面沉降作用下的管道安全评估提供理论参考。

点载荷作用下聚乙烯燃气管道的损伤分析

通过单轴拉伸试验获得了聚乙烯(PE)材料弹性及屈服参数。建立了点载荷下的管-土有限元模型,研究了埋地燃气PE在点载荷下的力学响应,分析了点载荷尺寸、管道内压及管道直径的影响。基于DFDI(ductile failure damage indicator)模型,结合有限元仿真结果,对点载荷下的PE管进行了定量损伤计算。结果表明,与无点载荷管道的损伤结果对比可知,点载荷的存在增大了管道损伤;管道内压变化时管道损伤变化较大;管道直径变化时对PE管损伤影响较小,各管径下的损伤值都比较接近。