聚乙烯压力管道抗快速裂纹扩展性能的实验研究

小尺寸稳态实验（简称S4实验）是模拟聚乙烯（PE）压力管道快速裂纹扩展的一种有效方法，可获得PE压力管道的止裂性能指标，已成为PE压力管道油气分配装置的设计规范和国际标准。介绍S4实验原理及天津大学自行研制开发的国内第一套S4实验装置，并在不同压力和不同温度下进行了S4实验，最后根据ISO－FDIS 13477规定，经实验得出了供试管材的止裂曲线。     

S4实验在聚乙烯管道中的应用

介绍了模拟聚乙烯压力管道的快速裂纹扩展的小尺寸稳定实验－－S4实验，该实验方法可以代替全尺寸实验获得压力管道的止裂性能指标，并应用到工程中去，主要介绍了S4实验装置与实验原理，温度、管壁厚度等因素对止裂性能的影响，并对S4实验结果和全尺寸实验结果进行了比较。     

聚乙烯压力管道裂纹快速扩展性及止裂性测试

聚乙烯压力管道在低温时易出现裂纹快速扩展，其破坏一般都具有突发性，难以预防。本文采用小尺寸稳态试验方法，测试了在不同温度下，裂纹扩展长度随压强的变化情况，同时也测试了在不同压强下，裂纹扩展长度随温度的变化情况。通过计算分析，确定了裂纹快速扩展的临界压强和临界温度。给出了影响该试验结果的因素如温度、压力、介质、裂纹扩展速度及裂纹尖端的流体减压等。并通过试验测试了焊缝以及套筒对塑料管道开裂的影响。最后给出了塑料管道在实际运行中的一些具体的止裂措施。     

二氧化碳管道意外泄漏减压过程的断裂控制研究进展

管道是二氧化碳捕集、利用和封存（carbon capture, utilization, and storage,CCUS）技术产业链中输运大量二氧化碳（CO₂）的最优方式,但其在运行中具有意外泄漏风险。本文从实验和计算机模拟两个方面综述了国内外开展CO₂管道泄漏减压、断裂扩展的研究进展,分析了相态、管材、埋地条件等初始状态对裂纹扩展规律的影响。阐述了状态方程、杂质因素、理论模型对开展实验和模拟计算研究的影响。归纳了适用于建立减压波预测模型的状态方程,开展流固耦合研究的理论方法和模拟仿真软件,设计CO₂输运管道参考的技术文档。总结了当前CO₂管道泄漏减压、断裂扩展控制研究方面需深入研究的科学问题,展望了亟待开展的研究内容,包括构建多元混合物状态方程在三相点、相间线的计算模型;探究裂纹裂间处CO₂热物性质与裂纹断裂扩展的耦合关系;建立管道止裂准则,开发、优化CO₂输运管道专用止裂器。     

数值模拟分析法在聚乙烯压力管道耐快速裂纹扩展现象中的应用

为避免聚乙烯压力管道在使用的过程中发生快速裂纹扩展现象（RCP）引起重大事故,可采用数值模拟分析方法来研究RCP,介绍了有限元法、有限体积法、有限差分法、最小二乘法这4种数值模拟分析方法的特点及其在RCP研究中的应用。认为这4种方法为国内外所常用,可为聚乙烯压力管道止裂性能的研究提供了重要依据。     

聚乙烯压力管道快速裂纹扩展的模拟分析方法和试验方法

聚乙烯压力管道的快速裂纹扩展现象是一种偶发性事故,一旦发生则会对人们的生命、财产造成重大损失。介绍了聚乙烯压力管道快速裂纹扩展的模拟分析方法,并简述了聚乙烯压力管道快速裂纹扩展的常见的几种试验方法。     

基于扩展有限元的钢结构钻孔止裂研究

通过以ABAQUS为平台,采用扩展有限元方法对钢结构钻孔止裂进行数值模拟,同时对循环载荷下止裂孔应力应变状态进行分析,对疲劳裂纹钻孔止裂处理机理进行了深入研究。研究表明,扩展有限元法分析疲劳裂纹扩展再生及钻孔止裂技术时不需要预先指定裂纹扩展方向,无须重新剖分网格,克服了常规有限元方法的弊端,为复杂形状裂纹问题提供了更优的解决方法;止裂孔减小了孔边应力集中部位的平均应力,延长了疲劳裂纹在止裂孔边的再生寿命;当止裂孔直径取为0.4倍疲劳裂纹长度时可以获得较好止裂效果,对钻孔止裂理论的研究具有一定参考意义。     

油气管道断裂扩展及止裂技术研究

近年来我国油气管道发展迅猛,同时也伴随着种种隐患,其中断裂及裂纹扩展问题复杂而多变,引起的后果也尤为严重。简述了油气管道断裂的内在原因及外在影响因素,介绍了在管道断裂方面的国内的研究现状及进展,也阐述了在裂纹扩展以及断裂控制领域国内的研究成果。为管道断裂、裂纹扩展及止裂问题的进一步研究,提供了参考。     

Q345R钢韧脆转变过渡区内临界事件的观察研究

通过三点弯曲COD卸载试验对Q345R钢3种显微组织在韧脆转变过渡区内的临界事件进行了研究:裂纹尖端首先是弹性张开,随后逐渐钝化,继而新裂纹产生,然后钝化,这个过程重复,直至最后断裂;当卸载温度为-70℃时,裂纹从碳化物起裂,此时临界事件是第二相质点裂纹扩展入母体晶粒的控制;当卸载温度为-90℃时,可明显看到是从铁素体晶粒边界起裂,然后沿着碳化物的方向扩展,此时临界事件是裂纹从铁素体晶粒边界起裂沿着碳化物扩展入母体铁素体晶粒的控制。     

化工设备存在缺陷的可能性及止裂、抑爆对策

分析了化工设备和大型管道由于制造、材料、介质、检测等方面造成裂纹缺陷存在的原因及破坏机理和后果,评述了国内外防止裂纹扩展与止焊抑爆的研究和处理方法,重点介绍了多层绕带式压力容器的诸多优点和采用在筒体外部加弧形贴板与钢丝缠绕进行止裂抑爆处理的方法及效果。     

聚乙烯注塑管件熔接线强度快速压扁检测方法探讨

介绍了聚乙烯（PE）注塑管件的压扁试验测试方法,并通过实际测试管件熔接线强度对比研究了压扁试验与静液压强度试验（165 h、80 ℃）的测试结果及规律。结果表明,压扁试验检测熔接线无裂缝则静液压强度试验也合格,而静液压强度试验合格,压扁试验中熔接线则存在有裂缝或无裂缝2种情况;压扁试验发现可以快速、有效地检验出PE注塑管件的熔接线强度是否满足要求,可及时调整工艺或改进模具等方案来改善与提高产品品质。     

Thermal-oxidative aging performance and life prediction of polyethylene pipe under cyclic and constant internal pressure

To study the aging characteristic of the polyethylene (PE) 100 pipe under constant and cyclic internal pressure, a new accelerated thermal-oxidative aging test equipment was developed. Thermal-oxidative aging behaviors of PE pipe under constant pressure and cyclic pressure were studied in various temperatures (80, 95, and 110 °C) by accelerated aging tests. The tensile test result shows that the fracture strength of PE pipe decreases as the aging time prolongs. Meanwhile, the pipe aged in the higher temperature behaves faster decreasing rate. A faster decreasing rate is also observed under the condition of cyclic pressure, compared to that under constant pressure. The thermal stability of the pipe gradually reduces and the reducing rate under cyclic pressure is higher than that under constant pressure. The result of infrared spectroscopy test suggests that oxygen-containing groups (i.e., CO) are formed on the surface of PE pipes, indicating that oxidative degradation phenomenon of PE pipes occurs during the aging process. Furthermore, based on the measured result of fracture strength, lifetime prediction models of PE 100 pipe under constant pressure and cyclic pressure are proposed. The result shows that the lifetime of PE 100 pipes obviously decreased under cyclic pressure, and it is 27.96% shorter than that under constant pressure. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47766.     

铝/改性PE复合管的研究

研究了在铝塑复合管的PE层配方中加入不同种类CaCO3和分散剂对PE层力学性能的影响，并对改性后的铝塑复合管的爆破强度、耐静压时间、环拉力等进行了测试。结果表明，加入适当分散剂处理的纳米CaCO3改性的PE层的性能明显提高，并且制得的管材各项性能指标均满足标准要求。     

The effect of a polypropylene skin on the structure and properties of PE/PP dual layer pressure pipe

A new and growing family of polyethylene (PE)‐based pressure pipes have a polypropylene (PP) skin. The effect of the PP skin on the structure and properties of the core PE pipe was investigated by comparing the skinned pipe with an uncoated pipe made from the same PE material and with the same dimensions. The annealing effect introduced by the skin changed the PE core pipe density profile across the wall thickness, increasing density in the PE core pipe near to its outer surface. The density at the bore of the coated and the uncoated pipe was similar. The melting temperature and enthalpy of melting data from DSC agreed with the density profile results. The melting temperature of PE core pipe material close to the PP skin increased with increasing skin thickness. Residual stress assessment indicated that, as the PP skin thickness increased, the PE core pipe had a lower level of overall residual stress in the hoop direction. Long‐term hydrostatic strength (LTHS) tests were carried out and showed a higher strength for the coated pipe than the uncoated one. The observed structural changes have been used to explain the relative strength of these two PE pipes. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

优化赫斯特工艺操作提升PE100级管材产品质量

介绍了中国石油吉林石化公司30万t/a高密度聚乙烯装置提升PE100级管材产品JHMGC100S质量情况。通过优化赫斯特低压淤浆法中催化剂制备和聚合等生产工艺,指出关键参数熔融指数、熔流比和密度的调整思路,使产品熔融指数稳定性、拉伸屈服应力、拉伸断裂标称应变、简支梁冲击强度等重要指标不断提升,逐步解决PE100级管材产品氧化诱导期不稳定、加工性能差、内壁有麻点、拉伸屈服强度不够和个别批次静液压实验通不过等诸多难题。     

Fracture prediction in tough polyethylene pipes using measured craze strength

In this study, an empirical model is developed that predicts the time to failure for PE pipes under combined pressure and deflection loads. The time‐dependent craze strength of different PE materials is measured using the circumferentially deep‐notched tensile (CDNT) test. In agreement with previous research, results indicate that bimodal materials with comonomer side‐chain densities biased toward high‐molecular‐weight PE molecules exhibit significantly higher long‐term craze strengths. A comparison of currently available PE materials with CDNT samples taken from a PE pipe that failed by slow crack growth in service clearly indicates the superior performance of new‐generation materials. Using measured craze strength data from the CDNT test, a simplified model for predicting failure in buried PE pipes is developed. Extending previous research, the reference stress concept is used to calculate an equivalent craze stress for a pipe subjected to combined internal pressure and deflection loads. Good agreement is obtained between the model predictions and observed failure times in an experimental test‐bed study of pipes under in‐service loading conditions. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

PVC corrugated drainage pipe

In the continuing struggle to obtain the most economical material for a given application, it is proposed that corrugated PVC can be quite competitive with corrugated PE. An advantage for PVC stems from a flexural modulus that is almost twice that of PE. Corrugated PVC pipe at 135 grams per foot competed with corrugated PE pipe at 140–150 grams per foot. PVC requires a different corrugation design than does PE. Proper attention to balancing flexural modulus and impact strength must be paid in formulation of PVC.     

Mechanical behaviour of adhesively bonded polyethylene tapping tees

The mechanical properties of adhesively bonded MDPE joints were studied. The lap-shear joints were prepared using PE80 polyethylene gas pipe and four adhesive types; two acrylic and two epoxy resins. The key mechanical properties of lap shear strength and impact resistance were investigated as a function of adhesive type and surface preparation technique. Mechanical abrasion of the PE80 surface increased the strength of the bonds from 40 to 460% for the four adhesives, with the best performing acrylic adhesive having a lap-shear strength of 1.76 MPa and impact strength of 2.5 kJ/m². When used to bond PE80 tapping tees to PE80 gas pipe, the acrylic adhesive produced a gas tight seal at both the standard test pressure of 0.4 MPa and at an increased pressure of 0.8 MPa, and outperformed the PE80 tapping tee during shear testing and withstood a maximum of 10 cycles of 175 J during impact testing. These results highlight the potential of adhesive bonding as a method of joining PE80 tapping tees to PE80 gas pipe.     

Multi‐Relaxation Test to Characterize PE Pipe Performance

A new concept is proposed, which uses results from a multi‐relaxation test to characterize transition of deformation mechanisms in polyethylene (PE) pipes, for plastic deformation from the amorphous phase only to the involvement of the crystalline phase. The former mechanism is believed to lead to brittle fracture, while the latter to ductile fracture. This phenomenon is believed to be related to the transition from ductile to brittle (DB) fracture that has been observed in creep tests of PE pipes by reducing the applied stress below a critical level. This paper presents results from 6 PE pipes of different density and molecular weight distribution. The results suggest that high‐density PE pipes require a higher deformation level for the DB transition than the medium‐density PE pipes. The results also suggest that the trend of change in the critical stress level for the DB transition is close to the trend of change in the hydrostatic design base, but the former takes less than two weeks to complete, while the latter more than 1 year. Therefore, the multi‐relaxation test can be used as an alternative method to characterize PE pipe performance, as a means for preliminary screening or in‐service monitoring of pipe performance.