Experimental study and numerical simulation of pipe-on-pipe impact

Experiments and numerical simulations were conducted to investigate the dynamic response in a pipe-on-pipe impact event, in which a missile (swinging) pipe with one end hinged and the other end free impinges on an orthogonal simply-supported/clamped target pipe at its centre. This study focuses on the effects of the impact location on the missile pipe and the wall thickness of the pipes. The experiments were carried out by using a spring-powered catapult impact setup, the specimens used were made of seamless steel pipes of two different thicknesses, 1 mm and 3 mm respectively, and the target pipes were clamped. Seven tests were carried out using the catapult. Numerical simulations using the explicit finite element code LS-DYNA were performed on an HPC360 workstation for each of the seven test cases. The results of the experiments and numerical simulations were compared, showing good agreement. Having confirmed the validity of the numerical model, numerical simulations were applied to the cases of a simply-supported target pipe, and the partitioning of the energy dissipation was calculated. As the response mode depends significantly on the initial impact position, the evolution of the response mode was examined numerically as the point of impact on the missile pipe was moved from the hinged end to the free end. It was found that there is a particular impact location for which the target pipe was most seriously damaged using the same impact speed.     

Statistical models for the analysis of water distribution system pipe break data

The deterioration of pipes leading to pipe breaks and leaks in urban water distribution systems is of concern to water utilities throughout the world. Pipe breaks and leaks may result in reduction in the water-carrying capacity of the pipes and contamination of water in the distribution systems. Water utilities incur large expenses in the replacement and rehabilitation of water mains, making it critical to evaluate the current and future condition of the system for maintenance decision-making. This paper compares different statistical regression models proposed in the literature for estimating the reliability of pipes in a water distribution system on the basis of short time histories. The goals of these models are to estimate the likelihood of pipe breaks in the future and determine the parameters that most affect the likelihood of pipe breaks. The data set used for the analysis comes from a major US city, and these data include approximately 85,000 pipe segments with nearly 2500 breaks from 2000 through 2005. The results show that the set of statistical models previously proposed for this problem do not provide good estimates with the test data set. However, logistic generalized linear models do provide good estimates of pipe reliability and can be useful for water utilities in planning pipe inspection and maintenance.     

Further experimental study on the failure of fully clamped steel pipes

In the present study experimental data recorded from 226 impact tests on seamless mild steel pipes are reported. The pipe specimens with different geometries were fully clamped at both ends, and impacted transversely by rigid wedge-shaped indenters at the positions of mid-span, one-quarter span and very close to a support, respectively. In order to model the fully clamped boundary conditions, a special clamping system was designed to hold the pipe specimens rigidly at each end to prevent any significant inward displacements from the supports. The impact velocities ranged up to 10.69 m/s and caused large inelastic indentations for the lower values and at higher values a loss of integrity near the supports. Particular attention was paid to obtaining the threshold value of initial impact energy that caused the onset of material rupture. Discussion is made for the influences of pipe geometry, impact position and internal pressure on the critical value of initial impact energy.     

Experimental and numerical study on the orthogonal and oblique impact on water filled pipes

A 300 mm long piece of copper (ASTM B280) pipe with an outer diameter of 35 mm and 0.7 mm wall thickness was subjected to a rigid steel pipe impact under a drop weight loading configuration where the pipe was simply supported at its ends. Differences in deformation features for a pipe filled with water and an empty pipe were investigated for two configurations namely orthogonal and oblique impact. Compared to orthogonal pipe impact the oblique pipe impact has not been reported in the literature. It is hoped that current work would serve as a first step in this direction. Finite Element Method coupled with Smooth Particle Hydrodynamics (SPH) available in LS-DYNA was used to simulate the empty and water filled pipe impacts under orthogonal and oblique configurations respectively. Fluid structure interaction (FSI) during the water filled pipe impact was successfully modeled using SPH which is a simple method for predicting the short duration FSI events. Experimental results of the effect of varying D/T ratio on the empty and water filled pipes have been reported.     

胜利油田垦东外输油管线频繁穿孔原因分析

通过外防腐层检验和管材分析对胜利油田垦东外输油管线服役不到3a(年)就频繁发生穿孔的原因进行了分析。结果表明:该管段裸管服役,管道设计壁厚偏薄,管道材料更换有误,加上垢下(闭塞电池)作用,导致管道穿孔漏油。     

Characteristics of corrosion sales and biofilm in aged pipe distribution systems with switching water source

Red water has occasionally been observed in the water distribution system of Beijing following a change in the city's water source. Aged cast iron pipes from both affected and unaffected areas were used to establish experimental drinking water distribution systems under different disinfection conditions. The scale deposits formed under different conditions were characterized by X-ray diffraction and scanning electron microscopy, and the bacterial characteristics of the corrosion scales were determined using several molecular methods. The water quality changed less in pipe samples from the unaffected areas than pipes from the affected areas. The pipe samples from the unaffected area included predominantly α-FeOOH, Fe₃O₄, and γ-FeOOH, and 24.2% nitrate-reducing bacteria (NRB) were predominant with fewer iron-oxidizing bacteria (IOB) being observed. The composition of corrosion products did not exhibit large variation over time although their crystallinity exhibited a slight decrease throughout the duration of the experiment. In contrast, in the pipe samples from the affected, α-FeOOH was the main compound with less γ-FeOOH and Fe₃O₄, and 3.3% IOB and 12% NRB with few IRB were observed. However, after transporting surface water containing disinfectants, the Fe₃O₄ and dense corrosion layer formed, inhibiting the release of iron. Moreover, IRB and NRB became dominant. 22.6% and 34.3% NRB appeared in the pipes after chlorination and chloramination, respectively. The synergistic interaction of IRB and NRB with the corrosion layer played a large role in the release of iron from a cast iron pipe following changes in water quality.     

Explosive welding of stainless steel–carbon steel coaxial pipes

Bi-metallic corrosion resistant steel pipes were produced through explosive welding process. The weldability window of the stainless steel pipe (inner pipe) and the carbon steel pipe (outer pipe) was determined by the use of available semi-empirical relations. The impact velocity of the pipes as the most important collision parameter was calculated by the finite element simulation. Direct effect of the explosive mass reduction on the bonding interface of the pipes was studied. Optical microscopy study showed that a transition from a wavy interface to a smooth one occurs with decrease in explosive load.     

The work of fracture in uniaxial and biaxial oriented unplasticised polyvinylchloride pipes

In oriented unplasticised polyvinylchloride (uPVC) pipes, cracks propagate tangentially rather than through the wall as in conventional pipe. Notched impact, a modified peel test and the specific work of fracture approach have been used to measure fracture toughness of a conventionally extruded, a uniaxially oriented and a biaxially oriented uPVC pipe in different directions. The different failure mode for the oriented pipes was found to result from an order of magnitude increase in the fracture toughness for cracks propagating perpendicular to the orientation direction. Differences in the fracture toughness between the oriented pipes were also related to their molecular orientation.     

Research on the impact velocity of magnetic impulse welding of pipe fitting

Magnetic impulse welding, which is uniquely advantageous in welding heterologous pipe fittings, is a new welding technology based on high-speed magnetic impulse shaping and solid-phase diffusion welding. The impact velocity of the welding points of Al–Fe heterologous pipe fittings was studied by combining numerical simulation and technological test with the assistance of constitutive relations of 3A21Al alloy under a high strain rate. The momentary movement speeds when the outer tube (A1) impacts the inner tube under four different voltages were analyzed to obtain the critical voltage for welding inner and outer tubes. The speed of the welding points of the outer tube noticeably increased with the rise in the discharge voltage. The weld interfaces of both the inner and outer tubes produced regular zigzag waves when the impact velocity reached 350 m/s. The energy spectrum analysis revealed that pipes undergo severe deformation under high-speed impact, and the increased temperature enhances the activity of the atoms among other elements, thus producing a surface mass flow under strong impact and granulated substances.     

大口径高性能聚氯乙烯管道研发与工程安全保障技术

该文围绕大口径高性能聚氯乙烯管道的混配料配方设计、制造设备研发、生产工艺优化、管材质量评定、管线工程安全评价、运行监测与病害修复等关键技术,通过产学研用相结合,持续10余年攻关取得一系列突破性创新成果：研发了新型聚氯乙烯管材复合改性增韧混配料,优化了管材材料配比,创新了大口径高性能聚氯乙烯管材模具与工艺,首创了国内唯一直径1800 mm大口径聚氯乙烯管生产线;研发了具有高强、高韧、高抗冲的聚氯乙烯管道新产品：ABR管(给水用丙烯酸酯共混聚氯乙烯管),建立了ABR管质量评价方法,开展了ABR管管材拉伸、热膨胀和ABR管内、外压结构承载性能试验;创建了复杂运营环境下大口径管线工程安全评价方法,系统开展了落石冲击、土体塌陷、滑坡和和地质断层等自然灾害作用下的埋地聚氯乙烯管线工程安全性能原型试验与数值模拟;开展了基于光纤传感技术的管道变形健康监测试验,研发了新型管道内检测设备—“谛听”机器人,结合“谛听”机器人与目标检测人工智能算法进行了管道缺陷定位识别与病害诊断,提出了Spetec注浆堵漏加固、不锈钢快速锁修复技术、树脂固化局部修复工艺、紫外光固化内衬的整体不开挖修复技术,实现了对聚氯乙烯管...     

Weibull analysis, extrapolations and implications for condition assessment of cast iron water mains

The applicability of Weibull statistics to the condition assessment of cast iron water distribution pipes has been considered. The effect of Weibull modulus, characteristic strength, sample size and mode of loading (tension or flexure) on the strength of cast iron water distribution pipes is investigated. The strength distribution of cast iron samples cut from sections of five different water distribution pipes recovered from the ground have been characterized. Strengths have been measured in flexure, at two different temperatures (ambient and 0 °C), and in tension at ambient temperature using two different sample sizes. It is shown that characteristic strength values in flexure decrease with increasing size of graphite flake and that there is no significant difference between the results at the two temperatures investigated. For samples of the same volume tested in tension and flexure, the reduced strength measured in tension is consistent with Weibull predictions. However, the strength of large samples tested in tension was not significantly different from the small samples, perhaps because the samples were of the same thickness and conventional Weibull scaling is not applicable. Finally, using a method which treats a large pipe as an assembly of small samples, the strength distributions from the small samples tested in tension are used to make a prediction of the strengths of 1 m span sections of pipe loaded in three‐point bending, which were reported in previous work. The predicted pipe strengths are close to the lower end of the measured pipe strength distribution. Overall, this work suggests that Weibull analysis is a useful tool to examine the strength distribution of removed from cast iron water pipes and so has the potential to contribute in the assessment of asset condition.     

Some observations on the strength and fatigue properties of samples extracted from cast iron water mains

The strength and fatigue properties of cast iron samples taken from water distribution mains have been investigated. Specimens were sourced from three sections of pipe which had experienced varying amounts of corrosion in service, enabling the variable of pipe condition to be incorporated within the study.
The strengths in four-point flexure of small specimens from the pipes examined were described using Weibull statistics; different characteristic strengths and Weibull moduli were obtained, according to the pipe condition. A further set of samples from each pipe were subjected to flexural fatigue at a range of stress levels (different stress levels were chosen for each pipe based on the short-term strength properties) and residual strength tests were carried out on the surviving samples from one stress level for each pipe. There is evidence of a fatigue effect for all sample sets. There were slight differences in the residual strength behaviour – the residual strength of the survivors was reduced in the samples from the section in best condition while the residual strength of the survivors from the other two pipe sections was relatively unaffected. These trends are discussed with reference to condition and fatigue stress level.
The results suggest that mechanical fatigue may be a factor in the failure of water distribution pipes. The results may have implications for large diameter trunk mains as well as the small diameter water distribution pipes tested here. To assess the effect in more detail, consideration needs to be given to scaling effects in fatigue and the likely levels of any fatigue stress seen in service.     

The Effect of Phosphate on the Properties of Copper Drinking Water Pipes Experiencing Localized Corrosion

Extensive localized or pitting corrosion of copper pipes used in household drinking water plumbing can eventually lead to pinhole water leaks that may result in water damage, mold growth, and costly repairs. Water chemistry has been recognized as the cause of some community-wide copper pinhole leak outbreaks. A large drinking water system in Florida recently switched from pH adjustment and orthophosphate addition to a blended ortho-polyphosphate chemical to address this problem. The objective of this study was to examine the impact of phosphates on the morphology and elemental composition of the interior surface of failed copper pipes removed from homes in the community. Scanning electron microscopy (SEM) and energy dispersive spectroscopy analysis of pipe surfaces revealed the build-up of phosphorus over time. Phosphorus was most greatly concentrated over areas of localized corrosion attack. Examination of the corrosion by-product mounds that covered corroding pits showed that phosphorus had migrated to the region adjacent to the copper pipe wall. Distinct copper–phosphorus solids were identified under SEM magnification; however, no crystalline copper–phosphate compound was identified by x-ray diffraction analysis.     

钢制管材在空调水系统中的选型及应用

阐述了空调水系统中几种常用钢管管材的应用范围和不同连接方式;分析了开式空调水系统和闭式空调水系统之间的区别,并结合不同的空调水处理方式给出了不同的空调水系统中推荐应用的钢管管材及其连接方式和几点应用原则。     

基于CFD的双声路超声水表研究

基于时差法的超声水表在中、大口径的水流量测量中,存在超声波信号易受外界干扰以及小流量的测量重复性较差等问题。针对以上问题,本文设计了具有缩径结构的管路模型。其次,通过CFD数值仿真研究了缩径管路模型在低流速下的流场分布情况。最后对本文设计的双声路超声水表样机进行了相关试验。试验结果表明,本文设计的管路模型有效提高了超声水表在小流量处的重复性与可靠性。     

Structural integrity analysis of HDPE pipes for water supplying network

A problem of reliability of polymer pipes manufactured with the high‐density polyethylene (HDPE) for drinking water supply was considered. The safety of the pipelines network was analyzed with taking into account two main factors: arising of sudden overpressure (water hammer phenomenon) and presence of defects on pipe surface. Based on elastoplastic fracture mechanics and using of J‐integral approach, the numerical model of cracked pipe was developed and verified by direct experimental test. The formula for calculation of crack initiation pressure, which is the function of pipe size and size of external surface defect, was derived. The validity of this relation was proved for pipes of diameter 450 to 800 mm. It was also shown that the pressure peaks of the water hammer phenomenon are quickly damped because of the high deformability of the polyethylene pipes and the defect depth that is equivalent to 40% of pipe wall thickness can be considered as acceptable. The applicability of developed tools was demonstrated under analysis in the real state of South Tunisian water supply network.     

Methods for determining the in-service life of polymer water pipes

A key requirement for polymer pipes, in having the ability to achieve a long in service life, is the retention by the polymeric material of its anti-oxidants. In dry air and other favourable environmental conditions the life-span of the polymer material can be many decades. However, when polymer pipes are transporting water and the pipes need to be installed in all kinds of ground conditions then the loss of anti-oxidant from the polymer can become more of a problem. To maintain integrity of water distribution networks, companies aim to plan for replacement of water pipes before they are likely to fail. This paper presents ways in which small scale evaluations of aged pipe material can be employed to assess remaining in-service life of water pipes. Small-scale chemical and physical evaluations have been devised to provide indicators of the ageing process with associated loss of mechanical properties. The presented studies were performed using MDPE and PE80 pipe materials. These materials were evaluated before and after ageing to identify which chemical and physical evaluations were the most appropriate to assess the remaining life of in service polymer pipes.     

The deformation mechanics of interlock tubes

Interlock tubes are one of the key structural layers of most flexible pipes of composite construction for offshore oil and gas transmission and water injection applications. The design and manufacture of such a tube based on a good understanding of its deformation mechanics are undoubtedly of significance to the integrity and safety of flexible pipes and pipe systems. This paper describes a semi-empirical model for the evaluation of the deformations in the critical sections of the interlock tube as it responds to the overall pipe loading and configuration. Results of a finite element analysis and radiographic tests are incorporated to verify and supplement the model.     

建筑隔震金属柔性管道抗震性能试验研究

隔震层中具有大变形需求的柔性管道显著影响隔震建筑的震后功能可恢复能力,然而目前对于柔性管道抗震性能的研究还相对较少。该文以量大面广且承载重要功能的竖向安装金属柔性管道为研究对象,考虑实际工程应用现状和相关规范建议,以400 mm变形为目标,以公称内径、管道安装长度、管道设计长度为研究变量,共设计了9组27个试件,进行了抗震性能试验,研究了金属柔性管道的损伤演化模式、关键损伤状态及其变形和承载能力。结果表明:目前工程上采用的柔性管道设计方案无法满足大变形需求或存在安全隐患,规范建议的方案则可很好地满足目标;对于破坏的柔性管道主要经历两个关键状态,即外金属套网绷直和单侧完全拔出破坏,破坏后无法承受工作压强需要更换;水平变形能力主要取决于管道安装长度和管道设计长度,随两者的增大而增大;破坏主要取决于管道受拉竖向荷载分量,该分量近似正比于公称内径,破坏水平荷载随着公称内径和极限水平位移的增大而增大。该文的研究成果可为建筑隔震金属柔性管道的抗震设计和易损性研究提供重要参考。