A Method of Measuring Through‐Thickness Internal Strains and Stresses in Graphite

Abstract: Currently, the structural integrity of the nuclear graphite reactor components is evaluated using irradiated material properties data obtained from test reactors. These data are applied to numerical or mathematical models to assess the integrity of the graphite components. On the other hand, there is a need to measure internal strains and stresses in reactor core graphite and to explore the potential for in‐situ measurement. The deep hole drilling (DHD) technique is a semi‐destructive method for measurement of the through thickness residual strains or stresses. Previously the technique has been applied successfully to metallic and composite materials. In this paper, the method for internal strain and stress measurement in polygranular graphite is examined particularly when a significant volume fraction of porosity is present. Finite element simulation shows that the method can be used to measure internal stresses generated by a thermal gradient. On the basis of this a series of experiments have been conducted using Pile Grade ‘A’ (PGA) and PG25 filter graphite; with the latter being a surrogate for service exposed material. Tests were conducted to illustrate that the bulk mechanical response was linear elastic for both graphites and elastic moduli were measured. The DHD method was then used to determine internal strain and stress profiles through the materials. The results were compared with the strain data obtained from strain gauges bonded to the samples. Overall, there was an excellent agreement between the measured through‐thickness internal strains and stresses and the surface strains and stresses determined from the applied loading.     

Mohr's circle in measurement of residual strains by through hole drilling technique: Effect of transverse sensitivity

The construction of Mohr's circle for measurement of residual strains in thin plates by the Hole Drilling Method is described. The relative errors in determining the location of the centre and the radius of Mohr's circle due to ignoring the effect of transverse sensitivity are calculated. For normal gauges with low cross sensitivity, these errors are shown to be negligible (less than 1%).     

Long-term service effect on the toughness of pipeline steel 17GS

A transit oil pipeline, 720 mm in diameter, 334 km in length, and made of steel 17GS, after 30 years of service was twice non-destructively tested with intelligent Pipeline Inspection Gauges (PIGs). Two segments of this pipeline were cut in order to investigate the steel structure, composition, and mechanical properties and to compare these properties with those of `archive' material. Metallographic and microprobe analyses revealed no significant difference between the `archive' and `aged' materials. Specimens for testing tensile mechanical properties, for fatigue-crack growth rate measurements, and for a Charpy test were used. All those specimens were fabricated from both the base and weld metal in longitudinal and circumferential directions. At room temperature, the ultimate strength of the aged steel was found to be 5% higher than that of the `archive' material, whereas the yield point was 18% higher for the aged material. Charpy energy changed more significantly; decreasing by approximately 40% at room temperature. In addition to conventional mechanical properties, new characteristics such as `microcleavage stress' R _MC (minimum brittle fracture stress) and the toughness index K _T were determined. It has been found that a long period of operation does not affect the values of the steel microcleavage stress R _MC and does not influence the hardening exponent significantly. The use of the local approach to fracture has shown that an increase in yield stress is the main cause of the decrease in its toughness after long-term service. It is shown that a minor (15%) increase in the yield stress results in a rise (by 40°) in the Charpy transition temperature and may cause a twofold reduction in the fracture toughness K _IC.     

Model test study on influence of freezing and thawing on the crude oil pipeline in cold regions

Buried pipelines are one of most economical and convenient methods for the transportation of large volumes of oil and gas. When a pipeline is buried in cold regions, it may suffer frost damage. Previous studies of pipelines and the surrounding soils in cold regions have tended to concentrate on the theory and practical engineering problems. This paper reports the results of a model test to investigate the stresses and strains on the buried pipeline and surrounding soils in the permafrost and seasonal frost areas based on the Mo'he-Daqing section of the China-Russia Crude Oil Pipeline (CRCOP). The temperature of the soils surrounding the pipeline, displacement and axial strain as well as stress in the pipeline induced by frost heave and thaw settlement are monitored and analyzed. The test results will have some significance in guiding the construction of the CRCOP in cold regions.     

在役腐蚀管道动态非概率可靠性分析简

 腐蚀失效是压力管道失效的主要形式之一,研究腐蚀管道的可靠性具有重要理论意义和应用价值.在对腐蚀管道可靠性分析时,概率可靠性模型和模糊可靠性模型对于数据信息的要求较高.而在掌握不确定性信息很少情况下,为了充分利用管道的不确定性信息弥补原始数据的不足,可将腐蚀管道可靠性分析中的材料屈服强度、管道直径、缺陷深度和操作压力等不确定参数视为区间变量,基于区间模型建立一种在役腐蚀管道动态非概率可靠性模型,给出了腐蚀管道剩余寿命预测的简便方法.结合工程实例计算与分析,表明了文中所提出方法的可行性和合理性,并在此基础上,分析了管道的壁厚、缺陷深度、实际压力和腐蚀速率这些区间变量的不同变异系数对非概率可靠性指标的影响,分析结果表明非概率可靠性指标对管道壁厚的变异系数最为敏感.     

高钢级钢管和高压输送:我国油气输送管道的重大技术进步

近年来,我国管道企业和相关科研院所联合攻关,取得了一批关键技术成果,这些成果包括:研制了X70,X80钢级高性能管线钢及焊管、管件;突破国际上螺旋缝埋弧焊管的使用禁区,确立了具有中国特色的"大口径高压输送主干线螺旋埋弧焊管与直缝埋弧焊管联合使用"的技术路线;在国内首次研究了高压输气管道动态断裂与止裂问题,采用Battelle双曲线模型预测了西气东输和西气东输二线等管道延性断裂的止裂韧性;在国内首次研究了油气管道基于应变的设计方法,解决了该设计方法及抗大变形管线钢管在强震区和活动断层管段应用的技术难题;解决了高强度焊管的腐蚀控制和应变时效控制等技术。     

G2.5超声波燃气表的仿真与实验研究

超声波流量计在中低压燃气测量领域中,由于燃气压力小、流量变化大、流速低等因素会导致其测量精度低.针对以上问题,设计两种不同的基表结构,通过流体动力学仿真计算,获得了两种基表结构在不同流量点的流场分布,通过对超声波传播路径区域的流场速度的大小和分布均匀性分析,确定更为合理的测量管路结构.最后通过设计相关实验,验证了流场仿...     

Full-field measurement technique and its application to the analysis of materials behaviour under plane strain mode

The purpose of the paper is to provide a comprehensive experimental and numerical analysis of one of the encountered and critical state modes in sheet metal forming processes. The study is carried out with the help of the full-field measurement techniques. In order to confer some generality to the proposed work, several materials and different specimen shapes are considered that exhibit more or less homogeneous strain field. The proposed experimental study of the plane strain test is completed by a preliminary identification of the material parameters for non-linear behaviour at finite strains, using heterogeneous strain field.     

基于Web服务的PDC钻头井底流场分析平台研究

为解决常规PDC(polycrystalline diamond compact)钻头井底流场水力性能数值模拟分析时存在的门槛高、耗时长、重复工作量多等问题,建立了基于Web服务的PDC钻头井底流场分析平台。平台框架由上至下分为软件接口层、分析服务层和结果输出层。在服务端通过知识封装技术实现钻头井底流场分析过程的自动化、参数化和集成化;利用Web封装技术对参数化流场分析模板进行封装和管理,从而实现客户端基于Web服务的PDC钻头井底流场的分析研究。实例验证表明,采用该平台分析PDC钻头水力性能可有效降低CFD软件的使用门槛,提高钻头井底流场的分析效率,节约人力与物力,能够为石油装备企业提供规范化的技术支持。     

细管道中流速的超声相关法测量

针对应用常规超声波方法测量极小管径(5 mm及以下)中流体速度的精度较低问题,文章应用相关函数法精确测量时延,降低噪声对测量结果的影响,提高了极小管径中流体速度的测量精度.首先,利用COMSOLMultiphysics有限元仿真软件建立管道传输模型,然后将被顺、逆水流影响后的超声波波形数据分别导入Matlab软件,用插...     

A new method of calibrating strain release coefficients in measuring welding stresses

The measured values of welding residual stresses often exceed material yield strength (σ_y) or tensile strength (σ_t), in measuring welding residual stresses in the welded joints of low carbon steel or stainless steel by drilling a blind hole. It is quite evident that measured values do not represent reality. Local plastic strain caused by residual stress concentrations round the blind hole has a main effect on the measuring error of welding residual stresses. This article presents a new method of calibrating strain coefficients A and B for eliminating influence of local plastic strain. In calibrating strain release coefficients A and B, calibrating stresses applied on the specimen were increased so that material round the blind hole produced local plastic deformation, ie coefficients A and B contained a component of the plastic strain. Numerial values of coefficients A and B were classified into four grades. Every grade coefficient contained a different quantity of the plastic strain for offseting the influence of the plastic strain round the blind hole. Test results have proved that by adopting these coefficients more satisfactory values for residual stresses can be obtained in practical engineering. The measuring average error in stainless steel (1Cr18Ni9Ti) reduces from 109% to 1.52%. The measuring average error in low carbon steel reduces from 54.69% to 3.21%.     

基坑开挖爆破作用邻近压力燃气管道动力响应特性研究

确保复杂城市环境基坑爆破开挖工程中邻近压力燃气管道的安全性是关键性问题。依托武汉地铁8号线二期竖井基坑爆破开挖工程,利用现场监测数据建立ANSYS/LS-DYNA三维有限元数值计算模型,分析计算了不同运行压力条件下埋地燃气管道的动力响应特性。研究结果表明:实际工况下管道截面峰值合振速为0.453 cm/s,单元峰值von-Mises应力4.95 MPa,压力燃气管道处于安全运行状态;管道截面峰值合振速大于其正上方地表振速,且两者存在线性关系,由此建立管道爆破振动速度的预测模型;管道截面峰值合振速、峰值von-Mises应力均位于迎爆侧,且随管道内压的增加而增加,内压为零时为最佳运行状态,由此建立了管道峰值von-Mises应力与内压、爆破参数的数学计算模型,为实际爆破工程的安全作业提供指导。     

天然气管道全尺寸止裂实验中的引燃实验

为了在天然气输气管道全尺寸止裂实验中,有效收集天然气管道爆燃后的热辐射、冲击波和管道止裂尺寸等数据,采用电子雷管及其芯片技术,对管道天然气泄漏扩散并发生爆燃进行了模拟实验。运用线型聚能切割器在内装天然气的管道上爆破切开1条初始裂缝,在管道周围布置引燃弹点燃泄漏天然气与空气的混合物,利用电子雷管及其芯片控制起爆及引燃弹的发射时间,实现了精确点火。输气管道失效爆破实验取得了预期效果,为天然气泄漏危害范围的研究和输气管道钢材质量的判断提供了科学依据。在天然气输气管道全尺寸止裂实验的爆破工程中成功运用了电子雷管及其芯片技术,对类似爆破工程具有一定的参考意义。     

X90钢级高压气体管道爆炸裂纹起裂与止裂实验研究

开展X90钢级高压气体管道爆炸模型实验,初步探索并解决了管道爆炸实验的关键技术问题,为管道全尺寸爆破实验提供数据和方法支撑。结果表明:实验方法及测试仪器的选择可靠有效,解决了管道封堵、初始裂纹引入、传感器安装及密封、动态参量测试以及测试系统构建等关键技术问题;填充空气的运行压力为12.3MPa的X90钢管裂纹最大扩展速度约为248m/s,临界止裂压力约为4.5MPa,临界止裂速度约为100m/s;裂纹止裂器止裂效果明显,可进一步优化其安装位置并适当加宽加厚,进一步提高止裂效果。     

X90钢级高压气体管道爆炸裂纹起裂与止裂实验研究

开展X90钢级高压气体管道爆炸模型实验,初步探索并解决了管道爆炸实验的关键技术问题,为管道全尺寸爆破实验提供数据和方法支撑。结果表明:实验方法及测试仪器的选择可靠有效,解决了管道封堵、初始裂纹引入、传感器安装及密封、动态参量测试以及测试系统构建等关键技术问题;填充空气的运行压力为12.3MPa的X90钢管裂纹最大扩展速度约为248m/s,临界止裂压力约为4.5MPa,临界止裂速度约为100m/s;裂纹止裂器止裂效果明显,可进一步优化其安装位置并适当加宽加厚,进一步提高止裂效果。     

A study on the induced drilling stresses in the centre hole method of residual stress measurement

This paper aims at the improvement of the accuracy of the centre hole method of residual stress measurement by reducing the error caused by the drilling itself. Based on the results of an intensive experimental investigation, a new approach is proposed for the determination of the induced drilling stresses caused by the mechanical drilling process. In this study, the electric discharge machining (EDM) technique was utilised to obtain a stress free sample from the bulk material. As compared to the annealing heat treatment method for obtaining a stress free sample, it was found that the EDM technique does not cause the changes of the structures and machining properties of the parent material. Thus, the induced drilling stresses in centre hole method can be evaluated more accurately by using a stress free sample obtained by EDM technique than by using an annealed one.     

精氩塔余气放空管道堵塞处理

在空分设备停车期间,因精氩冷凝器内存有液氮,造成精氩塔氩侧产生负压,使湿空气通过余气放空管道进入精氩塔,水分在低温处结冰后冻堵余气放空管。介绍处理措施和故障处理时的注意事项,并提出了防范措施。     

Performance Analysis of the Mesh‐Free Random Grid Method for Full‐Field Synthetic Strain Measurements

Abstract: In responding to the needs of the material characterization community, the recently developed mesh‐free random grid method (MFRGM) has been exhibiting very promising characteristics of accuracy, adaptability, implementation flexibility and efficiency. To address the design specification of the method according to an intended application, we are presenting a sensitivity analysis that aids into determining the effects of the experimental and computational parameters characterizing the MFRGM in terms of its performance. The performance characteristics of the MFRGM are mainly its accuracy, sensitivity, smoothing properties and efficiency. In this paper, we are presenting a classification of a set of parameters associated with the characteristics of the experimental set‐up and the random grid applied on the specimen under measurement. The applied sensitivity analysis is based on synthetic images produced from analytic solutions of specific isotropic and orthotropic elasticity boundary value problems. This analysis establishes the trends in the performance characteristics of the MFRGM that will enable the selection of the user controlled variables for a desired performance specification.     

原油成品油管道同沟敷设新技术中的热力分析

采用非结构化有限容积法,对原油成品油双管同沟敷设新技术进行数值模拟,详细研究了不同管间距下成品油管道对加热输送原油管道的热力影响,尤其是对热油油温的影响。     

X80管线钢不同缺陷类型的磁记忆检测试验研究

为探究X80管线钢不同缺陷类型的力磁耦合特性,设计了平板试件与穿孔、边缘切槽3种不同试件,通过金属磁记忆检测方法对X80管线钢试件不同缺陷类型的磁记忆信号特征进行了试验研究.采用材料试验机对试件导入不同程度的塑性损伤与应力集中,通过光学应变测量系统获取试件表面的实时应变情况,同时采用磁记忆检测仪对试件表面诱发磁场的法向分量与切向分量进行卸载离线检测.结果表明:随着塑性损伤程度的增加,无缺陷试件的磁记忆信号法向分量与切向分量从平缓趋向波动,但未出现明显的峰值;含穿孔与切槽试件磁记忆信号法向分量在缺陷处出现过零点与反对称双峰,切向分量出现单峰值,并且渐趋明显.初步探究了X80管线钢塑性损伤与磁记忆信号之间的关联性,为油气管道塑性损伤程度的无损定量评价奠定了基础.