A probabilistic approach to evaluate creep and fatigue damage in critical components

The subject of reliability assessment of plant components is of considerable importance to maintenance and operations engineers. There exist different degradation mechanisms such as creep and fatigue in the plant components operating under conditions of high pressure and temperature. Hence, the safety issue of these components must be addressed by a realistic reliability model so that the frequency of in-service inspection activities can be optimized. In this work, a probabilistic module based on first order reliability method and Markov model is used in order to calculate different failure state probabilities of an in-service thermal power plant pipe-bend. This procedure helps in online risk assessment of critical plant components. The method of determination partial safety factors of the above component for optimum design based on a target reliability level is also discussed.     

Life prediction of reprocessing (CORAL) components

The purpose of Compact Facility for Reprocessing of Advanced Fuels in Lead cell (CORAL) is for reprocessing of irradiated fuel. Towards arriving at life of CORAL, various critical components like titanium dissolvers, reflux condenser, waste storage tank and process tanks in the facility have been identified and analyzed for pressure and thermal loadings. All these components are operating below 126° C and hence there is no concern of creep damage. However, the junctions are subjected to cyclic thermal loadings which may restrict the design life. Moreover the various parts of the components such as tube and shell can have differential expansion leading to thermal stresses which along with stress concentration can restrict the fatigue life of the components. The stress analyses of all the critical components are carried out using Finite Element Software CAST3M, issued by CEA, France. The fatigue damage evaluation has been done as per the French design code RCC-MR 2002. It has been demonstrated that low cycle fatigue is not a major concern and the life of thin parts are governed by corrosion considerations. A small nozzle (8 NB) in the dissolver is found to govern the design life from corrosion consideration. The analyses, apart from helping to identify critical locations of various parts and design life of various mechanical components, also focused the importance of corrosion as the governing failure mode.     

高速线材轧机油膜轴承载荷工况在线测试

 为了研究高速线材轧机油膜轴承烧损原因,对国内某高速线材精轧机F15机架油膜轴承载荷工况及工作温度进行了在线测试,获得了大量有价值的试验数据。实验结果对研究高速线材轧机油膜轴承损伤机理、提高寿命和实现在线测控具有重要的参考价值。     

中厚板轧机工况在线监测系统的探讨

分析了中厚板轧机工况在线监测系统的必要性、实用性，同时对中厚板轧机工况在线监测系统的功能、构成、硬件和软件配置及应用前景做了详细的技术阐述。     

Use of Supervisory Control and Data Acquisition for Damage Location of Water Delivery Systems

Urban water delivery systems can be damaged by earthquakes or severely cold weather. In either case, the damage cannot easily be detected and located, especially immediately after the event. In recent years, real-time damage estimation and diagnosis of buried pipelines attracted much attention of researchers focusing on establishing the relationship between damage ratio (breaks per unit length of pipe) and ground motion, taking the soil condition into consideration. Due to the uncertainty and complexity of the parameters that affect the pipe damage mechanism, it is not easy to estimate the degree of physical damage only with a few numbers of parameters. As an alternative, this paper develops a methodology to detect and locate the damage in a water delivery system by monitoring water pressure on-line at some selected positions in the water delivery systems. For the purpose of on-line monitoring, emerging supervisory control and data acquisition technology can be well used. A neural network-based inverse analysis method is constructed for detecting the extent and location of damage based on the variation of water pressure. The neural network is trained by using analytically simulated data from the water delivery system with one location of damage, and validated by using a set of data that have never been used in the training. It is found that the method provides a quick, effective, and practical way in which the damage sustained by a water delivery system can be detected and located.     

Remaining life assessment issues in high Cr martensitic steels and development of new innovative tools for damage monitoring and integrity assessment

The relatively newer high Cr martensitic steels such as P91 have now been in use in power industry for over twenty years. Over this time, there have been a number of incidents of cracking and failure in components made from P91 steel, both in thick and thin section equipments mainly due to creep damage. The thick section components have been usually failing due to Type IV cracking associated with the weldments while thin section components have been failing due to higher than expected levels of steam oxidation resulting in enhanced metal loss, increase in metal temperature above design, creep cavitation and cracking. However, it has not been possible to detect early stage creep damage/cavitation in high Cr martensitic steels using conventional replication type methods. This is because unlike the low alloy CrMoV steels, spherodisation of microstructure does not occur in high Cr martensitic steels and cavitation clearly visible by traditional methods only appears later in life when the material is about to fail. Thus there has been a need to develop new tools and more sensitive methods for integrity and damage assessment in these steels. European Technology Development (ETD) together with its industrial collaborators from Europe, Japan and North America have been looking at the development of tools and methodologies for early stage damage detection and life prediction as a part of its international multi-client project ‘P91 Integrity’. The tools which have shown successful results are portable Scanning Force Microscopy, laser guided hardness tester and more innovative use of ultrasonic probes for detecting early stage creep damage. This paper discusses the issues involved and describes some of the developments in this project.     

深埋硬岩隧道围岩参数概率反演方法

在贝叶斯理论框架下, 提出了一种基于多源数据融合的深埋硬岩隧道围岩参数概率反演方法.首先, 分析硬岩隧道常用的启裂-剥落界限本构模型中围岩单轴抗压强度、启裂强度与抗压强度比及抗拉强度三个参数不确定性来源, 确定其概率统计特征; 其次, 利用粒子群算法优化多输出支持向量机, 建立反映反演参数与隧道监测数据间非线性映射关系的智能响应面; 最后, 结合贝叶斯分析方法构建概率反演模型, 运用马尔科夫链蒙特卡洛模拟算法实现了围岩参数的动态更新.将该方法应用到某深埋硬岩隧道中, 利用反演的围岩参数计算隧道拱顶下沉点、周边收敛点变化值及开挖损伤区深度, 与监测数据吻合较好.结果表明, 该方法可以实现围岩多参数快速概率反演, 更新后的参数可用于硬岩隧道施工安全风险评估与结构可靠性设计.      

浅淡尾矿库安全在线监测系统

介绍了尾矿库在线监测系统监测的主要内容及相关仪器设备的应用。相对于人工传统监测,尾矿库在线监测系统能够实现重要监测指标在各种气候条件下的连续实时监测,大幅降低尾矿库管理人员的工作强度,监测数据的精度高。并对尾矿库在线监测系统的发展提出了一些看法和建议。     

Consumed creep life fraction assessment of critical locations of an in-service super heater outlet header under surveillance programme

Boilers and turbines including high-energy piping and headers are operated round-the-clock in the creep regime. For the integrity of such components and equipments, it is essential to have a real-time monitoring system to identify and monitor the critical locations. As per statutory requirement of IBR Act 391A of 1998, a component is to be taken for surveillance programme, if its design life is exhausted. One such exercise was conducted at locations in close proximity to the header-stub weld joints of higher heat-flux zone after 1,12,547 hours of operation. The in-situ metallography technique developed indigenously within the country (i.e., cryogenic in-situ metallography) was adopted for assessment of locations closest to the identified weld joints of a superheater outlet header (SHOH) of a 210 MW unit of a super thermal power station. The qualitative assessment done using high resolution microscopy has indicated that the creep cavities correspond to stage-II of Neubauer’s classification diagram. Subsequently image analysis of in-situ replicated photomicrographs extracted from the investigating locations was carried out. The accrued creep damages (cavitation) at the locations were quantified for cavitated grain boundaries and correspondingly ldA” parameters were derived to evaluate the extent of life exhaustion of respective locations.     

Bayesian Probabilistic Approach to Structural Health Monitoring

A Bayesian probabilistic methodology for structural health monitoring is presented. The method uses a sequence of identified modal parameter data sets to compute the probability that continually updated model stiffness parameters are less than a specified fraction of the corresponding initial model stiffness parameters. In this approach, a high likelihood of reduction in model stiffness at a location is taken as a proxy for damage at the corresponding structural location. The concept extends the idea of using as indicators of damage the changes in structural model parameters that are identified from modal parameter data sets when the structure is initially in an undamaged state and then later in a possibly damaged state. The extension is needed, since effects such as variation in the identified modal parameters in the absence of damage, as well as unavoidable model error, lead to uncertainties in the updated model parameters that in practice obscure health assessment. The method is illustrated by simulating on-line monitoring, wherein specified modal parameters are identified on a regular basis and the probability of damage for each substructure is continually updated.     

Damage Assessment of FRP-Encased Concrete Using Ultrasonic Pulse Velocity

Since concrete members with fiber-reinforced polymer (FRP) reinforcement are not as ductile as conventional structures, and since concrete in retrofitted members is often covered and not readily available for visual inspection, development of nonintrusive and nondestructive damage assessment tools is essential. Ultrasonic pulse velocity (UPV) can provide such an assessment tool, and help quantify the extent and progression of damage in concrete. Continuous UPV monitoring of a number of concrete cylinders and concrete-filled FRP tubes showed the concrete-filled tubes to have higher sensitivity at lower stress ratios as compared to plain concrete. When compared with the axial strain energy, the UPV damage index has a much better resolution for stress ratios up to about 50% of ultimate strength. This ratio depends on the thickness of the jacket. It was also shown that the UPV has a strong correlation with volumetric strains after confinement is activated. Therefore, at high levels of axial loads when the confining pressure of the jacket results in volumetric compaction, the UPV increases by about 6% of the initial pulse velocity. Repeated loading generally induces the same rate of change of UPV damage index as that of the initial loading on the virgin specimen. This phenomenon occurs irrespective of the stress ratio at which the specimen is unloaded or reloaded. A comparison of the UPV damage index with the normalized acoustic emission counts reveals that the two methods have different sensitivities at different stages of loading and could potentially complement each other as a hybrid damage assessment tool.     

Inclusion of Crawl Tests and Long-Term Health Monitoring in Bridge Serviceability Analysis

Due to limited resources, structural health monitoring (SHM) of highway bridges has to be integrated in structural performance assessment in a cost-effective manner. The instrumentation and the long-term SHM procedures are generally chosen with emphasis on most critical bridge components for a particular failure mode. However, global structural analysis is necessary to obtain useful structural performance information. It is then a major challenge to use monitoring data at some locations to perform a structural reliability analysis at other locations. In this paper, a methodology for lifetime serviceability analysis of existing steel girder bridges including crawl tests and long-term monitoring information is presented. The case where the initial goal of monitoring is to provide data for a fatigue analysis of some bridge components is considered. The monitoring results are used to perform a structural reliability analysis of different sections that are critical considering serviceability of the bridge. Limit state equations are used firstly by adhering to the load and strength formulas and requirements set forth in AASHTO specifications, and secondly by integrating monitoring information. Serviceability with respect to permanent deformation under overload is estimated for the girders with these two different methods and a time-dependent performance analysis is conducted by considering corrosion penetration. The proposed approach is applied to the I-39 Northbound Bridge over the Wisconsin River in Wisconsin. A monitoring program of that bridge was performed by the Advanced Technology for Large Structural Systems Center at Lehigh University.     

Reliability-Based Assessment of Suspension Bridges: Application to the Innoshima Bridge

Many suspension and cable-stayed bridges were designed and constructed between Honshu Island and Shikoku Island in Japan. All these bridges were designed according to the allowable stress design method. In the allowable stress design method, it is not possible to quantify the reliabilities of both bridge components and the entire bridge system. Therefore, in light of current reliability-based design philosophy, there is an urgent need to assess the safety of suspension bridges from a probabilistic viewpoint. To develop cost-effective design and maintenance strategies, it is necessary to assess the condition of suspension bridges using a reliability-based approach. This is accomplished by a probabilistic finite-element geometrically nonlinear analysis. This study describes an investigation into the reliability assessment of suspension bridges. The combination of reliability analysis and geometrically nonlinear elastic analysis allows the determination of reliabilities of suspension bridges. A probabilistic finite-element geometrically nonlinear elastic code, created by interfacing a system reliability analysis program with a finite-element program, is used for reliability assessment of suspension bridges. An existing suspension bridge in Japan, the Innoshima Bridge, is assessed using the proposed code. The assessment is based on static load effects. Reliabilities of the bridge are obtained by using 2D and 3D geometrically nonlinear models. Furthermore, damage scenarios are considered to assess the effects of failure of various elements on the reliability of undamaged components and on the reliability of the bridge. Finally, sensitivity information is obtained to evaluate the dominant effects on bridge reliability.     

Design of new precision alloys

The design of precision alloys with specific physical properties and corresponding composites and products is considered. By state-of-the-art methods, not only the physical properties of the steel may be adjusted, but also the reliability of the alloys (and the corresponding composites and components) when operating in critical conditions.     

Experimental Analysis of Local Pressure Losses for Microirrigation Laterals

The accurate design of drip irrigation laterals needs to consider the variation of hydraulic head due to pipe elevation changes, head losses along the lines, and also, at a given operating pressure, emitter discharge variations related to manufacturing variability, clogging, and water temperature. Hydraulic head variations are consequent to both the friction losses and local losses due to the in-line or on-line emitters along the pipe, which determine the contraction and subsequent enlargement of the flow streamlines. Moreover, in-line emitters usually have a smaller diameter than the pipe, and therefore an additional friction loss must be considered. Evaluation of energy losses and consequently the design of drip irrigation lines is usually carried out by assuming the hypothesis that local losses can be neglected, even if previous experimental researches showed that local losses can become a significant percentage of total head losses as a consequence of the high number of emitters installed along the lines. This paper reports the results of an experimental investigation to evaluate local losses in integrated laterals in which coextruded emitters are installed inside the pipe. Local losses were measured for 10 different types of commercially available integrated laterals and for different Reynolds numbers. A practical power relationship was deduced between the α coefficient, expressing the amount of local losses as a fraction of the kinetic head, and a simple geometric parameter characterizing the geometry of the emitter and the pipe. Local losses obtained for integrated laterals were then compared with those due to the on-line emitters, previously determined as a function of the pipe-emitter geometry. The proposed criterion for calculating the local losses was finally verified by using a step-by-step procedure.     

Photorefractive keratectomy following radial keratotomy

A purification and on-line monitoring procedure for IgM was developed. Perfusion ion-exchange chromatography was used for rapid purification of IgM from ascites fluid and hybridoma supernatant. Crude ascites was directly loaded onto an ion exchanger. Due to the complexity of IgM, a two-step ion-exchange procedure had to be developed. This procedure involved a rapid cation-exchange chromatography capture step followed by further purification using anion-exchange chromatography. High linear velocities, in excess of 3500 cm/h, enabled separations to be performed under 5 min. Purity of the final product by SDS-PAGE was shown to be greater than 95%. Furthermore, the antibodies retained biological activity as measured by indirect immunofluorescence (IIF) and ELISA. The IgM peak was also monitored on-line using a novel peak tracking approach. This involved placing an antibody column (specific to the IgM) prior to the ion-exchange column and operating the ion-exchange column with and without the antibody column in-line. The missing peak that is identified by comparing the two chromatograms indicates where the IgM elutes.     

基于高精度倾角传感器的活塞倾斜度在线监测

通过对威金斯干式煤气柜活塞倾斜度在线监测系统的设计,实现了活塞倾斜度的实时跟踪、记录和监测,保障了气柜的安全运行,并提高了现场工厂的自动化作业水平。在活塞倾斜度在线监测系统的设计中,首次将高精度倾角传感器应用在硬件系统中,大大降低了初期投资,节约了成本,有较高的实际应用价值。     

Projectile Shape and Material Effects in Hypervelocity Impact Response of Dual‐Wall Structures

All large spacecraft are susceptible to impacts by meteoroids and pieces of orbiting space debris. These impacts occur at extremely high speeds and can damage flight‐critical systems, which can in turn lead to catastrophic failure of the spacecraft. A long‐duration spacecraft developed for a mission into this environment must include adequate protection against perforation of pressurized components by such impacts. This paper presents the results of an investigation into the effects of projectile shape and material on the perforation of aluminum dual‐wall structural systems. Impact damage is characterized according to the extent of perforation, crater, and spall damage in the structural systems as a result of hypervelocity projectile impact loadings. Analysis of the damage data shows that there are distinct differences in impact damage from cylindrical and sherical projectiles. Projectile density is also found to affect the type and extent of damage sustained by dual‐wall structural systems.     

Ironic processes of mental control.

A theory of ironic processes of mental control is proposed to account for the intentional and counterintentional effects that result from efforts at self-control of mental states. The theory holds that an attempt to control the mind introduces 2 processes: (1) an operating process that promotes the intended change by searching for mental contents consistent with the intended state and (2) a monitoring process that tests whether the operating process is needed by searching for mental contents inconsistent with the intended state. The operating process requires greater cognitive capacity and normally has more pronounced cognitive effects than the monitoring process, and the 2 working together thus promote whatever degree of mental control is enjoyed. Under conditions that reduce capacity, however, the monitoring process may supersede the operating process and thus enhance the person's sensitivity to mental contents that are the ironic opposite of those that are intended. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working surface of components made from high-alloy corrosion-resistant steel

The internal (working) surfaces of pipes and other components made from corrosion-resistant austenitic steel are investigated. The influence of the production parameters, the metal structure, and the operating conditions on the surface of critical components is established.