电站和化工厂压力容器与管道的失效模式及防御措施

罗列了有关压力容器与管道失效的知识。根据大量的参考文献的研究结果,对压力容器与管道的失效原因及相关的防御措施进行了综合评述。     

压力设备腐蚀失效案例统计分析

收集整理近年来有关压力容器管道的腐蚀失效案例,并对其进行了归纳与分析.从整体的腐蚀情况来看,应力腐蚀及其它应力作用下的腐蚀失效形式是压力容器管道比较突出的腐蚀失效问题,同时奥氏体不锈钢、碳钢及低合金钢三种材料的腐蚀失效较严重.     

数据库和模式识别技术在失效分析中的应用

介绍了数据库技术和模式识别技术在压力管道、压力容器腐蚀失效分析中的两个应用.以当前最流行的数据库技术SQL Server存储各种压力管道、压力容器腐蚀案例数据,ASP(Active Server Page)技术开发应用程序,实现了一个基于WEB方式的压力管道、压力容器腐蚀失效案例库;利用Hopfield神经网络工作原理,研究适用于腐蚀失效模式识别的学习、推理机模型.在此基础上,运用面向对象的编程技术及数据库技术,开发并实现能够学习、识别腐蚀失效模式的软件系统.     

埋地PVC管纵向断裂失效预测概率模型

针对存在初始裂纹缺陷的埋地PVC管在荷载作用下的纵向断裂失效问题,基于管道环向受力特性和裂纹扩展经验公式建立失效预测模型,并在此基础上运用蒙特卡罗法(MC)对模型和参数的不确定性进行随机模拟,给出管道失效风险率随服役时间变化的规律。计算结果表明:MC数值模拟结果与实测值吻合良好,说明失效预测模型的合理性;裂纹增长是一个由慢到快的过程,初始裂纹越大,失效时间越短;失效风险率在开始的20年内达到最高,随后逐渐减小;所有参数都作为随机变量考虑时与只有初始裂纹为随机变量时相比,失效风险率提高近一倍;管道初始裂纹、内压、残余应力和壁厚是影响管道失效时间的四个重要因素,管道内压和残余应力增加都导致管道失效率变大,准确的给出管道初始裂纹的分布对PVC管纵向断裂失效预测尤为重要。能够减小PVC管初始裂纹缺陷的生产工艺和施工技术可以有效提高管道的使用寿命。     

低温绝热压力容器失效因素与检验评定技术思考

在运行过程中低温绝热压力容器很容易出现失效的问题,这时候就需要认真分析失效的原因,选择恰当的检验和评定方式,只有这样才能妥善处理失效的低温绝热压力容器。本文对导致低温绝热压力容器失效的因素进行了分析,并且对其检验评定技术进行了探讨。     

两起压力容器失效原因分析及防范建议

压力容器裂纹导致失效已经成为化工企业生产装置中突出的安全隐患,直接影响了生产装置的健康稳定运行.随着国内生产企业数量日益增长,压力容器的使用数量快速增加,为了保障人民群众的生命及财产安全,对压力容器实施定期检验意义重大.通过对两起压力容器的裂纹失效案例进行分析,总结了裂纹产生的原因,提出了防范此类失效风险的建议,为国内...     

油气管道失效分析与完整性管理

论述了油气管道的失效模式和失效原因,以及完整性管理的概念、流程和关键技术.对失效分析和完整性管理的关系进行了讨论,认为失效分析是油气管道完整性管理的基础;完整性管理是油气管道失效分析的延伸,是全面、科学有效的预测、预防管道失效的措施.     

真空绝热压力容器定期检验评定方法研究

介绍了真空绝热压力容器定期检验和评定过程中存在的问题,首先根据检验经验,结合《压力容器定期检验规则》(TSG R7001—2013)等相关规程、标准,认为引起真空绝热压力容器的失效原因为马氏体组织引发的封头直边端开裂、夹层与气液相接管连接的角焊缝泄漏及安全附件失效,其中夹层真空失效是引发真空绝热压力容器失效的主要原因;其次结合失效原因,分析了真空度测量及检验项目设定中存在的问题;最后探讨了真空绝热压力容器的定期检验项目的设定及安全状况等级的评定。希望通过笔者的研究工作,对真空绝热压力容器的检验评定起到一定的指导作用。     

管道失效判据简析

在外部载荷超过管道所能承受范围时管道即发生失效。通过研究管道在外力作用下的力学性能,有助于确定管道失效时的应力或应变的临界值,根据是取应力还是取应变作为衡量管道失效时的指标,分别有基于应力的失效判据和基于应变的失效判据。合理选用管道失效判据,可以节约管道投资、延长管道使用时间。简介材料应力—应变曲线的一般特征,分析管道基于应力的失效判据和基于应变的失效判据的方法。     

城市埋地燃气管道的失效树建立与风险评估

依据失效分析理论,运用演绎法建立了城市埋地燃气管道失效树.通过最小割集和结构重要度分析确定了城市埋地燃气管道失效的主要原因及其相对重要程度.在此基础上,建立了适合我国国情的城市埋地燃气管道风险评估技术体系,包括管道区段的划分、失效可能性评分体系、失效后果评分体系和风险等级划分.     

Lattice Discrete Particle Model (LDPM) for failure behavior of concrete. I: Theory

This paper deals with the formulation, calibration, and validation of the Lattice Discrete Particle Model (LDPM) suitable for the simulation of the failure behavior of concrete. LDPM simulates concrete at the meso-scale considered to be the length scale of coarse aggregate pieces. LDPM is formulated in the framework of discrete models for which the unknown displacement field is not continuous but only defined at a finite number of points representing the center of aggregate particles. Size and distribution of the particles are obtained according to the actual aggregate size distribution of concrete. Discrete compatibility and equilibrium equations are used to formulate the governing equations of the LDPM computational framework. Particle contact behavior represents the mechanical interaction among adjacent aggregate particles through the embedding mortar. Such interaction is governed by meso-scale constitutive equations simulating meso-scale tensile fracturing with strain-softening, cohesive and frictional shearing, and nonlinear compressive behavior with strain-hardening. The present, Part I, of this two-part study deals with model formulation leaving model calibration and validation to the subsequent Part II.     

Failure analysis of seven masonry churches severely damaged during the 2012 Emilia-Romagna (Italy) earthquake: Non-linear dynamic analyses vs conventional static approaches

This study presents a detailed failure analysis of seven masonry churches, which were severely damaged during the 2012 Emilia-Romagna (Italy) seismic sequence, by means of 3D FE non-linear dynamic simulations. The main aims of the numerical investigations are: (1) to carry out a sufficiently wide sensitivity study on different specific case studies to have an insight into the role played by the geometry – which is always unique for churches – and by the irregularities; (2) to validate or address the limits of applicability of the most widespread conventional static approaches recommended by Italian Code, i.e. kinematic limit and pushover analyses. Non-linear dynamic analyses are carried out assuming that masonry behaves as a non-linear material exhibiting softening and damage, frictional behavior and different strength in tension and compression. The set of case studies investigated in this work shows how conventional static approaches are still capable of roughly identifying the most critical macro-elements that usually activate a failure mechanism, but that the results (e.g. collapse acceleration, behavior factor) are affected by a level of approximation that may considerably depend on in-plan irregularity and hypotheses done on the interlocking between contiguous walls. From the comparative analyses carried out, it is authors’ opinion that it is always beneficial to perform different types of analysis in order to have a comprehensive insight into the portions of the structure that can suffer a partial collapse with high probability. Once the active mechanism is identified, non-linear dynamic analyses, with more sophisticated material models and with refined FE discretizations of the critical regions, may be useful to deepen the knowledge of the behavior of such complex structures under seismic actions.     

Design oriented failure model for wood accounting for different tensile and compressive behavior

Recent biaxial experiments on clear-spruce wood allow to have a more complete understanding of fracture behavior of wood. An elliptic failure surface, like that of Tsai–Wu, has been previously proposed as a failure surface. Previous works in this area have shown the need for further developments. In this study a new failure model that accounts for existing different couplings and interactions in the longitudinal compressive and tensional domains is presented. The model is based on the fracture behavior of clear spruce wood and related experimental works. The model is more accurate compared to existing phenomenological models.     

Failure of a Freeze Dryer Slot Door

Freeze-drying is utilized in the biopharmaceutical industry to give higher stability, broader temperature tolerance, and longer shelf-life to formulations that are unstable in aqueous solution (Green and Perry, Perry’s Chemical Engineers’ Handbook, 1997). Freeze-drying equipment consists of a drying chamber, condensers, a cooling system, and a vacuum system. The drying chamber is where the product is placed to undergo the lyophilization process. The chamber has two access points: a maintenance door, located in a mechanical room, and a slot door, located in a sterile clean room. The maintenance door permits entry into the chamber. The slot door facilitates tray loading and unloading from the clean room using an automatic tray handling system. At 9:26 AM on March 2, 2008, a freeze-dryer failed during the steam-in-place (SIP) cycle. As a result of the failure, the slot door was plastically deformed. Several items in the proximity of the slot door sustained damage. Fortunately, no personnel were inside the clean room when the event occurred; there were no injuries or loss of life. The impact to production was severe. The event removed the freeze dryer from service for approximately 2 months, reducing bulk powder production capacity by 33% during the time it was down. The failure occurred because the slot door was not closed properly when the SIP cycle began. Instead of being completely restrained, it was allowed to become simply-supported, seriously compromising its pressure-containing ability.     

An Inadequate Weld Repair and a Consequent Rupture of a Pressure Vessel

The incident of concern involved a steam accumulator that was a component part of a steam generating facility. The accumulator ruptured during normal operating conditions that included an internal pressure of 120 psi (0.83 MPa). The rupture involved the complete fracture of a circumferential weld joining the bottom head to the accumulator cylindrical shell. An analysis of the fracture revealed the presence of a subsurface crack at the weld. This crack encompassed the entire weld line around the vessel and extended radially across nearly the full thickness of the weld. Using metallurgical analysis, this crack was determined to have been in place since the time when the accumulator was first manufactured. Eventually, a leak occurred at the weld line. The process to repair the leak failed to detect the condition of defect. The work of investigation also determined that the repair preceding the fracture was not conducted in accordance with the requirements of the National Boiler Inspection Code (NBIC). The condition of defect, which would have been detected if NBIC procedures had been used, was instead left in place and the accumulator, as a pressure vessel, ruptured as a result. An erratum to this article can be found at     

ESD induced degradation mechanisms of InGaAsP/InP lasers

The sensitivity of InGaAsP/InP buried crescent lasers to ESD phenomena was deeply analysed, starting from the need to explain and prevent sudden failures during equipment manufacturing and test. Failure analysis allowed us to localize the degradation, which can be explained by means of a simple phenomenological model; finally a physical model was implemented trying to correlate the results of the failure analysis with the proposed failure mechanism.     

Assessment on failure pressure of high strength pipeline with corrosion defects

An accurate prediction on the failure pressure of line pipe is very important in the engineering design and integrity assessment of oil and gas transmission pipelines. This paper analytically investigates the failure pressure of line pipes with or without corrosion defects, and focus on the high strength steels. Based on von Mises strength failure criterion, a classic strength failure criterion, the failure pressure of end-capped and defect-free pipe p_M is theoretically deduced with the strain hardening material. In order to derive a general solution for corrosion defect assessment of high strength pipelines, an extensive series of finite element analyses on various elliptical corrosion defects was performed. Finally, a new formula for predicting the failure pressure of corroded pipe in the material of high strength steels is formulated, based on the FE models and p_M, and is validated using 79 groups of full-scale burst test data, which contain the low, middle and high strength pipeline. The results indicated that the proposed formula for predicting the failure pressure is closely matches the experimental data for the high strength steels.     

正方形断面钢管混凝土短柱轴心受压极限承载力的研究

本文根据钢管混凝土柱轴压实验及有限元分析的结果，首次提出正方形断面钢管混凝土短柱轴心受压极限承载力计算模型．该模型将钢管视为平面应力状态，将核心的混凝土划分为双轴受压区与三轴受压区，利用Ｍｉｓｅｓ屈服曲面以及复杂应力状态混凝土的强度理论，可将钢管混凝土柱的承载力表示为钢管模向应力的函数．根据塑性理论中的下限定理，即可确定钢管混凝土柱的极限承载力。     

Modelling area-wide count outcomes with spatial correlation and heterogeneity: an analysis of London crash data

Count models such as negative binomial (NB) regression models are normally employed to establish a relationship between area-wide traffic crashes and the contributing factors. Since crash data are collected with reference to location measured as points in space, spatial dependence exists among the area-level crash observations. Although NB models can take account of the effect of unobserved heterogeneity (due to omitted variables in the model) among neighbourhoods, such models may not account for spatial correlation areas. It is then essential to adopt an econometric model that takes account of both spatial dependence and uncorrelated heterogeneity simultaneously among neighbouring units. In studying the spatial pattern of traffic crashes, two types of spatial models may be employed: (i) classical spatial models for higher levels of spatial aggregation such as states, counties, etc. and (ii) Bayesian hierarchical models for all spatial units, especially for smaller scale area-aggregations. Therefore, the primary objectives of this paper is to develop a series of relationships between area-wide different traffic casualties and the contributing factors associated with ward characteristics using both non-spatial models (such as NB models) and spatial models and to identify the similarities and differences among these relationships. The spatial units of the analysis are the 633 census wards from the Greater London metropolitan area. Ward-level casualty data are disaggregated by severity of the casualty (such as fatalities, serious injuries, and slight injuries) and by severity of the casualty related to various road users. The analysis implies that different ward-level factors affect traffic casualties differently. The results also suggest that Bayesian hierarchical models are more appropriate in developing a relationship between area-wide traffic crashes and the contributing factors associated with the road infrastructure, socioeconomic and traffic conditions of the area. This is because Bayesian models accurately take account of both spatial dependence and uncorrelated heterogeneity.