304不锈钢密封垫片开裂原因分析

采用化学成分分析、拉伸试验和断口分析等方法对304不锈钢裂解气压缩机出口法兰密封垫片的开裂原因进行了分析。结果表明：裂纹起源于螺栓槽处,氯离子的应力腐蚀开裂是造成垫片开裂的主要原因。含氯离子的沿海潮湿大气是导致垫片产生应力腐蚀的介质因素,装配不当造成螺栓槽处垫片过大的应力和应变是导致垫片出现应力腐蚀开裂的力学因素。     

法兰连接爆炸冲击动力响应分析数值模拟

运用LS-DYNA非线性有限元软件,建立了法兰连接结构的三维有限元模型,使用罚函数法实现了法兰盘-螺栓连接-法兰垫的非线性耦合作用,利用温度荷载法实现了螺栓连接结构的预紧力加载,采用ALE多物质流-固耦合算法研究了法兰连接结构在爆炸冲击荷载作用下的动力响应特性,分别研究了法兰连接在爆炸冲击荷载作用下冲击波入射角、螺栓连接预紧力、法兰垫厚度对其结构的影响,并考虑了垫片为金属材料(合金钢)以及非金属材料(橡胶)时的情况。结果表明,法兰盘为法兰连接的主要耗能构件。合金钢法兰垫片受冲击波入射角的影响较小,而螺栓连接则主要受冲击波入射角的影响。法兰盘在高压压缩波的作用下会产生相对于螺栓连接的不均匀压缩变形。厚垫片并非比薄垫片好,适当减小法兰垫片厚度,可以提高法兰结构的抗冲击能力。     

电流互感器铝合金法兰开裂失效分析

某福建沿海地区用于电流互感器的铝合金法兰发生多处开裂,采用宏观检验、化学成分分析、金相分析、扫描电镜以及能谱分析等方法对该法兰开裂原因进行了分析。结果表明:法兰开裂均起始于螺栓孔处,为在腐蚀介质和应力共同作用下发生的应力腐蚀开裂;法兰螺栓扭紧力高、服役环境氯离子含量高以及法兰所用铝合金材料应力腐蚀开裂敏感性高等是造成该法兰开裂的主要原因。最后针对法兰开裂原因提出了预防措施。     

制氢转化炉炉管下法兰失效分析

工程停修后制氢转化炉炉管下法兰开工试车时发生开裂泄漏.就此,对下法兰进行了裂纹宏观分析、化学成分分析、金相分析、断口形貌观察及腐蚀产物分析.结果表明,下法兰焊缝、热影响区及母材均发生了一定程度的敏化.下法兰的开裂属于敏化状态下的连多硫酸应力腐蚀开裂,这种开裂,除工作条件、环境因素外,还与材料不符合标准有关,建议选用双相不锈钢或耐热不锈钢加以避免.     

钢制安全壳用大直径法兰及密封的设计

换料大直径法兰的结构形式和密封形式是急需探讨的问题。为确保安全壳内发生严重事故时内压要求,应按照ASME相关要求对安全壳法兰和密封垫片进行设计,并进行有限元校核。     

微波传输系统真空法兰密封结构设计特点

为了提高微波传输系统最大输出功率,将波导管内维持真空状态,真空度达到或优于10-5Pa时,通过功率可提高几个数量级。但真空波导法兰密封结构设计是关键,对应不同的条件有不同的要求。首先,在橡胶密封圈的波导法兰上设计抗流结构,利用“等效电路”、“短路”和高频电流波节等相互关系,使法兰机械设计和制造工艺满足微波功率输出的要求;其次,金属密封垫片法兰根据方波导管高频电流分布的特点,采用法兰方波导宽边良好的电接触与真空密封结构分开设计的方式;再次,另一种在金属密封垫片法兰上加工一个与方波导管内壁一致的方形刀口,在螺栓力作用下刀口与密封圈四周挤压接触,既达到真空密封,又满足良好的电接触,设计、加工、装配简单。这三种法兰都不影响波导管电磁能量的传播,但真空密封性能、机械设计、加工等方面存在差异。     

某压缩机法兰与钢管焊接接头焊缝开裂失效分析

某平台湿气压缩机法兰与钢管焊接接头焊缝发生开裂失效,采用宏观观察、化学成分分析、金相检验、力学性能试验、扫描电镜分析和能谱分析等方法对焊缝的开裂原因进行了分析。结果表明:焊接接头结构的不合理和焊缝内部的未熔合缺陷造成局部应力集中,并导致焊接接头的疲劳极限下降,在应力作用下法兰一侧切口处焊缝根部与未完全熔合的法兰母材交界处形成裂纹源;在外部循环载荷作用下,裂纹逐渐向外表面扩展,当达到焊接接头的疲劳极限时,焊缝即发生开裂。     

16Mn Ⅲ钢法兰锻件焊接开裂原因分析

某16MnⅢ钢法兰锻件在和钢管对焊的焊接过程中发生开裂。通过宏观断口观察、金相检验、化学成分分析、力学性能测试、扫描电镜分析等方法对该法兰锻件焊接开裂的原因进行了分析。结果表明:焊接工艺不当、焊接前未预热是导致该法兰锻件开裂的关键原因。     

某稠油井用高温蒸汽注汽管爆裂失效分析

通过对某油田稠油井发生爆裂的高温蒸汽注汽管进行宏观分析、化学成分分析、金相检验、力学性能测试以及扫描电镜断口分析,找出了该管爆裂失效的原因.结果表明:该高温蒸汽注汽管线的爆裂性质为脆性开裂,开裂起源于管表面的两处机械损伤;导致其爆裂失效的主要原因是该管在服役过程中由于水击作用发生了胀径,使注汽管壁厚不均匀;同时管表面存...     

新型无石棉垫片——无石棉压缩垫片材料的设计、制造和安装

在工业设计中密封件往往是最后一个要考虑的元件。虽然在法兰设计时已经考虑了垫片密封的一些特性，但对于密封材料重要性的了解还是不够的。本文从设计的角度讨论工程师们应该了解的有关垫片的一些信息，包括垫片材料的短期性能和长期性能两个方面。     

电机连接轴失效分析

采用扫描电镜、电子能谱仪、光学显微镜和显微硬度计等检测方法,对发电机上一键槽的失效进行了分析。结果表明,造成该零件失效的原因是由于轴、轴孔和键槽配合不当,以及因加工刀痕形成的应力集中而引起多源扭转疲劳损坏。提出了提高材料使用寿命的建议。     

The crack evolution on the atomistic scale during the pyrolysis of carbon fibre reinforced plastics to carbon/carbon composites

The development of the crack patterns during the pyrolysis of carbon fibre reinforced plastics (CFRP) to carbon/carbon composites as the second manufacturing step in the liquid silicon infiltration (LSI) process was investigated. In the basic examination reported previously, it was discovered that a substantial amount of cracking occurs beyond 650 °C, when the mesoscopic crack pattern has already fully developed. This additional cracking could not be visualized by using standard microscopy. Thus additional investigations were conducted by using conventional and high-resolution transmission electron microscopy to obtain information on the atomistic scale on the assumed cracking activity.It was found that the crack development starts at pores that develop as a compensation for the rough fibre surface. Crack propagation takes place by evolution of new nanoscopic cracks caused by fibre–matrix-debonding in the tensile stress field in front of the crack tip and subsequent connection with the main crack. Thus the interconnection mechanism – cracking as the connection of cracks on a subordinated scale to form a new crack – is the second main cracking mechanism beside transversal cracking (leading to a regular mesoscopic crack pattern) active during the carbonization of CFRP components.     

Failure Analysis of Cracks Formed at Extrados of Bend Pipe of API 5L X65M Grade

A metallurgical and root cause analysis was performed on hot induction bent pipes that exhibited cracking at the extrados. The bent pipe of 1016 mm (40 in.) diameter by 18.5 mm wall thickness was API 5L X65 PSL2 line pipe containing a longitudinal submerged arc weld. A metallurgical cross section was removed at a crack on the bent pipe extrados to document the crack morphology using optical microscopy. In addition to the cracking, golden-yellow streaks were visible at the extrados of the bent pipe. The composition of the streaks was examined using scanning electron microscopy with energy dispersive spectroscopy.     

The crack-initiation threshold in ceramic materials subject to elastic/plastic indentation

The threshold for indentation cracking is established for a range of ceramic materials, using the techniques of scanning electron microscopy and acoustic emission. It is found that by taking into account indentation plasticity, currant theories may be successfully combined to predict threshold indentation loads and crack sizes. Threshold cracking is seen to relate to radial rather than median cracking.     

40Cr轧辊轴断裂原因分析

通过宏观分析、扫描电镜、光学显微镜等手段对轧辊轴的断裂进行了综合分析,结果表明以氢致裂纹为疲劳源,引发了轧辊轴的疲劳断裂.     

Failure analysis of the space shuttle Columbia RCC leading edge

Failure analysis of the Columbia shuttle left T-seal 9 and an unidentified fragment of leading edge reinforced carbon-carbon (RCC) composite material was carried out to determine the causes of failure. Standard metallographic and microscopy procedures were employed to identify and characterize the failure mode. The results indicate that erosion and cracking occurred. Erosion was caused by the extreme temperatures and stress conditions experienced during the shuttle breakup in the upper atmosphere. Porosity, glassy phase, pinholes, and cracking in the silicon carbide (SiC) layer of the RCC material accelerated erosion and mass loss. Brittle cracking was also found in the SiC layer, and crack propagation was apparently enhanced by the flaws in the microstructure.     

600 MPa级元宝梁用钢冲压开裂原因分析

为解决元宝梁冲压开裂问题,用OM和SEM等仪器与ABAQUS有限元仿真软件对600 MPa级元宝梁用钢冲压开裂原因进行了分析.结果表明:600 MPa级元宝梁用钢化学成分、力学性能与冷弯性能均满足标准要求,金相组织为准多边形铁素体与少量珠光体的混合组织,不存在带状组织;开裂件断口形貌呈现出明显鱼骨状形貌,钢板中心分层,两侧分布起源于中心分层并沿同一方向扩展的三角形台阶状断口,不同形貌断口均属于韧性断裂,而断口整体形貌显示材料在断裂前没有发生缩颈过程.利用ABAQUS软件对"先冲压再压边工艺"与"先压边再冲压工艺"两种工况进行有限元分析,结果显示:先冲压再压边工艺边部应力集中更严重,边部节点应力超过了材料抗拉强度从而导致撕裂现象的发生;由"先冲压再压边工艺"改为"先压边再冲压工艺"后元宝梁冲压开裂率由50%降至0,材料边部变形均匀,未见缩颈与开裂现象发生.     

Influence of oxidative environments on damage in c/epoxy laminates subjected to thermal cycling

The aim of this study is to characterise damage processes in carbon/epoxy laminates submitted to thermal cycling in neutral (nitrogen) and oxidative (air, oxygen) atmospheres. Observations of the polished edges of the specimens by optical microscopy and SEM have revealed the presence of matrix shrinkage and fibre/matrix debondings only on samples tested under oxidative atmospheres. Quantitative analyses of transverse matrix cracking by means of microscopy and X radiography have shown the accelerating effect of an oxidative atmosphere. Moreover, the higher the oxygen concentration, the more significant the acceleration of the cracking development. These results are analysed in terms of matrix oxidation, occurring at the highest temperatures of the cycle, and fatigue matrix cracking, occurring at the lowest ones and due to the prevented differential expansions of the plies. During a thermal cycling test performed in an oxidative atmosphere, a coupling effect between these two damage mechanisms would result in the acceleration of the micro cracking observed.     

Corrosion fatigue cracking of AISI 316L stainless steel screen mesh

This paper describes the failure of stainless steel screen mesh grade AISI 316L after being in service for only 8 months. The characterization methods included visual examination, optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and metallography. The results showed that the screen mesh failed by pitting corrosion and subsequent corrosion fatigue cracking. Pitting was initiated by the attack of chlorides from PVC powder and service environment as well as the action of excessive wear. Subsequent corrosion fatigue cracking arose from the presence of chlorides along with the residual and cyclic stress concentration at the pits. Failure prevention can be achieved by annealing after wire drawing, periodic surface cleaning, and proper material selection.     

The use of microfine cement to enhance the efficacy of carbon nanofibers with respect to drying shrinkage crack resistance of portland cement mortars

Significant research has recently been aimed at quantifying the effects of carbon nanofibers and carbon nanotubes in portland cement pastes and mortars. Such efforts have shown that mechanical properties can increase with low concentrations of carbon nanofibers but have marginal improvement or are negatively affected with high concentrations. The objective of this paper is to evaluate the use of a microfine cement to enhance the efficacy of carbon nanofibers in portland cement mortar with respect to cracking resistance via enabling higher nanofiber concentrations. Experiments are performed with concentrations of carbon nanofibers up to 3% by weight of cement using either Type I/II or microfine cement. The primary test implemented was a restrained ring drying shrinkage test; unrestrained drying shrinkage tests, elastic modulus tests, and scanning electron microscopy imaging were performed to provide supplemental data to explain the observations from the restrained ring drying shrinkage tests. It was found that Type I/II cement mortars either lost performance or had insignificant gains with respect to cracking resistance, and all Type I/II mortar mixtures had losses in stiffness with the addition of high concentrations of carbon nanofibers. In contrast, microfine cement mortars had increased shrinkage cracking resistance and no loss in stiffness with increasing amounts of carbon nanofibers (up to the 3% by weight of cement tested in this research). The microfine cement mortar with 3% carbon nanofibers by weight of cement delayed the experimentally measured time of cracking in the ring test by a factor of up to 3.89. The delay in visible cracking time was attributed to microcrack bridging by the carbon nanofibers as imaged by scanning electron microscopy.