给水管座开裂原因分析

锅炉锅筒的给水管座与锅筒在焊接和消除应力热处理后经探伤检查发现沿焊缝有环向裂纹,并扩展至给水管座的内壁形成纵向裂纹。采用化学成分分析、宏观和微观检验以及力学性能分析等方法对给水管座的裂纹产生原因进行了分析。结果表明：由于焊接工艺规范控制不当,未及时进行消氢处理,焊件的碳当量提高具有明显的淬硬倾向,焊接结构和较大的焊件厚度引起拘束应力等综合作用产生了延迟裂纹。     

D210塔简体泄漏原因分析

采用化学成分分析、金相检验和断口分析等方法,对304L钢D210塔筒体泄漏原因进行了分析。结果表明：D210塔筒体泄漏原因是由于氯离子的存在而产生应力腐蚀开裂所致。由于敏感材料、应力腐蚀环境及应力三个条件共同存在,在一定温度下使其产生应力腐蚀裂纹,裂纹起始于筒体外壁角焊缝处,而后向内壁扩展,最终穿透筒壁,致使该塔筒体在角焊缝处产生破裂泄漏。     

锅炉锅筒鼓包原因分析及预防

采用化学分析及金相检验等方法 ,对锅炉锅筒产生的鼓包原因进行了分析。结果表明 ,锅炉严重结垢使得锅筒底部钢板长期过热产生蠕变 ,从而导致锅炉锅筒产生鼓包变形     

小型锅炉锅筒开裂原因分析

采用化学成分分析,宏、微观组织检验,断口观察和腐蚀产物分析等方法对SUS304奥氏体不锈钢锅炉的锅筒开裂进行了分析。结果表明,环境中存在硫和氯等元素,造成在锅筒板与顶盖的焊接处发生腐蚀而形成腐蚀坑并萌生裂纹,在各种应力作用下裂纹不断扩展,最终导致开裂。     

外壁具有轴向裂纹的自增强厚壁圆筒的应力强度因子

<正> 一、前言工程中广泛采用自增强处理来提高厚壁圆筒的承载能力,经自增强处理后的厚壁筒,内壁保留有有利的残余压应力,外壁保留有拉应力。不恰当地增加自增强度,可能外壁先于内壁产生疲劳破坏。为了选择合理的自增强度,一般采用断裂力学理论对自增强厚壁筒的疲劳寿命进行分析。因此计算外壁出现裂纹的自增强厚壁筒的应力强度因子具有重要的     

锅炉锅简鼓包原因分析及预防

采用化学分析及金相检验等方法,对锅炉锅筒产生的鼓包原因进行了分析.结果表明,锅炉严重结垢使得锅筒底部钢板长期过热产生蠕变,从而导致锅炉锅筒产生鼓包变形.     

锅炉免筒鼓包原因分析及预防

采用化学分析及金相检验等方法，对锅炉锅筒产生的鼓包原因进行了分析。结果表明，锅炉严重结垢使得锅筒底部钢板长期过热产生蠕变，从而导致锅炉锅筒产生鼓包变形。     

奥氏体不锈钢应力腐蚀检测研究

材质为ASTM A240 316L不锈钢烘筒的筒体出现了，导致变形失效。通过现场观察、材质分析、金相检验等检测方法对简体内壁裂纹的宏观形貌、显微组织、腐蚀产物并结合烘筒的工况等进行分析。结果表明，不锈钢烘筒的简体在富含氯离子的环境中，在氯离子和拉应力的共同作用下，发生应力腐蚀开裂。烘筒失效的直接原因是因为裂纹失去强度，在布的外力作用下变形失效。     

灭菌器产生腐蚀裂纹的原因分析

本文主要分析了一台医用灭菌器内筒筒体产生应力腐蚀裂纹的原因及影响因素。通过对新旧医用灭菌器使用情况的分析,作者发现该台医用灭菌器产生裂纹的主要原因与其所使用的内筒材料、使用环境和应力集中有关。本文再次论证了不锈钢材料在有Cl存在的环境条件下,在结构突变有应力集中的部位极易产生应力腐蚀裂纹。本文从几个方面阐述了避免此类医用灭菌器产生应力腐蚀裂纹的方法,比如改变盛装介质器具、内筒材料的选取、改变内筒结构以及容器投用后的使用环节。     

枪炮管内壁出现轴裂纹时的安全性探讨

本文应用线弹性断裂力学理论,讨论了枪炮管内壁出现轴裂纹后的安全性问题。提出了动载情况下,疲劳裂纹扩展寿命的一种计算方法。由厚壁园筒制成的枪炮管,由于使用和制造等原因,常出现裂纹。继续使用,裂纹便不断地向长、向深方向发展,最后在连续射击的反复作用下,导致报废。为了监测出现裂纹以后的枪炮管是否可以继续使用,需要对它的安全性进行估计,现根据厚壁园筒理论和断裂力学知识,探讨如下:     

Fatigue Failure of 321 Stainless Steel Superheater Tubes from a Thermal Incinerator

Several boiler superheater tubes showed circumferential cracking at weld seams after 2 years in noncontinuous service (several shutdowns). On-site inspection revealed that several tubes were cracked and leaked; while many others were cracked, however, the severity was less pronounced. Two types of superheater tubes samples were collected: one with butt-welded tubes and the other with fillet-welded sleeve. The latter was found to be out of the boiler fireplace, and the sleeve was used as tubing support to the boiler shell. Detailed investigation showed that the butt-welded tubes contained circumferential fatigue cracks that initiated from the internal surface. The cracks initiated in the heat-affected zone and propagated as a result of tube vibration. The variations in the tube internal diameter and tube wall thickness are expected to play a role in tube fatigue failure. On the other hand, tubes with fillet-weld sleeve showed circumferential cracking as a result of fatigue crack initiation from weld defects on the tube external surface. The high vibration during several unscheduled shutdowns in addition to several other factors such as variations in tube inside diameter, wall thickness, and weld defects resulted in the initiation and propagation of fatigue cracks and premature failure. White deposits, similar to those observed when boiler tubes failed by caustic exposure, were seen in the vicinity of the tube cracks. Therefore, it was difficult to confirm whether the boiler tubes failed because of the fatigue cracks or because of the caustic salts (pH control chemical).     

Reliability analysis of hybrid ceramic/steel gun barrels

ABSTRACT Failure of the ceramic gun‐barrel lining during single‐shot and burst firing events has been studied by combining a finite‐element method based thermo‐mechanical analysis with a structural reliability analysis. An initial distribution of residual stresses in the lined barrel, as introduced during shrink‐fitting of the steel jacket over the ceramic lining, is taken into account. Forced‐convection boundary conditions at the inner surface of the barrel are determined by carrying out an internal‐ballistic analysis, followed by compressible boundary‐layer modeling of the heat transfer coefficient. The results obtained reveal that due to thermal expansion of the steel jacket during single‐shot and burst ballistic events, tensile axial stresses develop in the ceramic lining near the barrel ends. These stresses are sufficiently high, particularly in the case of burst firing, that they can induce formation of circumferential cracks and, in turn, failure of the lining. Using the Weibull structural reliability analysis, the failure probability for the lining has been computed as 0.0025 and 0.0121 for the single‐round and the 10‐round firing modes, respectively. Optimization of the main design, materials and processing parameters in order to minimize the failure probability for the lining is also discussed.     

某锅炉换热器换热管断裂原因分析

某锅炉换热器仅运行2 h即发生换热管断裂事故,采用光学显微镜、扫描电子显微镜、能谱仪、拉伸试验机和直读光谱仪等设备对换热管的断裂原因进行了分析。结果表明:该换热管外壁表面在运行前就已存在原始横向裂纹和机械损伤,在服役过程中这些裂纹和机械损伤处容易形成应力集中,加之换热管的使用温度较低,从而导致其在运行仅2 h后就发生早期脆性断裂。最后对该换热管的生产提出了建议。     

Stress Assisted Corrosion of Waterwall Tubes in Recovery Boiler Tubes: Failure Analysis

Waterside cracking of carbon-steel boiler tubes is one of the major safety and efficiency concerns in kraft recovery boilers in the pulp and paper industry, because any water leak into the furnace could cause a smelt-water explosion in the boiler. Failed carbon-steel boiler tubes from different kraft recovery boilers were examined to understand the role of carbon-steel microstructure on crack initiation and crack morphology. A number of carbon-steel tubes showed a deep decarburized layer on the inner surface (water-touched) and also an unusually large grain size at the inner tube surface. In some boiler tubes, cracks were found to initiate in areas with large-grained-decarburized microstructure. However, tubes without such microstructure were also found to have stress assisted corrosion (SAC) cracks. It was found that the decarburization and large grained microstructure may facilitate initiation and growth, but it is not necessary for SAC of carbon-steel boiler tubes.     

Fatigue life analysis of a cannon barrel

A steel cannon barrel was tested and analyzed in order to predict its lifetime. Mechanical properties, fracture toughness and fatigue behavior were determined experimentally. The cannon barrel was assumed to have a smooth inner surface. On that basis, finite element analyses were carried out in order to determine the stress intensity factor as a function of crack length for the case in which the cannon barrel contains two symmetrically located cracks. The fatigue data was assumed to follow the Paris–Erdogan law. A statistical Monte Carlo analysis for the fatigue life of the cannon barrel was carried out with many of the parameters assumed to be random variables.     

连铸钢板坯凝固壳横截面变形与内部裂纹的关系

对实际观察到的连铸钢板坯拉出结晶器时的横截面形状与最终形成的内部裂纹进行了理论分析，找到了凝固壳横截面形状变化与内部裂纹的形成及种类之间的因果关系及规律性，为预防连铸钢板坯内部裂纹提供了理论依据。同时对YB／T4003-1991标准中的有关问题进行了讨论，并从生产工艺角度概述了影响连铸钢板坯内部裂纹的各种因素。     

Evaluation of stress intensity factors for multiple surface cracks in bi-material tubes

This paper presents stress intensity factors (SIFs) of multiple semi-elliptical surface cracks in bi-material tubes subjected to internal pressure by boundary element method. In this case the water-tube boiler with oxide scale formed on the inner surface due to prolonged exposure at elevated temperature is considered as the bi-material tubes. Variations of modulus of elasticity and thickness for the oxide scale are used to evaluate their effects on the stress intensity factors. The increasing of thickness of the oxide scale causes decreasing values of the normalized stress intensity factor as the modulus of elasticity for the oxide scale is greater than that of the tube metal. Conversely, if the modulus of elasticity for the oxide scale is smaller, the increasing of thickness of the scale would also give increasing values of the normalized stress intensity factor.     

Hydrogen-Assisted Cracking in Boiler Steam Drums

A statutory inspection of a boiler steam drum that had seen 10 years of service revealed a few scattered cracks on the inner surface of the drum. The drum was used in the refinery and petrochemical industry. Remnant life assessment, including inspection of other drums, showed presence of several cracks in two out of seven boiler inspected. In situ microstructural analysis revealed a variation in the microstructure in the cracked regions compared to the microstructure in uncracked regions. Additionally, a wide variation in hardness was associated with the microstructural variation. Detailed study on a sample extracted from a cracked region demonstrated that the cracking occurred in a crescent zone similar in appearance to that of a heat affected zone (HAZ) generally associated with a spot weld or other sources of hot spots in the material. Subsequent examination of more samples confirmed that repair welding was carried out at several places on the inner surface of the drums before installation and commissioning and all the cracks were around the repair welds. The failure occurred by crack initiation in the HAZ of the repair welds and the cracks then propagated progressively across the inner surface of the drums. The failure mechanism was identified to be cold cracking and the failure analysis showed that all the factors required for cold cracking, namely, vulnerable microstructure, residual stresses and hydrogen atmosphere, during welding had been present in the drum material.     

LME induced failure of a combat aircraft gun

Premature catastrophic failures of gun barrel casings of a combat aircraft were reported. Magnetic particle fluorescent (MPF) and die penetrant inspections of in-service casings indicated cracks in various locations. Further investigations unveiled them to be multiple initiation fatigue cracks.The fracture surface of the failed casings showed chevron marks pointing towards the crack origin, where Pb, Cu and Zn were present in high concentrations. The finding construed that the failures were anticipated by liquid metal embrittlement.     

锅炉底板裂缝泄漏失效分析

摘要:某型号卧式蒸汽锅炉在使用1 a(年)后,其底板产生了贯穿裂缝,导致泄漏。经宏观观察、化学成分分析、金相检验以及能谱分析等方法对锅炉底板泄漏原因进行了分析。结果表明:该锅炉裂缝是一种垢下闭塞电池腐蚀裂纹;产生裂缝的主要原因是锅炉结构设计不当,造成封闭区域,并且使用未经预处理的原水,从而导致局部区域沉积大量的CaCO3水垢;CaCO3水垢的大量沉积,阻碍了O的正常流动,造成氧的浓度梯度,使垢下区域和暴露区域形成闭塞电池,导致垢下区域钢材快速腐蚀,从而形成裂缝泄漏。最后提出了避免垢下腐蚀裂纹的预防措施。