铜管焊接弯头开裂分析

利用光学金相显微镜、扫描电子显微镜、电子能谱仪等方法对开裂铜管焊接弯头进行失效分析,发现该铜管焊接弯头久置于腐蚀性介质中,当在腐蚀坑处应力集中,便产生了开裂失效.同时,还发现该工件在弯制时易形成微裂纹.     

机械装备的失效分析(续前) 第8讲 失效诊断与预防技术(4)

正3.4库存或运输中的失效诊断3.4.1残余内应力引起开裂失效(1)工件淬火热处理后其内部会产生较大的残余内应力,同时马氏体形成时的相互碰撞还会产生大量的显微裂纹,如果不及时回火,可能会导致工件开裂失效。(2)工件焊接后不但会产生较大的焊接应力,有时还会产生硬而脆的马氏体组织,若焊后不及时     

硫化氢环境下马氏体不锈钢的开裂原因分析

炼化离心压缩机在服役过程中马氏体不锈钢叶轮表面出现断裂失效现象。通过对叶轮失效件的断口宏观和微观形貌分析、硬度检测,并结合生产服役环境对叶轮裂纹的产生原因进行分析。结果表明:叶轮断口裂纹以沿晶腐蚀为萌生源,扩展后转变为穿晶腐蚀,呈现应力腐蚀特征。断口腐蚀产物分析表明,腐蚀产物中含有硫元素;结合叶轮的服役环境得出叶轮的断裂失效主要原因是硫化物应力腐蚀开裂。     

翅片管路焊接接头断裂原因分析

通过KYKY2800扫描电镜等技术手段对翅片管路焊接接头进行失效分析。分析表明,焊缝与2#环管的焊趾处存在有不连续的咬边,造成应力集中;在交变应力的作用下于咬边处产生微裂纹,并沿一定方向扩展（同时材料的不均匀性也为裂纹的扩展提供了有利条件）,直至最后疲劳断裂,造成失效。最后提出了预防措施。     

LNG储罐泄漏原因分析

某天然气公司LNG储罐在安装使用5a(年)后,内罐的底部封头部位发生泄漏。通过宏观检验、化学成分分析、金相检验、力学性能试验及断口分析等方法对该储罐泄漏原因进行了分析。结果表明:封头母材在成型过程中发生了形变诱发马氏体相变,部分奥氏体组织转变为形变马氏体,组织脆化;服役时,封头直边段需要承受较大介质内压,加之焊接残余应力以及充装过程中温差应力的共同作用,封头近焊缝部位出现沿晶裂纹,最终导致开裂失效。     

TiNi形状记忆合金精密脉冲电阻对焊接头相变温度变化规律的研究

通过示差热分析（DSC）和X射线衍射等分析手段，研究了焊接热量、焊接压力、随机后热处理等焊接参数以及冷热循环对焊接接头相变温度的影响，并总结了其影响规律。研究表明，焊接热量和焊接压力对焊接接头相变温度的影响较小，相变温度区间基本保持不变，焊接接头相变类型为单一的马氏体→奥氏体的转变。焊后随机后热处理对焊接接头相变温度具有一定的影响，马氏体向奥氏体转变的起始温度As和终了温度At均随后热处理时间的增加而提高。在热处理时间为99cyc时，在加热过程中首先发生马氏体→R相→奥氏体的转变，由于发生了R相变，延迟了奥氏体相变的温度，使TiNi形状记忆合金的温度滞后现象加剧，同时使奥氏体的相变区间缩小。冷热循环对焊接接头的相变过程和相变温度具有重要的影响，导致了R相变的出现。R相变进行的程度随着冷循环次数的增加而提高，并逐渐趋于稳定。     

带压补漏技术及应用

压力容器和管道在生产运行的过程中会随着老化和腐蚀带来泄露问题造成生产中断。因此,需要在不停产的情况下消除泄露。带压补漏是可以在不停产、不影响生产的情况下带温、带压、迅速、安全、可靠地消除泄露的一种技术。运用实践经验得出的焊接方法,能有效的达到管线穿孔时带压焊接的目的。     

架桥机移动模架销轴断裂分析

通过断口分析、化学成分分析、非金属夹杂物检验、力学性能测试、金相检验以及销轴受力及焊接工艺分析,对移动模架销轴的断裂原因进行了分析。结果表明:焊接接头结构设计或焊接工艺不当,形成粗大马氏体组织缺陷或裂纹,是造成该轴脆性断裂的主要原因,并提出了预防措施。     

裂纹对NiAl马氏体相变影响的微观机理

利用嵌入原子类型势函数,通过分析动力学模拟方法研究了裂纹对马氏体相变的影响。裂纹尖端的应变区未能诱发马氏体形核,而且妨碍了热诱发马氏体的长大。在外加拉应力作用下,应力诱发马氏体从裂纹尖端形核后,先形成蝶状马氏体;随后系统中上部也发生了马氏体形核;不同取向的马氏体在长大过程中逐渐转化和合并。分析了应变的变化特点,探讨了相变的微观机理。     

磨煤机电机轴断裂原因分析

利用光学金相显微镜、化学分析、硬度测试等实验手段,对35号钢电机轴在使用过程中发生的断裂原因进行分析。结果表明,电机轴表面的焊接热加工使得电机轴变径台肩处的次表面部位产生高硬度马氏体组织,造成该处的严重应力集中。在长期交变载荷的作用下,电机轴的变径台肩处产生微裂纹,构成多处裂纹源。随着这些裂纹长大并不断扩展,最终造成电机轴的疲劳断裂。     

Failure analysis of IEU drill pipe wash out

Many 127.0×9.19 mm IEU G105 drill pipe failures of wash out occurred after 2367 h of pure drilling time and 8726 m of penetration footage. This paper gives a detailed investigation on these failures and a systematic analysis is carried out on service and loading conditions of the drill pipes. Measurement and inspection were performed on configuration dimensions, chemical composition, mechanical performance, metallography, macro-fractography, micro-fractography, and corrosion products. Configuration stresses at the crack positions of the drill pipe were calculated by FEA. Crack extending velocity of the drill pipe material under corrosion medium was also measured. It is thought from test and analysis results that the drill pipe wash out or fracture accidents were premature corrosion fatigue failure accident. The failure courses were as the following: corrosion pits occurred first on the internal surface at the stress concentrating area of the drill pipe, and then fatigue cracks initiated in pit bottoms, and washed out or fractured subsequently as cracks penetrated through the wall thickness of the drill pipe. The reasons of drill pipe wash out were related to configuration, material quality, and load condition of the drill pipe string.     

12Cr1MoV联箱与支管焊缝裂纹分析

为研究某厂联箱与支管运行1.4×105h后发生开裂的原因,采用宏观渗透及光学显微镜、扫描电镜、能谱仪、显微硬度计等测试方法对失效管进行检测.研究表明:焊后存在焊接缺陷,大量的裂纹垂直于焊缝,加速裂纹的扩展,改变应力分布状态;部分夹杂物沿直线分布,使材料受力具有方向敏感性,导致材料开裂失效;断口表面主要是Fe的氧化物,焊件长期过热,外表面形成不均匀氧化层,产生应力集中,致使焊缝从管壁外侧开裂;母材硬度超标.优化焊接工艺方案,焊前预热焊后回火,消除管件外壁的氧化层及减少设备停机次数均能有效防止同类焊接结构开裂失效.     

Untersuchungen zur Initiierung interkristalliner Schwingungsrisse in interstitiell freien (IF-) Stählen

Investigations of initiation of intercrystalline fatigue cracks of interstitial free (IF-) steels While investigation the fatigue strength of interstitial free steels, intercrystalline fatigue cracks have occurred as a damage which could reduce the application range of this material, being wellknown for its excellent depth drawing features. Through metallographic examination the known causes of the damage like formation of grain cover tertiary zementit of precipitations on the grain boundaries could be excluded. In this paper investigation results are represented which are received through high-resolution analyses techniques (TEM, AES).     

含硅奥氏体钢管的晶间腐蚀裂纹分析

针对输送管产生的晶间腐蚀裂纹，采用光学显微镜观察其显微组织，并用直读光谱仪和透射电子显微镜对材料的成分和腐蚀产物进行了分析，找出了产生晶间腐蚀裂纹的原因。可采用超低碳含Mo的不锈钢来提高输送管使用寿命，经两年多的运行结果表明效果良好。     

Failure of large-scale pilot evaporator duct nozzle

Failure investigation was carried out on a 12'' water evaporator duct nozzle of a large-scale steam flood pilot which is used to inject steam into a heavy crude oil reservoir. The nozzle contained cracks at the pipe, shell, pad and welds. All the materials are made of UNS31803 grade 2205 duplex stainless steel. The cracks were initially formed at the welds and then propagated through the pipe, pad and shell. The cracks were running almost parallel in a straight manner. The cracks were transgranular in nature in the form of fissures associated with second phase precipitates. The results indicated that the nozzle was subjected to repeated welding thermal cycles and the heat input was relatively high, as manifested by the presence of intense heat tint, high percentage of austenite in the weld region (about 70%), and the presence of embrittling intermetallic phases. The investigation concluded that the primary reason of failure was poor welding practice, which facilitated brittle cracking. Fatigue was the mode of failure, which resulted from vibration in the piping system.     

某厂房地面工程混凝土裂缝病害分析

正确检测、分析混凝土结构裂缝的性状、成因及发展趋势,是鉴定结构安全性、实用性和耐久性及制定处理决策的技术依据。地面工程中混凝土结构易出现裂缝问题,大多由配合比、施工方法、环境等多种因素共同作用导致。本文结合工程实例,对某厂生产车间地面工程裂缝原因进行鉴定和分析,为其他类似工程防治裂缝与施工提供借鉴和参考。     

Root causes of fire in a solvent pipe at a petrochemical plant

The root causes of a leak followed by a small fire in a 2 in. solvent pipe in a Petrochemical Plant are discussed. The fire occurred during blanket heating to 300 °C to dissolve polymer clogs. Fractographic and metallographic analyses showed that the failure is characterized by intergranular through the thickness propagation of longitudinal cracks initiated at the outer pipe surface. This cracking mode is called r-type cavitation. The leaking solvent self ignited, polymer deposits inside the pipe carbonized, microstructure changed. All these indicate that pipe temperature during blanket heating reached 550 °C, much above the specified 300 °C maximum. At this temperature yield strength of the pipe material got below nominal hoop stress due to normal internal pressure. The failure of the temperature control system in one of the heating blanket sets was the main event that caused the fire. However, other conditions and exceeded barriers are discussed, related with safety procedures and insufficient support of the ongoing investigation by the contractor involved in the incident. As a result, changes in the declogging and safety procedures were introduced.     

The failure analysis of the star-separator of an aircraft cannon

This paper analyzes the causes of fracture of the double pipe aerial cannon stellate star-separator, which occurred during the fighting plane mission. The linear finite element method (FEM) is used to determine the stresses that the star-shaped star-separator is subjected to during the grenade belts withdrawal and introduction into the bearing tube during gun action and under finite load, which resulted in high strains concentration of the star-separator’s parts pulling the gun belt links.Therefore, in this paper we are particularly focusing on the static and dynamic behavior and the fatigue behavior of the star-separator which is an integral part of the cannon fire shutter mechanism used for the belt’s withdrawal. In this study, the techniques such as numerical analysis, hardness measurement and fractographic examination were used. The testing results showed that the peel and longitudinal cracks started from the low-cycle fatigue and wear of the surface material in the thinnest area of the star-separator tooth, but without influence of the stress load.     

Plastic damage analysis of oil and gas pipelines with unconstrained and constrained dents

Indentation resulting from mechanical damage is one of the main causes of pipeline rupture failure. The primary objective of this case study is to analyze the plastic damage of the pipelines with unconstrained and constrained dents using the existing plastic damage model, namely, the ductile failure damage indicator (DFDI) model. As part of this study, an attempt is made to clarify the influence of the constraint on the behavior of the pipeline. The investigation indicates that the plastic damage of the pipeline interior walls outweighs that of the pipeline exterior walls and cracks start frequently from the pipe interior walls. The position of the maximal circumferential plastic damage deviates from the deepest position of the dent when the critical displacement loading arriving due to the circumferential deformation of the pipeline. The total plastic damage of the unconstrained dented pipeline only depends on the initial displacement loading because the working pressure has very little influence on its behavior under the unconstrained condition. However, the total plastic damage of the constrained dented pipeline depends on the initial displacement loading and the working pressure because the working pressure has a significant effect on its behavior under the constrained condition. Under the same condition, the constrained dented pipeline is easier to crack compared to the unconstrained dented pipeline. In this paper, the model, results and the findings are summarized and discussed.     

5-1/2FH双台肩钻杆内螺纹接头断裂原因分析

采用宏观检验、化学成分分析、力学性能测试、金相检验和断口分析等方法对某5-1/2FH双台肩钻杆内螺纹接头的断裂原因进行了分析。结果表明:此双台肩钻杆内螺纹接头在副台肩第一完整螺纹根部发生了疲劳断裂失效。断裂具有多源特征,起源于内螺纹根部并向外壁扩展,当穿透壁厚形成通道时发生了刺漏,从而使断口表面形成了冲刷痕迹。上扣扭矩不足,同时接头承受的弯曲应力较大是造成接头疲劳断裂失效的主要原因,另外FH型螺纹固有的螺纹根部半径较小、应力集中较大,使接头失效的风险增大。