铀矿用不锈钢泵轴断裂原因分析

目的找到不锈钢泵轴断裂原因。方法通过对断裂的泵轴进行失效分析,利用扫描电镜、金相显微镜、直读光谱仪、显微硬度计等测试方法和手段,对失效泵轴的断口形貌、组织、化学成分、显微硬度等进行分析。结果断口形貌呈明显的脆性疲劳开裂特征,且裂纹源呈现多源特征,有疲劳辉纹和二次裂纹存在。316L泵轴材质成分和组织问题不大,在近表面存在大量夹杂物,同时泵轴表面观察到点蚀和微裂纹存在。结论近表面夹杂物在酸性环境中极易引起点蚀,同时泵轴与联轴器根部结合处存在变截面,形成应力集中。当泵轴受到腐蚀、应力以及电机交变载荷作用时,形成腐蚀疲劳裂纹源,裂纹扩展造成瞬断是此次不锈钢泵轴断裂的主要原因。     

泵轴失效分析

减顶泵在运行过程中,发生了泵轴的突然脆性断裂,通过对失效泵轴的化学成分、力学性能、金相组织以及蚀坑内的腐蚀产物等的检验以及分析.结果表明,泵轴失效的主要原因为：组织中的非金属夹杂物严重超标;显微组织不符合技术要求;泵轴的圆角过渡表面处截面尺寸的突变,并有蚀坑存在,圆角过渡表面处的圆角半径过小.这些缺陷起着尖端缺口的作用,在交变的旋转弯曲载荷作用下,在缺陷处将产生严重的缺口效应,形成了很高的局部应力集中,从而导致泵轴在缺陷处发生疲劳断裂而失效.明确了泵轴失效的原因,对延长泵轴的使用寿命,保证整套蒸馏装置的安全生产有重要意义.     

高压水泵轴断裂失效分析

某石化公司使用的高压水泵在运行过程中发生断裂.采用宏观、微观检验、化学成分分析等方法,对失效件进行了检测.结果表明泵轴在含有H2S等腐蚀性物质的循环水中,遭受电化学腐蚀形成疲劳源,泵轴转动形成的扭力加速裂纹的生成和发展,最终造成应力腐蚀开裂.     

30CrNi2MoV钢的腐蚀疲劳裂纹萌生与扩展行为研究

通过不同循环应力和不同浓度的盐酸腐蚀液的疲劳腐蚀实验,对30CrNi2MoV钢腐蚀疲劳裂纹萌生与扩展行为进行研究。结果表明:30CrNi2MoV钢试样腐蚀疲劳裂纹起源于试样表面的点蚀坑。在循环应力作用下,点蚀坑由于应力集中,萌生裂纹,在应力和盐酸的共同作用下,裂纹不断加深、增多,直至发生断裂。随着循环应力的增大,30CrNi2MoV钢的疲劳寿命明显下降。随着盐酸浓度的增加,试样的疲劳寿命有小幅下降。循环应力对30CrNi2MoV钢腐蚀疲劳裂纹的产生起主要作用,盐酸腐蚀液起辅助作用。     

基于动态贝叶斯网络的海底管道点蚀疲劳损伤失效模型研究

目的研究海底管道在点腐蚀和腐蚀疲劳双重影响下的整个破坏过程,基于动态贝叶斯网络构建系统失效模型,对海底管道系统不同疲劳寿命下的失效概率进行预测。方法将点蚀疲劳损伤过程分为腐蚀点成核、腐蚀坑增长、短裂纹扩展和长裂纹扩展四个阶段,采用蒙特卡洛模拟方法对腐蚀点形成到短裂纹发生前的管道破坏过程进行分析,结合疲劳裂纹扩展的动态贝叶斯网络结构图,在充分考虑相关影响因素不确定性的基础上,为海底点蚀管道系统提出一种创新性的概率分析方法,对点蚀管道疲劳寿命的失效概率进行科学预测。结果结合实例分析,通过蒙特卡洛模拟方法,求解得出腐蚀坑增长转变为短裂纹扩展状态的临界裂纹尺寸为0.8mm。采用动态贝叶斯网络分析方法,对未经受维修保养的点蚀管道进行疲劳寿命预测,当管道运行到第35年时将会面临失效风险。结论所构建的模型可以对海底点蚀管道腐蚀疲劳寿命失效概率进行合理预测,通过观测相关影响参数的变化,及时更新预测结果,有助于为海底管道系统制定有效的维修策略。     

316L不锈钢在模拟人体液内腐蚀疲劳裂纹萌生和扩展过程中应力的作用

探讨应力在316L不锈钢腐蚀疲劳过程中的作用。应力降低了不锈钢的点蚀电位,促进了腐蚀疲劳裂纹的萌生和扩展。初始疲劳裂纹在点蚀孔中的晶界上萌生,在应力的作用下,裂纹由沿晶变为穿晶扩展,并在断口上产生二次裂纹和疲劳辉纹。     

316L不锈钢在模拟人体液内腐蚀疲劳裂纹萌生和扩展过程中…

探讨应力在３１６Ｌ不锈钢腐蚀疲劳过程中的作用，应力降低了不锈钢的点蚀电位，促进了腐蚀疲劳裂纹的萌生和扩展，初始疲劳裂纹在点蚀孔中的晶界上萌生，在应力的作用下，裂纹由沿晶变为穿晶扩展，并在断口上产生二次裂纹和疲劳辉纹。     

压裂泵泵头体裂纹原因分析及应对措施

材质为38CrNi2MoVA的压裂泵泵头体,在使用仅30 h即出现裂纹。通过金相、宏观断口、化学成分分析、力学性能测试、扫描电镜分析等理化试验,对该泵头体裂纹原因进行了分析。结果表明,该38CrNi2MoVA泵头体化学成分中的C、Ni及强度和冲击韧性均低于技术要求,且泵头体内盐酸的强腐蚀作用,导致泵头体发生腐蚀疲劳裂纹。对泵头体内壁进行表面防腐渗氮处理及严控生产工艺,可预防裂纹的发生。     

交变载荷下点蚀坑的统计分布及演化SCIEI

通过海洋工程结构钢A537的喷盐雾腐蚀疲劳试验,经阶段取样观察及定量金相分析得到了各种蚀坑参数的统计分布及分布演化规律。经统计分析发现深径比是控制裂纹萌生的参数。还发现,疲劳载荷(应力幅)不影响蚀坑萌生的快慢,但影响由蚀坑中萌生裂纹的快慢,裂纹萌生之前的蚀坑演化阶段也能反映出腐蚀疲劳的一般规律。     

A7N01S-T5铝合金焊缝金属腐蚀疲劳裂纹萌生行为

以高速列车常用的A7N01S-T5铝合金型材ER5356焊缝金属为研究对象,采用扫描电镜观察不同时间节点焊缝部位腐蚀疲劳裂纹的萌生过程,并分析第二相在腐蚀疲劳裂纹萌生过程中的变化。结果表明,点蚀坑在第二相周围优先萌生,点蚀机理为阳极溶解,在交变应力的促进作用下,焊缝区腐蚀疲劳"短裂纹"沿着点蚀坑周围萌生。     

飞机平尾大轴断裂故障分析

某型飞机在试验中平尾大轴发生断裂。通过断口的观察分析、颤裂部位的金相分析、硬度检测,确定了平尾大轴的失效模式,并对其断裂原因进行了分析。结果表明,该平尾大轴的断裂性质为腐蚀疲劳断裂,裂纹均起源于衬套与筒体间的定位焊点处;定位焊点处选用了强度远低于基体的08A钢焊丝,导致焊点强度过低,在工作载荷作用下焊点处过早萌生了裂纹,焊接工艺不当是大轴断裂的主要因素;平尾大轴简体内壁涂敷防锈漆的质量较差,导致筒体内壁出现严重腐蚀。裂纹源区有腐蚀坑,且裂纹扩展过程中均有腐蚀特征,说明防腐蚀措施不当引起的腐蚀对大轴断裂也有重要影响。     

植入不锈钢腐蚀疲劳过程中的晶间腐蚀

用ＳＥＭ研究了浸在Ｈａｎｋ模拟体液中的轧态３１６Ｌ和铸态３１６Ｌ和铸态３１７Ｌ不锈钢在腐蚀疲劳期间产生的间晶腐蚀。结果表明，腐蚀疲劳初始裂纹是在腐蚀晶界上孕育产生的，在疲劳应力作用下，由沿晶扩展变为穿晶扩展；晶间腐蚀不是由碳化物析出造成晶界贫Ｃｒ产生的。而是一种非敏化晶间腐蚀。     

氯化物溶液中不锈钢腐蚀疲劳裂纹初始萌生的过程机理

研究了动应力（往复弯曲疲劳应力）对氯化物溶液中不锈钢点蚀敏感性的促进作用。 在固溶态３１６Ｌ不锈钢表面点蚀孔中产生了明显的非敏化态晶间腐蚀。在点蚀孔内受腐蚀晶界处孕育 产生了初态腐蚀疲劳裂纹,裂纹由沿晶转变为穿晶扩展,形成主裂纹并继续扩展直至材料失稳断裂。阐 述了在动应力和侵蚀性介质联合信息作用下ＣＦ裂纹萌生的过程机理。论述了动应力－环境介质－材料 特性在多种腐蚀类型交互作用中的贡献和相关性。     

微弧表面处理对AZ31B镁合金耐腐蚀及耐腐蚀疲劳性能的影响

采用微弧表面处理技术(微弧氧化MAO和微弧复合MCC)在AZ31B镁合金基体上制备出不同断面结构的防护涂层。通过电化学腐蚀及腐蚀疲劳测试方法,研究了MAO、MCC涂层的电化学腐蚀及腐蚀疲劳性能。结果表明,生长10 min的MAO涂层具有较好的耐电化学腐蚀性能。MAO涂层表面存在微孔和微裂纹,在应力条件下微孔和微裂纹作为疲劳断裂的裂纹萌生点,可加速裂纹的萌生与扩展,使其腐蚀疲劳寿命相较AZ31B合金基体降低了55%。而具有MCC涂层的AZ31B合金试样腐蚀疲劳极限为(64.0±5.4) MPa,比AZ31B合金基体提高了59%。在低应力载荷下(＜80 MPa),微弧复合涂层试样的腐蚀疲劳强度得到明显提高。     

SCC initiation for X65 pipeline steel in the “high” pH carbonate/bicarbonate solution

The initiation of stress corrosion cracking (SCC) was studied using scanning electron microscope observations of linearly increasing stress test specimens. SCC initiation from the following surfaces was studied: (i) initiation from the commercial pipe surface covered by the Zn coating, (ii) initiation from a mechanically polished surface with a deformed layer, and (iii) initiation from an electro-polished surface. SCC initiation involved different features for these surfaces as follows. (i) For the Zn coated commercial pipe surface, a crack in the Zn coating led to the dissolution of the deformed layer and when the deformed layer was penetrated, intergranular SCC initiation became possible. (ii) For a mechanically polished surface with a deformed layer, cracks in the surface oxide concentrated the anodic dissolution to such an extent that there was transgranular SCC in the deformed layer. SCC was intergranular when the deformed layer had been penetrated. Transgranular stress corrosion cracks were stopped at ferrite grain boundaries (GBs) oriented perpendicular to the SCC propagation direction. (iii) For an electro-polished surface, the surface oxide film was cracked at many locations, but intergranular SCC only propagated into the steel when the oxide crack corresponded to a GB. An oxide crack away from a GB is expected to be healed. The observed SCC initiation mechanism was not associated with simple preferential chemical attack of the ferrite GBs.     

Analysis of failed nuclear plant components

Argonne National Laboratory has conducted analyses of failed components from nuclear power- gener-ating stations since 1974. The considerations involved in working with and analyzing radioactive compo-nents are reviewed here, and the decontamination of these components is discussed. Analyses of four failed components from nuclear plants are then described to illustrate the kinds of failures seen in serv-ice. The failures discussed are (1) intergranular stress- corrosion cracking of core spray injection piping in a boiling water reactor, (2) failure of canopy seal welds in adapter tube assemblies in the control rod drive head of a pressurized water reactor, (3) thermal fatigue of a recirculation pump shaft in a boiling water reactor, and (4) failure of pump seal wear rings by nickel leaching in a boiling water reactor. Work supported by Commonwealth Edison Company under ACK 85026.     

飞机铝合金结构连接部位的腐蚀行为

简要阐述了飞机铝合金结构连接部位的腐蚀特点，采用加腐蚀试验方法研究了含有防腐涂层模拟件的腐蚀行为，在试验室条件下再现了服役期间飞机铝合金结构连接部位的腐蚀损伤历程，同时探讨了其腐蚀机理及其影响因素。结果表明，连接部位是飞机铝合金结构的腐蚀薄弱环节，是最容易出现腐蚀活性点和膜下腐蚀的区域，在腐蚀环境下连接部位缝隙处涂层最先出现鼓包和开裂，涂层剥落后金属基体有点蚀坑存在，随着腐蚀时间增加，点蚀向晶间腐蚀发展，最后出现剥蚀。     

The study of intergranular corrosion in aircraft aluminium alloys using X-ray tomography

Atmospheric corrosion is one of the leading causes of structural damage to aircraft. Of particular importance is pitting and intergranular corrosion, which can develop into fatigue cracks, stress corrosion cracks, or exfoliation. Therefore it is of interest to the Australian Defence Force (ADF) to understand how corrosion ensues in susceptible aircraft aluminium alloys, such as AA2024-T351 and 7050-T7451. However, there are many difficulties in measuring the extent of intergranular corrosion, since it is predominantly hidden below the surface. Traditionally, cross-sectioning has been used to view and measure the depth of attack. In the present work, 2 mm diameter pin specimens were contaminated with a droplet of 3.5% NaCl and exposed to constant humidity that resulted in intergranular corrosion. X-ray computed tomography was then used to non-destructively assess the depth and volume of corrosion both as a function of time in 97% relative humidity, and as a function of relative humidity after 168 h exposure. Both corrosion depth and volume increased with time, but there was evidence for a limiting depth in AA2024. Depth and volume also increased with relative humidity of the environment, for which the time-of-wetness and oxygen concentration of the droplets were considered the important factors in driving the corrosion process.     

空气滤网不锈钢丝开裂原因分析

对某电厂开裂失效的不锈钢丝编制的空气滤网的分析表明：其开裂是由晶间腐蚀和应力腐蚀联合作用引起的开裂.主裂纹是应力腐蚀裂纹，不锈钢丝冷加工残余拉应力及环境中Cl离子的存在是不锈钢丝发生应力腐蚀开裂的主要原因.而用材不当，导致发生了晶间腐蚀.晶间腐蚀作为裂纹的起源，诱发并促进了不锈钢丝的应力腐蚀开裂. 