600MW锅炉12Cr1MoV末级再热器管失效原因分析

某电厂600 MW亚临界机组的12Cr1MoV末级再热器管运行50000 h后发生泄漏。在迎烟气侧弯头背弧出现裂纹。采用光学显微镜、扫描电镜和能谱仪等方法对失效管样进行分析。结果表明,弯头向火侧氧化层过厚,组织球化严重;弯头向火侧管壁存在明显的蠕变孔洞和沿晶裂纹,裂纹沿着晶界发展并充满氧化物;基体出现合金元素贫化,导致组织劣化。综上,12Cr1MoV末级再热器管失效是由长期过热造成管件向火侧组织老化,蠕变开裂而引起泄漏。     

丙烯腈装置中反应气体冷却器用热电偶套管的泄漏原因

某丙烯腈装置反应气体冷却器热电偶套管在使用过程中发生泄漏。采用宏观观察、化学成分分析、显微组织观察、显微硬度测试、扫描电镜和能谱分析等方法,分析了该热电偶套管泄漏的原因。结果表明：该热电偶套管的开裂形式为应力腐蚀开裂,其泄漏的主要原因是套管热影响区和母材区的表面状态和显微组织差异产生应力,在硫化氢和氯化物共存的环境中,在热影响区优先形成应力腐蚀裂纹,裂纹沿着晶界向母材扩展,从而在套管与法兰凸台的焊缝连接处发生开裂,最终导致热电偶套管在使用过程中发生泄漏。     

过热器20G钢管爆裂原因分析

采用金相检验、化学分析、力学性能和扫描电镜对某钢厂锅炉顶棚过热器管爆裂原因进行了分析。结果表明,过热器长期过热导致管胀粗、局部减薄,最终形成裂纹。由于裂纹引起泄漏,使回路其余段内冷却工质的流量减小,导致泄漏处的下游发生短时过热爆管,出现大破口。锅炉短期使用的情况下爆管,且显微组织严重球化,证明失效过热器运行时内管壁温度远远超过额定温度318℃,20G钢安全余量不足是导致爆管的主要原因。     

高温再热器SA-213TP347H钢管裂纹原因分析

通过结构分析、断口检查、硬度测试、抗拉试验、显微组织观察及能谱分析,对电厂高温再热器SA-213TP347H钢管进行裂纹原因分析。结果表明:高温再热器在运行中容易晃动,裂纹处于管夹挤压的凹坑;裂纹处管材的拉伸性能、硬度均符合ASME A213/A213M对SA-213TP347H钢的要求;显微组织为奥氏体和沿晶界分布的含Cr碳化物,裂纹是沿晶裂纹,由管外壁向管内扩展;裂纹处腐蚀产物均含有O、S等非金属元素。分析表明:产生裂纹的原因是由于管夹挤压管道,同时管道结构易晃动,增加了挤压变形处的应力,促进了含Cr碳化物沿晶界析出,形成贫Cr区而导致晶界弱化,并在腐蚀性介质的作用下,导致晶间应力腐蚀开裂。     

12Cr1MoV钢末级再热器管失效分析

某电厂600 MW亚临界机组12Cr1MoV钢末级再热器管运行51020 h后发生爆裂。采用光学显微镜、扫描电镜等设备,从宏观检查、氧化层检测、组织分析和能谱分析方面对失效管样进行研究。结果显示,爆口呈长期过热开裂宏观特征。管样向火侧氧化层过厚,组织球化严重。爆口处向火侧管壁存在明显的蠕变孔洞和沿晶裂纹,裂纹沿着晶界发展并充满氧化物。能谱分析结果显示,末级再热器管向火侧管壁在长期服役过程中,基体出现固溶合金元素贫化,导致组织劣化。综上,12Cr1MoV钢末级再热器管失效是由长期过热引起管件向火侧组织劣化、蠕变开裂造成的。     

某电厂水冷壁管鳍片焊缝失效原因分析

通过取样对某电厂失效水冷壁鳍片焊缝进行宏观观察、光谱分析、显微组织及能谱分析,试验结果表明：泄漏水冷壁管鳍片焊缝存在长度约为95 mm的富铜聚集区,w(Cu)达85.14%,鳍片焊缝富铜聚集区及其与管子母材过渡层存在沿晶小裂纹,裂纹内填充有黄褐色的铜质合金。水冷壁管鳍片焊缝失效原因为在埋弧焊过程中,铜质导电嘴与管子母材接触发生短路,短路电流产生的高温使导电嘴与管子母材接触部分熔化,管子母材局部被烧穿,铜合金熔入到焊缝金属中,低熔点富铜合金沿母材和焊缝晶界扩散,导致晶界脆化并产生裂纹,最终发生熔铜开裂。     

超超临界锅炉T23钢水冷壁管开裂分析

以超超临界锅炉SA213?T23钢水冷壁失效管为试验对象,通过宏观检查、化学成分分析、金相检验和硬度试验,分析失效原因。结果表明:该水冷壁管化学成分正常,材质性能未发生明显劣化;水冷壁失效原因为鳍片焊缝开裂,该裂纹为沿晶界扩展的再热裂纹,起源于焊缝熔合线附近的热影响区粗晶区域,先沿热影响区横向扩展,然后扩展至母材区域,最终导致管壁泄漏失效;热影响区粗晶区域显微组织为粗大的马氏体和贝氏体组织,硬度明显偏高于焊缝熔合线另一侧的焊缝区域,脆性增大。两者在显微组织和硬度上的明显差别,使焊缝熔合线附近的热影响区粗晶区域容易产生应力集中,在高温运行中发生晶间开裂。     

瞬时过热对高铬镍奥氏体钢断裂和析出相形变的影响机理

某火电厂锅炉在进行试验管屏风压试验测试时,发现再热器管(22Cr-15Ni钢)与套管(18Cr-8Ni-Nb钢)的密封焊接处存在裂纹,通过样管宏观分析、裂纹金相分析和断口及析出相的SEM/EDS分析了其裂纹产生原因。结果表明,失效处附近存在机械应力输入和焊瘤应力集中的明显痕迹,焊瘤热输入导致局部组织过热,同时基体M₂₃C₆球状析出相异常长大造成微观拉应力。上述原因的综合作用最终导致机械应力从应力集中处输入产生微裂纹,并沿着过热弱化的晶界扩展,与基体析出相产生的微裂纹汇合,最终扩展成为环向断口。风压泄漏吹击断口,造成断面上因热输入异常长大的M₂₃C₆球状析出相上产生韧性变形凹坑和脆性开裂, 并显露内部枝状晶的微观断口形貌。     

氧氯协同作用下304不锈钢管的应力腐蚀开裂

某生活用直流锅炉的304不锈钢水冷壁管在服役4000多个小时后多处发生开裂,通过宏观形貌、化学成分、力学性能、显微组织、断口扫描及能谱等研究了水冷壁管开裂失效的根本原因。结果表明:水冷壁管内壁多处发生开裂,裂纹均沿晶界扩展,水垢中存在氯离子,为典型的应力腐蚀开裂。在高温服役条件下,溶解氧、氯离子和运行应力的协同作用最终造成了304不锈钢水冷壁管的开裂失效。     

UNS S31803双相不锈钢焊接三通开裂失效分析

某海上天然气气田井口管线立管焊接三通服役过程中出现贯穿裂纹,引起燃气泄漏事故。采用直读光谱仪分析化学成分,显微硬度计测试硬度,电子万能试验机测试力学性能,金相显微镜观察显微组织,扫描电镜观察微观形貌,EDS进行元素分析,XRD进行物相分析。结果表明,三通开裂失效裂纹形成机制为应力集中引起的腐蚀开裂,裂纹在根部焊缝形成以后,以穿晶形式向母材扩展,裂纹在母材区以沿晶断裂的形式穿过存在σ相的区域。     

热挤压成形GH3625合金管材组织及裂纹形成机理

通过对比热挤压成形管材和爆裂管材的组织以及对爆裂管材裂纹和断口的分析,研究了热挤压成形GH3625合金管材的组织及裂纹形成机理。结果表明:爆裂管材与成形管材的组织均为等轴晶,但爆裂管材的开裂使晶界处的应力集中得以释放,其组织中并没有形成变形孪晶,在管材径向方向上也不存在晶粒尺寸不均匀的现象。挤压比过高导致管材在热挤压过程中绝热升温严重,使低熔点的Laves相熔化并扩散到周围基体中,是裂纹形成的根本原因。在模具出口处高拉应力的作用下,这些裂纹不断扩展最终连接在一起,导致管材的爆裂现象。由于断口表面冷却速率较高,组织通过奥氏体区的时间较短,再结晶形核核心多且晶粒长大过程受阻,使断口表面形成了一层十分细小的再结晶晶粒。     

HP40裂解炉管组织及裂纹产生原因分析

本文用SEM、EDS、XRD对开裂的HP40裂解炉管进行分析,发现多数裂纹均位于焊缝附近,且均沿枝晶间和晶界开裂的碳化物扩展.经EDS成分分析和XRD结构分析,这些开裂的碳化物为M23C6和富Nb、Si的碳化物.新炉管组织为奥氏体和枝晶间分布的M7C3及高Nb、Si的共晶碳化物.新旧炉管比较可知,开裂炉管的结构和形态在长时间高温下均发生了明显变化,即M7C3转变为M23C6且明显粗化,在晶界呈连续分布.这种脆而硬的碳化物在组织应力和热应力作用下碎裂成为潜在的裂纹源,它们加速了裂纹扩展进程,缩短了炉管的使用寿命.沿裂纹打开断口发现,整个断面被这两种碳化物所覆盖.这进一步证实了造成裂解炉管早期开裂的原因是这种沿晶界连续分布的粗大碳化物的存在.     

奥氏体不锈钢管坯分层开裂分析

奥氏体不锈钢管坯在切割过程中发生分层开裂，对该管坯进行化学成分、微观组织及裂纹断口形貌的分析表明，管坯的开裂主要与条状铁素体和链状氮化钛夹杂有关。     

ZL111铝合金液压制动主缸的开裂分析

ZL111铝合金液压制动主缸体在外观检测时发现主缸开裂,密封检测漏气。为查找铝合金主缸开裂原因,对主缸裂纹、断口形貌、显微组织进行观察,检测其化学成分、相变点。结果表明,主缸的失效是因为组织存在过烧缺陷,降低了材料强度,且晶界存在呈圆角状分布的脆性共晶硅相,并聚集长大,进一步弱化晶界。在淬火应力作用下,缸体开裂,后续加工过程中裂纹扩展至宏观裂纹。讨论并分析主缸开裂的根本原因是成分中Mg元素含量偏高,降低了引起主缸过烧的温度。     

Effect of grain boundary ferrite on susceptibility to cold cracking in high-strength weld metal

Due to the practical limitations of lowering the diffusible hydrogen content of flux-containing welding consumables, it is now felt that modification of the weld microstructure would alleviate the risk of weld metal cracking in multi-pass weld deposits. Thus, this study aimed to identify and evaluate the effect of the weld microstructure on the cold cracking susceptibility of FCAW weld metals and then to provide a basic guideline for designing new welding consumables from a microstructural point of view. In order to identify the parameter(s) that can quantify the microstructural susceptibility of multi-pass weld deposit, two sets of FCAW wires with tensile strength of about 600 MPa were prepared by controlling the Ni content to allow sufficient variation in the weld microstructure, but with little change in weld metal strength. The cold crack susceptibility of those two chemistries was evaluated by a multi-pass weld metal cracking test at various levels of diffusible hydrogen content. All of the cold cracks developed were Chevron-type, and the occurrence of such cracks depended upon the proportion of grain boundary ferrite (%GF) as well as the diffusible hydrogen (HD) content. In fact, at the same level of HD, higher Ni (1.5%Ni) wire showed better resistance to cold cracking than lower Ni (0%Ni) wire even though the latter was stronger and also higher in carbon equivalent. This result could be explained solely by the difference in grain boundary ferrite content between those two welds since Chevron cracking preferentially initiates at and propagates along grain boundary ferrite. Therefore, we propose the use of a value of %GF as a parameter to quantify the microstructural susceptibility of ferritic multipass weld deposit with a strength level of about 600 MPa. It was further suggested that, in addition to the hydrogen control approach, microstructural modification in the form of reducing the %GF can be pursued to develop welding consumables with improved resistance to cold cracking.     

Effects of inclusion size and acicular ferrite on cold cracking for high-strength steel welds of YS 600 MPa grade

The influences of microstructure and inclusion on cold cracking were studied in high-strength steel welds of YS 600?MPa grade using the Y-groove test. The weld microstructure showed a mixture of acicular ferrite, bainite and predominantly martensite. Cold crack fractography identified intergranular fracture (IF) and quasi-cleavage fracture (QCF). Bainite and martensite predominated on the surface and subsurface of IF while the QCF showed inclusions that nucleated acicular ferrite. The influence of inclusions on cold cracking can be described as follows: (i) the inclusions acted as nucleation sites of QCF, (ii) the inclusions contributed to the nucleation and growth of micro-cracks and (iii) new cracks were produced from inclusions when a crack impinged on the inclusions. Inclusions smaller than 2?μm increased the cold crack resistance by contributing to the nucleation of acicular ferrite. Inclusions larger than 2?μm increased the cold crack susceptibility by inducing crack nucleation in welds.     

F65锻造方坯和轮毂超声波探伤缺陷分析

利用超声波检测、低倍检验、金相显微镜、拉伸试验机及扫描电镜对锻造厂的F65锻造方坯和轮毂锻件的裂纹成因进行宏观及显微组织分析,为深海采油高压传输管法兰的缺陷特征的研究提供可行的方法.结果表明:裂纹是组织残余应力所致,裂纹成因与材料冶金缺陷及氢致裂纹无关,裂纹主要沿条带组织中的贝氏体呈穿晶扩展,与粗大不均匀的铁素体与贝氏...     

Effect of weld metal microstructures on cold crack susceptibility of FCAW weld metal

The effect of microstructures on weld metal cold cracking has been studied using flux-cored are welding (FCAW) wires with a 600 MPa strength level. Two FCAW wires were prepared by controlling the Ni content to allow a sufficient variation in weld microstructures, but with little change in the weld metal strength. The microstructural analysis showed that there was a significant difference in the proportions of the microstructural constituents of the weld microstructure. The 1.5%Ni wire resulted in a weld microstructure with a lower grain boundary ferrite (GF) content associated with an increased proportion of acicular ferrite (AF) than the 0% Ni wire. The GF contents of 0%Ni and 1.5%Ni weld metal were measured to be 19% and 6%, respectively. The cold crack susceptibility of these two FCAW wires was evaluated using the gapped bead-on-plate (G-BOP) test at the two different levels of diffusible hydrogen content As a result of the G-BOP tests, it was demonstrated that the 1.5%Ni wire had better resistance to cold cracking than the 0% Ni wire because its weld deposit had a lower GF phase content. This implies that, in addition to the hydrogen control approach, microstructural modification can be pursued to develop new welding consumables with an improved resistance to cold cracking. In the discussion, the detrimental effect of GF against cold cracking is addressed based on the microstructural characteristics of cold cracks in ferritic weld metal.     

压气机整流器叶片裂纹分析

发动机在累计试车13h14min后,发现压气机前排整流器38片叶片中共有21片叶片进气边存在裂纹。对存在裂纹叶片的宏、微观特征进行了观察与分析,并对叶片的金相组织、硬度、化学成分进行了检测。结果表明,发动机双排整流器叶片的开裂性质为疲劳开裂,叶片的疲劳开裂是异常振动应力,加之材料碳含量偏高和组织中大量网状铁素体的存在导致钢的疲劳性能下降,多种因素综合作用导致了疲劳裂纹的萌生及扩展。