锅炉水冷壁管爆裂原因分析

针对某石化公司一支锅炉水冷壁管发生爆裂的问题,观察了其宏观形貌和微观组织,分析了其断口特征,结果表明:爆口毗邻炉管明显胀粗,壁厚显著减薄;爆口毗邻金属具有贝氏体+少量铁素体显微组织,而锅炉管正常组织为铁素体+珠光体;爆裂断口具有典型的韧窝断裂特征。综合分析认为,该锅炉水冷壁管的爆裂属于瞬时过热爆管。最后提出了该锅炉水冷壁管今后运行中应该注意的问题。     

某蒸气锅炉水冷壁管爆裂分析

对某电厂爆裂的水冷壁管正常管段和爆裂处管段分别进行了宏观分析、显微组织分析、能谱分析和电子探针分析.结果表明,锅炉水冷壁管爆裂的原因为水处理不良,特别是脱氧处理不够导致产生垢下溃疡性腐蚀,进而管壁减薄造成鼓胀及爆裂.通过断口分析,未发现材质缺陷.     

600MW超临界机组15CrMoG水冷壁管的爆管失效分析

通过宏观分析、硬度测量、金相组织观察和成分分析,对某电厂炉水冷壁15CrMoG管进行爆管原因分析。结果表明:管样化学成分分析结果符合GB 5310-2008中15CrMoG材料化学成分的要求;1#管样爆口处金相组织为铁素体+珠光体,晶粒呈拉伸纤维状。爆口及爆口附近金相组织为铁素体+珠光体;爆口及爆口附近管件截面显微硬度高于标准要求(ASTM A213/A213M-2013,≤170 HV),爆口处显微硬度高达240 HV0.2;室温拉伸试验结果符合GB5310-2008标准中15CrMoG材料的要求。结合现场实际情况,推测水冷壁管短时过热泄漏原因为水冷壁管内工质减少引起的,建议检查引起流量减小的原因。     

电厂水冷壁管爆管失效的原因

某电厂锅炉水冷壁管发生了爆管。通过失效管道宏观形貌和显微组织观察、管材化学成分和力学性能检测、腐蚀产物成分分析等对该水冷壁管爆管的原因进行了分析。结果表明：爆管位置有明显腐蚀沟槽，局部位置发生了Na元素浓缩，腐蚀产物主要为铁的氧化物(Fe₃O₄和Fe₂O₃)、水垢和一定量的NaFeO₂;断口无明显塑性变形，宏观形貌表现为脆断特征，微观形貌表现为沿晶断裂特征；爆管位置组织为铁素体+珠光体，组织中有大量沿晶裂纹；锅炉运行期间，锅炉水pH出现过一段时间较高(10.0～10.2)的情况。综合以上分析，确定水冷壁管失效原因为碱腐蚀引起的应力腐蚀开裂。     

电站锅炉水冷壁管腐蚀疲劳断口分析

对锅炉水冷壁开裂管样断口特征和断裂机理进行分析,结果表明裂纹源区于腐蚀坑,在扩展区可见疲劳弧线、腐蚀产物和腐蚀坑,局部区域可见疲劳条带和二次裂纹;在锅炉启停过程中,准解理型和韧窝型断口形貌特征交替出现;水冷壁管的腐蚀疲劳失效为交变温差应力与腐蚀介质共同作用的结果.     

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 某化工厂锅炉蒸发器吊挂管在运行了5年后突然发生爆裂失效。对该吊挂管进行了化学成分分析、金相检验、扫描电镜、X射线衍射分析及力学性能测定,结果表明：吊挂管爆口附近的碳含量和力学性能均低于相关标准规定值;管外壁脱碳;内部金相组织为过热组织。这些都是由于管内壁沉积有钙盐和硅酸盐类水垢,造成管体超温运行的结果。严重沉积的水垢还导致管内壁高温氢腐蚀,壁厚由原来的6 mm减至2～3 mm,因此发生了失效爆裂。根据分析结果提出了相应的解决方案。     

600MW电站锅炉水冷壁管泄漏原因分析

通过宏观分析、化学成分分析、金相组织和断口分析,对某电厂600 MW电站锅炉水冷壁管泄漏原因进行了综合分析。结果表明,水冷壁管泄漏的根本原因是腐蚀介质和热应力联合作用产生的疲劳裂纹所致。裂纹由外壁向内壁扩展,呈楔形穿晶为主。     

超临界锅炉水冷壁横向裂纹形成原因分析

对某超临界锅炉水冷壁管外壁横向裂纹的性质和形成原因等进行了分析,主要内容包括金相分析、硬度检测、拉伸性能试验、断口扫描电镜分析、外壁及断口附着物X射线能谱分析等。结果表明,锅炉侧墙向火侧水冷壁管外壁横向裂纹的形成原因是腐蚀性热疲劳,而炉内火焰对水冷壁的冲刷是造成热疲劳的主要原因。     

20G钢锅炉水冷壁管爆管原因分析

借助光学显微镜、扫描电镜、能谱分析仪、直读光谱仪对某热电厂203钢锅炉水冷壁失效管进行宏观分析、材质复检、断口分析、硬度测试、常温及高温力学性能测试等,分析其爆管原因.结果 表明:该水冷壁管在服役过程中经历了短时超温,且最高温度达到854℃以上,最终导致爆管的发生.     

锅炉水冷壁腐蚀及爆裂的原因分析和防止对策

锅炉水冷壁不仅在水气侧发生腐蚀,而且在烟气侧也能发生腐蚀,由于腐蚀引起的水冷壁爆裂具有突发性,一旦发生腐蚀,爆裂后果较为严重。高参数锅炉水冷壁腐蚀爆裂通常发生在燃烧器中心线位置标高附近,涉及范围较大,严重危及机组的安全运行,锅炉水冷壁腐蚀爆裂的部位通常在热负荷最     

超临界循环流化床锅炉高温过热器管开裂原因分析

某超临界循环流化床锅炉TP347H钢膜式壁高温过热器管频繁发生开裂,通过宏观检查、光谱分析、力学性能试验、显微组织分析以及运行情况分析等对其失效原因进行了研究。结果表明,取样管化学成分、力学性能均满足标准要求,显微组织未见异常;裂纹起源于管子与鳍片焊趾处,并从外壁向内壁扩展;管子开裂原因为:高温过热器管为大屏膜式壁结构,加之锅炉启动过程中,相邻管壁温度差较大且不断变化,造成管子在轴向方向的膨胀差较大并形成交变热应力,从而在焊趾应力集中部位产生热疲劳裂纹,同时管子与鳍片焊缝处的残余应力以及管子外表面存在的直道沟槽促进了裂纹的形成和扩展。     

大口径厚规格X80管线钢的低温断裂控制

以大口径(OD1422 mm)、大壁厚(38.5 mm)X80级管线钢热轧板为研究对象,采用光学显微镜和扫描电镜对其显微组织和-20℃低温落锤撕裂试验断口形貌进行分析,研究了断裂与组织之间的关系.结果表明,带状组织和不同厚度位置晶粒度大小不均,粒状贝氏体、退化珠光体、准多边形铁素体和马奥岛等混合组织会导致裂纹的萌生和扩...     

Effect of titanium addition on the microstructure and inclusion formation in submerged arc welded HSLA pipeline steel

The effect of titanium addition on the SAW weld metal microstructure of API 5L-X70 pipeline steel was investigated. The relationship between microstructure and toughness of the weld deposit was studied by means of full metallographic, longitudinal tensile, Charpy-V notch and HIC tests on the specimens cut transversely to the weld beads. The best combination of microstructure and impact properties was obtained in the range of 0.02–0.05% titanium. By further increasing of titanium content, the microstructure was changed from a mixture of acicular ferrite, grain-boundary ferrite and Widmanstätten ferrite to a mixture of acicular ferrite, grain-boundary ferrite, bainite and ferrite with M/A microconstituent. Therefore, the mode of fracture also changed from dimpled ductile to quasi-cleavage. The results showed an increase in the titanium content of inclusions with increased titanium levels of weld metal. Titanium-base inclusions improve impact toughness by increasing the formation of acicular ferrite in the microstructure. No HIC susceptibility was found in the weld metals with titanium contents less than 0.09%.     

重卡汽车齿轮开裂失效分析

某重卡汽车齿轮在使用过程中发生开裂。采用宏观、微观检验、化学成分分析及硬度检验等方法,对失效齿轮进行了分析。结果表明齿轮热处理不当造成组织不合格,存在大量铁素体,有效硬化层偏低,致使齿轮强度不高,无法承载设计载荷,最终使齿轮破裂。     

Effect of CO_2 partial pressure on SCC behavior of welded X80 pipeline in simulated soil solution

The stress corrosion cracking (SCC) behavior of welded X80 pipeline steel in simulated Ku'erle soil solution was studied by means of electrochemical impedance spectroscopy (EIS) and slow strain rate tests (SSRT).The microstructure of the welded steel was observed by optical microscopy (OM).It is demonstrated that the microstructure of the weld metal consists of acicular ferrite and grain boundary ferrite,while that of heat affected zone (HAZ) is a mixture of acicular ferrite and bainitic ferrite microconsti...     

Development of ferrite/bainite bands and study of bainite transformation retardation in HSLA steel during continuous cooling

The development of banded structure in HSLA steel during continuous cooling has been systematically studied using dilatometry and microstructural observations. At low cooling rates (<10 °C/min), the microstructure contains alternating bands of ferrite and a mixture of pearlite and bainite. At higher cooling rate (>10 °C/min), the formation of pearlite is suppressed, and the corresponding microstructure consists of banded ferrite and bainite. Dilatometric analysis indicates that as ferrite and pearlite transformation at low rates (or ferrite transformation at higher rates) completes, Manganese (Mn) and Carbon (C) concentration in austenite can retard the bainitic transformation and result in the transformation stagnancy phenomenon. The magnitude of retardation and the bainite morphology are affected by Mn and C concentration. The increased cooling rate decreases Mn and C content in bainite, and then the length of the stagnant stage decreases and bainite morphology changes from lower bainite to acicular ferrite.     

回火温度对热轧态高强度贝氏体钢管组织性能的影响

热轧态高强度新型贝氏体钢管具有较高强度,但冲击值较低,回火可以改善其冲击韧性。研究回火温度对热轧态高强度新型贝氏体钢管组织和性能的影响。试验结果表明:550℃以下温度回火,随回火温度提高,该新型贝氏体钢管的抗拉强度有降低趋势,但下降幅度不大;350℃以下温度回火,其冲击值随回火温度的提高而增加;400℃回火时冲击值降低,出现回火脆性;450℃以上温度回火时冲击值增加;250~350℃回火时钢管强度较高,550~650℃回火时韧性较高。400℃以下温度回火,该新型贝氏体钢管的组织均为板条贝氏体、粒状贝氏体、铁素体及残余奥氏体组织;回火温度超过500℃,残余奥氏体完全分解,组织为铁素体和粒状贝氏体。     

显微组织对管线钢硫化物应力腐蚀开裂的影响

研究了不同显微组织管线钢的抗硫化物应力腐蚀开裂（SSCC）行为,结果表明,细小针状铁素体为主的显微组织抗SSCC性能最佳,超细铁素体的显微组织次之,（铁素体 珠光体）的显微组织最差,分析表明,氢脆是高强度管线钢在SSCC中的主要破坏形式。针状铁素体为主的显微组织,其内部高密度缠结位错和弥散析出的碳氮化物起到了强烈的氢陷阱作用,表现出最佳的抗SSCC性能。     

Mechanical characterization of the welding of two experimental HSLA steels by microhardness and nanoindentation tests

The microhardness and nanohardness of the welding zone of two experimental HSLA steels were determined. The first steel has a microstructure of martensite and bainite, and the second one has a microstructure of quasipolygonal ferrite and acicular ferrite. In the bainitic - martensitic steel, softening of the heat affected zone was observed. This softening can be attributed to: the formation of polygonal ferrite in the recrystallization subzone, the formation of quasi-polygonal ferrite and the tempering of martensite in the intercritical subzone, and the tempering of martensite in the subcritical subzone. Besides the softening, with nanoindentation technique, hardening was observed at the position where the peak temperature reached the critical temperature A _c1, which can be attributed to a phenomenon of secondary hardening by precipitation of carbides of alloying elements. In the ferritic steel, a softening phenomenon did not appear since there was no martensite in its initial microstructure. Finally, it was noted that both polygonal ferrite and the bainite have similar behavior and nanohardness, this coincidence can be attributed to the effect of grain boundary.     

Effect of annealing temperature on pitting behavior and microstructure evolution of hyper‐duplex stainless steel 2707

Hyper‐duplex stainless steel (HDSS) 2707 is a competitive material for application in extremely caustic environments. In this study, different annealing temperatures ranging from 1020°C to 1200°C were examined by electrochemical tests and microstructure analysis. The microstructure characterization indicated that precipitations were detected when the annealing temperature was below 1050°C and a relatively balanced austenite–ferrite phase structure was obtained at 1100°C. Through electrochemical measurements in NaBr solution, it was revealed that with the increase of temperature the pitting resistance of HDSS 2707 first rose then declined, peaking at 1100°C. The highest critical pitting temperature was about 67°C. In addition, the pitting position shifted from austenite phase to austenite–ferrite boundary and finally to ferrite interior with the annealing temperature increasing, which was in agreement with the pitting resistance equivalent values (PREN) of the two phases.