锅炉再热器联箱拉拔管断裂分析

某锅炉再热器进口联箱南引出管与联箱拉拔管对接焊缝熔合线附近发生断裂。对失效管段进行宏观检查、金相、力学性能等试验分析,发现断裂断口起源于焊缝熔合线附近且位于结构应力集中部位,由于拉拔管热处理工艺不到位导致拉拔管侧母材金相组织异常,性能偏低,裂纹快速向联箱拉拔管侧母材扩展,引起断裂。为此建议在机组检修期间加强对联箱拉拔管母材的硬度检查、该部位焊口检查以及联箱的膨胀自由度检查,必要时对管路结构进行改型以避免较大的结构应力。     

威海工程再热器交叉管焊接裂纹问题研究

本文根据威海工程再热器交叉管产品生产过程中出现的角焊缝焊接裂纹,分析了裂纹产生的原因,找到了解决问题的办法,并对同类奥氏体不锈钢焊条的抗裂性进行了评估.     

1000t/h锅炉末级再热器出口集箱管座角焊缝产生裂纹的原因与措施

末级再热器出口集箱管座发生裂纹,是长期困扰燃煤电厂的重大设备隐患。通过分析末级再热器出口集箱管座上部角焊缝热影响区产生裂纹的原因及焊接装配形式的分析,认为不合理的焊接接头型式、较大的拘束应力和长期高温运行后导致金属热强性降低,是集箱管座产生裂纹的主要原因。为此,按照DL/T869—2012标准要求,将承插式焊接接头改为全焊透焊接接头,用加强型管座提高焊接接头强度,控制焊接工艺参数等措施,提高了焊接接头的强度和高温力学性能,消除了超标焊接隐患。12号锅炉从2011年12月大修后运行至今,末级再热器出口集箱焊口经过多次磁粉探伤,均未发现裂纹等超标缺陷,证实了改进集箱管座焊接接头型式是正确的。     

超临界机组低温再热器出口集箱12Cr1MoVG管座角焊缝裂纹原因分析

神华国能宁夏煤电有限公司1号机组低温再热器出口集箱管座角焊缝多次出现开裂问题,通过金相组织分析、电镜扫描、化学成分分析以及硬度试验,表明管座角焊缝产生裂纹的原因与材质及硬度无关;进一步进行小试样再热裂纹试验。结果表明:管接头在其工作温度区间具有较大的再热裂纹敏感性,而连接管在此温度的再热裂纹敏感性较低,即部分集箱管接头的再热裂纹敏感温度处于其工作温度区间,因此在热应力等因素的综合作用下产生了开裂。     

300 MW机组锅炉再热器出口集箱与连接管焊缝裂纹分析及治理

介绍了300 MW机组锅炉再热器出口集箱与连接管焊缝裂纹缺陷情况,分析了裂纹出现的原因,阐述了焊缝裂纹修补和热处理的过程,提出了提高技术人员专业技术水平的必要性。     

某电厂低温再热器三叉管表面缺陷原因分析

某电厂低温再热器材质为SA-182M F91的三叉管,运行数月后泄漏导致被迫停炉。通过宏观观察、化学成分分析、力学性能检测和金相组织观察等方法,分析确定三叉管发生泄漏的原因。分析认为,三叉管的化学成分和硬度均符合ASME SA-182M标准对F91材料的要求,三叉管外表面补焊产生的焊缝结构是导致裂纹萌生扩展并最终泄漏的主要原因,裂纹在三叉管最终热处理前已存在。     

电站锅炉的超温现象的检验与防护

在电厂锅炉设备中，水冷壁、过热器及出口集箱、集汽集箱、再热器及出口集箱、主蒸汽管等锅炉受压部件由超温引起的缺陷或事故是常见的安全问题。本文从分析以上锅炉受压部件的超温原因，提出防止出现超温现象的对策。     

中温中压锅炉集汽联箱管座角焊缝裂纹分析

在锅炉检验中 ,发现几台同类型锅炉的集汽联箱的管座角焊缝 ,均在相同一侧出现裂纹。通过详细分析得出 :应力集中、存在强度薄弱区、应力腐蚀是产生裂纹的主要原因。针对以上几种情况 ,介绍了正确的处理方法     

200 MW电厂再热器小径管焊口应力集中的研究

简述了200 MW电站锅炉再热器集箱小径管焊口的质量和安全的重要性.介绍了再热器焊区渗漏的3种原因,即设计不当、材料性能欠佳和运行工况恶劣,指出最重要的原因--结构设计不当.结合某电厂锅炉再热器集箱小径管的焊口,将实际问题理想化为符合实际的力学模型,分析了采用有限元法来求解该力学模型的必要性.给出了有限元法计算模型,研究了焊口倾角和焊缝厚度对焊口应力集中系数的影响.取尽可能小的焊口倾角和大的焊缝厚度,可减小应力集中系数.     

常熟发电厂1号炉高温再热器管屏变形原因分析

对高温再热器管壁温度、烟气温度的实时监测和分析计算表明，高温再热器的管屏变形不是由管壁或工质温度超限引起，而是由于进／出口温度差，以及同屏各管进／出口温度偏差所产生的胀差引起。同屏管夹破坏是因管子膨胀不畅，管夹焊缝应力超过许用应力，管夹的焊接强度不够而拉裂造成；定位管与各屏外管套的垂直膨胀最不同而产生相对位移，形成定位管脱开后错位。     

Thermal load deviation model for superheater and reheater of a utility boiler

The extreme steam temperature deviation experienced in the superheater and reheater of a utility boiler can seriously affect its economic and safe operation. This temperature deviation is one of the root causes of boiler tube failures (BTF), which causes about 40% of the forced power station outages. The steam temperature deviation is mainly due to the thermal load deviation in the lateral direction of the superheater and reheater. This variation is very difficult to measure in situ using direct experimental techniques. In this paper, we propose a thermal load model that is based on the power plant thermodynamic parameters, thermal deviation theory, and flow rate deviation theory. It is found that the calculated results from our model agree well with the in situ experimental results. The predicted BTF positions are the same as that in the reheater of a 300 MW utility boiler at Wujing Power Plant. The proposed model has been used to improve the design of utility boiler in Boiler Works, predict the possible BTF in the design stage, and assess the existing designs. This model can also be applied to utility boilers of different manufactures, and has been successfully applied to the BTF prediction and prevention in the Power Station.     

电厂锅炉再热器设计经济效益分析

再热器是汽轮机高压缸排汽返回锅炉重新加热到额定温度的锅炉受热面部件,主要目的是提高机组效率和热经济性.以A、B电厂为例,通过对锅炉再热器受热面管屏进行设计重量统计、投资效益分析、改造建议分析等,对实现机组更大经济效益有指导意义.     

炉内旋流数对热偏差影响的理论和试验研究

介绍了炉内旋流数Sw基本概念和计算方法，指出Sw实际表征的是炉内气流旋转速度与上升速度之比，其大小对水平烟道处的高温受热面的热偏差情况有直接影响；就二次风配风方式、锅炉负荷和一、二次风风率对Sw的影响进行了分析和讨论，并在实炉上就Sw的变化对再热器热偏差的影响进行了试验研究。理论分析和试验结果显示：在同样的负荷下，二次风配风方式对Sw有明显影响，均等配风时Sw最小，再热器的最大热偏差系数随Sw的增加而增加；在同样的二次风配风方式下，Sw随锅炉负荷的降低而增加，再热器的最大热偏差系数随Sw增加而增加．     

超临界锅炉高温受热面屏间热偏差在线优化研究

以锅炉过热器、再热器热偏差计算方法为基础,采用全局寻优方法,根据当前的负荷、磨煤机组合、燃烧器摆角、各层配风方式、末级过热器和再热器热偏差状况,对运行状况进行优化评判,从而降低管壁温度峰值,控制管壁超温幅度和超温时间,进而减缓氧化皮的生成速度,使锅炉运行的安全性和经济性得到双重保证.通过在某600 MW超临界锅炉上的在线优化运行,表明锅炉末级过热器屏间热偏差系数最大约为1.2,比以往的最大热偏差系数下降了10%.     

对锅炉高温管段产生氧化皮原因的分析和解决办法

以国内某电厂锅炉末级再热器发现氧化皮为例,针对锅炉末级再热器等高温管段易发生的氧化皮沉淀现象,本文从氧化皮的生成机理和预防脱落两方面详细阐述,并提出建议措施、注意事项和解决办法。     

电站锅炉再热器面积改变对过热器运行影响规律的研究

在对某发电厂200MW机组超温爆管进行的研究中发现,在尾部竖井中布置有分隔墙,低温过热器和低温再热器分别布置在分隔墙两侧,利用烟气挡板调节再热汽温的锅炉中,再热器面积的大小直接影响到过热器的运行情况。本文以该类型锅炉为研究对象,研究了再热器面积改变对过热器运行的影响规律,并提出通过适当养活再热器受热面来缓解过热器超温的思路。     

Residual stresses in girth butt welded pipes and treatments to modify these

A number of Type 304 stainless steel pipes are used in the primary cooling systems of nuclear plants. Intergranular stress corrosion cracks (IGSCC) were found at some welded joints in these piping systems due to very high tensile residual stress, sensitization of the material due to welding, and corrosive environment, all occurring simultaneously. Investigations have shown that at least one of the above factors must be eliminated to prevent IGSCC.

This report describes experimental results on the temperature variations during pipe welding by conventional techniques and by the heat sink welding (HSW) technique. The mechanism of residual stress generation due to welding is also discussed. The pipe used in these experiments was 4B Sch80 Type 304 stainless steel. It was found that the temperature distribution through the thickness of the pipes was almost uniform for the conventional welding technique, but had a very sharp gradient for HSW. In the pipe axial direction, the temperatures varied sharply for both welding techniques. This implies that the sensitization of metal due to HSW is lighter than that of conventional welding and that the residual stress on the inside surface of the heat sink welded pipe is compressive.

The induction heating stress improvement (IHSI) method has been investigated analytically and experimentally. In the IHSI method, a pipe is heated with an induction coil while cold water is pumped through it. This causes a temperature gradient throughout the pipe wall which generates high thermal stresses. This, in turn, generates compressive stresses on the inner surface of the pipe. This method is designed to eliminate tensile residual stresses near the weld heat affected zone on the inner surface.

Temperature analysis and subsequent thermoelastic-plastic analysis show that tensile weld residual stresses at a joint were changed into compressive stresses on the inner surface of a pipe. It was confirmed experimentally that these stresses suppressed fatigue crack propagation in the heat affected zone (HAZ) of a welded pipe. Therefore, the IHSI method is effective not only in preventing crack initiation but also in suppressing crack propagation.

As for the relaxation of residual stresses, no significant relaxation was measured when external loads were applied at as much as 80% of the yield strength in the experiments.     

1 025 t/h锅炉再热器超温处理及可行性分析

针对某1 025 t/h锅炉再热器管壁超温、减温水量大的问题,通过现场试验、数值模拟和热力计算等方法,分析管壁超温和减温水量大的原因,提出燃烧调整和受热面改造方案。研究表明：该锅炉末级再热器出口管壁温度存在较大偏差,烟道中间及右侧部分管壁超温,原因在于炉膛出口的烟温偏差;通过将燃尽风由四角均匀配风调整为左侧风门开度50%、右侧风门开度100%,降低了炉膛出口左右两侧的烟温偏差,进而减小了再热器出口的壁温偏差;针对锅炉再热器、过热器减温水量大的问题,进行二次风优化调整,当二次风正塔配风时炉膛出口温度比二次风均等配风和束腰配风时有所降低,有利于降低减温水量;该炉二次风配风优化难以从根本上解决减温水量大的问题,为此提出减少再热器、过热器受热面及增加省煤器受热面的改造方案,使减温水量在不同负荷下均能满足锅炉运行要求。     

Application of a thermal model to a power plant reheater with irregular tube temperatures

A three-dimensional thermal model for the reheater of a utility boiler is applied to a 350 MWe power plant. The model permits the consideration of non-uniform steam flow inside the tubes, which can lead to excessive temperature and hence thermal stress in a part of these. Parametric calculations are performed to examine the influence of various empirical coefficients included in the model. Experimental on-line and off-line data will be obtained and will be introduced as boundary conditions or used to validate the model. The steam flow distribution inside the tubes will be considered uniform or non-uniform depending on the tube serpentine of the reheater. The results predicted by the model of the temperature of the tubes at the reheater outlet and the outlet steam temperature are satisfactorily compared with the experimental measurements. Moreover, the results predicted for the temperature of the gases in an intermediate section of the reheater are analysed and compared with the experimental results from off-line measurements.