9FA燃气轮机压气机叶片断裂典型案例.doc

Failure of 9FA Gas Turbine Compressor A Unique Experience.9FA燃气轮机压气机叶片断裂-一个典型案例Dhabol power project of RGPPL, a Joint Venture of NTPC,GAIL & MSEB, consist of 6 numbers of GE make gas turbines and 3 number of GE make steam turbines with module configuration of 2 GT + 1 ST. Hence, there are 3 module and known as block -I, block -II and block -III. RGPPL电厂,印度国家电力集团的合资企业,有GE制造的6台燃机和3台汽机,采用2拖1的模式,三台机组分别称为I、II、III机组。Though there are 6 numbers of GE make gas turbines but all 6 gas turbines are not identical so far the capacity, TIT and heat rate are concerned. As per the data available at site and Tractable (Consultant to Indian lenders) report, the gas turbine of block -I is suppose to be PG 9331 and gas turbine of block -II and block-III are PG 9351 version. As per GE technical literature PG 9331 is known as 9FA+ and PG 9351 is known as 9FA+e model. From the technical literature available in internet, the technical specifications of 9FA+ & 9FA+e are as follows: 尽管有6台GE公司的燃机，但是到目前为止6台燃机的容量、透平入口温度、机组效率等不一致，根据机组收集的有用数据和印度的相关报告，I机组的燃机型号为PG9331，II、III机组的燃机型号为PG 9351。按照GE的技术通报文件PG9331称为9FA+，PG 9351称为9FA+e，从GE官方网站获取的9FA+和9FA+e参数如下：It can be seen from the technical specifications mentioned above in the table that technically there is substantial difference between PG 9351 and PG 9331. Though Block-II and Block-III gas turbines of Dabhol Power Project are suppose to be PG 9351 but due to failure of compressor of GT 2B and failure of tie rod of GT#3A, gas turbine rotor of GT#2B has been replaced with spare refurbished rotor of block -I and GT#3A rotor has been replaced with GT-1B/1A used rotor. Therefore, with the present configuration, block -II and block-III consists of one GT of PG 9351 and one GT of PG 9331 version. 从上表所述的关于PG 9351 和PG 9331的不同点已很详细。尽管II、III机组为PG9351燃机，但由于发生了压气机事故的为GT#2B和GT#3A的拉杆，燃机GT#2B转子更换为I机组的备用转子，GT#3A转子更换为GT-1B/1A使用过的转子。因此，目前的配置情况是，II和III燃机由PG 9351和PG 9331混合组成。The entire plant has been revived by GE experts and under their supervision. Not only this, before starting revival activities, GE carried out condition assessment of all 6 Gas Turbines and based on assessment result GE recommended spares to be replaced for healthy running of the plant and all the spares recommended by GE have been replaced during the restoration of respective Gas Turbine. 整个计划在GE专家的领导和监督之下完成。除了这些，在检修完成之后再次启动前，GE对6台燃机进行了状态评估，根据评估结果，GE建议为了设备的健康运行对备品按计划进行更换，因此，机组再次启动前对所有GE建议的备件进行了更换。But in-spite of this, RGPPL Dabhol has faced three catastrophic failure of 9 FA Gas Turbine Compressor with in a span of two years. And all three failures are of same nature that is High Cycle Fatigue. 但是让RGPPL电厂恼怒的是在两年之内发生了三起9FA压气机事故，三起压气机事故均是由于高周疲劳引起。It started with the failure of GT#2B on 05th Jan-2007, GT#2A on 19th Jan-2008 and GT#3A on 8th Nov-2008. And failure of GT#3B avoided due to premature unscheduled inspection. GT#2B发生压气机事故的时间是2007年1月5日，GT#2A是2008年1月19日，GT#3A是2008年11月8日，GT#3B避免发生类似的事故是因为进行了之前未计划的检查。In all three happenings, machines were running absolutely normal. In-spite of all normal running parameters, stable grid frequency and at steady load, all on a sudden , Gas Turbines have tripped on Hi-Vibration Protection on auto with very high sound, Abnormal sound was coming from the compressor side and rotor stopped rotating did not come on turning gear. On cooling, Compressor rotor inspected from compressor IGV end and damage of compressor moving blades & vanes observed. 在发生的三起事故前机组运行完全正常，运行时无任何异常参数的变化、电网频率稳定、机组负荷稳定，然而出乎意料的是，机组轴振高保护跳闸，现场明显听见高分贝的声音，异音从压气机侧开始直至转子转速到零盘车投入。在盘车期间，压气机转子检查从IGV末端、损坏的压气机动叶和静叶进行观察。Compressor SectionOn opening the compressor mid casing (Stage 2 to 12) upper half, catastrophic failure of Compressor Moving & Stationary blades from Row #2 to Last Stage in case of GT#2A& 3A and from R3 to Last Stage in case of GT#2B observed. The failure is so massive that failed moving & stationary blades have got melted and molten metallic debris(slag) deposited on compressor outlet area, air extraction lines and in blades/vanes cooling air duct as well as on entire the casing inner surface in case of GT#2A& 3A.压气机部分当打开压气机中缸上半部分时（第2至12级），GT#2A& 3A压气机动叶和静叶的灾难性事故从动叶和静叶第2列（R1、S1）到末级，GT#2B从R3到末级叶片。压气机动叶和静叶的损坏是巨大的，压气机出口区域聚集了大量熔化的金属碎屑，GT#2A& 3A事故中压气机抽气管道和动/静叶片的冷却空气通道同样堆积了大量熔化的金属碎屑。损坏的叶片附在压气机上大量熔化的金属碎屑On close observation, it is found that the failures are due to impact and on further examining it has been found that all moving Blades and stationary vanes failed from root and all failed surface are so badly deformed that it is very difficult to identify the primary failed blade. In case of GT#2A, on further observation, it was noticed that 2 nos. of moving blade of Row#2 failed from the platform but the failure pattern are different from the rest. Out of this two moving blades of row#2, one has failed from just above the platform and one piece has failed 5-8 mm below the platform and failed surfaces were found to be less deformed. Similarly in case of GT#3A, 8 nos. of moving blades of row#2, have failed 5-8 mm below the platform and failed surfaces were found to be less deformed. But in case of GT#2B, one no. of moving blades of row#3, one has failed from just above the platform. 继续观察发现，损坏的叶片受严重的冲击影响，进一步的检查发现所有的动叶和静叶从根部断裂，所有损坏的叶片表面已经严重变形以至于难以辨认叶片断裂的根源。在GT#2A事故中，进一步的检查发现动叶第二列（R1）的2号叶片从叶台断裂，这种断裂形式跟剩余的叶片完全不同。从R1的两片动叶发现,一片刚好在叶台上部断裂，令一片在叶台往下5-8mm断裂，同时在这些断裂的叶片表面发现少许的变形。类似的出现于GT#3A 的动叶第二列（R1）的8号叶片，在叶台往下5-8mm处断裂，同时在这些断裂的叶片表面发现少许的变形。但是GT#2B事故中的动叶第三列（R2），一片叶片刚好在叶台上部断裂。Gas Turbine冷却通道堵塞On opening the Turbine casing no major physical damage was found in the moving blade/ Vanes. But very huge metallic molten debris found in the cooling passage of vanes & blades of row#1 & Row#2. This is due the fact that the cooling air is extracted from the discharge of compressor and with the damage of compressor blades & vanes, very fine debris, have been carried by the cooling air, have entered in to cooling passages of blades and vanes and got deposited. 燃机透平打开燃机透平外壳后透平动叶/静叶未发现有明显的机械损伤，但是在第一级静叶、第一级动叶和第二级静叶、第二级动叶的冷却通道发现了非常多的金属碎屑。这些碎屑来源于压气机排气的冷却空气，当压气机叶片断裂发生后，很多极细的碎屑随着冷却空气被带入透平动叶和静叶的冷却空气通道堆积堵塞。Root Cause Analysis of FailuresOn visual inspection of failed surface and material flow on the damage surface of the moving blades & vanes, it appeared that the blades and vanes of the compressor have failed due to impact. For impact failure, the components have to be hit with an object. The object may come from out side and hit the component causing damage to the components and this type of damage is popularly known as Foreign Object damage (FOD). Or the object may be generated within the turbine and may hit the component causing damage to the components and this type of damage is known as Domestic Object damage (DOD). This is most common type of failure in gas turbine and takes place due to premature failure of gas turbine components. As mentioned above that the failure is due to impact and for impact failure, the material is to be hit by an object and this object may be external or internal, hence further investigation done on each and every stages of moving and stationary blades of compressor to identify the source of object. 叶片断裂根本原因分析基于叶片断裂表面的目视检查和出现在断裂叶片表面的物料，表明压气机叶片的断裂是受到了严重冲击。对于叶片断裂的冲击，部件必须受到目标的击打。击打目标可能来自压气机外部，外物击打部件造成的损伤通常被称为外物损伤。也可能来源于压气机内部，内部击打部件造成的损伤通常被称为内部损伤。这两个是造成压气机损坏的常见原因，通常会造成压气机部件过早失效。综上所述，叶片断裂常常是由于发生冲击和受到击打，叶片受到击打的源头可能是外部或内部目标，因此下一步的调查主要是针对压气机动叶和静叶的每一级、每一片叶片寻找断裂的源头。Damage due to Foreign Object If the damage was due to foreign object, then the material has to travel from out side the Gas Turbine, and it has to be entered in to the Gas turbine Compressor through Compressor inlet air plenum air flow path only. 外物击打损伤假设压气机损坏是由于外物的击打，那么，击打物肯定是从外部跟随气流进入压气机，当然，击打物要想进入压气机只有从压气机入口这一条路径进入。If the material entered through this path, then the object should have hit the IGV and 1st row i.e. R0 of compressor moving & stationary blades and those components would have damaged. But in all cases the IGV, Compressor moving blades of row#0 and stationary vanes of row#0 have been found to be OK(minute dent mark at trailing edge). FOD damage can not start from intermediate stage, hence the damage of compressor moving blades and vanes can not be due to the FOD. 如果外物沿着压气机入口进入，那么，击打应该从IGV和第一列开始，也就是压气机动叶和静叶第一列（R0、S0）这些部件也应损坏。但是在三起事故中，IGV、R0、S0均检查正常。外物击打不可能从中间级开始，因此，排除了压气机动叶和静叶损坏的外物击打可能性。Damage due to Domestic Object As the probability of damage due to FOD has already been ruled out therefore, the damage has to be due to DOD, in order to find the source of Domestic Object, when the compressor mid casing was opened, it was found that all most all moving & stationary blades have failed from the root just above platform with massive deformations and failed surface are totally distorted (clockwise). Therefore, though a nos. of moving & stationary blades have failed still question arises which has/have failed first and whether they have failed of their own (due to any reason) or they have also been hit by an object and this object has be generated with in compressor. Now Domestic Object will generate only because of any one or combination of the following:内部击打损坏在排除了外物击打损坏的可能性后，压气机损坏事故只有内部击打导致了，为了寻找击打的源头，当压气机中压缸打开时发现大部分的动叶和静叶由于巨大的变形从叶台根部断裂，断裂的叶片表面已经完全变形（顺时针方向）。因此，尽管一系列动叶和静叶已损坏，问题的关键是哪一片是第一片断裂的叶片，不论是这些断裂叶片中的一片还是被击打导致叶片断裂，但这些击打物都是来自压气机。因此，击打物通常是已断裂叶片中的任何一片或者以下的一些组合：1. Something left during last inspection 2. Failure of fixing material and hitting the other components 3. Dislodging of metallic piece from stationary blade and hitting the other components. 4. Dislodging of metallic piece from moving blades and hitting the other components. 5. Dislodging of metallic piece from moving and stationary blades and hitting the other components. In order to find the root cause, the factors mentioned above, theory of elimination have been applied to come to the final cause of failure. 1、上一次检查时遗留在压气机内部的物品。2、压气机的固定部件脱落击中了其他部件。3、压气机静叶中含金属物质的部件掉块击打了其他部件。4、压气机动叶中含金属物质的部件掉块击打了其他部件。5、压气机动叶和静叶中含金属物质的部件掉块击打了其他部件。为了寻找断裂的根源，综合如上所述的各项因素，采用排除法推测最终的叶片断裂源头。Failure due Something left during last inspection:-:-Inspection was carried out under the supervision of GE & BHEL hence chances of leaving some object inside the compressor is very remote, besides if some thing was left then the damages would have occurred during re commissioning itself when the machine was started & stopped for a number of times. Therefore the probability of damage of compressor blades due to left over material is very remote and can be ruled out. 若上一次检查时有物品遗留在压气机内，检查是在GE专家和印度巴拉特重型电气有限公司联合指导之下完成的，因此检查时有物品遗留在压气机内部基本是不可能的，假设确实有物品遗留，那么，压气机在试车时就会发生损坏事故，何况机组已经启停了许多次。因此，有物品遗留在压气机内部基本确定是不可能的，而且完全可以将其排除。Failure of fixing material: -If the source of DOD is due to the failure or dislodging of fixing material, then missing of fixing material would have observed but on physical inspection of compressor no fixing material was found to be missing. Hence the failure of compressor blades due to Failure of fixing material is ruled out. 若叶片断裂的源头是压气机的固定部件脱落击中了其他部件，那么，在压气机开缸进行检查时肯定会有固定部件脱落的痕迹，但是，实际上刚好相反。因此，压气机的固定部件脱落击中了其他部件也完全可以排除了。Failure due to dislodging of metallic piece from moving/ stationary blade: A number of moving as well as Stationary blades have been found to be uprooted from the platform. And this failure is sufficient to cause extensive damage. Now the question is why this component has failed. The component will fail due to the following reason :若压气机动叶或静叶中含金属物质的部件掉块击打了其他部件：动叶和静叶从叶台根部连根拔起的数量一样多。因此，这些大量的断裂叶片足够产生巨大的力量将压气机损坏。现在问题的关键是为什么这些叶片会断裂，叶片断裂无外乎如下原因：a) Fatigue A、疲劳. HCF 1、高周疲劳i. Resonance during critical Speed, 过临界转速时产生的共振。ii. Flow induced vibration-Flutter. 流量变化引起的振动-颤振iii. Rotating Stall. .旋转失速 LCF not applicable for compressor 2、低周疲劳不适用于压气机 Thermo mechanical Fatigue crack (TMF) is very rare for initial 5 stages of compressor blades. 3、热机械疲劳裂纹基本不会发生在压气机叶片的前5级b) Metallurgical Non Conformity. B、冶金工艺不合格c) Bending over load (Impact). C、叶片的挠曲故障d) Machining Defect (Notch, Tool mark) D、制造因素（刻痕、刀痕）e) Forging Defect E、锻造工艺的影响f) Over Load F、负荷过载g) Corrosion/Erosion. G、叶片腐蚀By doing the fractographic analysis of the failure surface of the failed component it is possible to know the exact cause of failure. But the fracture surface of the damaged uprooted stationary as well as moving blades are so badly deformed that fractographic analysis will not give any useful information. 通过断裂叶片部件表面的断口分析是可能发现导致断裂原因的。但是动叶和静叶叶片根部连根拔起产生的断裂面已经严重的变形，因此，断口分析很难得到有用的信息。In all cases the failed surface, the failed surface is having different colour (dark as well as bright) 这三起叶片断裂事故的叶片表面有不同的颜色（黑色和白色）相似的叶片断裂表面From the preliminary study and the failure pattern, cause of failure ofGT#2B,2A & 3A appears to be same.经过初步研究故障形式表明，导致GT#2B,2A & 3A叶片断裂的原因相同。压气机叶片颤振导致高周疲劳断裂Gas turbine hot path components are very prone to high temperature Creep, Thermo mechanical fatigue and Low Cycle fatigue failure. Designers, depending upon duty condition (Cyclic Load), design hot path components, considering Creep life/ fatigue life of almost 90% of the life of material after which development of these type of defect i.e. Creep Crack / fatigue crack is expected. 燃机透平的热通道部件非常容易遭受高温蠕变，热机械疲劳以及低周疲劳。从设计者角度说，这些取决于负载的条件（启停的负荷），设计热通道部件，必须考虑蠕变寿命、在材料寿命范围内承受90%的疲劳寿命，因此，在日后机组的运行中这些设计缺陷也即蠕变裂纹、疲劳裂纹在可预见期是会产生的。Depending upon the amplitude and frequency of cyclic load, cyclic fatigue is again classified in to Low cycle fatigue failure (LCF) where the amplitude of cyclic load is such that it reaches up to yield stress but the frequency of cyclic load is less. Where as in case of High cycle fatigue failure (HCF), the amplitude of cyclic load is much below the yield stress but the frequency of cyclic load is more. 机组日常启停中由于振动的幅度和频率，循环疲劳不停的重复出现各级的低周疲劳，当机组负荷变动时产生的振幅会达到屈服应力，但是负荷变动时的产生的频率较少发生。如果发生高周疲劳，那么，负荷变动产生的振幅低于屈服应力，但是负荷变动时的产生的频率较多发生。In any fatigue failure, the failed surface will have the following indications:. Beach mark in some cases Beach Marks is visible even with naked eye. . Thump Nail Shape, this is also visible with naked eye. . Striations this requires high resolution Microscope. When the cleaned failed surface is seen with high resolution microscope e.g. with Scanning Electron Microscope (SEM), then the presence of those indications are evidenced as shown below. 任何疲劳故障导致断裂的表面有如下特征：1、海滩状特征甚至在很多类似案例中用肉眼即可看见。2、重击形成的钉子形状，同样可以用肉眼看见。3、条纹状特征需要高分辨率的显微镜。当叶片断裂表面清理干净后，使用高分辨率的显微镜（例如电子显微镜），那么，就可看见如下图所示的特征：Presence of Thump Nail Shape, Beach mark with naked eye indicates that the failure mode is due to fatigue, obviously this is to be confirmed with Fractographic analysis and the cause of fatigue most likely will be due to flow induced vibrations coupled with rotating stall /resonance/ Flutter because of modulation of IGV with frequency. As a result of IGV modulation, change in GT load with change in frequency is more compare to change in GT load without IGV modulation. 肉眼可看见重击形成的钉子形状特征、海滩状特征表明叶片断裂的形式为疲劳断裂，断口分析可以确切地证明，叶片疲劳的原因最大可能是由于IGV频繁的调整导致流量变化引起自激振动，再加上旋转失速、共振、颤振。因为IGV的调整，燃机的负荷也跟着频繁的调整，结果燃机负荷超过了IGV的调整范围。This additional fluctuation of load due to modulation of IGV is creating more flow induced vibration which is pulsating in nature due to aerodynamic flow instabilities. This aerodynamic flow instabilities (separation of flow on both leading and trailing edges), tend to formation of vortex. The vortex Shedding frequency is determined by STROUHAL NUMBER(St).The Strouhal number is named after Vincenc Strouhal & is an integral part of fundamentals of fluid mechanics. 因为IGV的调整引起额外的负荷波动导致更多的自激振动，这种有规律的振动从空气动力学本质来看就是流动的不稳定。这些空气流动的不稳定（主导流量和跟随的流量是脱离的），经常容易形成涡流脱落，涡流脱落频率由斯特罗哈数所决定。斯特罗哈数在特劳哈尔数之后，他们都是流体力学不可或缺的组成部分。Vortex Shedding Frequency (Fv) = Strouhal No.(St) X Flow Velocity (Vf) / Vortex Shedder Width(Wv) which is a Hydraulic parameter and depends upon the angle of inlet and exit. Fv =St XVf /Wv =(StX Q)/(AXWv) Where Q is the flow &A is the area of flow 涡流脱落频率（Fv）=斯特罗哈数（St）流速(Vf)/涡流特征的宽度(Wv)，涡流特征的宽度(Wv)取决于涡流进入和离开时的角度Fv =St Vf /Wv =(StQ)/(AWv)，其中Q为涡流流量，A为涡流区域的面积Since for a particular, compressor St , Q, A, Wv are assumed to be constant, but in actual working condition St , Q, A remain constant but Vortex Shedder Width (Wv) varies with IGV position & fouling on compressor blades, as a result, Vortex Shedding Frequency changes . Since maximum fouling takes place in the initial stages of stationary & moving blades of compressor, hence even for a very less change in IGV angle, separation of flow takes place resulting in formation of vortex shedding. For Reynolds number in the range of 800 200,000 there exist two values of Strouhal number. The lower frequency is attributed to the large scale instability of the wake and is independent of Reynolds number. The higher frequency Strouhal number is caused by small scale instabilities from the separation of shear layer. If this Vortex Shedding Frequency coincides with natural frequency of Blade, the Blade will oscillate in harmony with the Vortex Shedding and begin to FLUTTER. FLUTTER imposes significant aerodynamic lateral and torsional forces on the blade, resulting in more than expected stress concentration just above the platform of the blade, at subsynchoronus frequency that can have a detrimental effect on blade life. 具体到本文案例来说，压气机的斯特罗哈数St、涡流流量Q、涡流区域面积A、涡流特征的宽度Wv假设是不变的，但是在真实的工作条件，压气机的斯特罗哈数St、涡流流量Q、涡流区域面积A保持不变，涡流特征的宽度Wv是随着IGV的角度和压气机叶片的结垢程度而变化，因此，涡流脱落频率也跟着改变。因为结垢最大的地方发生在压气机静叶和动叶的前面几级，因此，即使IGV改变一点点，发生空气气流分离就会产生涡流脱落。雷诺数在800-200，000范围之内有两种不同特罗哈数，大规模的不稳定气流会产生低频，而且不受雷诺数的影响。更高频率的斯特罗哈数由小规模的剪切层不稳定气流产生。如果涡流脱落的频率和叶片本身固有的频率一致，那么，叶片就会产生与涡流脱落频率同样的振动，然后开始发生颤振。颤振强加于气流的气动力侧面，同时扭矩力作用于叶片，结果是更多的应力集中在叶台上部就如推测的那样，这种频率影响叶片的寿命。As already mentioned above, fouling is more in the initial stages of compressor, therefore, initial stages are subjected to flutter induced vibration more compare to other stages because of flow separation. This is why the initial stages of compressor blades and