9FA燃气轮机压气机叶片断裂典型案例 - 图文

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 Section

On 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

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.

冷却通道堵塞

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 Failures

On 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, ①过临界转速时产生的共振。 ii. Flow induced vibration-Flutter. ② 流量变化引起的振动---颤振 iii. Rotating Stall. .③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 of

GT#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 =(St×Q)/(A×Wv)，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 vanes fail due to flutter. In case of RGPPL-Dabhol, the failures took place in R3 & R1; therefore, the following can be concluded:

综上所述，压气机前几级叶片很容易遭受污染、结垢，因此，因为气流脱离导致压气机前几级相比其他级要承受自激振动。这就解释了为什么压气机的前几级动叶和静叶因为颤振而发生叶片断裂。在RGPPL-Dabhol的案例中，叶片断裂的地方发生在压气机R3 & R1，因此，可考虑采取如下措施：

1. Presence of primary & secondary failed surfaces indicate that the crack developed much earlier and propagated gradually with loading cycle and finally the component has failed due is Tensile over load. Fractographic Analysis will confirm this observation

1、从目前的第一级和第二级叶片断裂表面表明，裂纹扩展更容易，随着负荷的变化逐步地传播，最终导致力矩过载断裂。断口分析可证实此推测。

2. Presence of Thump nail shape & Beach mark on the failed surface of the failed component, indicate that the failure mode of GT#2B , 2A&3A are due to High Cycle Fatigue.

2、通过分析叶片断裂表面表明重击形成的钉子状特征和条纹状特征是导致GT#2B , 2A&3A叶片断裂的主要原因是高周疲劳。

3. High Cycle fatigue is due to flow induced vibration called “Flutter”. 3、高周疲劳的发生是由流量变化时产生的自激振动也即颤振。

4. Flutter is due to higher frequency Strouhal number which is a design Criteria. 4、颤振是由设计原因造成的高频率斯特罗哈数。

5. Higher frequency Strouhal number is due to small scale instabilities from the separation of shear layer.

5、高频率斯特罗哈数由剪切层气流脱离导致小规模的气流不稳定造成。

6. Small scale instabilities from the separation of shear layer are due to modulation of IGV with frequency coupled with fouling &fluctuation in GT load. This can be confirmed by putting sensitive probe on casing just above the blades and if any side band frequency is observed and if this side band frequency is not a multiplication of Natural frequency then it can be concluded that this side band is not due to Resonance but because of Flutter. 6、剪切层气流脱离导致小规模的气流不稳定归因于IGV的频繁调整以及压气机的结垢和燃机负荷的波动。这可通过安装高敏感的探头于叶片上部进行检测，如果任何一侧探测到了B频段的频率，且此B段频率不会因为固有频率而增加，那么，可以这么认为这一侧B段频率不是因为雷诺数产生，而是因为颤振导致的。

But it is to be kept in mind that fatigue is not the root cause. Root cause is the factor caused the material to go under fatigue. By Fractographic analysis it is also possible to identify which factor/factors caused the material to be fatigue e.g. machining defect (Notch/Tool Mark), Design deficiency, forging defect, Metallurgical defect, Corrosion, Oxidation etc.

但是请记住疲劳不是发生问题的根源。问题的根源在于材质问题导致疲劳。通过断口分析同样能辨别是由那些因素导致金属疲劳，例如制造因素（刻痕、刀痕）、设计因素、锻造因素、冶金因素、腐蚀因素、氧化因素等等。

The study of failure surface with the help of high resolution microscope is known as fractigraphic analysis and this is a pure NDT Test and test specimen is not / should not be disturbed during the study. If the failed surface is even minutely disturbed, then the fractographic analysis will not give fruitful result.

通过高分辨率显微镜研究叶片断裂表面称之为断口分析，这是纯粹的无损检测试验，在研究期间进行试验取样不会也不应该受到干扰。如果叶片断裂表面每分钟都受到干扰，那么，断口分析将不会有任何富有成效的结果。

Corrective Measures in absence of Fractographic Result.

1. Increase in Frequency of Inspection:-On fractographic analysis, if it is found that the primary cause of failure is HCF (most likely, obviously with visual inspection but actual failure can only be confirmed after fractographic analysis) If on analysis, it is established that the failure is due to fatigue, then this is due to design deficiency and can not be rectified in situ until and unless these blades are replaced with modified blades. Under this circumstances, to avoid premature failure of the components, the machines are to be opened frequently for proper inspection so that the premature damage can be detected before reaching critical value/ failure and GE, most likely recommended more inspection compare to inspection interval mentioned in GER 3620K for other utilities.

断口分析结果缺乏矫正措施 1、增加检查的频率

断口分析中如果发现了最初高周疲劳断裂的原因（最大可能、最明显是用目视检查，但是实际应用时只有进行断口分析后才会被证实）。如果据分析，已经确定叶片断裂的原因为

疲劳，那么，这就是设计因素了，而且已安装机组无法在现场进行矫正，除非这些叶片更换为改进型叶片。基于这种情况下，为避免叶片过早地失效，那么，压气机需更频繁地打开进行合适的检查，这样才可避免在到达临界值时或断裂时发生类似的事件，同时GE最好建议其他同类型机组相比GER 3620K中建议的检修间隔进行更多的检查。

2. Vibration Measurement: -It is pertinent to mention here that the vibrations of Gas turbine bearings are monitored judiciously but the existing vibration monitoring system mounted on bearings of turbines can not detect this type of problem, however, if any increasing trend is observed then the vibration spectrum is to be analysed with a potable FFT analyzer. If on FFT analysis, the peak value is found to be corresponding to a blade pass frequency then the machine is to be stopped for inspection. Existing On line vibration monitoring system can not detect this problem. If special vibration pick up is directly mounted on the casing on stage from row#R0 to Row#4 (failure prone zone) and data is collected on continuous at various load and frequency. After carrying out FFT analysis, load/ Grid frequency at which the peak value is appearing, that particular load/ Frequency is to be avoided. The amplitude of peak value is to be monitored strictly. If any increase in amplitude is observed then the machine is to be stopped and after stopping, blade/vanes of stage corresponding to a blade pass frequency is to be thoroughly checked for development of Crack. 2、振动测量

在这提到燃机轴承的振动是因为目前的监控轴承振动监测系统是无法反应此类问题的，因此，发现任何轴承振动光谱增加趋势，必须立即利用便携的频谱分析仪进行分析。若在频谱分析仪中，发现振动峰值与叶片传递的频率一致，那么，机组应停机进行相关检查。目前轴承振动在线监测系统无法反应此类故障。若安装在R0列到第四列（S1）叶片（断裂高发区域）外壳探测器捕捉了特殊的振动，且收集的数据分布于不同负荷和频率。实施频谱分析后，负荷/电网频率波动时峰值均可捕捉到，那么，AGC必须避免投入，峰值的振幅必须严格地监视。观察到任何振幅的增加，机组必须停运，停运期间，各级动叶和静叶的频率与叶片传递的频率一致，必须彻底地检查裂纹的发展。

3. Monitoring of Compressor Efficiency: -Failure of Gas Turbine Compressor takes place mainly because of Rotating Stall / Surging and this takes place due to fouling. With the fouling, compressor efficiency decreases resulting reduction of air flow and the compressor operation regime is shifted towards the Surging. All OEM supplies the Compressor efficiency curve for different ambient temperature. If the measured efficiency value is close to the recommended value mentioned in the curve then compressor should be washed immediately either by On Line, if facility is there, or by OFF Line other wise surging will take place which will cause huge damage to the Compressor, Gas turbine may also damage. 3、监控压气机效率

压气机叶片的断裂主要发生在旋转失速喘振，这主要是因为压气机结垢所造成。压气机结垢后，压气机流量的减少从而导致压气机效率的降低，压气机的运行工况朝喘振边界线靠近。所有的压气机制造商提供了不同环境温度的效率曲线，若压气机效率值下降到建议的效率值，压气机应立即进行水洗，如果有条件那就进行在线水洗，或者离线水洗会发生喘振破坏压气机，燃机透平同样会被损坏。

4. Stopping of IGV Modulating at base load :-Normally GT is started with IGV in minimum position and after synchronizing of GT, as the GT load is increased IGV started opening at 60 to 65% of the base load. On load Control mode, IGV full opens when the load is ~ 80 to 85% of the base load. After this with further increase in load on load control mode, GT exhaust temperature

increases and finally GT control changed over to Temperature control mode from load control mode. And on temperature control mode since IGV remains full open so on temperature control, IGV has no control on quantity of air therefore, it regulates fuel flow to maintain the designed TIT hence IGV normally does not modulate. But in case of Dabhol, it has been noticed that though the GT is running at base load on temperature control mode, still IGV is modulating with frequency and the frequent modulation of IGV is causing flow induced vibration owing to fluctuation in air flow, matter is be taken up with OEM for such behavior of IGV. 4、满负荷时停止IGV的调整

正常启动时IGV在最小的位置直至机组并网，随着燃机负荷的增加，IGV开至满负荷时的60%至65%。在加负荷控制模式，当机组负荷升至满负荷的80-85%时IGV全开，若要在加负荷控制模式下再继续升负荷，燃机排气温度增加，最终控制切换至温度控制模式。在温度控制模式下，IGV依然保持全开状态，IGV无法改变空气流量，因此，为维持设计排气温度必须要有足够的燃料流量，所以，IGV正常情况下是不会调整的。但是在Dabhol电厂，虽然燃机在满负荷的温度控制模式，IGV仍然随着电网频率进行调整，频繁的调整IGV导致空气流量波动引起自激振动，IGV的这种行为对压气机制造商是感兴趣的事件。

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