Turbine Blade Breakdown Analysis and Prevention

This case study characterizes the degradation mechanism of rotor blade in gas turbine. It includes failure analysis and prevention, metallurgical and mechanical analysis, and numerical approach to finding the root cause. The chemical composition of the blade is discussed, and the importance of niobium is highlighted. The study concludes that the failure of the blade is due to a combined effect of temperature and induced stress.

Turbine blade breakdown analysis and prevention
1 | P a g e
Failure analysis and prevention

Turbine blade breakdown analysis and prevention
Contents
Section 1 Overview of case Study...................................................................................................3
Section 2 Detailed appraisal............................................................................................................5
Section 3 Legislation and regulation...............................................................................................8
2 | P a g e

Turbine blade breakdown analysis and prevention
Section 1 Overview of case Study
The given case study deals with characterising the degradation mechanism of rotor blade in gas
turbine. The given analysis describes the failure analysis of gas turbine, the capacity of this gas
turbine is 6.5 MW, which in operation around 6500 hours and failed occurred in air foils. The
examination carries out was fractography, microstructural characterisation, the equipment’s used
in this analysis is Scanning electron microscope, and energy dispersive X-ray (EDX)
As we know that blades of the rotors are one of the important components in gas turbine. The
degradation is due to the reason that, gas stream which is of high temperature passes through the
blades and continuously distortion is being occurred in root of blade as well as other part like
main bearing, rotor, stator etc. After degradation mechanism starts in any kind of gas turbine, the
countdown of service life. The studies about failure of turbines shows that, the most common
failure in gas turbine is due to creep, creep, damage, fatigue, corrosion and erosion attack.
Especially hot cracking is due to creep and fatigue mechanism. Most common failure of
component is due to reduced fatigue strength which caused due to creep damage. The failure of
gas turbine resulted in shutdown of power plant. In last few decades, the material used in any
industries has been improved significantly, the material used in rotor blade also considered for
improvement, The currently used material is nickel and cobalt based superalloy, which can be
able to withstand high stress and temperature (650 – 1100 o C), with paint and coating on it, it can
withstand even more temperature and strength. At the same time, it has high resistance to
corrosion and oxidising environment. This material is also known as supper alloy IN738LC.
In general, the chemical composition found in Nickel based supper alloy IN738LC is tabulated
below.
Table 1- Chemical composition of rotor blade material, Source - (Jiri Zyka, 2014)
Element Cr Co Ti. Al W Mo Ta Nb
.
Fe Si Mn C Cu Zr B Ni
Min 15.7 8.0 3.2 3.2 2.4 1.5 1.5 0.6 0.0 0 0 .09 0 .03 0.007 Bal
Max 16.3 9.0 3.7 3.7 2.8 2.0 2.0 1.1 0.35 0.3 0.2 0.13 0.1 0.08 0.012 Bal
The composition shown in table above is a standard composition analysis in various journals and
specially by (Jiri Zyka, 2014). Now we will look into the microstructure study given in failure
blade analysis, to analyse the chemical components in the structure, the test pieces were prepared
from aerofoil and root of the blade, first it was ground on different grit paper, polished with
diamond paste, followed by etching and studies under the optical microscope and scan electron
microscope, at the end EDX probe were used to analyse the local chemistry of the carbides
present in test samples, The distribution of carbides and their microstructure is presented below.
3 | P a g e

Turbine blade breakdown analysis and prevention
Element Cr Co Ti. Al W Mo Ta Nb. Fe Si Mn C Cu Zr B Ni
Wt.% 15.5 8.5 3.5 3.5 2.5 1.7 1.7 0 0.3 0 0 .09 0 .05 0.01 Bal
The further analysis about micro structure will be discussed in the section-2.
The structural analysis of the super alloy indicates that, in general IN738LC has multiphase
microstructure, the strength to overcome the temperature is gaining through γ’ intermetallic
compound phase (Ni3Al), which is nothing, but FCC solid solution based on nickel. The
formation of multiphase carbide takes place inside the grain, which is surrounded by M23C6 grain
boundaries. There is possibility of some element present in metallic carbide such as W, Ta, and
small amount of Cr and Ni. It all precipitates during cooling of alloys. The role played by M23C6
on grain boundary performs an important role in withstanding the temperature of about (760-980
o C). This happen due to highly saturated carbon present in the matrix of MC carbide. The
equation suggests that, in M23C6, the M can be Cr, W and Mo. The structure shown in the film
signifies that, there is discontinuity in the film of grain boundaries. The interior side of metallic
carbide grain is pinned by M23C6 along the boundaries, which try to stop the sliding of
boundaries, this helps to improve the creep resistance. The rate of propagation for crack is also
delayed by presence of M23C6. But due to operation performed in high temperature can cause to
change in distribution system of Metallic carbide and M23C6.
The figure above clearly shows that the effect on distribution system before and after operation.
The similar affect can also be seen in pinning of the grain boundaries, which are interlinked to
each other. From structural point of view, the change in microstructure affects the tensile and
creep properties of the material. The structure distribution abnormality is due to high
temperature, which shows precipitated phase of γ’ in irregular structure weak the material as
compared to new blade. The figure given below is comparison of pinning affect shown in blade
microstructure which is before and after.
4 | P a g e
Figure 1- Comparison of distribution, before operation and after. Source - (AM et al., 2017)

Turbine blade breakdown analysis and prevention
The
microstructural study taken in from samples of aerofoil also dictates the change in distribution of
microstructural phase. There is one significant observation in aerofoil is that, there is change in
size of γ’ phases in sample. This was observed with the help of scan electron microscope. The
size of γ’ present in aerofoil is much smaller than γ’ present in root. The gradual decomposition
of metallic carbide is also seen in samples. The chemical composition present in γ’ of aerofoil
consists of Ti, Ta, and Nb carbide, which is determined as metallic carbide.
The fractography analysis reveals that there are two zones in fracture surface, one of these zones
show dendrites which grown from edge to centre and another one clearly shows that, it is locally
melted and solidified after temperature getting down. Near the failure region, there are many
cracks generated and propagated through grain boundaries. The optical analysis of aerofoil
shows that, there is occurrence of dissolving the γ’ in the matrix during high temperature and
again redeposited during shutdown of turbine. The dissolving activity of γ’ occurs above 1160 o
C. The local melting also indicates that, the temperature should be more than 1000 o C for
several times. The conclusion also depicts the same thing as above discussed.
Section 2 Detailed appraisal
As the case study reviewed above, initially it was declared that, this case study is about
characterising the degradation mechanism of rotor blade in gas turbine. With the help of
fractography, microstructural characterisation using optical microscope, scan electron
microscope and X-ray diffraction techniques. The most important point is that writer is stick to
their guideline declared initially, and provided the very specific result, which is related to
metallurgical point of view. The study of micrograph shows that, the reason given for failure of
gas turbine with high accuracy of visual analysis of the microstructure of nickel based super
alloy. There is little more interest they have shown on chemical composition of the blade what
they found in fractography and microstructure study.
My suggestion in this regard is that, this chemical composition should align with standard
chemical composition generally found in material of rotor blade. The standard chemical
composition given by (Jiri Zyka, 2014), (Lakshay, Vineet and Krunal, 2018), (Ali, Seyed and
5 | P a g e
Figure 2-The interlinking of pinning after operation Source - (AM et al., 2017)

Turbine blade breakdown analysis and prevention
Seyed, 2013), clearly dictates the standard chemical composition found in rotor of the blades. A
comparative study is necessary for chemical composition found in failure blades. If we compare
the chemical composition from literature given above stated journal, it can be summarised that,
there is lack of at least three elements, and these elements are Cr, Nb, and nickel it. In all three
elements, there is slight deviation in presence of Chromium (Cr), and Nickel (Ni), but the
presence of Niobium is nil. The presence of niobium plays a very important role in super alloy
material, due to its high melting point (2468 o C) and light weight as compared to titanium and
nickel, provide great property of withstanding high temperature and lower the overall weight of
material, which further support in minimising centrifugal force acting upon the rotor blade. The
absence of this element may be one of the causes of getting high temperature by the blade (MC,
M and G, 2016).
From the review of the journal, there is significant cause of failure is high temperature absorbed
by the rotor blade and its component, in other word we can say that heat generation in rotor blade
is the main culprit behind the failure of Gas turbine. The further investigation should be done
related with gas turbine auxiliary system, the bleed system is primarily used for cooling the
internal part like, rotor blade in all stages, the good function of bleed system (cooling), always
reduces the risk of temperature getting high in critical components of gas turbine. Theses cooling
system equipped with temperature sensors, which records temperature throughout lifetime of gas
turbine. In a Gas turbine like 9HA.01/.02, which is quite heavy, has at least, twelve different
stages of cooling and bleed system, each of them equipped with temperature sensors, records the
temperature with very high automation system. The further analysis of these records answers
some question of high rise in temperature. The quality of air supply in bleed system, auxiliary
cooling system, can be checked from logged data during operation. The inadequate air supply,
malfunctioning of cooling system, and improper exhaust can lead to rise in temperature
(Kazempour, S and Akbari, 2011).
There is various scope of analysis can be done for finding the root cause analysis of failure of
turbine blade. It may be metallurgical analysis, which is described above. The other scope is
mechanical analysis, in this approach, focuses mainly on structural and thermal analysis of
turbine blade using finite element analysis method. The software can be used for finite element
analysis is ANSYS with the aid of Catia or Solid works. One of the analyses described here
which is adopted by Kumar and Rao, ( (V, IN and N, 2014). It describes that 3D modelling of
rotor blade and simulating the operation as the original one, will provide the data in two stages.
The results of this two-stage analysis are combined with the help of union Boolean operation.
The results obtained from Boolean operation simulation dictates that, there are mechanical
stresses, with elongation experienced by Gas turbine rotor blades. The stress generated on blades
not only due to centrifugal forces, on blades, but also stress due to gas forces applicable on it (S
et al., 2013).
6 | P a g e

Turbine blade breakdown analysis and prevention
The results obtained from finite element analysis show that, the deformation produce in the blade
is due to the forces acting on it. The stress due to gas and centrifugal forces, and temperature is
also taken into consideration in simulation.
The results of the FEA analysis also indicates that, there is deformation in length of the blade
which is maximum the tip of the blade (0.01237 m) and minimum at the root of the blade which
is. From both review, one thing is clear that that, there is not rubbing action taken place at the tip
of the blade with casing of the gas turbine. From the manual available on GE power, the
deformation due to forces is under acceptable limit. The maximum stress generated during
simulation is about 1.958 G Pa, and this occurs at the root section also. From the above figure,
we can see the temperature distribution at the tip and root of the blade. The maximum
temperature observed during simulation is 1246.8 o C. The temperature observed in the
simulation is par above the specified temperature range of acceptable limit, which is (650 – 1100
o C), but not outside the melting temperature of the blade. This suggests that there should be
combined effect of temperature as well as induced stress, results in failure of the blade (V, IN
and N, 2014).
The numerical approach to finding the root cause also one the important approach. There are
various literatures available which describes the numerical approach for rotor blade failure, one
them is given by (Ali, Seyed and Seyed, 2013). This mainly deals about numerical approach
related with angle of blade mounted on root. The performance of nay gas turbines is directly
proportional with angle given to blade with base. Generally, the acceptable limit of angle for gas
turbines varies between 14o to 19 o; the angle given in GE power gas turbine is about 15.5o. The
7 | P a g e
Figure 3-Metallurgical and mechanical (FEA) analysis of failure

Turbine blade breakdown analysis and prevention
numerical approach for 14o angle was simulated at 3000 rpm speed. The stress generated due to
rotation on blades area found within acceptable limit, and yet temperature is getting higher. But
when the angle of blade is changed, the and again simulated for same rpm, it was found that
temperature is rising. But in our case GE power gas turbine angle is not a problem, because it is
less than 19o. In both cases, the vibration making and important cause to giving stress on blade,
the modelling and harmonic analysis indicates that the natural frequency is too close to the
operation frequency, which is 50 Hz. It clearly means that any change in blade installation cause
the natural frequency to be like the operational frequency and consequently causes resonance
phenomena. The periodic force applied on blades that, sometime exceeds the endurance limit of
material, will reduce the life of the blade and lead to failure after sometimes (bishoy, 2018).
Section 3 Legislation and regulation
The guideline provided by Department of environment, food and Rural affairs (DEFRA), suggest
that, Emissions from gas turbines and combustion should in normal operation be free from
visible smoke. The smoke generation during start up and shutdown should be equivalent to Ring
Lemann Shade 1 as described in British standard BS 2742: 2009.In case of odour, it is suggested
that, the emission is free from offensive odour from outside the site boundaries.
As discussed in reviews about recording the data, the legislative requirement suggests that,
continuous monitoring should be done. Either it is quantitative or qualitative. The discharge of
emission should be measure in quantitative measure and it should in milligrams per cubic meter.
The acceptable limit of emission is 600 mg/m3 liquid fuels gas turbine. The variation or
reduction in monitoring frequency should not be permitted, where continuous quantitative or
indicative minoring is necessary. All operative time data should be kept as an evidence for
further analysing the problem. The place where non-continuous monitoring is required, the
monitoring variation can be done to some extent. The results which are ranges from 15 -45
mg/m3 might not qualify for reduction in monitoring.
The calibration of gas turbine is necessary using continuous monitor, or specific extractive test
carried-out at definite frequency agreed with the regulator. The extractive test should be carried
out at least 70% of operated efficiency of gas turbine.
The health and safety of operator of the process is prime concern for the environmentalist as well
as management. The requirement of authorisation permit should be approved before operation
and maintenance. The permit of authorisation must contain safety of operator as well as people
around that machinery; this is the prime responsibility of health and safety enforcing authority.
The new guiltiness which is going to be enforced, is suggested by gas turbine association
consists of 1200 lbs CO2 / MWh emission standard. From now onward, simple cycle gas turbine
is excluded and sliding capacity scale-based gas turbine efficiency is adopted. The start-up,
shutdown sampling should be done at 50% operating efficiency. The averaging in compliance is
excluded and new peak and low value data is adopted for sampling. The cut-off pint for capacity
8 | P a g e

Turbine blade breakdown analysis and prevention
for gas turbine will be 150MW, the lower that this capacity emits more smoke and damage
environment. The rules and regulation should be aligning to encourage the adaptation of
combined cycle gas operation. The method of computation of average should be simplified to 12
month rolling average. Prohibition of NSPS CO2 limit for simple cycle turbine and Co2 BACT
level should be adopted. There should be option for utilising new NSPS subpart TTTT versus
including language subparts Da or KKKK. In order to adjust within PM2.5 challenge the law is
being modified to accept the emission limit as low as 10-ton per year for PM2.5 and 15-ton per
year for PM10.
Based on the literature suggested, the multidimensional approach for finding root cause is
best approach suitable for Gas turbine. Because doing multidimensional analysis we found the
results in different perspective.
9 | P a g e

Turbine blade breakdown analysis and prevention
References
Ali, J., Seyed, E.M. and Seyed, M.Y. (2013) 'Failure Analysis (Experimental and Numerical
Approach) of gas turbine', National Engineering School of Metallurgy, vol. 1, no. 1, pp. 99-117.
AM, K., N, T., M, C. and MS, S. (2017) 'Failure analysis of gas turbine first stage blade made of
nickel based superalloy', Case Studies in Engineering Failure Analysis, vol. 1, no. 1, pp. 1-8.
bishoy, M. (2018) '9HA.01/.02 Gas Turbine', GE Power & Water, vol. 1, no. 1, pp. 1-2.
EZ, p. (2017) Fundamentals of Gas Turbine Engine, 1st edition, New Smyrna Beach, FL: Ezekiel
Enterprises.
G H, F., M, T., Masoumi, K.A., S, P. and M, M. (2011) Failure analysis of a gas turbine
compressor', Engineering Failure Analysis, vol. 1, no. 1, pp. 474-484.
Jiri Zyka, I.A. (2014) 'Mechanical properties and microstructure of IN738LC Nickel Super alloy
casting', Materials Science Forum, vol. 782, no. 1, pp. 437-440.
Kazempour, L., S, A. and Akbari, G. (2011) 'Failure analysis of a first stage gas turbine blade',
Engineering Failure Analysis, vol. 1, no. 1, pp. 517-522.
Lakshay, B., Vineet, k.R. and Krunal, M. (2018) 'A Review on Gas Turbine Blade Failure and
Preventive Techniques', International Journal of Engineering Research and General Science,
vol. 6, no. 3, pp. 54-62.
Managers, G. (2015) 'GE’s 7HA and 9HA plants rated at more than 61% CC efficiency', Gas
Turbine World, vol. 1, no. 1, pp. 1-5.
managers, G.E. (2018) HA Plant Solutions AdvantEDGE* Modular Power Island, New York:
Gas Power Systems.
MC, A.H., M, S. and G, J. (2016) 'Journal Indian Institute of metaullurgy', Root Cause Analysis
of Steam Turbine Blade Failure, vol. 69, no. 1, pp. 659-663.
Moskvitch, K. (2018) 'In numbers Gas turbine', Jounral of news article, vol. 1, no. 1, pp. 1-2.
P, B.S., R, K.M. and R, L. (2018) 'Finite Element Approach for Failure Analysis of a Gas
Turbine Blade', Journal of failure analysis and prevention, vol. 1, no. 1, pp. 1210-1215.
10 | P a g e

Turbine blade breakdown analysis and prevention
R K, M., Johney, T. and Syed, I.A. (2014) 'Fatigue Failure of LP Compressor Blade in an Aero
Gas Turbine Engine', Journal of Failure Analalysis and Prevention, vol. 1, no. 1, pp. 296-302.
R, B., M, R. and M, A. (2018) 'Failure Analysis of a Gas Turbine Blade Made of Inconel 738LC
Super Alloy', Amirkabir Journal of Mechanical Engineering, vol. 1, no. 1, pp. 1-4.
Rybnikov, G. and Leontiev, (2005) 'Failure Analysis of Gas Turbine Blades', Microscopy
Society of America, vol. 1, no. 1, pp. 1-2.
S, Q., C M, F., C, D., J F, T. and Z F, Z. (2013) 'Failure analysis of the 1st stage blades in gas
turbine engine', Engineering Failure Analysis, vol. 1, no. 1, pp. 292-303.
S, B., M, B., S, C. and P, P. (2011) 'Failure analysis of a third stage gas turbine blade',
Engineering Failure Analysis, vol. 1, no. 1, pp. 386-393.
Sweety, K., DVV, S. and M, S. (2014) 'Failure analysis of gas turbine rotor blades', Engineering
Failure Analysis, vol. 1, no. 1, pp. 1-11.
V, N.R., IN, N.K. and N, M. (2014) 'Mechanical Analysis of 1st Stage Marine Gas Turbine
Blade', International Journal of Advanced Science and Technology, vol. 68, no. 1, pp. 57-64.
11 | P a g e