Failure Analysis of Gas turbine blades

1. Ashutosh Kannawar
SKNCOE (Vadgaon)
TE Mech -2
SEAT NO:T120360925

2.  Propulsion system
 compressor
-Draw air&compress&deliver in combustion
chamber

3.  Aerodynamics
 Mechanical
 Thermal load
 Design ,Manufacturing
 Material selection
 Assembly etc
COMMON MODE OF FAILURE:
-Fatigue failure

4.  After disassembling the engine after a test run
 Take blade &analyse it, using visual&stereo binocular
method
 Stereo zoom microscope is used

5.  Fracture from hub region at leading edge
 Crack extends from fracture to centre of aerofoil
section
 Fatigue failure
 Crack origin near junction of the airofoil &stem region
at leading edge side

6. Blade Failure Pattern

7.  Machining marks
 Creates stress
concentration
 So fatigue crack
occur

8.  Compressor blade found to have failed in progressive
mode i.e.by fatigue
 Crack originate at blade hub-stem junction at the
leading edge side
 Presence of machining cracks is reason for failure

9.  To avoid stress concentration avoid machinig marks
 Avoid abrassive marks

10.  What are the blades:individual component which
makes turbine section of gas turbine & blades extract
energy from gas produced by combuster

 Different materials are used like nickel ,cobalt
 disadvantage of it :more complicated &costly.also
system must be strong to resist high pressure

11.  Desirable properties:corrosive resistant ,strong
 -cobalt (earlier used )
 -nickel (most common)
 Previosly cobalt is used

12.  Life is measured in hours before failure of blade
 Cobalt based blade have 50,000 hrs life
 Nickel based blade have 15,000 hrs life
 Also nickel based blades can work at high
temperature


13.  Failure cause :
 -microstructural changes
 -void formation
 -environmental effect
 Chemical damage

14.  Equipment –optical emission spectrometer
 EDS analyzer
 Three sections method(transverse)
 1)at root
 2)mid point
 3)top of airofoil


15. PROCEDURE:
 1)Take a blade which is failed
 2)Apply three sections method
 3)Put the blade below optical emission spectrometer
 4)Observe microstructure

16.  Hardness increases as we move towards fracture
 Ductility of the blade decreases due to high
temperature
 Chemical compossition of blade is same as IN-738LC
super alloy

17.  Gamma phase dissolve & disapper with increasing
distance from root
 Crack growth is interdendritic
 Hardness increases in fracture zone