fracture mechanics case study. reference Fracture mechanics by Anderson

1. SUBMITTED
BY
BAGGIOJOSE
13MD01
AN INVESTIGATION OF THE
FAILURE OF LOW PRESSURE
STEAM TURBINE BLADES

2. CONTENTS
1. INTRODUCTION
2. DESCRIPTION
3. TESTS & RESULTS
4. CONCLUSION
5. REFERANCE

3. INTRODUCTION
Steam turbine extracts energy from steam
3 types HP,IP & LP
Blades convert linear to rotary motion
Designed life 30 years
LP blades are prone to failure

4. DESCRIPTION
210 MW thermal power plant
Overhauled after 5 years shut down after 2 years
12% Cr steel with tempered martensite
Brazed joint b/w blade and steel rode
Striations & bleach marks
Fluctuation of loading

5. ACTUAL BLADE

6. POSSIBLE CAUSES
Mateial defects
Improper brazing operations
Improper plant operations

7. TESTS & RESULTS
Visual inspection
Brazed joints disjointed
Cracks from holes
Black scale(magnetite)

8. Contd…
Scanning electron microscope
Microstructure study
Martensitic for blade
Bianitic structure for rod BLAD
E
ROD

9. Contd…
Chemical analysis
Composition as per AISI 400 series stainless steel

10. Contd…
Mechanical properties
Hardness for blade 265 VPN
Hardness for rods 225 VPN
Hrdness of brazing wire 200 VPN

11. Contd…

12. Contd…
Fractography
Galvanic corrosion
Crack initiaion at hole and propagation

13. Contd …
High cycle fatigue test
0.7 static 0.5 dyn. 10000 cyc

14. CONCLUSION
Starts with corrosion of brazed joints
Fretting & metal removal
Cracks from holes
Fatigue assisted crack growth

15. COMMENTS
Improper brazing
Improper maintenance
Improper opertion

16. REFERANCE
Fracture analysis case studies 2
 D.R.H. Jones
An investigation of the failure of low pressure steam
turbine blades
 N.K Mukhopdhyay, S . Ghosh Chowdhury