An investigation of the failure of low pressure

SUBMITTED BY BAGGIOJOSE13MD01

AN INVESTIGATION OF THE FAILURE OF LOW PRESSURE

STEAM TURBINE BLADES

CONTENTS

1. INTRODUCTION2. DESCRIPTION3. TESTS & RESULTS4. CONCLUSION5. REFERANCE

INTRODUCTION

Steam turbine extracts energy from steam3 types HP,IP & LPBlades convert linear to rotary motionDesigned life 30 yearsLP blades are prone to failure

DESCRIPTION

210 MW thermal power plantOverhauled after 5 years shut down after 2

years12% Cr steel with tempered martensiteBrazed joint b/w blade and steel rodeStriations & bleach marksFluctuation of loading

ACTUAL BLADE

POSSIBLE CAUSES

Mateial defectsImproper brazing operationsImproper plant operations

TESTS & RESULTS

Visual inspection

Brazed joints disjointedCracks from holesBlack scale(magnetite)

Contd…

Scanning electron microscope

Microstructure studyMartensitic for bladeBianitic structure for rod

BLADE

ROD

Contd…

Chemical analysisComposition as per AISI 400 series stainless

steel

Contd…

Mechanical propertiesHardness for blade 265 VPNHardness for rods 225 VPNHrdness of brazing wire 200 VPN

Contd…

Contd…

FractographyGalvanic corrosionCrack initiaion at hole and propagation

Contd …

High cycle fatigue test0.7 static 0.5 dyn. 10000 cyc

CONCLUSION

Starts with corrosion of brazed jointsFretting & metal removalCracks from holesFatigue assisted crack growth

COMMENTS

Improper brazingImproper maintenanceImproper opertion

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