Turbina de gas

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Root Cause Failure Analysis:
Gas Turbines
Harold Simmons Sastry Cheruvu Klaus Brun Southwest Research Institute
www.gasturbines.swri.org Email: hsimmons@swri.org scheruvu@swri.org kbrun@swri.org

WHY FAILURE ANALYSIS?
To Reduce the Cost of Future Operation
Forced Outage, $ Million
$2.5 $2.0 $1.5 $1.0 $0.5 $0.0 1 6 Time

Gas Turbine Technology Center

Southwest Research InstituteForced Outage $
Historical Outage
RCFA RCFA



To Understand The Root Cause Of Failure
– Design/Fabrication – Operation – Maintenance/Repair

• • • •

To Reduce Risk of Future Failures To Improve Reliability To Increase Operation Availability To Settle Insurance Claims

Organization
1. Introduction 2. Diagnostic Tool Boxes 3. Case Histories 4. Group Discussion

11

Blade FailuresResponsible for 42% of All GT Forced Outages

Failure Causes
• Thermal / Mechanical Fatigue: • Creep:
– Firing Temperature – Cooling Flow – – – –

Failure Analysis Approaches
• Fault Tree
– Exhaustive Evaluation of All Conceivable Causes – Takes Time

– Start / Stop Cycles; Trips – ESD’s

• High Precision Models
– Takes Time and $$ – More Accurate – Necessary in Some Cases

•Coatings / Materials Life Issues
Oxidation Corrosion, Pitting Environmental Attack Brittle Coating

• Easter Egging
– Intuitive Feel for Cause – May Not Be Right

• Quick & Dirty
– May Be Inaccurate – Low Cost

• High Cycle Fatigue:

– Vibration; Stress Concentration – Fretting/Galling: Root, Shroud

Root Cause Diagnosis Steps
Objective: Improve Reliability & Availability by PreventingFuture Failures
• • • • • Forensics: Document Failure Scenario Metallurgy: Failure Mode - HCF, LCF,... NDE - Detect Other Flaws Mechanical/Thermal: Basic Conditions Mechanical Testing
– Material Properties – Resonant Frequencies & Stresses

First Responder’s Job
1.
– – –

Gas Turbine Technology Center
Southwest Research Institute

Secure All Data Sources
Backup All Data Recording PreventParts From Leaving Site Locate Log Books, Maintenance Records

2. 3. 4. 5. 6.
– – –

Identify All Personnel on Duty- Initial Interviews Notify All Parties Involved Appoint Failure Analysis Team – Cover All Disciplines Oversee Teardown – Photograph Everything Collect & Document All Evidence
Use Specimen Bags and/or Labels Collect Deposits, Parts Preserve Fracture Surfaces – Do

• FractureMechanics: Stress Range Timely Information Prevents Failures in Operating Fleet

NOT Clean

Forensic Investigation
What Failed First & Why
Scenario: •One Blade Fails •Strikes Case & Tumbles •Knocks Out Neighbors •Broken Parts Go Downstream •Damages Other Blades •Rotor Becomes Unbalanced •Tips Rub Severely

Basic Technical Background
Failure Analysis Toolboxes
• Metallurgy – Dr. SastryCheruvu • Aero/Thermo Analysis – Dr. Klaus Brun • Structural Dynamics – Harold Simmons

Flow

Primary Failure Evidence Partly Obliterated Challenge - To Separate Consequential Damage From Primary Failure.
(This Failure was a HCF Crack Starting From a Corrosion Pit at Base)

Root Cause Failure Analysis:
Gas Turbines

FAILURE ANALYSIS FLOW CHART
Metallurgical Investigation Operational DataReview Mechanical Analysis - System - Design
ROOT CAUSE OF FAILURE

Gas Turbine Technology Center
Southwest Research Institute

Metallurgy
Sastry Cheruvu

CORRECTIVE ACTIONS esign rocess -Operation -Maintenance

Southwest Research Institute

Turbine Materials/Coatings Failure Causes and Modes
• Materials/coatings
• Gas Turbine components operate over a range temperatures &stresses. Operating Conditions demand advanced materials & coatings • Turbine materials include Nickel and Cobalt based alloys • Parts are frequently coated with either Aluminide or MCrAlY with or without TBCs

Failure Modes Hot Corrosion And Oxidation
Hot Corrosion- Involves chemical attack of a component with its environment at elevated temperatures • Hot corrosion- reaction of a metal with...
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