Disc Life Analysis - Frame 6 Users Group

Liburdi Turbine Services
Remaining Life Analysis of
Gas Turbine Discs
www.liburdi.com
Disc Life Analysis - Outline
• How is disc life analysis different from HGP
components?
• Why do we do a disc life analysis?
• What is the expected outcome / value?
Disc Life vs HGP Life
Service Degradation factors affecting life limits
HGP Components – Blades, Vanes
– Very high temperatures – microstructure aging, depletion,
oxidation, hot corrosion,
– high stresses ( rotating or thermal mechanical, local stress
concentration)
Turbine Discs
– Relatively low temperature – no high temperature related effects (
if cooling is sufficient)
– High stresses (rotating centrifugal, local stress concentrations)
eventually can lead to creep damage – grain boundary wedge
cracks, creep voids
– Corrosion (aqueous, or hot corrosion)
Disc Life vs HGP Life
Analytical Techniques
HGP Components – Blades, Vanes
– Microstructure analysis, SEM microscopy to detect aging due to
high temperature / high time exposure
– Mechanical testing (Stress & Creep rupture) to quantify effects
of aged alloy, creep voids/ grain boundary deterioration
– Optical microscopy to identify– oxidation, hot corrosion, alloy
depletion
Turbine Discs
– Destructive analysis typically not effective – no aging,
oxidation, alloy depletion to identify
– Mechanical testing typically just reveals the original
manufactured properties – tensile tests, hardness ( no
measurable deterioration)
– Corrosion detected with NDT - effects of hot corrosion spiking
requires destructive inspection (cross-section)
– Mechanical modeling to determine areas of high stresses,
limiting factors and design margin
Mechanical Modeling of Rotor Discs
“Safe Life” Approach
Computer Model of disc/blade
assembly to determine:
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Design component stresses
Design operating temperature envelope
Expected material responses
Safety factors
Calculated minimum creep / fatigue crack
initiation point (life)
• Outcome – safe total service hours
– Effectively determines, using modern design computer
models, the design margin for the disc – effective safe
disc life
– Can assume design operating conditions or factors for
off-design
Stress, Temperature,
and Material Properties
CMM Scan and FEA Mesh Model
Heat Transfer Model –
Temperature Distribution
Temperature / Stress Model
Creep Life Model
Mechanical Modeling of Rotor Discs
• Damage Tolerance Approach
Built onto the initial Mechanical Model
to determine:
– Fractural mechanics
– Pre-existing initial flaws
– Crack growth rate
– Critical crack size
– Safe inspection interval (SII)
Mechanical Modeling of Rotor Discs
• Damage Tolerance Approach
• Outcome – Managed Disc Life
– Identify the safe frequency of inspections
(length of service interval for high hour
discs)
– Inspection determines that no cracks are
present
– AND that during the next service interval a
new crack cannot grow to critical size
Liburdi Group of Companies
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Liburdi Engineering Ltd
Liburdi Turbine Services Inc
Liburdi Automation Inc
Liburdi Dimetrics Corp
Dundas, Ontario Canada
Stoney Creek, Ontario, Canada
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Dundas, Ontario
Mooresville, North Carolina
Amsterdam
St Petersburg, Russia
Mooresville, NC, USA