2010 joint delta/vibrant asnt presentation

Delta TechOps | May 24, 2010 |

David Piotrowski Principal Engineer

ASNT Level III – UT, ET, PT

Lem HunterGreg Weaver

Leanne Jauriqui

Using Process Compensated Resonance Testing (PCRT) for Cost Savings and Increased Reliability

Delta TechOps | May 24, 2010 | 2

Outline Of Presentation

1. Description of PCRT2. JT8D T1 Blade

– Background/History– Overtemp project– Other defects

• IGA• Thin wall, cracking, core shift

3. PCRT – Results– Comparison to metallography

4. Other projects– CF6-80 Turbine blade– CFM56-7 Turbine Blade– Impeller– In development

5. Summary


Description of PCRT Process

PCRT System uses resonance spectra and complex algorithms to correctly sort acceptable from unacceptable partsResonant Frequencies determined by dimensions and material properties of “whole part”

fr ~ k/mfr = resonant frequencyk = stiffness (elastic properties e.g., Young’s Modulus)m = mass (dimensions, density)

Structural Defect = Strength reduction caused by degraded material properties or dimensional variation (localized chemistry change = localized modulus change)

e.g., a crack reduces stiffness and lowers the resonant frequencyDegree of resonant frequency shift is proportional to the severity of the defect

Resonance Spectra

Use of PCRT can detect changes in microstructure


PCRT Process

Simple resonance analysis is insufficient for defect detection since unacceptable and acceptable patterns are interlaced

PCRT calculations MTS (Mahalanobis-Taguchi System) characterizes acceptable parts & variation and a Bias score characterizes unacceptable parts

PCRT System Hardware• Simple part interface, PZT transducers• Precision spectrum analyzer & signal generatorPCRT System Software• PC computing power• Statistical analysis with Mahalanobis-Taguchi• Vibrational pattern recognition algorithms• Digital storage of spectra

PCRT Strengths

• Rigid, Hard Components• Characterizing Mature, Well-Controlled Manufacturing Processes• Sorting for Structural Integrity with a Single, Whole Body Test for Multiple

Defect Sources• Digital Historical Record of Resonant Spectra for Life-of-Part Surveillance • Elimination of Operator Error

MTS

Bias

Bads


Shop induction

PCRT

Send for repair/overhaul Flaws:

•Overtemp

•Core-shift/Thin wall

•IGA (intergranular attack)

•Cracking

Dimensional

FPI - cracking

Magnetoscope = IGA

UT- thin wall/core shift

Inspects for ~50% of the defects known to

cause failure

Inspects for 100% of the defects known to cause

failure with one PCRT test

Not required for -219

No OT inspection

•In service failures caused by:–Overtemp–IGA–Thin wall–Stress rupture

•Only inspections are UT wall thickness, visual/dimensional/FPI for cracking

•Poor method of determining if over-temped–1/64 blades sectioned per P&W manual

•No inspection for IGA

Background/History of JT8D 1st Stage Turbine Blade


Process Comparisons - Overtemp

PCRT- 100% inspection; all 64 blades inspected on suspect disks- Reduces scrap rate for suspect blades; saves greater than 1/3 of blades on

average of suspect disks- Additionally determines to scrap for other defects; dimensional, cracks, wall

thinning, core shift, intergranular attack (IGA), although other manual inspections are in place for some of these defects- dimensional, FPI, ultrasonic.

- Process time 20 seconds/blade

Current Process - JT8D Engine Manual , ATA 72-51-01, Inspection 02. - Overtemp evaluated by destructive cut-up on 1 of 64 bladed wheel for

suspect overtemp- Overtemp cut-up results in excessive blade scrap- No sensitivity in cut-up process to dimensional, cracks, wall thinning, core

shift, intergranular attack (IGA)- Process time – up to 48 hrs (one blade)


P&W Overtemp analysis requires destructive testing of 1 blade todetermine disposition of entire 64 blade set

P&W JT8D-219 EM OT Analysis 72-52-01, Inspection 02


P&W JT8D-219 EM OT Analysis 72-52-01, Inspection 02

•Subjective analysis

•Only one blade

–Only two sections

Overtemp limit = 2050 F (based on microstructure)


PCRT Test Data – Initial Feasibility Study

Delta Lab Results for Overtemp Study (Initial Feasibility Study)

yes- 210084yes- 210052100

yes- 205083yes- 205042050

yes- 205082no- approached 205032000

no- 205081no- approached 205021950

no- approached 205080no- no evidence of elevated temperatures11800

Delta Lab ResultBladeDelta Lab ResultBladeExposure Temperature (°F)

•5 new blades and 5 used blades

•Oven exposure

•JT8D EM limit = 2050 F

•Progressive steps

Initial

1800°F

1950°F

2000°F

2050°F

2100°F

Stacked Spectra (19-21.5 kHz) of Blade 5 through each of the oven temperature exposures


PCRT & IGA, Stress-rupture• Intergranular attack

– Stress rupture – stress, temp, time– Blockage of cooling passage, contaminants

• Coating depletion

• Localized hot spots– Strip & recoat repair – internal cavities

• Practice ceased, modified

– Failures attributed to IGA/stress rupture– No OEM inspection for IGA

• Quantified degree of IGA– Accept/reject Limit set at 0.003” IGA depth

(from internal cavity wall)– Amounts from 0.000134-0.0122”– Most samples with IGA also have other defects

Delta developed analysis for IGA and quantified reject limit ; OEM = no inspection

Photo by P&W JT8D World Conference


PCRT & Cracking, Thin Wall

PCRT has shown capability to detect cracking, thin wall


• Cracking typically on trailing edge

– Often due to thin wall (parent metal removal with stripping)

• Some blending operations

– UT Thickness check– Reject limit = 0.022” min

in critical areas– On-wing borescope

findings• UERs = $$$$

• PCRT aided in identifying cracked blades

– Easy, obvious detection

PCRT has shown capability to detect cracking, thin wall



PCRT & Cracking, Thin Wall


Statistics Summary of PCRT Inspectionfor Overtemp – JT8D T1 Blade

1. Blind Study Results- 16 Random Blades from suspect overtemp Engines

- 9 of the 16 cut-ups confirmed OT; PCRT confirmed all 9 as OT; 100% agreement

- 7 cut-ups confirmed No OT; PCRT passed all 7; 100 % agreement

2. 5000 Blades In Total Tested PCRT- Spectra Collected- Of the 5000, 202 random metallographic cut-up verification; possibly good or overtemp blades

- Of the 202, 128 OT (could have had other defects – IGA, thin wall/core shift, cracking, or combinations) ,74 good blades

- Of the 128, Lab cut-ups confirmed OT for all 128.

Result : 128 blades identified as overtemp- 128 confirmed by cut-up by current manual OT Inspection Process – 100%


PCRT Accomplishments – JT8D T1 blade1. Supplemental inspection = Eliminating bad blades.

– Inspecting each blade in OT sets that pass Lab OT cut-up.– Inspecting for IGA, thin wall, cracking, and OT, simultaneously.

2. Extensive experience - Over 5,000 blades scanned with PCRT; over 200 blades sectioned.

– Data collection for possible lifing.– PCRT correlation to Metallography results.

3. Incorporation of serialization.– Tracking, comparison back to itself in future visits.

• Correlate any changes in resonance with service

4. ‘Salvage’ program for high-time groups saved $1.1M in 2009 (Delta self-imposed limits).

5. Drastically reduced inspection time, while improving blade reliability– PCRT takes seconds and can test all 64 blades vs. Materials Lab taking 48+ hours

to inspect a single blade

– Risk of throwing-away good blades is reduced

– Risk of putting a potentially bad blade back in to service is greatly reduced (already achieved!)


• EXPENSIVE Issues:– 5 Failures attributed to brazed tip cap liberation

Results in loss of HPT blades and damage to downstream components

– 20+ unscheduled engine removals in ~2 years– Delta reliability initiative = Pull all blades with >

10,000 hrs and scrap/quarantineEstimate premature removal of 1500 blades with an average of 50% of life still remaining

• No Standard NDT available– Repair and Overhaul X-ray and FPI methods prove

to be inconclusive in detecting braze interface cracking.

– Blades returned as serviceable are still considered suspect.

• Blade potentially reclaimed by PCRT based on integrity of the brazed joint

– Blades which fail inspection could then possibly be repaired and salvaged

CF6-80A 1st Stage HPT Blades have caused considerable pain

Additional Projects – CF6-80 1st Stage TB


CF6-80A T1 Blade Classifications

• Initial teaching set provided– 325 blades of varying conditions

• Blades classified through:– X-ray (actual procedure)

ASNT Level III in Radiography– Visual for LE cracking– Computed Tomography Inspection (CT)

Sandia National Labs

• PCRT– Good correlation with other

methods

• Significant potential cost savings due to estimated 40% salvage rate!

PCRT results correlate well with other inspection techniques

CT Scan Showing Gapped Braze

CT Scan Showing Cracked Braze


Impellers• In-service failures prior to life limit

• Sample program:10 new OEM vs 10 new PMA (also 1 ‘timed-out’ OEM part)

• The frequency data easily discriminates the 2 part manufacturers. – The PMA resonant frequencies are

consistently lower, and less variable, while the OEM resonant frequencies are higher and more variable.

– The OEM parts are 3‐6% higherin frequency, and show about 3X more variation than the PMA parts.

• Violates New AC 33.83-1– “Comparative Method to Show

Equivalent Vibratory Stresses and High Cycle Fatigue Capability for Parts Manufacturer Approval of Turbine Engine and Auxiliary Power UnitParts”

PCRT has added to discussion about PMA vs OEM parts


CFM56-7 T1 Blade

• In-service failures– 3 recent failures; Fatigue cracking in 4 places on blade (some

uninspectable with current manual procedures).

• ‘Soft’ time-limit of 20K cycles– Increase confidence to operate up to soft-time limit.– Determine serviceability beyond the self-imposed 20,000 cycle limit.– Avoid unneeded blade replacement.– Comparing resonance signatures at future visits will provide a

warning of new defects (proactive vs reactive program).

• Other applications– Quality control for repair process– Additional blades for overtemp– Additional ‘salvage’ programs– Examination of wheels, bolts– Long-term: Lifing projects

Several application programs in development using PCRT


Summary

1. Delta TechOps has explored and partnered with Vibrant Corp todevelop new technology for detecting overtemp, IGA, cracking, and thin wall/core shift in JT8D-219 T1 blades.

– OT = Detects localized change in chemistry (at atomic level) as a result of overtemp, resulting in a localized change in elastic modulus

2. Test Data Results– 1:1 correspondence of PCRT overtemp inspection process achieved

compared with existing JT8D Engine Manual Cut-up process, ATA 72-51-01, Inspection 02). Total of 5000 blades inspected by PCRT.

3. Process Compensated Resonance Testing (PCRT) – Positive contribution to safety by providing better inspection, eliminating

bad blades.– Additional benefits:

• 100% Inspection • Sensitivity to new defects simultaneously.• Simultaneous positive contribution to safety and economics

4. Additional applications being developed for PCRT.– Opportunities: In-service issues, Reclaim scrap parts, PMA

validation, ‘Cradle-to-Grave’ tracking

2010 joint delta/vibrant asnt presentation

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