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

Transcription

1 Using Process Compensated Resonance Testing (PCRT) for Cost Savings and Increased Reliability David Piotrowski Principal Engineer ASNT Level III UT, ET, PT Lem Hunter Greg Weaver Leanne Jauriqui Delta TechOps May 24, 2010

2 Outline Of Presentation 1. Description of PCRT 2. 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 Delta TechOps May 24,

3 Description of PCRT Process PCRT System uses resonance spectra and complex algorithms to correctly sort acceptable from unacceptable parts Resonant Frequencies determined by dimensions and material properties of whole part f r ~ k/m f r = resonant frequency k = 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 frequency Degree of resonant frequency shift is proportional to the severity of the defect Resonance Spectra Use of PCRT can detect changes in microstructure Delta TechOps May 24,

4 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 generator PCRT System Software PC computing power MTS Statistical analysis with Mahalanobis-Taguchi Vibrational pattern recognition algorithms Digital storage of spectra Bias Bads 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 Delta TechOps May 24,

5 Background/History of JT8D 1 st Stage Turbine Blade Shop induction PCRT In service failures caused by: Overtemp IGA Thin wall Stress rupture Send for repair/overhaul Dimensional FPI - cracking Flaws: Overtemp Core-shift/Thin wall IGA (intergranular attack) Cracking 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 UT- thin wall/core shift No OT inspection Magnetoscope = IGA Inspects for ~50% of the defects known to cause failure Delta TechOps May 24, Not required for -219 Inspects for 100% of the defects known to cause failure with one PCRT test

6 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 , Inspection 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) Delta TechOps May 24,

7 P&W JT8D-219 EM OT Analysis , Inspection 02 P&W Overtemp analysis requires destructive testing of 1 blade to determine disposition of entire 64 blade set Delta TechOps May 24,

8 P&W JT8D-219 EM OT Analysis , Inspection 02 Subjective analysis Only one blade Only two sections Overtemp limit = 2050 F (based on microstructure) Delta TechOps May 24,

9 PCRT Test Data Initial Feasibility Study Exposure Temperature ( F) Blade Delta Lab Result no- no evidence of elevated temperatures no- approached 2050 no- approached 2050 yes yes Blade yes Delta Lab Results for Overtemp Study (Initial Feasibility Study) Delta Lab Result no- approached 2050 no yes yes new blades and 5 used blades Oven exposure JT8D EM limit = 2050 F Progressive steps Initial 1800 F 1950 F Stacked Spectra ( khz) of Blade 5 through each of the oven temperature exposures 2000 F 2050 F 2100 F Delta TechOps May 24,

10 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 Photo by P&W JT8D World Conference Quantified degree of IGA Accept/reject Limit set at IGA depth (from internal cavity wall) Amounts from Most samples with IGA also have other defects Delta developed analysis for IGA and quantified reject limit ; OEM = no inspection Delta TechOps May 24,

11 PCRT & Cracking, Thin Wall PCRT has shown capability to detect cracking, thin wall Delta TechOps May 24,

12 PCRT & 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 = min in critical areas On-wing borescope findings UERs = $$$$ Photo by P&W JT8D World Conference Photo by P&W JT8D World Conference PCRT aided in identifying cracked blades Easy, obvious detection PCRT has shown capability to detect cracking, thin wall Delta TechOps May 24,

13 Statistics Summary of PCRT Inspection for 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 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% Delta TechOps May 24,

14 PCRT Accomplishments JT8D T1 blade 1. 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 selfimposed 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!) Delta TechOps May 24,

15 Additional Projects CF st Stage TB 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/quarantine Estimate 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 Delta TechOps May 24,

16 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 CT Scan Showing Gapped Braze Computed Tomography Inspection (CT) Sandia National Labs PCRT Good correlation with other methods Significant potential cost savings due to estimated 40% salvage rate! CT Scan Showing Cracked Braze PCRT results correlate well with other inspection techniques Delta TechOps May 24,

17 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% higher in frequency, and show about 3X more variation than the PMA parts. Violates New AC Comparative Method to Show Equivalent Vibratory Stresses and High Cycle Fatigue Capability for Parts Manufacturer Approval of Turbine Engine and Auxiliary Power Unit Parts PCRT has added to discussion about PMA vs OEM parts Delta TechOps May 24,

18 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 Delta TechOps May 24,

19 Summary 1. Delta TechOps has explored and partnered with Vibrant Corp to develop 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 , 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 Delta TechOps May 24,