AC 33.70-5 A.4 Test Case Results.
A.4.1 OEM Results.
This test case has been analyzed independently by several OEMs, and a statistical analysis of their results, given in events per service life, is provided in table A-8 (where m = mean value; s = sample standard deviation).
Table A-8. Test Case Acceptable Component POF Results for the Slot Locations Location Failure Risk Events/Service Life Mean value: m m – 1.65 s m + 1.65 s Slot Surface Without in-service inspection With an in-service directed FPI inspection
9.15E-05
6.10E-05
8.14E-05
4.95E-05
1.03E-04
7.52E-05 Slot Edge Without in-service inspection With an in-service directed FPI inspection
4.74E-05
1.74E-05
3.74E-05
1.06E-06
6.02E-05
2.86E-05 A.4.2 Acceptance Criteria.
All results within the range (m-1.65s, m+1.65s) for both conditions are considered acceptable. This range is the interval centered on the mean value covering 90 percent of the result population assuming a log-normal distribution.
A.4.3 Geometry Verification.
Due to the complexity of axial blade slots (figures A-3 through A-8), verifying the geometry used in the finite element analysis is crucial. Based on results from seven independent analyses, the peak surface stress in the axial blade slot should fall within the range of 172 ksi to 177.1 ksi. Paragraph 1.3.3 provides neutral files that contain the test case geometry and may be used to generate the finite element model. Most commercial finite element software packages can read these files directly. If any conflicts arise between the geometry shown in figures A-3 through A-8 and the neutral files, use the neutral file.
A–21
AC 33.70-5 APPENDIX B. DEFAU LT ANOMALY DISTRIBUTION CURVES.
B.1 Manufacturing Anomaly Distribution Curve for Disk Axial Blade Slots.
B.1.1 Overview of Anomaly Distribution Curve.
This appendix provides the anomaly distribution curve for manufacturing-induced anomalies in axial blade slots of titanium and nickel engine rotors.
B.1.2 Explanation of Probability of Exceedance Curve.
Figure B-1 shows the probability of an exceedance curve for manufacturing-induced anomalies in axial blade slots. This curve represents the likelihood of having an anomaly greater than a given depth in a single disk slot.
• Horizontal Axis: Represents anomaly depth (in inches).
• Vertical Axis: Represents the probability of exceedance, or the chance that an anomaly larger than depth x exists in a single slot.
B.1.3 Tabular Data and Default Anomaly Exceedance Curve Equation.
Table B-1 provides the tabular data corresponding to the curve in figure B-1. The probability of exceedance for different anomaly depths is defined by the following equation:
• Imperial units: 𝐹𝐹(𝐾𝐾) = 1.97𝐸𝐸 − 06 ∗ 1.0635 ∗ 𝐸𝐸𝐸𝐸𝐸𝐸 (− 61.546 ∗ 𝐾𝐾)
• SI units: 𝐹𝐹(𝐾𝐾) = 1.97𝐸𝐸 − 06 ∗ 1.0635 ∗ 𝐸𝐸𝐸𝐸𝐸𝐸 (− 2.4230 ∗ 𝐾𝐾) Where:
• 𝐾𝐾 ≥ 0.001 in (or 𝐾𝐾 ≥ 0.0254 mm) is anomaly depth in inches (or millimeters)
• 𝐹𝐹(𝐾𝐾) is the exceedance probability per slot.
B.1.4 Application of the Exceedance Curve.
The exceedance curve shown in figure B-1 applies to both the slot bottom surface and the slot bottom edge. This distribution is based on a per-slot unit and does not account for size effects such as surface area or edge length at the slot bottom.
B–1
AC 33.70-5
Damage Depth (mm)
0.2540 2.54000.0254 Probability of Exceedance (-)
1.0E-09 1.0E-08 1.0E-07 1.0E-06 1.0E-05 0.001 0.010 0.100 Damage Depth (in) Figure B-1. Distribution for Manufacturing Induced Anomalies in Axial Blade Slots B–2
AC 33.70-5
Table B-1. Tabular Data for Figure B-1 Depth (in)
0.0010
0.0020
0.0030
0.0040
0.0050
0.0060
0.0070
0.0080
0.0090
0.0100
0.0110
0.0120
0.0130
0.0140
0.0150
0.0160
0.0170
0.0180
0.0190
0.0200
0.0210
0.0220
0.0230
0.0240
0.0250
0.0260
0.0270
0.0280
0.0290
0.0300
0.0350
0.0400
0.0500
0.0600
0.0700
0.0800
0.0900
0.1000 Depth (mm)
0.0254
0.0508
0.0762
0.1016
0.1270
0.1524
0.1778
0.2032
0.2286
0.2540
0.2794
0.3048
0.3302
0.3556
0.3810
0.4064
0.4318
0.4572
0.4826
0.5080
0.5334
0.5588
0.5842
0.6096
0.6350
0.6604
0.6858
0.7112
0.7366
0.7620
0.8890
1.0160
1.2700
1.5240
1.7780
2.0320
2.2860
2.5400 Exceedance (-)
1.970E-06
1.852E-06
1.742E-06
1.638E-06
1.540E-06
1.448E-06
1.362E-06
1.280E-06
1.204E-06
1.132E-06
1.065E-06
1.001E-06
9.413E-07
8.851E-07
8.323E-07
7.826E-07
7.359E-07
6.919E-07
6.506E-07
6.118E-07
5.753E-07
5.409E-07
5.087E-07
4.783E-07
4.497E-07
4.229E-07
3.977E-07
3.739E-07
3.516E-07
3.306E-07
2.430E-07
1.787E-07
9.655E-08
5.217E-08
2.819E-08
1.524E-08
8.233E-09
4.449E-09 B–3
AC 33.70-5 APPENDIX C. DEFAULT PROBABILITY OF DETECTION (POD) APPLICABILITY C.1 Use of Default Probability of Detection (POD) Data.
C.1.1 Use of Default POD Data.
C.1.1.1 This appendix defines conditions for using accepted estimates of POD for specific anomalies and nondestructive evaluation/inspection techniques.
These estimates may be used as default values under appropriately similar conditions.
C.1.1.2 It is important to note that the conditions in this appendix do not guarantee the validity of these POD values. For example, if key inspection parameters, such as penetrant concentration or temperature, are not properly controlled, the penetrant’s capability will not be attained—even if the correct penetrant is used. A written plan for controlling and monitoring inspection processes is recommended (see paragraph C.3).
C.1.2 Importance of Inspection Conditions.
If the inspection conditions described in this appendix are not met, inspection capability and reliability will be reduced. In such cases, the default POD values in appendix D would not apply and could lead to an overly optimistic damage tolerance assessment.
C.2 Demonstrating Inspection Capability.
C.2.1 Use of Default ECI POD Curve.
A default POD curve for ECI is provided in appendix D. The use of this default curve must be based on a demonstration that the stated calibration and reject signal levels are achievable on the component being inspected. Conditions such as noise or geometric features should not interfere with these levels. To demonstrate inspectability, the following conditions must be met:
• Proper calibration is maintained.
• Reject signal levels are achieved.
• Conditions such as surface features, depth to be inspected, and proximity to edges are considered.
No further demonstration of capability is required if these conditions are satisfied (see paragraphs C.3 through C.5).
C.2.2 Improving POD Through Demonstration.
For well-controlled inspection techniques, manufacturers may achieve better POD values than the default values. Improved capability may be used if supported by a welldocumented demonstration program. Similarly, if inspection conditions fall outside of C–1
AC 33.70-5 the default values, a demonstration program may be necessary to establish appropriate POD values.
C.3 General Applicability and Restrictions.
C.3.1 Inspection Process Control.
The inspection process must be controlled and performed in accordance with acceptable procedures, such as those outlined in the engine standard practices manual. Procedures should align with good industrial practices, such as MIL-STDs or equivalent industry standards.
C.3.2 Written Procedures for Inspection Parameters.
Parameters such as coverage, probe indexing, and scanning speeds should be governed by written procedures (see paragraph 3.5 of chapter 3 and paragraphs C.4-C.5 of this appendix). Inspection plans and fixturing should be designed to minimize human and other sources of variability.
C.3.3 Inspector Qualifications.
Inspectors must be fully qualified and trained under one of the following standards:
• NAS410 prEN4179
• MIL-STD-410
• ASNT-TC-1A
• ATA-105
• Equivalent standards Inspectors must also receive specific training for the inspection method used.
C.3.4 Material and Geometric Considerations.
The default ECI and FPI POD data apply to all materials. However, geometric conditions such as radii and edges may prevent inspection. There are also limitations on the depth of penetration and near-surface resolution. Areas of high compressive residual stress may negatively affect inspection capability, particularly for penetrant inspection.
See paragraphs C.4 and C.5 for conditions under which the default data were acquired.
Seek advice about the equivalence of alternative conditions from those experienced in NDE.
C.3.5 Surface Conditions.
The default POD data only applies to components with normal surface conditions that have been properly cleaned according to shop manual requirements. No special preinspection cleaning or polishing is required.
C–2
AC 33.70-5 C.4 ECI: Applicability and Restrictions.
C.4.1 ECI Overview.
ECI is used to detect surface or near-surface anomalies, particularly in engine-run components. The default POD data were acquired under the following conditions:
• Probes containing absolute coils, with inspection frequencies between 2-6 MHz.
• Probe fixtures capable of following surface contours of the component being inspected, with controlled lift-off, scan indexing, and attitude.
• The scan direction was parallel to uniform feature changes.
• Automatic recording or alarm triggering, or both, when inspection thresholds were exceeded.
C.5 Penetrant Inspection (PT/FPI): Applicability and Restrictions.
C.5.1 Penetrant Inspection Overview.
Penetrant Testing (PT) is an inspection technique suitable for detection of anomalies that are open to the inspected surface. For the purposes of this AC, PT is intended primarily for application to engine-run components. The default POD data were acquired under the following conditions:
• FPI qualified to level 4 (per MIL-I-25135 or equivalent), used with dry powder developer as a minimum.
• Application of penetrant and developer was automated or followed standard practices (e.g., MIL-STD-6866, AMS-2847).
• Parts could be manipulated to present an unimpeded surface view to the inspector.
C.6 Crack Characteristics and Limitations C.6.1 The default POD data apply to surface-connected, low-cycle fatigue cracks. Cracks are assumed to have a 2:1 aspect (length to depth) ratio. Crack sizes are plotted in terms of the length at the surface. The inspection PODs provided relate the flaw detection probability to the flaw length. Different interpretations are possible for what constitutes the flaw “length”, particularly for corner flaws. For consistency, the flaw length is defined using the convention in figure C-1.
C.6.2 Cracks must not be obscured by oxide, contaminants, etc. Inspected surfaces should be flat or only moderately curved. The choice of the appropriate POD curve from those provided must be based on component demonstration of the attainable inspection sensitivity (see paragraph C.2).
C–3
AC 33.70-5
a a FPI length = 2c ECI length = 2c FPI length = a + c ECI length = a = c Figure C-1. Crack Dimension Conventions to be Used with POD Curves C–4
AC 33.70-5 APPENDIX D. DEFAULT POD CURVES D.1 Overview.
This appendix provides default POD curves that can be used for assessing manufacturing-induced anomalies in axial blade slots. The following figures and tables present the relevant POD data for FPI and ECI.
D.1.1 Figure D-1 illustrates the POD for FPI of finish-machined surfaces, with detection probabilities versus anomaly length.
MEAN (50% CONFIDENCE) POD FOR FLUORESCENT
PENETRANT INSPECTION OF FINISH-MACHINED SURFACES Anomaly Length (mm) 10
1.0 ‡-
0.9 Applicability
0.8 MIL-I-25135 Level 4 penetrants with dry powder developer (as
0.7 minimum) Percent POD 0.6
0.5
0.4
0.3 - FPI Full Field Inspection
0.2 - - - FPI Directed Inspection
0.1
0.0 10 100 1000 Anomaly Length (inches* 1e-3) Figure D-1. POD for FPI of Finish Machined Surfaces D~1
AC 33.70-5 D.1.2 Table D-1 provides tabulated data for FPI directed inspection, providing POD values versus anomaly lengths in both inches and millimeters.
Table D-1. Tabulated FPI POD (Directed Inspection) FPI Directed Inspection Length (inches*1e-3) Length (mm) Percent POD
1.595769 0.04053254 1.0E-09
24.00028 0.6096072 1.0E -09
24.00553 0.6097406 1.0E -02
26.93207 0.6840747 2.0E -02
28.97132 0.7358715 3.0E -02
30.60642 0.7774030 4.0E -02
32.00434 0.8129103 5.0E -02
37.30716 0.9476018 1.0E -01
41.37288 1.050871 1.5E-01
44.91788 1.140914 2.0E-01
48.20028 1.224287 2.5E-01
51.35204 1.304342 3.0E-01
57.57499 1.462405 4.0E-01
64.07147 1.627415 5.0E-01
71.30106 1.811047 6.0E-01
79.94166 2.030518 7.0E-01
85.16879 2.163287 7.5E-01
91.39258 2.321372 8.0E-01
99.22348 2.520276 8.5E-01
110.0367 2.794932 9.0E-01
128.2688 3.258027 9.5E-01
134.1273 3.406834 9.6E-01
141.6973 3.599111 9.7E-01
152.4264 3.871630 9.8E-01
171.0088 4.343624 9.9E-01 D–2
AC 33.70-5 D.1.3 Table D-2 provides tabulated data for FPI fu ll-field inspection, providing POD values versus anomaly lengths in both inches and millimeters.
Table D-2. Tabulated FPI POD (Full Field Inspection) FPI Full Field Inspection Length (inches*1e-3) Length (mm) Percent POD
1.595769 0.04053254 1.0E-09
35.09967 0.8915315 1.0E -09
35.10289 0.8916135 1.0E -02
39.38237 1.000312 2.0E-02
42.36435 1.076054 3.0E-02
44.75531 1.136785 4.0E-02
46.79948 1.188707 5.0E-02
54.55360 1.385662 1.0E-01
60.49880 1.536670 1.5E-01
65.68272 1.668341 2.0E-01
70.48261 1.790258 2.5E-01
75.09107 1.907313 3.0E-01
84.19100 2.138451 4.0E-01
93.69081 2.379747 5.0E-01
104.2626 2.648270 6.0E-01
116.8975 2.969196 7.0E-01
124.5410 3.163340 7.5E-01
133.6419 3.394505 8.0E-01
145.0930 3.685362 8.5E-01
160.9054 4.086998 9.0E-01
187.5657 4.764168 9.5E-01
196.1323 4.981760 9.6E-01
207.2019 5.262928 9.7E-01
222.8907 5.661425 9.8E-01
250.0637 6.351618 9.9E-01 D–3
AC 33.70-5 D.1.4 Figure D-2 illustrates the POD for ECI of finish-machined surfaces, with detection probabilities versus anomaly length.
MEAN (50% CONFIDENCE) POD FOR EDDY CURRENT OF
FINISH MACHINED SURFACES Anomaly Length (mm)
1.0
0.9 • Reject at the calibration notch threshold response
0.8
- - Reject at one half the calibration 2 0.6 O.7 notch threshold
0.5
0.4 = 0.3 Applicability - Absolute coils, 2-6 MHz inspection frequency
0.2 - Calibration on 0.030" × 0.015" notch
- Applicable only if the indicated O.1 O.0 .... sensitivity is attainable 10 100 Anomaly Length (inches*1e-3) Figure D-2. POD for ECI of Finish Machined Surfaces D-4