The document summarizes a research project analyzing corrosion on the internal surfaces of aircraft metal fluid lines using non-destructive testing (NDT) methods. The researchers tested specimens from aluminum pneumatic lines of a PT-06 aircraft that had experienced repeated failures after inspections. Using eddy current testing, chemical analysis, and metallography, they found the lines failed due to stress corrosion caused by moisture acting as an electrolyte under high pressure. They recommend using borescope visual inspection and eddy current testing with an encircling probe to check for corrosion during maintenance.

1. General Sir John Kotelawala Defence University
Final Year Research Project Presentation:Group-06
COMPREHENSIVE ANALYSIS OF CORROSION ON THE INTERNAL SURFACES OF
AIRCRAFT METAL FLUID LINES USING NDT METHODS.
By:-
HMV Dissanayake (ENG/AE/12/0002)
SFMF Marikkar (3883)
AMDN Atapattu (ENG/AE/12/0011)
LLY Srimal (ENG/AE/12/0044)
Supervised By:-
Wg Cmdr. DJK Lokupathriage
Head of the Department
Department of Aeronautical Engineering
Faculty of Engineering
Kotelawala Defence University 1

2. OUTLINE
• Introduction
• Time Plan
• Objectives
• Research Background
• Methodology
• Results
• Causes
• Root Causes
• Recommendations & Limitations
• Conclusion
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3. INTRODUCTION
• PT-06 Aircraft – Used for training purposes
• Aluminium pneumatic lines - located between distribution and solenoid
valves
• Repeated failures soon after major inspections – Bursts
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4. TIME PLAN
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Task 2014 2015
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Refer Reference Material
Gather Background Information
Obtain Test Specimen
Perform The Test And Gather Results
Compilation Of Results
Report Writing
Monitoring Recommendations
Preparation of Report
Finalization Of Report

5. OBJECTIVES
• Completely analyze corrosion on the internal surfaces of the aircraft metal fluid
lines using NDT methods
• Find root causes for such corrosion
• Make recommendations for alternations in maintenance practices of aircraft
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6. RESEARCH BACKGROUND
• Non-destructive testing methods
• Types of Corrosion
• Detection of Corrosion
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7. RESEARCH BACKGROUND cont...
NON-DESTRUCTIVE TESTING METHODS
• Why Non-Destructive Testing methods are used?
• Contrast between Destructive and Non-Destructive Testing methods
• Benefits of Non-Destructive Testing
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8. RESEARCH BACKGROUND cont...
NON-DESTRUCTIVE TESTING METHODS
• Liquid Penetrant Testing (PT)
• Magnetic Particle Testing (MT)
• Radiographic Testing (RT)
• Ultrasonic Testing (UT)
• Acoustic Emission Inspection (AE)
• Guided Wave Testing (GW)
• Laser Testing (LT)
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9. RESEARCH BACKGROUND cont...
NON-DESTRUCTIVE TESTING METHODS
• Holographic Testing
• Laser Profilometry
• Laser Shearography
• Magnetic Flux Leakage (MFL)
• Thermal / Infrared Testing (IR)
• Visual Testing
• Eddy Current Testing (ET)
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10. RESEARCH BACKGROUND cont...
NON-DESTRUCTIVE TESTING METHODS
Eddy Current Testing Method
• Eddy Current Testing instruments are usually small and portable.
• The method is used only on electrically conductive materials
• Only a small area can be inspected at a time.
• An energized electromagnetic coil induces an AC magnetic field into the tested specimen.
• The fluctuating magnetic field generates a circulating electric eddy current.
• The presence of a flaw increases the resistance to the flow of eddy currents.
• This is indicated by a deflection on the measuring instruments.
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11. RESEARCH BACKGROUND cont...
NON-DESTRUCTIVE TESTING METHODS
Testing of Tubes using Eddy Current Inspection
• The Reflection Method
• The Transmission Method
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12. RESEARCH BACKGROUND cont...
TYPES OF CORROSION
• Uniform Attack
• Galvanic or Two Metal Corrosion
• Crevice Corrosion
• Pitting Corrosion
• Intergranular Corrosion
• Erosion Corrosion
• Stress Corrosion
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13. RESEARCH BACKGROUND cont...
DETECTION OF CORROSION
• Transient Eddy Current Method
• Pulsed Eddy Current Method
• Other Methods
• Single Layer Corrosion Detection
• Two Layer Corrosion Detection
• The Limited Penetration Method
• Dual Frequency Method
• Variable Frequency Method
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14. METHODOLOGY
• Examine the chemical composition of test specimen
• Perform a Three Dimensional Eddy Current inspection on the specimen
• Perform a comparison between corroded and non-corroded specimens using a
3D Eddy Current inspection.
• Perform a micro and macro structural examination (Metallography)
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15. METHODOLOGY cont.…
EXAMINING THE CHEMICAL COMPOSITION OF TEST SPECIMEN
• Sampling
• Sample Preparation
• Chemical Analysis
• Interpretation of Results
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16. METHODOLOGY cont.…
PERFORMING A THREE DIMENSIONAL EDDY CURRENT INSPECTION
ON THE SPECIMEN
• Appropriate probes were selected
• 2 MHz 90 degree surface probe
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17. PERFORMING A THREE DIMENSIONAL EDDY CURRENT INSPECTION ON
THE SPECIMEN
• The gain and phase were set accordingly
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METHODOLOGY cont.…

18. PERFORMING A THREE DIMENSIONAL EDDY CURRENT INSPECTION ON THE
SPECIMEN
• The probe was balanced.
• The test was performed.
• The results were recorded.
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METHODOLOGY cont.…

19. METHODOLOGY cont.…
PERFORM A COMPARISON BETWEEN CORRODED AND NON-
CORRODED SPECIMEN USING A THREE DIMENSIONAL EDDY CURRENT
INSPECTION
• Two samples of equal dimensions were prepared out of the original specimen.
• Specimen dimensions obtained through Vernier caliper
• Length: 7.9 cm
• Outer diameter: 6mm
• Inner diameter: 4mm
• Thickness: 1mm
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20. PERFORM A COMPARISON BETWEEN CORRODED AND NON-
CORRODED SPECIMEN USING A THREE DIMENSIONAL EDDY CURRENT
INSPECTION
• Paint and other applied coatings were removed from the surfaces of the
specimens.
• One specimen were dipped in a high concentrated solution of sodium chloride and
kept for a week.
• A 3D eddy current test was carried out to check for cracks inside the tubes,
following the aforementioned procedure.
• Here, a 2 MHz surface probe and a 200kHz surface probe were employed.
• The results were compared for both specimens.
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METHODOLOGY cont.…

21. METHODOLOGY cont.…
PERFORMING A MICRO AND MACRO STRUCTURAL EXAMINATION
(METALLOGRAPHY)
• The samples were sectioned
• Then, the samples were mounted
• Coarse grinding was carried out
• Then, medium and fine grinding was carried out
• The samples were mechanically polished
• After that, the samples were etched
• Microscopic Examination was carried out employing a microscope
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22. RESULTS
• CHEMICAL ANALYSIS
Element % By Mass
Al 96.55%
Mg 2.84%
Mn 0.25%
Fe 0.16%
Ni 0.04%
Si 0.09%
Cr 0.01%
Ti 0.04%
Mo 0.02%
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23. RESULTS cont.…
THREE DIMENSIONAL EDDY CURRENT INSPECTION ON THE SPECIMEN
Indicated undue liftoffs
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24. RESULTS cont.…
COMPARISON BETWEEN CORRODED AND NON-CORRODED SPECIMEN
USING A THREE DIMENSIONAL EDDY CURRENT INSPECTION
• The probe:
• 2MHz Surface probe
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25. RESULTS cont.…
COMPARISON BETWEEN CORRODED AND NON-CORRODED SPECIMEN
USING A THREE DIMENSIONAL EDDY CURRENT INSPECTION
• Corroded and non-corroded test specimen results – 2 MHz Surface probe
Non-corroded Corroded
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26. COMPARISON BETWEEN CORRODED AND NON-CORRODED SPECIMEN
USING A THREE DIMENSIONAL EDDY CURRENT INSPECTION
• The probe:
• 200kHz surface probe
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RESULTS cont.…

27. COMPARISON BETWEEN CORRODED AND NON-CORRODED SPECIMEN
USING A THREE DIMENSIONAL EDDY CURRENT INSPECTION
• Comparison between corroded and non-corroded test specimens – 200 kHz Surface
probe
Non-corroded Corroded
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RESULTS cont.…

28. Original test specimen Macrostructural view of the specimen
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RESULTS cont.…
MACROSTRUCTURAL ANALYSIS OF THE PNEUMATIC SPECIMEN

29. X50 X200
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RESULTS cont.…
MICROSTRUCTURAL ANALYSIS OF THE PNEUMATIC SPECIMEN

30. CAUSES
• Stress corrosion
• Ductile failure
• Porosity
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31. ROOT CAUSES
• Salinity of the atmosphere
• High turbidity in seawater
• High pH value in seawater around the operating airfield
Caustic Embrittlement - A type of stress corrosion, which occurs due to:
• A susceptible material (aluminum alloy)
• A specific chemical species (a hydroxide)
• Tensile and compressive stresses (acting radially in and out)
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32. RECOMMENDATIONS & LIMITATIONS
RECOMMENDATIONS
• Charge the pneumatic bottles one hour prior to flight.
• To test the metal fluid lines follow the given procedure below:
• For visual examination, perform a Bore-scope test.
• To detect internal and external defects and flaws such as corrosion, perform an eddy current test
using an encircling probe.
• For a thorough examination, proceed with an x-ray photographic testing.
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33. RECOMMENDATIONS & LIMITATIONS
LIMITATIONS - EDDY CURRENT TESTING
• Only conductivity probes, surface probes and bolt-hole probes are available in SL.
• The aforementioned probes cannot be used to test small diameter due to higher lift off errors caused
by the unevenness of the surface.
• Also the probe does not fully align with axis of the tube.
• Length of the bolt hole probe is insufficient to go inside the metal tube and cannot be inserted into
curved tubes.
• Expensive encircling probe.
• Costly experiments
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34. RECOMMENDATIONS & LIMITATIONS
LIMITATIONS – MICRO AND MACRO STRUCTURAL ANALYSIS
• Erroneous interpretations resulted while determining the cause of failure.
• Damages due to grinding and preparing of the sample, being
misinterpreted as flaws and defects.
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35. CONCLUSION
• The PT-06 aircraft in question was operated near a high saline area around China Bay,
Trincomalee.
• Repeated failures were observed on aluminum pneumatic lines.
• A failed line specimen and a non-failed line specimen were compared.
• Micro and Macro structural analysis were performed to determine the cause of failure.
• High pressure in the tubes leads to moisture formation, which acts as an electrolyte.
• Fluctuating corrosion and moisture results stress corrosion.
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36. CONCLUSION cont.…
• For inspection for corrosion using NDT methods the following methods
were suggested.
• Bore-scope for visual inspection
• Eddy current testing using an encircling probe
• It is evidently impractical to spend so much money when there is no
mention of such maintenance activity in the aircraft maintenance manuals.
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37. Thank You!
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