final project presentation - comprehensive analysis of corrosion on the internal surfaces of...

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

OUTLINE

• Introduction

• Time Plan

• Objectives

• Research Background

• Methodology

• Results

• Causes

• Root Causes

• Recommendations & Limitations

• Conclusion

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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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TIME PLAN

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Task 2014 2015

Au

g

Sep

Oct

No

v

Dec

Jan

Feb

Mar

Ap

r

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

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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RESEARCH BACKGROUND

• Non-destructive testing methods

• Types of Corrosion

• Detection of Corrosion

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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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• 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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• Holographic Testing

• Laser Profilometry

• Laser Shearography

• Magnetic Flux Leakage (MFL)

• Thermal / Infrared Testing (IR)

• Visual Testing

• Eddy Current Testing (ET)

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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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Testing of Tubes using Eddy Current Inspection

• The Reflection Method

• The Transmission Method

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TYPES OF CORROSION

• Uniform Attack

• Galvanic or Two Metal Corrosion

• Crevice Corrosion

• Pitting Corrosion

• Intergranular Corrosion

• Erosion Corrosion

• Stress Corrosion

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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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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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METHODOLOGY cont.…

EXAMINING THE CHEMICAL COMPOSITION OF TEST SPECIMEN

• Sampling

• Sample Preparation

• Chemical Analysis

• Interpretation of Results

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PERFORMING A THREE DIMENSIONAL EDDY CURRENT INSPECTION ON THE SPECIMEN

• Appropriate probes were selected• 2 MHz 90 degree surface probe

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• The gain and phase were set accordingly

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• The probe was balanced.

• The test was performed.

• The results were recorded.

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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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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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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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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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RESULTS cont.…

THREE DIMENSIONAL EDDY CURRENT INSPECTION ON THE SPECIMEN

Indicated undue liftoffs

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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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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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• The probe:

• 200kHz surface probe

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RESULTS cont.…


• Comparison between corroded and non-corroded test specimens – 200 kHz Surface probe

Non-corroded Corroded

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RESULTS cont.…

Original test specimen Macrostructural view of the specimen2824/02/2016

RESULTS cont.…

MACROSTRUCTURAL ANALYSIS OF THE PNEUMATIC SPECIMEN

X50 X200

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RESULTS cont.…

MICROSTRUCTURAL ANALYSIS OF THE PNEUMATIC SPECIMEN

CAUSES

• Stress corrosion

• Ductile failure

• Porosity

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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)3124/02/2016

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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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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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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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. 3524/02/2016

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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Thank You!

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final project presentation - comprehensive analysis of corrosion on the internal surfaces of...

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