Non Destructive Testing

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Introduction to

Non-Destructive

Testing

By : E. E. Reas o, J r.

I. Properties of Materials

II. Types of DefectsIII.What is NDT?

IV.Who are capable to perform

NDT? V. What are the references used ?

VI. What are the different methods

of NDT?

VII.Reporting/recording of findings.

I. Properties of Material

(Metallic & Non-Metallic)

1) Elasticity

- The property that enables a metal to return to itsoriginal size and shape when the force which causes the

change of shape is removed.

- Elasticity is a property extremely valuable because it

would be highly undesirable to have a part permanentlydistorted after an applied load was removed.

- In aircraft construction, members and parts are so

designed that the maximum loads to which they aresubjected will not stress them beyond their elastic limit.

2) Strength

- The ability of a material to resist change in shape orsize (deformation) when external forces are applied.

- Strength is also the ability of a material to resist stress

without breaking.

- The type of load or stress on the material affects the

strength exhibits.

- Fuselage is designed to withstand both radial and

longitudinal stress

- Wing designed to with stand bending stress during

static and flight.

3) Hardness

- The ability of a material to resist abrasion,penetration, cutting action, or permanent distortion.

Hardness may be increased by cold working the metal

and in case of steel and certain aluminum alloys, byheat treatment.

structural parts are often formed from metals in their

soft state and are then heat treated to harden them sothat the finished shape will be retained.

4) Ductility

- The property of a metal which permits it to bepermanently drawn, bent, or twisted into various shapes

without breaking.

4) Ductility

- this property is essential for metals used in makingwire and tubing

4) Ductility

-greatly prefered for aircraft use because of ease of forming and resistance to failure under shock loads.

4) Ductility

-for this reason, aluminum alloys are used for cowlrings, fuselage and wing skin, and formed or extruded

parts, such as ribs, spars and bulkhead.

5) Malleability

- The property that allows a metal to deformpermanently when loaded in compression.

6) Brittleness

- The property of a metal which allows little bending ordeforming without shattering.

6) Brittleness

- because structural metals are often subjected to shockloads, brittleness is not very desirable property

7) Conductivity

- The property which enables a metal to carry heat orelectricity.

7) Conductivity

- the heat conductivity of a metal is especially importantin welding because it governs the amount of heat that

will be required for proper fusion.

7) Conductivity

- in aircraft, electrical conductivity must also beconsidered in conjunction with bonding, to eliminate

radio interference.

7) Conductivity

- the aircraft is designed to redirect and discharge high voltage from lightning strike.

8) Density

- The weight of a unit volume of a material

8) Density

- in aircraft work, the specified weight of a material percubic inch is preferred since this figure can be used in

determining the weight of a part before actual

manufacture.

9) Toughness

- a material which possesses toughness will withstandtearing or shearing and may be stretched or otherwise

deformed without breaking.

10) Fusibility

- the ability of a metal to become liquid by theapplication of heat.

11) Thermal Expansion

- Refers to the contraction and expansion that arereactions produced in metal as result of heating or

cooling.

II. Types of Defects

1) Casting Defects

2) Porosity

3) Slag Inclusions

4) Shrinkage

- Casting defect that occurs during the middle and laterstages of solidification of the cast metal.

5) Cracks

6) Corrosion

III. What is Non-destructive

Testing (NDT)?

- NDT is a wide group of analysis

techniques used in science and

industry to evaluate the properties

of a material, component or system

without causing damage.

IV. Who are capable to perform

Non-Destructive Testing (NDT) training is provided for

people working in many industries.

Successful and consistent application of NDT techniques

depends heavily on personnel training, experience andintegrity.

It is generally necessary that the candidate successfully

completes a theoretical and practical training program, as well as have performed several hundred hours of practical

application of the particular method they wish to be trained

Personnel involved in application of industrial NDT methods

and interpretation of results should be certified, and in

some industrial sectors certification is enforced by law orby the applied codes and standards

Three (3) Levels of NDT Personnel:

Level I

-technicians qualified to perform only

specific calibrations and tests under close supervision

and direction by higher level personnel.

- They can only report test results.

- Normally they work following specific work

instructions for testing procedures and rejection

criteria.

Three (3) Levels of NDT Personnel:

Level III

- specialized engineers or very experienced

technicians. They can establish NDT techniques and

procedures and interpret codes and standards.

- They also direct NDT laboratories and have central

role in personnel certification.

- They are expected to have wider knowledge covering

materials, fabrication and product technology.

V. What are the references used in

1) NDT Manuals

2) International Standards

3) Regulatory Issued Publication

4) Manufacturer’s Service Bulletin

5) Engineering Order

VI. What are the Different

Methods of NDT?

NDT is divided into various methods of testing, each

based on a particular scientific principle.

These methods may be further subdivided into various techniques.

The various methods and techniques, due to their

particular natures, may lend themselves especially well

to certain applications and be of little or no value at allin other applications.

Therefore choosing the right method and technique is

an important part of the performance of NDT.

The Basic NDT Methods are:

1) Penetrant Inspection

2) Magnetic Particle Inspection

3) Eddy Current Inspection

4) Ultrasonic Inspection

5) Radiographic Inspection

6) Visual Inspection

PENETRANT

INSPECTION

1) PENETRANT INSPECTION

-a widely applied and low-cost inspection method usedto locate surface-breaking defects in all non-

porous materials (metals, plastics, or ceramics).

-The penetrant may be applied to all non-ferrousmaterials and ferrous materials, although for ferrous

components magnetic-particle inspection is often used

instead for its subsurface detection capability.

- LPI is used to detect casting, forging and weldingsurface defects such as hairline cracks, surface

porosity, leaks in new products, and fatigue cracks on

in-service components.

a) Principle

- penetrant inspection is based upon capillary action,

where low surface tension fluid penetrates into cleanand dry surface-breaking discontinuities.

Capillary Action

- is the ability of a liquid to flow in narrow spaces

without the assistance of, and in opposition to,

external forces like gravity.

- The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a

thin tube, in porous materials such as paper, in

some non-porous materials such as

liquified carbon fiber, or in a cell.

- penetrant may be applied to the test component by:

- Brushing.

a) Principle (cont’d)

- Dipping the component/part

- Spraying

- After adequate penetration time has been allowed, the

excess penetrant is removed, a developer is applied.

- The developer helps to draw penetrant out of the flaw

where an invisible indication becomes visible to theinspector.

- Inspection is performed under ultraviolet light when

using a fluorescent penetrant, or

- Inspection is performed on visible light when using

visible dye penetrant (red dye)

b) Materials/Equipments Used

- Penetrant

b) Materials/Equipments Used (cont’d)

- Developer

- Solvent Cleaners

- Blacklight

c) Inspection Procedure

- Pre-cleaning

- The test surface is cleaned to remove any dirt,paint, oil, grease or any loose scale that could either

keep penetrant out of a defect, or cause irrelevant or

false indications

c) Inspection Procedure (cont’d)

- Application of Penetrant

- The penetrant is then applied to the surface of theitem being tested.

- Application of Penetrant-The penetrant is allowed "dwell time" to soak into

any flaws (generally 5 to 30 minutes).

- The dwell time mainly depends upon the penetrant

being used, material being tested and the size of

flaws sought.

- As expected, smaller flaws require a longer

penetration time.

- Removal of Excess of Penetrant

-The excess penetrant is then removed from the surface.The removal method is controlled by the type of

penetrant used.

-Water-washable, solvent-removable, lipophilic post-

emulsifiable, or hydrophilic post-emulsifiable are thecommon choices. Emulsifiers represent the highest

sensitivity level, and chemically interact with the oily

penetrant to make it removable with a water spray.

-When using solvent remover and lint-free cloth it is

important to not spray the solvent on the test surface

directly, because this can remove the penetrant from the

flaws.

Solvent

RemovablePenetrant

Water-washable

Penetrant

-If excess penetrant is not properly removed, once the

developer is applied, it may leave a background in the

developed area that can mask indications or defects.

-In addition, this may also produce false indications

severely hindering your ability to do a proper inspection.

- Removal of Excess of Penetrant

- Application of Developer

- After excess penetrant has been removed a whitedeveloper is applied to the sample. Several developer

types are available, including: non-aqueous wet

developer, dry powder, water suspendable, and water

soluble..

The developer draws

penetrant from defects

out onto the surface to

form a visible indication,

commonly known as

bleed-out.

Any areas that bleed-out

can indicate the location,

orientation and possible

types of defects on the

surface.

- Inspection-The inspector will use visible light with adequate

intensity (100 foot-candles) for visible dye penetrant.

- Ultraviolet (UV) radiation of adequate intensity

(1,000 micro-watts per centimeter squared is

common), along with low ambient light levels (less

than 2 foot-candles) for fluorescent penetrant

examinations.

- Inspection of the test surface should take place after

10 to 30 minute development time

- Post-Cleaning

-The test surface is often cleaned after inspection andrecording of defects, especially if post-inspection

coating processes are scheduled.

d) Advantages & Disadvantages

- Advantages

- the speed of the test and the low cost- Disadvantages

- the detection of only surface flaws, skin irritation,

and the inspection should be on a smooth clean

surface where excessive penetrant can be removed

prior to being developed.

- Conducting the test on rough surfaces, such-as "as-

welded" welds, will make it difficult to remove any

excessive penetrant and could result in false

indications.- Also, on certain surfaces a great enough color

contrast cannot be achieved or the dye will stain the

workpiece.

MAGNETIC

PARTICLE

INSPECTION

2) MAGNETIC PARTICLE INSPECTION

- is an NDT method for detecting surface and slightlysubsurface discontinuities in ferroelectric materials.

-The process puts a magnetic field into the part. The

piece can be magnetized by direct or indirect

magnetization.

-Direct magnetization occurs when the electric current

is passed through the test object and a magnetic field is

formed in the material.

-Indirect magnetization occurs when no electric currentis passed through the test object, but a magnetic field is

applied from an outside source.

Classification of Magnetizing the Material

a) Principle

- Right Hand Rule.

-The magnetic lines of force are perpendicular to the

direction of the electric current.

- The presence of a surface or subsurface

discontinuity in the material allows the magnetic

flux to leak, since air cannot support as much

magnetic field per unit volume as metals.

-Ferrous iron particles are then applied to the part.

-If an area of flux leakage is present the particles

will be attracted to this area.

Th i l ill b ild h f l k

-The particles will build up at the area of leakage

and form what is known as an indication.

-The indication can then be evaluated to determine

what it is, what may have caused it, and what action

should be taken, if any.

Two Types of Magnetization

i) Longitudinal Magnetization

Two Types of Magnetization

ii) Circular Magnetization

Different Technique on Magnetizing

i) ElectroMagnetic Yoke Technique

ii) Bench Technique

iii) Cable Wrap Technique

iv) Prod Technique

- Electromagnetic Yoke

- Bench

- Cable Wrap

- Prods

- Blacklight

- Magnetic Particle

- Solvent Cleaner

c) Inspection Procedure

- Pre-cleaning- The test surface is cleaned to remove any dirt,

paint, oil, grease or any loose scale that could either

keep penetrant out of a defect, or cause irrelevant or

false indications

- Magnetizing of Parts using Mobile Equipment

- Magnetizing of Parts using Stationary Equipment

- Application of Particle

- Inspection

- Demagnetization

- Advantages- Fast results can be obtained

- Inspection results are reliable.

- Disdvantages

- Can only be used in ferromagnetic materials

EDDY CURRENT

INSPECTION

3) EDDY CURRENT INSPECTION

- uses electromagnetic induction to detect flawsin conductive materials.

- a circular coil carrying current is placed in proximity

a circular coil carrying current is placed in proximity

to the test specimen (which must be electrically

conductive).-The alternating current in the coil generates changing

magnetic field which interacts with test specimen and

generates eddy current

- Variations in the electrical conductivity or magnetic

Variations in the electrical conductivity or magnetic

permeability of the test object, or the presence of any

flaws, will cause a change in eddy current and acorresponding change in the phase and amplitude of the

measured current.

a) Principle

- Right Hand Rule.

-The magnetic lines of force are perpendicular to the

direction of the electric current.

- Electromagnetic field is induced in the conductive

material.

- a discontinuity/flaw will disturb the flow of eddy

current.

- the disturbance (change in impedance) will create a

graphical signal on the CRT screen.

b) M t i l /E i t U d

- Eddy Current Equipment

b) M t i l /E i t U d ( t’d)

- Eddy Current Probes & Cables

- Battery & Charger

- Calibration Blocks

) I ti

c) Inspection

- Calibration of Equipment

c) Inspection (cont’d)

- Inspection on the area of concern (fan blades)

- Inspection on the area of concern (wheel hubs)

- Inspection on the area of concern (components)

- Inspection on the area of concern (welds)

c) Inspection (cont d)

- Inspection on the area of concern (tubes)

- Inspection on the area of concern (airframe)

-Inspection on the area of concern (airframe)

- Identification of Coating Thickness

- Conductivity Testing

- Advantages

- Fast results can be obtained

- Inspection results are reliable.

- Disdvantages

- only conductive materials can be tested

- the surface of the material must be accessible

- the finish of the material may cause bad readings,

- the depth of penetration into the material is limited

by the materials' conductivity,

- flaws that lie parallel to the probe may be

undetectable

ULTRASONIC

INSPECTION

4) ULTRASONIC INSPECTION

- very short ultrasonic pulse-waves with center

frequencies ranging from 0.1-15 MHz and occasionallyup to 50 MHz are launched into materials to detect

internal flaws or to characterize materials.

4) ULTRASONIC INSPECTION (cont’d)

- Ultrasonic testing is often performed on steel and

other metals and alloys, though it can also be used onconcrete, wood and composites.

a) Principle

- current is applied on the piezoelectric crystal inside

the probe/transducer.-The transducer vibrates at a constant frequency

producing the high frequency sound wave.

Th Pi l t i ff t d ib th l ti b t

-The Piezoelectric effect describes the relation between

a mechanical stress and an electrical voltage in solids

- A probe sends a sound wave into a test material.

- there are two indications, one from the initial pulse of

the probe, and the second due to the back wall echo.

Th hi di l h l i h f f

- The machine displays these results in the form of a

signal with an amplitude representing the intensity of the reflection and the distance, representing the arrival

time of the reflection

Different UT Scanning Technique

- A Scan

- B Scan

-It is a graphical presentation method of the results

of a series of thickness measurements that shows, in

scale, the cross-section of the component or the

inspected part.

- C Scan

- provides a plan-type view of the location and size of

test specimen features.

- UT Equipment

- Transducers

- Calibration Blocks

- Couplant

c) Inspection

- Calibration of equipment

- Inspection on the area of concern (industrial)

- Advantages

- High penetrating power, which allows the

detection of flaws deep in the part.

- High sensitivity, permitting the detection of

extremely small flaws.

- Only one surface needs to be accessible.- Greater accuracy than other nondestructive

methods in determining the depth of internal

flaws and the thickness of parts with parallel

surfaces.

- Some capability of estimating the size,orientation, shape and nature of defects.

- Non hazardous to operations

- Disadvantages

- Manual operation requires careful attention by

experienced technicians- Extensive technical knowledge is required for

the development of inspection procedures.

- Parts that are rough, irregular in shape, very

small or thin, or not homogeneous are difficult to

inspect.

- Couplants are needed to provide effective

transfer of soundwave between transducers and

parts being inspected unless a non-contact

technique is used.

- Inspected items must be water resistant, when

using water based couplants that do not contain

rust inhibitors.

RADIOGRAPHIC

INSPECTION

5) RADIOGRAPHIC INSPECTION

- is an NDT method used to evaluate objects and

components for signs of flaws which could interfere with

their function.

5) RADIOGRAPHIC INSPECTION

- It is accomplished with the use of radiographs, images

generated by bombarding the object under inspection

with radiation

Radiation Source

- X-Ray

Radiation Source

- Gamma Ray

a) Principle

- Radiation was produced by the X-Ray machine

What is X-Ray?

-is a form of electromagnetic radiation with

wavelengths shorter than visible light.

How is X-Ray produced?

- Xrays are generated by an X-ray tube, a vacuum

y g y y ,

tube that uses high voltage to accelerate the electrons

released by a hot cathode to a high velocity.

-The high velocity electrons collide with a metal target,

the anode, creating the X-rays.

a) Principle

- Since the amount of radiation emerging from the

opposite side of the material can be detected and

measured, variations in this amount (or intensity) of

radiation are used to determine thickness or

composition of material.

b) Materials & Equipment Used

- X-Ray Machine

b) Materials & Equipment Used (cont’d)

- Films

P i T k

- Processing Tanks

W i Si

- Warning Signs

- Dosimeters

- Survey Meter

I Q lit I di t (IQI)

- Image Quality Indicators (IQI)

c) Inspection

- Set-up of Film

- Set-up of X-Ray Tube

- Securing and clearing the Area before exposure

- Exposure of film

- Developing of film

- Evaluation of radiograph

-Radiographic images

- Advantages

- Technique is not limited by material type ordensity.-Can inspect assembled components.-Minimum surface preparation required.-Sensitive to changes in thickness, corrosion, voids,cracks, and material density changes.

-Detects both surface and subsurface defects.-Provides a permanent record of the inspection.

d) Advantages & Disadvantages (cont’d)

- Disadvantages

- Many safety precautions for the use of highintensity radiation.-Many hours of technician training prior to use.- Access to both sides of sample required.-Orientation of equipment and flaw can be critical.-Determining flaw depth is impossible without

additional angled exposures.-Expensive initial equipment cost.

VISUAL INSPECTION

6) VISUAL INSPECTION

- is a common method of quality control, data

acquisition, and data analysis. Visual Inspection, usedin maintenance of facilities, mean inspection of

equipment and structures using either or all of raw

human senses such as vision, hearing, touch and smell

and/or any non-specialized inspection equipment.

a) Materials & Equipment

- Magnifying Glass

a) Materials & Equipment (cont’d)

- Flashlight

a) Materials & Equipment (cont’d)

- Borescope / Videoscope

b) Inspection

- Borescope inspection on Engines

b) Inspection (cont’d)

- Borescope inspection on Engines

c) Advantages & Disadvantages

- Advantages

- The most accurate inspectors made the fewest eye

fixations and were the fastest.

- Disadvantages

- can’t detect very fine crack not visible to eye.- cannot detect discontinuity that are inaccessible.

Borescope Inspection of Compressor Turbine Blades – PT6 Engine

VII. Reporting & Recording of

Findings

1) Photos / Images

1) Photos / Images (cont’d)

2) Reporting

Thank You

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