Non Destructive Tests-Imtiaz Ali Shaikh

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NON DESTRUCTIVE TESTS

By: Imtiaz Ali Shaikh (500410641)

To: Dr. Ravi Ravindran

February 29th 2012 ME8109 Course Project


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Contents

Introduction

Purposes of Non-Destructive Testing

Selection of the NDT Method

y urren es ng Liquid Penetrating Testing

Magnetic Particle Testing

Radiographic Testing

Ultrasonic Testing


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Introduction

Non destructive examination is the testing of

materials without destroying the integrity of the

material.

mainly for three types of defects

1)Inherent defects which are created during the initial

production of the material.

2)Processing defects which are created during the

processing/manufacturing of the equipment

3)Service defects which are created in the equipmentduring service


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Purposes of Non-destructive testing

Modern Non-destructive tests are used by

manufacturers To avoid failures, prevent accidents and save

human life

To make a profit for the user To ensure customer satisfaction and maintain

the manufacturer's reputation

To aid in better product design To control manufacturing processes


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Selection of the NDT method

The selection of one method over another is

based on the following factors: Type and origin of discontinuityMaterial manufacturing process

Accessibility of the component to perform NDT Type of equipment available Time availableCost


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1) Eddy Current Testing

Eddy current testing has its origins with Michael

Faradays discovery of electromagnetic induction. According to Faradays Law states when a magnetic

field cuts a conductor or when a conductor cuts a

magnetic field, an electric current will flow through theconductor.

From Oersteds discovery, a magnetic flux exists around

a coil carrying current proportional to the number ofturns in the coil and the current.


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Principles

The relative motion causes a circulating flow of

electrons, or current, within the conductorAccording to French physicist Leon, Eddy currentis caused when a moving (or changing) magneticfield intersects a conductor, or vice-versa.

According to Lenz law, These circulating eddies

of current create electromagnets with magneticfields that oppose the effect of the appliedmagnetic field .

This opposing magnetic field, coming from thematerial, has a weakening effect on the primary

magnetic field and the test can sense this change. In effect, the impedance of the test coil isreduced proportionally as eddy currents areincreased in the test piece.


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Important points

ECT is primarily used for testing non

ferromagnetic conducting materials. However,with modification, it can also be used for

testing ferromagnetic materials.

Cracks l in arallel to the current ath will

not cause any significant interruption and maynot be detected crack.

ECT is very important because often the

defects that we are looking for not visible

because paint or some other coating maycover them. There might also be defects that

are so small they cannot be seen with our eyes

or any other visual method of inspection.


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2) Liquid Penetrating Testing

Liquid penetrating testing detects the flaws that are

open to the surface and is a type of visualinspection.

This method is based upon the principle of capillary

action. Penetrants are of two types, fluorescent or non

fluorescent (visible).

Several developer types are available, including:non-aqueous wet developer, dry powder, water

suspendible, and water soluble.


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Essential steps

There are four essential steps required

for this test1) Selection of material with a surface-breaking crack that is not visible to thenaked eye.

2) Penetrant application

3) Excess penetrant removal

4) Developer application

Inspection is performed underultraviolet or white light, dependingupon the type of dye used - fluorescentor non fluorescent (visible).


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3) Magnetic Particle Testing

This method detects flaws that are either surface or

subsurface This can be considered as a combination of two non-

destructive testing methods: magnetic flux leakage

testing and visual testing. A magnetic flux is send through the material, at the

location of the imperfection a leakage field is

formed. This attracts metal iron dust, which issprayed onto the surface.


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Principles

A magnetic flux is send through the material by

energising coils. At the location of thediscontinuities a leakage field is formed.

The leakage is a function of the orientation of thediscontinuities to the magnetic field(flex lines).

The leakage is greatest when the discontinuity isperpendicular to the magnetic field.

When the leakage of the magnetic field is greatenough, a pair of magnetic poles is established atthe discontinuity.

B y applying magnetic particles, the particlesare attracted to the poles and will gather at thediscontinuity, indicating a surface or sub-surfaceflaw.


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4) Radiographic Testing

Radiography testing detects flaws that are internal or on the insidesurface.

Penetrating radiation can be x-rays or gamma rays.

In the presence of flaws, there will be a differential

absor tion of enetratin radiation.

The unabsorbed radiation passes through the test component andexposes a film.

The basic principle of radiographic inspection of welds is the same asthat for medical radiography.

The most disadvantage of the use of RT is the possible hazards dueto exposure to radiation if proper care is not taken.

Therefore only suitably trained and qualified personnel shouldpractice this type of testing.


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5) Ultrasonic Testing

Ultrasonic testing uses high frequency sound wavesto find hidden internal flaws.

UT is the only practical method having widespreaduse in underwater inspection applications forlocating and sizing subsurface defects incomponents.

s t e test o ect s soun ve oc ty s nown,therefore it is possible to determine the distance ofthe reflector using simple calculation and thus itsexact position in the test object as shown in figure.

The name of the method used in most areas of

application for material testing with Ultrasonic's isthe Pulse Echo Method.

Sound reflections in the audio range are calledechoes


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Conclusions

It is very difficult to weld or mould a solid object that has no riskof breaking in service, so testing at manufacture and during useis often essential.

During the process of casting a metal object, for example, themetal may shrink as it cools, and crack or introduce voids insidethe structure. Even the best welders (and welding machines) donot make 100% perfect welds. Some typical weld defects thatneed to be found and repaired are lack of fusion of the weldto the metal and porous bubbles inside the weld, both of whichcould cause a structure to break or a pipeline to rupture.

During their service lives, many industrial components needregular non-destructive tests to detect damage that may bedifficult or expensive to find by everyday methods.


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References

[1] Power Engineering Reference material, Third class, Southern AlbertaInstitute of Technology, Calgary.

[2] Baldev Raj T. Jayakumar M. Thavasimuthu, Second Edition Practical Non-

destructive Testing Narosa Publishing House New Delhi

[3] Power Engineering Reference material, Second class, Southern AlbertaInstitute of Technology, Calgary.

[4] R Halmshaw, Non-destructive Testing, 2nd ed ., Edward Arnold, Division

of Hodder and Sloughton, London, 1991.

[5] Anonymous. PR Newswire. New York: Feb 7, 2008 [6] joe.buckley.net/papers/eddyc.pdf


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[7] PAUL E. MIX Introduction to Non-destructive Testing A Training Guide, 2nd Edition

A JOHN

WILEY & SONS, INC., PUBLICATION

[8] International ATOMIC ENERGY AGENCY, a Non-destructive Testing in Nuclear

Technology

. . - ,

COMPANY LTD [10] C.A HOGARTH, Ph.D and j.Blitz, M.Sc, Technique of Non-destructive Testing

[11] Composite.about.com/library/glossary/r/bldef-r4410.htm

[12] PJ Mudge, Practical aspects of NDT reliability in non-destructive testing, Vol. 2,

Pergamon Press, England, 1988


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Non Destructive Tests-Imtiaz Ali Shaikh

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