NON DESTRUCTIVE TESTS

By: Imtiaz Ali Shaikh (500410641)

To: Dr. Ravi Ravindran

February 29th 2012 ME8109 Course Project

Contents

� Introduction

� Purposes of Non-Destructive Testing

� Selection of the NDT Method

� Eddy Current Testing� Eddy Current Testing

� Liquid Penetrating Testing

� Magnetic Particle Testing

� Radiographic Testing

� Ultrasonic Testing

Introduction

� Non destructive examination is the testing of materials without destroying the integrity of the material.

� NDT techniques are used for testing materials � NDT techniques are used for testing materials 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 equipment during service

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 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

Selection of the NDT method

The selection of one method over another is based on the following factors:

� Type and origin of discontinuity�Material manufacturing processAccessibility of the component to perform NDT�Accessibility of the component to perform NDT

� Type of equipment available� Time available�Cost

1) Eddy Current Testing

� Eddy current testing has its origins with Michael Faraday’s discovery of electromagnetic induction.

� According to Faraday’s Law states when a magneticfield cuts a conductor or when a conductor cuts afield cuts a conductor or when a conductor cuts amagnetic field, an electric current will flow through theconductor.

� From Oersted’s discovery, a magnetic flux exists arounda coil carrying current proportional to the number ofturns in the coil and the current.

Principles

� The relative motion causes a circulating flow ofelectrons, 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�According to Lenz’ law, These circulating eddiesof 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 primarymagnetic 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.

� A crack in the test material

obstructs the eddy current

flow, lengthens the eddy

current path, reduces the

secondary magnetic field, and

increases the coil impedance.

�If a test coil is moved over a

test piece at constant rate oftest piece at constant rate of

speed, a momentary change

will occur in the coil reactance

and coil current. This change

can be detected, amplified,

and displayed by an eddy

current detector.

Important points

�ECT is primarily used for testing nonferromagnetic conducting materials. However,with modification, it can also be used fortesting ferromagnetic materials.

�Cracks lying parallel to the current path will�Cracks lying parallel to the current path willnot cause any significant interruption and maynot be detected crack.

�ECT is very important because often thedefects that we are looking for not visiblebecause paint or some other coating maycover them. There might also be defects thatare so small they cannot be seen with our eyesor any other visual method of inspection.

2) Liquid Penetrating Testing

Liquid penetrating testing detects the flaws that are open to the surface and is a type of visual inspection.

� This method is based upon the principle of capillaryThis method is based upon the principle of capillaryaction.

� Penetrants are of two types, fluorescent or nonfluorescent (visible).

� Several developer types are available, including:non-aqueous wet developer, dry powder, watersuspendible, and water soluble.

Essential steps

There are four essential steps requiredfor this test

1) 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).

�After excess penetrant has been

removed a white developer is

applied to the sample.

�The developer draws penetrant

from defects out onto the surface

to form a visible indication. Any

coloured stains indicate the

positions and types of defects onpositions and types of defects on

the surface under inspection.

�Visible penetrants are typically

red in color. Fluorescent penetrants

contain two or more dyes that

fluorescence when excited by

ultraviolet radiation.

3) Magnetic Particle Testing

� This method detects flaws that are either surface orsubsurface

� This can be considered as a combination of two non-destructive testing methods: magnetic flux leakagetesting and visual testing.testing and visual testing.

� A magnetic flux is send through the material, at thelocation of the imperfection a leakage field isformed. This attracts metal iron dust, which issprayed onto the surface.

Principles

�A magnetic flux is send through the material byenergising 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 is�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.

4) Radiographic Testing

� Radiography testing detects flaws that are internal or on the inside surface.

� Penetrating radiation can be x-rays or gamma rays.

� In the presence of flaws, there will be a differential

absorption of penetrating radiation.absorption of penetrating radiation.

� The unabsorbed radiation passes through the test component and exposes a film.

� The basic principle of radiographic inspection of welds is the same as that for medical radiography.

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

� Therefore only suitably trained and qualified personnel should practice this type of testing.

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.

As the test object's sound velocity is known,� As the test object's sound velocity is known,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 ofapplication for material testing with Ultrasonic's isthe Pulse Echo Method.

� Sound reflections in the audio range are calledechoes

�The electrical transmission pulse

triggers the sound pulse at the probe

crystal. At the same time this voltage

pulse is feed to the input of the amplifier

so that the high voltage causes a vertical

deflection of the display sweep, this is

called the initial pulse.

�The speed of the pulse is dependent�The speed of the pulse is dependent

on the material of the test object (sound

velocity = material constant).

�The speed of the display sweep can be

exactly matched to the sound velocity. In

our example the electron beam reaches

scale division 4 while the pulse is at the

opposing side of the test object.

�The part of the sound pulse,

which is transmitted through the

couplant and into the probe,

generates a small electrical

reception signal at the crystal

which, via the amplifier, causes

vertical deflection of the beamvertical deflection of the beam

spot, this is the back wall echo.

� Intermediate echo is caused by

partial reflection of the sound

wave on a discontinuity between

the initial and the back wall echo.

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) dothe 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.

References

� [1] Power Engineering Reference material, Third class, Southern Alberta Institute 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 Alberta Institute 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

� [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

� [9] J. H. LAMBLE Principles and Practice of Non-destructive Testing, HEYWOOD & � [9] J. H. LAMBLE Principles and Practice of Non-destructive Testing, HEYWOOD & 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

THANK YOUTHANK YOU