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Does not permanently alter the article being inspected

Save both money and time in product evaluation,

troubleshooting and research

Can be used to detect flaws in an in-process machine

part


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NDT methods rely upon use of electromagnetic

radiation, sound, and inherent properties of materials

(such as thermal, chemical, magnetic etc.) to examine

samples.


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Ultrasonic Testing

Magnetic particle inspection

Dye penetrant inspection/Liquid penetrant inspection

Radiographic testing

Eddy-current testing


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Aerospace engineering

Mechanical engineering

Electrical engineering

Civil engineering

Systems engineering

Medicines


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Very short ultrasonic pulse-waves are launched into

materials to detect internal flaws.

Used for steel and other metals and alloys, can also be

used on concrete, wood and composites (with less

resolution).

Used in many industries including aerospace,

automotive and other transportation sectors.


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Two methods of receiving the ultrasound waveform:

Reflection

Through Transmission


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Principle:

LEFT: 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.

RIGHT: A defect creates a third indication and simultaneously reduces the amplitude of the

back wall indication. The depth of the defect is determined by the ratio D/Ep.


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Part is magnetized.

Presence of a surface or subsurface discontinuity in the

material allows the magnetic flux to leak, since air cannotsupport as much magnetic field per unit volume as metals.

Ferrous iron particles are then applied to the part.

Particles will build up at the area of leakage and form what

is known as an indication.


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Penetrant may be applied to the test component by

dipping, spraying, or brushing

After adequate penetration time, the excess penetrantis removed, a developer is applied.

Developer helps to draw penetrant out of the flaw

where an invisible indication becomes visible to the

inspector


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1. Section of material with

a surface-breaking crack

that is not visible to thenaked eye.

2. Penetrant is applied to

the surface.3. Excess penetrant is

removed.

4. Developer is applied,rendering the crack

visible.


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Short wavelength electromagnetic radiation (high

energy photons) to penetrate various materials.

The amount of radiation emerging from the opposite

side of the material can be detected and measured


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Tube exhibiting no cracking Tube exhibiting light cracking

Tube exhibiting moderate cracking Tube exhibiting severe cracking


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Uses electromagnetic induction to detect flaws inconductive materials.


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Variations in the phase and magnitude of these eddy

currents can be monitored using a second 'receiver' coil, or

by measuring changes to the current flowing in the

primary 'excitation' coil.

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 a corresponding

change in the phase and amplitude of the measured

current.


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NDT Technique Nature of defect

Ultrasonic Testing Sub-surface, interstitial

Magnetic Particle Inspection Surface and slightly subsurface discontinuities

in ferroelectric materials

Dye Penetrant Inspection Surface-breaking defects in all non-porous

materials

Radiographic Testing Surface, Sub-surface defects

Eddy-Current Testing Surface, Sub-surface defects (depending on

conductivity)


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A process plant contained two stainless steel vesselswhich had been operating for 21 years. The contents ofthe vessels were flammable, mildly toxic andcontained 500 ppm of chlorides. The vessels wereoperated from full vacuum up to 15 psi for 20 cycles perday. They contained an agitator which was used in partof the process. Both vessels had been hydraulicallytested to 70 psi when new but had not been subjectedto a test since


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Company thought that stainless steel would not break.

Hence, no leak detection equipment had beeninstalled and reliance was placed on plant operatorsnoticing the smell or observing drips.

A competent Person from a large insurance companyprescribed external visual examination supplementedby a hammer test every 2 years.

Was this suitable?


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The combination of stainless steel and chloridesimmediately raises concerns regarding the possibilityof stress corrosion cracking. While the cracks werelikely to initiate on the inner surface, an external

examination could detect the presence of through wallcracks only. However, stress corrosion cracks can bevery tight and difficult to see with the naked eye. Thehammer test offers no benefit - who knows what a

good vessel should sound like!


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During a thorough examination, it was found thatvessel developed leaks at 40 psi. Further investigationof the vessel found thousands of through wall cracks.The vessel had not leaked in service because thecontents were too viscous to pass through the tightstress corrosion cracks.

Finally it was decided to go for NDT with DyePenetrant Inspection using fluorescent dyes, which

give a higher sensitivity and much better results in theconfined, dark space of the vessel.


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NDT techniques provide cost-effective and reliable analysis

under realistic conditions.

Each NDT technique has certain capabilities and

limitations and often more than one technique is used to

cover various parts.

Increasing availability of robotic scanners improve the

speed of testing large surfaces, hence minimizing the

testing time.


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THE IMPORTANCE OF WELDING QUALITY CONTROL,K.M. WONG& Scarlett YEUNG,A.E.S. Destructive & Non-Destructive Testing Ltd

http://www.hse.gov.uk/comah/sragtech/techmeasndt.htm#CaseStudie

s

http://en.wikipedia.org/wiki/Nondestructive_testing#Methods_and_techniques

http://testex-ndt.com/from-the-field/corrosion-detected-in-pipelines-using-lfet/


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