Presentation onNon-Destructive Testing (NDT)

Mahar Nadir

Non-destructive testing is Defined as testing that causes no structurally significant damage to concreet. It is the testing of materials, for surface or internal flaws or metallurgical condition, without interfering in any way with the integrity of the material or its suitability for service.

Non-Destructive Testing (NDT)

i.e. Inspect or measure without doing harm.

MORE ABOUT NDT….!

For such tests separate specimen is not taken like cube test or cylinder test etc. So information collected by such test is related with original structure. Whereas other tests give the information about the specimen taken for the test.

1. NDT increases the safety and reliability of the product during operation.

2. It decreases the cost of the product by reducing scrap and conserving materials, labor and energy.

3. Does not permanently alter the article being inspected.4. Save both money and time in product evaluation,

troubleshooting and research.5. NDT is for both old and New Structures.6. NDT can be applied to both old and new structure.

Importance of NDT

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WHY NDT TESTS ARE CARRIED OUT??

These tests are more reliable.Quick assessment of the structure Time is not wasted on preparing the

test reportThese test give the exact information

about the structure.

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NDT is used to determine

NDT

Strength

Density

Modulus Of

Elasticity

Cracks and Voids

Reinforcement Location

Surface Hardness

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Methods of NDT

Visual Inspection

Liquid Penetrant

Magnetic Particle

Eddy Current Mathod

Ultrasonic

X-ray

Mathod

Microwave Mathod

Acoustic Emission Mathod

Thermography Mathod

Replication Mathod

Flux Leakage Mathod

Acoustic Microscopy Mathod

Magnetic Measurements Mathod

Tap Testing Mathod

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Six Most Common NDT Methods

• Ultrasonic Testing (UT) • Dye Penetrant Testing (DPT)• Magnetic Particle Testing (MPT)• Visual Testing (VT)• Eddy Current Testing (ECT)• Radiography Testing (RT)• Reboung Hammer Test

Ultrasonic Testing

This technique is used for the detection of internal surface (particularly distant surface) defects in sound conducting materials. In this method high frequency sound waves are introduced into a material and they are reflected back from surface and flaws. Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen showing the depth of features.

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Piezoelectric Transducer

Signal wire

Piezoelectric element

case

Test Techniques: Normal and Angle Beam

• In normal beam testing, the sound beam is introduced into the test article at 90 degree to the surface.

• In angle beam testing, the sound beam is introduced into the test article at some angles other than 90.

• The choice between normal and angle beam inspection usually depends on two considerations:

- The orientation of the feature of interest – the sound should be directed to produce the largest reflection from the feature.

- Obstructions on the surface of the part that must be worked around.

Advantages of Ultrasonic Testing

Thickness and lengths up to 30 ft can be tested. Position, size and type of defect can be determined. Instant test results. Portable. Capable of being fully automated. Access to only one side necessary.

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Limitations of Ultrasonic Testing

The operator can decide whether the test piece is defective or not while the test is in progress.

Considerable degree of skill necessary to obtain the fullest information from the test.

Very thin sections can prove difficult.

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Visual TestingVisual testing is the most basic and common inspection method involves in using of human eyes to look for defects. But now it is done by the use special tools such as video scopes, magnifying glasses, mirrors, or borescopes to gain access and more closely inspect the subject area.

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Visual Testing Equipments:

• Mirrors (especially small, angled mirrors), • Magnifying glasses, • Microscopes (optical and electron),• Borescopes and fiber optic borescopes,• Closed circuit television (CCTV) systems,• Videoscope.

Signs of Distress

• Cracks

• Pop-outs

• Spalling

Signs of Distress

• Dis-integration

• Color change

• Weathering

• Surface blemishes

• Lack of Uniformity

Visual Testing Equipments

Fig: Advanced VideoscopeFig: Videoscope

Fig: Magnifying glass

Fig: Borescopes

Fig. Microscope

10. REBOUND HAMMER TEST

Principle.

It consists essentially of a metal plunger, one end of which is held against the concrete surface while the free end is struck by a spring- loaded mass which rebounds to a point on a graduated scale. The point is indicated by an index rider. The amount of rebound increases with increase in concrete strength for a particular concrete mix.

10. REBOUND HAMMER TEST

Main applications.

It measures the surface hardness of concrete and provides an estimation of surface compressive strength, uniformity and quality of concrete.

Advantages.

It gives accurate assessment of the strength of the surface layer of material. The entire structure can be tested in its 'as-built' condition.

Procedure

Dye Penetrant Testing

This method is commonly used for detect the surface cracks or defects. Dye penetrant Testing (DPT) is one of the most widely used nondestructive Testing (NDT) methods. DPT can be used to inspect almost any material provided that its surface is not extremely rough.

Dye Penetrant Testing Process

Three liquids areused in this method.

1. Cleaner2. Penetrant3. Developer

Dye Penetrant Testing of a Boiler

At first the surface of the material that is to be tested is cleaned by a liquid. The liquid is called cleaner.

Dye Penetrant Testing of a Boiler

Then a liquid with high surface wetting characteristics is applied to the surface of the part and allowed time to seep into surface breaking defects. This liquid is called penetrant. After five or ten minutes the excess penetrant is removed from the surface.

Then another liquid is applied to pull the trapped penetrant out the defect and spread it on the surface where it can be seen. This liquid is called deveoper.

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Dye Penetrant Testing of a Boiler

Findings

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After Dye Penetrant Testing

there are two surface cracks are

Detected.

Two surface cracks

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Advantages of Dye Penetrant Testing

This method has high sensitivity to small surface discontinuities.

Large areas and large volumes of parts/materials can be inspected rapidly and at low cost.

Indications are produced directly on the surface of the part and constitute a visual representation of the flaw.

Aerosol spray can make penetrant materials very portable. Penetrant materials and associated equipments are relatively

inexpensive.

Limitations of Dye Penetrant Testing

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Only surface breaking defects can be detected. Precleaning is critical since contaminants can mask defects. The inspector must have direct access to the surface being

inspected. Surface finish and roughness can affect inspection sensitivity. Post cleaning of acceptable parts or materials is required. Chemical handling and proper disposal is required.

Magnetic Particle Testing

This method is suitable for the detection of surface and near surface discontinuities in magnetic material. Magnetic particle Testing (MPT) is a nondestructive testing method used for defect detection. MPT is fast and relatively easy to apply, and material surface preparation is not as critical as it is for some other NDT methods.

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In the first figure the magnetized metal has no crack and there only two poles that is north pole and south pole. And in second figure the magnetized metal has a crack and at the crack point there creates another north and south pole for the magnetic flux leakage.

SNS N

N S

Magnetic Flux Line

Fig.1: Magnetized Metal with no crack Fig.2: Magnetized Metal with crack

CrackMagnetic Flux Leakage

Basic Principle of MPT

It does not need very stringent pre-cleaning operation. It is the best method for the detection of surface and near to

the surface cracks in ferromagnetic materials. Fast and relatively simple NDT method. Generally inexpensive. Will work through thin coating. Highly portable NDT method. It is quicker.

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Advantages Magnetic Particle Testing

Limitations of Magnetic Particle Testing

Material must be ferromagnetic. Orientation and strength of magnetic field is critical. Detects surface and near-to-surface discontinuities only. Large currents sometimes require.

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Eddy Current Testing

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This method is widely used to detect surface flaws, to measure thin walls from one surface only, to measure thin coatings and in some applications to measure depth. This method is applicable to electrically conductive materials only. In this method eddy currents are produced in the product by bringing it close to an alternating current carrying coil. The main applications of the eddy current technique are for the detection of surface or subsurface flaws, conductivity measurement and coating thickness measurement.

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Application of ECT

Crack DetectionCorrosion MonitoringMaterial Thickness MeasurementsCoating Thickness MeasurementsConductivity Measurements

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Eddy Current Testing Equipments

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Advantages of Eddy Current Testing

Sensitive to small cracks and other defectsDetect surface and near surface defectsInspection gives immediate resultsEquipment is very portableMethod can be used for much more than flaw detectionInspects complex shapes and sizes of conductive materials

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Limitations of Eddy Current Testing

Only conductive materials can be inspected. Surface must be accessible to the probe.Skill and training required is more extensive than other techniques.Surface finish and roughness may interfere.Depth of penetration is limited.

Radiography Testing

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Radiography Testing (RT), or industrial radiography is a nondestructive testing (NDT) method of inspecting materials for hidden flaws by using the ability of short wavelength electromagnetic radiation (high energy photons) to penetrate various materials.  

Radiographic Testing Method is nothing but to take the shadow picture of an object onto a film by the passage of X-ray or Gamma ray through it. It is the same as the medical radiography (X-ray). Only difference in their wave length.

Radiography Testing Process

The principles are the same for both X and Gamma radiography. In X-radiography the penetrating power is determined by the number of volts applied to the X-Ray tube - in steel approximately 1000 volts per inch thickness is necessary. To produce an X or Gamma radiograph, the film package is placed close to the surface of the subject. The source of radiation is positioned on the other side of the subject some distance away, so that the radiation passes through the subject and on to the film.

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X-ray film

Top view of developed film

Electrons

-+

Radiation Penetrate the Sample

Radiography Testing Process

X-ray Generator or Radioactive Source Creates Radiation

Radioactive Source

Information is presented pictorially. A permanent record is provided which may be viewed at a time and place distant from the test.Useful for thin sections.Sensitivity declared on each film suitable for any material.

Advantages of Radiography Testing

Possible health hazard. Need to direct the beam accurately for two-dimensional

defects. Film processing and viewing facilities are necessary Not suitable for automation. Not suitable for surface defects.

Limitations of Radiography Testing

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