Introduction to Non Destructive Testing

Introduction to Non Destructive Testing

NDT 

Ability to detect the condition of the object without destroying the functionality of the object

BASIC METHODS 

Visual Inspec Inspection tion - VT

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Penetr Pen etrant ant Test Testing ing - PT

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Magnetic Magne tic Particle Particle Testin estingg- MT

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Ultrasonic Ultra sonic Testin esting g - UT

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Radiographi Radio graphicc Testin Testing g - RT

Visual Inspection 

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Inspection object surface visually is called Visual Inspection May or may not use accessories Gauges for identifying the dimensions of surface Magnifying glasses Borescope for internal inspection Thermal chalks, Thermocouple, for the temperature measurement Etching for checking surface condition

Etching 

for identification of gross metallurgical metallurg ical discontinuity such as in welds.

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For detecting the surface opening –  opening  – Fore Fore runner to Penetrantt Testing Penetran Testing

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Different Etchants available for different metals

 Advantages & Disadvantages Advantages 

Simple

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Less training required

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Relatively less costly equipment

Disadvantages 

Slow

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Inspector Fatigue is more

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Surrounding environmental factors are important

Penetrant Inspection 

Is a method that reveals discontinuities open to surface by the seepage of a liquid penetrant medium into a surface open discontinuity which seeps out after removing the excess penetrant revealing the discontinuity

Stages of Penetrant Testing 

Pre cleaning

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Application of penetrant

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Dwell Time

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Cleaning of Excess  penetrant

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Application of Developer 

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Inspection

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Post Cleaning

DYE SYSTEMS

SOLVENT REMOVABLE DYE

DYE SYSTEMS

WATER WASHABLE DYE

POST EMULSIFICATION DYE

PT Indications

Penetrant Testing Advantages 

Simple method

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Easy to train personnel

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Cheap

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Quick 

Disadvantages 

Only open defects can be detected

Magnetic Particle Testing 

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When a ferromagnetic material is magnetised the flux lines flow inside the component When there is a discontinuity in the material there is flux leakage The leaking flux attracts a magnetic medium resulting in an indication.

Types of magnetisation 

Longitudinal Magnetisation

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Circular Magnetisation

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AC Magnetisation

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DC Magnetisation

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HWDC magnetisation

Magnetic Particle Testing COIL METHOD

YOKE METHOD.

Types of Magnetisation Circular Magnetisation

HEAD SHOT METHOD

PROD METHOD

CENTRAL CONDUCTOR 

Magnetic Particle Testing

PROD METHOD

MAGNETIC MEDIUM 

Dry

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Wet

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Fluorescent  –  Requires Ultra violet lamp in darkened area  –  More sensitive than

 Non – Fluorescent

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Magnetic Medium - Dry 

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Dry Medium

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Medium about 30 – 50 microns Mixture of spherical and elongated powders Spherical shape helps in mobility Elongated shape helps in alignment to magnetic field

MAGNETIC MEDIUM - WET 

Oxides of iron used in suspension with water, kerosene, petroleum oil.

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Size : 20- 30 microns

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More sensitive than dry medium

Demagnetisation Residual magnetism affects further operation such as welding.  Demagnetisation is  preferably done with AC  Object is moved slowly away from coil  After demagnetisation residual magnetism is checked with gauss meters 

Magnetic Particle Testing 

Pre - Cleaning

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Magnetisation

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Applying magnetic medium

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Inspection

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Post cleaning

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Demagnetization

Magnetisation Magnetisation to be applied in two mutually perpendicular direction  Magnetic medium to applied when the magnetisation is ‘ON’  Adequacy of field to be checked by field indicator ( Pie Gage )  Magnetic medium could be wet or dry / Fluorescent or non-fluorescent 

 Advantages & Disadvantages Advantages  For detecting surface & sub-surface discontinuity  Can be tested rapidly   Not very costly  Relatively less skill required for testing Disadvantages  Only useful in ferro-magnetic materials  Demagnetisation may be required for many of the  parts

Ultrasonic Testing 

A beam of high frequency wave is introduced into the test object which gets reflected from the surface of any discontinuity

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Used to detect and locate the surface and internal discontinuities

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Amplitude of a reflected sound pulse is nearly  proportional to the size of the reflector

Ultrasonic Testing 

For Detecting internal flaws

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For almost all the materials –  metals, ceramic, rubber, composites etc..

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Requires only one side access

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Portable equipment

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 Non hazardous

Can test up to about 10 m of steel

Ultrasonic Testing 

ULTRASONIC TESTING

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PULSE ECHO TECHNIQUE Transducer acts as a pulser and receiver  Can detect the location and depth of defect Only one side access is required

ULTRASONIC TESTING THROUGH TRANSMISSION TECHNIQUE  –

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Separate transmitter  and receiver   Accurate Alignement of  transmitter  and receiver required Cannot locate the depth of defect

PROBES

NORMAL BEAM PROBE

DUAL CRYSTAL PROBE

Test Procedure     

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Scanning patterns

Calculate scanning zones Calibrate unit Draw DAC Scan When indications observed - check the height of signal, location Calculate location and size of discontinuity

Location of defects BP : Beam Path Depth of defect : BP

D = BP Cos α Position of defect P = BP Sin α

IE

DEFECT ECHO

Radiography Testing 

Employs x rays or gamma rays to penetrate an object, detect discontinuities by recording the difference on a recording device

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For internal flaws

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Permanent record

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Radiation Safety is a major concern

Basic Principle 

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X ray machines or Ir 192 or Co 60 main sources of radiation Hole type or Wire type  penetrameters used for checking sensitivity of radiograph

Source

Radiation

Radiography 

Uses Penetrameters for ensuring the quality of the radiography procedure

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Penetrameters are hole type and wire type

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Sufficient radiographic density is required for the radiograph for proper evaluation

Techniques

Double wall Single image

Single Wall Single Image Job

Film

Weld

Source

Radiation

Techniques

Panoramic Exposure

Double Wall Double Image

Job

Film

Weld

Source

Radiation

DOUBLE WALL DOUBLE IMAGE ASTM Hole Type Penetrameter

SINGLE WALL SINGLE IMAGE

DIN Wire Type Penetrameter Tungsten Tungsten Inclusion Inclusion

Porosity

Porosity

Slag Inclusion

POROSITY