Introduction to Nondestructive Testing

Nondestructive testing

(NDT) has been defined as comprising those test methods which are used to examine an object, material or system without impairing its future usefulness. -Determine the integrity of a material, component or structure- or Definition of NDT Quantitatively measure- some characteristic of an object.

Characteristics of NDT

• Tested parts are not damaged
• Various tests can be performed on the same product
• Does not affect the future usefulness – of the object or material.
• Can be performed on parts that are in service
• Low time consumption
• Low cost

Some Uses of NDE Methods

• Flaw Detection – and Evaluation
• Leak Detection • Dimensional Measurements
• Structure and Microstructure Characterization
• Estimation of Mechanical Properties
• Material Sorting and Chemical Composition Determination
• To verify proper assembly
• To inspect for in-service damage

When are NDE Methods Used?

• There are NDE application at almost any stage in the production or life cycle of a component.
• To ensure the quality right from raw material stage through fabrication and processing to preservice and in-service inspection.
• NDT finds extensive applications for condition monitoring, residual life assessment

Principle of NDT

• Energy source or medium used to probe the test object (such as X-rays in radiography)
• Nature of the signals or signature resulting from interaction with the test object (attenuation of X-rays)
• Means of detecting or sensing resulting signals (photo emulsion effect)
• Method of indicating or recording signals (radiographic film)

Most Common NDT Methods

1. Visual and optical  Testing (VT)
2.  Liquid Penetrant Testing (PT)
3.  Magnetic Particle Testing (MT)
4.  Ultrasonic Testing (UT)
5.  Eddy Current Testing / Electromagnetic Testing  (ET)
6.  Radiography Testing (RT)
7.  Acoustic emission Testing (AE)
8.  Leak Testing (LT)
9.  Neutron Radiographic testing (NR)
10. Vibration Analysis Testing (VA)
11. Infrared / Thermal Testing (IR)

Principle of NDT methods

1. Vibration Analysis Testing (VA)-One of the most interesting and useful applications of shearographic interferometry is the detection, visualisation and measurement of the mechanical vibration of opaque objects.
2. Visual and optical  testing (VT)- Used in maintenance of facilities, mean inspection of equipment and structures using either or all of raw human senses such as vision, hearing, touch and smell and/or any non-specialized inspection equipment.
3.  Leak Testing (LT)-A leak test procedure is a quality control step to assure a device integrity, and is one-time nondestructive test.
4. Acoustic emission Testing (AE)-Acoustic Emission analysis provides overall information on the physical condition and leakproofness of the tested object.
5. Infrared / Thermal Testing (IR)-Aims at the detection of subsurface features (i.e. subsurface defects, anomalies, etc.), owing to temperature differences (DT) observed on the investigated surface during monitoring by an infrared camera.
6.  Neutron Radiographic testing (NR)-  utilizes transmission of radiation to obtain visual information on the structure and/or inner processes of a given object.
7. Radiography  Testing (RT) -Attenuation of Electromagnetic Radiation
8. Ultrasonic Testing (UT) -Reflection, refraction, Diffraction, etc of high frequency sound wave.
9. Magnetic particle Testing (MT) -Leakage of magnetic flux due to any discontinuity.
10. Penetrant Testing (PT) -Capillary action  and blotting action of liquid penetrant.
11. Eddy current Testing (ET) -Disturbance of electromagnetic induction.

CLASSIFICATION

• Surface Methods: NDT methods which are suitable for the examination of surface only. –Visual Testing –Liquid Penetrant Testing
• Subsurface Methods: Suitable for detecting surface as well as subsurface discontinuities. –Magnetic Particle Testing –Eddy Current Testing
• Volumetric Methods: Suitable for the examination of whole volume of the object. –Ultrasonic Testing, – Radiography Testing –

Applications Inspection of Raw Products

• Forgings
• Castings Rolling etc.

Inspection Following Secondary Processing

• Machining
• Welding
• Grinding
• Heat treating
• Plating

Inspection For In-Service Damage

• Cracking
• Corrosion
• Erosion/Wear