Soalan Exam

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CHAPTER 1 : INTRODUCTION TO NON- DESTRUCTIVE TESTING TECHNIQUE. DEFINITION Non- destructive testing (NDT) is the testing of material to detect internal and surface defects or discontinuities using methods that do not damage or destroy the material under test. There are three important elements in this definition namely.  Defects or discontinuities  Methods  Materials These elements will be discussed separately in the next following chapters. REASON FOR APPLYING NDT Generally NDT is employed in various industries for the following reasons.  To prevent accidents and save human lives  To improve product realibility  To give profil to the user by:    

Ensuring customer satisfaction Helping in better product design Lowering manufacturing processes Maintaining a uniform quality level.

NDT METHODS There are five major NDT methods namely:    

Radiography testing (RT) Magnetic particle testing (MT) Liquid penetrant testing (PT) Eddy current testing (ET)

Other NDT methods;    

Visual testing Leak Testing Strain gauging Acoustic emission , etc

Each non-destructive test is designed to provide visual evidence of discontinuities in parts,which are not normally visible to the unaided eye.The visual evidence left by each method is called an indication.The indication may be the penetrant appears on the surface after applying the developer as in liquid penetrant testing.It is the accumulation of penetrant at certain place that we see and not the crack.Other indication may be an accumulation of magnetic particles as in magnetic particles testing or in the form of a cathode ray tube reading for ultrasonic testing. Homever there is no single NDT method capable of detecting all type of discontinuities.Thus it is not guite right to say that one NDT method is better than the other.In conclusion it may be said that each of the NDT methods is better than the other.In conclusion it may be said that each of the NDT methods are complimentary the others.

The principle of five major NDT methods, their application and limition are summarized as follows:Radiography Principle of Opearion Using electromagnetic radiation to penetrate through materials. Discontinuties is recorded on film. Aplication Application to almost all metals and non-metals Capable of detecting (and subsequently on the film) surface and internal discontinuities. Limitations  High capital and running cost  Require source of electricity (in the case of X-ray)  Trained and skill operators are necessary  Pose potential radiation hazard  Not sensitive to planner defects. Radiographic Testing (RT)

Fig : Basic Radiography Arrangement

Ultrasonic Testing (UT) Principle of Operation Using high frequency sound to penetrate through materials. Signal due to discontinuities is presented on cathode ray tube screen (CRT) Application  Applicarion to almost all metals and non metals  Capable of detecting surface and internal discontinuties.  Automatic inspection and new computerized image processing allows signal to be permanently recorded on paper.  Measure thickness  Material characterization . Limitations.  Relatively high capital cost.  Arequires highly trained and experieuced operator  Interpretation of results can be extremely difficult.  Not sensitive to defects parallel to the beam direction. Magnetic Particle Testing (MT)  Principle of Operation  Using magnetic of current flow to produce magnetic field in the materials  The pattern of field distribution provides indication of the existence of discontinuities. Application  Application to ferromagnetic materials  Capables of detecting surface and sub – surface discontinuties.  Easily operated portable equipment makes it suitable for field inspection Limitations  Not applicable to non-ferromagnetic materials  Requires a source of electricity  Magnetization in teo perpendicular directions is necessary.  Inspected object have to be demagnetized.

Figure : Basic Ultrasonic Testing.

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