NON DESTRUCTIVE TEST

wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage

does not permanently alter the article being inspected, it is a highly valuable technique that can save both money and time in product evaluation, troubleshooting, and research

the common method in non destructive test is :- - DYE PENETRANT METHOD - MAGNETIC PARTICLE METHOD - ULTRASONIC METHOD - RADIOGRAPHIC METHOD

DYE PENETRANT TEST is a widely applied and low-cost inspection method used to locate surface-

breaking defects in all non-porous materials (metals, plastics, or ceramics ) used to detect casting, forging and welding surface defects such as

hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components

DPI is based upon capillary action, where low surface tension fluid penetrates into clean and dry surface-breaking discontinuities

Penetrant may be applied to the test component by dipping, spraying, or brushing

After adequate penetration time has been allowed, the excess penetrant is removed and a developer is applied. The developer helps to draw penetrant out of the flaw so that an invisible indication becomes visible to the inspector

Inspection is performed under ultraviolet or white light, depending on the type of dye used

STAGES OF DYE PENETRANT METHOD

MAGNETIC PARTICLE TEST process for detecting surface and slightly subsurface discontinuities in

ferromagnetic materials such as iron nickel, cobalt, and some of their alloys

The piece can be magnetized by direct or indirect magnetization The presence of a surface or subsurface discontinuity in the material

allows the magnetic flux to leak, since air cannot support as much magnetic field per unit volume as metals

If an area of flux leakage is present, the particles will be attracted to this area. The particles will build up at the area of leakage and form what is known as an indication. The indication can then be evaluated to determine what it is, what may have caused it, and what action should be taken

There are two types of magnetic field :- - longitudinal magnetic field - circular magnetic field

LONGITUDINAL MAGNETIC FIELD A longitudinal magnetic field is usually established by placing the part

near the inside. This produces magnetic lines of force that are parallel to the long axis of the test part.

Permanent magnets and electromagnetic yokes are also often used to produce a longitudinal magnetic field. The magnetic lines of force run from one pole to the other, and the poles are positioned such that any flaws present run normal to these lines of force.

CIRCULAR MAGNETIC FIELD Circular magnetic fields are produced by passing current through the

part or by placing the part in a strong circular magnet field.

Clamping the component between two electrical contacts in a special piece of equipment. Current is passed through the component and a circular magnetic field is established in and around the component. When the magnetizing current is stopped, a residual magnetic field will remain within the component. The strength of the induced magnetic field is proportional to the amount of current passed through the component.

Magnetic Field

ElectricCurrent

ULTRASONIC TEST It based on the propagation of ultrasonic waves in the object or material

tested. Very short ultrasonic pulse-waves with center frequencies ranging from

0.1- 15 MHz, and occasionally up to 50 MHz, are transmitted into materials to detect internal flaws or to characterize materials .

Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on concrete, wood and composites, albeit with less resolution.

HOW ULTRASONIC TEST WORK ultrasound transducer connected to a diagnostic machine is passed over the

object being inspected. The transducer is typically separated from the test object by a couplant (such as

oil) or by water, as in immersion testing. In reflection (or pulse-echo) mode, the transducer performs both the sending and

the receiving of the pulsed waves as the "sound" is reflected back to the device. Reflected ultrasound comes from an interface, such as the back wall of the object

or from an imperfection within the object. The diagnostic machine displays these results in the form of a signal with an

amplitude representing the intensity of the reflection and the distance, representing the arrival time of the reflection

RADIOGRAPHIC TEST

In radiographic testing, the part to be inspected is placed between the radiation source and a piece of radiation sensitive film. The radiation source can either be an Xray machine or a radioactive source (Ir-192, Co-60, or in rare cases Cs-137). The part will stop some of the radiation where thicker and more dense areas will stop more of the radiation. The radiation that passes through the part will expose the film and forms a shadowgraph of the part. The film darkness (density) will vary with the amount of radiation reaching the film through the test object where darker areas indicate more exposure (higher radiation intensity) and liter areas indicate less exposure (higher radiation intensity). This variation in the image darkness can be used to determine thickness or composition of material and would also reveal the presence of any flaws or discontinuities inside the material.

BENEFITS OF RADIAGRAPHIC TEST• Can inspect assembled components• Minimum surface preparation required• Detects both surface and subsurface defects• Provides a permanent record of the inspection• Verify internal flaws on complex structures• Isolate and inspect internal components• Automatically detect and measure internal flaws• Measure dimensions and angles within the sample without sectioning• Sensitive to changes in thickness, corrosion, flaws and material density

changes