Importance of ndt

IMPORTANCE OF NDT IN DESIGNING OF ANY MINI OR

MEGA STRUCTURE

Muhammad Ans

Department of Mechenical Engineering

CIIT Sahiwal

G.T Road Sahiwal

Department of Mechanical Engineering

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Testing


Testing comprise all the techniques of materials or products under different types of loadings. This way, the reliability of product to end user is assured and the process of material selection is done with a lot of ease.

Testing can be classified in two main categories

depending upon destruction of products as • Destructive Testing• Non-Destructive Testing

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Destructive Testing


These comprises all those techniques which are highly regulated on some standard in which specimen is broken/destructed.

Major destructive testing used these days are

Tensile Testing Impact Testing Burst Testing Fatigue Testing Creep Testing

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NDT:


Non-destructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage.

Another terms for NDT is NDE

Highly valuable technique that can save both money and time in product evaluation.


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Why NDT IS USED:

Accident prevention and to reduce costs

To improve product reliability

To determine acceptance to a given requirement

To quick information on repair criteria.

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NDT METHODS:


Visual Inspection

Acoustic Emission

Eddy Current

Liquid Penetrant

X-Ray/ Radiography

Magnetic method


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Visual inspection

Visual and optical inspection (or testing) is still a basic method for many applications. Visual inspection involves using an inspector's eyes to look for defects. The inspector may also use special tools such as magnifying glasses, mirrors, or bore scopes to gain access and more closely inspect the subject area. Visual examiners follow procedures that range from simple to very complex.


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Acoustic Emission Analysis

Detection and analysis of AE signals can supply valuable information regarding the origin and importance of a discontinuity in a material.

It has many industrial applications

Assessing structural integrity (Welding)

Detecting flaws

Testing for leaks (Pressure Vessel)

Monitoring weld quality

Research tool.


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Eddy Current test

In a standard eddy current testing a circular coil carrying current is which generates eddy current then the presence of any flaws, will cause a change in eddy current and a corresponding change in the phase and amplitude of the measured current.

Applications: Surface Breaking Cracks SBC using Sliding Probes Tube Inspection Conductivity Heat Treat Verification


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Penetrant Techniques

In it the defects/cracks are studied using a penetrant/dye. 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


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X-Ray/Radiography

X-rays are just like any other kind of electromagnetic radiation. They can be produced in parcels of energy called photons, just like light.

These are used to produce images of objects using film or other detector that is sensitive to radiation. The test specimen in placed between the radiator source and detector. These are used where thickness of materials is to be measured; it confirms location of hidden parts in assembly.


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Magnetic Inspection

A magnetic field is established in a component made from ferromagnetic material. The magnetic lines of force travel through the material and exit and re-enter the material at the poles. Defects such as crack or voids cannot support as much flux, and force some of the flux outside of the part. Magnetic particles distributed over the component will be attracted to areas of flux leakage and produce a visible indication.

Applications:

To detect ferromagnetic materials.


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Applications:

Weld verification.

Structural mechanics.

Radiography in medicine.


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Weld verification:

In manufacturing, welds are commonly used to join two or more metal parts. Because these connections may encounter loads and fatigue during product lifetime, there is a chance that they may fail if not created to proper specification.

Welds may be tested using NDT techniques such as industrial radiography or industrial CT scanning using X-rays or gamma rays,ultrasonic testing, liquid penetrant testing, magnetic particle inspection or via eddy current.

In a proper weld, these tests would indicate a lack of cracks in the radiograph, show clear passage of sound through the weld and back, or indicate a clear surface without penetrant captured in cracks.


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Structural mechanics:

Structure can be complex systems that undergo different loads during their lifetime.

Engineers will commonly model these structures as coupled second-order systems, approximating dynamic structure components with springs, masses, and dampers.

In NDT, the structure undergoes a dynamic input, such as the tap of a hammer or a controlled impulse. Key properties, such as displacement or acceleration at different points of the structure, are measured as the corresponding output.


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Radiography in medicine:

The human body is difficult to model as a complete transfer function.

Bones or molecules, have a known response to certain radiographic inputs, such as x-rays or magnetic resonance.

Coupled with the controlled introduction of a known element, such as digested barium, radiography can be used to image parts or functions of the body by measuring and interpreting the response to the radiographic input. In this manner, many bone fractures and diseases may be detected and localized in preparation for treatment. X-rays may also be used to examine the interior of mechanical systems in manufacturing using NDT techniques, as well


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IMPORTANCE AND NEED OF NON-DESTRUCTIVE TESTING:

NDT plays a crucial role in everyday life and is necessary to assure safety and reliability. Typical examples are found in aircraft, spacecraft (shuttle), motor vehicles, pipelines, bridges, trains, power stations, refineries, buildings and oil platforms which are all inspected using NDT.

NDT is a Quality Assurance management tool which can give impressive results when used correctly. It requires an understanding of the various methods available, their capabilities and limitations, knowledge of the relevant standards and specifications for performing the tests.

Materials, products and equipment which fail to achieve their design requirements or projected life due to undetected defects may require expensive repair or early replacement. Such defects may also be the cause of unsafe conditions or catastrophic failure, as well as loss of revenue due to unplanned plant shutdown.