Monday, March 23, 2015

Non Destructive Testing (NDT)Cousre for Mechanical Diploma/ITI Students..

25 days Non Destructive Testing and Quality Control training program as per institute  module. They are also providing corporate training based on customer needs. They will  provides the right combination of classroom and laboratory NDT training to support industry standards for Level I Level II qualifications according to the guidance of SNT-TC-1A, in accordance with American Society for Nondestructive Testing (ASNT). 
Non-destructive testing is the branch of engineering concerned with all methods of detecting and evaluating flaws in materials. Flaws can affect the serviceability of the material or structure, so NDT is important in guaranteeing safe operation as well as in quality control and assessing plant life. The flaws may be cracks or inclusions in welds and castings, or variations in structural properties which can lead to loss of strength or failure in service.

Non-destructive testing is used for in-service inspection and for condition monitoring of operating plant. It is also used for measurement of components and spacings and for the measurement of physical properties such as hardness and internal stress.
The essential feature of NDT is that the test process itself produces no deleterious effects on the material or structure under test.
The subject of NDT has no clearly defined boundaries; it ranges from simple techniques such as visual examination of surfaces, through the well-established methods of radiography, ultrasonic testing, magnetic particle crack detection, to new and very specialised methods such as the measurement of Barkhausen noise and positron annihilation.
NDT methods can be adapted to automated production processes as well as to the inspection of localised problem areas.
1. Ultrasonic Testing 
It is a non-destructive testing (NDT) method in which beams of high frequency sound waves that are introduced into the material being tested are used to detect surface and sub-surface flaws. The sound waves travel through the materials with some attenuation of energy and are reflected at interfaces. The reflected beam is detected and analyzed to define the presence and location of flaws.
Ultrasonic waves are almost completely reflected at metal gas interfaces. Partial reflection occurs at metal liquid or metal solid interfaces, with the specific percentage of reflected energy depending mainly on the ratios of certain properties of the matter on opposite sides of the interface.
Cracks, laminations, shrinkage, cavities, bursts, flakes, pores, bonding faults and other discontinuities that can act as metal-gas interfaces can be easily detected. Inclusions and other inhomogeneities in the metal being inspected can also detected by causing partial reflection or scattering of the ultrasonic waves, or by producing some other detectable effect on the ultrasonic waves.
Most of the ultrasonic inspection instruments detect flaws by monitoring one or more of the following: Reflection of energy from metal-gas interfaces, metal-liquid interfaces or discontinuities within the metal itself
Time of transit of a sound wave through the test piece from the entrance point at the sending (transmitting) transducer to the exit point at the receiving transducer, and Attenuation of the beam of sound waves by absorption and scattering within the test piece.
Ultrasonic methods
Ultrasonic methods of NDT use beams of mechanical waves (vibrations) of short wavelength and high-frequency, transmitted from a small probe and detected by the same or other probes. Such mechanical waves can travel large distances in fine-grain metal, in the form of a divergent wave with progressive attenuation.
The frequency is in the range 0.1 to 20 MHz and the wavelength in the range 1 to 10 mm. The velocity depends on the material and is in the range 1000-6000 m/s.
The technique detects internal, hidden discontinuities that may be deep below the surface. Transducers and coupling wedges are available to generate waves of several types, including longitudinal, shear and surface waves. Applications range from thickness measurements of thin steel plate to internal testing of large turbine rotors.
Most non-porous, resilient materials used for structural purposes (steel, aluminium, titanium, magnesium and ceramics) can be penetrated. Even large cross-sections can be tested successfully for minute discontinuities.
Ultrasonic testing techniques are widely accepted for quality control and materials testing in many industries, including electric power generation, production of steel, aluminium and titanium, in the fabrication of airframes, jet engine manufacture and ship building.
Ultrasonic advanced methods (TOFD, phased array etc)
There have been many developments and refinements to the fundamental ultrasonic technique to cater for improved performance and/or results.
For example, AUT refers to Automated Ultrasonic Testing. Although this is a generic term which relates to the computerised collection of ultrasonic data, the three letter acronym AUT is now used to refer specifically to the automated ultrasonic inspection of pipe girth welds. Such systems have two sets of ultrasonic probes scanned circumferentially on either side of the weld. The sets of probes are selected to provide coverage of specific zones of the weld and the fusion face.
Time-of-Flight Diffraction – TOFD – is an ultrasonic technique which measures the time of flight of a pulse as it travels from a transmitting probe to a receiving probe. Divergent beams are used and it is necessary to scan the TOFD probe pair over the flaw for the technique to function correctly.
What distinguishes the technique from a standard pitch-catch configuration is the D which stands for diffraction. The technique relies on the detection of the diffracted sound wave which is generated from both the top and bottom edges of a planar defect.
The time of arrival of the diffracted signals from the flaw tips is measured with respect to the probe firing time. Time measurement can be done to great accuracy. The combination of this accuracy and the fact that the scattering source is the flaw tip forms the basis of a highly accurate sizing technique.
Phased array is the name given to a special type of ultrasonic probe.
An array is a group of transmitters, receivers or transmitter/receivers, generally called array elements. When used as a transmitter, firing the elements at different times can lead to interference between the sound waves produced by each individual element. This interference can be both constructive (waves add together) and destructive (waves cancel).
It is this interference which gives the array probe its main advantage – the ability to change beam shape and angle depending upon the timing at which elements are fired. When an array is used as a receiver, the difference between the times at which a pulse arrives at each array element contains information about the location of the pulse source.
Ultrasonic thickness gauging
Because in ultrasonic pulse-echo testing the time of travel of the pulse to a reflector is measured and displayed, it is a very simple adaptation to use this measurement as a thickness gauge. Low-cost small hand-held instruments are available, and the usual read-out is a digital display rather than an oscilloscope screen. Such thickness gauges require either calibration or a knowledge of the ultrasonic velocity in the material under test.
Usually, pulsed beams of ultrasound are used and in the simplest instruments a single probe, hand-held, is placed on the specimen surface. An oscilloscope display with a time-base shows the time that it takes for an ultrasonic pulse to travel to a reflector (a flaw, the back surface, or other free surface) in terms of distance across the oscilloscope screen – the so-called A-scan display. The height of the reflected pulse is related to the flaw size as seen from the transmitter probe. The relationships of flaw size, flaw distance and flaw reflectivity are complex and considerable skill is required to interpret the display.
Complex multiprobe systems are also used with mechanical probe movement and digitisation of the signals, followed by computer storage; methods of computer interpretation are developing rapidly.
There are several forms of mechanical vibration, depending on the direction of particle movement in the wave motion, and so there are several forms of ultrasonic waves, the most widely used in NDT being compressional and transverse (shear) waves.
By suitable design of probe, ultrasonic beams can be introduced into solid material at almost any angle.
Compressional waves will also travel through liquids and a common technique is to immerse the specimen in a large tank and use a stand-off probe with a mechanised movement. With such equipment, alternative methods of displaying the signals are possible and a two-dimensional ultrasonic image can be produced (B-scan and C-scan displays).
Generally, a single probe acts as both transmitter and receiver, so that inspection can be done from one side only of the specimen. Large-grain materials such as austenitic steel welding, copper castings etc produce severe attenuation and scattering and are at present difficult to inspect with ultrasound, but large thicknesses of fine-grain material such as forged steel can be tested without difficulty.
Because the usual indication of a flaw is a pulse on an oscilloscope trace, flaws must be characterised and also sized. New techniques such as time-of-flight diffraction, TOFD, have been developed to assist this technique.
Ultrasonic attenuation and ultrasonic velocity measurements are used to study various material properties.
The use of ultrasonics for sizing flaws
Once flaws have been detected it is often desirable to determine their size. For flaws smaller than the ultrasonic beam width, a pseudo-sizing can be obtained by comparing the flaw signal amplitude with that of a reference reflector (flat-bottomed or side-drilled hole) at the same range. When the flaw size is greater than the ultrasonic beam width, conventional probe movement sizing techniques can often be used to provide an estimate of flaw size. The maximum amplitude technique uses a measure of the probe movement between the maximised signals from flaw extremities to size flaws. The 6 dB and 20 dB drop techniques use the reduction in the signal amplitude from the flaw as the probe passes over the edge of the flaw as an indicator of flaw dimensions. However, the interaction between the ultrasonic beam and flaw, depending as it does on flaw nature and orientation, limits the effectiveness of these techniques, when dealing with complex and mis-orientated flaws.
Techniques which make use of the diffracted signal from the flaw extremities to locate and size flaws are most effective in sizing planar flaws. The time-of-flight diffraction (TOFD) technique uses the ultrasonic transit time between probe(s) and flaw extremities to locate and size flaws. Flaw sizing accuracies of better than ±2 mm can be achieved with optimised techniques (see also Ultrasonic advanced methods).

2. Radiography Testing 
Industrial radiography is used for a variety of applications but is commonly performed using two different sources of radiation, X-Ray and Gamma ray sources. The choice of radiation sources and their strength depends on a variety of factors including size of the component and the material thickness. Within the broad group of X-Ray and Gamma ray sources are a variety of camera choices with varying radiation strengths. MISTRAS Services X-Ray capabilities run the gamut from 4 MEV units utilized to radiograph extremely large and thick castings and forgings, to portable X-Ray cameras used for field weld applications and thin wall material inspection. Gamma sources vary from very low level fluoroscopic units to perform real time corrosion under insulation surveys, to Iridium (Ir192) and Selenium (Se 75) sources used for a variety of weld inspections, to Cobalt (Co 60) inspections for thick component testing.

There are many advantages to radiography including: inspection of a wide variety of material types with varying density, ability to inspect assembled components, minimum surface preparation required, sensitivity to changes in thickness corrosion, voids, cracks and material density changes, the ability to detect both surface and subsurface defects and the ability to provide a permanent record of the inspection. The disadvantages of radiography are: safety precautions are required for the safe use of radiation, access to both sides of the specimen are required, orientation of the sample is critical, and determining flaw depth is impossible without additional angled exposures.

MISTRAS NDT Services supplies a complete line of radiographic services for both shop and field applications. Our staff of qualified, certified, professional radiographers operate within strict safety parameters and produce high quality radiographs that allow us to utilize our interpretation skills honed through many years of experience to determine if an anomaly is actually a defect or can be accepted per code requirements.

DIGITAL RADIOGRAPHY

Digital Radiography is one of the newest forms of radiographic imaging. Since no film is required, digital radiographic images are captured using either special phosphor screens or flat panels containing micro-electronic sensors. Captured images can be digitally enhanced for increased detail and are easily archived.

There are a number of forms of digital radiographic imaging including:
  • Computed Radiography (CR): digital imaging process that uses a special imaging plate which employs storage phosphors.
  • Real-Time Radiography (RTR): a form of radiography that allows electronic images to be captured and viewed in real time.
  • Direct Radiography (DR): a form of real-time radiography that uses a special flat panel detector.
  • Computed Tomography (CT): uses a real-time inspection system employing a sample positioning system and special software.
MISTRAS Services employs a wide array of digital radiographic systems to solve specific industrial problems. Thickness profiles of piping systems, both insulated and uninsulated, are performed using computed radiography, while large production runs of smaller parts are inspected using direct radiography. Real time radiography is utilized for large "real time" inspections of insulated piping systems looking for areas of pipe degradation.
More Details..     
www.nde-ed.org/EducationResources/CommunityCollege/Radiography/cc_rad_index.htm

3. Liquid Penetrant Testing 
Liquid penetrant examination is one of the most popular Nondestructive Examination (NDE) methods in the industry. It is economical, versatile, and requires minimal training when compared to other NDE methods. Liquid penetrant exams check for material flaws open to the surface by flowing very thin liquid into the flaw and then drawing the liquid out with a chalk-like developer. Welds are the most common item inspected, but plate, bars, pipes, castings, and forgings are also commonly inspected using liquid penetrant examination.
Over the years, liquid penetrant examination has been called many names: penetrant testing (PT), liquid penetrant testing (LP), and dye penetrant testing (DP). The American Society for Nondestructive Testing (ASNT) uses the name liquid penetrant testing (PT). The American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME B & PVC) and the National Board Inspection Code (NBIC) use the name liquid penetrant examination (PT).
 
The first documented use of PT was in the railroad industry. Cast railroad wheels were dipped in used oil, dried off, and then coated with powder chalk or suspension of chalk in alcohol.  Once the wheels were dry, any oil stored in the flaw would bleed out into the chalk and be detected. This was called the oil and whiting method.
 
The ASME Boiler & Pressure Vessel Code recognizes six different techniques of PT. They vary by type of penetrant and method of cleaning before applying a developer. The two penetrant types are either fluorescent or color contrast (dye) penetrant. They can then be used with any of the three methods of cleaning – water washable, post-emulsifying, and solvent removable. The most popular is dye penetrant that is solvent removable. This method is referenced throughout the article.
 
The dye penetrant solvent removable method is most popular because it is low cost and very versatile. It typically comes in three aerosol cans – cleaner, penetrant, and developer. The cans can be purchased from welding supply distributors for typically $5 to $15 a can. For less than $50 you can have all the equipment you need to conduct liquid penetrant examinations. The aerosol cans are very versatile which allow them to be taken up ladders, inside boilers, down into pits, and into very tight places. Most nonporous materials (steel, stainless steel, cast iron, aluminum, brass, bronze, titanium, rubber, plastics, and glass) can be examined using PT. Porous materials (concrete, wood, paper, cloth, and some types of fiberglass if the fibers are exposed to the surface) should not be examined using PT. 

4. Magnetic Particle Testing 
In theory, magnetic particle inspection (MPI) is a relatively simple concept. It can be considered as a combination of two nondestructive testing methods: magnetic flux leakage testing and visual testing. Consider the case of a bar magnet. It has a magnetic field in and around the magnet. Any place that a magnetic line of force exits or enters the magnet is called a pole. A pole where a magnetic line of force exits the magnet is called a north pole and a pole where a line of force enters the magnet is called a south pole.
When a bar magnet is broken in the center of its length, two complete bar magnets with magnetic poles on each end of each piece will result. If the magnet is just cracked but not broken completely in two, a north and south pole will form at each edge of the crack. The magnetic field exits the north pole and reenters at the south pole. The magnetic field spreads out when it encounters the small air gap created by the crack because the air cannot support as much magnetic field per unit volume as the magnet can. When the field spreads out, it appears to leak out of the material and, thus is called a flux leakage field.
If iron particles are sprinkled on a cracked magnet, the particles will be attracted to and cluster not only at the poles at the ends of the magnet, but also at the poles at the edges of the crack. This cluster of particles is much easier to see than the actual crack and this is the basis for magnetic particle inspection.
The first step in a magnetic particle inspection is to magnetize the component that is to be inspected. If any defects on or near the surface are present, the defects will create a leakage field. After the component has been magnetized, iron particles, either in a dry or wet suspended form, are applied to the surface of the magnetized part. The particles will be attracted and cluster at the flux leakage fields, thus forming a visible indication that the inspector can detect

5. Visual Testing
 Visual Testing (VT) is the oldest and most widely used Nondestructive test method.  This online course is appropriate for individuals with little or no inspection training and is an ideal course to begin ones career in NDT.
Subjects include illumination requirements, surface conditions, test specimen attributes to be evaluated, and the various discontinuities and conditions that may be encountered. Both direct and indirect (remote) visual techniques are thoroughly presented and demonstrated. The different visual tools, gages and other measuring devices in addition to the VT instruments are discussed and demonstrated.
A wide range of common applications are included making this course a must for anyone considering a future NDT or inspection fields. This course is highly recommended for those planning to take other NDT courses or for personnel who are planning to become certified in VT.


6. Radiographic Film Interpretation 
The NDT Radiography Interpretation training course will provide theory lectures and practical training to provide the candidate with full understanding of Radiography and film Interpretation. The course will encourage group discussions around practical problems and provide field expertise on how to resolve them. At the end of this course the candidate will understand how to perform review of radiographic films and report the identified defects for corrective action. The course will cover -
  • Basic principles on Radiography Testing.
  • Equipment & Materials.
  • Techniques and calibration
  • Radiography Interpretation – Welds
  • Radiography Interpretation - Casting
  • ASTM and ASME standards and specifications.
How will you and your company benefit from this course?
Qualified to review radiography films and evaluate results as per applicable codes, standards and specifications. Should be familiar with radiography interpretation technique and report the results.

To view detailed information about the courses they offer, select the method you require from the list.they can provide various courses for each method, each suited to your particular requirements. The type of course you choose depends on how much experience you have, whether you have received training previously or currently hold a certificate, and also what type of certification you are working towards.The certification is valid globally. All the leading inspection agencies and govt.bodies/public sector undertakings/ private or Organizations, recognizes the certificates issued by thier institute.

www.ndttrainingcenter.org.in

www.labequipmentschennai.com

Prepared & Collection by M.Ajmal Khan.

1 comment:

  1. You seem to be more practicable! keep it up the good work! Ndt

    ReplyDelete