Know – How about Nondestructive Testing

5265
nondestructive testing
Nondestructive Testing

Nondestructive testing is a wide group of analysis techniques used to evaluate the properties of a material, component or system without causing damage. The terms nondestructive examination (NDE), nondestructive inspection (NDI), and nondestructive evaluation (NDE) are also commonly used to describe this technology. Because NDT 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 six most frequently used NDT methods are eddy-current, magnetic-particle, liquid penetrant, radiographic, ultrasonic, and visual testing. NDT is commonly used in forensic engineering, mechanical engineering, petroleum engineering, electrical engineering, civil engineering, systems engineering, aeronautical engineering, medicine, and art. Innovations in the field of nondestructive testing have had a profound impact on medical imaging, including on echocardiography, medical ultrasonography, and digital radiography.

The factors guiding the process

Various national and international trade associations exist to promote the industry, knowledge about non-destructive testing, and to develop standard methods and training. These include the American Society for Nondestructive Testing, the Non-Destructive Testing Management Association, the International Committee for Non-Destructive Testing, the European Federation for Non-Destructive Testing and the British Institute of Non-Destructive Testing.

NDT methods rely upon use of electromagnetic radiation, sound and other signal conversions to examine a wide variety of articles (metallic and non-metallic, food-product, artifacts and antiquities, infrastructure) for integrity, composition, or condition with no alteration of the article undergoing examination. Visual inspection (VT), the most commonly applied NDT method, is quite often enhanced by the use of magnification, borescopes, cameras, or other optical arrangements for direct or remote viewing. The internal structure of a sample can be examined for a volumetric inspection with penetrating radiation (RT), such as X-rays, neutrons or gamma radiation. Sound waves are utilized in the case of ultrasonic testing (UT), another volumetric NDT method – the mechanical signal (sound) being reflected by conditions in the test article and evaluated for amplitude and distance from the search unit (transducer). Another commonly used NDT method used on ferrous materials involves the application of fine iron particles (either suspended in liquid or dry powder – fluorescent or colored) that are applied to a part while it is magnetized, either continually or residually. The particles will be attracted to leakage fields of magnetism on or in the test object, and form indications (particle collection) on the object’s surface, which are evaluated visually. Contrast and probability of detection for a visual examination by the unaided eye is often enhanced by using liquids to penetrate the test article surface, allowing for visualization of flaws or other surface conditions. This method (liquid penetrant testing) (PT) involves using dyes, fluorescent or colored (typically red), suspended in fluids and is used for non-magnetic materials, usually metals.

Applications

NDT is used in a variety of settings that covers a wide range of industrial activity, with new NDT methods and applications being continuously developed. Nondestructive testing methods are routinely applied in industries where a failure of a component would cause significant hazard or economic loss, such as in transportation, pressure vessels, building structures, piping, and hoisting equipment.

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. For example, the base metal must reach a certain temperature during the welding process, must cool at a specific rate, and must be welded with compatible materials or the joint may not be strong enough to hold the parts together, or cracks may form in the weld causing it to fail. The typical welding defects (lack of fusion of the weld to the base metal, cracks or porosity inside the weld, and variations in weld density) could cause a structure to break or a pipeline to rupture.

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.

Welding techniques may also be actively monitored with acoustic emission techniques before production to design the best set of parameters to use to properly join two materials. In the case of high stress or safety critical welds, weld monitoring will be employed to confirm the specified welding parameters (arc current, arc voltage, travel speed, heat input etc.) are being adhered to those stated in the welding procedure. This verifies the weld as correct to procedure prior to nondestructive evaluation and metallurgy tests.

Structural mechanics

Structures can be complex systems that undergo different loads during their lifetime, e.g. Lithium-ion batteries. Some complex structures, such as the turbo machinery in a liquid-fuel rocket, can also cost millions of dollars. Engineers will commonly model these structures as coupled second-order systems, approximating dynamic structure components with springs, masses, and dampers. The resulting sets of differential equations are then used to derive a transfer function that models the behavior of the system.

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. This output is recorded and compared to the corresponding output given by the transfer function and the known input. Differences may indicate an inappropriate model (which may alert engineers to unpredicted instabilities or performance outside of tolerances), failed components, or an inadequate control system.

Reference standards, which are structures that intentionally flawed in order to be compared with components intended for use in the field, are often used in NDT. Reference standards can be with many NDT techniques, such as UT, RT and VT.

Nondestructive testing

Different types of nondestructive testing

Ultrasonic testing

Ultrasonic testing uses high-frequency sound waves called ultrasonic pulse waves to detect flaws or other imperfections or defects in metal components, and it can also be used to identify and monitor changes like shifts in thickness within the components that may result in failure or other problems in the future. One of the most common uses of ultrasonic testing is to evaluate corrosion in pipelines and other enclosed structures or components. Ultrasonic testing is most commonly performed on metals and metallic alloys, but it can also be used to test concrete and composites, and sometimes even wood. Although the method offers the advantage of deep penetration to evaluate problems within components, ultrasonic testing requires a high degree of training and competence to apply the method and interpret the results. Results also may be affected by surface imperfections or irregularities.

Magnetic particle testing

Also called magnetic particle inspection (MPI), this technique can be used in metals that have magnetic properties (also called ferromagnetic materials) such as iron, cobalt, nickel and some alloys. MPI works by issuing a magnetic field into the component being tested – essentially magnetizing the component. Next, iron particles are applied to the surface either in a dry form or suspended in liquid. Because even the tiniest cracks and fissures will allow some of the magnetism to “leak” out, these particles become attracted to the tiny cracks, building up and providing evidence of a leak, or “indication.” The component may be magnetized by an electrical current, called direct magnetization, or indirectly by applying a magnetic field to the outside of the component. Like ultrasonic testing, this approach requires considerable training and expertise.

Liquid penetrant testing

Liquid penetrant testing is one of the oldest methods of non-destructive testing. In this method, two solutions are used – a penetrant that is first applied to the surface of the component to be tested and a developer that combines with the penetrant to help reveal tiny cracks or other imperfections. After the penetrant is applied, it is allowed to “soak in” for a prescribed period of time to help reveal defects that extend below the component’s surface. Liquid penetrant testing is used in a wide variety of industries and is one of the most popular techniques of non-destructive testing because it is relatively inexpensive, requires no costly special equipment and relies on limited experience and training, making it widely accessible to companies of all sizes.

Radiographic testing

Radiographic testing uses x-rays or radioactive isotopes to evaluate components in much the same way a doctor uses an x-ray to evaluate the structures inside a human body. This type of testing works by sending the radiation through the component and measuring the amount that emerges on the opposite side. The result is a photographic-type image that reflects areas of different densities, including areas where material may be missing or thinned, such as in cracks or areas of weakness. Radiographic testing can be difficult to use on components with irregular surface areas since those irregularities can influence the thickness of the materials that are being evaluated.

Nondestructive testing

Types of nondestructive equipments

Portable ultrasonic flaw detectors

Portable ultrasonic flaw detectors (UT) provides leading-edge capabilities for locating discontinuities and other flaws. We offer a range of software, measurement features, and application-specific options for flaw detection applications that include locating and sizing hidden cracks, voids, disbands, and similar discontinuities in welds, forgings, turbines, and other structural components.

Thickness gages

Thickness gages for the accurate measurement of nearly any material. Thickness gages include a range of features for enhanced performance. Ultrasonic thickness gages can measure virtually any material including plastics, metals, metal composites, rubber, and internally corroded materials.

Probes and transducers

Probes and transducers are available in a range of frequencies, configurations, connector styles, and cable types to help you meet demanding inspection requirements. If you don’t see the probe or transducer that fits your application, ask us about custom configurations.

Bar inspection

Bar inspection systems use advanced technologies, such as ultrasonic phased array, eddy current array, and X-ray fluorescence spectroscopy, to inspect the full volume and surface of round or square bars and pipes.

Seamless and welded tube

Seamless and welded tube inspection systems use ultrasonic phased array and X-ray fluorescence spectroscopy technologies for comprehensive inspection.

Industrial XY (motorized and manual) and manual weld inspection scanners

Industrial XY (motorized and manual) and manual weld inspection scanners provide reliable, accurate performance in a range of heavy duty industrial applications where scanners are used to improve quality and reduce costs. Phased array scanners and accessories such as motor controllers and water pumps complete the Olympus line of scanner products.

Rebar Scanner equipments

Rebar Scanner equipments provides the capability to detect, location of rebar in concrete, measure rebar cover, rebar diameter and significant capability at an economical price.

Concrete Cover Meter instruments

Concrete Cover Meter instruments provide rebar location, rebar sizing and cover measurement & ideal for onsite usage.

Ultrasonic Pulse Velocity Tester

Ultrasonic Pulse Velocity Tester equipments are high performance, microprocessor based UPV devices that measures velocity, transit time & other parameters for evaluating uniformity, cavities, cracks, delimitation & deterioration for determining quality of concrete and other masonry materials.

Digital Concrete Test Hammer

Digital Concrete Test Hammer Non Destructive Test Instruments is used for comparative testing, referenced against a concrete with known strength or against a concrete verified as conforming to a particular strength class.

Concrete Moisture Meter

Concrete Moisture Meter provide perfect solution to identify and monitor moisture in concrete.

Concrete Wall Scanner

Concrete Wall Scanner equipments locates conduits behind walls, floors, and ceilings. It also locates metal as well as live AC electrical wiring.

Nondestructive testing

Eddy Current Testers

Eddy current testing relies on the principle of electromagnetic induction to detect flaws in conductive metals. An eddy current tester sends an alternating current through a coil which generates an oscillating magnetic field. When the probe is placed near the surface of a conductive metal, a circular flow of electrons, an eddy current, begins to move through the metal and generate its own magnetic field which interacts with the magnetic field created by the coil. Flaws or other changes in the metal will cause changes in the amplitude of the eddy current and the magnetic fields it creates. This, in turn, affects the movement of electrons in the coil by varying the electrical impedance of the coil. By noting the changes to the impedance amplitude and phase angle, a trained technician can identify inconsistencies in the metal being tested which could indicate flaws.

Flaw Detectors

Flaw detectors use well-established and completely non-destructive ultrasonic technology to pass sound waves through metals, composites, plastics, and ceramics to detect hidden flaws such as cracks, voids and softness which can lead to failure. Sound waves act in highly predictable ways and produce distinctive echo patterns that can be displayed and recorded by portable instruments making them quite useful as an inspection tool. As an ultrasonic device, flaw detectors use a transducer to both create vibrations and receive the echo that returns. As those vibrations pass through a medium they do so in a predicable direction and at speeds and velocities specific to the medium. When a boundary, such as a new medium or a flaw, is reached, the vibrations will echo back to the transducer, again, in a predictable manner. The returning signal is converted into a waveform pattern that can be analyzed for inconsistencies.

Hardness Testers

Hardness is a complex concept that generally pertains to the resistance of a solid material to permanent deformation when force is applied. The term can apply to deformation from indentation, scratching, cutting or bending. Materials exhibit hardness in different ways making it not an intrinsic physical property of the material but, rather, a composite property that includes a number of factors such as the ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity of the material being tested. Hardness measurements are widely used for the quality control of materials. From an engineering standpoint, resistance to wear by friction or erosion generally increases with hardness. Proper testing ensures materials are suitable for their intended use.

Ultrasonic Thickness Gauges

Ultrasonic thickness gauges determine the thickness of a sample by very precisely measuring how long it takes for a sound pulse that has been generated the transducer to travel through a test piece and reflect back from the inside surface or far wall. By comparing this measured interval of time with known data about the material type, it possible to calculate the thickness of the sample to an extremely high accuracy. Ultrasonic thickness gauges are quite similar in several respects to flaw detectors but, whereas, flaw detectors display A-scans of ultrasonic waveforms, thickness detectors generally provide a numerical format of exact measurements.

Ultrasonic thickness gauges have a number of applications in the field of non-destructive testing. Because sound waves reflect from boundaries between dissimilar materials they are excellent tools for measuring the thickness of paints and other coatings as part of a quality control program. Thickness gauges are also routinely used to scan storage tanks, pipelines, ship hulls, and many other things for any signs of damage or weakness that may have been caused by corrosion, environmental damage or just simply wear and tear.

Calibrator

Like most test and measurement equipment, non-destructive testing equipment needs to be periodically calibrated to maintain accuracy. In the case of NDT equipment, calibrations are performed using precision test blocks that simulate conditions and serve as reference standards. Different types of test blocks simulate different conditions. Test blocks can include steps of different thicknesses for use with thickness gauges, holes and other “flaws” for use with flaw detectors, or predetermined hardness for hardness detectors.

Magnetic particle instrument

Magnetic particle inspection is used to detect irregularities inside and outside test pieces that are made of ferromagnetic material. Inspection is performed with either movable or stationary test equipment, depending on the size and mobility of the test piece. The test piece is magnetized, either by having a current passed through it, or by having an external magnetic field applied to it. Then ferromagnetic particles (either dry or in suspension) are applied to the test piece. Discontinuities in the resulting visual field indicate irregularities in the test piece.

Rigid borescopes

Rigid borescopes are an excellent piece of equipment for inspecting the inside of tubes or pipes. They were originally used to inspect the bores of rifles and cannons.

Hand-held lenses

Hand-held lenses are available from 1.5× up to 10× magnification. They are very useful for magnifying fine small detail to enable a better assessment to be made. The better quality, higher power lenses are of complex designs: doublet or triplet lens types are made from different types of optical glass cemented together, this type of design will remove chromatic aberration effects

Measuring magnifiers

Measuring magnifiers incorporate a measuring scale to enable the surface condition to be measured. Some types of magnifier incorporate a small battery-powered bulb to provide illumination of the test-surface. Anglepoise magnifiers have up to 10× magnification and often have a circular fluorescent tube built in to provide uniform illumination

Endoscope

The endoscope is flexible due to the use of fiber optics for both the light guide and the image guide.

Robotic technologies

Drones have become increasingly autonomous with their services and usability. Drones started as a consumer and hobbyist phenomenon, but more recently they have grown into the field of remote visual inspection of industrial assets and sensing and other enterprise use cases. IPC utilizes GPS positioning and coordinates specific inspection zones to create safe detailed infrastructure assessments that utilize high definition video mounted on aerial drones to inspect hard to reach places on infrastructure assets worldwide. Utilizing drones to inspect infrastructure is faster, more efficient and less expensive than conventional methods. Utilizing drones, modern technology and robotics for bridge inspections and other hard to reach infrastructure assets can help us quickly restore our infrastructure at a fraction of the price that current conventional methods are able.

Conclusion

Nondestructive testing (NDT) is the process of inspecting, testing, or evaluating materials, components or assemblies for discontinuities, or differences in characteristics without destroying the serviceability of the part or system. In other words, when the inspection or test is completed the part can still be used.