Ultrasonic testing

Ultrasonic testing

An example of Ultrasonic Testing (UT) on blade roots of a V2500 IAE aircraft engine.
Step 1: The UT probe is placed on the root of the blades to be inspected with the help of a special borescope tool (video probe).
Step 2: Instrument settings are input.
Step 3: The probe is scanned over the blade root. In this case, an indication (peak in the data) through the red line (or gate) indicates a good blade; an indication to the left of that range indicates a crack.
Principle of ultrasonic testing. LEFT: A probe sends a sound wave into a test material. There are two indications, one from the initial pulse of the probe, and the second due to the back wall echo. RIGHT: A defect creates a third indication and simultaneously reduces the amplitude of the back wall indication. The depth of the defect is determined by the ratio D/Ep

Ultrasonic testing (UT) is a family of non-destructive testing techniques based on the propagation of ultrasonic waves in the object or material tested. In most common UT applications, 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. A common example is ultrasonic thickness measurement, which tests the thickness of the test object, for example, to monitor pipework corrosion.

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. It is used in many industries including steel and aluminium construction, metallurgy, manufacturing, aerospace, automotive and other transportation sectors.

History

On May 27, 1940, U.S. researcher Dr. Floyd Firestone of the University of Michigan applies for a U.S. invention patent for the first practical ultrasonic testing method. The patent is granted on April 21, 1942 as U.S. Patent No. 2,280,226, titled "Flaw Detecting Device and Measuring Instrument". Extracts from the first two paragraphs of the patent for this entirely new nondestructive testing method succinctly describe the basics of such ultrasonic testing. "My invention pertains to a device for detecting the presence of inhomogeneities of density or elasticity in materials. For instance if a casting has a hole or a crack within it, my device allows the presence of the flaw to be detected and its position located, even though the flaw lies entirely within the casting and no portion of it extends out to the surface. ... The general principle of my device consists of sending high frequency vibrations into the part to be inspected, and the determination of the time intervals of arrival of the direct and reflected vibrations at one or more stations on the surface of the part."

James F. McNulty (U.S. radio engineer) of Automation Industries, Inc., then, in El Segundo, California, an early improver of the many foibles and limits of this and other nondestructive testing methods, teaches in further detail on ultrasonic testing in his U.S. Patent 3,260,105 (application filed December 21, 1962, granted July 12, 1966, titled “Ultrasonic Testing Apparatus and Method”) that “Basically ultrasonic testing is performed by applying to a piezoelectric crystal transducer periodic electrical pulses of ultrasonic frequency. The crystal vibrates at the ultrasonic frequency and is mechanically coupled to the surface of the specimen to be tested. This coupling may be effected by immersion of both the transducer and the specimen in a body of liquid or by actual contact through a thin film of liquid such as oil. The ultrasonic vibrations pass through the specimen and are reflected by any discontinuities which may be encountered. The echo pulses that are reflected are received by the same or by a different transducer and are converted into electrical signals which indicate the presence of the defect.” To characterize micro-structural features in the early stages of fatigue or creep damage, more advanced nonlinear ultrasonic tests should be employed. These nonlinear methods are based on the fact that an intensive ultrasonic wave is getting distorted as it faces micro damages in the material.[1] The intensity of distortion is correlated with the level of damage. This intensity can be quantified by acoustic non-linearity parameter (β). β is related to first and second harmonic amplitudes. These amplitudes can be measured by harmonic decomposition of the ultrasonic signal through fast Fourier transformation or wavelet transformation.[2]

How it works

At a construction site, a technician tests a pipeline weld for defects using an ultrasonic phased array instrument. The scanner, which consists of a frame with magnetic wheels, holds the probe in contact with the pipe by a spring. The wet area is the ultrasonic couplant that allows the sound to pass into the pipe wall.
Non-destructive testing of a swing shaft showing spline cracking

In ultrasonic testing, an 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. However, when ultrasonic testing is conducted with an Electromagnetic Acoustic Transducer (EMAT) the use of couplant is not required.

There are two methods of receiving the ultrasound waveform: reflection and attenuation. 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. In attenuation (or through-transmission) mode, a transmitter sends ultrasound through one surface, and a separate receiver detects the amount that has reached it on another surface after traveling through the medium. Imperfections or other conditions in the space between the transmitter and receiver reduce the amount of sound transmitted, thus revealing their presence. Using the couplant increases the efficiency of the process by reducing the losses in the ultrasonic wave energy due to separation between the surfaces.

Features

Advantages

  1. High penetrating power, which allows the detection of flaws deep in the part.
  2. High sensitivity, permitting the detection of extremely small flaws.
  3. In many cases only one surface needs to be accessible.
  4. Greater accuracy than other nondestructive methods in determining the depth of internal flaws and the thickness of parts with parallel surfaces.
  5. Some capability of estimating the size, orientation, shape and nature of defects.
  6. Some capability of estimating the structure of alloys of components with different acoustic properties
  7. Non hazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity.
  8. Capable of portable or highly automated operation.
  9. Results are immediate. Hence on the spot decisions can be made.

Disadvantages

  1. Manual operation requires careful attention by experienced technicians. The transducers alert to both normal structure of some materials, tolerable anomalies of other specimens (both termed “noise”) and to faults therein severe enough to compromise specimen integrity. These signals must be distinguished by a skilled technician, possibly requiring follow up with other nondestructive testing methods.[3]
  2. Extensive technical knowledge is required for the development of inspection procedures.
  3. Parts that are rough, irregular in shape, very small or thin, or not homogeneous are difficult to inspect.
  4. Surface must be prepared by cleaning and removing loose scale, paint, etc., although paint that is properly bonded to a surface need not be removed.
  5. Couplants are needed to provide effective transfer of ultrasonic wave energy between transducers and parts being inspected unless a non-contact technique is used. Non-contact techniques include Laser and Electro Magnetic Acoustic Transducers (EMAT).
  6. Inspected items must be water resistant, when using water based couplants that do not contain rust inhibitors. In these cases anti-freeze liquids with inhibitors are often used.

Standards

International Organization for Standardization (ISO)
  • ISO 2400: Non-destructive testing - Ultrasonic testing - Specification for calibration block No. 1 (2012)
  • ISO 7963: Non-destructive testing — Ultrasonic testing — Specification for calibration block No. 2 (2006)
  • ISO 10863: Non-destructive testing of welds -- Ultrasonic testing -- Use of time-of-flight diffraction technique (TOFD) (2011)
  • ISO 11666: Non-destructive testing of welds — Ultrasonic testing — Acceptance levels (2010)
  • ISO 16809: Non-destructive testing -- Ultrasonic thickness measurement (2012)
  • ISO 16831: Non-destructive testing -- Ultrasonic testing -- Characterization and verification of ultrasonic thickness measuring equipment (2012)
  • ISO 17640: Non-destructive testing of welds - Ultrasonic testing - Techniques, testing levels, and assessment (2010)
  • ISO 22825, Non-destructive testing of welds - Ultrasonic testing - Testing of welds in austenitic steels and nickel-based alloys (2012)
  • ISO 5577: Non-destructive testing -- Ultrasonic inspection -- Vocabulary (2000)
European Committee for Standardization (CEN)
  • EN 583, Non-destructive testing - Ultrasonic examination
  • EN 1330-4, Non destructive testing - Terminology - Part 4: Terms used in ultrasonic testing
  • EN 12668-1, Non-destructive testing - Characterization and verification of ultrasonic examination equipment - Part 1: Instruments
  • EN 12668-2, Non-destructive testing - Characterization and verification of ultrasonic examination equipment - Part 2: Probes
  • EN 12668-3, Non-destructive testing - Characterization and verification of ultrasonic examination equipment - Part 3: Combined equipment
  • EN 12680, Founding - Ultrasonic examination
  • EN 14127, Non-destructive testing - Ultrasonic thickness measurement

(Note: Part of CEN standards in Germany accepted as DIN EN, in Czech Republic as CSN EN.)

See also

References

  1. ^ Matlack, K. H.; Kim, J.-Y.; Jacobs, L. J.; Qu, J. (2015-03-01). "Review of Second Harmonic Generation Measurement Techniques for Material State Determination in Metals". Journal of Nondestructive Evaluation. 34 (1): 273. doi:10.1007/s10921-014-0273-5. ISSN 0195-9298. 
  2. ^ Mostavi, Amir; Kamali, Negar; Tehrani, Niloofar; Chi, Sheng-Wei; Ozevin, Didem; Indacochea, J. Ernesto (2017). "Wavelet Based Harmonics Decomposition of Ultrasonic Signal in Assessment of Plastic Strain in Aluminum". Measurement. 106: 66. doi:10.1016/j.measurement.2017.04.013. 
  3. ^ U.S. Patent 3,260,105 for Ultrasonic Testing Apparatus and Method to James F. McNulty at lines 37-48 and 60-72 of Column 1 and lines 1-4 of Column 2.

Further reading

  • Albert S. Birks, Robert E. Green, Jr., technical editors ; Paul McIntire, editor. Ultrasonic testing, 2nd ed. Columbus, OH : American Society for Nondestructive Testing, 1991. ISBN 0-931403-04-9.
  • Josef Krautkrämer, Herbert Krautkrämer. Ultrasonic testing of materials, 4th fully rev. ed. Berlin; New York: Springer-Verlag, 1990. ISBN 3-540-51231-4.
  • J.C. Drury. Ultrasonic Flaw Detection for Technicians, 3rd ed., UK: Silverwing Ltd. 2004. (See Chapter 1 online (PDF, 61 kB)).
  • Nondestructive Testing Handbook, Third ed.: Volume 7, Ultrasonic Testing. Columbus, OH: American Society for Nondestructive Testing.
  • Detection and location of defects in electronic devices by means of scanning ultrasonic microscopy and the wavelet transform measurement, Volume 31, Issue 2, March 2002, Pages 77–91, L. Angrisani, L. Bechou, D. Dallet, P. Daponte, Y. Ousten
  • Charles Hellier (2003). "Chapter 7 - Ultrasonic Testing". Handbook of Nondestructive Evaluation. McGraw-Hill. ISBN 0-07-028121-1. 

External links

Industrial radiography

Industrial radiography

Making a radiograph

Industrial radiography is a method of non-destructive testing where many types of manufactured components can be examined to verify the internal structure and integrity of the specimen. Industrial Radiography can be performed utilizing either X-rays or gamma rays. Both are forms of electromagnetic radiation. The difference between various forms of electromagnetic energy is related to the wavelength. X and gamma rays have the shortest wavelength and this property leads to the ability to penetrate, travel through, and exit various materials such as carbon steel and other metals.

History

Radiography started in 1895 with the discovery of X-rays (later also called Röntgen rays after the man who first described their properties in detail), a type of electromagnetic radiation. Soon after the discovery of X-rays, radioactivity was discovered. By using radioactive sources such as radium, far higher photon energies could be obtained than those from normal X-ray generators. Soon these found various applications, with one of the earliest users being Loughborough College.[1] X-rays and gamma rays were put to use very early, before the dangers of ionizing radiation were discovered. After World War II new isotopes such as caesium-137, iridium-192 and cobalt-60 became available for industrial radiography, and the use of radium and radon decreased.

Applications

Inspection of products

A portable wireless controlled battery powered X-ray generator for use in non-destructive testing and security.

Gamma radiation sources, most commonly iridium-192 and cobalt-60, are used to inspect a variety of materials. The vast majority of radiography concerns the testing and grading of welds on pressurized piping, pressure vessels, high-capacity storage containers, pipelines, and some structural welds. Other tested materials include concrete (locating rebar or conduit), welder's test , machined parts, plate metal, or pipewall (locating anomalies due to corrosion or mechanical damage). Non-metal components such as ceramics used in the aerospace industries are also regularly tested. Theoretically, industrial radiographers could radiograph any solid, flat material (walls, ceilings, floors, square or rectangular containers) or any hollow cylindrical or spherical object.

Inspection of welds

The beam of radiation must be directed to the middle of the section under examination and must be normal to the material surface at that point, except in special techniques where known defects are best revealed by a different alignment of the beam. The length of weld under examination for each exposure shall be such that the thickness of the material at the diagnostic extremities, measured in the direction of the incident beam, does not exceed the actual thickness at that point by more than 6%. The specimen to be inspected is placed between the source of radiation and the detecting device, usually the film in a light tight holder or cassette, and the radiation is allowed to penetrate the part for the required length of time to be adequately recorded.

The result is a two-dimensional projection of the part onto the film, producing a latent image of varying densities according to the amount of radiation reaching each area. It is known as a radio graph, as distinct from a photograph produced by light. Because film is cumulative in its response (the exposure increasing as it absorbs more radiation), relatively weak radiation can be detected by prolonging the exposure until the film can record an image that will be visible after development. The radiograph is examined as a negative, without printing as a positive as in photography. This is because, in printing, some of the detail is always lost and no useful purpose is served.

Before commencing a radiographic examination, it is always advisable to examine the component with one's own eyes, to eliminate any possible external defects. If the surface of a weld is too irregular, it may be desirable to grind it to obtain a smooth finish, but this is likely to be limited to those cases in which the surface irregularities (which will be visible on the radio graph) may make detecting internal defects difficult.

After this visual examination, the operator will have a clear idea of the possibilities of access to the two faces of the weld, which is important both for the setting up of the equipment and for the choice of the most appropriate technique.

Defects such as delaminations and planar cracks are difficult to detect using radiography, particularly to the untrained eye.

Without overlooking the negatives of radiographic inspection, Radiography does hold many significant benefits over ultrasonics, particularly insomuch that as a 'picture' is produced keeping a semi permanent record for the life cycle of the film, more accurate identification of the defect can be made, and by more interpreters. Very important as most construction standards permit some level of defect acceptance, depending on the type and size of the defect.

To the trained Radiographer, subtle variations in visible film density provide the technician the ability to not only accurately locate a defect, but identify its type, size and location; an interpretation that can be physically reviewed and confirmed by others, possibly eliminating the need for expensive and unnecessary repairs.

For purposes of inspection, including weld inspection, there exist several exposure arrangements.

First, there is the panoramic, one of the four single-wall exposure/single-wall view (SWE/SWV) arrangements. This exposure is created when the radiographer places the source of radiation at the center of a sphere, cone, or cylinder (including tanks, vessels, and piping). Depending upon client requirements, the radiographer would then place film cassettes on the outside of the surface to be examined. This exposure arrangement is nearly ideal – when properly arranged and exposed, all portions of all exposed film will be of the same approximate density. It also has the advantage of taking less time than other arrangements since the source must only penetrate the total wall thickness (WT) once and must only travel the radius of the inspection item, not its full diameter. The major disadvantage of the panoramic is that it may be impractical to reach the center of the item (enclosed pipe) or the source may be too weak to perform in this arrangement (large vessels or tanks).

The second SWE/SWV arrangement is an interior placement of the source in an enclosed inspection item without having the source centered up. The source does not come in direct contact with the item, but is placed a distance away, depending on client requirements. The third is an exterior placement with similar characteristics. The fourth is reserved for flat objects, such as plate metal, and is also radiographed without the source coming in direct contact with the item. In each case, the radiographic film is located on the opposite side of the inspection item from the source. In all four cases, only one wall is exposed, and only one wall is viewed on the radiograph.

Of the other exposure arrangements, only the contact shot has the source located on the inspection item. This type of radiograph exposes both walls, but only resolves the image on the wall nearest the film. This exposure arrangement takes more time than a panoramic, as the source must first penetrate the WT twice and travel the entire outside diameter of the pipe or vessel to reach the film on the opposite side. This is a double wall exposure/single wall view DWE/SWV arrangement. Another is the superimposure (wherein the source is placed on one side of the item, not in direct contact with it, with the film on the opposite side). This arrangement is usually reserved for very small diameter piping or parts. The last DWE/SWV exposure arrangement is the elliptical, in which the source is offset from the plane of the inspection item (usually a weld in pipe) and the elliptical image of the weld furthest from the source is cast onto the film.

Airport security

Both hold luggage and carry-on hand luggage are normally examined by X-ray machines using X-ray radiography. See airport security for more details.

Non-intrusive cargo scanning

Gamma-ray image of intermodal cargo container with stowaways

Gamma radiography and high-energy X-ray radiography are currently used to scan intermodal freight cargo containers in US and other countries. Also research is being done on adapting other types of radiography like or muon radiography for scanning intermodal cargo containers.

Sources

A high-energy X-ray machine or a radioactive source, like Ir-192, Co-60, or in rarer cases Cs-137 are used in an X-ray computed tomography machine as a source of photons. Penetrating radiations are those restricted to that part of the electromagnetic spectrum of wavelength less than about 10 nanometres. Radioisotope sources have the advantage that they do not need a supply of electrical power to function, but they can not be turned off. Also it is difficult using radioactivity to create a small and compact source that offers the photon flux possible with a normal sealed X-ray tube.

It might be possible to use caesium-137 as a photon source for radiography but this isotope is always diluted with inactive caesium isotopes. This makes it difficult to get a physically small source, and a large volume of the source makes it impossible to capture fine details in a radiographic examination.

Both cobalt-60 and caesium-137 have only a few gamma energies, which makes them close to monochromatic. The photon energy of cobalt-60 is higher than that of caesium-137, which allows cobalt sources to be used to examine thicker sections of metals than those that could be examined with Cs-137. Iridium-192 has a lower photon energy than cobalt-60 and its gamma spectrum is complex (many lines of very different energies), but this can be an advantage as this can give better contrast for the final photographs.

It has been known for many years that an inactive iridium or cobalt metal object can be machined to size. In the case of cobalt it is common to alloy it with nickel to improve the mechanical properties. In the case of iridium a thin wire or rod could be used. These precursor materials can then be placed in stainless steel containers that have been leak tested before being converted into radioactive sources. These objects can be processed by neutron activation to form gamma-emitting radioisotopes. The stainless steel has only a small ability to be activated and the small activity due to 55Fe and 63Ni are unlikely to pose a problem in the final application because these isotopes are beta emitters, which have very weak gamma emission. The 59Fe isotope which might form has a short half-life, so by allowing a cobalt source to stand for a year much of this isotope will decay away.

The source is often a very small object, which must be transported to the work site in a shielded container. It is normal to place the film in industrial radiography, clear the area where the work is to be done, add shielding (collimators) to reduce the size of the controlled area before exposing the radioactive source. A series of different designs have been developed for radiographic "cameras". Rather than the "camera" being a device that accepts photons to record a picture, the "camera" in industrial radiography is the radioactive photon source.

Neutrons

In some rare cases, radiography is done with neutrons. This type of radiography is called neutron radiography (NR, Nray, N-ray) or neutron imaging. Neutron radiography provides different images than X-rays, because neutrons can pass with ease through lead and steel but are stopped by plastics, water and oils. Neutron sources include radioactive (241Am/Be and Cf) sources, electrically driven D-T reactions in vacuum tubes and conventional critical nuclear reactors. It might be possible to use a neutron amplifier to increase the neutron flux.[2]

Since the amount of radiation emerging from the opposite side of the material can be detected and measured, variations in this amount (or intensity) of radiation are used to determine thickness or composition of material. Penetrating radiations are those restricted to that part of the electromagnetic spectrum of wavelength less than about 20 nanometers.

Radiographic cameras

Most industries are moving from film based radiography to a digital sensor based radiography much the same way that traditional photography has made this move.[3] Since the amount of radiation emerging from the opposite side of the material can be detected and measured, variations in this amount (or intensity) of radiation are used to determine thickness or composition of material.

Torch design

One design is best thought of as being like a torch. The radioactive source is placed inside a shielded box, a hinge allows part of the shielding to be opened exposing the source, allowing photons to exit the radiography camera.

This torch-type camera uses a hinge. The radioactive source is in red, the shielding is blue/green, and the gamma rays are yellow.

Another design for a torch is where the source is placed in a metal wheel, which can turn inside the camera to move between the expose and storage positions.

This torch-type camera uses a wheel design. The radioactive source is in red, and the gamma rays are yellow.

Cable-based design

One group of designs use a radioactive source, which connects to a drive cable contained shielded exposure device. In one design of equipment the source is stored in a block of lead or depleted uranium shielding that has an S-shaped tube-like hole through the block. In the safe position the source is in the center of the block and is attached to a metal wire that extends in both directions, to use the source a guide tube is attached to one side of the device while a drive cable is attached to the other end of the short cable. Using a hand-operated winch the source is then pushed out of the shield and along the source guide tube to the tip of the tube to expose the film, then cranked back into its fully shielded position.

A diagram of the S-shaped hole through a metal block; the source is stored at point A and is driven out on a cable through a hole to point B. It often goes a long way along a guide tube to where it is needed.

Contrast agents

Defects such as delaminations and planar cracks are difficult to detect using radiography, which is why penetrants are often used to enhance the contrast in the detection of such defects. Penetrants used include silver nitrate, zinc iodide, chloroform and diiodomethane. Choice of the penetrant is determined by the ease with which it can penetrate the cracks and also with which it can be removed. Diiodomethane has the advantages of high opacity, ease of penetration, and ease of removal because it evaporates relatively quickly. However, it can cause skin burns.

Safety

Industrial radiographers are in many locations required by governing authorities to use certain types of safety equipment and to work in pairs. Depending on location industrial radiographers may have been required to obtain permits, licenses and/or undertake special training. Prior to conducting any testing the nearby area should always first be cleared of all other persons and measures taken to ensure that people do not accidentally enter into an area that may expose them to a large dose of radiation.

The safety equipment usually includes four basic items: a radiation survey meter (such as a Geiger/Mueller counter), an alarming dosimeter or rate meter, a gas-charged dosimeter, and a film badge or thermoluminescent dosimeter (TLD). The easiest way to remember what each of these items does is to compare them to gauges on an automobile.

The survey meter could be compared to the speedometer, as it measures the speed, or rate, at which radiation is being picked up. When properly calibrated, used, and maintained, it allows the radiographer to see the current exposure to radiation at the meter. It can usually be set for different intensities, and is used to prevent the radiographer from being overexposed to the radioactive source, as well as for verifying the boundary that radiographers are required to maintain around the exposed source during radiographic operations.

The alarming dosimeter could be most closely compared with the tachometer, as it alarms when the radiographer "redlines" or is exposed to too much radiation. When properly calibrated, activated, and worn on the radiographer's person, it will emit an alarm when the meter measures a radiation level in excess of a preset threshold. This device is intended to prevent the radiographer from inadvertently walking up on an exposed source.

The gas-charged dosimeter is like a trip meter in that it measures the total radiation received, but can be reset. It is designed to help the radiographer measure his/her total periodic dose of radiation. When properly calibrated, recharged, and worn on the radiographer's person, it can tell the radiographer at a glance how much radiation to which the device has been exposed since it was last recharged. Radiographers in many states are required to log their radiation exposures and generate an exposure report. In many countries personal dosimeters are not required to be used by radiographers as the dose rates they show are not always correctly recorded.

The film badge or TLD is more like a car's odometer. It is actually a specialized piece of radiographic film in a rugged container. It is meant to measure the radiographer's total exposure over time (usually a month) and is used by regulating authorities to monitor the total exposure of certified radiographers in a certain jurisdiction. At the end of the month, the film badge is turned in and is processed. A report of the radiographer's total dose is generated and is kept on file.

When these safety devices are properly calibrated, maintained, and used, it is virtually impossible for a radiographer to be injured by a radioactive overexposure. Sadly, the elimination of just one of these devices can jeopardize the safety of the radiographer and all those who are nearby. Without the survey meter, the radiation received may be just below the threshold of the rate alarm, and it may be several hours before the radiographer checks the dosimeter, and up to a month or more before the film badge is developed to detect a low intensity overexposure. Without the rate alarm, one radiographer may inadvertently walk up on the source exposed by the other radiographer. Without the dosimeter, the radiographer may be unaware of an overexposure, or even a radiation burn, which may take weeks to result in noticeable injury. And without the film badge, the radiographer is deprived of an important tool designed to protect him or her from the effects of a long-term overexposure to occupationally obtained radiation, and thus may suffer long-term health problems as a result.

There are three ways a radiographer will ensure they are not exposed to higher than required levels of radiation, time, distance, shielding. The less time that a person is exposed to radiation the lower their dose will be. The further a person is from a radioactive source the lower the level of radiation they receive, this is largely due to the inverse square law. Lastly the more a radioactive source is shielded by either better or greater amounts of shielding the lower the levels of radiation that will escape from the testing area. The most commonly used shielding materials in use are sand, lead (sheets or shot), steel, spent (non-radioactive uranium) tungsten and in suitable situations water.

Industrial radiography appears to have one of the worst safety profiles of the radiation professions, possibly because there are many operators using strong gamma sources (> 2 Ci) in remote sites with little supervision when compared with workers within the nuclear industry or within hospitals.[4] Due to the levels of radiation present whilst they are working many radiographers are also required to work late at night when there are few other people present as most industrial radiography is carried out 'in the open' rather than in purpose built exposure booths or rooms. Fatigue, carelessness and lack of proper training are the three most common factors attributed to industrial radiography accidents. Many of the "lost source" accidents commented on by the International Atomic Energy Agency involve radiography equipment. Lost source accidents have the potential to cause a considerable loss of human life. One scenario is that a passerby finds the radiography source and not knowing what it is, takes it home.[5] The person shortly afterwards becomes ill and dies as a result of the radiation dose. The source remains in their home where it continues to irradiate other members of the household.[6] Such an event occurred in March 1984 in Casablanca, Morocco. This is related to the more famous Goiânia accident, where a related chain of events caused members of the public to be exposed to radiation sources.

Microsecond X-ray pulses

It is possible using a particle accelerator to generate a short pulse of high energy electrons, these electrons are used to create X-rays by braking radiation.[7] The X-rays are detected using a semiconductor detector, which is an array of silicon diodes. Such equipment has been used for the X-ray version of high speed flash photography. For example, diesel fuel that has been doped with cerium has been used to investigate the operation of fuel injectors in a diesel engine.[8][9][a]

As an alternative high energy pulsed proton beams can be used for the high speed examination of objects.[10]

List of standards

International Organization for Standardization (ISO)

  • ISO 4993, Steel and iron castings – Radiographic inspection
  • ISO 5579, Non-destructive testing – Radiographic examination of metallic materials by X- and gamma-rays – Basic rules
  • ISO 10675-1, Non-destructive testing of welds – Acceptance levels for radiographic testing – Part 1: Steel, nickel, titanium and their alloys
  • ISO 11699-1, Non-destructive testing – Industrial radiographic films – Part 1: Classification of film systems for industrial radiography
  • ISO 11699-2, Non-destructive testing – Industrial radiographic films – Part 2: Control of film processing by means of reference values
  • ISO 14096-1, Non-destructive testing – Qualification of radiographic film digitisation systems – Part 1: Definitions, quantitative measurements of image quality parameters, standard reference film and qualitative control
  • ISO 14096-2, Non-destructive testing – Qualification of radiographic film digitisation systems – Part 2: Minimum requirements
  • ISO 17636-1: Non-destructive testing of welds. Radiographic testing. X- and gamma-ray techniques with film
  • ISO 17636-2: Non-destructive testing of welds. Radiographic testing. X- and gamma-ray techniques with digital detectors
  • ISO 19232, Non-destructive testing – Image quality of radiographs

European Committee for Standardization (CEN)

  • EN 444, Non-destructive testing; general principles for the radiographic examination of metallic materials using X-rays and gamma-rays
  • EN 462-1: Non-destructive testing – image quality of radiographs – Part 1: Image quality indicators (wire type) – determination of image quality value
  • EN 462-2, Non-destructive testing – image quality of radiographs – Part 2: image quality indicators (step/hole type) determination of image quality value
  • EN 462-3, Non-destructive testing – Image quality of radiogrammes – Part 3: Image quality classes for ferrous metals
  • EN 462-4, Non-destructive testing – Image quality of radiographs – Part 4: Experimental evaluation of image quality values and image quality tables
  • EN 462-5, Non-destructive testing – Image quality of radiographs – Part 5: Image quality of indicators (duplex wire type), determination of image unsharpness value
  • EN 584-1, Non-destructive testing – Industrial radiographic film – Part 1: Classification of film systems for industrial radiography
  • EN 584-2, Non-destructive testing – Industrial radiographic film – Part 2: Control of film processing by means of reference values
  • EN 1330-3, Non-destructive testing – Terminology – Part 3: Terms used in industrial radiographic testing
  • EN 2002–21, Aerospace series – Metallic materials; test methods – Part 21: Radiographic testing of castings
  • EN 10246-10, Non-destructive testing of steel tubes – Part 10: Radiographic testing of the weld seam of automatic fusion arc welded steel tubes for the detection of imperfections
  • EN 12517-1, Non-destructive testing of welds – Part 1: Evaluation of welded joints in steel, nickel, titanium and their alloys by radiography – Acceptance levels
  • EN 12517-2, Non-destructive testing of welds – Part 2: Evaluation of welded joints in aluminium and its alloys by radiography – Acceptance levels
  • EN 12679, Non-destructive testing – Determination of the size of industrial radiographic sources – Radiographic method
  • EN 12681, Founding – Radiographic examination
  • EN 13068, Non-destructive testing – Radioscopic testing
  • EN 14096, Non-destructive testing – Qualification of radiographic film digitisation systems
  • EN 14784-1, Non-destructive testing – Industrial computed radiography with storage phosphor imaging plates – Part 1: Classification of systems
  • EN 14584-2, Non-destructive testing – Industrial computed radiography with storage phosphor imaging plates – Part 2: General principles for testing of metallic materials using X-rays and gamma rays

ASTM International (ASTM)

  • ASTM E 94, Standard Guide for Radiographic Examination
  • ASTM E 155, Standard Reference Radiographs for Inspection of Aluminum and Magnesium Castings
  • ASTM E 592, Standard Guide to Obtainable ASTM Equivalent Penetrameter Sensitivity for Radiography of Steel Plates 1/4 to 2 in. [6 to 51 mm] Thick with X Rays and 1 to 6 in. [25 to 152 mm] Thick with Cobalt-60
  • ASTM E 747, Standard Practice for Design, Manufacture and Material Grouping Classification of Wire Image Quality Indicators (IQI) Used for Radiology
  • ASTM E 801, Standard Practice for Controlling Quality of Radiological Examination of Electronic Devices
  • ASTM E 1030, Standard Test Method for Radiographic Examination of Metallic Castings
  • ASTM E 1032, Standard Test Method for Radiographic Examination of Weldments
  • ASTM 1161, Standard Practice for Radiologic Examination of Semiconductors and Electronic Components
  • ASTM E 1648, Standard Reference Radiographs for Examination of Aluminum Fusion Welds
  • ASTM E 1735, Standard Test Method for Determining Relative Image Quality of Industrial Radiographic Film Exposed to X-Radiation from 4 to 25 MeV
  • ASTM E 1815, Standard Test Method for Classification of Film Systems for Industrial Radiography
  • ASTM E 1817, Standard Practice for Controlling Quality of Radiological Examination by Using Representative Quality Indicators (RQIs)
  • ASTM E 2104, Standard Practice for Radiographic Examination of Advanced Aero and Turbine Materials and Components

American Society of Mechanical Engineers (ASME)

  • BPVC Section V, Nondestructive Examination: Article 2 Radiographic Examination

American Petroleum Institute (API)

  • API 1104, Welding of Pipelines and Related Facilities: 11.1 Radiographic Test Methods

See also

Notes

  1. ^ Some examples of radiography using a 5 MeV electron LINAC driving a bremsstrahlung source (1 mm Tungsten on a 9 mm copper sheet) can be seen here.

References

  1. ^ Loughborough University Library – Spotlight Archive Archived 2008-12-07 at the Wayback Machine.. Lboro.ac.uk (2010-10-13). Retrieved on 2011-12-29.
  2. ^ J. Magill, P. Peerani, and J. van Geel Basic aspects of sub-critical systems using thin fissile layers. European Commission, Institute for Transuranium Elements, Karlsruhe, Germany
  3. ^ Hogan, Hank (Summer 2015). "Nondestructive Technology". Aviation Aftermarket Defense. 11: 35. 
  4. ^ Radiation protection and safety in industrial radiography. Safety reports series No. 13. IAEA, Austria, January 1999 ISBN 92-0-100399-4
  5. ^ P. Ortiz, M. Oresegun, J. Wheatley Lessons from Major Radiation Accidents. International Atomic Energy Agency
  6. ^ Alain Biau Radiation protection of the workers in industrial radiography: the point of view of the regulatory body in France. Office de Protection contre les Rayonnements Ionisants
  7. ^ http://accelconf.web.cern.ch/AccelConf/p01/PAPERS/WOAA008.PDF
  8. ^ https://web.archive.org/web/20060907150218/http://www.chess.cornell.edu/Test/pubs/2002/research/microsecond.pdf
  9. ^ http://www.dxcicdd.com/05/PDF/Jin_Wang_1.pdf
  10. ^ http://www.lanl.gov/quarterly/q_w03/pro_rad.shtml

External links

Dye penetrant inspection

Dye penetrant inspection

1. Section of material with a surface-breaking crack that is not visible to the naked eye.
2. Penetrant is applied to the surface.
3. Excess penetrant is removed.
4. Developer is applied, rendering the crack visible.

Dye penetrant inspection (DPI), also called liquid penetrate inspection (LPI) or penetrant testing (PT), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials (metals, plastics, or ceramics). The penetrant may be applied to all non-ferrous materials and ferrous materials, although for ferrous components magnetic-particle inspection is often used instead for its subsurface detection capability. LPI is 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.

History

The oil and whiting method used in the railroad industry in the early 1900s was the first recognized use of the principles of penetrants to detect cracks. The oil and whiting method used an oil solvent for cleaning followed by the application of a whiting or chalk coating, which absorbed oil from the cracks revealing their locations. Soon a dye was added to the liquid. By the 1940s, fluorescent or visible dye was added to the oil used to penetrate test objects.

Experience showed that temperature and soak time were important. This started the practice of written instructions to provide standard, uniform results. The use of written procedures has evolved, giving the ability for design engineers and manufacturers to get the high standard results from any properly trained and certified liquid penetrant testing technician.

Principles

DPI is based upon capillary action, where high 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 - fluorescent or nonfluorescent (visible).

Inspection steps

Below are the main steps of Liquid Penetrant Inspection:

1. Pre-cleaning:

The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or cause irrelevant or false indications. Cleaning methods may include solvents, alkaline cleaning steps, vapor degreasing, or media blasting. The end goal of this step is a clean surface where any defects present are open to the surface, dry, and free of contamination. Note that if media blasting is used, it may "work over" small discontinuities in the part, and an etching bath is recommended as a post-blasting treatment.

Application of the penetrant to a part in a ventilated test area.

2. Application of Penetrant:

The penetrant is then applied to the surface of the item being tested. The penetrant is allowed "dwell time" to soak into any flaws (generally 5 to 30 minutes). The dwell time mainly depends upon the penetrant being used, material being tested and the size of flaws sought. As expected, smaller flaws require a longer penetration time. Due to their incompatible nature one must be careful not to apply solvent-based penetrant to a surface which is to be inspected with a water-washable penetrant.

3. Excess Penetrant Removal:

The excess penetrant is then removed from the surface. The removal method is controlled by the type of penetrant used. Water-washable, solvent-removable, lipophilic post-emulsifiable, or hydrophilic post-emulsifiable are the common choices. Emulsifiers represent the highest sensitivity level, and chemically interact with the oily penetrant to make it removable with a water spray. When using solvent remover and lint-free cloth it is important to not spray the solvent on the test surface directly, because this can remove the penetrant from the flaws. If excess penetrant is not properly removed, once the developer is applied, it may leave a background in the developed area that can mask indications or defects. In addition, this may also produce false indications severely hindering the ability to do a proper inspection. Also, the removal of excessive penetrant is done towards one direction either vertically or horizontally as the case may be.

4. Application of Developer:

After excess penetrant has been removed, a white developer is applied to the sample. Several developer types are available, including: , dry powder, water-suspendable, and water-soluble. Choice of developer is governed by penetrant compatibility (one can't use water-soluble or -suspendable developer with water-washable penetrant), and by inspection conditions. When using non-aqueous wet developer (NAWD) or dry powder, the sample must be dried prior to application, while soluble and suspendable developers are applied with the part still wet from the previous step. NAWD is commercially available in aerosol spray cans, and may employ acetone, isopropyl alcohol, or a propellant that is a combination of the two. Developer should form a semi-transparent, even coating on the surface.

The developer draws penetrant from defects out onto the surface to form a visible indication, commonly known as bleed-out. Any areas that bleed out can indicate the location, orientation and possible types of defects on the surface. Interpreting the results and characterizing defects from the indications found may require some training and/or experience [the indication size is not the actual size of the defect].

5. Inspection:

The inspector will use visible light with adequate intensity (100 foot-candles or 1100 lux is typical) for visible dye penetrant. Ultraviolet (UV-A) radiation of adequate intensity (1,000 micro-watts per centimeter squared is common), along with low ambient light levels (less than 2 foot-candles) for fluorescent penetrant examinations. Inspection of the test surface should take place after 10- to 30-minute development time, and is dependent on the penetrant and developer used. This time delay allows the blotting action to occur. The inspector may observe the sample for indication formation when using visible dye. It is also good practice to observe indications as they form because the characteristics of the bleed out are a significant part of interpretation characterization of flaws.

6. Post Cleaning:

The test surface is often cleaned after inspection and recording of defects, especially if post-inspection coating processes are scheduled.

Advantages and disadvantages

The main advantages of DPI are the speed of the test and the low cost. Disadvantages include the detection of only surface flaws, skin irritation, and the inspection should be on a smooth clean surface where excessive penetrant can be removed prior to being developed. Conducting the test on rough surfaces, such as "as-welded" welds, will make it difficult to remove any excessive penetrant and could result in false indications. Water-washable penetrant should be considered here if no other option is available. Also, on certain surfaces a great enough color contrast cannot be achieved or the dye will stain the workpiece.[1]

Limited training is required for the operator — although experience is quite valuable. Proper cleaning is necessary to assure that surface contaminants have been removed and any defects present are clean and dry. Some cleaning methods have been shown to be detrimental to test sensitivity, so acid etching to remove metal smearing and re-open the defect may be necessary.[2]

Standards

International Organization for Standardization (ISO)
  • ISO 3059, Non-destructive testing - Penetration testing and magnetic particle testing - Viewing conditions
  • ISO 3452-1, Non-destructive testing. Penetrant testing. Part 1. General principles
  • ISO 3452-2, Non-destructive testing - Penetrant testing - Part 2: Testing of penetrant materials
  • ISO 3452-3, Non-destructive testing - Penetrant testing - Part 3: Reference test blocks
  • ISO 3452-4, Non-destructive testing - Penetrant testing - Part 4: Equipment
  • ISO 3452-5, Non-destructive testing - Penetrant testing - Part 5: Penetrant testing at temperatures higher than 50 °C
  • ISO 3452-6, Non-destructive testing - Penetrant testing - Part 6: Penetrant testing at temperatures lower than 10 °C
  • ISO 10893-4: Non-destructive testing of steel tubes. Liquid penetrant inspection of seamless and welded steel tubes for the detection of surface imperfections.
  • ISO 12706, Non-destructive testing - Penetrant testing - Vocabulary
  • ISO 23277, Non-destructive testing of welds - Penetrant testing of welds - Acceptance levels
European Committee for Standardization (CEN)
  • EN 1371-1, Founding - Liquid penetrant inspection - Part 1: Sand, gravity die and low pressure die castings
  • EN 1371-2, Founding - Liquid penetrant inspection - Part 2: Investment castings
  • EN 2002-16, Aerospace series - Metallic materials; test methods - Part 16: Non-destructive testing, penetrant testing
  • EN 10228-2, Non-destructive testing of steel forgings - Part 2: Penetrant testing
ASTM International (ASTM)
  • ASTM E 165, Standard Practice for Liquid Penetrant Examination for General Industry
  • ASTM E 1417, Standard Practice for Liquid Penetrant Testing
American Society of Mechanical Engineers (ASME)
  • ASME Boiler and Pressure Vessel Code, Section V, Art. 6, Liquid Penetrant Examination
  • ASME Boiler and Pressure Vessel Code, Section V, Art. 24 Standard Test Method for Liquid Penetrant Examination SE-165 (identical with ASTM E-165)

See also

References

  1. ^ Kohan, Anthony Lawrence (1997), Boiler operator's guide (4th ed.), McGraw-Hill Professional, p. 240, ISBN 978-0-07-036574-2. 
  2. ^ http://www.ndt-ed.org/EducationResources/CommunityCollege/PenetrantTest/MethodsTech/materialsmear.htm

External links

Magnetic particle inspection

Magnetic particle inspection

A technician performs MPI on a pipeline to check for stress corrosion cracking using what is known as the "black and white" method. No indications of cracking appear in this picture; the only marks are the "footprints" of the magnetic yoke and drip marks.
A close-up of the surface of a (different) pipeline showing indications of stress corrosion cracking (two clusters of small black lines) revealed by MPI. Cracks that would normally have been invisible are detectable due to the magnetic particles clustering at the crack openings. The scale at the bottom is numbered in centimetres.

Magnetic particle Inspection (MPI) is a non-destructive testing (NDT) process for detecting surface and slightly subsurface discontinuities in ferromagnetic materials such as iron, nickel, cobalt, and some of their alloys. The process puts a magnetic field into the part. The piece can be magnetized by direct or indirect magnetization. Direct magnetization occurs when the electric current is passed through the test object and a magnetic field is formed in the material. Indirect magnetization occurs when no electric current is passed through the test object, but a magnetic field is applied from an outside source. The magnetic lines of force are perpendicular to the direction of the electric current, which may be either alternating current (AC) or some form of direct current (DC) (rectified AC).

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.

To identify a leak, ferrous particles, either dry or in a wet suspension, are applied to a part. These are attracted to an area of flux leakage and form what is known as an indication, which is evaluated to determine its nature, cause, and course of action, if any.

Types of electrical currents used

There are several types of electrical currents used in magnetic particle inspection. For a proper current to be selected one needs to consider the part geometry, material, the type of discontinuity one is seeking, and how far the magnetic field needs to penetrate into the part.

  • Alternating current (AC) is commonly used to detect surface discontinuities. Using AC to detect subsurface discontinuities is limited due to what is known as the skin effect, where the current runs along the surface of the part. Because the current alternates in polarity at 50 to 60 cycles per second it does not penetrate much past the surface of the test object. This means the magnetic domains will only be aligned equal to the distance AC current penetration into the part. The frequency of the alternating current determines how deep the penetration.
  • Full wave DC[clarification needed - discussion] (FWDC) is used to detect subsurface discontinuities where AC can not penetrate deep enough to magnetize the part at the depth needed. The amount of magnetic penetration depends on the amount of current through the part.[1] DC is also limited on very large cross-sectional parts in terms of how effectively it will magnetize the part.
  • Half wave DC (HWDC, pulsating DC) works similar to full wave DC, but allows for detection of surface breaking indications and has more magnetic penetration into the part than FWDC. HWDC is advantageous for inspection process as it actually helps move the magnetic particles during the bathing of the test object. The aid in particle mobility is caused by the half-wave pulsating current waveform. In a typical mag pulse of 0.5 seconds there are 15 pulses of current using HWDC. This gives the particle more of an opportunity to come in contact with areas of magnetic flux leakage.

An AC electromagnet is the preferred method for find surface breaking indication. The use of an electromagnet to find subsurface indications is difficult. An AC electromagnet is a better means to detect a surface indication than HWDC, DC, or permanent magnet, while some form of DC is better for subsurface defects.

Equipment

A wet horizontal MPI machine with a 36 in (910 mm) coil
Using a similar machine, a U.S. Navy technician sprays magnetic particles on a test part under ultraviolet light.
An automatic wet horizontal MPI machine with an external power supply, conveyor, and demagnetizing system. It is used to inspect engine cranks.
  • A wet horizontal MPI machine is the most commonly used mass-production inspection machine. The machine has a head and tail stock where the part is placed to magnetize it. In between the head and tail stock is typically an induction coil, which is used to change the orientation of the magnetic field by 90° from the head stock. Most of the equipment is built for a specific application.
  • Mobile power packs are custom-built magnetizing power supplies used in wire wrapping applications.
  • Magnetic yoke is a hand-held device that induces a magnetic field between two poles. Common applications are for outdoor use, remote locations, and weld inspection. The draw back of magnetic yokes is that they only induce a magnetic field between the poles, so large-scale inspections using the device can be time-consuming. For proper inspection the yoke needs to be rotated 90 degrees for every inspection area to detect horizontal and vertical discontinuities. Subsurface detection using a yoke is limited. These systems used dry magnetic powders, wet powders, or aerosols.

Demagnetizing parts

A pull through AC demagnetizing unit

After the part has been magnetized it needs to be demagnetized. This requires special equipment that works the opposite way of the magnetizing equipment. The magnetization is normally done with a high current pulse that reaches a peak current very quickly and instantaneously turns off leaving the part magnetized. To demagnetize a part, the current or magnetic field needed has to be equal to or greater than the current or magnetic field used to magnetize the part. The current or magnetic field is then slowly reduced to zero, leaving the part demagnetized.

  • AC demagnetizing
    • Pull-through AC demagnetizing coils: seen in the figure to the right are AC powered devices that generate a high magnetic field where the part is slowly pulled through by hand or on a conveyor. The act of pulling the part through and away from the coil's magnetic field slows drops the magnetic field in the part. Note that many AC demagnetizing coils have power cycles of several seconds so the part must be passed through the coil and be several feet (meters) away before the demagnetizing cycle finishes or the part will have residual magnetization.
    • AC decaying demagnetizing: this is built into most single phase MPI equipment. During the process the part is subjected to an equal or greater AC current, after which the current is reduced over a fixed period of time (typically 18 seconds) until zero output current is reached. As AC is alternating from a positive to a negative polarity this will leave the magnetic domains of the part randomized.
    • AC demag does have significant limitations on its ability to demag a part depending on the geometry and the alloys used.
  • Reversing full wave DC demagnetizing: this is a demagnetizing method that must be built into the machine during manufacturing. It is similar to AC decaying except the DC current is stopped at intervals of half a second, during which the current is reduced by a quantity and its direction is reversed. Then current is passed through the part again. The process of stopping, reducing and reversing the current will leave the magnetic domains randomized. This process is continued until zero current is passed through the part. The normal reversing DC demag cycle on modern equipment should be 18 seconds or longer. This method of demag was developed to overcome the limitations presented by the AC demag method where part geometry and certain alloys prevented the AC demag method from working.
  • Halfwave DC demagnetizing (HWDC): this process is identical to full-wave DC demagnetization, except the waveform is half-wave. This method of demagnetization is new to the industry and only available from a single manufacturer. It was developed to be a cost-effective method to demagnetize without needing a full-wave DC bridge design power supply. This method is only found on single-phase AC/HWDC power supplies. HWDC demagnetization is just as effective as full-wave DC, without the extra cost and added complexity. Of course, other limitations apply due to inductive losses when using HWDC waveform on large-diameter parts. Also, HWDC effectiveness is limited past 410 mm (16 in) diameter using a 12-volt power supply.

Magnetic particle powder

A common particle used to detect cracks is iron oxide, for both dry and wet systems.

  • Wet system particle range in size from less than 0.5 micrometres to 10 micrometres for use with water or oil carriers. Particles used in wet systems have pigments applied that fluoresce at 365 nm (ultraviolet A) requiring 1000 µW/cm2 (10 W/m2) at the surface of the part for proper inspection. If the particles do not have the correct light applied in a darkroom the particles cannot be detected/seen. It is industry practice to use UV goggles/glasses to filter the UV light and amplify the visible light spectrum (normally green and yellow) created by the fluorescing particles. Green and yellow fluorescence was chosen, because the human eye reacts best to these colors.
After applying wet magnetic particles, a U.S. navy technician examines a bolt for cracks under ultraviolet light.
  • Dry particle powders range in size from 5 to 170 micrometres, designed to be seen in white light conditions. The particles are not designed to be used in wet environments. Dry powders are normally applied using hand operated air powder applicators.
  • Aerosol applied particles are similar to wet systems, sold in premixed aerosol cans similar to hair spray.

Magnetic particle carriers

It is common industry practice to use specifically designed oil and water-based carriers for magnetic particles. Deodorized kerosene and mineral spirits have not been commonly used in the industry for 40 years. It is dangerous to use kerosene or mineral spirits as a carrier due to their low flash points, and inhalation of fumes by the operators.

Inspection

The following are general steps for inspecting on a wet horizontal machine:

  1. Part is cleaned of oil and other contaminants.
  2. Necessary calculations done to know the amount of current required to magnetize the part. Refer ASTM E1444/E1444M for formulas.
  3. The magnetizing pulse is applied for 0.5 seconds, during which the operator washes the part with the particle, stopping before the magnetic pulse is completed. Failure to stop prior to end of the magnetic pulse will wash away indications.
  4. UV light is applied while the operator looks for indications of defects that are 0 to ±45 degrees from path the current flowed through the part. Indications only appear 45 to 90 degrees of the magnetic field applied. The easiest way to quickly figure out which way the magnetic field is running is grab the part with either hand between the head stocks laying your thumb against the part (do not wrap your thumb around the part) this is called either left or right thumb rule or right hand grip rule. The direction the thumb points tell us the direction current is flowing, the magnetic field will be running 90 degrees from the current path. On complex geometry, like a crankshaft, the operator needs to visualize the changing direction of the current and magnetic field created. The current starts at 0 degrees then 45 degrees to 90 degree back to 45 degrees to 0 then -45 to -90 to -45 to 0 and this is repeated for each crankpin. Thus, it can be time consuming to find indications that are only 45 to 90 degrees from the magnetic field.
  5. The part is either accepted or rejected, based on pre-defined criteria.
  6. The part is demagnetized.
  7. Depending on requirements, the orientation of the magnetic field may need to be changed 90 degrees to inspect for indications that cannot be detected from steps 3 to 5. The most common way to change magnetic field orientation is to use a "coil shot". In Fig 1 a 36 inch coil can be seen then steps 4, 5, and 6 are repeated.

Standards

International Organization for Standardization (ISO)
  • ISO 3059, Non-destructive testing - Penetrant testing and magnetic particle testing - Viewing conditions
  • ISO 9934-1, Non-destructive testing - Magnetic particle testing - Part 1: General principles
  • ISO 9934-2, Non-destructive testing - Magnetic particle testing - Part 2: Detection media
  • ISO 9934-3, Non-destructive testing - Magnetic particle testing - Part 3: Equipment
  • ISO 10893-5, Non-destructive testing of steel tubes. Magnetic particle inspection of seamless and welded ferromagnetic steel tubes for the detection of surface imperfections
  • ISO 17638, Non-destructive testing of welds - Magnetic particle testing
  • ISO 23278, Non-destructive testing of welds - Magnetic particle testing of welds - Acceptance levels
European Committee for Standardization (CEN)
  • EN 1330-7, Non-destructive testing - Terminology - Part 7: Terms used in magnetic particle testing
  • EN 1369, Founding - Magnetic particle inspection
  • EN 10228-1, Non-destructive testing of steel forgings - Part 1: Magnetic particle inspection
American Society of Testing and Materials (ASTM)
  • ASTM E1444/E1444M Standard Practice for Magnetic Particle Testing
  • ASTM A 275/A 275M Test Method for Magnetic Particle Examination of Steel Forgings
  • ASTM A456 Specification for Magnetic Particle Inspection of Large Crankshaft Forgings
  • ASTM E543 Practice Standard Specification for Evaluating Agencies that Performing Nondestructive Testing
  • ASTM E 709 Guide for Magnetic Particle Testing Examination
  • ASTM E 1316 Terminology for Nondestructive Examinations
  • ASTM E 2297 Standard Guide for Use of UV-A and Visible Light Sources and Meters used in the Liquid Penetrant and Magnetic Particle Methods
Canadian Standards Association (CSA)
  • CSA W59
Society of Automotive Engineers (SAE)
  • AMS 2641 Magnetic Particle Inspection Vehicle
  • AMS 3040 Magnetic Particles, Nonfluorescent, Dry Method
  • AMS 3041 Magnetic Particles, Nonfluorescent, Wet Method, Oil Vehicle, Ready-To-Use
  • AMS 3042 Magnetic Particles, Nonfluorescent, Wet Method, Dry Powder
  • AMS 3043 Magnetic Particles, Nonfluorescent, Wet Method, Oil Vehicle, Aerosol Packaged
  • AMS 3044 Magnetic Particles, Fluorescent, Wet Method, Dry Powder
  • AMS 3045 Magnetic Particles, Fluorescent, Wet Method, Oil Vehicle, Ready-To-Use
  • AMS 3046 Magnetic Particles, Fluorescent, Wet Method, Oil Vehicle, Aerosol Packaged5
  • AMS 5062 Steel, Low Carbon Bars, Forgings, Tubing, Sheet, Strip, and Plate 0.25 Carbon, Maximum
  • AMS 5355 Investment Castings
  • AMS I-83387 Inspection Process, Magnetic Rubber
  • AMS-STD-2175 Castings, Classification and Inspection of AS 4792 Water Conditioning Agents for Aqueous Magnetic Particle Inspection AS 5282 Tool Steel Ring Standard for Magnetic Particle Inspection AS5371 Reference Standards Notched Shims for Magnetic Particle Inspection
United States Military Standard
  • A-A-59230 Fluid, Magnetic Particle Inspection, Suspension

References

  1. ^ Betz, C. E. (1985), Principles of Magnetic Particle Testing (PDF), American Society for Nondestructive Testing, p. 234, ISBN 978-0-318-21485-6. 

Further reading

External links

Nondestructive testing (NDT)

Nondestructive testing

Nondestructive testing or non-destructive testing (NDT) is a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage.[1] The terms nondestructive examination (NDE), nondestructive inspection (NDI), and nondestructive evaluation (NDE) are also commonly used to describe this technology.[2] 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.[3] NDT is commonly used in forensic engineering, mechanical engineering, petroleum engineering, electrical engineering, civil engineering, systems engineering, aeronautical engineering, medicine, and art.[1] Innovations in the field of nondestructive testing have had a profound impact on medical imaging, including on echocardiography, medical ultrasonography, and digital radiography.

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 objects 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.


Analyzing and documenting a nondestructive failure mode can also be accomplished using a high-speed camera recording continuously (movie-loop) until the failure is detected. Detecting the failure can be accomplished using a sound detector or stress gauge which produces a signal to trigger the high-speed camera. These high-speed cameras have advanced recording modes to capture some non-destructive failures.[4] After the failure the high-speed camera will stop recording. The capture images can be played back in slow motion showing precisely what happen before, during and after the nondestructive event, image by image.

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

  1. Section of material with a surface-breaking crack that is not visible to the naked eye.
  2. Penetrant is applied to the surface.
  3. Excess penetrant is removed.
  4. Developer is applied, rendering the crack visible.

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.[5] 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

Structure can be complex systems that undergo different loads during their lifetime, e.g. Lithium-ion batteries.[6] 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.

Relation to Medical Procedures

Chest radiography indicating a peripheral bronchial carcinoma.

Several NDT methods are related to clinical procedures, such as Radiography, Ultrasonic Testing, and Visual Testing. Technological improvements or upgrades in these NDT methods have migrated over from medical equipment advances, including Digital Radiography (DR), Phased Array Ultrasonic Testing (PAUT), and Endoscopy (Borescope or Assisted Visual Inspection).

Notable events in early academic and industrial NDT

  • 1854 Hartford, Connecticut — A boiler at the Fales and Gray Car works explodes, killing 21 people and seriously injuring 50. Within a decade, the State of Connecticut passes a law requiring annual inspection (in this case visual) of boilers.
  • 1880-1920 — The "Oil and Whiting" method of crack detection[7] is used in the railroad industry to find cracks in heavy steel parts. (A part is soaked in thinned oil, then painted with a white coating that dries to a powder. Oil seeping out from cracks turns the white powder brown, allowing the cracks to be detected.) This was the precursor to modern liquid penetrant tests.
  • 1895 — Wilhelm Conrad Röntgen discovers what are now known as X-rays. In his first paper he discusses the possibility of flaw detection.
  • 1920 — Dr. H. H. Lester begins development of industrial radiography for metals.
  • 1924 — Lester uses radiography to examine castings to be installed in a Boston Edison Company steam pressure power plant.
  • 1926 — The first electromagnetic eddy current instrument is available to measure material thicknesses.
  • 1927-1928 — Magnetic induction system to detect flaws in railroad track developed by Dr. Elmer Sperry and H.C. Drake.
  • 1929 — Magnetic particle methods and equipment pioneered (A.V. DeForest and F.B. Doane.)
  • 1930s — Robert F. Mehl demonstrates radiographic imaging using gamma radiation from Radium, which can examine thicker components than the low-energy X-ray machines available at the time.
  • 1935-1940 — Liquid penetrant tests developed (Betz, Doane, and DeForest)
  • 1935-1940s — Eddy current instruments developed (H.C. Knerr, C. Farrow, Theo Zuschlag, and Fr. F. Foerster).
  • 1940-1944 — Ultrasonic test method developed in USA by Dr. Floyd Firestone, who applies for a U.S. invention patent for same on May 27, 1940 and is issued the U.S. patent as grant no. 2,280,226 on April 21, 1942. Extracts from the first two paragraphs of this seminal patent for a nondestructive testing method succinctly describe the basics of ultrasonic testing. "My invention pertains to a device for detecting the presence of inhomogeneities of density or elasticity in materials. For instance if a casting has a hole or a crack within it, my device allows the presence of the flaw to be detected and its position located, even though the flaw lies entirely within the casting and no portion of it extends out to the surface." Additionally, "The general principle of my device consists of sending high frequency vibrations into the part to be inspected, and the determination of the time intervals of arrival of the direct and reflected vibrations at one or more stations on the surface of the part." Medical echocardiography is an offshoot of this technology.[8]
  • 1946 — First neutron radiographs produced by Peters.
  • 1950 — The Schmidt Hammer (also known as "Swiss Hammer") is invented. The instrument uses the world’s first patented non-destructive testing method for concrete.
  • 1950 — J. Kaiser introduces acoustic emission as an NDT method.

(Basic Source for above: Hellier, 2001) Note the number of advancements made during the WWII era, a time when industrial quality control was growing in importance.

  • 1963 — Frederick G. Weighart's[9] and James F. McNulty (U.S. radio engineer)’s[10] co-invention of Digital radiography is an offshoot of the pairs development of nondestructive test equipment at Automation Industries, Inc., then, in El Segundo, California. See James F. McNulty also at article Ultrasonic testing.
  • 1996 — Rolf Diederichs founded the first Open Access NDT Journal in the Internet. Today the Open Access NDT Database NDT.net
  • 2008 — Academia NDT International has been officially founded and has its base office in Brescia (Italy) www.academia-ndt.org

Methods and techniques

An example of a 3D replicating technique. The flexible high-resolution replicas allow surfaces to be examined and measured under laboratory conditions. A replica can be taken from all solid materials.

NDT is divided into various methods of nondestructive testing, each based on a particular scientific principle. These methods may be further subdivided into various techniques. The various methods and techniques, due to their particular natures, may lend themselves especially well to certain applications and be of little or no value at all in other applications. Therefore, choosing the right method and technique is an important part of the performance of NDT.

Combination of PAUT and TOFD is proving an alternate of radiography in industry

Personnel training, qualification and certification

Successful and consistent application of nondestructive testing techniques depends heavily on personnel training, experience and integrity. Personnel involved in application of industrial NDT methods and interpretation of results should be certified, and in some industrial sectors certification is enforced by law or by the applied codes and standards.[14]

NDT professionals and managers who seek to further their growth, knowledge and experience to remain competitive in the rapidly advancing technology field of nondestructive testing should consider joining NDTMA, a member organization comprised of NDT Managers and Executives who work to provide a forum for the open exchange of managerial, technical and regulatory information critical to the successful management of NDT personnel and activities. Their annual conference at the Golden Nugget in Las Vegas is a popular for its informative and relevant programming and exhibition space

Definitions

The following definitions for qualification and certification are given in ISO 9712:[15]

  • Certification: Procedure, used by the certification body to confirm that the qualification requirements for a method, level and sector have been fulfilled, leading to the issuing of a certificate.
  • Qualification: Demonstration of physical attributes, knowledge, skill, training and experience required to properly perform NDT tasks.

In US standards and codes, while a very similar definition of qualification is included in ASNT SNT-TC-1A, certification is simply defined as: "Written testimony of qualification".

In the aerospace sector, EN 4179:2009 contains the following definitions:[16]

  • Certification: Written statement by an employer that an individual has met the applicable requirements of this standard.
  • Qualification: The skills, training, knowledge, examinations, experience and visual capability required for personnel to properly perform to a particular level.

Training

Non-Destructive Testing (NDT) training is provided for people working in many industries. It is generally necessary that the candidate successfully completes a theoretical and practical training program, as well as have performed several hundred hours of practical application of the particular method they wish to be trained in. At this point, they may pass a certification examination. While online training has become more popular, many certifying bodies will require additional practical training.

Certification schemes

There are two approaches in personnel certification:[17]

  1. Employer Based Certification: Under this concept the employer compiles their own Written Practice. The written practice defines the responsibilities of each level of certification, as implemented by the company, and describes the training, experience and examination requirements for each level of certification. In industrial sectors the written practices are usually based on recommended practice SNT-TC-1A of the American Society for Nondestructive Testing.[18] ANSI standard CP-189 outlines requirements for any written practice that conforms to the standard.[19] For aviation, space, and defense (ASD) applications NAS 410 sets further requirements for NDT personnel, and is published by AIA - Aerospace Industries Association, which is made up of US aerospace airframe and powerplant manufacturers. This is the basis document for EN 4179[16] and other (USA) NIST-recognized aerospace standards for the Qualification and Certification (employer-based) of Nondestructive Testing personnel. NAS 410 also sets the requirements also for "National NDT Boards", which allow and proscribe personal certification schemes. NAS 410 allows ASNT Certification as a portion of the qualifications needed for ASD certification.[20]
  2. Personal Central Certification: The concept of central certification is that an NDT operator can obtain certification from a central certification authority, that is recognized by most employers, third parties and/or government authorities. Industrial standards for central certification schemes include ISO 9712,[15] and ANSI/ASNT CP-106[21] (used for the ASNT ACCP [22] scheme). Certification under these standards involves training, work experience under supervision and passing a written and practical examination set up by the independent certification authority. EN 473[23] was another central certification scheme, very similar to ISO 9712, which was withdrawn when CEN replaced it with EN ISO 9712 in 2012.

In the United States employer based schemes are the norm, however central certification schemes exist as well. The most notable is ASNT Level III (established in 1976-1977), which is organized by the American Society for Nondestructive Testing for Level 3 NDT personnel.[24] NAVSEA 250-1500 is another US central certification scheme, specifically developed for use in the naval nuclear program.[25]

Central certification is more widely used in the European Union, where certifications are issued by accredited bodies (independent organizations conforming to ISO 17024 and accredited by a national accreditation authority like UKAS). The Pressure Equipment Directive (97/23/EC) actually enforces central personnel certification for the initial testing of steam boilers and some categories of pressure vessels and piping.[26] European Standards harmonized with this directive specify personnel certification to EN 473. Certifications issued by a national NDT society which is a member of the (EFNDT) are mutually acceptable by the other member societies [27] under a multilateral recognition agreement.

Canada also implements an ISO 9712 central certification scheme, which is administered by Natural Resources Canada, a government department.[28][29][30]

The aerospace sector worldwide sticks to employer based schemes.[31] In America it is based mostly on AIA-NAS-410 [32] and in the European Union on the equivalent and very similar standard EN 4179.[16] However EN 4179:2009 includes an option for central qualification and certification by a National aerospace NDT board or NANDTB (paragraph 4.5.2).

Levels of certification

Most NDT personnel certification schemes listed above specify three "levels" of qualification and/or certification, usually designated as Level 1, Level 2 and Level 3 (although some codes specify Roman numerals, like Level II). The roles and responsibilities of personnel in each level are generally as follows (there are slight differences or variations between different codes and standards):[15][16]

  • Level 1 are technicians qualified to perform only specific calibrations and tests under close supervision and direction by higher level personnel. They can only report test results. Normally they work following specific work instructions for testing procedures and rejection criteria.
  • Level 2 are engineers or experienced technicians who are able to set up and calibrate testing equipment, conduct the inspection according to codes and standards (instead of following work instructions) and compile work instructions for Level 1 technicians. They are also authorized to report, interpret, evaluate and document testing results. They can also supervise and train Level 1 technicians. In addition to testing methods, they must be familiar with applicable codes and standards and have some knowledge of the manufacture and service of tested products.
  • Level 3 are usually specialized engineers or very experienced technicians. They can establish NDT techniques and procedures and interpret codes and standards. They also direct NDT laboratories and have central role in personnel certification. They are expected to have wider knowledge covering materials, fabrication and product technology.

Terminology

The standard US terminology for Nondestructive testing is defined in standard ASTM E-1316.[33] Some definitions may be different in European standard EN 1330.

Indication 
The response or evidence from an examination, such as a blip on the screen of an instrument. Indications are classified as true or false. False indications are those caused by factors not related to the principles of the testing method or by improper implementation of the method, like film damage in radiography, electrical interference in ultrasonic testing etc. True indications are further classified as relevant and non relevant. Relevant indications are those caused by flaws. Non relevant indications are those caused by known features of the tested object, like gaps, threads, case hardening etc.
Interpretation 
Determining if an indication is of a type to be investigated. For example, in electromagnetic testing, indications from metal loss are considered flaws because they should usually be investigated, but indications due to variations in the material properties may be harmless and nonrelevant.
Flaw 
A type of discontinuity that must be investigated to see if it is rejectable. For example, porosity in a weld or metal loss.
Evaluation 
Determining if a flaw is rejectable. For example, is porosity in a weld larger than acceptable by code?
Defect 
A flaw that is rejectable — i.e. does not meet acceptance criteria. Defects are generally removed or repaired.[33]

Reliability and statistics

Probability of detection (POD) tests are a standard way to evaluate a nondestructive testing technique in a given set of circumstances, for example "What is the POD of lack of fusion flaws in pipe welds using manual ultrasonic testing?" The POD will usually increase with flaw size. A common error in POD tests is to assume that the percentage of flaws detected is the POD, whereas the percentage of flaws detected is merely the first step in the analysis. Since the number of flaws tested is necessarily a limited number (non-infinite), statistical methods must be used to determine the POD for all possible defects, beyond the limited number tested. Another common error in POD tests is to define the statistical sampling units (test items) as flaws, whereas a true sampling unit is an item that may or may not contain a flaw.[34][35] Guidelines for correct application of statistical methods to POD tests can be found in ASTM E2862 Standard Practice for Probability of Detection Analysis for Hit/Miss Data and MIL-HDBK-1823A Nondestructive Evaluation System Reliability Assessment, from the U.S. Department of Defense Handbook.

See also

References

  1. ^ a b Cartz, Louis (1995). Nondestructive Testing. A S M International. ISBN 978-0-87170-517-4. 
  2. ^ Charles Hellier (2003). Handbook of Nondestructive Evaluation. McGraw-Hill. p. 1.1. ISBN 0-07-028121-1. 
  3. ^ Introduction to Nondestructive Testing, The American Society for Nondestructive Testing
  4. ^ Bridges, Andrew. "High Speed Cameras for Non-Destructive Testing". NASA TechBriefs. Retrieved 1 November 2013. 
  5. ^ Blitz, Jack; G. Simpson (1991). Ultrasonic Methods of Non-Destructive Testing. Springer-Verlag New York, LLC. ISBN 978-0-412-60470-6. 
  6. ^ Waldmann, T. (2014). "A Mechanical Aging Mechanism in Lithium-Ion Batteries". Journal of the Electrochemical Society. 161: A1742. doi:10.1149/2.1001410jes. 
  7. ^ Introduction and History of Penetrant Inspection
  8. ^ Singh S, Goyal A (2007). "The origin of echocardiography: a tribute to Inge Edler". Tex Heart Inst J. 34: 431–8. PMC 2170493Freely accessible. PMID 18172524. 
  9. ^ U.S. Patent 3,277,302, titled "X-Ray Apparatus Having Means for Supplying An Alternating Square Wave Voltage to the X-Ray Tube", granted to Weighart on October 4, 1964, showing its patent application date as May 10, 1963 and at lines 1-6 of its column 4, also, noting James F. McNulty’s earlier filed co-pending application for an essential component of invention
  10. ^ U.S. Patent 3,289,000, titled "Means for Separately Controlling the Filament Current and Voltage on a X-Ray Tube", granted to McNulty on November 29, 1966 and showing its patent application date as March 5, 1963
  11. ^ ASTM E1351: "Standard Practice for Production and Evaluation of Field Metallographic Replicas" (2006)
  12. ^ BS ISO 3057 "Non-destructive testing - Metallographic replica techniques of surface examination" (1998)
  13. ^ "Fundamentals of Resonant Acoustic Method NDT" (2005)
  14. ^ "ICNDT Guide to Qualification and Certification of Personnel for NDT" (PDF). International Committee for NDT. 2012. 
  15. ^ a b c ISO 9712: Non-destructive testing -- Qualification and certification of NDT personnel (2012)
  16. ^ a b c d EN 4179: "Aerospace series. Qualification and approval of personnel for non-destructive testing" (2009)
  17. ^ John Thompson (November 2006). Global review of qualification and certification of personnel for NDT and condition monitoring. 12th A-PCNDT 2006 – Asia-Pacific Conference on NDT. Auckland, New Zealand. 
  18. ^ Recommended Practice No. SNT-TC-1A: Personnel Qualification and Certification in Nondestructive Testing, (2006)
  19. ^ ANSI/ASNT CP-189: ASNT Standard for Qualification and Certification of Nondestructive Testing Personnel, (2006)
  20. ^ AIA NAS410
  21. ^ ANSI/ASNT CP-106: "ASNT Standard for Qualification and Certification of Nondestructive Testing Personnel" (2008)
  22. ^ "ASNT Central Certification Program", ASNT Document ACCP-CP-1, Rev. 7 (2010)
  23. ^ EN 473: Non-destructive testing. Qualification and certification of NDT personnel. General principles, (2008)
  24. ^ Charles Hellier (2003). Handbook of Nondestructive Evaluation. McGraw-Hill. p. 1.25. ISBN 0-07-028121-1. 
  25. ^ Charles Hellier (2003). Handbook of Nondestructive Evaluation. McGraw-Hill. p. 1.26. ISBN 0-07-028121-1. 
  26. ^ Directive 97/23/EC of the European Parliament and of the Council of 29 May 1997 on the approximation of the laws of the Member States concerning pressure equipment, Annex I, paragraph 3.1.3
  27. ^ EFNDT/SEC/P/05-006: Agreement for EFNDT multilateral recognition of NDT personnel certification schemes (2005)
  28. ^ http://www.nrcan-rncan.gc.ca/smm-mms/ndt-end/index-eng.htm : The NDT Certifying Agency (CANMET-MTL)
  29. ^ The relevant national standard for Canada is CAN/CGSB-48.9712-2006 "Qualification and Certification of Non-Destructive Testing Personnel.", which complies with the requirements of ISO 9712:2005 and EN 473:2000.
  30. ^ Charles Hellier (2003). Handbook of Nondestructive Evaluation. McGraw-Hill. p. 1.27. ISBN 0-07-028121-1. 
  31. ^ R. Marini and P. Ranos: "Current Issues in Qualification and Certification of Non-Destructive Testing Personnel in the Aerospace Industry", ECNDT 2006 - Th.3.6.5
  32. ^ AIA-NAS-410: "Aerospace Industries Association, National Aerospace Standard, NAS Certification and Qualification of Nondestructive Test Personnel"
  33. ^ a b ASTM E-1316: "Standard Terminology for Nondestructive Examinations", The American Society for Testing and Materials, in Volume 03.03 NDT, 1997
  34. ^ T. Oldberg and R. Christensen (1999). "Erratic Measure". 4 (5). NDT.net. 
  35. ^ T. Oldberg (2005). "An Ethical Problem in the Statistics of Defect Detection Test Reliability". 10 (5). NDT.net. 

Bibliography

  • ASTM International, ASTM Volume 03.03 Nondestructive Testing
    • ASTM E1316-13a: "Standard Terminology for Nondestructive Examinations" (2013)
  • ASNT, Nondestructive Testing Handbook
  • Bray, D.E. and R.K. Stanley, 1997, Nondestructive Evaluation: A Tool for Design, Manufacturing and Service; CRC Press, 1996.
  • Charles Hellier (2003). Handbook of Nondestructive Evaluation. McGraw-Hill. ISBN 0-07-028121-1. 
  • Shull, P.J., Nondestructive Evaluation: Theory, Techniques, and Applications, Marcel Dekker Inc., 2002.
  • EN 1330: Non-destructive testing. Terminology. Nine parts. Parts 5 and 6 replaced by equivalent ISO standards.
    • EN 1330-1: Non-destructive testing. Terminology. List of general terms (1998)
    • EN 1330-2: Non-destructive testing. Terminology. Terms common to the non-destructive testing methods (1998)
    • EN 1330-3: Non-destructive testing. Terminology. Terms used in industrial radiographic testing (1997)
    • EN 1330-4: Non-destructive testing. Terminology. Terms used in ultrasonic testing (2010)
    • EN 1330-7: Non-destructive testing. Terminology. Terms used in magnetic particle testing (2005)
    • EN 1330-8: Non-destructive testing. Terminology. Terms used in leak tightness testing (1998)
    • EN 1330-9: Non-destructive testing. Terminology. Terms used in acoustic emission testing (2009)
    • EN 1330-10: Non-destructive testing. Terminology. Terms used in visual testing (2003)
    • EN 1330-11: Non-destructive testing. Terminology. Terms used in X-ray diffraction from polycrystalline and amorphous materials (2007)
  • ISO 12706: Non-destructive testing. Penetrant testing. Vocabulary (2009)
  • ISO 12718: Non-destructive testing. Eddy current testing. Vocabulary (2008)
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