FACTOID # 55: NationMaster.com is now 40 times the size of the CIA World Factbook!
 
 Home   Encyclopedia   Statistics   Countries A-Z   Flags   Maps   Education   Forum   FAQ   About 
 
WHAT'S NEW
RECENT ARTICLES
More Recent Articles »
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Nondestructive testing

Contents

Nondestructive testing (also called NDT, nondestructive evaluation, NDE, and nondestructive inspection, NDI) is testing that does not destroy the test object. NDE is vital for constructing and maintaining all types of components and structures. To detect different defects such as cracking and corrosion, there are different methods of testing available, such as X-ray (where cracks show up on the film) and ultrasound (where cracks show up as an echo blip on the screen). This article is aimed mainly at industrial NDT, but many of the methods described here can be used to test the human body. In fact methods from the medical field, where there tends to be more development funding available, have often been adapted for industrial use, as was the case with Phased array ultrasonics and Computed radiography. Phased Array (PA) ultrasonics is an advanced method of testing that has applications in medical imaging and industrial nondestructive testing. ... // Computed Radiography (CR) uses very similar equipment to conventional radiography except that in place of a film to create the image, an imaging plate is used. ...


While destructive testing usually provides a more reliable assessment of the state of the test object, destruction of the test object usually makes this type of test more costly to the test object's owner than nondestructive testing. Destructive testing is also inappropriate in many circumstances, such as forensic investigation. That there is a tradeoff between the cost of the test and its reliability favors a strategy in which most test objects are inspected nondestructively; destructive testing is performed on a sampling of test objects that is drawn randomly for the purpose of characterizing the testing reliability of the nondestructive test. In destructive testing, tests are carried out to the specimen’s failure. ... Forensics or forensic science is the application of science to questions which are of interest to the legal system. ... A set of two probabilities, the definition of which vary by field. ...


The need for NDT

It is actually very difficult to weld or mold a solid object that has no risk of breaking in service, so testing at manufacture and during use is often essential. During the process of molding a metal object, for example, the metal may shrink as it cools, and crack or introduce voids inside the structure. Even the best welders (and welding machines) don't make 100% perfect welds. Some typical weld defects that need to be found and repaired are lack of fusion of the weld to the metal and porous bubbles inside the weld, both of which could cause a structure to break or a pipeline to rupture.


During their service lives, many industrial components need regular nondestructive tests to detect damage that may be difficult or expensive to find by everyday methods. For example:

  • aircraft skins need regular checking to detect cracks;
  • underground pipelines are subject to corrosion and stress corrosion cracking;
  • pipes in industrial plants may be subject to erosion and corrosion from the products they carry;
  • concrete structures may be weakened if the inner reinforcing steel is corroded;
  • pressure vessels may develop cracks in welds;
  • the wire ropes in suspension bridges are subject to weather, vibration, and high loads, so testing for broken wires and other damage is important.

Over the past centuries, swordsmiths, blacksmiths, and bell-makers would listen to the ring of the objects they were creating to get an indication of the soundness of the material — a function that is now carried out by instrumentation and referred to as acoustic emission. In the cowboy days, it was quite common for a gun to kill the shooter rather than the person they were aiming at. From the 1992 Clint Eastwood western Unforgiven, here's a quote that reflects historical reality: Corrosion is deterioration of intrinsic properties in a material due to reactions with its environment. ... Stress corrosion cracking (SCC) is the unexpected sudden failure of normally ductile metals subjected to a constant tensile stress in a corrosive environment, especially at elevated temperature. ... A pressure vessel is a container designed to hold gases or liquids at a pressure different from the ambient pressure. ...

Little Bill Daggett: "... Bob's as good as dead because ... Corky ... takes careful aim and BAM!, the cylinder explodes in that Walker Colt he was carrying; a failing common to that model. It would have been better if Corky had two guns..., 'cause Bob walks over and shoots him."

Too bad for "Corky" that in those days X-ray was not available to allow the gun-maker to check for defects.


Notable events in early industrial NDT

  • 1854 Hartford, Connecticut: a boiler at the Fales and Gay 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.
  • 1895 Wilhelm Conrad Röntgen discovers what are now known as X-rays. In his first paper he discusses the possibility of flaw detection.
  • 1880 - 1920 The "Oil and Whiting" method of crack detection 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.
  • 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 (source).
  • 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.
  • 1950 J. Kaiser introduces acoustic emission as an NDT method.

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


Applications

NDT is used in a variety of settings that covers a wide range of industrial activity.

Car redirects here. ... An engine is something that produces some effect from a given input. ... Look up Frame in Wiktionary, the free dictionary. ... First flight, December 17, 1903 Aviation or air transport refers to the activities surrounding human flight and the aircraft industry. ... Look up aerospace in Wiktionary, the free dictionary. ... Airframe is a novel by renowned author Michael Crichton first published in hardback edition in 1996 and as a paperback edition in 1997. ... Simplified space frame roof with the nearest unit polygon hightlighted in blue A space frame is a truss-like, light weight rigid structure constructed from interlocking struts in a geometric pattern. ... Components of a typical, four stroke cycle, DOHC piston engine. ... A Pratt and Whitney turbofan engine for the F-15 Eagle is tested at Robins Air Force Base, Georgia, USA. The tunnel behind the engine muffles noise and allows exhaust to escape. ... A rocket is a vehicle, missile or aircraft which obtains thrust by the reaction to the ejection of fast moving exhaust from within a rocket engine. ... Cranes are essential in large construction projects, such as this skyscraper In project architecture and civil engineering, construction is the building or assembly of any infrastructure on a site. ... Look up Structure in Wiktionary, the free dictionary. ... A log bridge in the French Alps near Vallorcine. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... A blacksmiths forge For finery forges (making iron) see finery forge. ... Nuclear engineering is the practical application of the atomic nucleus gleaned from principles of nuclear physics and the interaction between radiation and matter. ... A petrochemical is any chemical derived from fossil fuels. ... Oil power plant in Iraq A power station or power plant is a facility for the generation of electric power. ... View of Shell Oil Refinery in Martinez, California. ... An International Paper mill in South Carolina The global pulp and paper industry is dominated by North American (United States, Canada), northern European (Sweden, Finland) and East Asian countries (such as Japan). ... A typical steel fabrication shop Fabrication is an industrial term generally applied to the building of metal machines and structures. ... The examples and perspective in this article or section may not represent a worldwide view. ... A pressure vessel is a container designed to hold gases or liquids at a pressure different from the ambient pressure. ... // A tank is a container, usually for liquids, sometimes for gases. ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ... A boiler is a closed vessel in which water or other fluid is heated under pressure. ... A heat exchanger is a device built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are directly contacted. ... WWII era steam turbine used for ship propulsion. ... Piping is used to convey fluids (usually liquids and gases but sometimes loose solids) from one location to another. ... This article or section needs to be wikified. ... A pig used in natural gas pipelines A Pipeline inspection gauge or pig in the pipeline industry is a tool that is sent down a pipeline and propelled by the pressure of the product in the pipeline itself. ... Rail inspection is the practice of examining rail tracks for flaws that could lead to catastrophic failures. ... This article, image, template or category should belong in one or more categories. ... Tubing refers to a flexible hose or pipe used in plumbing, irrigation, and other industries. ... Amusement park (also called theme park) is the generic term for a collection of rides and other entertainment attractions assembled for the purpose of entertaining a fairly large group of people. ... It has been suggested that this article or section be merged into Radiology. ... Medical physics is a branch of applied physics concerning the application of physics to medicine. ...

Methods and techniques

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.

Dye Penetrant Inspection. ... Radiographic Testing (RT), or industrial radiography, is a nondestructive testing (NDT) method of inspecting materials for hidden flaws by using the ability of short wavelength electromagnetic radiation (high energy photons) to penetrate various materials. ... Radiography is the creation of images by exposing a photographic film or other image receptor to X-rays. ... // Computed Radiography (CR) uses very similar equipment to conventional radiography except that in place of a film to create the image, an imaging plate is used. ... CT apparatus in a hospital Computed tomography (CT), originally known as computed axial tomography (CAT or CT scan) and body section roentgenography, is a medical imaging method employing tomography where digital geometry processing is used to generate a three-dimensional image of the internals of an object from a large... This article needs to be cleaned up to conform to a higher standard of quality. ... Phased Array (PA) ultrasonics is an advanced method of testing that has applications in medical imaging and industrial nondestructive testing. ... Time of Flight Diffraction (TOFD) method of Ultrasonic inspection is a very sensitive and accurate method for nondestructive testing of welds for defects. ... Ellipsometer M-2000 RCE by J A Woollam Co Ellipsometry is a versatile optical technique that has applications in many different fields, from the microelectronics and semiconductor industries (for characterizing oxides or photoresists on silicon wafers, for example) to biology. ... Pipeline video inspection is a form of telepresence used to visually inspect the interiors of pipelines. ... Electromagnetism is the unified phenomena of magnetic field produced by an electric current and electric currents produced by a time-changing magnetic field. Electromagnetic Testing (ET), as a form of nondestructive testing, is the process of inducing electric currents or magnetic fields or both inside a test object and observing... Eddy-Current testing uses electromagnetic induction to detect flaws in conductive materials, amongst other operations. ... Remote Field Testing (RFT) is an electromagnetic method of nondestructive testing whose main application is finding defects in steel pipes and tubes. ... Magnetic Particle Inspection processes are non-destructive methods for the detection of defects in ferrous materials. ... Magnetic flux leakage (MFL) is a magnetic method of nondestructive testing that is used to detect corrosion and pitting in steel structures, most commonly pipelines and storage tanks. ... Acoustic Emission (AE) is a type of nondestructive testing technology whereby ultrasonic transient elastic waves within a material are monitored in order to locate and define their source event. ... Holography (from the Greek, Όλος-holos whole + γραφή-graphe writing) is the science of producing holograms; it is an advanced form of photography that allows an image to be recorded in three dimensions. ...

Elements

Regardless of application or method, all nondestructive testing shares the same basic elements:

Source 
Source provides a medium for testing.
Modification 
The probing material must get modified due to variation in the source.
Detection 
A detector which will determine the changes on the probing medium.
Indication 
The response (blip on a screen) or evidence from an examination
Interpretation 
A method of interpreting indications.

Reliability and statistics

Its testing reliability is defined by its relationship to a perfect gold standard test, which measures the value of the test object without fail, denoted by a binary variable, termed OK/not_OK, whose values are elements in the set {OK, not_OK}. By definition, the nondestructive test errs when its measurement of OK/not_OK differs from the measurement of the same quantity by the perfect gold standard test. The Cartesian product of the sets of values respectively measured by the perfect gold standard test and the nondestructive test defines the four, possible events that belong to a measurement: a "false negative" occurs when the test object is not_OK but it is identified as OK by NDT; a "false positive" occurs when the test object is OK but it is identified as not_OK by NDT; similarly, a "true positive" occurs when the test object is not_OK and it is identified as not_OK by NDT and a "true negative" occurs when the test object is OK and NDT identifies it as OK. A set of two probabilities, the definition of which vary by field. ... The binary numeral system represents numeric values using two symbols, typically 0 and 1. ... In mathematics, the Cartesian product (or direct product) of two sets X and Y, denoted X × Y, is the set of all possible ordered pairs whose first component is a member of X and whose second component is a member of Y: The Cartesian product is named after René Descartes...


Defect detection tests

NDT's defect detection tests attempt to detect defects (e.g., cracks, intergranular corrosion, pits and inclusions) before they can cause structural failure, leaks or other, unfavorable outcomes. The existence of a "probability of detection," corresponding to the probability of a true positive given a true positive OR false negative (inclusive disjunction implied by OR) is more often asserted for these tests than delivered by their design. Similarly, the existence of a "probability of false call," corresponding to the probability of a false positive given a false positive OR true negative is more often asserted than delivered. This topic is amplified below. OR logic gate. ...


Violations of probability theory

Oldberg and Christensen (1995) and Oldberg (2005) report that today's defect detection tests violate probability theory empirically. Often, a probability of false call is not defined. Sometimes, the "probability" of detection is not a probability. In these ways, the testing reliability is ill-defined. Probability theory is the mathematical study of probability. ... A set of two probabilities, the definition of which vary by field. ...


The false impression that the testing reliability is well defined can be established by the use of terms that imply the preservation of probability theory under conditions in which probability theory is empirically violated. An article that is posted by the U.S. Nuclear Regulatory Commission, 2000 at its Web site provides a case in point. In the article, the agency applies the terms "probability of detection," "signal" and "noise" to a Defect Detection Test that is used in the safety inspections of nuclear power reactors. The terms "signal" and "noise" imply that probability theory is unconditionally preserved, but Oldberg and Christensen (1995) demonstrate that it is only conditionally preserved in this test. The term "probability of detection" implies that probability theory is preserved, given the event of a true positive OR false negative but Oldberg and Christensen (1995) demonstrate that, for this test, this is not true. A set of two probabilities, the definition of which vary by field. ... Probability theory is the mathematical study of probability. ... Probability theory is the mathematical study of probability. ...


Some of the consequences of this kind of terminological abuse are: a) it appears that the testing reliability can be determined when it can't b) it appears that the expected utility of testing can be determined when it cannot and c) it appears that decisions can be made about testing on a basis that is considered rational by decision analysts when one's ability to make such decisions is actually crippled. In a defect-sensitive technology such as nuclear power, a further consequence might be significant, unnecessary loss of life and property damage. A set of two probabilities, the definition of which vary by field. ... The expected utility hypothesis is the hypothesis in economics that the utility of an agent facing uncertainty is calculated by considering utility in each possible state and constructing a weighted average. ... Decision analysts are people who use formal methods, particularly Expected Utility Theory, to assist others in decision making. ...


Potential and actual users of Defect Detection Tests should also be aware of the fact that the expected utility of such a test depends upon a) the nature of the statistical populations to be tested and b) the utilities of the user. As the populations are undefined and the associated utilities vary by user, claims that testing with a particular technology has a greater, expected utility than non-testing or that testing with a particular technology as a greater, expected utility than testing with another technology should be met with skepticism. The expected utility hypothesis is the hypothesis in economics that the utility of an agent facing uncertainty is calculated by considering utility in each possible state and constructing a weighted average. ...


See also

To meet Wikipedias quality standards, this article or section may require cleanup. ... Predictive maintenance (PdM) techniques help determine the condition of in-service equipment in order to predict when maintenance should be performed. ... Failure analysis is the process of determining the cause of failure, collecting and analyzing data, and developing conclusions to eliminate the failure mechanism causing specific device or system failures. ...

References

NDT Books

  • Bray, D.E. and R.K. Stanley, 1997, Nondestructive Evaluation: A Tool for Design, Manufacturing and Service; CRC Press, 1996.
  • Chuck Hellier, Handbook of Nondestructive Evaluation, McGraw-Hill Professional; 2001
  • Peter J. Shull, Nondestructive Evaluation: Theory, Techniques, and Applications, Marcel Dekker Inc., 2002.
  • ASTM International, Annual Book of ASTM Standards, Volume 03.03 Nondestructive Testing
  • ASNT, Nondestructive Testing Handbook

Statistics in NDT

External links

General NDT, Online Information

NDT Published Journals

NDT Societies

NDT Trade Sites

NDT Research

Collections of NDT Links

  • Links from ASNT
  • Links from CINDE
  • Links from NDT World Wide
  • Links from NTIAC (the Nondestructive Testing Information Analysis Center — archived, no longer kept up to date)
  • Links from SwRI

NDT Events

  • Events from ASNT
  • Events from CINDE
  • Events from ICNDT
  • Events from NDT World
  • International Exhibition on Non-Destructive Testing Equipment and Devices (Russia)
  • 17th World Conference On Non-destructive Testing, Shanghai, China, August 26-30, 2008.
  • 18th World Conference On Non-destructive Testing, Durban, South Africa, 2012.
  • Review of Progress in Quantitative Nondestructive Evaluation (QNDE) — annual conference
  • European Conference for Non-Destructive Testing (ECNDT), Berlin, Germany, September 25th-29th 2006

See also

Inspection | Maintenance testing | Reliability engineering | Quality control | Product certification Inspection in software engineering, refers to peer review of any work product by trained individuals who look for defects using a well defined process. ... Maintenance testing is that testing which is performed to either identify equipment problems, diagnose equipment problems or to confirm that repair measures have been effective. ... Reliability engineering is the discipline of ensuring that a system will be reliable when operated in a specified manner. ... In engineering and manufacturing, quality control and quality engineering are involved in developing systems which ensure that products or services are designed and produced to meet or exceed customer requirements and expectations. ... Product certification or product qualification is the cornerstone of all bounding and the process of certifying that a certain product has passed performance and/or quality assurance tests or qualification requirements stipulated in regulations such as a building code and nationally accredited test standards, or that it complies with a...


  Results from FactBites:
 
Nondestructive testing - Wikipedia, the free encyclopedia (1822 words)
That there is a tradeoff between the cost of the test and its reliability favors a strategy in which most test objects are inspected nondestructively; destructive testing is performed on a sampling of test objects that is drawn randomly for the purpose of characterizing the testing reliability of the nondestructive test.
The false impression that the testing reliability is well defined can be established by the use of terms that imply the preservation of probability theory under conditions in which probability theory is empirically violated.
Potential and actual users of Defect Detection Tests should also be aware of the fact that the expected utility of such a test depends upon a) the nature of the statistical populations to be tested and b) the utilities of the user.
The American Society for Nondestructive Testing (NDT) (808 words)
Nondestructive testing is used to investigate the material integrity of the test object.
Nondestructive testing asks "Is there something wrong with this material?" Various performance and proof tests, in contrast, ask "Does this component work?" This is the reason that it is not considered nondestructive testing when an inspector checks a circuit by running electric current through it.
Nondestructive material characterization is a growing field concerned with material properties including material identification and microstructural characteristics - such as resin curing, case hardening and stress - that have a direct influence on the service life of the test object.
  More results at FactBites »


 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments
Please enter the 5-letter protection code

Want to know more?
Search encyclopedia, statistics and forums:
 


Lesson Plans | Student Area | Student FAQ | Reviews | Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms.