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Nondestructive testing

Nondestructive testing or Non-destructive testing

(NDT) is a wide group of analysis techniques used in
valuable technique that can save both money and time in
liquid penetrant, radiographic, remote visual inspection
Innovations in the eld of nondestructive testing have
had a profound impact on medical imaging, including on
echocardiography, medical ultrasonography, and digital

defects within the part. Thermoelectric eect (or use

of the Seebeck eect) uses thermal properties of an alloy to quickly and easily characterize many alloys. The
methods, such as electrochemical fatigue crack sensors,

2 Applications

Analyzing and documenting a non-destructive 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 highspeed cameras have advanced recording modes to capture some non-destructive failures.[5] After the failure the
what happen before, during and after the non-destructive
event, image by image.


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

of the sample may be enhanced for visual examination
by the unaided eye by using liquids to penetrate fatigue
cracks. One method (liquid penetrant testing) involves
using dyes, uorescent or non-uorescent, in uids for
non-magnetic materials, usually metals. Another commonly used NDT method used on ferrous materials involves the application of ne iron particles (either liquid
externally magnetized state (magnetic-particle testing).
The particles will be attracted to leakage elds within the
test object, and form on the objects surface. Magnetic
particle testing can reveal surface & some sub-surface

2.1 Weld verication

In manufacturing, welds are commonly used to join two
is a chance that they may fail if not created to proper
specication. For example, the base metal must reach
a certain temperature during the welding process, must
cool at a specic rate, and must be welded with compatible materials or the joint may not be strong enough to hold
of the weld to the base metal, cracks or porosity inside
the weld, and variations in weld density) could cause a


In NDT, the structure undergoes a dynamic input, such as

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

2.3 Radiography in medicine


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.

structure to break or a pipeline to rupture.

Welds may be tested using NDT techniques such as
industrial radiography or industrial CT scanning using Xrays 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 Chest radiography indicating a peripheral bronchial carcinoma.
without penetrant captured in cracks.
As a system, the human body is dicult to model as a
Welding techniques may also be actively monitored with
complete transfer function. Elements of the body, howacoustic emission techniques before production to design
ever, such as bones or molecules, have a known response
the best set of parameters to use to properly join two
to certain radiographic inputs, such as x-rays or magnetic
materials.[6] In the case of high stress or safety critical
resonance. Coupled with the controlled introduction of a
welds, weld monitoring will be employed to conrm the
known element, such as digested barium, radiography can
specied welding parameters (arc current, arc voltage,
be used to image parts or functions of the body by meatravel speed, heat input etc.) are being adhered to those
suring and interpreting the response to the radiographic
stated in the welding procedure. This veries the weld
input. In this manner, many bone fractures and diseases
as correct to procedure prior to nondestructive evaluation
may be detected and localized in preparation for treatand metallurgy tests.
ment. X-rays may also be used to examine the interior of
mechanical systems in manufacturing using NDT techniques, as well.
2.2 Structural mechanics
Structure can be complex systems that undergo dierent
loads during their lifetime, e.g. Lithium-ion batteries.[7]
Some complex structures, such as the turbo machinery in
second-order systems, approximating dynamic structure
components with springs, masses, and dampers. The resulting sets of dierential equations are then used to derive a transfer function that models the behavior of the

3 Notable events in early industrial

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[8] is used in the railroad industry to nd
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.

1946 First neutron radiographs produced by Peters.

1950 The Schmidt Hammer (also known as Swiss
Hammer) is invented. The instrument uses the
worlds rst patented non-destructive testing method
for concrete.
1950 J. Kaiser introduces acoustic emission as an
NDT method.

1895 Wilhelm Conrad Rntgen discovers what are

now known as X-rays. In his rst paper he discusses (Basic Source for above: Hellier, 2001) Note the number
of advancements made during the WWII era, a time when
the possibility of aw detection.
industrial quality control was growing in importance.
1963 Frederick G. Weigharts[10] and James F. Mc 1924 Lester uses radiography to examine castings
Nulty (U.S. radio engineer)s[11] co-invention of
to be installed in a Boston Edison Company steam
Digital radiography is an oshoot of the pairs depressure power plant.
velopment of nondestructive test equipment at Automation Industries, Inc., then, in El Segundo, Cal 1926 The rst electromagnetic eddy current instruifornia. See James F. McNulty also at article
ment is available to measure material thicknesses.
Ultrasonic testing.
1927 - 1928 Magnetic induction system to detect
1996 Rolf Diederichs founded the rst Open Access
aws in railroad track developed by Dr. Elmer
NDT Journal in the Internet. Today the Open AcSperry and H.C. Drake.
cess NDT Database
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.

4 Methods and techniques

1935 - 1940 Liquid penetrant tests developed (Betz,

Doane, and DeForest)
1935 - 1940s Eddy current instruments developed
1940 - 1944 Ultrasonic test method developed in
21, 1942. Extracts from the rst 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
presence of the aw to be detected and its position
located, even though the aw 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 reected vibrations at one or more stations on the surface of the
part. Medical echocardiography is an oshoot of
this technology.[9]

An example of a 3D replicating technique. The exible highresolution 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 scientic 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

Acoustic emission testing (AE or AT)

Hydrogen leak testing

Mass spectrometer leak testing
Tracer-gas leak testing method Helium, Hydrogen and refrigerant gases
Magnetic resonance imaging (MRI) and NMR spectroscopy

Blue Etch Anodize (BEA)

Dye penetrant inspection or Liquid penetrant Testing (PT or LPI)

Metallographic replicas [12][13]

Electromagnetic testing (ET) or Electromagnetic Inspection (commonly known as EMI)

Optical microscopy





Alternating current potential drop measurement (ACPD)

Barkhausen testing
Direct current potential drop measurement
Eddy-current testing (ECT)
Magnetic ux leakage testing (MFL) for
pipelines, tank oors, and wire rope
Magnetic-particle inspection (MT or MPI)
Remote eld testing (RFT)
Endoscope inspection
Guided wave testing (GWT)
Hardness testing
Impulse excitation technique (IET)
Terahertz nondestructive evaluation(THz)
Infrared and thermal testing (IR)
Thermographic inspection
Infrared thermal microscopy
Laser testing

Near-infrared spectroscopy (NIRS)

Positive Material Identication (PMI)
Radiographic testing (RT) (see also Industrial radiography and Radiography)

Computed radiography
Digital radiography (real-time)
Neutron Imaging
SCAR (Small Controlled Area Radiography)
X-ray computed tomography (CT)

Resonant Inspection
Resonant Acoustic Method (RAM) [14]
Scanning electron microscopy
Surface Temper Etch (Nital Etch)
Ultrasonic testing (UT)
ART (Acoustic Resonance Technology)
Angle beam testing
Electro Magnetic Acoustic Transducer
(EMAT) (non-contact)
Laser ultrasonics (LUT)
Internal rotary inspection system (IRIS) ultrasonics for tubes
Phased array ultrasonics
Thickness measurement
Time of ight diraction ultrasonics (TOFD)
Time of Flight Ultrasonic Determination of
3D Elastic Constants (TOF)

Electronic speckle pattern interferometry

Vibration Analysis

Holographic interferometry

Visual inspection (VT)

Low coherence interferometry

Leak testing (LT) or Leak detection
Absolute pressure leak testing (pressure

Pipeline video inspection

Weight and load testing of structures
3D Computed Tomography
Industrial CT Scanning

Bubble testing

Heat Exchanger Life Assessment System

Halogen diode leak testing

RTJ Flange Special Ultrasonic Testing


Certication schemes

Personnel training, qualication

and certication

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 certied, and in some industrial sectors
certication is enforced by law or by the applied codes
and standards.[15]



The following denitions for qualication and certication are given in ISO 9712:[16]
Certication: Procedure, used by the certication
body to conrm that the qualication requirements
for a method, level and sector have been fullled,
leading to the issuing of a certicate.
Qualication: Demonstration of physical attributes, knowledge, skill, training and experience
required to properly perform NDT tasks.
In US standards and codes, while a very similar denition of qualication is included in ASNT SNT-TC-1A,
certication is simply dened as: Written testimony of
In the aerospace sector, EN 4179:2009 contains the following denitions:[17]
Certication: Written statement by an employer
that an individual has met the applicable requirements of this standard.



1. Employer Based Certication: Under this concept the employer compiles their own Written Practice. The written practice denes the responsibilities of each level of certication, as implemented
of certication. In industrial sectors the written
practices are usually based on recommended practice SNT-TC-1A of the American Society for Nondestructive Testing.[19] ANSI standard CP-189 outlines requirements for any written practice that conforms to the standard.[20] For aviation, space, and
defense (ASD) applications NAS 410 sets further
requirements for NDT personnel, and is published
by AIA - Aerospace Industries Association, which
for EN 4179[17] and other (USA) NIST-recognized
aerospace standards for the Qualication and Certication (employer-based) of Nondestructive Testing personnel. NAS 410 also sets the requirements
also for National NDT Boards, which allow and
proscribe personal certication schemes. NAS 410
allows ASNT Certication as a portion of the qualications needed for ASD certication.[21]
2. Personal Central Certication: The concept of
central certication is that an NDT operator can
obtain certication from a central certication authority, that is recognized by most employers, third
parties and/or government authorities. Industrial
standards for central certication schemes include
ISO 9712,[16] and ANSI/ASNT CP-106[22] (used
for the ASNT ACCP [23] scheme). Certication under these standards involves training, work experience under supervision and passing a written and
practical examination set up by the independent certication authority. EN 473[24] was another central certication 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 certication schemes exist as well.
The most notable is ASNT Level III (established in 19761977), which is organized by the American Society for
Nondestructive Testing for Level 3 NDT personnel.[25]
NAVSEA 250-1500 is another US central certication
scheme, specically developed for use in the naval nuclear program.[26]

Non-Destructive Testing (NDT) training is provided for

the particular method they wish to be trained in. At this
point, they may pass a certication examination. While Central certication is more widely used in the European
online training has become more popular, many certify- Union, where certications are issued by accredited bodies (independent organizations conforming to ISO 17024
ing bodies will require additional practical training.
and accredited by a national accreditation authority like
actually enforces central personnel certication for the
5.3 Certication schemes
initial testing of steam boilers and some categories of
There are two approaches in personnel certication:[18]
pressure vessels and piping.[27] European Standards har-


monized with this directive specify personnel certica- 6 Terminology

tion to EN 473. Certications issued by a national NDT
society which is a member of the European Federation The standard US terminology for Nondestructive testing
of NDT (EFNDT) are mutually acceptable by the other is dened in standard ASTM E-1316.[34] Some denitions
member societies [28] under a multilateral recognition may be dierent in European standard EN 1330.
Canada also implements an ISO 9712 central certica- Indication The response or evidence from an examination scheme, which is administered by Natural Resources
tion, such as a blip on the screen of an instrument.
Canada, a government department.[29][30][31]
Indications are classied as true or false. False indications are those caused by factors not related to the
The aerospace sector worldwide sticks to employer based
principles of the testing method or by improper imschemes.[32] In America it is based mostly on AIA-NASplementation of the method, like lm damage in ra410 [33] and in the European Union on the equivalent
diography, electrical interference in ultrasonic testand very similar standard EN 4179.[17] However EN
ing etc. True indications are further classied as
4179:2009 includes an option for central qualication
relevant and non relevant. Relevant indications are
and certication by a National aerospace NDT board or
those caused by aws. Non relevant indications are
NANDTB (paragraph 4.5.2).
those caused by known features of the tested object,
like gaps, threads, case hardening etc.


Levels of certication

Interpretation Determining if an indication is of a type

to be investigated. For example, in electromagnetic testing, indications from metal loss are considered aws because they should usually be investigated, but indications due to variations in the material properties may be harmless and nonrelevant.

Most NDT personnel certication schemes listed above

specify three levels of qualication and/or certication, 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 Flaw A type of discontinuity that must be investigated
dierences or variations between dierent codes and
weld or metal loss.

Evaluation Determining if a aw is rejectable. For ex Level 1 are technicians qualied to perform only
ample, is porosity in a weld larger than acceptable
specic calibrations and tests under close superviby code?
sion and direction by higher level personnel. They
can only report test results. Normally they work fol- Defect A aw that is rejectable i.e. does not meet
lowing specic work instructions for testing proceacceptance criteria. Defects are generally removed
dures and rejection criteria.
or repaired.[34]
Level 2 are engineers or experienced technicians
standards (instead of following work instructions)
evaluate and document testing results. They can also
supervise and train Level 1 technicians. In addition
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 certication. They are

7 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 aws in pipe welds using manual ultrasonic
testing?" The POD will usually increase with aw size. A
common error in POD tests is to assume that the percentage of aws detected is the POD, whereas the percentage of aws detected is merely the rst step in the
analysis. Since the number of aws tested is necessarily
a limited number (non-innite), statistical methods must
in POD tests is to dene the statistical sampling units (test
items) as aws, whereas a true sampling unit is an item
that may or may not contain a aw.[35][36] 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 MILHDBK-1823A Nondestructive Evaluation System Reliability Assessment, from the U.S. Department of Defense

See also
Destructive testing
Maintenance testing
Product certication
Quality control
Risk-based inspection
Failure analysis
Forensic engineering
Materials science
Predictive maintenance
Reliability engineering
Stress testing
Terahertz nondestructive evaluation
Robotic Non-Destructive Testing



[3] Dufour, M. L.; Lamouche, G.; Detalle, V.; Gauthier, B.; Sammut, P. (April 2005). Low-Coherence
Interferometry, an Advanced Technique for Optical
Metrology in Industry. Insight - Non-Destructive Test47 (4): 216219.
ing and Condition Monitoring.
doi:10.1784/insi. ISSN 1354-2575.
[4] Losert, Robert. (March 31, 2009). Solution for NDT
Inspection. NDT Magazine. Retrieved December 15,
[5] Bridges, Andrew. High Speed Cameras for NonDestructive Testing. NASA TechBriefs. Retrieved 1
November 2013.
[6] Blitz, Jack; G. Simpson (1991). Ultrasonic Methods
of Non-Destructive Testing. Springer-Verlag New York,

[7] Waldmann, T. (2014). A Mechanical Aging Mechanism

in Lithium-Ion Batteries. Journal of the Electrochemical
Society. 161: A1742. doi:10.1149/2.1001410jes.
[8] Introduction and History of Penetrant Inspection
[9] Full Article Siddharth, S. & Goyal, A. (2007). The
origin of echocardiography. Tex Heart Institute J., 34(4),
[10] 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
F. McNultys earlier led co-pending application for an
essential component of invention
[11] 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
[12] ASTM E1351: Standard Practice for Production and
Evaluation of Field Metallographic Replicas (2006)
[13] BS ISO 3057 Non-destructive testing - Metallographic
replica techniques of surface examination (1998)
[14] Fundamentals of Resonant Acoustic Method NDT
[15] ICNDT Guide to Qualication and Certication of Personnel for NDT (PDF). International Committee for
NDT. 2012.
[16] ISO 9712: Non-destructive testing -- Qualication and certication of NDT personnel (2012)
[17] EN 4179: Aerospace series. Qualication and approval
of personnel for non-destructive testing (2009)
[18] John Thompson (November 2006). Global review of
qualication and certication of personnel for NDT and
condition monitoring. 12th A-PCNDT 2006 AsiaPacic Conference on NDT. Auckland, New Zealand.
[19] Recommended Practice No. SNT-TC-1A: Personnel
Qualication and Certication in Nondestructive Testing,
[20] ANSI/ASNT CP-189: ASNT Standard for Qualication and Certication of Nondestructive Testing Personnel,
[21] AIA NAS410
[22] ANSI/ASNT CP-106: ASNT Standard for Qualication
and Certication of Nondestructive Testing Personnel
[23] ASNT Central Certication Program, ASNT Document
ACCP-CP-1, Rev. 7 (2010)
[24] EN 473: Non-destructive testing. Qualication and certication of NDT personnel. General principles, (2008)




[27] Directive 97/23/EC of the European Parliament and of the

Council of 29 May 1997 on the approximation of the laws


[28] EFNDT/SEC/P/05-006: Agreement for EFNDT multilateral recognition of NDT personnel certication schemes
The NDT Certifying Agency
index-eng.htm :
[30] The relevant national standard for Canada is CAN/CGSB48.9712-2006 Qualication and Certication of NonDestructive Testing Personnel., which complies with the
requirements of ISO 9712:2005 and EN 473:2000.
[32] R. Marini and P. Ranos: "Current Issues in Qualication
and Certication of Non-Destructive Testing Personnel in
the Aerospace Industry", ECNDT 2006 - Th.3.6.5
[33] AIA-NAS-410: Aerospace Industries Association, National Aerospace Standard, NAS Certication and Qualication of Nondestructive Test Personnel
[34] ASTM E-1316: Standard Terminology for Nondestructive Examinations, The American Society for Testing and
Materials, in Volume 03.03 NDT, 1997
[35] T. Oldberg and R. Christensen (1999). Erratic Measure.
4 (5).
[36] T. Oldberg (2005). An Ethical Problem in the Statistics
of Defect Detection Test Reliability. 10 (5).



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
Shull, P.J., Nondestructive Evaluation: Theory,
Techniques, and Applications, Marcel Dekker Inc.,
EN 1330: Non-destructive testing. Terminology.
Nine parts. Parts 5 and 6 replaced by equivalent ISO

from polycrystalline and amorphous materials
ISO 12718: Non-destructive testing. Eddy current
testing. Vocabulary (2008)


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