February 14, 2022
Introduction to NDT
During the last webinar, a gentleman courageously stepped forward and asked about
the equipment and method we were demonstrating. It was clear that thus far in his career with
NVI, he hadn’t had the opportunity to be exposed to what most of us consider to be a very
common method of nondestructive testing, ultrasonic testing. After that discussion, I began to
wonder just how many others throughout our great company have not had the opportunity to
be exposed to some of the other common NDT methods that some of us use every day. So, I
thought now may be a good time to do a brief introduction to a few of these methods and tell
you a little about how they work. Who knows, maybe one day you will find yourself in a
training class or performing one or more of these methods as a Level II technician.
First, we are going to define NDT. ASTM E1316 defines nondestructive testing as the
development and application of technical methods to examine materials or components in
ways that do not impair future usefulness and serviceability in order to detect, locate, measure
and evaluate flaws; to assess integrity, properties and composition; and to measure
geometrical characteristics. The key point here being the inspection process we will use will do
no harm to the component being tested. For all the methods we are going to talk about today,
once the testing is complete, the item can still perform its intended use.
What are some of the uses of NDT? The most common of these is flaw detection and
evaluation. In most cases our client has just manufactured a component or product. Now they
are calling on us to inspect that product to give them some assurance that it doesn’t contain
flaws or imperfections that would negatively impact the service life of that product. Depending
on the method being applied, there are numerous other characteristics that can be determined.
It all boils down to making sure the items we test are structurally sound and meet the necessary
criteria.
When is NDT Used? NDT can and is used at practically every stage in the life cycle of
products or components. NDT can be used during the inspection of the original castings or
ingots which are cooled into solid material from liquid metal. It can be used at various stages
throughout the processing of those raw materials into the basic shapes and components we
use every day such as during rolling, forging, machining, or welding operations. It can also be
used after a component has been put into service to monitor for service induced damage.
Nondestructive testing can be used for a variety of applications including developing products;
screening or sorting materials; monitoring, improving, or controlling manufacturing processes;
and verifying proper assembly of complex components; just to name a few.
nvindt.com
Office: 985.876.5559
Toll Free: 877-NDT-NVI1
Fax: 985.876.9355
CORPORATE OFFICE
2449 W. Park Ave.
P.O. Box 1690
Gray, LA 70359
Aransas Pass, TX • Carthage, TX • Houston, TX
Odessa, TX • Lafayette, LA • New Iberia, LA
Sulphur, LA • Theodore, AL • Northglenn, CO Depew, NY •
Pittsburgh, PA
While radiographic testing is the most common method utilized here at NVI, there are
quite a few other methods of nondestructive testing. ASNT currently recognizes a total of 16
different methods of nondestructive testing including more obscure methods such as Acoustic
Emission, Vibration Analysis Testing, Microwave Technology Testing, and Leak Testing.
The methods we are going to focus on in this webinar will be the six most commonly
used methods in our industry. Visual Testing, Liquid Penetrant Testing, Magnetic Particle
Testing, Radiographic Testing, Electromagnetic Testing, and Ultrasonic Testing.
Visual Testing
Visual Testing is the most basic and common inspection method. This kind of inspection
does not necessarily require any special equipment, but it does require special training so that
the inspector knows what to look for as they visually examine the component. This type of
inspection can be very basic such as visually inspecting a finished fillet weld for workmanship or
very complex such an API qualified inspector walking down an entire boiler or pressure system
visually reviewing every single part of it. The amount of training, experience, and type of
equipment required can vary depending on the scope of the inspection task.
Direct visual examination is described as a visual examination technique performed by
eye and without any visual aids. Lighting equipment, mirrors, magnifiers, and a variety of weld
measurement tools are common equipment used for this type of inspection. It typically
requires you to be able to position your eye within 24 inches of the part and your line of sight
near perpendicular to the examination surface. Visual examinations must be performed under
adequate lighting conditions and the lighting angle may need to be adjusted to minimize glare.
Remote visual examination is described as a visual examination technique used with
visual aids for conditions where the area to be examined is inaccessible for direct visual
examination. This type of visual inspection would make use of equipment such as borescopes,
video probes, or possibly robotic crawler equipment with video capabilities. Drones are also
now beginning to provide real value for remote visual inspections. These new types of
equipment can provide very high resolution views of equipment which may otherwise not be
accessible with traditional techniques without significant time, effort, and cost.
Liquid Penetrant Testing
Liquid Penetrant Testing, also known as PT, is a non-destructive testing process for
revealing surface breaking flaws in a wide variety of solid, non-porous materials. It is a simple
and economical method which requires minimal training compared to more complex inspection
methods. The basics of penetrant testing involve the application of a “Penetrant” on the
nvindt.com
Office: 985.876.5559
Toll Free: 877-NDT-NVI1
Fax: 985.876.9355
CORPORATE OFFICE
2449 W. Park Ave.
P.O. Box 1690
Gray, LA 70359
Aransas Pass, TX • Carthage, TX • Houston, TX
Odessa, TX • Lafayette, LA • New Iberia, LA
Sulphur, LA • Theodore, AL • Northglenn, CO Depew, NY •
Pittsburgh, PA
testing surface, allowing it to dwell on the surface for a specified period, the removal of the
excess penetrant and finally the application of a developer.
Penetrant testing is one of the most widely used NDT methods. This is mainly because
of its ease of use and its flexibility. This method can be used on almost any material provided
that the surface is not extremely rough or porous. Penetrant testing can be as simple as a few
cans and some rags or as complex as an entire assembly line system of tanks, electrostatic
sprayers, overhead cranes, and viewing booths that can take up an entire warehouse
depending on the size of the parts to be inspected.
Magnetic Particle Testing
Magnetic Particle Testing, also known as MT, is a non-destructive testing process for
detecting discontinuities in ferromagnetic materials such as iron, nickel, cobalt, and some of
their alloys. This method provides a quick and efficient way of revealing both slightly
subsurface and surface discontinuities, including those that are too small or tight to be seen by
the unaided eye.
Magnetic Particle Testing works by introducing a strong magnetic field into the part,
then dusting or coating the part with fine ferromagnetic particles which can be attracted to the
small leakage fields created by discontinuities within the material. In our industry the most
common way to introduce this magnetic field is by using what is called an electromagnetic
yoke. This yoke is basically a horseshoe magnet which uses electricity to create a magnetic field
which is strongest in the area right between the pole pieces. The particles used come in a
variety of colors to provide high contrast on materials with different surfaces as well as particles
that will fluoresce and glow yellow-green under ultraviolet light.
Radiographic Testing
Radiographic Testing uses very high energy ionizing radiation obtained from either the
radioactive decay of a radioactive isotope or from an x-ray tube. The radiation we use for
radiographic testing is very much like visible light, but of a much shorter wavelength and thus
higher energy. This higher energy level allows it to penetrate most solid materials such as
aluminum, steel, and concrete. We can use radiography to examine the internal structure of
solid materials for defects that would not be otherwise detectable.
For radiography we need access to both sides of the specimen. The radiation source is
placed on one side of the specimen and a piece of film or other imaging media is placed on the
opposite side. Some of the radiation will pass through the object and some of the radiation will
be absorbed. Areas that are thicker will absorb more radiation and thus produce lighter areas
nvindt.com
Office: 985.876.5559
Toll Free: 877-NDT-NVI1
Fax: 985.876.9355
CORPORATE OFFICE
2449 W. Park Ave.
P.O. Box 1690
Gray, LA 70359
Aransas Pass, TX • Carthage, TX • Houston, TX
Odessa, TX • Lafayette, LA • New Iberia, LA
Sulphur, LA • Theodore, AL • Northglenn, CO Depew, NY •
Pittsburgh, PA
on the film. Areas that are thinner or that contain voids or defects will absorb less of the
radiation and produce darkened areas on the film.
Almost anything can be examined using radiography. It is a very versatile method and
depending on the energy and technique chosen can be used on items such as welds, castings,
circuit boards, electronic components, composite or plastic materials, paper and paper
products. We can use radiography to inspect items for defects or to confirm proper assembly
of more complex items such as valves.
Electromagnetic Testing
Electromagnetic Testing, sometimes referred to as Eddy Current Testing is a method
that utilizes the principles of electromagnetic induction on material which will conduct
electricity. It can be used on most materials that are conductive, whether they are
ferromagnetic or not. ET is well suited for detecting surface defects, can measure the thickness
of thin materials, can make measurements of a component’s conductivity, and measure the
thickness of coatings.
The basic principles behind how electromagnetic testing works is relatively simple. An
alternating current is passed through a small coil. When a current passes through the coil a
magnetic field is created by the coil. When this coil is brought near a conductive material, the
magnetic field will induce small circular currents in the part. These small circular currents,
called eddy currents, will then produce their own magnetic field. The magnetic field produced
by the eddy current opposes or is in the opposite direction of the coil’s magnetic field. As long
as the part contains no defects and the distance between the coil and the inspection surface
remains consistent, the magnetic fields between the coil and the part can be balanced.
However, when the coil encounters an area of the part with a flaw, this interrupts the eddy
currents which disrupts the balance of the magnetic fields. This disruption can then be
displayed on the instrument and interpreted.
Electromagnetic Testing is most commonly used to inspect surfaces and tubes. It is an
incredibly sensitive testing method and can identify even very small flaws or cracks in a surface
or just beneath it. There are several individual techniques that fall under the umbrella of the
electromagnetic testing method such as eddy current, remote field testing (RFT), and
alternating current field measurement (ACFM). As with anything, the complexity of the
equipment used to perform this method can vary greatly based on the scope of the job. Basic
surface measurements can be made with a relatively simple instrument such as the Nortec 600
shown here and a surface coil. Other applications may require complex automated scanners
with arrays of dozens of coils and very sophisticated computer controlled equipment.
nvindt.com
Office: 985.876.5559
Toll Free: 877-NDT-NVI1
Fax: 985.876.9355
CORPORATE OFFICE
2449 W. Park Ave.
P.O. Box 1690
Gray, LA 70359
Aransas Pass, TX • Carthage, TX • Houston, TX
Odessa, TX • Lafayette, LA • New Iberia, LA
Sulphur, LA • Theodore, AL • Northglenn, CO Depew, NY •
Pittsburgh, PA
Ultrasonic Testing
Ultrasonic Testing uses the principles of sound wave’s ability to move through solids to
inspect a wide variety of materials and components. It is a thorough inspection technique that
like radiography, can locate and size indications which are contained within the material and
not visible from the surfaces. Here at NVI the two main uses for ultrasonic testing are to
measure the remaining wall thickness or to inspect welds or components for defects.
The basics of ultrasonic thickness testing are relatively simple. Sound waves will move
through an object at a set speed or velocity. How fast the sound waves travel are based on the
properties of the material they are passing through. Like different streets will have different
speed limits, different types of materials have different acoustic velocities. For instance, if I told
you to drive 40 miles per hour and it took you 3 hours to get to your destination, we can
calculate that you travelled 120 miles. Ultrasonic thickness testing works the same way. The
instrument uses a transducer to introduce a pulse of ultrasonic energy into a part perpendicular
to its surface, and then listens for its echo or returning signal from the opposite side. So, if we
know how fast the sound waves travel and we can measure how long it takes for the energy to
get to the other side and echo back, we can calculate how far the sound has traveled and thus
how thick the material must be.
Ultrasonic testing utilizing shear waves for flaw detection will typically introduce the
sound wave at an angle to the surface. This is because we are normally looking for indications
that will be at an oblique angle to the inspection surface. This orientation of the expected flaws
will be determined by the joint configuration used to create the weld. This technique relies on
striking the flaws as closely to perpendicular as we can so we can get an echo to return to the
transducer. This technique also needs us to do a bit more than just calculate the travel time of
the reflected echo. Angle beam testing will require a bit of trigonometry to determine the
location and depth of the returning ultrasonic energy. If we know the angle of the sound wave,
the thickness of the part, and the timing of the echo energy, we can calculate the position of
the reflector and plot it very accurately within the volume of the component.
Once a technician has mastered the techniques of both straight-beam and angle-beam
ultrasonic testing, they can move on to learning about the advanced techniques of UT such as
Phased Array, Time of Flight Diffraction, and Full Matrix Capture. These advanced methods
utilize much more sophisticated equipment to provide enhanced coverage, data capture
capabilities, as well as advanced display visualizations that improve detectability and aid in the
interpretation of the ultrasonic data.
nvindt.com
Office: 985.876.5559
Toll Free: 877-NDT-NVI1
Fax: 985.876.9355
CORPORATE OFFICE
2449 W. Park Ave.
P.O. Box 1690
Gray, LA 70359
Aransas Pass, TX • Carthage, TX • Houston, TX
Odessa, TX • Lafayette, LA • New Iberia, LA
Sulphur, LA • Theodore, AL • Northglenn, CO Depew, NY •
Pittsburgh, PA
Summary
Clearly, we have only scratched the surface here. These methods and the others not
described in detail can be very complex. But these methods and techniques can be powerful
tools when utilized correctly by properly trained and qualified personnel. NVI has the resources
to give you the skills necessary to perform these inspections, and to do so with a high level of
confidence. Nondestructive testing is applied in practically every industry to some degree or
another and is crucial for assuring that each of us and our loved ones are safe.
nvindt.com
Office: 985.876.5559
Toll Free: 877-NDT-NVI1
Fax: 985.876.9355
CORPORATE OFFICE
2449 W. Park Ave.
P.O. Box 1690
Gray, LA 70359
Aransas Pass, TX • Carthage, TX • Houston, TX
Odessa, TX • Lafayette, LA • New Iberia, LA
Sulphur, LA • Theodore, AL • Northglenn, CO Depew, NY •
Pittsburgh, PA
Introduction to
Nondestructive Testing
Introduction to
Nondestructive Testing
Definition of NDT
• The use of noninvasive
techniques to determine the
integrity of a material,
component or structure or;
• quantitatively measure some
characteristic of an object.
• i.e. Inspect or measure without
doing harm.
What are Some Uses of NDT?
• Flaw Detection and Evaluation
• Leak Detection
• Location Determination
• Dimensional Measurements
• Structure and Microstructure Characterization
• Estimation of Mechanical and Physical Properties
Fluorescent Penetrant Indication
• Stress (Strain) and Dynamic Response Measurements
• Material Sorting and Chemical Composition Determination
When is NDT Used?
There are NDT applications used at almost every stage
in the production or life-cycle of a component.
• To assist in product development
• To screen or sort incoming materials
• To monitor, improve or control manufacturing processes
• To verify proper processing such as heat treating
• To verify proper assembly
• To inspect for in‐service damage
Methods of NDT
Acoustic Emission
Thermal/Infrared Testing
Ground Penetrating Radar
Microwave Technology Testing
Laser Testing
Guided Wave Testing
Magnetic Flux Leakage
Leak Testing
Vibration Analysis
Six Most Common NDT Methods
• Visual Testing
• Liquid Penetrant Testing
• Magnetic Particle Testing
• Radiographic Testing
• Electromagnetic Testing
• Ultrasonic Testing
Visual Testing (Direct)
Most basic and common
inspection method.
Tools include light sources,
magnifiers, mirrors, weld
measurement gages.
Typically requires view of the subject without
the use of elaborate visual aids.
Visual Testing (Remote)
Tools include
fiberscopes,
borescopes,
crawlers, and
drones.
Robotic crawlers permit
observation in hazardous or
tight areas, such as air
ducts, reactors, pipelines.
Portable video inspection
unit with zoom capability
allows inspection of large
tanks and vessels, railroad
tank cars, sewer lines.
Liquid Penetrant Testing
• A liquid with high surface wetting characteristics is applied to the surface of the
part and allowed time to seep into surface breaking defects.
• The excess liquid is removed from the surface of the part.
• A developer (powder) is applied to pull the trapped penetrant out the defect and
spread it on the surface where it can be seen.
Liquid Penetrant Testing
• Visual inspection is the final step in
the process.
• The penetrant used is often loaded
with a fluorescent dye and the
inspection is done under UV light to
increase test sensitivity.
Magnetic Particle Testing
• The part is magnetized.
• Finely milled iron particles coated with a dye
pigment are then applied to the specimen.
Magnetic Particle Testing
• These particles are attracted to magnetic flux
leakage fields and will cluster to form an
indication directly over the discontinuity.
• This indication can be visually detected under
proper lighting conditions.
Radiographic Testing
• The radiation used in radiography is a higher energy
(shorter wavelength) version of the electromagnetic
waves that we see as visible light. The radiation can
come from an X‐ray generator or a radioactive source.
High Electrical Potential
Electrons
+
-
X-ray Generator
or Radioactive
Source Creates
Radiation
Radiation
Penetrates
the Sample
Exposure Recording Device
Film Radiography
The part is placed between the radiation source
and a piece of film. The part will stop some of the
radiation. Thicker and more dense areas will stop
more of the radiation.
X-Ray film
The film darkness (density) will vary with the
amount of radiation reaching the film
through the test object.
= less exposure / lighter film density
Top view of developed film
= more exposure / darker film density
Radiographic Images
Electromagnetic Testing
• Electromagnetic testing is particularly well suited for detecting surface cracks but
can also be used to make electrical conductivity and coating thickness
measurements. Here a small surface probe is scanned over the part surface to
detect a crack.
Electromagnetic Testing
Coil
Coil's
magnetic field
Eddy current's
magnetic field
Eddy
currents
Conductive
material
Electromagnetic Testing
Ultrasonic Testing
f
Ultrasonic Thickness Testing
• High frequency sound waves are introduced into a material using a
transducer and they are reflected back from surfaces or flaws.
• Reflected sound energy is displayed versus time, and inspector can
visualize a cross section of the specimen showing the depth of features
f
that reflect sound.
initial
pulse
back surface
echo
lamination
echo
lamination
0
2
4
6
8
Oscilloscope, or flaw
detector screen
10
plate
Ultrasonic Angle‐Beam
• Angle beam inspections require sound waves to strike indications and
return to the transducer. Position can then be determined using
trigonometry.
Ultrasonic Testing (Advanced Techniques)
Phased Array
(PAUT)
Time of Flight Diffraction
(TOFD)
Full Matric Capture
(FMC)
Contact Information
www.nvindt.com
1‐877‐NDT‐NVI1
30