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Non-Destructive Testing (NDT)
Non-Destructive Testing (NDT) is the process of inspecting, testing, or evaluating materials,
components or assemblies for discontinuities, or differences in characteristics without
destroying the serviceability of the part or system. The terms nondestructive
examination (NDE), nondestructive inspection (NDI), and nondestructive evaluation (NDE) are
also commonly used to describe this technology

NDT is commonly used in forensic engineering, mechanical engineering, petroleum

engineering, electrical engineering, civil engineering, systems engineering, aeronautical
engineering, medicine, and art

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.

Today modern nondestructive tests are used in manufacturing, fabrication and in-service
inspections to ensure product integrity and reliability, to control manufacturing processes,
lower production costs and to maintain a uniform quality level. During construction, NDT is
used to ensure the quality of materials and joining processes during the fabrication and
erection phases, and in-service NDT inspections are used to ensure that the products in use
continue to have the integrity necessary to ensure their usefulness and the safety of the public.

NDT is used typically for the following reasons:

 Accident prevention and to reduce costs
 To improve product reliability
 To determine acceptance to a given requirement
 To give information on repair criteria.

NDT Test Methods

Test method names often refer to the type of penetrating medium or the equipment used to
perform that test.

The six (6) most frequently used test methods are the following:
Magnetic Particle Testing (MT)
Magnetic Particle Testing (MT), also referred to as Magnetic Particle Inspection/Examination, is
a nondestructive examination (NDE) technique used to detect surface and slightly subsurface
flaws in most ferromagnetic materials such as iron, nickel, and cobalt, and some of their alloys.
Because it does not necessitate the degree of surface preparation required by other
nondestructive test methods, conducting MT is relatively fast and easy. This has made it one of
the more commonly utilized NDE techniques.

How MT Works
 
When ferromagnetic material (typically iron or steel) is defect-free, it will transfer lines of
magnetic flux (field) through the material without any interruption.
 

But when a crack or

other discontinuity is
present, the magnetic
flux leaks out of the
material. As it leaks,
magnetic flux (magnetic field) will collect ferromagnetic particles (iron powder), making the size
and shape of the discontinuity easily visible.

However, the magnetic flux will only leak out of the material if the discontinuity is generally
perpendicular to its flow. If the discontinuity, such as a crack, is parallel to the lines of magnetic
flux, there will be no leakage and therefore no indication observed. To resolve this issue, each
area needs to be examined twice. The second examination needs to be perpendicular to the
first so discontinuities in any direction are detected. The examiner must ensure that enough
overlap of areas of magnetic flux is maintained throughout the examination process so
discontinuities are not missed.
History of Magnetic Particle Testing
 
Magnetism was first used as early as 1868 to check for cannon barrel defects. Cannon barrels
were first magnetized and then a magnetic compass was moved down the length of the barrel.
If a discontinuity was present, the magnetic flux would leak out and cause the compass needle
to move. Defects could be easily located with this technique.
 
In the early 1920s, William Hoke noticed metallic grindings from hard steel parts (held by a
magnetic chuck while being ground) formed patterns that followed the cracks in the surface of
parts he was machining. He also found that by applying fine ferromagnetic powder to the parts,
there was a build-up of powder at the discontinuities which formed a more visible indication.
 
By the 1930s, MT was quickly replacing the oil and whiting method of NDE (liquid penetrant
[PT]) in the railroad industry. It was quicker and did not leave behind the white powder that
required clean-up. After an MT evaluation, only iron powder was left behind, which could easily
fall off the part or be blown away.

Different Techniques
 
There are many different techniques and combinations of techniques of MT. The ASME Boiler
and Pressure Vessel Code, Section V, Article 7, recognizes five different techniques of
magnetization:

1. Prod technique
2. Longitudinal magnetization technique
3. Circular magnetization technique
4. Yoke technique
5. Multidirectional magnetization technique

There are two different ferromagnetic examination media: dry particles and wet particles. Both
forms can be either fluorescent or non-fluorescent (visible, color contrast) and come in a
variety of colors to contrast with the tested material.

Most-Used Methods
 
Two of the most-used methods are the stationary horizontal system, using longitudinal and
circular magnetization techniques, and the very portable yoke technique. 
A stationary magnetic particle testing system set up for longitudinal and circular magnetization
using wet fluorescent particles.

Stationary horizontal systems are generally used for smaller parts such as crank shafts and
valve stems. They are often found indoors around machine shops and heat-treating facilities.
Typically they have a headstock and tailstock. Parts can be clamped between stocks for
magnetization. There is also a coil placed around the part to magnetize it in the perpendicular
direction. Stationary horizontal systems use the wet particle technique with a circulation tank
below the equipment. Wet particles flow over the examined part and drain into the circulation
tank. Wet particles have more mobility flowing in a liquid than dry particles. This mobility helps
sensitivity by allowing particles to easily move to the discontinuities. Fluorescent particles are
commonly used with stationary horizontal systems because indoor operation makes it easy to
darken the area; required ultraviolet (black) light can then be used to evaluate the parts. Both
wet method examinations have about the same sensitivity, but under correct lighting
conditions, fluorescent indications are much easier to see.

External longitudinal seam of an inservice boiler being checked with magnetic particle
examination using an AC yoke with dry powder.
The MT yoke technique is the most portable and lowest-cost method, and therefore the most
popular method. Most yokes can operate in alternating current (AC) or direct current (DC)
modes. DC gives the most penetration and is recommended if subsurface discontinuities need
to be detected. AC is recommended if the surface is rough, because AC gives the particles more
mobility than DC. A yoke has an electric coil in the unit creating a longitudinal magnetic field
that transfers through the legs to the examined part. The yoke technique is easy to use with
minimal training. It can be used indoors, outdoors, inside vessels and tanks, and in all
positions. Prior to use, the magnetizing power of electromagnetic yoke shall have been checked
within the past year. An AC yoke must have a lifting power of at least 10 lb and a DC yoke of at
least 40 lb.

Typical Examples of ASME Code-Required Inspections

 
In the ASME codes of construction, magnetic particle examination or liquid penetrant
examination is specified many times to detect the possibility of surface defects. If material is
nonmagnetic, the only choice is liquid penetrant examination. However, if material is
ferromagnetic, magnetic particle examination is generally used. Some typical examples of ASME
Code-required inspections include, but are not limited to:

 Castings for surface defects

 Plates for laminations in corner joints when the edge of one plate is exposed and not
fused into the weld joint
 Head spin hole plug welds
 Weld metal build-up on plates
 Areas where defects have been removed before weld repair

Once boilers and pressure vessels are in service, MPT can be a widely-used examination
method. The National Board Inspection Code (NBIC) specifies MPT may be used for the
inspection of items such as:

 Internal and external surfaces of boiler and pressure vessels

 Vessels in liquid ammonia service
 Components subjected to fire damage
 Locomotive and historical boilers
 Yankee dryers
 Cargo tanks
 Vessels in LP gas service
 Weld repairs and alterations to pressure-retaining items

Advantages and Disadvantages of Using Magnetic Particle Testing

 
Advantages:
 
 Can detect both surface and near-surface indications.
 Surface preparation is not as critical compared to other NDE methods. Most surface
contaminants will not hinder detection of a discontinuity.
 A relatively fast method of examination.
 Indications are visible directly on the surface.
 Low-cost compared too many other NDE methods.
 A portable NDE method, especially when used with battery-powered yoke equipment.
 Post-cleaning generally not necessary.
 A relatively safe technique; materials generally not combustible or hazardous.
 Indications can show relative size and shape of the discontinuity.
 Easy to use and requires minimal amount of training.
 
Disadvantages:
 
 Non-ferrous materials, such as aluminum, magnesium, or most stainless steels, cannot
be inspected.
 Examination of large parts may require use of equipment with special power
requirements.
 May require removal of coating or plating to achieve desired sensitivity.
 Limited subsurface discontinuity detection capabilities.
 Post-demagnetization is often necessary.
 Alignment between magnetic flux and indications is important.
 Each part needs to be examined in two different directions.
 Only small sections or small parts can be examined at one time.
Liquid Penetrant Examination (PT)

Liquid Penetrant Examination is one of the most popular Non-Destructive Testing (NDT)
methods in the industry. It is economical, versatile, and requires minimal training when
compared to other NDT methods. Liquid penetrant testing check for material flaws open to the
surface by flowing very thin liquid into the flaw and then drawing the liquid out with a chalk-like
developer. Welds are the most common item inspected, but plate, bars, pipes, castings, and
forgings are also commonly inspected using liquid penetrant examination.

Over the years, liquid penetrant examination has been called many names: penetrant testing
(PT), liquid penetrant testing (LP), and dye penetrant testing (DP). The American Society for
Nondestructive Testing (ASNT) uses the name liquid penetrant testing (PT). The American
Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME B & PVC) and
the National Board Inspection Code (NBIC) use the name liquid penetrant examination (PT).
 
The first documented use of PT was in the railroad industry. Cast railroad wheels were dipped
in used oil, dried off, and then coated with powder chalk or suspension of chalk in alcohol. 
Once the wheels were dry, any oil stored in the flaw would bleed out into the chalk and be
detected. This was called the oil and whiting method.
 
The ASME Boiler & Pressure Vessel Code recognizes six different techniques of PT. They vary by
type of penetrant and method of cleaning before applying a developer. The two penetrant
types are either fluorescent or color contrast (dye) penetrant. They can then be used with any
of the three methods of cleaning:

Solvent Removable Penetrants - are those penetrants that require a solvent other than water
to remove the excess penetrant.

Water-Washable Penetrants - have an emulsifier included in the penetrant that allows the

penetrant to be removed using a water spray.

Post-Emulsifiable Penetrants - are penetrants that do not have an emulsifier included in its

chemical make-up like water-washable penetrants. 

The most popular is dye penetrant that is solvent removable.

 
The dye penetrant solvent removable method is most popular because it is low cost and very
versatile. It typically comes in three aerosol cans – cleaner, penetrant, and developer. The
aerosol cans are very versatile which allow them to be taken up ladders, inside boilers, down
into pits, and into very tight places. Most nonporous materials (steel, stainless steel, cast iron,
aluminum, brass, bronze, titanium, rubber, plastics, and glass) can be examined using PT.
Porous materials (concrete, wood, paper, cloth, and some types of fiberglass if the fibers are
exposed to the surface) should not be examined using PT. 

Advantages and Disadvantages of Using Liquid Penetrant Examination

 
Advantages:

 High sensitivity to small surface discontinuities

 Easy inspection of parts with complex shapes
 Quick and inexpensive inspection of large areas and large volumes of parts/materials
 Few material limitations (metallic and nonmetallic, magnetic and nonmagnetic, and
conductive and nonconductive can all be inspected)
 A visual representation of the flaw are indicated directly on the part surface
 Aerosol spray cans make the process portable, convenient, and inexpensive
 Indications can reveal relative size, shape, and depth of the flaw
 It is easy and requires minimal amount of training

Disadvantages:

 Detects flaws only open to the surface

 Materials with porous surfaces cannot be examined using this process
 Only clean, smooth surfaces can be inspected. (Rust, dirt, paint, oil and grease must be
removed.)
  Metal smearing from power wire brushing, shot blasting, or grit blasting must be
removed prior to liquid penetrant examination
 Examiner must have direct access to surface being examined
 Surface finish and roughness can affect examination sensitivity. (It may be necessary to
grind surfaces before PT.)
 Multiple process steps must be performed and controlled
 Post cleaning of parts and material is required, especially if welding is to be performed
 Proper handling and disposal of chemicals is required
 Fumes can be hazardous and flammable without proper ventilation

Radiographic Testing (RT)

History of radiographic testing
The history of radiographic testing actually involves two beginnings. The first commenced with
the discovery of x-Rays by Wilhelm Conrad Röntgen in 1895 and the second with the
announcement by Marie Curie, in December of 1898, that the demonstrated the existence of a
new radioactive material called "Radium".
What is Radiographic Testing?

Radiographic Testing (RT or X-ray or Gamma ray) is a non-destructive testing (NDT) method that
examines the volume of a specimen. Radiography uses X-rays and Gamma-rays to produce a
radiograph of a specimen, showing any changes in thickness, defects (internal and external),
and assembly details to ensure optimum quality in your operation. X-rays are produced by an X-
ray tube, and gamma rays are produced by a radioactive isotope.
RT usually is suitable for testing welded joints that can be accessed from both sides, with the
exception of double-wall signal image techniques used on some pipe. Although this is a slow
and expensive NDT method, it is a dependable way to detect porosity, inclusions, cracks, and
voids in weld interiors.
Industrial radiography involves exposing a test object to penetrating radiation so that the
radiation passes through the object being inspected and a recording medium placed against the
opposite side of that object.  For thinner or less dense materials such as aluminum, electrically
generated x-radiation (X-rays) are commonly used, and for thicker or denser materials, gamma
radiation is generally used.

Gamma radiation is given off by decaying radioactive materials, with the two most commonly
used sources of gamma radiation being Iridium-192 (Ir-192) and Cobalt-60 (Co-60).  IR-192 is
generally used for steel up to 2-1/2 - 3 inches, depending on the Curie strength of the source,
and Co-60 is usually used for thicker materials due to its greater penetrating ability. 

The recording media can be industrial x-ray film or one of several types of digital radiation
detectors.  With both, the radiation passing through the test object exposes the media, causing
an end effect of having darker areas where more radiation has passed through the part and
lighter areas where less radiation has penetrated.  If there is a void or defect in the part, more
radiation passes through, causing a darker image on the film or detector, as shown in Figure 8.

RT Techniques

Computed Radiography
Computed radiography (CR) is a transitional technology between film and direct
digital radiography. This technique uses a reusable, flexible, photo-stimulated phosphor
(PSP) plate which is loaded into a cassette and is exposed in a manner similar to
traditional film radiography. The cassette is then placed in a laser reader where it is
scanned and translated into a digital image, which take from one to five minutes.  The
image can then be uploaded to a computer or other electronic media for interpretation
and storage.

Computed Tomography

Computed tomography (CT) uses a computer to reconstruct an image of a cross

sectional plane of an object as opposed to a conventional radiograph, as shown in Figure
9.  The CT image is developed from multiple views taken at different viewing angles that
are reconstructed using a computer. With traditional radiography, the position of
internal discontinuities cannot be accurately determined without making exposures
from several angles to locate the item by triangulation.  With computed tomography,
the computer triangulates using every point in the plane as viewed from many different
directions.

Digital Radiography
Digital radiography (DR) digitizes the radiation that passes through an object
directly into an image that can be displayed on a computer monitor.  The three principle
technologies used in direct digital imaging are amorphous silicon, charge coupled
devices (CCDs), and complementary metal oxide semiconductors (CMOSs).  These
images are available for viewing and analysis in seconds compared to the time needed
to scan in computed radiography images. The increased processing speed is a result of
the unique construction of the pixels; an arrangement that also allows a superior
resolution than is found in computed radiography and most film applications.

Film Radiography
Film radiography uses a film made up of a thin transparent plastic coated with a
fine layer of silver bromide on one or both sides of the plastic.  When exposed to
 radiation these crystals undergo a reaction that allows them, when developed, to
convert to black metallic silver.  That silver is then "fixed" to the plastic during the
developing process, and when dried, becomes a finished radiographic film.

To be a usable film, the area of interest (weld area, etc.) on the film must be
within a certain density (darkness) range and must show enough contrast and sensitivity
so that discontinuities of interest can be seen.  These items are a function of the
strength of the radiation, the distance of the source from the film and the thickness of
the part being inspected.  If any of these parameters are not met, another exposure
("shot") must be made for that area of the part.

Advantages and Disadvantages of Using Radiographic Testing

Advantages:
 It has a very few material limitations.
 Detection of internal defects for thick materials (e.g. pipelines).
 Minimal or no part preparation is required.
 One of the major advantages of RT is its documentation capability. RT provides images
of the object under inspection.
 The probability of misinterpretation of results is minimized since each image can be
reviewed by multiple operators.

Disadvantages:
 The impact of radiation to health and environment can be considered as one of major
disadvantages of radiographic testing since a few seconds of being exposed to radiation
can result in severe injuries.
 High degree of skill and experience is required for exposure and interpretation.
 The high voltage needed to create X-rays is dangerous for human health also.
 It is quite expensive method.
 Ineffective for planar defects and for surface defects.

Ultrasonic Testing (UT)

Ultrasonic Testing (UT) is a group of Non-Destructive Testing (NDT) techniques that use short,
high-frequency ultrasonic waves to identify flaws in a material. They generally work by emitting
waves into a material. By measuring these waves, the properties of the material and internal
flaws can be identified. Most UT devices consist of many separate units. These can include
pulsers and receivers, transducers, and display monitors. The components included depend on
the type of UT that the inspector is performing.
 Ultrasonic testing uses the same principle as is used in naval SONAR and fish finders. 
Ultra-high frequency sound is introduced into the part being inspected and if the sound hits a
material with a different acoustic impedance (density and acoustic velocity), some of the sound
will reflect back to the sending unit and can be presented on a visual display.  By knowing the
speed of the sound through the part (the acoustic velocity) and the time required for the sound
to return to the sending unit, the distance to the reflector (the indication with the different
acoustic impedance) can be determined.  The most common sound frequencies used in UT are
between 1.0 and 10.0 MHz, which are too high to be heard and do not travel through air.   The
lower frequencies have greater penetrating power but less sensitivity (the ability to "see" small
indications), while the higher frequencies don't penetrate as deeply but can detect smaller
indications.
 The two most commonly used types of sound waves used in industrial inspections are
the compression (longitudinal) wave and the shear (transverse) wave, as shown in Figure 10. 
Compression waves cause the atoms in a part to vibrate back and forth parallel to the sound
direction and shear waves cause the atoms to vibrate perpendicularly (from side to side) to the
direction of the sound.  Shear waves travel at approximately half the speed of longitudinal
waves. 

Sound is introduced into the part using an ultrasonic transducer ("probe") that converts
electrical impulses from the UT machine into sound waves, then converts returning sound back
into electric impulses that can be displayed as a visual representation on a digital or LCD screen
(on older machines, a CRT screen).  If the machine is properly calibrated, the operator can
determine the distance from the transducer to the reflector, and in many cases, an experienced
operator can determine the type of discontinuity (like slag, porosity or cracks in a weld) that
caused the reflector.  Because ultrasound will not travel through air (the atoms in air molecules
are too far apart to transmit ultrasound), a liquid or gel called "couplant" is used between the
face of the transducer and the surface of the part to allow the sound to be transmitted into the
part.

UT Techniques
 Straight Beam
 Angle Beam
 Immersion Testing
 Through Transmission
 Phased Array
  Time of Flight Diffraction

Advantages and Disadvantages of Using Ultrasonic Testing

Advantages

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

Disadvantages

 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.
 Extensive technical knowledge is required for the development of inspection
procedures.
 Parts that are rough, irregular in shape, very small or thin, or not homogeneous are
difficult to inspect.
 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.
 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).
 Equipment can be expensive
Electromagnetic Testing (ET)

Electromagnetic testing is a form of non-destructive testing and it is the process of

inducing electric currents or magnetic fields or both inside a test object and observing
the electromagnetic response. If the test is set up properly, a defect inside the test object
creates a measurable response.

ET Techniques
Eddy Current Testing (ECT)
Eddy Current Testing uses the fact that when a an alternating current coil induces an
electromagnetic field into a conductive test piece, a small current is created around the
magnetic flux field, much like a magnetic field is generated around an electric current.  The flow
pattern of this secondary current, called an "eddy" current, will be affected when it encounters
a discontinuity in the test piece, and the change in the eddy current density can be detected
and used to characterize the discontinuity causing that change.  A simplified schematic of eddy
currents generated by an alternating current coil ("probe") is shown in Figure 14-a.  By varying
the type of coil, this test method can be applied to flat surfaces or tubular products.  This
technique works best on smooth surfaces and has limited penetration, usually less than ¼".
Encircling coils (Figure 14-b) are used to test tubular and bar-shaped products. The tube or bar
can be fed through the coil at a relatively high speed, allowing the full cross-section of the test
object to be interrogated.  However, due to the direction of the flux lines, circumferentially
oriented discontinuities may not be detected with this application.

Tube Inspection with Remote Field Testing (RFT)

Remote field testing (RFT) is being used to successfully inspect ferromagnetic tubing such as
carbon steel or ferritic stainless steel. This technology offers good sensitivity when detecting
and measuring volumetric defects resulting from erosion, corrosion, wear, and baffle cuts.
Remote field probes are used all around the world to successfully inspect heat exchangers,
feed-water heaters, and boiler tubes.
RFT with up to four different frequencies and real-time mixes
This feature provides more flexibility for mixing and defect validation. The detection and sizing
of flaws at the support plate is made easier with multifrequency inspections and dual-driver
operations.
RFT with frequencies ranging from 20 Hz to 250 kHz
The high frequency available in the market extends RFT inspection to thin materials with low
permeability, such as 400-series stainless steel, and other ferromagnetic alloys.

Tube Inspection With Near Field Testing (NFT)

Near field testing (NFT) technology is a rapid and inexpensive solution intended specifically for
fin-fan carbon-steel tubing inspection. This new technology relies on a simple driver-pickup
eddy current probe design providing very simple signal analysis.
NFT probes can be successfully used to inspect carbon steel heat exchangers, and air cooler
tubes.
NFT is specifically suited to the detection of internal corrosion, erosion, or pitting on the inside
of carbon steel tubing. The NFT probes measure lift-off or “fill factor,” and convert it to
amplitude-based signals (no phase analysis). Because the eddy current penetration is limited to
the inner surface of the tube, NFT probes are not affected by the fin geometry on the outside of
the tubes.
Magnetic flux leakage (MFL)

Magnetic flux leakage (MFL) is a fast inspection technique, suitable for measuring wall loss and
detecting sharp defects such as pitting, grooving, and circumferential cracks. MFL is effective for
aluminum-finned carbon steel tubes, because the magnetic field is almost completely
unaffected by the presence of such fins.
NFT probes can be successfully used to inspect feed water heater tubes, air cooler tubes and
carbon steel heat exchanger tubes

Advantages and Disadvantages of Using Electromagnetic Testing

Advantages:
 Sensitivity to surface defects
 Can detect through several layers
 Can detect through surface coatings
 Accurate conductivity measurements
 Can be automated
 Little pre-cleaning required
 Portability
Disadvantages:

 Very susceptible to magnetic permeability changes

 Only effective on conductive materials
 Will not detect defects parallel to surface
  Not suitable for large areas and/or complex geometries
 Signal interpretation required
 No permanent record (unless automated)

Visual Testing (VT)

Visual Testing (VT) is the oldest, most versatile, and most commonly used non-destructive test
(NDT) method. It is simple, easy to apply, quickly carried out and usually low in cost. The basic
principle used in visual inspection is to illuminate the test specimen with light and examine the
specimen with the eye. In many instances aids are used to assist in the examination. Visual
inspection can be used for internal and external surface inspection of a variety of equipment
types, including storage tanks, pressure vessels, piping, and other equipment. VT inspections
may be by Direct Viewing, using line-of sight vision, or may be enhanced with the use of optical
instruments such as magnifying glasses, mirrors, borescopes, charge-coupled devices (CCDs)
and computer-assisted viewing systems (Remote Viewing).  Corrosion, misalignment of parts,
physical damage and cracks are just some of the discontinuities that may be detected by visual
examinations.

This method is mainly used:

i) to magnify defects which cannot be detected by the unaided eye,
ii) to assist in the inspection of defects and,
iii) to permit visual checks of areas not accessible to unaided eye.

Example of Visual Testing

Drone-based Visual Inspection

During the drone-based visual inspection, a collision tolerant drone can be
deployed in confined spaces or inaccessible areas. A team composed of an inspector and
a drone pilot conduct the inspection from a safe location enabled by a powerful lighting
system, a 4k video camera and a thermal camera which is installed on the drone.
3D Scan
3D scanner inspection and the application of 3D technology are new techniques
that were introduced in various areas, such as the inspection of surfaces and metrology.
3D scanners along with their dedicated software allow for the integrity
analysis of components and facilitate a precise assessment of their dimensions.

In refineries, 3D scanning is used to characterize corrosion and mechanical

damages, offe ring efficient
acquisition and analysis. The
acquired data can easily be
combined with ultrasound data
for a complete profile of the part
section, 3D providing the surface
data while ultrasound provides
the volumetric profile.
 Remote Visual Inspection
RVI is the inspection of objects or areas usually inaccessible to the eye without
disassembling surrounding structures or machinery. It allows inspectors to discover
hidden discontinuities before they may cause major problems, e.g. poor welding,
surface defects, corrosion pits, general condition, degradation, blockages and foreign
materials. RVI equipment such as flexible borescopes, videoscopes or similar equipment
penetrates remote places, utilizing small openings and sending images directly back to
the observer or to a video monitor.

Applications:
 Gearbox Inspection.
 Orbital Weld Inspection.
 Headers, water and steam lines, pumps, valves, heat exchangers tube, etc. in power
plant, refinery and processing industry.
 Wind turbine blades and gearbox.
 Engines of ship and aircraft
 Nuclear Power Stations – contaminated areas
 Any areas where it is dangerous, small or costly to view directly
 Reduces or eliminates need for Confined Space Entry
Advantages and Disadvantages of Using Visual Testing

Advantages:

 Portability
  Immediate result.
 Minimum special skills.
 Minimum part preparation.
 No disassembly or lost production time for in-service inspection
 Recording for future reference
 Removes humans from potentially unsafe conditions
 Reduces or eliminates need for Confined Space Entry

Disadvantages:

 Surface indications only

 Generally only able to detect large flaws
 Possible misinterpretation of flaws

The less often used test methods are:

Acoustic Emission Testing (AE)
Guided wave testing 
Laser Testing Methods (LM)
Leak Testing (LT)
Magnetic Flux Leakage (MFL)
Neutron Radiographic Testing (NR)
Thermal/Infrared Testing (IR)
Vibration Analysis (VA)