Welding Assignment

Assignment 1
Ans 1
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by
causing coalescence. This is often done by melting the workpieces and adding a filler material to form a
pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes
used in conjunction with heat, or by itself, to produce the weld.
In general various welding processes are classified as follows.
1: Gas Welding
(a): Air Acetylene
(b): Oxy Acetylene
(c): Oxy Hydrogen Welding
2: Arc Welding
(a): Carbon Arc welding
(b); Plasma Arc welding
(c): Shield Metal Arc Welding
(d): T.I.G. ( Tungsten Inert Gas Welding)
(e): M.I.G. ( Metal Inert Gas Welding)
3: Resistance Welding:
(a): Spot welding
(b): Seam welding
(c): Projection welding
(d): Resistance Butt welding
(e): Flash Butt welding
4: Solid State Welding:
(a): Cold welding
(b): Diffusion welding
(c): Forge welding
(d): Fabrication welding
(e): Hot pressure welding
(f): Roll welding

5: Thermo Chemical Welding
(a): Thermit welding
(b): Atomic welding
6: Radiant Energy Welding
(a): Electric Beam Welding
(b): Laser Beam Welding
Ans 2
Submerged arc welding (SAW) is a common arc welding process.
the process requires a continuously fed consumable solid or tubular (metal cored) electrode.[1] The
molten weld and the arc zone are protected from atmospheric contamination by being "submerged"
under a blanket of granular fusible flux consisting of lime, silica, manganese oxide, calcium fluoride, and
other compounds. When molten, the flux becomes conductive, and provides a current path between
the electrode and the work. This thick layer of flux completely covers the molten metal thus preventing
spatter and sparks as well as suppressing the intense ultraviolet radiation and fumes that are a part of
the shielded metal arc welding (SMAW) process.
Advantages
High deposition rates (over 45 kg/h (100 lb/h) have been reported).
High operating factors in mechanized applications.
Deep weld penetration.
Sound welds are readily made (with good process design and control).
High speed welding of thin sheet steels up to 5 m/min (16 ft/min) is possible.
Minimal welding fume or arc light is emitted.
Limitations
Limited to ferrous (steel or stainless steels) and some nickel-based alloys.

Normally limited to the 1F, 1G, and 2F positions.
Normally limited to long straight seams or rotated pipes or vessels.
Requires relatively troublesome flux handling systems.
Flux and slag residue can present a health and safety concern.
Requires inter-pass and post weld slag removal.
Ans 3
Oxy-fuel welding (commonly called oxyacetylene welding, oxy welding, or gas welding in the
U.S.) and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals,
respectively.
Oxy-gas torches are or have been used for:
 Welding metal: see below.
 Cutting metal: see below.
 Depositing metal to build up a surface, as in hardfacing.
 Also, oxy-hydrogen flames are used:
 in stone working for "flaming" where the stone is heated and a top layer crackles and
breaks. A steel circular brush is attached to an angle grinder and used to remove the first
layer leaving behind a bumpy surface similar to hammered bronze.
 in the glass industry for "fire polishing".
 in jewelry production for "water welding" using a water torch (an oxyhydrogen torch whose
gas supply is generated immediately by electrolysis of water).
 in automotive repair, removing a seized bolt.
 formerly, to heat lumps of quicklime to obtain a bright white light called limelight, in theatres
or optical ("magic") lanterns.
 formerly, in platinum works, as platinum is fusible only in the oxyhydrogen flame[citation
needed]
and in an electric furnace.

ans 4

Soldering is a process in which two or more metal items are joined together by melting and flowing
a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining
metal. Soldering differs from welding in that soldering does not involve melting the work pieces.
Inbrazing, the filler metal melts at a higher temperature, but the work piece metal does not melt. In
the past, nearly all solders contained lead, but environmental concerns have increasingly dictated
use of lead-free alloys for electronics and plumbing purposes.
Soldering is used in plumbing, electronics, and metalwork from flashing to jewellery.
Soldering provides reasonably permanent but reversible connections between copper pipes
in plumbing systems as well as joints in sheet metal objects such as food cans, roof flashing, rain
gutters and automobile radiators.
Brazing is a metal-joining process whereby a filler metal is heated above melting point and
distributed between two or more close-fitting parts by capillary action. The filler metal is brought
slightly above its melting (liquidus) temperature while protected by a suitable atmosphere, usually
a flux. It then flows over the base metal (known as wetting) and is then cooled to join the workpieces
together.[1]
It is similar to soldering, except the temperatures used to melt the filler metal are higher
for brazing.
Brazing has many advantages over other metal-joining techniques, such as welding. Since brazing
does not melt the base metal of the joint, it allows much tighter control over tolerances and produces
a clean joint without the need for secondary finishing. Additionally, dissimilar metals and non-metals
(i.e. metalized ceramics) can be brazed.[13]
In general, brazing also produces less thermal distortion
than welding due to the uniform heating of a brazed piece. Complex and multi-part assemblies can
be brazed cost-effectively
One of the main disadvantages is: the lack of joint strength as compared to a welded joint due to the
softer filler metals used.[1][dubious – discuss]
The strength of the brazed joint is likely to be less than that of
the base metal(s) but greater than the filler metal.[citation needed][16]
Another disadvantage is that brazed
joints can be damaged under high service temperatures.[1]
Brazed joints require a high degree of
base-metal cleanliness when done in an industrial setting.
Ans 5
Electron beam welding (EBW) is a fusion welding process in which a beam of high-
velocity electrons is applied to two materials to be joined. The workpieces melt and flow together as
the kinetic energy of the electrons is transformed into heat upon impact. EBW is often performed
under vacuum conditions to prevent dissipation of the electron beam
Laser beam welding (LBW) is a weldingtechnique used to join multiple pieces of metal through the
use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and
high welding rates. The process is frequently used in high volume applications, such as in the
automotive industry.
Some of the advantages of LBW in comparison to EBW are as follows:
- the laser beam can be transmitted through air rather than requiring a vacuum,
- the process is easily automated with robotic machinery,
- x-rays are not generated, and

- LBW results in higher quality welds.

ANS 6
Gas tungsten arc welding (GTAW), also known as tungsten inert gas(TIG) welding, is an arc
weldingprocess that uses a non-consumabletungsten electrode to produce theweld. The weld area
is protected from atmospheric contamination by an inert shielding gas (argon orhelium), and a filler
metal is normally used, though some welds, known as autogenous welds, do not require it.
A constant-current welding power supply produces energy which is conducted across the arc
through a column of highly ionized gas and metal vapors known as a plasma.
GTAW is most commonly used to weld thin sections of stainless steel and non-ferrous metals such
as aluminum, magnesium, and copper alloys. The process grants the operator greater control over
the weld than competing processes such as shielded metal arc welding and gas metal arc welding,
allowing for stronger, higher quality welds. However, GTAW is comparatively more complex and
difficult to master, and furthermore, it is significantly slower than most other welding techniques. A
related process, plasma arc welding, uses a slightly different welding torch to create a more focused
welding arc and as a result is often automated.[1]
GTAW can be dangerous if proper precautions are not taken. Welders wear protective clothing,
including light and thin leather gloves and protective long sleeve shirts with high neck collars, to
avoid exposure to strong ultraviolet light.
Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert
gas (MIG)welding or metal active gas (MAG) welding, is a welding process in which an electric
arc forms between a consumable wire electrode and the workpiece metal(s), which heats the

workpiece metal(s), causing them to melt, and join. Along with the wire electrode, a shielding
gas feeds through the welding gun, which shields the process from contaminants in the air. The
process can be semi-automatic or automatic. A constantvoltage, direct current power source is most
commonly used with GMAW, but constant currentsystems, as well as alternating current, can be
used. There are four primary methods of metal transfer in GMAW, called globular, short-circuiting,
spray, and pulsed-spray, each of which has distinct properties and corresponding advantages and
limitations.
Gas metal arc welding can be dangerous if proper precautions are not taken. Since GMAW employs
an electric arc, welders wear protective clothing, including heavy leather gloves and protective long
sleeve jackets, to avoid exposure to extreme heat and flames. In addition, the brightness of the
electric arc is a source of the condition known as arc eye, an inflammation of the cornea caused
by ultraviolet light and, in prolonged exposure, possible burning of the retina in the eye.
ANS 7
Shielded metal arc welding(SMAW), also known as manual metal arc
welding (MMA orMMAW), flux shielded arc welding[1]
or informally as stick welding, is a
manual arc weldingprocess that uses a consumableelectrode coated in flux to lay the weld.
An electric current, in the form of either alternating current or direct current from a welding power
supply, is used to form an electric arcbetween the electrode and themetals to be joined. As the weld
is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as ashielding
gas and providing a layer of slag, both of which protect the weld area from atmospheric
contamination.
Because of the versatility of the process and the simplicity of its equipment and operation, shielded
metal arc welding is one of the world's most popular welding processes. It dominates other welding
processes in the maintenance and repair industry, and thoughflux-cored arc welding is growing in
popularity, SMAW continues to be used extensively in the construction of steel structures and in
industrial fabrication. The process is used primarily to weld iron and steels (including stainless steel)
but aluminium, nickel andcopper alloys can also be welded with this method.
SMAW welding, like other welding methods, can be a dangerous and unhealthy practice if proper
precautions are not taken. The process uses an open electric arc, which presents a risk of burns
which are prevented by personal protective equipment in the form of heavyleather gloves and long
sleeve jackets.
SMAW is often used to weld carbon steel, low and high alloy steel, stainless steel, cast iron,
and ductile iron. While less popular for nonferrous materials, it can be used on nickel and copper
and their alloys and, in rare cases, on aluminium.

ANS 8Diffusion bonding is a solid-state welding technique used in metalworking, capable of joining
similar and dissimilar metals. It operates on the materials science principle of solid-state diffusion,
wherein the atoms of two solid, metallic surfaces intermingle over time under elevated temperature.
Diffusion bonding is typically implemented by applying both high pressure and high temperature to
the materials to be welded; it is most commonly used to weld "sandwiches" of alternating layers of
thin metal foil and metal wires or filaments.
Diffusion bonding is performed by clamping the two pieces to be welded with their surfaces abutting
each other. Prior to welding, these surfaces must be machined to as smooth a finishas economically
viable, and kept as free from chemical contaminants or other detritus as possible. Any intervening
material between the two metallic surfaces may prevent adequate diffusion of material. Once
clamped, pressure and heat are applied to the components, usually for many hours
ANS 9
Butt Joint

A butt weld, or a square-groove, is the most common and easiest to use. Consisting of two flat pieces that are
parallel to one another, it also is an economical option. It is the universally used method of joining a pipe to itself, as
well as flanges, valves, fittings, or other equipment. However, it is limited by any thickness exceeding 3/16”.
Corner Joint
A corner weld is a type of joint that is between two metal parts and is located at right angles to one another in the
form of a L. As the name indicates, it is used to connect two pieces together, forming a corner. This weld is most
often used in the sheet metal industry and is performed on the outside edge of the piece.
Edge Joint
Edge welding joints, a groove type of weld, are placed side by side and welded on the same edge. They are the most
commonly replaced type of joints due to build up accumulating on the edges. They are often applied to parts of sheet
metal that have edges flanging up or formed at a place where a weld must be made to join two adjacent pieces
together.
Lap Joint
This is formed when two pieces are placed atop each other while also over lapping each other for a certain distance
along the edge. Considered a fillet type of a welding joint, the weld can be made on one or both sides, depending
upon the welding symbol or drawing requirements. It is most often used to join two pieces together with differing
levels of thickness.
Tee Joint
Tee joints, considered a fillet type of weld, form when two members intersect at 90° resulting in the edges coming
together in the middle of a component or plate. It may also be formed when a tube or pipe is placed on a baseplate.

ANS 10
1. Introduction
Common weld defects include:
i. Lack of fusion
ii. Lack of penetration or excess penetration
iii. Porosity
iv. Inclusions
v. Cracking
vi. Undercut
vii. Lamellar tearing
Any of these defects are potentially disastorous as they can all give rise to high stress intensities which
may result in sudden unexpected failure below the design load or in the case of cyclic loading, failure
after fewer load cycles than predicted.
2. Types of Defects
i and ii. - To achieve a good quality join it is essential that the fusion zone extends the full thickness of
the sheets being joined. Thin sheet material can be joined with a single pass and a clean square edge will

be a satisfactory basis for a join. However thicker material will normally need edges cut at a V angle and
may need several passes to fill the V with weld metal. Where both sides are accessible one or more
passes may be made along the reverse side to ensure the joint extends the full thickness of the metal.
Lack of fusion results from too little heat input and / or too rapid traverse of the welding torch (gas or
electric).
Excess penetration arises from to high a heat input and / or too slow transverse of the welding torch
(gas or electric). Excess penetration - burning through - is more of a problem with thin sheet as a higher
level of skill is needed to balance heat input and torch traverse when welding thin metal.
ii. Porosity - This occurs when gases are trapped in the solidifying weld metal. These may arise from
damp consumables or metal or, from dirt, particularly oil or grease, on the metal in the vicinity of the
weld. This can be avoided by ensuring all consumables are stored in dry conditions and work is carefully
cleaned and degreased prior to welding.
iv. Inclusions - These can occur when several runs are made along a V join when joining thick plate using
flux cored or flux coated rods and the slag covering a run is not totally removed after every run before
the following run.
v. Cracking - This can occur due just to thermal shrinkage or due to a combination of strain
accompanying phase change and thermal shrinkage.
In the case of welded stiff frames, a combination of poor design and inappropriate procedure may result
in high residual stresses and cracking.
Where alloy steels or steels with a carbon content greater than about 0.2% are being welded, self
cooling may be rapid enough to cause some (brittle) martensite to form. This will easily develop cracks.
To prevent these problems a process of pre-heating in stages may be needed and after welding a slow
controlled post cooling in stages will be required. This can greatly increase the cost of welded joins, but
for high strength steels, such as those used in petrochemical plant and piping, there may well be no
alternative.
Solidification Cracking
This is also called centreline or hot cracking. They are called hot cracks because they occur immediately
after welds are completed and sometimes while the welds are being made. These defects, which are
often caused by sulphur and phosphorus, are more likely to occur in higher carbon steels.
Solidification cracks are normally distinguishable from other types of cracks by the following features:

they occur only in the weld metal - although the parent metal is almost always the source of the low
melting point contaminants associated with the cracking
they normally appear in straight lines along the centreline of the weld bead, but may occasionally
appear as transverse cracking
solidification cracks in the final crater may have a branching appearance
as the cracks are 'open' they are visible to the naked eye
A schematic diagram of a centreline crack is shown below:
On breaking open the weld the crack surface may have a blue appearance, showing the cracks formed
while the metal was still hot. The cracks form at the solidification boundaries and are characteristically
inter dendritic. There may be evidence of segregation associated with the solidification boundary.
The main cause of solidification cracking is that the weld bead in the final stage of solidification has
insufficient strength to withstand the contraction stresses generated as the weld pool solidifies. Factors
which increase the risk include:
insufficient weld bead size or inappropriate shape
welding under excessive restraint
material properties - such as a high impurity content or a relatively large shrinkage on solidification
Joint design can have an influence on the level of residual stresses. Large gaps between conponents will
increase the strain on the solidifying weld metal, especially if the depth of penetration is small. Hence
weld beads with a small depth to width ratio, such as is formed when bridging a large wide gap with a
thin bead, will be more susceptible to solidification cracking.
In steels, cracking is associated with impurities, particularly sulphur and phosphorus and is promoted by
carbon, whereas manganese and sulphur can help to reduce the risk. To minimise the risk of cracking,
fillers with low carbon and impurity levels and a relatively high manganese content are preferred. As a
general rule, for carbon manganese steels, the total sulphur and phosphorus content should be no
greater than 0.06%. However when welding a highly restrained joint using high strength steels, a
combined level below 0.03% might be needed.
Weld metal composition is dominated by the filler and as this is usually cleaner than the metal being
welded, cracking is less likely with low dilution processes such as MMA and MIG. Parent metal
composition becomes more important with autogenous welding techniques, such as TIG with no filler.

Avoiding Solidification Cracking
Apart from choice of material and filler, the main techniques for avoiding solidification cracking are:
control the joint fit up to reduce the gaps
clean off all contaminants before welding
ensure that the welding sequence will not lead to a buildup of thermally induced stresses
choose welding parameters to produce a weld bead with adequate depth to width ratio or with
sufficient throat thickness (fillet weld) to ensure the bead has sufficient resistance to solidificatiuon
stresses. Recommended minimum depth to width ratio is 0.5:1
avoid producing too large a depth to width ratio which will encourage segregation and excessive
transverse strains. As a rule, weld beads with a depth to width ratio exceeds 2:1 will be prone to
solidification cracking
avoid high welding speeds (at high current levels) which increase segregation and stress levels accross
the weld bead
at the run stop, ensure adequate filling of the crater to avoid an unfavourable concave shape
Hydrogen induced cracking (HIC) - also referred to as hydrogen cracking or hydrogen assisted cracking,
can occur in steels during manufacture, during fabrication or during service. When HIC occurs as a result
of welding, the cracks are in the heat affected zone (HAZ) or in the weld metal itself.
Four requirements for HIC to occur are:
a) Hydrogen be present, this may come from moisture in any flux or from other sources. It is absorbed
by the weld pool and diffuses int o the HAZ.
b) A HAZ microstructure susceptible to hydrogen cracking.
c) Tensile stresses act on the weld
d) The assembly has cooled to close to ambient - less than 150oC
HIC in the HAZ is often at the weld toe, but can be under the weld bead or at the weld root. In fillet
welds cracks are normally parallel to the weld run but in butt welds cracks can be transverse to the
welding direction.
vi Undercutting - In this case the thickness of one (or both) of the sheets is reduced at the toe of the
weld. This is due to incorrect settings / procedure. There is already a stress concentration at the toe of
the weld and any undercut will reduce the strength of the join.

vii Lamellar tearing - This is mainly a problem with low quality steels. It occurs in plate that has a low
ductility in the through thickness direction, which is caused by non metallic inclusions, such as suphides
and oxides that have been elongated during the rolling process. These inclusions mean that the plate
can not tolerate the contraction stresses in the short transverse direction.
Lamellar tearing can occur in both fillet and butt welds, but the most vulnerable joints are 'T' and corner
joints, where the fusion boundary is parallel to the rolling plane.
These problem can be overcome by using better quality steel, 'buttering' the weld area with a ductile
material and possibly by redesigning the joint.
3. Detection
Visual Inspection
Prior to any welding, the materials should be visually inspected to see that they are clean, aligned
correctly, machine settings, filler selection checked, etc.
As a first stage of inspection of all completed welds, visual inspected under good lighting should be
carried out. A magnifying glass and straight edge may be used as a part of this process.
Undercutting can be detected with the naked eye and (provided there is access to the reverse side)
excess penetration can often be visually detected.
Liquid Penetrant Inspection
Serious cases of surface cracking can be detected by the naked eye but for most cases some type of aid
is needed and the use of dye penetrant methods are quite efficient when used by a trained operator.
This procedure is as follows:
Clean the surface of the weld and the weld vicinity
Spray the surface with a liquid dye that has good penetrating properties
Carefully wipe all the die off the surface
Spray the surface with a white powder
Any cracks will have trapped some die which will weep out and discolour the white coating and be
clearly visible
X - Ray Inspection

Sub-surface cracks and inclusions can be detected 'X' ray examination. This is expensive, but for safety
critical joints - eg in submarines and nuclear power plants - 100% 'X' ray examination of welded joints
will normally be carried out.
Ultrasonic Inspection
Surface and sub-surface defects can also be detected by ultrasonic inspection. This involves directing a
high frequency sound beam through the base metal and weld on a predictable path. When the beam
strikes a discontinuity some of it is reflected beck. This reflected beam is received and amplified and
processed and from the time delay, the location of a flaw estimated.
Porosity, however, in the form of numerous gas bubbles causes a lot of low amplitude reflections which
are difficult to separate from the background noise.
Results from any ultrasonic inspection require skilled interpretation.
Magnetic Particle Inspection
This process can be used to detect surface and slightly sub-surface cracks in ferro-magnetic materials (it
can not therefore be used with austenitic stainless steels).
The process involves placing a probe on each side of the area to be inspected and passing a high current
between them. This produces a magnetic flux at right angles to the flow of the current. When these lines
of force meet a discontinuity, such as a longitudinal crack, they are diverted and leak through the
surface, creating magnetic poles or points of attraction. A magnetic powder dusted onto the surface will
cling to the leakage area more than elsewhere, indicating the location of any discontinuities.
This process may be carried out wet or dry, the wet process is more sensitive as finer particles may be
used which can detect very small defects. Fluorescent powders can also be used to enhance sensitivity
when used in conjunction with ultra violet illumination.
4. Repair
Any detected cracks must be ground out and the area re-welded to give the required profile and then
the joint must be inspected again.
ANS 11
1. Pre-cleaning:
The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep
penetrant out of a defect, or cause irrelevant or false indications. Cleaning methods may include
solvents, alkaline cleaning steps, vapor degreasing, or media blasting. The end goal of this step is a clean
surface where any defects present are open to the surface, dry, and free of contamination. Note that if

media blasting is used, it may "work over" small discontinuities in the part, and an etching bath is
recommended as a post-blasting treatment.
Application of the penetrant to a part in a ventilated test area.
2. Application of Penetrant:
The penetrant is then applied to the surface of the item being tested. The penetrant is allowed "dwell
time" to soak into any flaws (generally 5 to 30 minutes). The dwell time mainly depends upon the
penetrant being used, material being tested and the size of flaws sought. As expected, smaller flaws
require a longer penetration time. Due to their incompatible nature one must be careful not to apply
solvent-based penetrant to a surface which is to be inspected with a water-washable penetrant.
3. Excess Penetrant Removal:
The excess penetrant is then removed from the surface. The removal method is controlled by the type
of penetrant used. Water-washable, solvent-removable, lipophilic post-emulsifiable, or hydrophilic post-
emulsifiable are the common choices. Emulsifiers represent the highest sensitivity level, and chemically
interact with the oily penetrant to make it removable with a water spray. When using solvent remover
and lint-free cloth it is important to not spray the solvent on the test surface directly, because this can
remove the penetrant from the flaws. If excess penetrant is not properly removed, once the developer
is applied, it may leave a background in the developed area that can mask indications or defects. In
addition, this may also produce false indications severely hindering your ability to do a proper
inspection.
4. Application of Developer:
After excess penetrant has been removed a white developer is applied to the sample. Several developer
types are available, including: non-aqueous wet developer, dry powder, water suspendable, and water
soluble. Choice of developer is governed by penetrant compatibility (one can't use water-soluble or
suspendable developer with water-washable penetrant), and by inspection conditions. When using non-
aqueous wet developer (NAWD) or dry powder, the sample must be dried prior to application, while
soluble and suspendable developers are applied with the part still wet from the previous step. NAWD is
commercially available in aerosol spray cans, and may employ acetone, isopropyl alcohol, or a
propellant that is a combination of the two. Developer should form a semi-transparent, even coating on
the surface.

The developer draws penetrant from defects out onto the surface to form a visible indication,
commonly known as bleed-out. Any areas that bleed-out can indicate the location, orientation and
possible types of defects on the surface. Interpreting the results and characterizing defects from the
indications found may require some training and/or experience [the indication size is not the actual size
of the defect]
5. Inspection:
The inspector will use visible light with adequate intensity (100 foot-candles or 1100 lux is typical) for
visible dye penetrant. Ultraviolet (UV-A) radiation of adequate intensity (1,000 micro-watts per
centimeter squared is common), along with low ambient light levels (less than 2 foot-candles) for
fluorescent penetrant examinations. Inspection of the test surface should take place after 10 to 30
minute development time, depends of product kind. This time delay allows the blotting action to occur.
The inspector may observe the sample for indication formation when using visible dye. It is also good
practice to observe indications as they form because the characteristics of the bleed out are a significant
part of interpretation characterization of flaws.
6. Post Cleaning:
The main advantages of DPI are the speed of the test and the low cost. Disadvantages include the
detection of only surface flaws, skin irritation, and the inspection should be on a smooth clean
surface where excessive penetrant can be removed prior to being developed.
ANS 11 B
Ultrasonic testing (UT) is a family of non-destructive testing techniques based in the propagation of
ultrasonic waves in the object or material tested. In most common UT applications, very short ultrasonic
pulse-waves with center frequencies ranging from 0.1-15 MHz, and occasionally up to 50 MHz, are
transmitted into materials to detect internal flaws or to characterize materials. A common example is
ultrasonic thickness measurement, which tests the thickness of the test object, for example, to monitor
pipework corrosion.
Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on
concrete, wood and composites, albeit with less resolution. It is used in many industries including steel
and aluminium construction, metallurgy, manufacturing, aerospace, automotive and other
transportation sectors.
Advantages[edit]

High penetrating power, which allows the detection of flaws deep in the part.
High sensitivity, permitting the detection of extremely small flaws.
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.
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.
Disadvantages[edit]
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, after follow up with other nondestructive testing methods.[1]
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).
Inspected items must be water resistant, when using water based couplants that do not contain rust
inhibitors

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