PRINCIPLES OF WELDING

PROCESSES, METALLURGY &

TESTING AND INSPECTION
OF WELDS

BY: ENGR. NIEL IVAN Q. VERGARA

ENGR. LIZA L. ACOSTA
Joining Processes: Soldering, Brazing & Welding
Soldering
is a process in which two or more
items are joined by melting and
putting a filler metal (solder) into
the joint, the filler metal having a
lower melting point than the
adjoining metal. Unlike welding,
soldering does not involve melting
the work pieces.
Brazing
Brazing is a metal-joining process in which two or more metal items are joined together by melting and
flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining
metal.

The brazing principle is the same as soldering

where a combination of heat, filler material, and
flux works to join the metals together. But in
brazing, a flux solution between the filler metal and
base metal is used to join in heating.
Principles of Welding
Process
Welding
is a metal joining process in which two or more parts are joined or coalesced at
their contacting surfaces by suitable application of heat or/and pressure.

• Some times, welding is done just by applying heat alone, with no pressure
applied

• In some cases, both heat and pressure are applied; and in other cases only
pressure is applied, without any external heat.

• In some welding processes a filler material is added to facilitate

coalescence(Joining)
Published 1 Sep 2022
The Occupational Safety and Health Administration (OSHA) outlined specific requirements
for welding, cutting, and brazing in 29 CFR 1910 Subpart Q. While their implementation
may be dependent on the context of the company, consider starting to apply these rules
below in daily business operations.
The Safety Gear required:

1. Boots- are to be worn to ensure sparks that land on or near your feet,
do not set your boots a light causing a fire and your feet getting burnt
2. Gloves - are a must requirement, they prevent your hands catching on
fire and possibly melting
3. Earmuffs/plugs- help prevent sparks from burning you and possible
splatters from getting into your ears
4. Fire/flame resistant clothing and aprons- in order to prevent
splatters and sparks from causing a fire and serious injury to the
person, wearing fire/flame resistant clothing and aprons are strongly
required
5. Respirator- wearing a respirator (breathable mouth cover), can help
breathing and ensure the air being breathed in is clean and free from
harmful substances
6. Welding helmet, head shield or goggles- wearing the helmet will
help ensure your eyes aren't exposed to the bright light that comes out
of the nozzle of the welder. not wearing it can occur in blindness if
you look at the bright light which is extremely dangerous. Wearing a
welding helmet also helps stop radiation from soaking into your skin
and making you ill.
 Hand shields or helmets provide eye protection by
using an assembly of components:
Helmet shell - must be opaque to light and resistant to
impact, heat and electricity.
Outer cover plate made of polycarbonate plastic
which protects from radiation, impact and scratches.
Filter lens made of glass containing a filler which
reduces the amount of light passing through to the eyes.
Filters are available in different shade numbers ranging
from 2 to 14. The higher the number, the darker the
filter and the less light passes through the lens. Clear
retainer lens made of plastic prevents any broken pieces
of the filter lens from reaching the eye. Gasket made of
heat insulating material between the cover lens and the
filter lens protects the lens from sudden heat changes
which could cause it to break. In some models the heat
insulation is provided by the frame mount instead of a
separate gasket.
Welder's Helmet and Eye Protection Assembly
Advantages of welding:
• Welding provides a permanent joint.
• Welded joint can be stronger than the parent materials if a proper filler metal
is used that has strength properties better than that of parent base material and
if defect less welding is done.
• It is the economical way to join components in terms of material usage and
fabrication costs. Other methods of assembly require, for example, drilling of
holes and usage of rivets or bolts which will produce a heavier structure.

Disadvantages of welding:
• Labor costs are more since manual welding is done mostly.
• Dangerous to use because of presence of high heat and pressure.
• Disassembly is not possible as welding produces strong joints.
• Some of the welding defects cannot be identified which will reduce the
strength.
Classification of Welding Processes
• Arc Welding
1) Shielded metal arc welding(SMAW)
2) Gas tungsten arc welding(TIG) or (GTAW)
3) Gas metal arc welding(MIG) or (GMAW)
4) Flux cored arc welding(FCAW)
5) Plasma arc welding
6) Submerged arc welding
• Resistance welding
1) Spot welding
2) Seam welding
3) Projection welding
4) Butt welding
 • Gas welding
1) Oxy-acetylene welding
2) Oxy-hydrogen welding
3) Pressure Gas welding
• Thermo Chemical Welding Process
1) Thermit welding
2) Atomic hydrogen welding
• Radient Energy Welding Process
1) Electron beam welding
2) Laser beam welding
 ARC WELDING
It is a fusion welding process in which the melting and joining of metals is done by the heat energy
generated by the arc between the work and electrode. An electric arc is generated when the electrode
contacts the work and then quickly separated to maintain the gap. A temperature of 5500°C is
generated by this arc. This temperature is sufficient to melt most of the metals. The molten metal,
consisting of base metal and filler, solidifies in the weld region. In order to have seam weld, the power
source moves along the weld line.
1) Shielded Metal Arc Welding (SMAW)
also known as manual metal arc welding (MMA or MMAW), flux shielded arc welding or informally
as stick welding, is a manual arc welding process that uses a consumable electrode covered with a flux to
lay the weld.

SMAW can be used for a variety of metal

types and various thicknesses. It is often
used for heavy-duty work involving
industrial iron and steel, like carbon steel
and cast iron, as well as work involving low-
and high-alloy steels and nickel alloys.
SMAW Electrode Designation
2. Gas tungsten arc welding(TIG) or (GTAW)
Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is
an arc welding process that uses a non consumable tungsten electrode to produce the weld.
The weld area and electrode are protected from oxidation or other atmospheric contamination
by an inert shielding gas (argon or helium).
3. Gas metal arc welding(MIG) or
(GMAW)
Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG)
and metal active gas (MAG) is a welding process in which an electric arc forms between a
consumable MIG wire electrode and the workpiece metal(s), which heats the workpiece metal(s),
causing them to fuse (melt and join). Along with the wire electrode, a shielding gas feeds through
the welding gun, which shields the process from atmospheric contamination.

Originally developed in the 1940s for

welding aluminium and other non-ferrous materials,
GMAW was soon applied to steels because it provided
faster welding time compared to other welding
processes. The cost of inert gas limited its use in
steels until several years later, when the use of
semi-inert gases such as carbon dioxide became
common.

GMAW torch nozzle cutaway image. (1) Torch handle, (2) Molded phenolic
dielectric (shown in white) and threaded metal nut insert
(yellow), (3) Shielding gas diffuser, (4) Contact tip, (5) Nozzle output face
4. Flux cored arc welding(FCAW)
Flux-cored arc welding (FCAW or FCA) is a semi-automatic or automatic arc welding process.
FCAW requires a continuously-fed consumable tubular electrode containing a flux and a
constant-voltage or, less commonly, a constant-current welding power supply. An externally
supplied shielding gas is sometimes used, but often the flux itself is relied upon to generate the
necessary protection from the atmosphere, producing both gaseous protection and
liquid slag protecting the weld

The most common shielding gases

include carbon dioxide and blends
of argon (75%) and carbon dioxide
(25%). The shielding carbon dioxide
gas, provided externally using a
high-pressure gas cylinder,
safeguards the weld pool from
oxidation.
 AWS Standards Specific to GTAW and GMAW Electrodes

AWS Classification for Solid Steel Wires FCAW Electrode

Classification

AWS Classification for Composite Steel Wires

5. Plasma arc welding
PAW is an arc welding process similar to gas tungsten arc welding (GTAW). The electric arc is formed
between an electrode (which is usually but not always made of sintered tungsten) and the workpiece.
The key difference from GTAW is that in PAW, the electrode is positioned within the body of the torch,
so the plasma arc is separated from the shielding gas envelope. The plasma is then forced through a
fine-bore copper nozzle which constricts the arc and the plasma exits the orifice at high velocities
(approaching the speed of sound) and a temperature approaching 28,000 °C (50,000 °F) or higher.

Plasma arc welding is an arc welding process

wherein coalescence is produced by the heat obtained
from a constricted arc setup between a tungsten/alloy
tungsten electrode and the water-cooled (constricting)
nozzle (non-transferred arc) or between a
tungsten/alloy tungsten electrode and the job
(transferred arc). The process employs two inert gases,
one forms the arc plasma and the second shields the
arc plasma. Filler metal may or may not be added.

1. Gas plasma, 2. Nozzle protection, 3. Shield Gas, 4.

Electrode, 5. Nozzle constriction, 6. Electric arc
6. Submerged arc welding
Submerged-arc welding (SAW) is a common arc welding process that involves the formation
of an arc between a continuously fed electrode and the workpiece. A blanket of powdered
flux generates a protective gas shield and a slag (and may also be used to add alloying elements
to the weld pool) which protects the weld zone.

The difference between submerged arc welding

https://www.youtube.com/watch?v=lNMJA2f_Fpk
and regular arc welding is that the welding
wire, arc, and weld joint are covered by a
layer of flux. The flux creates a pathway for the
https://youtu.be/7srOHVAjyGU arc to travel through to the material that is being
welded.
Resistance Welding / Electric Resistance Welding
is the joining of metals by applying pressure and passing current for a length of time
through the metal area which is to be joined. The key advantage of resistance welding is that no
other materials are needed to create the bond, which makes this process extremely cost effective.

1. Spot welding
Spot welding is a resistance welding method
used to join two or more overlapping metal
sheets, studs, projections, electrical wiring
hangers, some heat exchanger fins, and
some tubing. Usually power sources and
welding equipment are sized to the specific
thickness and material being welded
together. The thickness is limited by the
output of the welding power source and thus
the equipment range due to the current
required for each application.
2. Seam welding
The welding process in which two similar or dissimilar materials are joined at the seam by the
application of heat generated from electrical resistance is known as seam welding. The seam
welding is a types of resistance welding, in which weld is produced by roller electrodes instead of
tipped electrodes.

https://www.youtube.com/watch?v=n5bssD7GTlc

3. Projection welding
Projection welding is a form of resistance welding which uses pressure and electrical current to join
two or more metal parts that have been designed to meet at one or more specific points with the
maximum amount of contact. This allows for more efficient welding with less energy and greater
weld strength.
https://www.youtube.com/watch?v=vS9X1uFH_tc
4. Butt welding
Butt welding is when two pieces of metal are placed end-to-end without overlap and then welded along
the joint (as opposed to lap joint weld, where one piece of metal is laid on top of the other, or plug
welding, where one piece of metal is inserted into the other). Importantly, in a butt joint, the surfaces of
the workpieces being joined are on the same plane and the weld metal remains within the planes of the
surfaces.
Two Types of butt welding
Flash welding is a type of resistance welding that
does not use any filler metals. The pieces of metal
to be welded are set apart at a predetermined
distance based on material thickness, material
composition, and desired properties of the finished
weld. Current is applied to the metal, and the gap
between the two pieces creates resistance and
produces the arc required to melt the metal. Once
the pieces of metal reach the proper temperature,
they are pressed together, effectively forge welding
them together
Resistance Butt Welding

In resistance butt welding or upset welding

the pieces to be welded are held in clamps
supported on two platens, one of which is
fixed and the other moveable. The ends to
be welded touch each other before the
current is switched on, as shown in Fig.
2.23. A heavy current is then passed from
one piece to another and the contacting
faces are heated up due to the contact
resistance.
 Gas Welding
Is a fusion welding in which the required heat is obtained from a gas flame.
 Oxy-acetylene welding commonly
referred to as gas welding, is a process
that relies on the combustion of oxygen
and acetylene. When mixed together in
correct proportions within a hand-held
torch or blowpipe, a relatively hot flame
is produced with a temperature of about
3,200 deg.C.

Acetylene is the only fuel gas suitable for gas welding because
of its favorable flame characteristics of both high temperature
and high propagation rates. Other fuel gases, such as propane,
propylene or natural gas, produce insufficient heat input for
welding but are used for cutting, torch brazing and soldering.

https://www.youtube.com/watch?v=-SA4D098u-Q
2. Oxy-hydrogen welding
An oxyhydrogen flame is used for cutting and welding of two metallic pieces together due
to the heat produced by the flame , i.e , 2800 ° C . At this temperature the metal gets
melted easily and hence it can easily be cut apart or welded together

3. Pressure Gas Welding

Pressure Gas Welding is a Gas Welding, in which the welded parts are pressed to
each other when heated by a gas flame. The process is similar to Resistance Butt
Welding. Pressure Gas Welding does not require filler material. Pressure gas welding is
used for joining pipes, rods, railroad rails
https://www.youtube.com/watch?v=6ilCeczypeo
 • Thermo Chemical Welding Process

1) Thermit welding
Thermit welding is a chemical welding process in which an exothermic
chemical reaction is used to supply the essential heat energy. That
reaction involves the burning of Thermit, which is a mixture of fine
aluminum powder and iron oxide in the ratio of about 1:3 by weight.

https://www.yourarticlelibrary.com/metallurgy/thermit-welding-process-operation-and-uses-with-diagram/
95988
2. Atomic hydrogen welding
Atomic hydrogen arc welding is used in the
applications where fast welding process is required
such as for welding the stainless steel, etc. This
welding process can be used for welding most of the
ferrous and non-ferrous metals. It is used for very
precision welding. It is also used for welding thin
sheets of metal.

Today, this process is sometimes replaced by

gas metal arc welding. As the inexpensive inert
gases are present at the larger amount, gas metal arc
welding is used instead of the Atomic Hydrogen
Welding.

https://en.wikipedia.org/wiki/Atomic_hydrogen_welding
• Radient Energy Welding Process
1. Electron beam welding
Electron beam (EB) welding is a fusion welding process whereby electrons are generated
by an electron gun and accelerated to high speeds using electrical fields. This high speed
stream of electrons is tightly focused using magnetic fields and applied to the materials to be
joined.
https://www.youtube.com/watch?v=zX9tvdTEAEo

2. Laser beam welding

Laser welding is normally a liquid-phase (fusion) welding process, i.e. it joins metals by melting
their interfaces and causing the mixing of the molten metal which solidifies on removal of the
laser heat source.
https://www.sciencedirect.com/topics/materials-science/laser-be
From: Laser Welding, 1992 am-welding
SEN & REP
Types of Welding
Joint
Tee Joint
Tee welding joints are formed when two members intersect at a 90° angle which
makes the edges come together in the center of a plate or component. Tee Joints
are considered a type of fillet weld, and can also be made when a pipe or tube is
welded onto a base plate. Extra care is required to ensure effective penetration
into the roof of the weld.

Lap Joint
Lap welding joints are used most often to joint two pieces with differing
thicknesses together. Also considered a fillet type, the weld can be made on one
or both sides. A Lap Joint is formed when 2 pieces are placed in an over lapping
pattern on top of each other.
Edge Joint
Edge welding Joints are often applied to sheet metal parts that have flanging edges or
are placed at a location where a weld must be made to attach to adjacent pieces.
Being a groove type weld, Edge Joints, the pieces are set side by side and welded on
the same edge. For heavier applications filler metal is added to melt or fuse the edge
completely and to reinforce the plate.

Corner Joint
Being one of the most popular welds in the sheet metal industry the Corner welding
joint is used on the outer edge of the piece. This weld is a type of joint that comes
together at right angles between two metal parts to form an L. These are common in
the construction of boxes, box frames and similar fabrications.
 Butt Joint
Being the universally accepted method for attaching a pipe to itself it’s also used
for valves, flanges, fittings, and other equipment. A butt welding joint is also
known as a square grove weld. It’s the easiest and probably the most common
weld there is. It consists of two flat pieces that are side by side parallel. It’s a very
affordable option.

Fillet Welded Joints

Fillet Welded Joints are just another terminology for corner, lap, and tee joints. Fillet Welded Joints are
the most common type of welding joint and accounts for nearly 75% of joints made with arc welding.
You do not need to prepare the edge and this type of joint make it easy to weld piping systems. Butt
welds are more expensive than fillet welds. Fillet welds are mostly used in piping systems to join pipe
to socket joints.
Welding Symbols

https://www.youtube.com/watch?v=gAyceJb5OWc
Parts Of Weld Explained
• Weld Toe - The interface of the weld face and base metal.
• Weld Face - The exposed weld surface on the side where the torch created the weld.
• Weld Root - The interface of the weld and base metal at the “bottom” of the weld., opposite the face.
• Weld Leg - The distance from the weld toe to the weld root.
• Fusion Zone - The zone of base metal melted during the weld (as determined with a cross-section). Sometimes
referred to as filler penetration.
• Weld Reinforcement - Height of the portion of the weld above the base metal surface.
• Fillet Weld Throat - The theoretical throat is the perpendicular distance of the weld from the hypotenuse of the
largest right triangle that can be inscribed within the fillet weld cross-section (i.e., a line that connects the toe on
each side of the root) to the root.

The actual throat is the distance from the root of a fillet weld to the center of its face.
 Welding Metallurgy

1. Basics of Welding Metallurgy

2. Carbon and Low Alloy Steels

https://www.nrc.gov/docs/ML1215/ML12157A607.pdf
Carbon and Low Alloy Steels
Slow Cooling → Ferrite + Pearlite
Fast Cooling → Martensite
Inspection and Testing of
Welds
1. Inspection after welding
2. Testing of Welds
- Destructive Testing
- Non-Destructive Testing
Inspection After Welding
1. Check weld against code and standards.
2. Dimensional
Check size with gauges and prints.
Check finish and contour.
3. Check for cracks against standards.
Look for overlap.
Check undercut.
Determine if spatter is at acceptable levels.
Visual Inspection (VT) Visual inspection is a non-destructive testing (NDT) weld quality
testing process where a weld is examined with the eye to determine surface discontinuities
Weld handheld fillet gauge measures:
• The flatness of the weld
• Convexity (how the weld is welded outward)
• Concavity (how the weld is rounded inward)
Welding Defects, Causes and
Remedies Undercut
portion remains unfilled near the toe side of the weld metal.

Causes
• Too much current over-heats the parent metal.
• Not keeping the electrode at the edges for a sufficient time during
weaving.
• 'V' being wider.
• Shifted of welding centerline

Remedies
Always use low current.
• Change the welding technique and stop for some time at the
undercut edge.
• Decrease the welding speed.
• Use the correct edge preparation.
• Cleaning the plate before welding.
Porosity
small pores of gas are formed and are spread in the weld metal.

Causes
• An overheated electrode.
• The wrong electrode for the metal to be welded has excess
moisture.

Remedies
• Use low current.
• To avoid porosity always use the correct electrode like weld bright
steels, medium carbon steels, and alloy steels with low hydrogen
electrodes.
• The electrode should be dry, for this; they are kept in a warm and
dry place.
• Rework by grinding and re-weld wherever needed
Slag Inclusion

The molten flux adsorbs the oxide from the parent metal surface and
floats on the molten weld metal.

Some of the flux (slag) goes into the molten metal due to which slag is
incorporated.

Causes
• If the weld pool is not hot enough, the slag solidifies inside the weld.
• This may be due to low current, insufficient heat input, or excessive
weaving.
• An undercut in the preceding run or too little space between the
plates.

Remedies
• Increase the current or use narrower weaving.
• Repairs by the grinding and weld again.
• Prepare the plates in such a way that there is no blockage in them
and the slag can float.
Cracks

This is a dislocation in the weld metal, due to the effect of cooling or

stress.

Causes
• The high strength of joint.
• High rate of cooling.
• Use of wrong electrodes.
• Use of improper welding technique.

Remedies
• Use joint key pre-heating and/or post heating if necessary.
• Cool the welded joint slowly.
• Use another sequence for welding.
Excessive Penetration

In welding of a butt joint, square edge preparation for 3 mm plates and

'V' preparation for thick plates are used.
This allows for penetration up to full thickness.
Excessive penetration is not acceptable.

Causes
• Running electrodes incorrectly.
• Overheating of the weld pool.
• Incorrect size and type of electrodes.

Remedies
• Use low current.
• Use the correct size and type of electrodes.
• Use the correct dimensioned root face and root gap
 Lack of Penetration

If the weld metal is not fully penetrated to the root of the

joint, it results in a lack of penetration.

Causes
• Low ampere current.
• Faster travel speed during welding.
• Low preheat.
• Inappropriate edge preparation.

Remedies
• Use high current.
• Reduce the welding speed.
• Use the correct edge preparation according to the
thickness of the plates.

https://www.mechical.com/2021/09/welding-defects.html
http://www.timewelder.com/uppic/woed/TWI_Welding_Training_3.pdf
Destructive Weld Testing - as the name suggests, involves the
physical destruction of the completed weld in order to evaluate its
characteristics.

• Macro Etch Testing. This method requires the removal of small

samples from the welded joint.

• Fillet Weld Break Test. This type of testing involves breaking a

sample fillet weld that is welded on one side only.

• Transverse Tension Test

• Guided Bend Test.

Macro etch test is a technique used to test a weld by revealing the structure of the
base material and weld. It’s a destructive testing method that is used to evaluate the
characteristics of the weld. First, the sample is cut to expose the profile of the weld.
This allows us to see how the weld is adhering to the base metal, and also shows us
other characteristics like penetration or cracks.

Profile of a MIG weld after cutting The polished surface of the weld with a 240 grit sandpaper
After polishing to the required level, different acid-based solutions can be used to etch the surface and reveal
even more detail. A combination of ethanol and nitric acid is usually used. Other industrial-grade rust removers
can also be used for this purpose (for example, Rust Off from Bunnings Warehouse or other phosphoric acid
solutions). Make sure you use proper personal protection equipment (P.P.E – such as gloves and eye
protection) and follow the local regulations for disposal of these solutions as they are usually classified as
harmful and corrosive.

The etchant acid reacting with the metal The profile after etching revealing the weld boundary

After etching the sample in the acid-based solution for a few minutes, the boundaries of the base metal and
weld become visible. The visual inspection at this point can reveal additional information about the weld
Fillet Weld Break Test

The fillet weld break test is a mechanical testing process for examining the root
penetration in a destructive manner. While the macro-etch test provides
penetration depth of the specimen in a given area, the fillet weld break test
examines the root penetration for the entirety of the specimen.

https://www.youtube.com/watch?v=Kr4Lf-ASojc

https://www.youtube.com/watch?v=9CSbyR3sgiU
Transverse tensile testing — In this process, a tensile bar is extracted from the
transverse axis of the plate (perpendicular to the axis of the weld). As a result,
both the weld metal and base metal are tested, capturing the interaction between
the two
Guided Bend Test
The guided bend test is a relatively quick and, usually, a comparatively economical
method of establishing the soundness of a groove weld. This test is designed to help
determine whether the weldment tested contains discontinuities such as cracks, lack
of fusion, inadequate penetration or severe porosity.

https://www.youtube.com/watch?v=7tr4kVtNsrM
Non-destructive testing (NDT) is a testing and analysis technique
used by industry to evaluate the properties of a material, component,
structure or system for characteristic differences or welding defects
and discontinuities without causing damage to the original part

The most common types of nondestructive testing for welds,

excluding simple sensory examinations, are liquid penetrant,
radiography, magnetic particle, eddy current, and ultrasonic testing
Liquid penetrant
Liquid Penetrant Testing (PT) is used to detect casting, forging and welding surface defects such as
hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.

There are six basic steps to follow when using the dye penetrant solvent removable
method.
1. Pre-clean part. This can range from grinding and wire brushing to merely wiping the
part with a rag moistened with the cleaner/ remover. ...
2. Apply penetrant
3. Remove penetrant
4. Apply developer
5. Evaluate indications
6. Post-clean part

https://www.youtube.com/watch?v=QpU5JyhNVgQ
Radiographic Testing (RT) is a non-destructive testing (NDT) method which uses
either x-rays or gamma rays to examine the internal structure of manufactured
components identifying any flaws or defects. In Radiography Testing the test-part is
placed between the radiation source and film (or detector).

https://www.youtube.com/watch?v=zrrHbK3kKF8
Ultrasonic testing (UT) comprises a range of non-destructive testing (NDT)
techniques that send ultrasonic waves through an object or material. These high
frequency sound waves are transmitted into materials to characterize the material
or for flaw detecting.
In ultrasonic testing, an inspector will use a probe or some
other kind of transducer to send sound waves through the
material they want to test. If there are no defects in the
material, the sound waves will pass through it, but if the sound
waves hit a defect they will bounce off of it, indicating its
presence

The major difference between RT & UT is that Radiographic method is better for detection of
discontinuities having major dimension perpendicular to the surface (parallel to the direction of
radiation) and Ultrasonic method is better for detection of discontinuities orientated parallel to the
surface.
Magnetic particle inspection (MPI) testing of welds is a very effective form of
surface-examination that aids in detecting surface and shallow subsurface
discontinuities, or flaws, in ferromagnetic materials such as iron or steel.
https://www.youtube.com/watch?v=q61owS66CkU

The method can detect surface or near-surface flaws such as cracks, laps, seams
and inclusions in ferromagnetic materials such as iron and steel. One of the main
advantages of magnetic particle inspection is that it can give an immediate
indication of defects and discontinuities.
Eddy current testing (also known as eddy current inspection) is a method used in
non-destructive testing, employing electromagnetism to detect surface breaking
and slightly sub-surface flaws in materials.

https://www.youtube.com/watch?v=p2qaxa1AKys
Reference:

https://www.ccohs.ca/oshanswers/safety_haz/welding/ppe.html

https://www.cruxweld.com/blog/the-difference-between-soldering-and-brazing/

https://www.cruxweld.com/blog/types-of-weld-tests/
Thank you