Internal Training

Projects Department, MOL Office FFL.

Trainer: Muhammad Zubair Basra

Designation: Graduate Trainee Engineer (GTE)
 PRESENTATION LAYOUT
WELDING PROCESSES CLASSIFICATION
ARC WELDING PROCESSES
• ARC WELDING PROCESSES CLASSIFICATION AND BASICS
• SHIELDED META ARC WELDING (SMAW)
• PROCESS DESCRIPTION
• ELECTRODES
• WELDING CURRENTS
• CAPABILITIES AND LIMITATIONS
• OTHER CONSUMABLE ELECTRODE WELDING
• GAST TUNGSTEN ARC WELDING (GTAW)
• PROCESS DESCRIPTIONS
• ELECTRODES
• SHIELDING GASSES
• WELDING CURRENTS
• CAPABILITIES AND LIMITATIONS
• OTHER NON CONSUMABLE ELECTRODE WELDING
SOLID STATE WELDING PROCESS
WELD DEFECTS
PRE AND POST WELD HEAT TREATMENT
 WELDING PROCESSES
Welding is a joining process in which
two metals are brought to intimate
proximity and heating the place of
WELDING
contact to state of fusion or plasticity. PROCESSES
This leads to inter-penetration of
atoms of metal in the weld zone.
Pressure is also applied in some
welding processes along with heat. FUSION
SOLID STATE
WELDING
WELDING
PROCESSES

RESISTANCE OXYFUEL GAS DIFFUSION ULTRASONIC

ARC WELDING
WELDING WELDING WELDING WELDING
ARC WELDING PROCESSES BASICS
Welding process in which coalescence is produced by the heat of an electrical arc
produced between electrode and work piece

To initiate the arc,

electrode is brought close Current flows through the Temperature approaching
to the work piece and then thermally ionized column 5500 C which is sufficiently
immediately separated of gas ( called plasma) hot to melt any metal.
from it by a short distance

A pool of molten metal is

As the arc moves along the produced near the tip of
joint, the molten weld pool electrode containing base
solidifies in its wake metal and filler metal (if
one is used)
 WELD JOINTS

Butt joint Corner Joint Lap Joint Tee Joint Edge Joint
 TYPES OF WELDS
Fillet Weld
Used to fill the edges of the plate created
by corner, lap and tree joints
Minimum edge penetration
Can be single or double and continuous or
intermittent

Groove Weld
Edge of the part are shaped into the groove Square Bevel V
to facilitate weld penetration
Include square, bevel, V, U and J on one or
both sides
More weld penetration and strength
U J V- on both
sides
 TECHNOLOGY OF ARC WELDING
PROCESSES
Consumable Electrodes
• Act as a filler material
• Available as either rod or wire
ARC SHIELDING
• Welding rods are required to be
changed periodically where as wires WHY?
are constantly fed into the weld pool, • High temperature in welding process INERT GAS
thus avoiding frequent interruptions causes metal to be reactive with • Helium and argon
nitrogen, oxygen and hydrogen in air. FLUX
Non-consumable Electrodes
• Mechanical properties can be • Prevent formation of
• Usually made up of tungsten that
seriously degraded. oxides and unwanted
resists melting with arc
• Filler metal is provided in separately HOW? contaminants
in wire form • Accomplished by covering the • It melts and becomes
electrode tip, arc and molten weld slag, covering and
pool with a blanket of inert gas or protecting the molten
flux or both which inhibits metal weld metal.
exposure to air • Hardened on cooling
and removed by
chipping or brushing
 ARC Welding Processes
ARC WELDING Non- Consumable
PROCESSES Electrode

Gas Tungsten Arc Plasma Arc

Welding Welding
GTAW PAW
Consumable
Electrode

Shielded Metal Gas Metal Arc Flux Cored Arc Submerged Arc
Arc Welding Welding Welding Welding
SMAW GMAW FCAW SAW
 INTRODUCTION
• Coalescence of the metal is obtained by the heat from an electrical
arc that is maintained between the electrode tip and work-piece.
• This process uses a consumable electrode consisting of filler metal
rod coated with chemicals that provide flux and shielding.
• Heat of the arc melts the electrode coating providing a protective
environment and slag for the welding process.
• The filler metal in electrode provides the arc stability by conducting
the current to the arc.
 Process
Arc Shielding and Electrode consists of either a
volume of slag produced solid metal rod or one produced
varies from type to type. by encasing the metal powder in
In some electrodes, a metallic sheath.
largely gas shielding in
used where as in other
largely slag covers the The coating consists of
molten pool and filler powdered cellulose (i.e., cotton
metal. and wood powders) mixed with
oxides, carbonates, and other
ingredients, held together by a
Globules of molten filler
silicate binder.
metal covered with slag
are carried by arc to
weld pool. Since slag is
lighter, it floats over the
pool covering it.
 Principle of Operation
Welding is initiated by the electrical arc produced
between the electrode and work-piece

Intense heat melts the tip of electrode and work-piece

surface close to arc.

Tiny globules of the molten filler metal formed at the tip

of electrode are carried by the arc stream to molten
weld pool

The circuit consists of following

Filler metal is deposited as electrode is consumed. Arc is
• Power source
moved over the work-piece at certain speed
• Welding cables
• Electrode holder
• Electrode
Molten pool solidifies in the wake of the electrode
travel. • Work-piece connection
• Work-piece
 ELECTRODE FLUX
Coating of electrode(flux) contains following elements and additives
• Slag producing elements: Protect the molten weld pool against reaction with air (Oxygen and
Nitrogen) by forming molten slag and gasses (usually CO2) developed from coating
• Arc Stabilizing elements : Improve the arc stability specially during the AC power source by
providing the ionizing gasses that remain ionize during cycle reversal. Arc stabilizing substances
include titanium, zirconium and magnesium.
• Weld Penetration enhancing additives: Provide sufficient penetration into the base
material. Penetration is determined by the amount of hot gasses (carbonates and cellulose
compounds) released.
• Deoxidizers: Helps remove the excess oxygen from weld metal created by the rust or scale on
the metal.
• Alloying elements : Alloying elements like Ferro-Alloys of manganese, molybdenum etc. may
be added to impart special properties to the weld.
• Elements for High Deposition: Improve the deposition rate (Usually some carbon and low
alloy steel electrodes contains iron powder).
• Binders : Hold the additives together so that flux will not chip off the electrode.
Electrodes Types- Slag composition
Acid • Include iron and manganese oxides
• Smooth and shiny weld beads, slag solidifies slowly and easy to remove
Electrodes • Weld metal however has low tensile strength

• Contains large quantities of mineral oxides like TiO2.

Rutile • Provides greater arc stability
Electrodes • Produce higher hydrogen content in weld metal which can cause hydrogen
embrittlement and cracking

• Contains calcium fluoride in the coating

Basic • Slag reacts as base, thus leaving low sulphur and oxygen contents in weld metal
Electrodes •
•
Good strength of weld, Hydrogen content is low, low risk or slag inclusion
Hygroscopic, requires dry condition for storage.

•
Cellulose •
Contain organic matter usually cellulose which comprises of 30 % by wt. of total flux
Zirconium silicate is added for arc stabilizer
Electrodes • Hydrogen present in the covering allow the deep weld penetration.
COVERED ELECTRODES CLASSIFICATION SYSTEM

E-6011 = (60 ksi) + All positions + AC or DC and High cellulose

Potassium
COVERED ELECTRODES CLASSIFICATION SYSTEM
 WELDING CURRENT
• Selection of the proper power parameters depends on the metals being welded, electrode
type and length, and depth of weld penetration required.
• Currents typically used in SMAW range between 30 and 300 A at voltages from 15 to 45 V.

Current Sources DCSP: Work-piece is positive and welding

electrode is negative. Also called as DC
electrode negative (DN – or DCEN)

DCRP: Work piece is negative and welding

Alternating electrode is positive. Also called as DC
Direct Current
Current electrode positive (DC + or DCEP)
DC AC

Direct Current Direct Current

Straight Polarity Reverse Polarity
DCSP DCRP
 EFFECT ON WELD POOL SHAPE
DCSP
Deep weld with 70 % of the weld heat in the work-piece

DCRP
Shallow weld with 70 % of the weld heat of the arc in
electrode
Strong cleaning action due to bombarding of heavy ions

AC
Fairly balanced distribution of heat from arc into the
electrode and work-piece.
Intermediate profile with some surface cleaning

Primary purpose of any power source is to

provide electrical power of proper current and
voltage to maintain a controllable and stable arc
 CAPABILITIES AND LIMITATIONS
• Simple, inexpensive and portable equipment
• Auxiliary gas shielding or granular flux is not required.
• Less sensitive to winds and draft
• Very suitable for thickness from 1/8 to 1.5 inches.
• Can be used in all positions (flat, horizontal, vertical, overhead) and in areas of limited
accessibility
• SMAW electrodes are available to weld carbon and low alloy steels, stainless steels, cast
irons, copper, and nickel and their alloys, and for some aluminum applications.
• Low melting metals, such as lead, tin, and zinc, and their alloys, are not welded with
SMAW because the intense heat of the arc is too high for them.
• SMAW is not suitable for reactive metals such as titanium, zirconium, tantalum, and
columbium because the shielding provided is inadequate to prevent oxygen
contamination of the weld.
• Mostly used in construction, maintenance and repair work, pipelines
GAS METAL ARC WELDING (GMAW)
• Also called as MIG welding
• Electrode is bare metal wire
• Wire is fed continuously and automatically by
welding gun
• Shielding is done with the shielding gas
• Shielding gasses argon and helium used to weld
aluminum and CO2 to weld steels
• Elimination of slag removal, higher deposition rate
and good versatility and automation capacity.
• Mostly used Automotive industry

FLUX CORED ARC WELDING (FCAW)

• Electrode is a continuous consumable tubing that
contains flux and other ingredients in its core.
• Flux cored ‘‘wire’’ is flexible and can therefore be
supplied in the form of coils continuously
• Self shielded or Gas shielded
• High quality weld and high welding speed than SMAW
for steels and stainless steels
• Shop fabrication and maintenance, areas where base
metal to be welded has some rust, scale and other
contaminations
SUBMERGED ARC WELDING (SAW)
• Uses a continuous, consumable bare wire
electrode (fed automatically), and arc shielding
is provided by a cover of granular flux.
• Flux is introduced into the joint slightly ahead of
the weld arc by gravity from a hopper.
• Flux completely submerges the welding
operation, preventing sparks, spatter, and
radiation.
• Widely used in steel fabrication for structural
shapes (e.g. welded I-beams); longitudinal and
circumferential seams for large diameter pipes,
tanks, and pressure vessels
• Steel plates of 25-mm (1.0-in) thickness and
heavier are routinely welded
 GAS TUGSTEN ARC WELDING (GTAW)
Also called as Tungsten Filler metal may or may not
Inert Gas (TIG) welding, be used. When used, added
Tungsten arc welding or to the weld pool from
HeliArc Welding separate rod or wire, melted
by heat of the arc

Electrode, weld pool, arc and

Heat is produced by the
adjacent heated areas of the
arc between the non-
workpiece are protected
consumable tungsten
from atmospheric
electrode and the work
contamination by the
metal.
gaseous shield.

Used extensively for welding stainless steels, aluminum, magnesium,

copper and reactive materials like titanium and tantalum.
Can also be used for carbon and alloy steels
 ELECTRODE

Pure Tungsten Thoriated Tungsten (2%

• More sensitive to contamination ThO2) Tungsten + (2%) Rare Earth
• Low service life-cycle • Excellent resistance to
• Higher tip deterioration
elements
contamination • Rare earth elements are
• Used in welding aluminum and • Stable arc and easy arc starting lanthanum, yttrium and cerium
magnesium alloys on AC • Safety concerns as ThO2 is • Better operational characteristics
• Can also be used with DC radioactive than thoriated tungsten
electrode
• Used in welding Carbon and
Zirconiated Tungsten stainless steels, nickel and
• Excellent for AC due to good arc starting, high resistance to contamination titanium alloys
small tip shape deterioration
 SHIELDING GASSES
• Prevent atmospheric contamination that • Arc Stability by providing suitable
can cause weld defects ionization potential

Argon Helium or Helium/Argon

Argon with upto 5 % H2
• Low ionization potential (30-80% He) mixtures • Hydrogen increases arc voltage
• Heavier than air, thus provide good • Higher ionization potential and consequently heat input
shield • High voltage for arc initiation • Increase weld penetration and
• Less expensive than helium • Thick aluminum and high- weld travel speed
• Carbon, stainless steels and low conductive materials such as • Welding austenitic steels, copper-
thickness aluminum alloy copper alloys. nickel alloys
components • Increased welding speed

Flow rate of shielding gasses depend upon weld thickness, 4-10 l/min for argon and 10-15 l/min for He.
 WELDING TORCH

• Welding torches hold non-consumable electrodes, assuring transfer of current to

electrode and flow of shielding gasses to weld pool
• Gas cooled (upto 200 A) or Water cooled (200-500 A)
 WELDING CURRENT
a) DCEN (Mostly Used)
Deep weld with 70 % of the weld heat
in the work-piece
Good weld speed and penetration
b) DCEP
Shallow weld with 70 % of the weld
heat of the arc in electrode
Rapid heating and degradation of the
electrodes, therefore heavy electrode
is used.
DC pulsed current( 10 Hz to 30 kHz)
produce more penetration while
minimizing the total heat applied to
the part. It also allows the weld pool to
cool between the pulses and decrease
porosity. This allows the welding of
heat sensitive metals with minimum
distortion.
 WELDING CURRENT
c) AC
Square wave AC used instead of sine wave as it facilitate arc restrike each half cycle
and allow adjusting of arc cleaning effect or penetration depth.
 PROCESS VARIANTS
• GTAW is high quality welding process, but low welding speed, deposition rate and
require highly skilled labour.
• Variants are employed to improve the deposition rate, penetration depth and welding
speed.
• HOT WIRE GTAW : Resistance heated filler wire is fed to melted weld pool at constant
rate. Deposition rate upto 14 kg/hr can be obtained
• Dual Shielding GTAW technique: Additional gas shield (Electrode gas) gives constriction
to arc to increase welding speed and penetration depth. Electrode gas and shielding gas
may be same or different
 CAPABILITIES AND LIMITATIONS
• High quality, low distortion welds
• Free of spattering associated with other methods
• Can be used with or without filler material CAN WE WELD THE THICK
• Weld almost all materials METALS WITH GTAW ?
• Precise control of welding heat
• Aerospace and Nuclear Industry
• High speed autogenous welding of tubes and sheets. Thin gauge metals and close to heat
sensitive areas. Can also be used for spot welding in sheet metal application.

• Has low deposition rate as compared to consumable electrode processes

• Require more skill
• Less economical for thickness greater that 3/8 inches
• Problematic in drafty situations because of difficulty in shielding the weld zone properly
• Contamination or porosity caused by coolant leakage from water cooled torches.
• Arc blow or arc deflection can be the problem
PLASMA ARC WELDING
• Special form of gas tungsten arc welding in
which a constricted plasma arc is directed at the
weld area.
• A tungsten electrode is contained in a specially
designed nozzle that focuses a high-velocity
stream of inert gas (e.g., argon or argon–
hydrogen mixtures) into the region of the arc to
form a high velocity, intensely hot plasma arc
stream.
• Temperatures reach 17,000 C or greater.
• Excellent weld quality, better penetration, high
travel speed
• Welds all the metals, including tungsten
• Bronze, lead and magnesium are difficult to
weld with this technology
Oxyfuel Gas Welding Resistance Welding Process
• Burn various fuels mixed with oxygen to perform • Uses a combination of heat and pressure to
welding. accomplish coalescence, the heat being generated by
• Oxyacetylene welding is most commonly used electrical resistance to current flow at the junction to
• The flame is directed by a welding torch. A filler metal be welded.
is sometimes added, and pressure is occasionally • No shielding gases, flux, or filler metal; and the
applied electrodes that conduct electrical power to the
• The filler is often coated with a flux that helps to clean process are non consumable.
the surfaces and prevent oxidation, thus creating a • Spot welding and Seam Welding
better weld joint • Used in shield metal working and Seam Welded Pipes
• Safety concerns with storage of gasses and their
inflammability
 SOLID STATE WELDING PROCESS

• Coalescence of the part surfaces is achieved

by pressure alone, or heat and pressure

• Fusion of the parts would not occur using only

the heat that is externally applied in these
processes.
Roll Welding
• The combination of heat and pressure, or the
particular manner in which pressure alone is
applied, generates sufficient energy to cause
localized melting of the faying surfaces

Friction Welding
 WELD DEFECTS
Porosity
• Small voids in weld metal formed by the gasses entrapped during solidification
• Spherical (Blow holes) to elongated (worm holes)
• Inclusion of atmospheric gases, sulphur in weld metal or surface contaminants
Inclusions
• Non metallic solid material entrapped in the weld metal or between weld metal and base metal
Incomplete fusion
• Failure to fuse the weld metal to base metal
• Due to improper welding technique and failure to melt the base metal
Inadequate Joint penetration
• Weld fails to penetrate the area of weld joint , unpenetrated area is a discontinuity
• Due to poor welding arc control, improper joint design (too much material for welding arc to penetrate)
Cracks
• Localized stresses exceeds the ultimate tensile strength of the metal
• Stress amplification near discontinuities in welds and base metal.
Undercut
• Melting away of the groove face of a joint at the edge of a layer or bead of weld metal.
Underfill
• Failure of the welder to fill the joint with weld metal
 POROSITY

SOLID INCLUSIONS

INCOMPLETE FUSION
 PRE-WELD HEAT TREATMENT
• Reduce the thermal strains
• Thermal strains may be developed during welding which can cause cracking
• Magnitude is reduced by heating before welding

• Reduce higher cooling rates

• High thermal conductivity in thick metal sheets
• Loss of heat from weld area rapidly
• Copper and aluminum alloys are severely required to be pre-heated

• Prevention of excessive hardening

• Undesirable structures that may cause cracking

• Hydrogen diffusion
• Increase hydrogen diffusion from weld area
• Removes the moisture in weld area as moisture breaks down to oxygen and hydrogen by
electrical arc
 PRE-WELD HEAT TREATMENT
C- Equivalent
• A criterion of determining pre-heat temperature
• For high carbon steels, there is generally greater necessity for preheating
• Along with carbon, other elements in steel are also responsible for
hardening and loss of ductility
• Total hardenability is thus calculated in terms of Carbon Equivalent which
measures the effect of carbon and other alloying elements on hardening
%𝑀𝑛 %𝑁𝑖 % 𝐶𝑟+ %𝑀𝑜 +% 𝑉
• For example C.E. = %𝐶 [ + + ]
20 15 10
• After calculating C.E. , pre weld heat treatment temperature is estimated.
 WELD ZONES
• Fusion zone
• Filler metal + Base metal that has completely
melted and then cooled
• Weld defects
• Weld Interface
• Thin band of base metal that was melted and then
solidified before mixing with metal in fusion zone
• Heat Affected Zone (HAZ)
• Temperature below melting point
• Microstructural changes
• Mechanical properties are affected
• Susceptible to cracking, usually undetected
• Stress development
• Unaffected base metal High level residual stresses can occur in weldment due to
• No metallurgical change occurs
restraint by parent metal during solidification.
 POST WELD HEAT TREATMENT
• Main purpose is to increase resistance to brittle fracture and relaxing residual stresses.
• Slow and uniform heating to suitable temperature (1100 – 1200 F), holding long enough to reduce
residual stresses and then slow cooling to minimize development of new stresses.
• Heating and cooling are usually kept under 400 F/hr per inch of thickest cross section.
• Soaking time is usually one hour per inch thickness.
• For low-alloy Cr-Mo steels ( Cr ½ to 2 ¼ % & Mo upto 1 %) , stress relief range is 1250 – 1300 F.
• High alloy steels may require more temperature and more soaking time.
• It provides following benefits
• More ductility in weld metal and a lowering of hardness
• Improved resistance to corrosion and caustic embrittlement
• Improved machining stability
• Relaxes residual stresses
 POST WELD HEAT TREATMENT
• Post weld heat treatment is performed in furnace or locally on site using the heater blanket.
• Rule of thumb is to heat component for one hour per inch thickness.