Welding distortion and its control

1 2 3 4 5 6
1
1
Welding Distortion and ITS Control
By JGC Annamalai

A1 A 2
A2 A 3
A3 A 4
A4 A 5
A5 A 10
A6 A 12
A7 A 13
A8 A 14
A9 A 16
A10 A 19
A11 A 22
A12 A 23
B1 B 24
B2 B 25
B3 B 26
B4 B 27
B5 B 29
B6 B 30
B7 B 31
B8 B 32
B9 B 33
B10 B 35
C1 Case Studies, Distortion, all C 37
C2 Case Studies, Distortion at Pressure Vessel Nozzle & its Controls C 38
C3 Case Studies, Distortion at Pressure Vessel Saddle & its Controls C 39
C4 Case Studies, Distortion at Pressure Vessel Level Gage Nozzle & its Controls C 40
C5 C 41
C6 C 42
C7 C 43
C8 C 44
C9 C 45
C10 C 46
C11 C 47
C12 C 48
D1 D 49
D2 D 50
D3 D 52
Authored by R.Annamalai, (former Chief Equipment Engineer, JGC Corporation), rannamalai.jgc@gmail.com
Page
Case Studies, Distortion at Pressure Vessel L-Seams
Physical & Thermal Properties of Materials -Tables
Physical & Mechanical Properties of Materials-changes with Temperatures
Direction of Welding Distortion / Finding Center of Bending Curvature
Case Studies, Shell & Tube Heat Exchanger, Tube to Tube Sheet Welding, Distortion
Case Studies, Distortion / mis-alignment at Connecting Flanges to Machineries
Case Studies, Distortion / Bowing of Machinery Base Plates
Case Studies, Distortion / tilting of Lugs for the Platforms / ladders / stairs / structures
Case Studies, Distortion / Dome on Boiler wall panels at fillet weld side
Case Studies, Distortion at Boiler Headers, Banana
Case Studies, Distortion at Pressure Vessel C-Seams
Distortion Control by positioning welding about Neutral Axis
Distortion Control by Withdrawal of Heat
Distortion Control by Clamp Down & Restraints
Welding Distortion & Its Control
(A). Basic Information on Welding Distortion
(B). Various Methods to Control Distortion
(C). Welding Distortion - Case Studies
Distortion Control by Thermal Tensioning
Distortion Control by Stress Relieving-PWHT
Causes for Welding Distortion
Distortion Control by Pre-Setting
Distortion Control by Preventive Measures, Sequences
Distortion Control by Welding Improvement
Distortion Control by Design Improvement
Control of Welding Distortion-an Introduction
Advises at Welding Procedures and Distortion Control Methods, are clashing
Distortion in Stainless Steel Welding
Residual Stresses due to Welding
Quantitative Welding Distortion
(D). Annexure List
Chapter-A1 Topics / Chapters
Factors Influencing Weld Distortion
Distortion, how it happens (Theory of Weld Distortion)
Examples - Welding Distortion in Industry
Introduction to Welding Distortion
Chapters / Topic List
Recent Development in Distortion Control
Remedies
Types of Welding Distortion
By JGC Annamalai
2
(Total Pages-53)

Chapter-A2
Some of the ways to control the Welding Distortion
(1). Avoid welding. Use ready made shapes as much as possible.
(2).
(3). Design size is the desired. Over welding, will lead to Distortion
(4). Distribute the heat. Use intermittent / staggered welding
(5). Minimize the number of weld passes
(6). Plan and Weld, on/about the neutral axis
(7). Use balance welding, like back-step/skip weld/scatter weld technique
(8). Pre-set parts to counter distortion
(9). Clamp/restrain the object from moving during welding
(10). Use Restoration Methods(Thermal Tensioning, PWHT),
to correct distortion
(1). Distortion of Machines or object will have mismatching or may affect the original intended service.
(2). Rectification of the mismatch will result in repair/ rework and will have time and cost impact or more distortion
(3). Distortion and repair work, may affect the functional requirements and load carrying capacity
(4). It may be difficult to maintain the original shape or metallurgy and may affect aesthetics appearance
(5).
(Note : Unless otherwise mentioned, this Document is written mainly for Distortion in Carbon Steel and Low Alloy Steel
objects, as majority of the works are from CS and LAS. There is a separate chapter for Distortion on Stainless Steel Weld
Distortion. The Distortion behavior of SS, is similar CS and LAS)
Consequences of Welding Distortion are :
Remedies
(1). Weld Distortion
(2). Weld Shrinkage
(3). Contraction due to Welding
(4). Weld warpage
(5). Bowing due to Welding
(6). Sagging due to Welding
Larger the weld bead size in butt & fillet joints, smaller the Distortion
Welding causes either Distortion and / or Residual Stresses. If the system is clamped or restrained, the
distortion effect will change to Residual Stresses. The stresses may be tensile or compressive or both. If the
equipment is in service, the system operating stresses will add up or cancel with residual stresses. If the
cumulative stresses reaches yield stress, the system will result in permanent deformation in shape or
equipment will fail. Residual stress effect should be considered for equipments in service , like Stress
Corrosion Cracking, Fatigue, Cryogenic Temperatures, Brittle failure areas etc, They are expected to have
premature failure if excess residual stresses are present.
Welding Defects like porosity, crack, slag, undercut etc can be fully controlled or
eliminated. But the effects of Welding Distortion (like residual stresses, grain
size changes, shape changes, dimensional changes, etc), cannot be fully
controlled or eliminated. Distortion or residual stresses can only be partially
controlled/ rectified. We discuss some ways to control the Distortion and
Residual Stresses and Restoration Methods.
Every time, we add localized heat/unbalanced heat (by welding, torch heat, spatter etc.) to the base metal, Expansion and
Shrinkage happens to the base metal. If the object is restrained or clamped, Distortion will change to Residual Stresses.
Introduction to Welding Distortion
Welding is a process of joining metal and alloys in industry, mostly by melting and joining base metals. Welding is used to
make assembly of equipments, pipes, structures etc.
Distortion is a perennial problem faced by Fabrication Engineers because of welding. The shape change or deformations
and change in the dimensions that occur after welding is termed as distortion, leading to various undesirable consequences.
Different names of
Welding Distortion :
On Carbon Steel and low alloy steels : If the object, as a whole, is heated,
uniformly and gradually(as in furnace, for heat treatments and stress relieving or
in local stress reliving for pipes etc), between room temperature and 600°C
(below the first phase transformation line at 723°C in the Constitution
diagrams), the object expands uniformly and contracts uniformly, thus, the
residual stresses are either removed or lowered. Pressure Vessel Codes
requires such stress relieving, after weld completion, but before taking hydro
testing pressure stresses or system stresses in service .
By JGC Annamalai
Pg.A2.1
3

RemediesChapter-A3 Welding & Heat Distortion & Controls - Examples
Ca
Hig
By JGC Annamalai
Distorted Objects
Pg.A3.1
4

RemediesChapter-A3 Welding & Heat Distortion & Controls - Examples
Ca
Hig
By JGC Annamalai
4
Pg.A3.2
The above set up (similar to a lathe machine) is to weld, Nuclear Fuel Control Rods, made up of SS-304 (5" &6" dia,
10 tk, 2 butt welds, each pipe 20' long). After completion of root pass and 2 stabilizing passes with Argon shielding
& purging (low heat, GTAW), to control distortion and sensitization, further fill welding was done using GTAW, with
water circulation inside the pipes, to cool the weld and HAZ during welding .
The straight line alignment requirement of the pipe assembly after welding, was 0.75mm for 6m (20ft) length.
Distortion
Controls
Refinery
Reformer
Headers
Pg.3.1
5
Nuclear
Power
Plant
Reactor
Fuel Control
Rods
Precision
Welding

Now, we see how the Weld Distortion happens and the theory behind it.
Remedies
On most of the welded assembly cases, Weld Distortion is observed (it changes the shape, changes the dimensions,
causes difficulty during assembly of parts and makes the machineries difficult to work smoothly. As welded assemblies
contain, residual stresses, it is not suitable for services like Stress Corrosion Cracking, Fatigue, Cryogenics and areas
where brittle fracture is expected). Differential/Gradient Temperatures on an object or on an area ,cause stresses
and strains.
If the structure is strong or complex or the thickness of the material is heavy or the structure is restrained or clamped to
avoid distortion, there will be no distortion or controlled distortion. Instead, all the expanding forces , contracting forces,
due to heat, will stay as Residual Stresses.
Chapter-A4 Weld Distortion, How it Happens ? Or Theory of Distortion
Case-1, a thin Disc(Base Metal), about 5mm tk, and 50 mm dia. Heat in the form of Weld or Spatter or Heating Torch is
applied at the Center. The Disc analysis shown, below, is the temperatures, just after weld solidification
(Max.temp.reached).
1. A drop of weld metal is added on the base metal(this may also be a spatter or a local gas heating)
3. The specimen is strained by the same plate, at the outer periphery, as there is no increase in Temperature
2. The heat spreads radially and through the thickness. The sketch at the right gives the gradient temperature, in a
(T,T1,T2,T3,T4). T4 is room Temperature.
4. Due to heat losses by radiation, convection, conduction etc, the temperature drops, approximately in the
exponential form. Often, with thickness, 10mm & over, beyond 300mm from weld fusion line, the temperature
By JGC Annamalai
Shrinkage of the "weld" itself comprises only approx. 10% of the actual shrinkage. Most of the shrinkage takes place in base metal
To find out Center of Bending Curvature: (If many welds, take group center of gravity of all welds )
Neutral Axis of structure >> Weld Center >> Center of Bend.(They are in line).
Thumb Rule:
Pg.A4.1
(3). Moderate temperatutre .
Weak in strength. Elastic
range. Stays as residual
stress
Expanding
Forces
T
T4
T1
T2
T3
C
Pool
Temperature
Ring-
Ring-
Ring-
Ring-
Ring-
(5). Room Temperature. Strong &
rigid. No change in shape
(2). High temperature.
Yielding. Change in shape.
(1). Liquid to Solid phase
change. No change in
(4). Strong, yielding. plastic range &
permanent set.
Expanding
Forces
Happenings:
6
7

RemediesChapter-A4 Weld Distortion, How it Happens ? Or Theory of Distortion
By JGC Annamalai
stress
Expanding
Forces
T
T4
T1
T2
T3
C
Pool
Temperature
Ring-
Ring-
Ring-
Ring-
Ring-
permanent set.
Expanding
Forces
6
5. Increase in length due to temperature rise or decrease in length due to temperature fall ,
L, is the length of the piece, heated/cooled, mm
α, Linear Thermal Expansion Coefficient, mm/mm/°C
(for CS=11.7x10-6mm/mm/°C; for SS=17.3x10-6mm/mm/°C)
6. Axial thrust due to change in Temperature: Fail case - Critical Buckling Thrust
Based on Distortion/compression: Based on Critical Buckling Load: (Euler Formula) :
Force, F, developed due to the change in length , ∆L F
E =Stress / Strain
=(F/A)/(∆L/L)=FL/(A.∆L)
F =EA(∆L/L)=EA(LαT)/(L)=EATα
F =EATα
Stress =F/A=ETα I=bh3
/12
F=2.5E.(b*h*(h2
)/12)/(L2
)=2.5EAh2
/(12L2
)
(h=thickness, for a rectangular section)
F/A=Buckling Stress=(2.5Eh2
)/(12L2
)
(1). Temperature, (5). Yield Stress,
(2). Co-efficient of Thermal Expansion, (6). Young's Modulus,
(3). Thermal Conductivity
(4). Specific Heat
Expanding Forces are radial, from weld pool center point
∆L = LαT, mm
7. Expanding: Ring-1, The weld side of the Disc is hotter than the rear side of weld. The yield stress and Young's
Modulus are temperature dependant. Close to weld fusion line (say about 10 mm length) the area is facing very
high temperatures(temperature, close to weld puddle temperature) and more likely candidate for failure.
The temperature is continuously falling(exponentially), beyond weld puddle / weld pool. The co-efficient of thermal
expansion is temperature dependent. Higher the temperature, higher the co-efficient of thermal expansion.
(Similarly, the co-efficient of thermal expansion, at Absolute Zero Temperature, is considered as Zero). So, we
need to make small, small segment and use average co-efficient of thermal expansions, to calculate the forces
due to thermal expansion.
(7). Freedom or Flexibility to distort (imposed Restrains /
Clamps etc will retard or prevent distortion)
Distortion is dependant, on the following (Base Metal) :
(1).Due to temperature rise, increment in length(∆L = LαT) and expansion forces(F=EATα) pushes, radially.
As Outer ring is rigid and cannot expand, the expanding forces pushes metal towards the center(yielding).
Immediate to the weld, the temperature is high and the yield stress and Young's Modulus are very low and
ready to fail.
(2). Due to space constrains, the hot metal grows/distorts in the lateral direction/Buckles, near weld puddle.
(3). Due to plastic strains, Residual stresses are set at the rigid areas(Ring-1 & Ring-2).
=the Force required to buckle, due to the
axial force F, on a column, one end fixed and
another end free, is also called 'the Critical
Buckling Load or Buckling Thrust
The Critical Thrust = EI(π/2L)2
= 2.5EI/(L2
)
is hand bearable, in single bead weld. Multiple passes and thick beads, may cause the base metal, more hot.
T, in °C, the formula is for constant temperature, on L. (if the temperature is not uniform through the Length, L, take
average temperature(from room temperature to operating temperature) and use equivalent co-efficient of thermal
expansion. If the temperature difference is high , split the temperature into many segments for calculation).
∆L = LαT, mm
Temperature Distribution
at the Top & Bottom Surface
(just at end of liquid to solid )
Weld, initially liquid metal. After Heat
Dissipation solidified into solid metal
Base Metal
l
j
Normally, the surface temperature
is dropping exponentially
Weld , Spatter or
Torch Heat
Normally, at room temperature, for the
common thickness and length, buckling
does not happen. At welding temperature,
say around 1500°C, yield stress and Young's
Modules are very small and buckling
Euler assumes slenderness ratio, L/r > 120 for
calculating Column Failures by Buckling. (L , column
length ; r, radius of gyration, smallest of Ix/A or Iy/A)
Pg.A4.2
Steel : SS : Al : Cu = 1.0 : 1.5 : 1.9 : 1.4
Relative Co-Efficient of Thermal Expansion :
7
8

RemediesChapter-A4 Weld Distortion, How it Happens ? Or Theory of Distortion
By JGC Annamalai
stress
Expanding
Forces
T
T4
T1
T2
T3
C
Pool
Temperature
Ring-
Ring-
Ring-
Ring-
Ring-
permanent set.
Expanding
Forces
6
The net resultant Distortion is due to the effect of Expansion and Contraction
Shrinking Forces are radial, from outer ring periphery towards center
Case-1. Butt Welds:
Case-2. Fillet Welds:
(3). The thickness, moment of Inertia and radius of gyration are huge in real situation.
Actual Distortion may be high or absorbed and null or may be reversed.
In Butt welds, the base metals are in same plane. But, in fillet welds,
the base metals are in perpendicular planes.
The effect of expansion and contractions, are very similar to butt
welds. The distortion, in the fillet welds are moving the outer base
metal ends , closer. If one base metal, is fixed, the distortion or the
displacement will be on the other base metal(flexible).
In Reality: We explained here a simple case. However, the real
distortion is not so simple. The issue is very complex due to the
following :
(1). Weld Volume: We assumed a small amount of local heating.
However, in reality, we will have large amount of welding/heating
to complete the job.
(2). The job is not small in shape. Often the job involves, large number of
parts and shapes.
9. Direction of Lift:
The center of bending curvature can be found by this thumb rule:
Ring-4: During cooling, the farthest outer ring, is at or near room temperature, unaffected periphery, due to
temperature, will stay as rigid.
Ring-2: The inner ring, immediate to the weld, is soft & ductile and take the contraction and shrink. The
shrinking forces will pull the immediate inner ring(Ring-1).
Ring-3: The next inner ring, which was pushed by hot inner area, was deformed to plastic state with
Residual Stress. Part of the residual stresses recoils during cooling.
Here we have large welds. The distortions are
from different direction. Various Weld Distortion
Types on butt welds are explained in the
following sketches
(If the welded assembly is complex and there are many
welds, often average neutral axis line and average weld
center is calculated, as it is done in Strength of Materials).
Neutral Axis >> Weld Center Line >> Center point of bend curvature.
The Expansion and Contraction forces of the base metal and weld, causes weak location to buckle/distort the base
metal. The direction of buckling or curvature of bending is moment of inertia dependent. Ring-1 & 2, the base metal
is permanently set / deformed as the metal yield stress is lower than the applied stress.
Ring-1: The innermost ring will shrink and pull the ends or lift. Weld Puddle: The weld puddle is solid now
and start shrinking and start pulling the base metal, immediately next to the weld puddle/fusion line.
8. Shrinking (during cooling) :
Temperature
Distribution at the
Top Surface
Weld, initially liquid
metal. Later solidified
into solid metal
l
A
A2
B1
B3
Base Metal
BaseMetal
B2
j
k
Below
Yield Point
B4
Temperature
Distribution
on weld side &
other side
B1, B2, Room Temperature
B3, Yield Point, Yielding
B4, Melting Temperature
Welding Distortion Types:
Pg.A4.3
8

x10-6
in./in./°F
x10-6
m./m./°C
x10-6
in./in./°F
x10-6
m./m./°C
Age Hardenable Stainless Steels 6.944 12.5 Molybdenum 2.900 5.22
Alloy Steels 7.222 13 Molybdenum & its Alloys 3.333 6
Alloy Steels (cast) 8.056 14.5 Molybdenum Di-silicide 5.000 9
Alumina Ceramics 3.611 6.5 Monel 400 6.400 11.52
Alumina Cermets 5.000 9 Nichrome (80% NI-20% Cr) 7.300 13.14
Aluminum 13.100 23.58 Nickel 5.800 10.44
Aluminum & its Alloys 12.778 23 Nickel & its Alloys 8.333 15
Aluminum Bronzes (cast) 9.444 17 Nickel-Base Superalloys 10.000 18
Antimony 6.111 11 Nitriding Steels 6.667 12
Austenitic Stainless Steels 9.444 17 Nodular or Ductile Irons (cast) 8.333 15
Beryllia &, Thoria 5.000 9 Osmium and Tantalum 3.333 6
Beryllium 6.111 11 Palladium 6.667 12
Beryllium Carbide 5.556 10 Phosphor Silicon Bronzes 9.722 17.5
Beryllium Copper 9.444 17 Plain & Leaded Brasses 11.111 20
Boron Carbide 1.667 3 Platinum 5.000 9
Boron Nitride 4.444 8 Platinum 4.900 8.82
Brass (Yellow) 11.200 20.16 Rhodium 4.444 8
Carbon and Graphite 1.667 3 Ruthenium 5.000 9
Carbon Free-Cutting Steels 8.333 15 Silicon Carbide 2.222 4
Chromium Carbide Cermets 6.111 11 Silver 11.111 20
Cobalt 6.667 12 Silver 10.800 19.44
Cobalt-Base Superalloys 8.333 15 Solder (50% Pb-50% Sn) 13.100 23.58
Columbium & its Alloys 3.889 7 SS(Austenite) 304,304L321,347 9.600 17.28
Copper 9.800 17.64 SS(Austenite), 316,316L 9.722 17.5
Coppers 8.889 16 SS(Ferrite), 430, 409,434 6.000 10.8
Cr-Ni-Co-Fe Superalloys 8.333 15 SS(Martensite), 410,420,440 5.500 9.9
Cr-Ni-Fe Superalloys 10.000 18 Stainless Steels (cast) 8.333 15
Cupro-Nickels & Nickel Silvers 9.167 16.5 Steatite 3.611 6.5
Electrical Ceramics 2.222 4 Steel, mild 6.700 12.06
Ferritic Stainless Steels 6.111 11 Tantalum 3.600 6.48
Gold 7.778 14 Tantalum Carbide 4.444 8
Gold 7.900 14.22 Thorium 6.111 11
Gray Irons (cast) 6.111 11 Tin & Aluminum Brasses 11.111 20
Hafnium 3.333 6 Tin & its Alloys 12.778 23
Heat Resistant Alloys (cast) 8.333 15 Tin Bronzes (cast) 10.000 18
High Temperature Steels 7.222 13 Tin, solid 13.000 23.4
Incoloy 800 7.900 14.22 Titanium & its Alloys 6.111 11
Inconel 600 5.800 10.44 Titanium 99.0% 4.700 8.46
Invar, 64%Fe-35%Ni 0.500 0.9 Titanium Carbide 3.889 7
Iridium 3.889 7 Titanium Carbide Cermets 5.556 10
Iron, Cast 6.000 10.8 Tungsten 2.222 4
Lead & its Alloys 15.278 27.5 Tungsten 2.500 4.5
Lead, solid 16.400 29.52 Tungsten Carbide Cermets 2.778 5
Low Expansion Nickel Alloys’ 3.333 6 Ultra High Strength Steels 7.222 13
Magnesium 14.000 25.2 Vanadium 5.000 9
Magnesium Alloys 15.000 27 Zinc 22.100 39.78
Malleable Irons 6.667 12 Zirconium 3.200 5.76
Martensitic Stainless Steels 6.111 11 Zinc 22.100 39.78
Molybdenum 2.900 5.22 Zirconium 3.200 5.76
Shrinkage Allowance (Foundry) inch/foot mm/foot mm/1000mm Shrinkage Allowance (Foundry) inch/foot mm/foot mm/1000mm
Aluminum 5/32 3.97 13.02 Copper 3/16 4.76 15.24
Bismuth 5/32 3.97 13.02 Lead 5/16 7.94 25.40
Brass 3/16 4.76 15.62 Monel 1/4 6.40 20.48
Bronze 3/16 4.76 15.62 Magnesium 1/8-5/32 3.2 to 4.0 10.5 to 13
Aluminum Bronze 7/32 5.56 18.22 Steel 1/4 6.40 20.48
Manganese Bronze 7/32 5.56 18.22 Stainless Steel(SS-304) 5/16 8.125 26.00
Cast Iron 1/10-1/8 2.5 to 3.2 8.2 to 10.5 Tin 1/4 6.40 20.48
Cast Iron Wrought 1/8 3.20 10.50 Zinc 5/16 7.94 25.40
Coefficient of Thermal Expansion
of Materials
Coefficient of Thermal Expansion
of Materials
PgA4.4
9

(1).
(2). Co-efficient of thermal expansion (5). Thickness of the welding.
(3). Thermal conductivity (6). Structure of the Object
(4). Yield strength (7). Young's Modulus
(1a). Heat Input Controls: (Higher the heat input, higher the deflection or distortion)
High Power Density gives low heat input. Eg :
(1b). Distortion control by Temperature Controls:
Temperature Contour / Temperature Distribution at the Weld Tip and Temperature around the Welding :
Higher the temperature, higher the Deflection or
Distortion. Shown below, is sketches for the
Temperature Distribution at the Welding Tip and
the Temperature Contour around the weld. The tip
temperature is by simulation and radiation study and
the temperature around weld is by measuring
temperature, by thermocouples and infrared
thermometers.
For , lower weld distortion, it is better to use,
Higher Power Density or low heat input
sources, like EBW or LBW process.
We saw how the Weld Distortion happened and the theory behind it.
Distortion is influenced by :
(please refer to Annex-2, to see the change in Physical and Mechanical Properties
with Temperature, for CS and SS) :
Low Power Density or high heat input Process, cause damage to the work
piece(say Distortion). Example :
(1). Low energy group includes-Gas Welding/Oxy-fuel (OAW).
(2). Medium energy includes-Arc Welding
Process (SMAW, GTAW, PAW, GMAW,
FCAW, SAW, ESW),
Heat & Temperature : Distortion happens because of local heating and
cooling and when the object is strained by external forces or by its own
structure configuration. Heat is function of Temperature and Power Density of
the Welding Process.
Higher the heat input, higher the temperature
and higher the Distortion
(3). High energy group includes-Electron
Beam Welding (EBW) and Laser Beam
Welding (LBW)
EBW and LBW. The cost of the equipments
are high, gives higher weld penetration, higher
welding speed, higher welding quality.
Remedies
Most of us, know the effect of Weld Distortion(it changes the shape, changes the dimensions, causes difficulty during
assembly of parts and makes the machineries difficult to work smoothly, not suitable for services like Stress Corrosion
Cracking, Fatigue, Cryogenics, areas where brittle structure is formed, etc.)
Chapter-A5 Factors Influencing Weld Distortion
By JGC Annamalai
Electrode Tip temperature (SMAW) Temperature Distribution around the Weld (SMAW) for CS
(1). Welding speed: 2.4 mm/s; heat input: 3200 W; material, similar to SA36
Pg.A5.1
Sr.
No.
Welding Process Welding
Process
Heat
Density
(W/cm2)
Arc
Temperature,
°C
1 Gas welding OFW 10
2
-10
3
2500-3500
2 Shielded meta arc welding SMAW 10
4
>6000
3 Gas Tungston Arc Welding GTAW 19,400
4 Gas metal arc welding GMAW 10
5
8000-10000
5 Plasma arc welding PAW 106
15000-30000
6 Electron beam welding EBW 107
-108
20,000-30000
7 Laser beam welding LBW >108
>30,000
10

RemediesChapter-A5 Factors Influencing Weld Distortion
By JGC Annamalai
Sr.
No.
Welding Process Welding
Process
Heat
Density
(W/cm2)
Arc
Temperature,
°C
1 Gas welding OFW 10
2
-10
3
2500-3500
2 Shielded meta arc welding SMAW 10
4
>6000
3 Gas Tungston Arc Welding GTAW 19,400
4 Gas metal arc welding GMAW 10
5
8000-10000
5 Plasma arc welding PAW 106
15000-30000
6 Electron beam welding EBW 107
-108
20,000-30000
7 Laser beam welding LBW >108
>30,000
(2). Co-efficient of Thermal Expansion (higher the co-efficient of thermal expansion, higher the Deflection or Distortion)
(3). Thermal Conductivity (Higher the thermal conductivity, the heat drain is faster, distortion is less)
(4). Yield Strength (higher the yield strength, lower the Deflection or Distortion)
(5). Thickness of the Welding.
(6). The shape and complexity of the Structure
(7). E, Young's Modulus (also called Modulus of Elasticity), (Higher the E, more stiffer, lower the Deflection or Distortion)
Different materials, at the same temperature, having, higher Young's Modulus, will have higher rigidity. Material to
material, the Young's modulus will change. So, to have less distortion, have higher modulus of Elasticity or Young's
Modulus.
For most of the materials, as the temperature increases, the Young's Modulus for a particular material decreases.
So, the structure at higher temperature, will not be rigid. The structure at higher temperatures, will deform/distort
more.
The expansion and contraction is function of co-efficient of thermal expansion. Higher the thermal coefficient higher
the distortion. Stainless steel and Aluminum have high thermal coefficient. So they will expand and distort more. For
steel, thermal co-efficient is increasing as the temperature increasing.
Thermal Conductivity plays a major role in Distortion. If the heat from weld pool is transferred/drained fast, the
distortion effects or less. Material with low thermal conductivity, like SS, will accumulate the heat and delay the heat
transfer and cause more distortion.
Each material has yield strength. Higher the yield strength, higher the strength and resist plastic deformation and
failure. As the temperature increases, yield stress of most of the materials decreases. Material with lower yield
strength may fail fast at lower loads. To meet the strength and to lower the weight of the structure, often Designers
prefer higher yield strength material. During welding, yield strength of the material is inversely proportional to the
welding temperature. Material with Higher yield strength at high temperature will have less weld distortion
Volume of Metal: Higher the material thickness is higher the 2nd moment of inertia and will resist distortion. Often
lower thickness material will have higher distortion. Higher thickness material will have faster spread of heat.
Volume of Weld/Thickness of Weld : Higher weld thickness or more volume of weld material, will have more
distortion.
(b). On CS and LAS welding, it is problem for fast cooling, as it often leads to action similar to quenching and
formation of hard martensitic material and crack. Preheat will slow down the spread of heat. People pre-heat the
whole structure, so that faster heat draining will be prevented.
The distortion will be easily observed on simple structure, as in simple butt weld on 2 plates or on fillet weld with 2
plates . It is difficult to see the Distortion on more complex Structure. The rigidity of the structure make the distortion
absorbed /or controlled by other members or inside the structure and will stay as residual stress.
(c). Less harmful distortion, happens, on Stainless Steel, if we cool fast and drain away the welding heat. As there
is no phase change in SS, no hardening or grain change happens. On SS, area beyond weld fusion line is force
cooled, by icing or water cooling.
The following are the actions for Temperature Controls :
(a). Temperature spreads from high temperature to low temperature. If the high temperature is kept, for long time,
it will spread to more area. If the area will have high temperature for long time and more area may have yielding
further and will have more distortion. So, the welding should be completed fast. Higher the temperature, lower the
yield stress and will have more distortion.
Pg.A5.2
(1). Welding speed: 2.4 mm/s; heat input: 3200 W; material, similar to SA36
(2). Welding speed: 6.2 mm/s and heat input of 5000W. material, similar to Isotherm curves
are very similar, but the ellipses are compressed in Y axis and elongated in X axis
Ref: ASME Sec II, D, Page-568
Temperature, °C >>>>
−30to
40 65 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500 525
Carbon steels SA36 248 233 227 223 219 216 213 209 204 199 194 188 183 177 171 166 162 158 154 150
Material Group G [SS-304, plate]207 184 170 161 154 148 144 139 135 132 129 126 123 121 118 117 114 112 110 108
Yield Strength, MPa (Multiply by 1000 to Obtain kPa), for Metal Temperature, °C, Not Exceeding
Ref: ASME Sec II, D, Page-696
Temperature, °C >>>> −200 −125 −75 25 100 150 200 250 300 350 400 450 500 550 600 650 700
Carbon steels with C ≤ 0.30% 216 212 209 202 198 195 192 189 185 179 171 162 151 137 . . . . . . . . .
Material Group G [SS-304 etc] 209 204 201 195 189 186 183 179 176 172 169 165 160 156 151 146 140
(Youngs Modulus) Modulus of Elasticity E = Value Given x 103
Mpa(or in Gpa), for Temperature, °C
Temp.°C 20°C 40°C 70°C 100°C 120°C 150°C 180°C 200°C 230°C 260°C 280°C 320°C 350°C 370°C 400°C 430°C 450°C 480°C 500°C 540°C 570°C 600°C 620°C 650°C 680°C 700°C 730°C 760°C 800°C 820°C
CS 11.52 11.70 11.88 12.06 12.24 12.42 12.60 12.78 12.96 13.14 13.14 13.32 13.50 13.68 13.86 14.04 14.22 14.22 14.40 14.58 14.58 14.76 14.94 14.94 15.12 15.12 … … … …
Aus SS 15.30 15.48 15.84 16.02 16.38 16.56 16.92 17.10 17.28 17.46 17.64 17.82 17.82 18.00 18.00 18.18 18.36 18.36 18.54 18.54 18.72 18.72 18.90 19.08 19.08 19.26 19.26 19.44 19.44 19.44
Coefficients forCarbonand LowAlloy(Coefficient is the meancoefficientofthermalexpansion×10
−6
(mm./mm./°C)ingoing from20°C,(Interpolated fromASME,SecII,D,Table-TE1)
11

Cause for Welding Distortions RemediesReal Happening
(1). Instead of applying heat, in a local
area, apply the heat, distributed over a
full ring area(as in pipe welding). Pre-
heat preferred.
(2). Follow, all Weld distortion
controls, explained in Chapter-9.
(3). (a). The object shall be restrained
or clamped and welding completed.
(b). Subsequently, PWHT completed,
with the clamps/restrain in position
during PWHT.
(c). Machining may be taken, after
PWHT.
If the above sequence is not followed,
residual stress may not disappear
and distortion may re-appear.
(1). Majority of the welding cases, distortion
and residual stresses happen and both are
ignored at the fabrication stage, as the real
effect is not known to some of the
Fabrication Shops.
(2). Precision Dimension requirements and
the welding distortion controls are explained
in Chapter-9, and Case-Studies in Chapter-
10).
Causes for Welding Distortions and remedies are discussed in most of the Chapters. Here, we give only the consolidation of main
points.
If the material is thin or the structure or the
area is flexible to adjust to the expansion or
contraction, there will be no distortion. If free
distortion is not allowed, remaining part of the
expansion / contraction will change to residual
stresses.
If the expansion or contraction is restrained/
clamped, there will be no distortion and the
dimensions may be maintained, but residual
stresses, will stay as hidden stresses in the
metal. Residual stresses may add up or
subtract to the system operating stress and
may partially neutralize or cause metal yielding
or may cause distortion at later date or continue
as hidden residual stresses for later stage
venting/ neutralization/ destruction.
(1). Localized Heating: Welding, thermal
cutting, local (spot) heating by torch, spatters
etc on metals are the sources for local heat
addition to the metal. Localized or unbalanced
heat will set up differential / gradient
temperature distribution to a local area and will
cause expanding or contracting stresses,
around the heated area. As the non-heated
area, outer periphery acts as rigid object and
does not allow or resist the metal to expand or
to contract, residual stresses will set up.
Chapter-A6 Causes for Welding Distortions
If the object is heated locally, it will
produce either distortion and / or
residual stresses. It is difficult, to
remove full distortion and full residual
stress. A compromise is to be made,
which is tolerable - distortion or
residual stress.
Most of the structures are made, with
min. distortion and assuming residual
stress will not harm. But, there are
cases, the residual stress will harm in
the following cases:, (1). Stress
Corrosion Cracking,
(2). Fatigue members,
(3). Members subjected to Cryogenic
Temperatures,
(4). Members subject to unexpected
shock loads. Fatigue stresses,
cryogenic temperature service etc
require fully residual stresses free.
(5). Mild shock loads(as in case of
loading and unloading, peening), will
release the residual stresses and set
in the distortion.
(2b). Release of Residual Stresses: The object
is distortion controlled by restraining or by
clamping. The residual stresses during heating
and cooling will release, later if the object is
heated or peened or shock load applied ,
during transport or during service. Combined
effect will either have distortion and residual
stresses. If the residual stresses are not
neutralized/ not released, in the worst case the
metal will fail, mostly by brittle failure.
(1). During transport by Sea, materials were
stored, in Ships, at different deck floors
(each about 20 ft high). One time, a Ship,
loaded with Air Fin Coolers(AFC), had
faced stormy weather around Arabian Sea.
AFC, stored in the top floor, fell from Top
Deck to the immediate mezzanine floor. The
AFC headers were made of ductile material
(SA516-70, about 1 1/2" tk). When the AFC
was received, at Site, the AFC header
boxes, were found, crushed like mud pot.
All brittle failure. (failed because of residual
stresses and shock load).
(2). Fully machined pump base plates were
ok at the Shop, but when received at Site,
they were, found bowed upwards(distorted
during loading, unloading or with shock
loads).
(3). Stress Corrosion Crack is very common
on Stainless Steel objects due to
sensitization . Corrosion and stress will
cause crack initiation. Further crack/ failure
may be accelerated by residual stresses
and service stresses.
(4). Failure Analysis showed the Titanic
Ship , Liberty Ships/ SS Schenectady Ships
faced cold temperature and the material
used were low quality materials (not suitable
for low temperature service). First cracks
were started from the weld residual stress
areas.
(5). Many bridges also failed due to excess
weld residual stresses.
C
H
Pg.A6.1
By JGC Annamalai
12

Types of Distortion
(1). Longitudinal(along weld axis) - shrinkage is parallel to the weld axis
(2). Transverse - Shrinkage is perpendicular to weld axis
(3). Angular - Change in the angle
(4). Rotational Shrinkage
(5). Bending Distortion
(6). Buckling - While welding thin sheets using SMAW :
Check List : to study and take counter action to control Distortion for each weld :
(1) Longitudinal Shrinkage (4) Angular Distortion
(2) Transverse Shrinkage (5) Rotational Distortion
(3) Bending Distortion (6) Buckling
Note: One or many of the Weld Distortion Type may occur simultaneously, on a weld. Welder, Fabricator, Shop Engineer
should study each weld and take action.
When we weld a long weld/bead or joint, the longitudinal
shrinkage happens. Due to this, the ends of the base plate
are shrunk. If the plate is thin, due to the end thrust, by
shrinking forces, the plate is buckled.
Controls: By Clamping/restraint, or by low heat welding, or
by having low volume of weld metal (smaller weld groove).
Balance welding at top and bottom. Use stiffener, on both
side of welding & also at top & bottom.
When we weld a long weld/bead or joint, the longitudinal
shrinkage happens. If the V finishing/filling is at the top, ,
the ends of the base plate are shrunk and lift up.
Controls: Use double V joint. By Clamping/restraint, or by
low heat welding, or by having low volume of weld metal
(smaller weld groove). Use stiffener at top and bottom and
at sides of weld
When we weld a long weld/bead or joint and only from one side,
the Angular Distortion happens. Due to this, the ends of the base
plate are move up.
Controls: By changing the groove from single V to double V and
welding alternatively at top and bottom or use cross stiffener to the
weld axis or by Clamping/restraint or by low heat welding, by having
low volume of weld metal (smaller weld groove).
When we weld a long weld/bead or joint, the Rotational Distortion
happens. Due to this, the root gap, at the closing end is closed.
Controls: Adding stronger tack welds or by Clamping/restraint or
by low heat welding or by having low volume of weld metal (smaller
weld groove) or by balance welding(skip welding, scatter welding,
back-step welding), like weld in the order 1,5,2,4,3
When we weld a long weld/bead or joint, the transverse / lateral
shrinkage happens. Due to this, the perpendicular edges of the
base plate are shrunk.
Controls: By Clamping/restrain or by low heat welding or by having
low volume of weld metal (smaller weld groove). Preheating or
cooling the whole body, gradually and slowly will reduce distortion.
Remedies
When we weld a long weld/bead or joint, the longitudinal shrinkage
happens. Due to this, the ends of the base plate are shrunk.
Controls: By Clamping/restraint or by low heat welding or by
having low volume of weld metal (smaller weld groove, double V,
instead of single V). Preheating or cooling the whole body,
gradually and slowly will reduce distortion.
Every time, we add heat(by welding, torch heat, spatter etc.) to the base metal, Shrinkage happens to the base
metal. The following shrinkages and distortions types are most common. To understand the effect of shrinkage,
the total shrinkage is classified to several types.
Chapter-A7 Welding Distortion - Types
By JGC Annamalai
Pg.A5.1
Pg.A7.1
13

Quantitative Distortions: Thumb Rules, AWS HB Vol-1, Chapter-7, Recommendations :
Butt Welds : C=Co-efficient,
=0.2 for plate tk, >1"(25mm)
=0.18 for plate tk, <1"(25mm)
∆S = Transverse shrinkage, in. (mm);
A w
Transverse Reaction Stress : t = Thickness of plates, in. (mm);
d = Root opening, in. (mm).
σ = Reaction stress, ksi (MPa);

E = Modulus of elasticity, ksi (MPa);
(b). Longitudinal Shrinkage: S = Transverse shrinkage, in. (mm);
B = Width of the joint, in. (mm).
∆ L = Longitudinal shrinkage, in. (mm);
I = Welding current, A;
L = Length of weld, in. (mm); and
t = Plate thickness, in. (mm).
S = Transverse shrinkage, in. (mm);
D f = Fillet leg length, in. (mm);
Fillet Welds
(b). Angular Distortion :
= Cross-sectional area of weld, in. ( mm
2
);
Remedies
Most of us, know the effect of Weld Distortion(it changes the shape, changes the dimensions, causes difficulty during
assembly of parts and makes the machineries difficult to work smoothly. Residual Stresses are normally not accepted for
services like Stress Corrosion Cracking, Fatigue, Cryogenics or areas where brittle structure is formed(like caustic, H2S),
ASME codes specify PWHT (Stress Relieving) on welds, mandatory for such services.
Weld Type & Details Formula & Details Abbreviations & Details
(a). Transverse Shrinkage (inch or
mm):
Chapter-A8 Quantitative Welding Distortion (Thumb Rules)
C 1 = 0.04 and 1.02 when S, L, and tb are in
inches and millimeters, respectively;
t b = Thickness of the bottom plate,
in. (mm).
C 3 = 12 and 305 when L and t are in
inches and millimeters, respectively;
The amount of longitudinal shrinkage
that occurs in butt joints is
approximately 1/1000 of the weld
length. This is much less than
transverse shrinkage.
Distortion – Angular, Welded Structures:
(A) a Free Joint and (B) a Restrained Joint
(1). Transverse Shrinkage(inch or
mm) (Alternative):
By JGC Annamalai
Butt Welds:
Transverse Shrinkage
Controls: To have Strong-backs or
clamping or follow allowance per
Transverse Welds
APg.A8.1
14
15

RemediesChapter-A8 Quantitative Welding Distortion (Thumb Rules)
By JGC Annamalai
Fillet Welds Butt Welds
14Quantitative Distortions, Thumb Rules, TWI Recommendations :
Note : The formulas given here, are thumb rules for simple cases.
If the structure involves large number of welds or the structure is complex, it is better to measure the actual distortion, after
welding and take counter action to control the Distortion.
0.8mm per weld where the leg
length does not exceed 3/4
(75%) plate thickness
1.5 to 3mm per weld for 60° V joint, depending on
number of runs. (Normally, the root gap length, at
the fit-up, is considered as equivalent to the weld
metal shrinkage).
0.8mm per 3m of weld 3mm per 3m of weld
General-Fillet Welds: More the
Leg Length of Fillet Welds,
larger the Shrinkage.
General: Butt Welds: More the weld volume and
more the reinforcement, larger the Shrinkage
Longitudinal Shrinkage
PgA8.2
15

Residual Stresses are also called Internal Stresses or Buried Stresses or Hidden Stresses or Invisible Stresses
Plot of Shrinkage stresses due to Longitudinal Shrinkage, perpendicular to weld(areas where the weld and material
had reached the room temperature) :
Longitudinal Residual Stresses on the Weld, at different points on the Weld :
Residual Stresses, when the welding
temperatures reach room temperature
Normally, the area from fusion line to B
and fusion line to D are said as Heat
Affected Zone (HAZ). Many users'
specification, avoid, welding in the HAZ
area due to cumulative effect of Residual
Stresses. If it is difficulty to avoid welding
in the HAZ area, some people, check the
area with RT or MT or LT, before welding.
Effect of Residual Stresses : Residual stresses coupled with Applied Stress / Service Stress and stresses at stress raiser
points, crevice corrosion, sensitization corrosion etc points, fatigue, low and cryogenic temperature locations, will lead to
premature failures.
Analysis of the welding residual stresses, show: The stresses along the weld axis, is tensile stresses and it exists till few
millimeters from weld fusion line and then, the stress changes to compressive stresses, and they exist beyond null stress point,
few cm away.
If the base metal thickness is high and the weld is multi pass weld , the max. tensile and compressive stresses value will be
higher and similarly "no stress" point will move further away from fusion line.
RemediesChapter-A9 Welding Residual Stresses
Temperature due to Welding, creates forces and stresses on the material. If the material is flexible, the shape and size change
and distortion occurs. If the material/structure is rigid and/or it is restrained by outside clamps etc and did not yield to the stresses
due to welding temperature, the stresses due to expansion and contraction are absorbed/stays in the material as "Residual
Stresses".
Most of the cases, welding creates distortion as well as residual stresses in the material.
Amount of Residual Stress: The sketch here shows a single
side butt welded(multiple beads/runs, from one side) plate
structure and the distortions happened due to the welding.
This distorted plate is useless and does not serve the
purpose. If we use presses and straighten the distorted plate
in all directions, the plates may be flat or straight and may be
used. The amount of energy buried inside the plates, after
straightening, is equal to the total distortion energy or
residual stresses if we use clamps and other restrains and
maintain the straightness or no distortion.
If the press forces, clamps/restrains are removed, it is likely
that the spring back will happen and the distortion will appear.
The plates are free and not restrained and assumed no
residual stress now. It has max.distortion.
By JGC Annamalai
Pg.A9.1
16

By JGC Annamalai
16Cumulative Effect of Residual Stresses and Applied Stresses, leading to failures:
The Effect : The high residual stresses locked into a welded joint
Control of Residual Stresses:
(1). If Distortion, can be tolerated and allowed, Residual Stresses can be reduced
(2). Various Control Methods (without restraining), to control Distortions, like:
(a). Avoiding Distortion, by following various Design Improvements (Refer Chapter-9a)
(b). Avoiding Distortion, by following various Weld Design Improvements. (Refer Chapter-9b)
(c). Avoiding Distortion, by following various Preventive Methods. (Refer Chapter-9c)
(d). Avoiding Distortion, by faster withdrawal of Heat from weld area or from the assembly (Refer Chapter-9f)
(e). Stress Relieving or PWHT on the welded assembly or on the Welds (Annex-3)
Methods to Remove Shrinkage Forces/stresses after Welding
(1). Peening is one way to release the shrinkage forces/stresses of a weld bead as it cools. Essentially, peening the bead
stretches it and makes it thinner, thus relieving (by plastic deformation) the stresses induced by contraction as the metal
cools. But this method must be used with care. For example, a root bead should never be peened, because of the danger
of either concealing a crack or causing one. Generally, peening is not permitted on the final pass, because of the
possibility of covering a crack and interfering with inspection, and because of the undesirable work-hardening effect.
Thus, the application of the technique is limited, even though there have been instances where between-pass peening
proved to be the only solution for a distortion or cracking problem. Before peening is used on a job, engineering approval
should be obtained. (ASME codes, do not allow peening on welds for reducing or removing Residual Stresses).
Cumulative of Residual Stresses and Stresses due to Applied
Load-1 and -2, and their net stresses crosses Ultimate Tensile
Strength, then the material will have Failure. Applied load will
also include Residual Stresses, transferred from earlier
manufacturing process(like hot & cold rolling, cutting, forging,
extrusion, etc).
Painting on welding and HAZ: If the weld is not stress
relieved, the residual stresses in the weld and in the HAZ will
wait for release. Any shake or shock may be ok, to release
some amount of trapped residual stresses. The relaxing
processes is continuous, after weld completion. When
painting is done on weld and on HAZ, normally the paint will
not stick or will fall. This can be checked by applying a brittle
paint. So, service paints applied on welds and on HAZ are
normally elastic type.
(1). may cause deformation/distortion outside acceptable dimension limits to occur when (a). The holding tack-
welds/clamps/restraints during welding are removed, (b). the item is machined or (c). when it enters service.
(2). High residual stresses in carbon and low alloy steels can increase the risk of brittle fracture by providing a driving
force for crack propagation.
(3). Residual stresses will cause stress corrosion cracking to occur in the corrosive environment eg carbon and low alloy
steels in caustic service or general and intergranual grain attacked stainless steel exposed to chlorides(like sea water)
Clamping down the object or restraining the object from forming Distortion, will eliminate or reduce Distortion but,
proportion to the Distortion Control, it will increase the Residual Stresses.
The sketch shows the effect of weld residual stresses &
Applied Tensile Loads, at room temperature.
Design Load : Applied Load-1 and Applied Load-2 or their
cumulative, are below the yield point and are safe.
Cumulative of Residual Stresses and Stresses due to Applied
Load-1 crosses Yield Point and the material will have
permanent set.
17
Pg.A9.2

By JGC Annamalai
16
Effect of Residual Stresses due to Cold Work on SS :
Measurement of Residual Stresses in Weldments
A-1 Stress relaxation using electric and Mechanical Strain Gauges
Techniques applicable primarily to plates
1. Sectioning using electric resistance strain gauges
2. Gunnert drilling
3. Mathar-Soete drilling
4. Stäblein successive milling Techniques applicable primarily to solid cylinders and tubes
5. Heyn-Bauer successive machining
6. Mesnager-Sachs boring out
Techniques applicable primarily to three-dimensional solids
7. Gunnert drilling
8. Rosenthal-Norton sectioning
A-2 Stress relaxation using apparatus other than electric and Mechanical Strain Gauges
9 Grid system dividing
10 Brittle coating drilling
11 Photoelastic coating drilling
B Diffraction
12. X-ray film
13. Conventional scanning X-ray diffractometer
14. Stress X-ray diffractometer
15. Neutron diffraction
C Cracking
16 Hydrogen-induced cracking
D 17 Computer Simulation / FEM
Classification of
Techniques for the
For long time, Quantitative measure of Residual Stresses were not ready or a crude method of low accuracy was
available. Recent time, we have more accurate measure of Residual Stresses:
(3). Time Bound: Residual stress release / relaxing is continuous from the time, the weld is completed. Some
percentage, will release, during shack or shock or jolt, or during peening, or during sand blasting/transport or in
installation or in operation. It will take many years to stabilize.
So to avoid any trouble, during service, the structure/equipments is stress relieved.
(2). Stress Relieving/PWHT : Another method for removing shrinkage stresses / forces is by Thermal Stress
Relieving - controlled heating of the weldment to an elevated temperature, followed by controlled cooling. Sometimes
two identical weldments are clamped back to back, welded, and then stress-relieved while being held in this straight
condition. The residual stresses that would tend to distort the weldments are thus minimized. Stress relieving, relieves, as
much as 90% residual stresses(Details are found in Chapter-B10, Distortion Control, by Stress Relieving)
The picture shows, a household utensil cap, expected, SS-
304. The cap was made by cold work-pressing, drawing,
spinning, flanging etc. After few years of service, cracks
appeared on the flange of the cap. The cracking is due to
residual stresses(+service stress), high hardened material,
created by repeated cold working on SS during fabrication.
Also it may be low grade, say, SS-201 or SS-202.
Remedy: To avoid residual stress cracking,
(1). Use annealed, SS-304,
(2). Need lubrication during fabrication,
(3). The rate of metal flow/press ram speed should be Slow
(4). Solution annealing at different stages of fabrication.
Stress Relieving: Stress Relieving, <400°C. Note: Opening the temporary tack welds
or removing the clamps and strong-backs before stress relieving will allow spring
back with distortion or partly distorted condition. So, if the temporary tack welds or
clamps or strong-back or the structure holding the assembly or back-to-back
assembled and welded structures as one piece etc are used to stop/prevent distortion
during welding, the same clamps / restraints should be allowed to stay during stress
relieving.
Pg.A9.3
18

L, length of observation α, Thermal expansion co-efficient
T, Temperature max, from room temperature(if variation in Temp., take small
Physical & Mechanical Properties of CS & SS, variation with Temperatures
Remedies
Among Distortion in CS and SS, major factors controlling the Distortion are
(1). Co-efficient of Thermal Expansion and (2). Thermal Conductivity.
Other factors causing Distortion, are near equal in CS and SS.
Most of the earlier chapters, we discussed about the distortion in carbon steel. In this chapter, we discusses about
Distortion in stainless steels. The distortion in Stainless Steels are very similar to carbon steels, but distortion is higher in SS.
The melting point, Young's Modulus and Specific Heat of carbon steel and stainless steels are very close. However, the thermal
expansion is high(1.5X), thermal conductivity is low(0.3X). With same size and shape, Stainless Steels, normally will have
more distortion, compared to Carbon Steels. Ferritic and Martensitic SS has Co-efficient of thermal expansion, close to Steel.
E, Young's modulus A, area of cross sectionincrements)
Chapter-A10 Weld Distortion in Stainless Steels
Controls: CS and LAS form harmful martensite and hardening, if we cool fast from 723°C temperature line to room
temperature. SS has more distortion compared to CS. But SS does not have any harmful metallurgical effect(grains, phases,
ductility etc) if, we cool fast from liquid metals to room temperature. So, manufacturers, doing SS jobs, are often cooling the
base metal, just away from fusion line, by icing or by copper cladding/ducting or water spray or water wiping. This will reduce
distortion and decrease weld decay.
(1). Co-efficient of Thermal Expansion, mm/(mm°C): The following
table, gives the average co-efficient of thermal expansion of Carbon Steels
and Stainless Steels, (0°C to 300°C). Stainless steel, has higher
coefficient of thermal expansion, about 1.5 times CS. So for the same
length and temperature range, the increment in expansion in SS,
comparing to CS, will be 150%.
Consequence-1: Welding Electrode Length: Compared to CS, SS has Thermal conductivity normally low and
Thermal Expansion high. To safeguard the welding electrode flux coating from peeling off and to avoid the electrode
bowing due to over heating, welding electrode length of SS are shorter. Normally CS electrode length is used to have
18" and SS electrode length is shorter and it is around 10" or 12".
Consequence-2: Thin SS Sheets: Major use of SS is in sheet metal works. Excess distortion happened due to weld
distortion, causing dents and bulges on the thin sheet metal surface and also make the job difficult in assembly.
Yield stress, between, 1200 to 1400°C, is about 20MPa
or less, compared to 270 MPa, at room temperature.(2). Heat Transfer, Thermal Conductivity, W/(m°C): At room
temperature, the Thermal Conductivity, for CS is 52W/(m°C) and
for SS, it is 15W/(m°C). Thermal conductivity of SS, comparing
to CS is about 3.5 times less. So, SS is poor conductor of heat,
comparing to CS. The heat added to the SS metal surface, (with
high temperature) is transferred very slowly to the
next segment (having low temperature). This causes, heat to build up or to stagnant at the welding area or near to that and
have more distortion. Thermal conductivity of SS, at 1300°C is decreased about 1/4 times the thermal conductivity at 1400°C
By JGC Annamalai
Alloy Liquid metal Shrinkage/
Pattern Allowane
(SFSA), mm for 1000mm
Linear Thermal
Expansion(ASM)
mm/mm/°C
Carbon and low alloy steel 20.8 11.7x10
-6
High alloy steels (SS304 etc) 26 17.3x10
-6
I
E
Pg.A10.1
19
Alloy around
20°C
around
1300°C
around
1400°C
Carbon and low alloy steel 52 27 28
High alloy steels (SS304 etc) 15 33 90
Thermal Conductivity, W/(m°C)
20

RemediesChapter-A10 Weld Distortion in Stainless Steels
By JGC Annamalai
Pattern Allowane
Linear Thermal
Expansion(ASM)
mm/mm/°C
-6
-6
I
E
19
Alloy around
20°C
around
1300°C
around
1400°C
Stress-Strain curves with change in Temperatures, for SS-316
Physical-Thermal Properties of some common metals / alloys :
Welding Temperature Contour for Steel, SS-304, Aluminum.
Properties of Some common Alloys and Metals :
Heat affected zone(HAZ) area for SS is much higher
than CS.
For SS, the temperature distribution contour lines for
Aluminum Carbon Steel and Stainless Steel are given,
at the right side. We see, 1300°C to 1500°C , the SS
has very high thermal conductivity, weld puddle is very
large and from 1300°C to 600°C temperature contour
lines are congested or near stagnant, due to SS low
thermal conductivity.
Pg.A10.
2
Steel
StainlessSteel
Copper
Aluminum
Thermal
Expansions
(comparative)
20

RemediesChapter-A10 Weld Distortion in Stainless Steels
By JGC Annamalai
Pattern Allowane
Linear Thermal
Expansion(ASM)
mm/mm/°C
-6
-6
I
E
19
Alloy around
20°C
around
1300°C
around
1400°C
Comparison of physical and thermal properties
of Steel, Austenitic, straight Chrome
stainless steel (Ferritic, Martensitic),
influencing Distortion:
Distortion Control in Austenitic, Precipitation Hardening, and Duplex (Ferritic–Austenitic) Stainless Steels
(3). Without fixtures , tack weld the joint every couple of inches and peen the tacks to remove shrinkage stresses.
Finish the joint with a welding sequence designed to minimize distortion.
(4). A planned sequence of weld ing always helps control distortion. The techniques used in mild steel welding
can be used. Skip welding and back-step welding are recommended for light gauge steels.
(5). Low current and stringer beads reduce distortion by limiting the amount of heat at the weld. Also, do not
deposit excessive weld metal. It seldom adds to the strength of the weld and does increase heat input and
promotes distortion. If a structure of heavy steel is not rigidly held during welding, many small beads will cause
more total distortion than a few large beads.
Austenitic Stainless steels have a (a). 50% greater coefficient of expansion and (b). 30% lower heat conductivity than mild
steel. Duplex stainless steels are only slightly better.
Allowance must be made for the greater expansion and contraction when designing austenitic stainless steel structures.
More care is required to control the greater distortion tendencies. Here are some specific distortion control hints:
(1). Rigid jigs and fixtures hold parts to be welded in proper alignment. Distortion is minimized by allowing the
weld to cool in the fixture.
(2). Copper chill bars placed close to the weld zone help remove heat and prevent distortion caused by
expansion. Back-up chill bars under the joint are always recommended when butt welding 14 gauge (2.0mm) and
thinner material. A groove in the bar helps form the bead shape. NOTE: Keep the arc away from the copper.
Copper contamination of the weld causes cracking.
21

N
o(1)
.
(2)
(3)
.
(4)
.
(5)
.
For general purpose work, this may be ok.
For critical work, such mechanical press work may
damage the weld/base metal. If used, PT, MT, RT etc
checks are necessary to qualify the weld joints.
This is correction
work. This process is
traditional and
popularly used by all
Black Smiths and
fitters, for general
purpose works.
Fig-X is continuous weld, resulting in Distortion.
Fig-Y is Intermittent Weld, to control distortion. But this is
not acceptable to Process Industries, as there is gap. The
gaps may have corrosion in the voids.
Fig-Z is a compromise to meet Distortion Control and the
Process Industries. Here, Initially Intermittent
welds(A1,B1,A2,B2,A3,B3) are used. Later, the gaps(A4,
B4, A5, B5) are filled. The weld is continuous.
Do not weld, more than the drawing requirement.
Distortion due to
weld shrinkage is
only 10% of total
shrinkage. 90% of
Distortion is due to
base metal distortion,
due to non-uniform /
gradient heating. If
this heat is removed,
distortion will be less
CS and LAS: Forced cooling is not allowed on CS and
LAS material as fast cooling will increase martensite
formation and the surface will have high strength, high
hardness and crack prone.
However, Austenitic Stainless Steel welds do not change
phases, if we sudden cool from welding temperature to
room temperature. The phase is always, Austenitic. So,
forced cooling may be allowed to control distortion on
Austenitic welds. Avoiding 430 to 900°C sensitization
zone, the welds will have no weld decay.
One of the
technique, to correct
the distorted weld is
Thermal Tensioning
Base metal-CS: If the heat correction band temperature is
below 600°C, there will be no phase or grain size change.
The strains are relieved. As the band cools it contracts and
make reverse distortion and the weld and the base metal is
straight.
If the head band temperature, goes about 700°C, the
Engineering Departments has to decide on the acceptance
of the weld, depending on the service.
Due to distortion reversing, both weld side and on heat
band side, PT, MT, RT or other additional QC checks
may be needed, if the job is critical.
Often, Process
Industries, where the
environment is
corrosive,
intermittent welds are
not permitted, to
control general
corrosion and crevice
corrosion.
Welding Distortion & Control
Some of the advices to control Distortion are against the advices on Welding Procedure. Probably, it is due to Welding
Inspectors and Welding Engineers follow AWS and ASME codes and traditional advices on better welding.
Whereas , the advices on Weld Distortion Controls are mostly from Production and Shop People.
However, the advices on Weld Distortion controls are found in AWS Volume-1, Chapter-7 and Welding Metallurgy by Linnert,
Volume-1 and Welding Metallurgy, by Kou. So, The Production and Shop people are also following Welding Metallurgy.
Welding Inspector and Welding Engineers are also following Welding Metallurgy. Then how clashing can happen. We discuss
some of the classing points here.
Illustration
Distortion is
proportional to the
amount of heat
added to complete
the weld. So, use the
welding process
which gives lesser
heat
Description
Remedies
Justifications
Procedure: To have fine grains, small beads are preferred.
ANSI specify min.2 beads for a weld. AWS specify
weaving max. 6 times electrode size, but 3 times is
preferred.
Distortion is controlled, by adding large amount of weld,
instead of several beads. Max temperature is same.
Several beads, adds heat and hold for longer time, leading
to temperature spread for more area and increase the
distortion.
(a). Use automation. (b). Use process which adds large
volume of metal quickly, like SAW . (c). Use heavy
thickness SMAW electrodes and fast filling..
Chapter-A11 13. Advices on Welding Procedure and Weld Distortion Control methods are clashing
By JGC Annamalai
Pg.A11.1
22

Recent Study and Developments on Weld Distortion
Typical Areas of present Distortion Study and Research are :
(1). Residual Stress Predictions & Weld Distortion.
(2). Modeling and Implementation on Welding Distortion
(3). Welding Distortion on Thin Plate Panel Structure
(4). Control of Distortion of Welded Aluminum Structures
(5). Phase Transformation Effects on Weld Distortion
(6). Residual Stress Engineering by Low Transformation Temperature Alloys
- State of the Art and Recent Developments
(7). Prediction of Welding Distortion
(8). Laser Welding Technologies
Welding Distortion & Control
Weld Distortion Control and Residual Stress Control are related. To meet the Client/Users requirements, we should
consider steps or methods to reduce both Distortion and Residual Stresses. Qualified procedure and qualified personnel are
used to analyze and control weld distortion.
Now, Research and Development Groups work on Distortion Measurements and Control and Residual Stress Measurements
and Control are taken up, at Research Laboratories and Universities. The awareness is spreading. New ideas and procedures
are now available. Specific areas of Developments in Distortion and Residual Stresses are on measurements, modeling,
simulation study etc:
The Author thinks this Document will create awareness on Weld Distortions-Residual Stress and their impact and help
people, to follow Distortion Control Methods and Residual Stress Control Techniques so that assembly problems at the
Project Site and Operating Plants will be reduced.
Remedies
Many Users / Inspectors still consider welding and NDE are the main consideration for acceptance. If weld flaws or
imperfections and NDE are ok, the system is accepted. There are many cases, Distortion measurements and controls , action
on Residual Stresses are ignored or not listed in their ITP. Now, because of the advantages on Distortion Controls failures of
objects due to welding Residual Stresses, Awareness is spreading to use Distortion & Residual Stress Controls methods on
non-critical objects also.
Only critical users, specify and follow Distortion Controls / Residual Stress Control methods. For general purpose works, daily,
Tons of welding work is done, without following weld distortion controls. Majority of the grills in the house gates and similar
works, has only tack welds. Probably, this serves the purpose and has no distortion. If we use, fillet size equal to plate
thickness or full penetration welds etc, as required in in some codes and spec, we may end up with buckled gates.
The Author had worked in the following Industries : Space Research, Nuclear Power Plant, Thermal Power Plants, Oil & Gas
Industries. Among industry people, the author found, the awareness on Weld Distortion and Residual Stresses is not full.
Probably, for those people welding work may not be so sophisticated or not critical. Sometime, Vendors supplying equipments
to critical and non-critical areas, treat critical equipments as the non-critical equipments. Vendors are often taught about
Impact of Distortion and its control.
The problems shown in Case Studies, on Distortions are real and the author had experienced.
Chapter-A12 Recent Development in Weld Distortion Controls
By JGC Annamalai
Pg.A12.1
23

Various Methods to Control Weld Distortions:
Controls (Prevention) : Correction:
(a) Distortion Control-Introduction (i) Distortion Control-by Heat Correction, Thermal Tensioning
(b) Distortion Control-by Design Improvement (j) Distortion Control-by Stress Relieving
(c) Distortion Control-by Weld Improvement
(d) Distortion Control-by Preventive Measures
(e) Distortion Control-by Pre-setting
(f) Distortion Control-by Clamp Down-Restraints
(g) Distortion Control-by Withdrawal of Heat from Weld zone
(h) Distortion Control-by Welding on or about Neutral Axis
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Remedies
The following chapters will suggest ways to control or to reduce Weld Distortion by Heat control, Design Improvement
and various methods.
Weld Reinforcement: Do not over weld-Excess Weld
reinforcement will be a stress riser. This will cause .
excess distortion and residual stresses, will not
meet Code & User Requirements
Checklist to minimize or to prevent Distortion: Illustration
Chapter-B1 Control of Distortion - Introduction
For groove welds, use joints that will minimize the
volume of weld metal. Consider double-sided joints
instead of single-sided joints
Use welding positioners to achieve the maximum
amount of flat-position welding. The flat position
permits the use of large-diameter electrodes and high-
deposition-rate welding procedures
Even Distribution: Sequence sub-assemblies and final
assemblies so that the welds being made continually
balance each other around the neutral axis of the
section
Control fit-up-Excess root gap, excess weld bevel
angle, irregular weld edge etc will add up more weld
metal and more distortion
Use intermittent welds where possible and consistent
with design requirements
Use the smallest leg permissible(dwg) size when fillet
welding
Weld alternately on either side of the joint when
possible with multiple-pass welds
Weld toward the unrestrained part of the member
Use clamps, fixtures, and strong-backs, tack-welds to
maintain fit-up and alignment
Pre-setting: Pre-bend the members or preset the joints
to let shrinkage pull them back into alignment
Low energy group includes-Gas Welding/Oxy-fuel (OAW).
Medium energy includes-Arc Welding Process (SMAW, GTAW,
PAW, GMAW, FCAW,
Use minimal number of weld passes
Use low heat input procedures. This generally means
high energy / deposition rates and higher travel speeds
Balance welds about the neutral axis of the member
Distribute the welding heat as evenly as possible
through a planned welding sequence and weldment
positioning
Bevel Angle=35 to 40
Root Gap,
0 to 1.5 mm
Root Landing,
0.5 to 1.5mm
By JGC Annamalai
Correct Weld reinforcementExcess Weld reinforcement.
Butt weld, with double
V-joint(Volume-0.5Vol)
Vessel&plate,
accesstotheInside
weldavailable
Min. Number of Weld Passes
Excess Bevel Angle>40
ExcessRoot Gap,
> 1.5 mm
Irregular
welding
edge
Pg.B1.1
1
2
4
5
9
6
1
2
7
13
3
10
11
14
11
11
8
13
24

No.
(1).
(2).
(3)
(4)
(5).
(6).
(7)
(8)
(9).
(10).
(11).
Follow Stress Relief
(Post Weld Heat
Treatment, PWHT)
to control Distortion
and to reduce
Residual Stresses
Critical welding / construction codes / Owner
Specification requires Stress Relief, after welding to
reduce distortion and Residual Stresses. (The
clamps and hold-ups and Restraints should be in
place, during PWHT).
General structures, requiring distortion control,
should also be stress relieved.
Bevel T stiffener
joint
Reduce insert thick-
thin transition
Reduce design
weld size
More the volume of weld more the distortion. So,
avoid, as much welding as possible or weld size.
Employ intermittent
welding If the intermittent weld, can give sufficient strength
instead of continuous weld, the welds can be
changed to intermittent weld. (Designers do not like
intermittent welds, in fatigue, vibrating, corrosion etc
services)
Reduce stiffener
spacing
If the plate shows warping / dishing, additional
stiffener with lesser span, should be used. Use
smaller welds.
Increase plate
thickness
To increase the Moment of Inertia of the Section and
to improve the rigidity, use next heavy plate
Reduce cut-outs If the plate has many cut-outs, to reduce weight, this
will increase the distortion. So avoid cut outs.
Remedies
Technique To follow to reduce Weld Distortion Illustrations
The Distortion caused is because of welding Heat only. So, this chapter considers, primarily to control weld
parameters so that Distortion of Heat is controlled or balanced.
To Avoid Welding To avoid weld distortion and residual stresses, the
product design should consider possibility of other
methods of fabrication, like casting, forming by
forging, extrusion etc.
Place the welding at the neutral axis or close to the
neutral axis of the members or group center of weld
on neutral axis of the sub-assembly or the total
assembly
Use welding such
that the weld is on
Neutral Axis or
close to Neutral
Axis
To use, ready made
shapes, instead of
welding
Use as much as possible, ready made components,
structural shapes, which require less welding.
Chapter-B2 Welding Distortion Control by Design Improvements
C
H
By JGC Annamalai
Pg.B2.1
1
2
3
4
1
3
2
9
3 5
9
25

No.
(1).
(2).
(3).
(4).
(5).
(6).
(7).
(8)
Remedies
IllustrationsTechnique To follow to reduce Weld Distortion
Welding Heat causes Welding Distortions. So, this chapter considers, primarily to control welding heat parameters so that
Distortion is controlled. Following these techniques , the Distortion as well as Residual Stresses will be reduced.
Chapter-B3 Control of Distortion by Welding and its Parameters - Improvements
Many weld passes
increase the total
heat
For the same weld volume, increasing the number of
weld passes, will increase the total Heat and weld
Distortion. So limit the weld passes. Sequence /
balance the weld.
Reduce weld
repairs.
Improve Fit up
(weld volume
reduced means
Total Heat is
reduced. Heat
contour is reduced).
(1). Have weld bevel, just sufficient : Normally butt weld
single bevel angle is 35 to 40°. If the welder is skilled
& the electrode can have access to the weld, it is better
to have lower value of the bevel angle(say 30°)
(2). Have root gap, just sufficient. Normally 0.7 to 1.5
mm gap is provided. Root Gap is for full penetration. If
the welder is skilled, the root gap may be reduced. Use
"welding insert" for full penetration and to have less
weld metal. Rule of thumb is that the weld shrinks,
equal to the root gap width.
(3). if the weld groove size/weld volume is much
reduced, we will have less distortion, if narrow gap
welding, using "J" or "U" groove and torch modification,
on SAW or MIG or Electro-slag welding
process/multiple-torch are followed.
Minimize tack weld
size.
Welding Parameter
control
QC checking on
reinforcement.
Use mechanization
to weld
Welding heat is the source for Weld Distortion. So, use
only just required heat. Repairs will add additional heat
and more distortion. Many people use, repairs, 3 times
max. But for distortion control, this should be reduced
to 2 times.
Use low energy
welding process
Larger the tack weld size or number of tacks are more,
the weld distortion will be more. Use less tacks and
smaller size tacks, for flexibility. Use, if possible,
mechanical joint positioners.
If tacks are removed and rewelded, heat is added twice
and lead to more distortion.
Distortion is proportional to the amount of heat added
to complete the weld. So, use the welding process
which gives high energy and gives lesser heat to the
metal.
Manual welding is slow and may cause
defects/distortion. So, use mechanization to weld. This
will give higher weld rate and faster work completion
and will reduce distortion. Mechanization also gives
lesser defects.
Excess weld reinforcement, will increase distortion. To
follow smaller weld volume/reinforcement to reduce
Weld Distortion
Higher the current , higher the melt. Increase the speed
so that the heat will not spread to more areas and
cause distortion. Use high energy welding process, like
EBW, LAW. Distortion is inversely proportional to Heat
Energy of the process and heat transfer speed.
By JGC Annamalai
Weld reinforcement, meeting the
Code and User Requirements
Excess Weld reinforcement. It will
be a stress riser. This will cause excess
distortion and residual stresses, will not
Vessel&plate,
accesstotheInside
weldavailable
Narrow Gap Welding
Butt weld, with single
U-joint(Volume-0.7Vol)
Pipe,noaccessto
theInsideweld
V-joint(Volume-Vol), reference
Normal Practice
Improvement
30°to 35°
Bevel Angle=35 to 40°
Root Gap=
0 to 1.5 mm
Root Landing=
0.5 to 1.5mm
Pg.B3.1
1
1
1
1
4
4
8
8
1
26
Vol

Chapter-B4
No.
(1)
(2)
(a)
(b)
(c)
(d).
(e) Thermal Tensioning
or Heat Correction
Thermal tensioning is a corrective method, on
distorted objects. After study on the distorted objects,
suitable corrective method is applied to rectify the
Distortion.
Thermal tensioning is a corrective method, on
distorted objects. After study on the distorted objects,
suitable corrective method is applied to rectify the
Distortion.
Details and illustrations are found
in Chapter B5.
in Chapter B6.
Weld such that the center of a single weld or center of
group of welds are balanced or on the neutral axis.
Weld on the
Neutral Axis or
Balance the
Welding about the
Neutral Axis.
Forced cooling Carbon steel and low alloy steel are found to form
martensitic formation due to sudden cooling and which
may lead to hardening and crack. If allowed, controlled
cooling can be applied. On SS(Aus), the phase and
structure do not change, so, fast cooling(outside the
weld fusion area) can be applied, to control the
distortion.
Balance or Distribute
the Welding Heat about
the Neutral Axis
On long run welds, to distribute or balance the heat such that better distortion control can be
achieved/ residual stresses are reduced.
Action: The weld heat is distributed / scattered. The long welds need to be broken into many segments and sequence
finalized. Distribute the welding such that heat is spread or scattered and also the weld center line is spread about
structure Neutral axis.
Actions: Weld Joints: More the weld volume means, larger Distortion. So, (1). use double V Butt joints, instead of single V
joints. (2). Use J bevels instead of V bevels. (3). Use welding inserts. (more info found in Chapter 9a).
Remedies
The Distortion caused is because of welding Heat only`. Preventive weld distortion control is based on experience and taking
action, based on the study of the past or reverse action to Distortion. Ways to reduce Distortion and / or Residual Stresses are
given here,
To follow to reduce Weld Distortion / IllustrationsTechnique
To distribute or balance the heat such that better distortion control can be
achieved/residual stresses are reduced.
Smaller the volume of weld
metal, smaller the Distortion
Control of Distortion by Preventive Measures, Better Sequences
in Chapter B7.
in Chapter B8.
in Chapter B9.
Pre-setting From distortion experience on earlier job, one can
study / measure the distortion and find out counter
measures. Reverse distortion measures can create
counter action to the normal distortion.
Thermal Tensioning
or Heat Correction
C
H
By JGC Annamalai
Narrow Gap Welding
Pipe,noaccessto
theInsideweld
Vessel&plate,
accesstotheInside
weldavailable
Instead of Single V, use
double V or narrow U type
Grooves
Pg.B4.1
27
12

Chapter-B4 RemediesControl of Distortion by Preventive Measures, Better Sequences
C
H
By JGC Annamalai
Narrow Gap Welding
Pipe,noaccessto
theInsideweld
Vessel&plate,
accesstotheInside
weldavailable
Some of the Common Structures and their Preferred Assembly Welding Sequence for Distortion Control
(a). Manufacture of Box Section, from Channels: (b). Manufacture of H or I Sections, from Plates:
X' is welding on rear side
(c). Manufacture of Panel, made from plates / sheets: (d). Manufacture of Cylindrical shell, made from plates:
Sequence to fabricate all Cylindrical Shells:
(1). Fabricate, assemble and weld first,
the longitudinal(L) seams (1,2,3,4,5,6)
(2). Later, Fabricate, assemble and weld the
Circomferencial(C) Seams (7,8)
(3). Use strong backs, to control distortion, on L-seams
(4). Use spiders, inside, to control distortion on C-seams
(5). Install, nozzles, supports etc, on completion of C-seams
(follow the distortion control
methods, recommended earlier)
(d). Manufacture of Vertical Cylindrical shell,
made from plates / sheets:
Note: Basic Distortion Control Sequences, like:
Narrow Bevel angle, not excess welding, Back-step
welding, skip welding etc , should be followed during
assembly welding also.
Box Section
from Channel
Pad Plate
j
kl
m
Preferred Weld
Sequence-1,3,2,4
Bad Weld
Sequence-1,4,3,2
Poor Weld
Sequence-1,2,3,4
11
12
7
8
65 109
4
3
21
13
14
Preferred Weld Sequence - 1,2,1',2',3,4,3',4',5,6,5',6',
7,8,7',8',9,10,9',10',11,12,11',12',13,14,13',14'
WW'
4
15 1716
117
3
1312
8
1814
65
109
21
Preferred Weld Sequence - 1,2,3,4,5,6,7,8,9,10,
11,12,13,14,15,16,17,18
7
8
5 6
43
21
(for clarity, hidden view are not shown, by --- line
28

(3)
Presetting:
(b)
wc Precamber in the unloaded structural member
w1 Initial part of the deflection under permanent loads of the relevant combination of
actions according to expressions (6.14a) to (6.16b)
w2 Long-term part of the deflection under permanent loads
w3
wtot Total deflection as sum of w1 , w2 , w3
wmax Remaining total deflection taking into account the precamber
(c).
Back bending fillet
joints
Precambering
Beams: (creating an
intentional reverse
curvature)
This is a preventive method. Beams normally have deflection, due to dead load and live load and
moving load. Max. deflection is limited due to failure of ceramic tiles or cracking on surface or water
stagnation. So, beams of building floors, bridges etc are often pre-cambered (reverse curved) before
taking the load. On loading the structure will have deflection in the acceptable range
Additional part of the deflection due to the variable actions of
the relevant combination of actions according to expressions
(6.14a) to (6.16b)
When the one side fillet weld is completed, the included angle will reduce. If
the base is strong, the vertical will tilt. So the vertical plate, should have
reverse bending angle to counter the distortion
Floor deflection,
(1). L/250 max is for general purpose floors(to avoid surface cracks, tile cracks, water stagnation etc.
(2). L/1700 max is for high precision floors(eg. EOT crane rails)
Remedies
Distortion control by Pre-setting, is based on experience and taking counter action, based on the study of the past and counter
/ reverse action to Distortion control.
Anticipate Distortion
and take Counter
measures:
Presetting the fillet and butt welds. After weld completion, the distortion must be measured. On the
next similar welding, take counter measure such that the base metal is preset to counter the
distortion.
Control of Distortion by Preventive Measures (Presetting)Chapter-B5
By JGC Annamalai
Beam with Concrete Slab/Floor on Top
Pre-Cambered Beam
Pg.B5.1
29

No
.
(1)
1
(2)
.
(3)
(4)
.
(5)
Remedies
Chapter-B6
Most of the Shops, follow the Clamp down or Restraint method to control Distortion. Using this method, Distortion is
controlled.
Once clamp is removed, the residual stresses will be dominant and it is likely that the residual stresses will force the
object and distortion may return by spring back .
To control Residual Stresses, Stress Relieving(PWHT) should be followed, with all clamps/restraints, in place. Stress
Relieving is found to relieve 90% Residual Stresses.
Control of Distortion by Clamp Down or Restraining
Employ egg-
crate Type
This is similar to fixing boxed stiffeners / construction
Remove the
cut-outs
Fillet welds:
side supports
Use side gussets to support the plates or pipes with fillet
welds
If tacks welds are used, to reduce
distortion, they should be placed in a
sequence.
Tack-Weld
Employ
tooling /
fixtures
If the job is repeating, often, a special device for holding purpose or fixture (strong-back) is used.
(a). Root Tacks: Tack welds are used, to hold the joint in
position. There are two tack weld types.
(1). Tack welds are part of weld : Tacks will hold the
joint and it will be consumed, when the weld is in progress
and later, it will be part of main weld. So, the tack welds are
expected quality weld, without defects.
(2). Removable tacks: For critical services, Users do
not allow tacks, as part of the weld. It is considered as a
temporary weld to hold the joint. During root welding, when
approaching the tacks, the tacks are ground and new root
weld is made.
(b). Bevel Tack : There are also people, insisting that the
tacks should be made at the bevel area, with a solid bar
tacked or a bridge type tack is made at the bevel are. Both
tacks are removed as the welder approaches the tack weld
area for root welding.
(c). Tack welds are also used temporarily to hold the main
job by brackets or gussets or structures/strong-backs,
during welding
If cut-outs are planned on the area where welding also exists. Finish welding and then remove the cut-
outs.
Tack welds are placed in some sequence
so that distortion is reduced. (a), (b). (c)
are the some of the tack weld options.
By JGC Annamalai
Pg.B6.1
Weld
Tack Welds
Weld
GussetGusset
30

Anticipate Distortion and take Counter measures, based on study and experience :
No.
(1)
(2)
Example-1:
Example-2:
SS Welding:
Remedies
Technique
The Distortion is caused because of gradient welding Heat only. So, this chapter considers, how to take away the heat from
welding area and preventing it to travel into the base metal and thus not much affecting the base metal.
Control of Distortion by Preventive Measures - Forced CoolingChapter-B7
Many workshop cool the weld area (away from weld fusion
line), just after weld completion, by icing, by placing
copper plate sinks, wet cloths, by placing water tubes &
salt, etc.
Caution: Sufficient care should be taken, not to spill water
on the liquid weld puddle. It will create spatters or liquid
metal spill on the welders or people near-by and porosity
or crack. Cooling should be well away from fusion line.
On SS(Aus), the phase and structure do not change,
when we cool from Austenite phase to room
temperature, so, fast cooling(outside the weld fusion
area) can be applied, to control the distortion.
Hardness and ductility are also not changing.
Heat transfer on metals, is proportional to Time. If time is more the heat will spread to more area and
will cause more distortion. So, one of our aim to control distortion is quicker method of completing the
welding. Another way is to remove the welding heat, from welding HAZ area, without travelling into
the base metal. Additional Cooler or Sink, will take away the heat from HAZ area. Quantity of heat, in base
metal is less so it will not spread to more area and will not cause much distortion.
With controlled heating during SS welding, using heat sink, we notice the
following : (1). stainless steel welds are better and faster. (2). It discolors
(tint) less, (3). SS warps(distorts) less (4). Heating stainless steel surface in
the range 450 to 850°C will form Chromium Carbide(weld decay or
sensitization) and will lose its corrosion resistant properties. Heat sink will
control the heat in that range to the original . There will be less weld decay.
Carbon steel(CS) and low alloy steel(LAS) are found
to form martensitic structure due to fast/ sudden
cooling. This may lead to hardening and crack. If
allowed, controlled /slow cooling can be applied.
Stainless Steel
(Austenitic): Forced
cooling, during
welding is allowed,
Welding the joint of a flange joint. The weld area is cooled
by water in copper tube to control the distortion.
The Nuclear component(Fuel Rod Control) : 20 ft pipe
spool assembly set up was similar to a lathe machine.
The pipes are 5" & 4" OD with wall thickness 10mm.
Base metal is SS 304 and welded with SS 308L welding
rod.
The Welding and assembly related informations are
provided in the figure. Welding process is automatic
GTAW. The root was made using consumable welding
insert and 8 additional thin beads, to control limited
welding heat. The joint was argon gas purged and argon
gas used for GTAW shielding.
After completion of root pass and another 2 stabilization
passes, additional welding of the pipe was cooled from
inside, by water flow for dimensional control and for
sensitization control.
Requirement: The straight line alignment requirement of
the pipe assembly was 0.75mm over 20 ft length. This
was achieved by the above procedure.
To follow to reduce Weld Distortion Illustrations
Carbon Steel &
Low Alloy Steel.
No Forced cooling,
during welding.
By JGC Annamalai
Fast Cooling the Stainless Steel welding, phase does not change,
from Austenite to room temperature, refer Annex-2)
Pg.B7.1
31

No.
(1)
Remedies
Balancing the welds
or group of welds
about the Neutral
axis of the Structure
The Distortion or weld deflection or deviation
from normal drawing position is controlled by
placing welds center line or group of the weld
center line, at the Neutral axis or near to the
Neutral axis of the Structure.
After modification: Clockwise and anti-clockwise
bending moment at the weld , about the neutral
axis is equal or near equal and net bending
moment is zero. Practically, there is no
deflection or no distortion. (There may be
Distortion in Z-axis. This should be separately
studied and action taken.)
Chapter-B8 Control of Distortion by placing Welding about Neutral Axis
This chapter considers, Weld Distortion control by placing welding about or on Neutral Axis of the structure. Here, we try to
keep the weld group center on or near to Neutral Axis. The deflection or distortion causing moments due to welding are
getting cancelled and the structure is near free of Distortion.
By JGC Annamalai
Poor Good
(1). Modifying the weld groove and
placing the welds, about Neutral Axis,
results in no distortion
(2). Modifying the structure and placing the
welds, about Neutral Axis,
(3). Modifying the structure joint location and
placing the welds, about Neutral Axis,
(4). Modifying the bracket structure location
and placing the welds, about Neutral Axis,
. Pg.B8.1
32

(1)
(2)
.
(3)
(4)
.
(5)
(6)
This chapter discusses some of the Distorted objects and their correction by Heat.
Principle: When we apply heat in a band shape, on the back/reverse side, reverse thing to distortion happens. During cooling,
the tension or pulling the farther end from the weld occurs and this will straighten the object.
Objects / Illustrations
Thermal Tensioning is also called Heat Correction. Heated & corrected on the Convex side.
H beam,
bent
Tee joint:
Bent Plate
An I or H beam is bent into a Z shaped object. Heat
correction will straighten the flanges and web and make
as straight beam.
This is not welding case. This is cambered(heat & bend)
object. Thermal tensioning will straighten the cambered
object.(Cambering is a technique of bending a beam (by
heat or roller) to an arc shape)
Often, we find this in Boiler or heater wall panels. The box
section, surrounded by frame works often find a dishing/
buckling, due to welding. Heat correction will bring the
dished plate, as flat.
Rectangula
r box
constructio
n, corners,
lifted up
Often, we find this
in Boiler or heater
wall panels. The
box section,
surrounded by
frame works often
find a dishing/
buckling (lifting on
convex side), due
to welding. Heat
correction will bring
the dished plate, as
Boiler wall
Panel.
Lifting
inside the
frame
works(at
the weld
side).
A kink on
the edge of
the plate
Thermal Tensioning temperature - 60 to 650°C (dull red hot color). Temperature over 700°C, will result change in mechanical
properties.
Chapter-B9 RemediesCorrectionControl of Distortion by Thermal Tensioning & Mechanical Pressing
No. Some of the objects, being corrected with Thermal
Tensioning method
This is not welding case. The strip or slab
has a kink, due to handling or transport.
Heat correction at the kink area, straighten
the surface.
The rectangular box construction, shows the
opposite edges lifting. Heat corrosion brings
the surface in level
By JGC Annamalai
When heat from welding or gas torch is
removed, the material start cooling and
shrinking and this will create tension
from heated/ cooling areas and the
material will lift or bend. Analogy is to
Pg.B9.1
Heat Band, for correction workLegend -
OR
33
34

Chapter-B9 RemediesCorrectionControl of Distortion by Thermal Tensioning & Mechanical Pressing
By JGC Annamalai
33(7).
Heating Methods: Spot, line or wedge-shaped heating techniques can all be used in Heat correction of distortion.
(a).Spot Heating:
(b) Wedge Shaped heating
(c) Line heating
The following points should be considered/adopted when using thermal techniques to remove distortion:
(a). use spot heating to remove buckling in thin sheet structures
(b). other than in spot heating of thin panels, use a wedge-shaped heating technique
(c) use line heating to correct angular distortion in plate
(d) restrict the area of heating to avoid over-shrinking the component
{e) limit the temperature to 60° to 650°C (dull red heat) in steels to prevent metallurgical damage
(f) in wedge heating, heat from the base to the apex of the wedge, penetrate evenly through the plate
thickness and maintain an even temperature
Mechanical Straightening:
The following should be adopted when using pressing techniques to remove distortion:
(1). Use packing pieces which will over correct the distortion so that spring-back will return the component
to the correct shape
(2). Check that the component is adequately supported during pressing to prevent buckling
(3). Use a former (or rolling) to achieve a straight component or produce a curvature
(4). As unsecured packing pieces may fly out from the press, the following safe practice must be adopted:
- bolt the packing pieces to the platen
- place a metal plate of adequate thickness to intercept the 'missile'
- clear personnel from the hazard area
Most of the distortions in a small shop are corrected by mechanical press bending: One such reverse bending is shown
below:
Transient Thermal Tensioning(TTT), (similar to preheating):
Sudden temperature gradient is slowed down. Here, both sides of
welding at about 80mm(3")distance, heat is supplied by flame or
electrical heat and preheated to about 200°C.
Advantages are :
(1).The distortion can be reduced by TTT weld treatment
(2).Heating at 200 °C of TTT treatment is the most optimum to
reduce distortion
(3).The number of acicular ferrite can be improved by TTT weld
treatment
(4). Both mechanical properties and fatigue life time can be
upgraded by TTT weld treatment.
Pg.B9.2
Example-1 Example-2 34

Stress Relieving is also called, PWHT, Heat Treatment. The treatment is below A1 line and there is no grain/phase change.
Clamping or Restraining the welding area or the structure will limit the Distortion. However, it will result in Residual
stresses. Stress Relieving will give, reduction in Residual Stresses, up to 80%. When we heat, 600 to 700°C, the strains
are redistributed or relaxed. Recommended Procedure to be followed while heating/cooling/holding vessel for stress relieve
a Vessel/ structure/ pipe, to avoid unacceptable (a).Distortion, (b). Permanent Setting, (c). Structural Damages, (d).
Residual Stresses.
Uniform and gradual/ slow heating on the whole object, below A1 line, is done so that there will be no appreciable thermal
stress or strain.
ASME Sec VIII, Div-1, UCS-56:
Thermocouples:
Vessel: Sizes over 15 Ft(4.6m):
Thermocouples(TC) are to be installed, such
that the distance from one thermocouple to
another does not exceed 15 ft(4.6m) in any
direction. Install TC at all suspected places.
Local heating by electric coil bands, at the
butt welds of pipes, vessel nozzles etc:
minimum 4 thermocouples, at least one at the
bottom & one at the top
Heating Cycle:
Para-(d.1) The temperature of the furnace
shall not exceed 800°F(425°C) at the time of
the vessel or part is placed in it
(d.2). Above 800°F(425°C), the rate of heating
shall be not more than 400°F/hr(222°C/hr)
divided by the max. metal thickness of the
shell or head plate in inches, but in no case
more than 400°F/hr(222°C/hr; During the
heating period, there shall not be a greater
variation in temperature throughout the
portion of the vessel being heated than
250°F(120°C within any 15 ft (4.6m) interval
of length.
Holding or Dwelling:
During holding period there shall not be a
greater difference than 150°F(83°C), between
the highest and lowest temperature
throughout the portion of the vessel being
heated, except where the range is further
limited in Table UCS-56.
(The rates of heating and cooling need not be
less than 100°F/hr(56°C/hr). However, in all
cases consideration of closed chambers and
complex structures may indicate reduced
rates of heating and cooling to avoid structural
damage due to excessive thermal gradients.)
Cooling Cycle:
Above 800°F(425°C) , the cooling shall be done in a
closed furnace or the cooling chamber at a rate not
greater than 500°F/hr (280°C/hr). From
800°F(425°C) to room Temp., the vessel may be
cooled in still air.
Local Butt Joint: ANSI B31.1,3,4 etc. codes allow,
local stress relieving. Here local means, full
circumferential(360°) joint at Site, as a belt.
Nozzle joint : Nozzle may be locally stress relieved,
provided, full circumferential belt with the nozzle, is
also included in the set up.
RemediesChapter-B10 CorrectionStress Relieving or PWHT per ASME Codes
By JGC Annamalai
Pg.B10.1
Temperature
Time
800 F(425 C)
1100 F(600 C)
(normally 1 hr holding per 1" tk)
Heating Rate
max.400 F/hr
(222 C/hr)
Cooling Rate
max.500 F/hr
(280 C/hr)
Room Temperature
During Holding, max. difference
150 F (83 C),at any two points
on vessel
Furnace
Heating/Cooling
Install thermocouples at all suspected locations
(max. separated length, 15 ft, (4.6m))
(Typical ASME Stress Relieving(PWHT) Cycle)
(Furnace Heating, min. recorded PWHT cycle. 2.35 Hr)
35
36

RemediesChapter-B10 CorrectionStress Relieving or PWHT per ASME Codes
By JGC Annamalai
Temperature
Time
800 F(425 C)
1100 F(600 C)
(normally 1 hr holding per 1" tk)
Heating Rate
max.400 F/hr
(222 C/hr)
Cooling Rate
max.500 F/hr
(280 C/hr)
Room Temperature
During Holding, max. difference
150 F (83 C),at any two points
on vessel
Furnace
Heating/Cooling
Install thermocouples at all suspected locations
(max. separated length, 15 ft, (4.6m))
35
Plot of 0.2% proof stress Vs Temperature :
Soaking(Dwelling or Holding) Temperatures for some of the Steel Materials :
Carbon steel (max.0.35% C)
Carbon–1/2% Mo steel
1/2% Cr–1/2% Mo steel
1% Cr–1/2% Mo steel
1 1/4% Cr–1/2% Mo steel
2 1/4% Cr–1% Mo steel
5% Cr–1/2% Mo (Type 502) steel
9% Cr–1% Mo steel
12% Cr (Type 410) steel SS410
16% Cr (Type 430) steel SS430
1 1/4% Mn–1/2% Mo steel
Low-alloy Cr–Ni–Mo steels
2–5% Ni steels
9% Ni steels
Quenched and tempered steels
Austenitic Stainless Steel
Typical Thermal Treatments
(Stress Relieving of Weldments)
705–760
705–770
705–770
705–760
Soaking
Temperature
(°C)
705–760
620–730
595–720
595–720
595–680
400 to 430
540–550
550–585
595–650
595–680
605–680
760–815
760–815
705–760
Material(Base-Metal & Welding)
(AWS HB, Vol-1)
Grade
Pg.B10.2
TimeRoom Temperature
36

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