2. CONTENTS
Introduction: Distortion in Welding
Significance of Material Properties
Influence of Welding Processes & Procedures
Types of Welding Distortions
Welding Suitability Index based on Distortion
Measurement of Distortion
Control of Distortion in Weldments
Correction of Distorted Weldments
Future Scope in Measuring Weld Distortions
2
3. Introduction: Distortion in
Welding
Q. What is Distortion ?
Any unwanted physical change or departure from
specifications in a fabricated structure or component, as
a consequence of welding
Figure: Distortion in Sheet due to Welding Figure: Simulation for T-Joint Welding
3
4. Introduction: Distortion in
Welding
Main Causes of Distortion
Non-Uniform Expansion and Contraction, i.e. Shrinkage
due to plastic thermal strain, of the weld metal and base
metal during the heating and cooling cycle
Internal stresses formed in base metal due to removing
restraints given to welds by fixed components surrounding
it
So, both Welding processes & procedures and Material
properties
affect the extent of distortion
Effects of Distortion:
Complicate further fabrication
Reduced application of the structure
4
5. Significance of Material
Properties
5
Properties of Materials Effects
(Requirements for Less
Distortion)
Coefficient of Thermal
Expansion (α)
Lower coefficient of thermal expansion
Thermal Conductivity (K) High Thermal Conductivity leads to low
thermal gradients
Yield Strength (ơy) Lower the yield strength of the parent
material, lower the residual stresses causing
distortions
Modulus of Elasticity (E) Higher the Modulus of Elasticity (stiffness) of
the parent material
6. Influence of Welding Processes &
Procedures
6
Factors affecting
Volume of Heated
Metal
Effects
(Requirements for Less
Distortion)
Welding Processes •Concentrated heat source
•High welding speeds
•Deep penetration
•Single Pass Welding, Least Weld runs
Amount of Weld Metal •Minimum amount of weld metal
Welding Speed Maximum Welding speed Minimizes heat
spread and built-up, Solidification of weld
metal should be controlled
Edge Preparation and Fit-
up
Uniform Edge Preparations to allow consistent
shrinkage along the joint, Close Fit-Ups
Welding Procedure • Mechanised, Single Pass, High Speed
9. Longitudinal Shrinkage
9
Shrinkage in the direction of the weld axis
Cause:
Preheat or fast cooling problem
Shrinkage stresses in high constraint areas
Prevention:
Weld toward areas of less constraint
Weld short length
Also preheat to even out the cooling rates
Straightening press, jacks, clamps should be
used
Figure: Longitudinal
Shrinkage
10. Longitudinal Shrinkage
10
Butt Welds
• ẟL= longitudinal shrinkage, mm
• I = welding current, amps
• T = length of the weld, mm
• t=plate thickness, mm
Fillet Welds
• ẟL = longitudinal Shrinkage
• Aw = Cross-sectional area of the weld metal
• Ap = Cross-sectional area of the resisting structure
Figure: Butt Joint
Figure: T-joint with two fillet
welds
11. Transverse Shrinkage
11
Shrinkage running into or inside a weld, transverse to the weld axis
direction
Cause: Weld metal hardness problem,
Constraints applied to weld-joints
Figure: Transverse
Shrinkage
Butt Welds :
ẟt = transverse Shrinkage
∆w = Cross-sectional area of weld,
mm2
t = plate thicknes, mm
Figure: Butt Joint
12. Transverse Shrinkage
12
Fillet Weld :
For a T-joint with two fillet welds :
ẟt = transverse Shrinkage
l= leg of fillet weld, mm
t = plate thickness, mm
For fillet weld(s) in Lap Joint :
ẟt = transverse Shrinkage
l= leg of fillet weld, mm
t = plate thickness, mm
Figure: T-joint with two fillet
welds
Figure: Fillet weld in Lap Joint
13. Longitudinal Vs Transverse
Shrinkage
13
Longitudinal Shrinkage Transverse Shrinkage
Butt
Welds
• 3mm per 3m of weld • 1.5 to 3mm per weld for 60°
V joint, depending on number
of runs
• Amount of transverse shrinkage in a butt weld is much more (i.e.
1000th times of the weld length) than the longitudinal shrinkage
Fillet
Welds
• 0.8mm per 3m of weld • 0.8mm per weld where the
leg length does not exceed 3/4
plate thickness
• Increasing the leg length of fillet welds increases shrinkage
14. Angular Distortion
14
Weld tends to be wider at the top than
the bottom, causing more solidification
shrinkage and thermal contraction
For Double-V Edge Butt weld-joint, it
depends upon root face and root gap
Fillet weld-joints, it depends upon
flange width, weld leg length and
flange thickness
Depends Upon :
Width and depth of fusion zone relative
to plate thickness
Type of joint
Weld pass sequence
Thermo-mechanical material properties
Heat input per unit length of weld,
Figure: Angular Distortion in Butt Weld-
joint
Figure: Angular Distortion in Fillet Weld-
Joint
15. Angular Distortion
15
Occurs at butt, lap, T, corner joints due to single-sided as well as
asymmetrical double-sided welding
Prevention:
Reducing volume of weld metal
Using double-V joint and alternate welding
Placing welds around neutral axis
Presetting: By compensating the amount of distortion to occur in
welding
Elastic pre-springing can reduce angular changes after restraint
is removed.
Preheating and post weld treatment
16. Bowing or Longitudinal
Bending
16
A = cross-sectional area of the weld,mm2
d = distance from C.G. to outermost fibre, mm
L = length of the weld, mm
I = Moment of Inertia of the section, mm4
Figure: Longitudinal Bending
Weld line does not coincide with neutral axis of a weld
structure
Longitudinal shrinkage of the weld metal induces bending
moments
Amount of distortion depends on :
Shrinkage moment
Resistance of the member to bending
17. Rotational Distortion
17
In this, sheets being butt welded either come closer to each other or
the distance between them is widened
Depends upon:
Thickness of parent material
Temperature difference between a molten pool and the unheaten parent
material (difference in heat flow)
Speed of Welding,
Heat Source
Figure: Rotational Distortions
18. Rotational Distortion
18
Progressively welding
material at
widely different heat inputs
Expanding & Contracting Zones in
arc butt welding
Here, Manual welds are termed as slow welds, while Automatic
welds are termed as fast welds
19. Buckling Distortions
19
When thin plates are welded, considerable residual stresses occur in
areas away from the weld and cause “Buckling”
Occurs when Specimen Length exceeds the Critical Length for a given
thickness
Amount of deformation of Buckling distortion is much greater than that
in Bending
Buckling due to welding of a panel increases directly as the thickness
decreases
Figure: Bucking Distortion Figure: Relationship for buckling
distortion of butt weld for different
20. Twisting Distortions
20
When a weld is made along the centre
of a member, the weld area tends to
shrink and become shorter
To satisfy the conditions of a member that
has outer edges longer than its centreline,
the member must twist
Twisting is the due to low torsional resistance on thin
materials
21. Buckling And Twisting
21
Prevention:
Minimize Shrinkage by decreasing volume of weld
metal and highest compatible speed
Keep the length of the welded member as short as
practical
Incorporate torsional resistances to twisting as much
feasible
22. Welding Suitability Index
22
Welding Suitability Index based on Distortion
(λƐ)
where,
Tm, a, α, E, ơy, refers to material under consideration
Tm*, a*, α*, E*, ơy
* refers to those of reference material
Tm: Melting Temperature, (°C)
a : Thermal Diffusivity, (mm2 / sec)
α : Thermal Expansion, (1/°C) *10-6
E : Elastic Modulus, (kN/mm2)
ơ : Yield Limit, (N/mm2)
23. 23
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5 6 7 8
Welding Suitability Indices in
Distortion
Welding Suitability
Indices in Distortion
Base Metal
Melting
Temperature,
Tm (°C)
Thermal
Diffusivity, a
(mm2 / sec)
Thermal
Expansion, α
(1/°C) *10-6
Elastic
Modulus, E
(kN/mm2)
Yield Limit,
ơy, (N/mm2)
Welding
Suitability
Indices in
Distortion
Low Alloy Steel 1520 7.5-9.5 11 210 200-700 1
High Alloy Steel 1400 5.0-7.5 16 200 250-550 0.86
Aluminium Alloy 600 75-100 24 65 80-280 0.01
Titanium Alloy 1800 6 8.5 110 500-700 1.08
Copper Alloy 1080 120 18 130 30-420 0.02
Nickel Alloy 1435 15 13 215 120-630 0.43
24. Measurement of Distortion
24
Distortion in the post weld cooled state is determined by
applying length and angular measuring techniques
Transverse and Longitudinal Shrinkage are determined by
Measuring Tape
Angular Shrinkage is measured on a measuring plate by
means of straight edge set agaisnt the component (as shown
in below figure)
Figure: Measuring Longitudinal
& Transverse Shrinkage
Figure: Measuring Angular Distortions
25. Measurement of Distortion
25
Measuring Bending or Angular Distortion
Figure: Measuring Angular Distortions or
Bending
Figure: Measuring Angular Distortions
Figure: Measuring Bending
26. Measurement of Distortion
26
Circumferential
measurements on spherical
and cylindrical shells are
performed by string wrapped
around the structure
Vertically extended
components, e.g. Pillars,
supports and tank walls,
inclinations and deflections
are measured by means of
strings hanging exactly
vertically and tensioning
weight immersing in water
Figure: Distortions in Circumferential Figure: Distortions in vertically Extended
27. Measurement of Distortion
27
Linear Variable Differential Transformer (LVDT)
Figure: LVDT set-up with Workpiece
Dimensions
Figure: Anticipated displacements
Figure: Measured results (FEM vs LVDT)
28. Measurement of Distortion
28
Small Scale Distortions using a Stereoscopic
Video Imaging system
Figure: 3d deformation measurement using a stereoscopic video imaging
system
29. Control of Distortion in
Weldments
29
Welding Residual stresses and Welding Distortion behave in
a contrary way
Least root gap:
As small as possible, but sufficient for good penetration
Excessive gaps should be avoided
Included angle should not exceed 60°
For heavy sections, double-V preparation should be preferred
30. Control of Distortion in
Weldments
30
Tack Welding
Sufficiently long tack welds
transmit shrinkage forces
Tack weld length should be
two-three times the plate
thickness
Preheating, slag removal and
further defect removal
methods are employed to
counter undesired
phenomenon due to tack weld
Narrow Groove Section in
Welding
Least as possible to produce least
heat concentration
U shape groove is preferable than
Vee shape
Symmetrical weld groove reduces
angular shrinkage, but residual
stresses are increased
Double-sided fillet weld is selected
over single-sided fillet weld
31. Control of Distortion in
Weldments
31
Direction of Welding :
Away from the point of restraint and towards the point of maximum
freedom
Weld Metal Deposited :
No excess metal should be deposited
Block Sequence and Cascade Sequence :
To deposit long welds of high thickness
Layer deposited until the effective throat thickness is achieved
Figure: Block
Sequence
Figure: Cascade
Sequence
32. Control of Distortion in
Weldments
32
Welding Sequnce :
For large surface area consisting of several
plates, transverse seams should be welded
first followed by longitudinal seams
In welding I- or H- beam joints within each
web plate and flange are to welded first,
followed by butt joints between web plates
and flanges of a beam
Figure: Welding Sequence
for large plates
Figure: Welding Sequence for I or H Beam
33. Control of Distortion in
Weldments
33
For cylindrical vessel, longitudinal seams
should be welded first, followed by the
circumferential seams
In welding frames of different length and thicknesses, least
distortionwould result if weld 1 & 2 are done simultaneously followed by
3 & 4, as shown in given figure
Figure: Welding Sequence for cylindrical
vessel
Figure: Various Welding
Sequence for Welding
Frames
34. Control of Distortion in
Weldments
34
Back- Step Welding Sequence :
Measure to counteract the wedge shaped-opening and closing(rotational
distortion)
Reduces transverse and longitudinal shrinkage
Used widely in fabrication of large structures, such as ships, storage
tanks
Figure: Back-Step Welding Sequence
35. Control of Distortion in
Weldments
35
Counter or Opposing Set-up
Figure: Warpage in a T-beam and
Suggested Counter setup
Figure: Counter Set-up for Angular Distortion
36. Control of Distortion in
Weldments
36
Distortion control in Thin Plates and Sheets
Used in light gauges
Copper abstract heat from weld
reducing heating and warpage or
buckling of the plates
Water-cooled jig, Copper Clamps,
Copper tubes used
Figure: Water Cooled Jig for rapid removal of
heat to control distortion in welding shheet
metal
Fixing :
Fixing parts, to be joined by welding, in a frame or rigidly as possible
To reduce back-spring shrinkage
37. Correction of Distorted
Weldments
37
If a weldment warps despite the precautions taken, there are
ways and means of correcting the defect using one of the
following two methods:
Methods for Correction of
Distorted Weldments
Mechanical
Methods
Presses, Jack Screws
, Straightening Rolls,
Sledges, Special
Fixtures
Thermal
Methods
Oxy-
acetylen
e torch
Carbon
Arc
Powerful
oil or
gas
burners
38. Future Scope
38
Artificial Neural Networks used to measure the distortion
more precisely
Mechanised techniques with proper simulation can give
least distortion in the welded product
39. References
39
R. S. Parmar, Welding Engineering and Technology, Khanna
Publishers, 2010
Zhili Fen, Processes and mechanisms of welding residual
stress and distortion, 2005, Pg 209-216
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