Welding

An Overview

Introduction
Topics that will be covered
1. Welding process
A Brief Overview
2. General welding information
Types Of Welds And Weld Symbols
3. Design of welds
Selection of weld type : Basic Guidelines
Designers Guidelines to Welding Economics
4. Frequently Asked Questions Related To Welding
(c) Tanusree Chakraborty

Introduction
Topics that will NOT be covered
1. Welding Metallurgy
2. Defects of Welding
3. Testing of Welds and WPS

(c) Tanusree Chakraborty

Welding process
A Brief Overview

(c) Tanusree Chakraborty

What is welding?

Welding is a fusion process, in which metal parts are

heated to the melting point and fused together, usually
with a filler of the same material melted alongwith the
parent material.
(c) Tanusree Chakraborty

General welding information

Types Of Welds
and
Welded Joints

(c) Tanusree Chakraborty

Types Of Joints
Lap Joint

Corner Joint

Butt Joint

Edge

Tee Joint

(c) Tanusree Chakraborty

Types Of Weld
1. Fillet weld

2. Butt or Groove weld

3. Plug weld

4. Slot weld
(c) Tanusree Chakraborty

Fillet Weld 1

Basic features

Generally shaped like a right-angular triangle in

cross- section

Most commonly used

Can be loaded in any direction in shear,

compression or tension

Irrespective of the direction, the applied loading

always acts as shear force on the weld

The failure plane of the weld is through the

throat of the weld.

(c) Tanusree Chakraborty

Fillet Weld 2

Components of Fillet Weld

(c) Tanusree Chakraborty

Fillet Weld 3

Single sided

Double sided

Intermittent

(c) Tanusree Chakraborty

Butt or Groove Weld 1

Basic features

Much stronger than fillet weld

Strength of the joint using full penetration butt

weld is better than the parent material.

In design, the strength is considered to be the

same as the parent material.

Single-V butt joint is not recommended for use

when subjected to bending at the root.

The failure plane of the weld depends on the

relative strength of the plate and weld material

(c) Tanusree Chakraborty

Frequently ask ed questions 1

Why is butt weld stronger than fillet?
Stress flow in Butt weld

Stress flow in Fillet weld

Transverse Fillet weld

Longitudinal Fillet weld

(c) Tanusree Chakraborty

Frequently ask ed questions 1

Why is Full Pen weld stronger than the parent metal?

Properly deposited welds are much stronger than even the parent
metal (with matching electrodes) for the following reasons :
Superior specification of electrode material
Controlled welding process leading to uniformity in weld
metal texture

(c) Tanusree Chakraborty

Butt or Groove Weld 2

Components of Butt Weld

(c) Tanusree Chakraborty

Butt or Groove Weld components

Groove
angle

Root
face

Butt or Groove Weld 3

Single & Double / Full or partial penetration welds

Beveled

Square

Partial
Penetration
(c) Tanusree Chakraborty

General welding information

Weld Symbols

(c) Tanusree Chakraborty

Weld symbols General

(c) Tanusree Chakraborty

Weld symbols Fillets

1. Fillet weld

Single sided

Double sided

Intermittent

(c) Tanusree Chakraborty

Weld symbols Full Pen

2. Full Pen (Butt) weld

Single & Double / Full or partial penetration

(c) Tanusree Chakraborty

Weld symbols Other

3. Other weld symbols

(c) Tanusree Chakraborty

Weld symbols Points to remember

Inclined line is always on the right

Flag to face away from the arrow

Arrow to always point the beveled surface

(c) Tanusree Chakraborty

Design of Welds
Selection of weld type :
Basic Guidelines

(c) Tanusree Chakraborty

Suitability of weld types1

Factors to be considered in determining the suitability of welds: Strength and safety requirement
Type of loading (comp, tension, fatigue, bending)
Application of loading (static, dynamic)
Cost of preparing the joint
Type of joint & joint efficiency

(c) Tanusree Chakraborty

Suitability of weld types2

Joint efficiency
o
o

Ratio of strength of the joint to the strength of the base metal

The most efficient joint is the one which is just as strong as the
base metal

Suitability of weld types Fillet weld

Fillet Weld
Strength and safety requirement
o Strength assessment of weld is necessary for connection design.
o Due to lack of quality assurance, cannot be trusted for important joints
Type of loading (comp, tension, fatigue, bending) & application of loading (static,
dynamic)
o For fatigue condition, strength assessment of weld is extremely important.
Cost of preparing the joint
o No joint preparation is necessary; Only proper fit-up is required
Joint efficiency
o

Depends on design. Full strength joints using fillet weld are mostly
uneconomic.
(c) Tanusree Chakraborty

Suitability of weld types Full Pen

Full-penetration Butt Weld

o
o
o
o
o
o
o

Strength and safety requirement

For joints having higher degree of importance. E.g. Moment connection
Single-V butt welds are not advisable for bending at the root.
Type of loading (comp, tension, fatigue, bending) & application of loading (static,
dynamic)
Double beveled Butt joint is suitable for all types of loading as mentioned above
Cost of preparing the joint
Groove preparation and fit-up is expensive and time consuming.
Material wastage (run-on/run-off plates)
Skilled welders are necessary
Joint efficiency
Joints are very efficient
(c) Tanusree Chakraborty

Suitability of weld types Partial-Pen

Partial-penetration Butt Weld
Strength and safety requirement
o Strength assessment of weld is necessary as this is not a full-strength
connection
o Effective for section building, field splices etc.
Type of loading (comp, tension, fatigue, bending) & application of loading
(static, dynamic)
o Not preferred for fatigue, cyclic or dynamic loading.
Cost of preparing the joint
o Groove preparation cost is less compared to full-pen butt.
Joint efficiency
o Depends on design.
(c) Tanusree Chakraborty

Design of Fillet Welds :

Guiding Weld Dimensions
: Size, Length, Clearance

Allowable Stresses

(c) Tanusree Chakraborty

Design of Fillet Weld 1 : sizes of welds

Maximum and Minimum sizes

Maximum Minimum Size of Fillet Welds
Thickness of Thinner Part
Inch
To 1/4" Inclusive
Over 1/4" To 1/2" (Inclusive)
Over 1/2" To 3/4" (Inclusive)
Over 3/4"

Minimum Weld
Size
Inch
1/8
3/16
1/4
5/16

Maximum Weld Size

Inch
Plate thickness

Plate thickness 1/16

(see note)

Note: Unless the weld is specially designated on the drawings to be built out to full
throat thickness
1/16

(c) Tanusree Chakraborty

Frequently asked questions 2

Whats wrong with oversized welds

Oversized welds leads to increase of weld metal

without any considerable increase in the strength.
If avoided, it is possible to achieve faster welding
speed
Excessive distortion and other unnecessary welding
heat related problems (e.g. lamellar tearing etc).
These sizes require more unnecessary weld passes,
with a subsequent increase in preparation, welding,
and finishing time.
(c) Tanusree Chakraborty

Frequently asked questions 3

Whats wrong with undersized welds ?

Development of initial stress due to differential

contraction of base and weld metal.
Development of cracks.
Slow cooling leading to excessive hardness, lowered
ductility and brittle weld structure.
Increased chances of slag trapping and hydrogen
induced cracking.
(c) Tanusree Chakraborty

Design of Fillet Weld 2 : min length of

weld
Effective Length (Leff)
Length of the weld having the specified size and throat thickness.
Minimum Length of longitudinal weld
Minimum length of longitudinal weld
= 4 x Leg size of weld.
LD
& D < 16 x thickness of thinner plate in the joint
Or 200mm whichever is less
else supplemented by slot or transverse weld
(c) Tanusree Chakraborty

Frequently ask ed questions M in L

Why is there minimum lap length restriction?

Fig-1

Fig-2

Minimum length of lap = 5 x thickness of thinner plate

or 25mm whichever is greater
Read J2.2 b
Spacing between longitudinal welds
(c) Tanusree Chakraborty

Frequently asked questions LD

Why should L be greater than or equal to D?

(c) Tanusree Chakraborty

Design of Fillet Weld 3 : Max. length of

weld
Maximum Length of longitudinal weld (AISC J2.2b )
If weld length L < 100 x leg size of weld,
effective weld length, Leff = L
If weld length L < 300 x leg size of weld,
Leff = L (1.2 - 0.002 x L/weld size)
If weld length L > 300 x leg size of weld,
Leff = 0.6 x L
(c) Tanusree Chakraborty

Design of Fillet Weld 4 : weld

terminations
Weld terminations (AISC J2.2b )
Fillet welds terminate at a distance > leg size of weld from the
edges
Weld return around corners > 2 x leg size of weld
Flexible connections return length < 4 x leg size
While welds are in different
plane around a plate, corners
should not be tied together

(c) Tanusree Chakraborty

Design of Fillet Weld 6 : allowable

stresses
Shear on effective area (Table 2.3, AWS D1.1-96 )
0.3 x Nominal tensile strength of filler metal (FEXX)
(Table 2.3, AWS D1.1-96 )
0.3 x FEXX x ( 1.0 + 0.5 sin 1.5 )
Where, = angle of loading measured from the
weld longitudinal axis in degrees
(Clause 2.14.4, AWS D1.1-96 )
Also see Clause 2.14.5, AWS D1.1-96, for weld group
subjected to in-plane loading analyzed using an
instantaneous centre of rotation method
(c) Tanusree Chakraborty

Design of Fillet Weld 7 : other cases

Skewed fillet welds
Allowable stresses as per
Table 2.3, AWS D1.1 -96 )
Effective throat, and hence
load capacity, is a function
of the dihedral angle.
Z-loss is considered for
< 60o
For < 30o, the acute side
weld is ignored

(c) Tanusree Chakraborty

Design of Full Pen (Butt) Welds :

(c) Tanusree Chakraborty

Design of Butt Weld 1 : full-pen butt

welds
Effective throat
Thickness of thinner plate
in series connection

Thickness of plate joined

in T- joint

Design of Butt Weld 2 :

max. allowable plate thickness

Maximum plate thicknesses (te)

Square butt

1/4 with or without backing strips

1/8 without root opening

V-butt single

3/4 without backing strips

Unlimited with backing strips

V-butt double

Unlimited
with or without spacer bar

Bevel-butt single

3/4 without backing strips

Unlimited with backing strips

Bevel-butt double, J & U Unlimited

(c) Tanusree Chakraborty

Design of Butt Weld 3 : partial-pen butt

welds
Effective throat thickness (te)
= chamfer
for beveled weld with
included angle (IA) > 60o,
and all J and U profiles
= (chamfer 1/8)
for 45o < IA< 60o
Minimum effective throat =

tp
6

where, tp = thickness of
plate (thinner)
(c) Tanusree Chakraborty

Design of Butt Weld 4 :

partial-pen butt welds reinforced with fillet welds
Effective throat
If w (t-1/8)
te= 0.707 x ( t 1/8 + w )
If w (t-1/8)
te=

2
t
+
w

Note: dimensions are in inches

(c) Tanusree Chakraborty

Design of Welds:
Slot / Plug / Intermittent

(c) Tanusree Chakraborty

Design of Slot / plug Weld 1 :

Design Criteria
Design shall be based on shear in the plane of
faying surfaces
Slot weld is not allowed for quenched and
tempered steel.
L
Plate thickness = tp
W
Stra

Slon

(c) Tanusree Chakraborty

Design of Slot / plug Weld 2 :

L

Design parameters
1 Minimum Spacing
(ref. 2.5.3 AWS D1.1-96)
2 Length & Width of Slot
(ref. 3.10.2 AWS D1.1-96)

Plate thickness = tp

Stra

>4xW

Slon

>2xL

W
Stra

Slon

L > 10 x tp
W < tp + 8 mm
W > min W + 3 mm
W > 2.25 x tp

3 Depth of Filling (d)

(ref. 3.10.3 AWS D1.1-96)

4 Slot ends
(ref. 2.5.4 AWS D1.1-96)

d = tp
d > 0.5 x tp
d > 15.875 mm
i) Semicircular
ii) R < tp

if tp is < 15.9 mm
if tp is > 15.9 mm

No bend on slot for the ends extending to the edge of the part.
5 Effective Area
(ref. 2.5.1 AWS D1.1-96)

Nominal area of slot in the plane

of faying surfaces
Allowable weld stress = 0.4 x Fy
(c) Tanusree Chakraborty

Design of Intermittent Weld 1 :

Max. length of weld
Maximum Clear Spacing (C)
For weld in tension,
C = min of (24 x thickness of thinner plate) OR 12
For weld in compression,
C = min of (4000*tthinner)/root over sigma y OR 12
For intermediate stiffeners,
C = min of (16*tweb)/ OR 10
(c) Tanusree Chakraborty

Design of Welds:
Special Attentions

(c) Tanusree Chakraborty

Welding Positions 1
FLAT

HORIZONTAL

(c) Tanusree Chakraborty

Welding Positions 2
VERTICAL

OVERHEAD

(c) Tanusree Chakraborty

Special attention1: Inaccessible

welds

Inconsistent and inferior weld quality

Stuck weld
Undersized weld
Mislocated /edge welds
Distortion
2. min= 30o

2. Not recommended

1. Prohibited

Frequently asked questions

Why overhead welding is not preferred?

Slag entrapment
Working against gravity
Awkward stance of the welder
Chances of inferior weld quality
Safety hazard

(c) Tanusree Chakraborty

Reserve strength of weld

Back-pocket Factors for hidden strength

In calculation of throat thickness

o Direction of loading - longitudinal / transverse

For transversely loaded welds, the strength is about 50%
higher than the theoretical value for longitudinal welds.
o Deep root penetration using SAW
Throat = leg size if fillet size is 3/8 inch
= (0.707 x leg size + 0.11 inch) for > 3/8 inch
(c) Tanusree Chakraborty

Frequently ask ed questions

Why is transverse fillet weld stronger than
longitudinal fillet weld?

Stress flow in Fillet weld

Transverse Fillet weld

Longitudinal Fillet weld

(c) Tanusree Chakraborty

Reserve strength of weld 2

Back-pocket Factors for hidden strength contd

In calculation of weld strength :
Properly deposited welds have a tremendous reserve of strength or
factor of safety, far beyond the industry specifications usually
recognize, for the following reasons
Superior specification of electrode material
Complete shielding of metal during welding
Controlled welding process leading to uniformity in weld metal
texture

(c) Tanusree Chakraborty

Welding Economics:
And other points to ponder

(c) Tanusree Chakraborty

Welding Economics for Design Engineers

Summary of welding economics

(c) Tanusree Chakraborty

Positive aspects of welded connection

As compared to bolted connection:
Fully Rigid connections are possible
Economical
Connection of tubular members possible
Quicker process
Efficiency of joint is improved
Better aesthetics
Alterations are easier

(c) Tanusree Chakraborty

Negative aspects of welded connection

As compared to bolted connection:
Proper fit-up is essential for a built-up member and also for
a sound connection
Distortion of members due to heat leads to misalignment
Possibility of brittle failure
Inspection is expensive but mandatory for primary members
with high importance weightage.
More skilled person is required to make a welded joint.
For field connection , welded joints are not recommended
for less allowable strength and possible power supply
problem
(c) Tanusree Chakraborty

SUMMARY-1

Check list of items influencing weld capacity

Welding position
Welding process
Geometry of groove in butt welds
Welding current and travel speed of electrode
Proper fit-up
Skill of welders

(c) Tanusree Chakraborty

SUMMARY2

Some points to remember

Maximum size of weld in a single pass = 8mm (GMAW), and
12mm using tandem arc welding
UNO, the allowable stress increase factor on welded
connection is 25% (not 33%)
Volume of weld is proportional to square of its leg size
The leg size of a weld can be optimized by using SAW, because
of the greater root penetration
For T-joints on thicker plates, double fillet weld is proffered to
avoid lamellar tearing

(c) Tanusree Chakraborty

SUMMARY3
Some points to remember
Single-V or single bevel weld w/o backing strip is
considered as prohibited in primary member connections
as per AWS.
Fillet welds less than 3/16 (5mm) is prohibited in primary
members.
Bearing type bolted connection is not to be supplemented by
weld to transfer load . Welds in slip-critical connection is
allowed.

(c) Tanusree Chakraborty

THE END

Presented By
Tanusree Chakraborty
(c) Tanusree Chakraborty