Section 2
Section 2
Section 2
Brazing
A process of joining generally applied to metals in which, during or after
heating, molten filler metal is drawn into or retained in the space between
closely adjacent surfaces of the parts to be joined by capillary attraction. In
general, the melting point of the filler metal is above 450C but always below
the melting temperature of the parent material.
Braze welding
The joining of metals using a technique similar to fusion welding and a filler
metal with a lower melting point than the parent metal, but neither using
capillary action as in brazing nor intentionally melting the parent metal.
Joint
A connection where the individual components, suitably prepared and
assembled, are joined by welding or brazing.
Weld
A union of pieces of metal made by welding.
Welding
An operation in which two or more parts are united by means of heat, pressure
or both, in such a way that there is continuity in the nature of the metal
between these parts.
WIS5-90516b
Terms and Definitions 2-1 Copyright © TWI Ltd
Table 2.1 Joint types, sketches and definitions.
Type of Sketch Definition
joint
WIS5-90516b
Terms and Definitions 2-2 Copyright © TWI Ltd
2.1 Types of weld
2.1.1 From the configuration point of view (as per 2.2)
In a butt joint
In a corner joint
Autogenous weld
A fusion weld made without filler metal by TIG, plasma, electron beam, laser or
oxy-fuel gas welding.
Slot weld
A joint between two overlapping components made by depositing a fillet weld
round the periphery of a hole in one component so as to join it to the surface of
the other component exposed through the hole.
WIS5-90516b
Terms and Definitions 2-3 Copyright © TWI Ltd
Plug weld
A weld made by filling a hole in one component of a workpiece with filler metal
so as to join it to the surface of an overlapping component exposed through the
hole (the hole can be circular or oval).
Heterogeneous
Welded joint in which the weld metal and parent material have significant
differences in mechanical properties and/or chemical composition. Example: A
repair weld of a cast iron item performed with a nickel-based electrode.
WIS5-90516b
Terms and Definitions 2-4 Copyright © TWI Ltd
Dissimilar/Transition
Welded joint in which the parent materials have significant differences in
mechanical properties and/or chemical composition. Example: A carbon steel
lifting lug welded onto an austenitic stainless steel pressure vessel.
Filler metal
Metal added during welding, braze welding, brazing or surfacing.
Weld metal
All metal melted during the making of a weld and retained in the weld.
Fusion line
Boundary between the weld metal and the HAZ in a fusion weld.
Weld zone
Zone containing the weld metal and the HAZ.
Weld face
The surface of a fusion weld exposed on the side from which the weld has
been made.
Root
Zone on the side of the first run furthest from the welder.
Toe
Boundary between a weld face and the parent metal or between runs. This
is a very important feature of a weld since toes are points of high stress
concentration and often are initiation points for different types of cracks (eg
fatigue and cold cracks). To reduce the stress concentration, toes must
blend smoothly into the parent metal surface.
WIS5-90516b
Terms and Definitions 2-5 Copyright © TWI Ltd
Weld
Parent zone
Weld
face metal
Parent
metal
Toe
HAZ
Weld
metal Root Fusion
line Excess weld
metal
Penetration
Parent metal
Excess
weld metal
Weld zone
Toe
Fusion
line
Weld face
WIS5-90516b
Terms and Definitions 2-6 Copyright © TWI Ltd
2.4 Weld preparation
A preparation for making a connection where the individual components,
suitably prepared and assembled, are joined by welding or brazing. The
dimensions below can vary depending on WPS.
Included angle
The angle between the planes of the fusion faces of parts to be welded. For
single and double V or U this angle is twice the bevel angle. In the case of
single or double bevel, single or double J bevel, the included angle is equal to
the bevel angle.
Root face
The portion of a fusion face at the root that is not bevelled or grooved. Its value
depends on the welding process used, parent material to be welded and
application; for a full penetration weld on carbon steel plates, it has a value of
1-2mm (for the common welding processes).
Gap
The minimum distance at any cross-section between edges, ends or surfaces to
be joined. Its value depends on the welding process used and application; for a
full penetration weld on carbon steel plates, it has a value of 1-4mm.
Root radius
The radius of the curved portion of the fusion face in a component prepared for
a single or double J or U, weld.
Land
Straight portion of a fusion face between the root face and the radius part of a J
or U preparation can be 0. Usually present in weld preparations for MIG welding
of aluminium alloys.
WIS5-90516b
Terms and Definitions 2-7 Copyright © TWI Ltd
2.4.2 Types of preparation
Open square butt preparation
Used for welding thin components from one or both sides. If the root gap is
zero (ie if components are in contact), this preparation becomes a closed
square butt preparation (not recommended due to problems caused by lack of
penetration)!
Single V preparation
One of the most common preparations used in welding and can be produced
using flame or plasma cutting (cheap and fast). For thicker plates a double V
preparation is preferred since it requires less filler material to complete the joint
and the residual stresses can be balanced on both sides of the joint resulting in
lower angular distortion.
Included angle
Angle of
bevel
Root face
Root gap
Double V preparation
The depth of preparation can be the same on both sides (symmetric double V
preparation) or deeper on one side (asymmetric double V preparation). Usually,
in this situation the depth of preparation is distributed as 2/3 of the thickness of
the plate on the first side with the remaining 1/3 on the backside. This
asymmetric preparation allows for a balanced welding sequence with root back
gouging, giving lower angular distortions. Whilst a single V preparation allows
welding from one side, double V preparation requires access to both sides (the
same applies for all double sided preparations).
WIS5-90516b
Terms and Definitions 2-8 Copyright © TWI Ltd
Figure 2.12 Symmetric double V preparation.
Single U preparation
U preparations can be produced only by machining (slow and expensive),
however, tighter tolerances give a better fit-up than with V preparations.
Usually applied to thicker plates compared with single V preparation as it
requires less filler material to complete the joint, lower residual stresses and
distortions. Like for V preparations, with very thick sections a double U
preparation can be used.
Included angle
Angle of
bevel
Root
radius
Root face
Root gap
Land
Double U preparation
Usually this type of preparation does not require a land, (except for aluminium
alloys).
WIS5-90516b
Terms and Definitions 2-9 Copyright © TWI Ltd
Single V preparation with backing strip
Backing strips allow production of full penetration welds with increased current
and hence increased deposition rates/productivity without the danger of burn-
through. Backing strips can be permanent or temporary.
Permanent types are made of the same material as being joined and are tack
welded in place. The main problems with this type of weld are poor fatigue
resistance and the probability of crevice corrosion between the parent metal
and the backing strip.
It is also difficult to examine by NDT due to the built-in crevice at the root of
the joint. Temporary types include copper strips, ceramic tiles and fluxes.
WIS5-90516b
Terms and Definitions 2-10 Copyright © TWI Ltd
Figure 2.18 Single J preparation.
WIS5-90516b
Terms and Definitions 2-11 Copyright © TWI Ltd
As a general rule:
Design throat
Actual throat thickness = maximum thickness =
thickness through the joint thickness of the
thinner plate
Run (pass)
The metal melted or deposited during one pass of an electrode, torch or
blowpipe.
Layer
A stratum of weld metal consisting of one or more runs.
WIS5-90516b
Terms and Definitions 2-12 Copyright © TWI Ltd
2.6 Fillet weld
A fusion weld, other than a butt, edge or fusion spot weld, which is
approximately triangular in transverse cross-section.
Leg length
Distance from the actual or projected intersection of the fusion faces and the
toe of a fillet weld, measured across the fusion face (z on drawings).
Actual throat
thickness
Leg
length
Leg length
Design throat
thickness
a = 0.707 z or z = 1.41 a
WIS5-90516b
Terms and Definitions 2-13 Copyright © TWI Ltd
Figure 2.29 Mitre fillet weld.
Due to the smooth blending between the weld face and the surrounding parent
material, the stress concentration effect at the toes of the weld is reduced
compared with the previous type. This is why this type of weld is highly desired
in applications subjected to cyclic loads where fatigue phenomena might be a
major cause for failure.
WIS5-90516b
Terms and Definitions 2-14 Copyright © TWI Ltd
Asymmetrical fillet weld
A fillet weld in which the vertical leg length is not equal to the horizontal leg
length. The relation between leg length and design throat thickness is not valid
for this type of weld because the cross-section is not an isosceles triangle.
Horizontal leg
size
Vertical leg
size
Throat size
To produce consistent and constant penetration, the travel speed must be kept
constant at a high value. Consequently this type of weld is usually produced
using mechanised or automatic welding processes. Also, the high depth-to-
width ratio increases the probability of solidification centreline cracking. To
differentiate this type of weld from the previous types, the throat thickness is
symbolised with s instead of a.
WIS5-90516b
Terms and Definitions 2-15 Copyright © TWI Ltd
Bevel
Fillet
weld weld
Weld slope
Angle between root line and the positive X axis of the horizontal reference
plane, measured in mathematically positive direction (ie counter-clockwise).
Weld rotation
Angle between the centreline of the weld and the positive Z axis or a line
parallel to the Y axis, measured in the mathematically positive direction (ie
counter-clockwise) in the plane of the transverse cross-section of the weld in
question.
WIS5-90516b
Terms and Definitions 2-16 Copyright © TWI Ltd
Table 2.2 Welding position, sketches and definition.
Welding Sketch Definition and symbol
position according to ISO 6947
PA.
PB.
PC.
PF.
PF
PE.
PD.
WIS5-90516b
Terms and Definitions 2-17 Copyright © TWI Ltd
Figure 2.37 Tolerances for the welding positions.
2.8 Weaving
Transverse oscillation of an electrode or blowpipe nozzle during the deposition
of weld metal, generally used in vertical-up welds.
Stringer bead
A run of weld metal made with little or no weaving motion.
WIS5-90516b
Terms and Definitions 2-18 Copyright © TWI Ltd
Terminology Objective
Section 2
T Edge Cruciform
2-1
Single Sided Butt Preparations Double Sided Butt Preparations
Single sided preparations are normally made on thinner Double sided preparations are normally made on thicker
materials, or when access form both sides is restricted. materials, or when access form both sides is unrestricted.
Land
Root
Radius
Root Gap Root Gap Root Face
Root Face
Root Gap Root Radius Root Face
Root Face Land
Root Gap
Fillet weld Edge weld Compound weld A butt welded butt joint
Butt weld Plug weld Spot weld A compound welded butt joint
2-2
Welded T Joints Welded Lap Joints
Face
A B
A fillet welded closed corner joint
Weld
metal
A butt welded closed corner joint
Heat
Affected Weld
Zone Boundary
Excess Root
Penetration
2-3
Heat Affected Zone (HAZ) Toe Blend
Concave fillet
A concave profile is preferred for
joints subjected to fatigue
loading.
Convex fillet
2-4
Deep Penetration Fillet Weld Features Deep Penetration Fillet Weld Features
a
b
a = Design throat thickness
b = Actual throat thickness
60° 120°
Question: The design throat is 10mm.
What is the leg length?
2-5
Features to Consider Features to Consider
The design throat thickness of a flat or convex fillet Importance of fillet weld leg length size
weld connecting parts with the fusion faces which
form an angle between 600 and 1200 may be a b
calculated by multiplying the leg length by the
appropriate factors as given below:
Importance of fillet weld leg length size Importance of fillet weld leg length size
2-6
Joint Design and Weld Preparation Joint Design and Weld Preparation
Welding process impacts upon weld preparation Welding process impacts upon weld preparation
MMA MAG
High heat input process allow a larger root face, less weld
metal required, less distortions, higher productivity.
2-7
Weld Preparation Weld Preparations
Preparation method impacts upon weld preparation Access impacts upon weld preparation
Access impacts upon weld preparation Access impacts upon weld preparation
Pipe weld preparation - one side access only!
Type of joint impacts upon weld preparation Type of joint impacts upon weld preparation
Corner joints require offset Lap and square edge butt joints do not require
preparation.
offset
2-8
Weld Preparations Weld Preparations
Type of parent material impacts upon weld preparation Thickness of parent material impacts upon weld preparation
To reduce distortions on stainless steels welds, reduce A single bevel groove requires a volume of weld metal
included angle and increase root face. proportional to the square of plate thickness
To avoid lack of side wall fusion problems aluminium Its lack of symmetry lead to distortions
require larger included angles than steel.
60º 70-90º
35-45º Reduce shrinkage by:
30º Reducing weld volume.
Using single pass welding.
Steel Aluminium
Thickness of parent material impacts upon weld Thickness of parent material impacts upon weld
preparation preparation
Thickness of parent material impacts upon weld Thickness of parent material impacts upon weld
preparation preparation
t/3
t
2-9
Weld Preparation Weld Preparation
Welding position impacts upon weld preparation Type of loading impacts upon weld preparation
Type of loading impacts upon weld preparation Type of loading impacts upon weld preparation
Static loads - equal throat T joints Static loads - equal throat T beams in bending
13mm
13mm
neutral axis neutral axis
60°
Weld area = 160mm2 Weld area = 90mm2 Normal fillet welds Deep penetration
fillet welds
No preparation required. Preparation required.
Danger of lamellar Reduced distortions. Lower neutral axis is more advantageous (also helps
tearing. to reduce residual distortions!)
?
Cyclic load
2-10
Section 3
Welding Imperfections
and Materials Inspection