Specifications

8
312 AU : IPRM 2007 : SECTION 8 : CONSUMABLES
WARNING Welding can give rise to electric shock, excessive noise, eye and skin burns due to the arc rays, and a potential health hazard if you breathe in the emitted fumes and gases.
Read all the manufacturer’s instructions to achieve the correct welding conditions and ask your employer for the Materials Safety Data Sheets. Refer to www.boc.com.au or www.boc.co.nz
Fundamentals of Manual Metal Arc (MMA) Welding
Fillet Welds
A fillet weld is approximately triangular in section, joining two
surfaces not in the same plane and forming a lap joint, tee joint or
corner joint. Joints made with fillet welds do not require extensive
edge preparation, as is the case with butt welded joints, since the
weld does not necessarily penetrate the full thickness of either
member. It is, however, important that the parts to be joined be
clean, close fitting, and that all the edges on which welding is to be
carried out are square. On sheared plate, it is advisable to entirely
remove any ‘false cut’ on the edges prior to welding.
Fillet welds are used in the following types of joints:
‘T’ Joints
A fillet weld may be placed either on
one or both sides, depending on the
requirements of the work. The weld metal
should fuse into or penetrate the corner
formed between the two members. Where
possible, the joint should be placed in such
a position as to form a ‘Natural ‘V’ fillet’
since this is the easiest and fastest method
of fillet welding.
Lap Joints
In this case, a fillet weld may be placed
either on one or both sides of the
joint, depending on accessibility and the
requirements of the joint. However, lap
joints, where only one weld is accessible,
should be avoided where possible and
must never constitute the joints of tanks
or other fabrications where corrosion is
likely to occur behind the lapped plates. In
applying fillet welds to lapped joints, it is
important that the amount of overlap of
the plates be not less than five times the
thickness of the thinner part. Where it is
required to preserve the outside face or
contour of a structure, one plate may be
joggled.
Corner Joints
The members are fitted as shown, leaving
a ‘V’-shaped groove in which a fillet weld
is deposited. Fusion should be complete
for the full thickness of the metal. In
practice, it is generally necessary to have
a gap or a slight overlap on the corner.
The use of a 1.0–2.5 mm gap has the
advantage of assisting penetration at the
root, although setting up is a problem. The
provision of an overlap largely overcomes
the problem of setting up, but prevents
complete penetration at the root and
should therefore be kept to a minimum
(i.e. 1.0–2.5 mm).
The following terms and definitions are important in specifying and
describing fillet welds.
Leg Length
A fusion face of a fillet weld, as shown below. In Australia and NZ,
specifications for fillet weld sizes are based on leg length.
Throat Thickness
A measurement taken through the centre of a weld from the root
to the face, along the line that bisects the angle formed by the
members to be joined. Many countries use throat thickness rather
than leg length.
Effective throat thickness is a measurement on which the strength
of a weld is calculated. The effective throat thickness is based on a
mitre fillet (Concave Fillet Weld), which has a throat thickness equal
to 70% of the leg length. For example, in the case of a 20 mm fillet,
the effective throat thickness will be 14 mm.
Convex Fillet Weld
A fillet weld in which the contour of the weld metal lies outside
a straight line joining the toes of the weld. A convex fillet weld of
specified leg length has a throat thickness in excess of the effective
measurement.
Convex Fillet Weld
1
2
3
4
4
5
5
6
1
Actual Throat
2
Effective Throat
3
Convexity
4
Leg
5
Size
6
Theoretical Throat
Concave Fillet Weld
A fillet in which the contour of the weld is below a straight line
joining the toes of the weld. It should be noted that a concave fillet
weld of a specified leg length has a throat thickness less than the
effective throat thickness for that size fillet. This means that, when
a concave fillet weld is used, the throat thickness must not be less
than the effective measurement. This entails an increase in leg length
beyond the specified measurement.
Concave Fillet Weld
1 2
3
6
54
5
4
1
Actual Throat
2
Effective Throat
3
Concavity
4
Leg
5
Size
6
Theoretical Throat
Fundamentals of Manual Metal Arc (MMA) Welding