Linde BOC RAPTOR Operating Manual page 44

'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.
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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. All
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.
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.