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Steel Designers' Manual - 6th Edition (2003)
694 Welds and design for welding
Welder approval and availability of approved welders
Welds are more difficult in the overhead (PD and PE) positions than in the
downhand (PA and PB) positions. Consequently it is more difficult for a welder
to gain approval, and fewer approved welders are available for the more difficult
positions.
Weld quality
Welds made in the more difficult PD, PE, and PF positions are likely to contain
more defects than similar welds made in easier positions. Aim for the maximum
number of welds to be made in the PA or PB positions with minimum repositioning
of the components.
Weld metal properties
Weld metal toughness, strength, and hardness are influenced not only by the choice
of consumables but also by the size of the weld pool, which controls the heat input
into the weld. When impact properties and hardness limits are specified, they must
be tested at the low and high ends of the heat input range. If all welds can be made
in the PA and PB positions only one set of tests need be made.
The components of a structure will require joints to be made from one or more
of five configurations. The most common are butt (in-line), T, corner, and lap joints.
Each type of joint may be connected by several types of weld. The weld types (not
to be confused with joint types) recognized by BS 499: Part 1 22 are fillet, butt, compound
welds (consisting of both fillet and butt), plug welds, and edge welds. The
choice of joint and weld is a major factor in welding costs. They may have similar
costs of materials, but significantly different fabrication costs. About 80% of structural
joints have a T-configuration, which might require either fillet welds or butt
welds. Except where in-line butt joints are necessary, designers should always
attempt to choose joints that can be made with fillet welds. Significant costs can be
saved by using fillet welds wherever possible; where a butt weld is essential a partial
penetration weld should be selected if possible, bearing in mind strength, fatigue
and corrosion limitations.
24.3.2 Fillet welds
Fillet welds have triangular cross section and they are commonly used to make
T-joints, corner joints with several variations, and lap joints, shown in Fig. 24.4.
In this welding position, 8 mm is the maximum leg length that can be made in
a single-pass weld. Single fillet welds should not be used where tension would