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Steel Designers' Manual - 6th Edition (2003)
Recommendations for cost reduction 693
just within the cross-section of the weld; it should not be taken as greater than 0.7
times the effective leg length, which is what is measured during inspection. Unnecessary
weld metal raises costs, and it increases distortion to no good effect. Designers
should therefore indicate the throat size required for fillet and butt welds,
and give steelwork contractors the responsibility to produce and confirm consistent
production of that size.
Care is required in the design of welds for regions where members are closely
spaced, and where joints have to be made inside assemblies. Any weld joint should
be designed for easy access, and the welder or machine operator must be able to
see where the weld is to be made, and be able to apply an MMA electrode or
MIG/MAG gun so that the arc is directed down to the bottom of the joint and at
the correct angle to ensure root penetration. A MIG/MAG gun is essentially a large
pistol with a 20 mm barrel, 100 mm long, at 60° to the handle, attached to a heavy
cable. MMA welds need space for the manipulation of electrodes that are either
350 mm or 450 mm long, with a flux coating diameter that often exceeds 6 mm, and
held in tongs or a holder attached to the welding cable. Where access might be
restricted it is recommended that designers should consult a welding engineer to
confirm feasibility.
Welding position, shown in Fig. 24.3, is one of the important variables that
influence the ease of fabrication, the costs of fabrication, and the mechanical
properties of the weld.
PAPB
Fig. 24.3 Designations of welding positions
Welding position influences many important factors:
Deposition rate
The PA and PB welding positions allow the highest deposition rates. High deposition
rates cannot be used when making welds in the vertical (PF and PG) and
especially the overhead (PD and PE) positions.