Page 216 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 201

of tungsten, a metal with a very high melting point. Between the
tungsten and the work, an arc is established that results in heating of
the base material. A filler rod may or may not be used. The area is
shielded with an inert gas, typically argon, although helium may be
used. GTAW is ideally suited for welding on nonferrous materials,
such as stainless steel and aluminum. Moreover, it is very effective
when joining thin sections.
One area where gas-tungsten arc welding may be used in structural
applications is when it is applied for the purpose of “TIG dressing.”
The TIG dressing technique has been used to extend the fatigue life of
fillet welds. With this technique, the gas-tungsten arc process is used
to heat and melt the toes of fillet welds, resulting in a new distribu-
tion of residual stresses and perhaps improved contour of the toe of
the fillet. This has been used to retrofit structures where fatigue
cracking is expected. The process is inherently expensive, but may be
justified if it extends the life of the structure.

3.4 Welding Process Selection
Any of the common arc-welding processes can be used to achieve the
quality required for structural steel applications. While each may
have a particular area of strength and/or weakness, the primary con-
sideration as to which process will be used is largely cost-driven. The
availability of specialized equipment in one fabrication shop com-
pared to the capabilities of a second shop may dictate significantly
different approaches, both of which may prove to be cost-effective. A
history of successful usage offers a strong incentive for the fabricator
to continue using a given process. The reasons for this go well beyond
familiarity and comfort with a specific approach. When welders and
procedures are established with a given process, significant costs will
be incurred with any change to a new approach.

3.4.1 Joint requirements
Each individual weld-joint configuration and preparation has certain
process requirements in order to achieve low-cost welding. Four char-
acteristics must be considered: deposition rate, penetration ability,
out-of-position capability, and high travel-speed capacity. Each
process exhibits different capabilities in these realms. Once the joint
and its associated requirements are analyzed, they should be com-
pared to the various process options and the ability of the process to
achieve those requirements. A proper match of weld-joint require-
ments and process capabilities will lead to dependable and economi-
cal fabrication.

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