Page 220 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 205

The requirement for high travel speed capability for welding structural
steel members is fairly limited. This typically consists of the travel speed
1
associated with making a ⁄ 4 -in fillet weld. All of the popular processes,
1
with the exception of electroslag/electrogas, are capable of making ⁄ 4 -in
fillet welds under the proper conditions. Among the variables that need
to be considered are electrode size and procedure variables. A common
mistake of fabricators is to utilize a process and procedure capable of
extremely high deposition rates but limited travel speeds. Oversized
welds can result from the inability to achieve high travel speeds. A more
economical approach would be to optimize the procedure according to the
desired travel speed. This may result in a lower deposition rate but a
lower overall cost because overwelding has been eliminated.

3.4.3 Special situations
Self-shielded flux-cored welding is ideal for outdoor conditions.
Quality deposits may be obtained without the erection of special wind
shields and protection from drafts. Shielded metal arc welding is also
suitable for these conditions but is considerably slower.
The welding process of choice for field erectors for the last 25 years
has been FCAW-ss. It has been the commonly used process for fabri-
cation of steel structures throughout the United States. Its advan-
tages are reviewed in order to provide an understanding of why it has
been the preferred process. In addition, its limitations are outlined to
highlight areas of potential concern.
The chief advantage of the FCAW-ss process is its ability to deposit
quality weld metal under field conditions, which usually involve
wind. The code specifically limits wind velocity in the vicinity of a
weld to a maximum of 5 mi/h. In order to utilize gas-shielded processes
under these conditions, it is necessary to erect windshields to preclude
movement of the shielding gas with respect to the molten weld pud-
dle. While tents and other housings can be created to minimize this
problem, such activities can be costly and are often a fire hazard. In
addition, adequate ventilation must be provided for the welder. The
most efficient windshields may preclude adequate ventilation. Under
conditions of severe shielding loss, weld porosity will be exhibited. At
much lower levels of shielding loss, the mechanical properties (notch
toughness and ductility) may be negatively affected, although there
will be no obvious evidence that this is taking place.
A variety of other gas-related issues are also eliminated, including
ensuring availability of gas, handling of high-pressure cylinders (always
a safety concern), theft of cylinders, protection of gas-distribution hosing
under field conditions, and the cost of shielding gas. Leaks in the deliv-
ery system obviously waste shielding gas, but a leak can also allow

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