4
Joint Design Again,
regardless of the material to be welded, there are a few general practices that
should be considered when
designing the weld joints. Plate
3/16 in., (4.8mm) thick or less may be butt welded with
square edges using the short arc process or a low
current spray arc (aluminum) if a root gap of 0 to 1/32 in. (0.8mm) is maintained.
Plate thicknesses of 3/16
in., (4.8mm) and 1/4 in. (6.4mm) may be square butt welded with the spray arc
process when a 1/32 to 3/32
in. (0.8-2.4mm) root gap is used. In all cases, a single pass can be used if a
permanent or temporary backup
bar is used. When welding in the overhead position, it is usual practice to always
butt weld using a backup
bar. However, if a backup of any kind is not used for 1/8 in. (3.2mm) thick plate
and above, two passes
are usually necessary – one from each side. A bead overlap greater than the
original root gap is desired
to prevent centerline porosity and poor fusion. Maximum
overlap is attainable if the backhand technique
is used on the second side. Plates
1/4 in. (6.4mm) thick and thicker generally require single or double Vee grooves
with 45 deg. to 70 deg.
included angles (depending on base material and thickness) to produce quality
welds. A 0 to 1/16 in. (1.6mm)
root face with a 1/32 in. (0.8mm) root opening is used. In single Vee grooves
where no backup is used,
a sealing pass from the back side will generally be required.
