29 face has several
advantages. The square edges simplify assembly. Excellent penetration and reinforcement
can be obtained and normal practical variations in voltage,
current, welding speed, and edge preparation cause
minimum damage to the backing. Relatively small quantities of wire are used because
Vee preparation gives the desired penetration
without excessive current and the volume of the Vee is considerably
less than that required by other welding methods. With
non-fusible backing, the root face dimension is 1/8 to 3/16-in. Root gap should
not exceed 1/16-in. Fusible metallic backing
is also used with this preparation with a root gap of at least 1/8-in.
The single-Vee groove butt joint with root face and without
external backing is also used for two pass welds where
plate thickness exceeds 5/8-in. The first weld, usually the larger, is the backing
weld made in the Vee side of the joint;
the work is then turned over and the finishing weld made on the flat side. The
finishing weld penetrates down into and
refuses a portion of the backing weld to ensure complete penetration (Fig. 13).
The root face is approximately 3/8-in. for all commercially
welded plate thicknesses. The plate edges must be
tightly butted (1/32-in. maximum gap) as with the square butt joint. When the
welding composition is retained by a support
below the joint, slightly greater root gaps are permissible; if the root gap exceeds
1/16- in., submerged arc welding flux should
be tamped into the gap ahead of the weld. b)
Single-Vee Groove Without Root Face (Fig. 12c.) The
single-vee groove without root face is commonly used for nearly all thicknesses
when using submerged arc backing flux.
It is not commonly used below 3/8-in. thickness since adequate penetration can
be obtained for these thicknesses without
beveling. The single-vee groove butt joint
without root face must always have weld backing since the mass of metal at
the joint root is not sufficient to provide weld metal
support. Reasonable misalignment in fit-up and variation in
root gap can be tolerated when using submerged arc backing flux because the granular
material will shift to accommodate them.
Copper backing is not recommended because of the tendency of the weld metal to
fuse to the backing piece. Fusible metallic backing is
acceptable if there is no objection to its remaining as part
of the completed weld.
