27 Basic
Joint Types Introduction
The type of joint selected for any welding job may materially
affect the quality and strength of the weld; the cost
of labor and materials; the time and expense involved in preparing, jigging, and
positioning the work; and other factors
of like importance. The selection of the proper joint type depends on a number
of factors, such as joint thickness and
material, desired physical properties in the finished joint, size of the pieces
being welded, accessibility of the joint,
fit-up obtainable, available edge preparation equipment, number of pieces
to be welded, and specifications of regulatory codes (if
applicable). A number of joint types used
for submerged arc welding will be described. Butt
Joint Welds Square
Groove Butt Joint (Fig. 12a.). Good
quality single pass welds up to 5/16-in. thick can be made using the square groove
butt joint without root opening and with
suitable backing. Weld reinforcement, which tends to become excessive for
thicker welds, can be controlled by adjusting the root
opening. Variations in root opening, alignment of welding
wire with the joint, and the amount of weld metal required generally limit the
thickness of this type of weld to 3/4-in.
Two pass welds up to 5/8-in. thick are made without root
opening. It is essential in two-pass welds that the edges
be closely butted since weld backing is not used. The maximum permissible root
opening is 1/32-in. unless the joint
is backed sufficiently to prevent the welding composition from flowing through
the root opening. With such support greater
root openings can be used. When the root opening exceeds 1/16-in.,
however, the opening should be closely filled with submerged
arc welding flux ahead of the weld. The maximum
root opening is approximately 1/8-in. because of the difficulty of refusing the
welding flux at the base of the first pass
weld. If the root gap is maintained constant for the entire length of the seam,
plate up to 3/4-in. can be welded with
square butt joints. The first weld is a backing weld made on the reverse side
of the joint; the work is then turned over
and the finishing weld is made. The finishing weld penetrates down
into and refuses a portion of the backing weld to ensure
a continuous weld structure throughout the plate thickness.
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