When a material is required to protect the base metal
from chemicals, heat, abrasion, or other forms of wear, a
layer of weld metal is placed on the surface. Overlaying
a weld in this manner is called surfacing or cladding,
Figure 6-13.
Pipe joints often require a special backing ring for
assembling and welding the joint. The type of material
flowing through the pipe influences the ring’s design.
Because the weld metal penetrates the backing ring, it is not
removable once welding is completed. See Figure 6-14.
Welding Terms and Symbols
Communication between the designer and the
welder is essential in the welding operation. Weld and
weld joint terminology must be mutually understood,
Figure 6-15. The welding symbol designated by the
American Welding Society is used as a standard through-
out the industry, Figure 6-16. The symbol is used on
drawings to indicate type of weld, weld joint, and weld
placement. The welding symbol may also include infor-
mation regarding finish contours and testing.
Part of the welding symbol is the weld symbol. It is
important to study and understand each part. Figure 6-17
shows basic weld symbols, which direct the welder to
select the proper weld joint. The flat line on which a sym-
bol is placed is called the reference line. An arrow on one
end points to the weld joint and indicates where the weld
should be made. The line to the arrow is always at an
angle to the reference line. Whenever the weld symbol is
placed below the reference line, the weld is to be made on
Chapter 6 Weld Joints and Weld Types 51
Figure 6-13. Overlay welds protect the base material from wear
or contamination.
Figure 6-14. Cross sections of various types of backing rings
for pipe joints.
Bevel angle
Root face
thickness
Groove
angle
Root opening
Riser
Crown
height
Weld toe
Weld crown
Weld toe
Root penetration
Root
penetration
Weld crown
Weld throat
Leg length
Leg length
A
B
Figure 6-15. Welding terminology. A—For the weld. B—For the
weld joint.