Melt-thru and Back or Backing Weld Symbols
Back and Backing Weld Symbol
The backing or back weld symbol (fig. 3-50) must be used to indicate bead-type back/backing welds of single-groove welds.
Back/backing welds of single-groove welds must
be shown by placing a back or backing weld symbol on the side of the
reference line opposite the groove weld symbol (fig. 3-50).
Dimensions of back or backing welds should not be
shown on the welding symbol. If it is desired to specify these
dimensions, they must be shown on the drawing.
Back or Backing Weld Symbol
Surface Contour of Back or Backing Welds. The contour symbols (fig.
3-55) for back or backing welds are indicated in the same manner as that
for fillet welds.
Overview Melt Thru Weld Symbol
The melt-thru symbol shall be used where at least 100 percent joint penetration of the weld through the material is required in welds made from one side only (fig. 3-56).
Melt-thru welds shall be shown by placing the melt-thru weld symbol on
the side of the reference line opposite the groove weld, flange, tee, or
corner weld symbol (fig. 3-56).
Dimensions of melt-thru welds should rot be shown on the welding symbol. If it is desired to specify these dimensions, they must be shown on the drawing.
Surface Contour of Melt-thru Welds. The contour symbols for melt-thru welds are indicated in the same manner as that for fillet welds (fig. 3-57).
Overview Surfacing Weld Symbol
The surfacing weld symbol shall be used to indicate surfaces built up
by welding (fig. 3-58), whether built up by single-or multiple-pass
Symbol for Size of Surfaces Built Up By Welding
The surfacing weld symbol does not indicate the welding of a joint
and thus has no arrow or other side significance. This symbol shall be
drawn on the side of the reference line toward the reader and the arrow
shall point clearly to the surface on which the weld is to be deposited.
Size of Built-up Surfaces
The size (height) of a
surface built up by welding shall be indicated by showing the minimum
height of the weld deposit to the left of the weld symbol. The
dimensions shall always be on the same side of the reference line as the
weld symbol (fig. 3-58). When no specific height of weld deposit is
desired, no size dimension need be shown on the welding symbol.
Extent, Location and Orientation of Surfaces Built Up By Welding
When the entire area of a plane or curved surface is to
be built up by welding, no dimension, other than size, need be shown on
the welding symbol. If only a portion of the area of a plane or curved
surface is to be built up by welding, the extent, location, and
orientation of the area to be built up shall be indicated on the
For Additional Reading on the Surfacing, Melt-thru and Backing Weld Symbol
Welding Symbols and Definitions
Page Author: Jeff Grill