# Deciphering Welding Symbols

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DECIPHERING WELD SYMBOLS
When welds are specified on engineering and fabrication drawings, a cryptic set of
symbols issued as a sort of shorthand for describing the type of weld, its size, and other
processing and finishing information. The purpose of this page is to introduce you to the
common symbols and their meaning. The complete set of symbols is given in a standard
Society: ANSI/AWS A2.4, Symbols for Welding and Nondestructive Testing.
The structure of the welding symbol

The horizontal line--called the reference line--is the anchor to which all the other welding
symbols are tied. The instructions for making the weld are strung along the reference line.
An arrow connects the reference line to the joint that is to be welded. In the example
above, the arrow is shown growing out of the right end of the reference line and heading
down and to the right, but many other combinations are allowed.

Quite often, there are two sides to the joint to which the arrow points, and therefore two
potential places for a weld. For example, when two steel plates are joined together into a
T shape, welding may be done on either side of the stem of the T.

The weld symbol distinguishes between the two sides of a joint by using the arrow and
the spaces above and below the reference line. The side of the joint to which the arrow
points is known (rather prosaically) as the arrow side, and its weld is made according to
the instructions given below the reference line. The other side of the joint is known (even
more prosaically) as the other side, and its weld is made according to the instructions
given above the reference line. The below=arrow and above=other rules apply regardless

of the arrow's direction. The flag growing out of the junction of the reference line and the
arrow is present if the weld is to be made in the field during erection of the structure. A
weld symbol without a flag indicates that the weld is to be made in the shop. In older
drawings, a field weld may be denoted by a filled black circle at the junction between the
arrow and the reference line.
The open circle at the arrow/reference line junction is present if the weld is to go all
around the joint, as in the example below.

The tail of the weld symbol is the place for supplementary information on the weld. It
may contain a reference to the welding process, the electrode, a detail drawing, any
information that aids in the making of the weld that does not have its own special place
on the symbol.
Types of welds and their symbols
Each type of weld has its own basic symbol, which is typically placed near the center of
the reference line (and above or below it, depending on which side of the joint it's on).
The symbol is a small drawing that can usually be interpreted as a simplified cross-
section of the weld. In the descriptions below, the symbol is shown in both its arrow-side
and other-side positions.
Fillet Welds
Groove Welds
Plug Welds and Slot Welds

Fillet Welds

The fillet weld (pronounced "fill-it") is used to make lap joints, corner joints, and T
joints. As its symbol suggests, the fillet weld is roughly triangular in cross-section,
although its shape is not always a right triangle or an isosceles triangle. Weld metal is
deposited in a corner formed by the fit-up of the two members and penetrates and fuses
with the base metal to form the joint. (Note: for the sake of graphical clarity, the drawings
below do not show the penetration of the weld metal. Recognize, however, that the
degree of penetration is important in determining the quality of the weld.)

The perpendicular leg of the triangle is always drawn on the left side of the symbol,
regardless of the orientation of the weld itself. The leg size is written to the left of the
weld symbol. If the two legs of the weld are to be the same size, only one dimension is
given; if the weld is to have unequal legs (much less common than the equal-legged
weld), both dimensions are given and there is an indication on the drawing as to which
leg is longer.

The length of the weld is given to the right of the symbol.

If no length is given, then the weld is to be placed between specified dimension lines (if
given) or between those points where an abrupt change in the weld direction would occur
(like at the end of the plates in the example above).
For intermittent welds, the length of each portion of the weld and the spacing of the
welds are separated by a dash (length first, spacing second) and placed to the right of the
fillet weld symbol.

Notice that the spacing, or pitch, is not the clear space between the welds, but the center-
to-center (or end-to-end) distance.

Testing.

Groove Welds

The groove weld is commonly used to make edge-to-edge joints, although it is also often
used in corner joints, T joints, and joints between curved and flat pieces. As suggested by
the variety of groove weld symbols, there are many ways to make a groove weld, the
differences depending primarily on the geometry of the parts to be joined and the
preparation of their edges. Weld metal is deposited within the groove and penetrates and
fuses with the base metal to form the joint. (Note: for the sake of graphical clarity, the
drawings below generally do not show the penetration of the weld metal. Recognize,
however, that the degree of penetration is important in determining the quality of the
weld.)
The various types of groove weld are:

Square Groove Welds
The "groove" is created by either a tight fit or a slight separation of the edges. The
amount of separation, if any, is given on the weld symbol.

V-Groove Welds
The edges of both pieces are chamfered, either singly or doubly, to create the groove. The
angle of the V is given on the weld symbol, as is the separation at the root (if any).

If the depth of the V is not the full thickness--or half the thickness in the case of a double
V--the depth is given to the left of the weld symbol.

If the penetration of the weld is to be greater than the depth of the groove, the depth of
the effective throat is given in parentheses after the depth of the V.

Bevel Groove Weld
The edge of one of the pieces is chamfered and the other is left square. The bevel
symbol's perpendicular line is always drawn on the left side, regardless of the orientation

of the weld itself. The arrow points toward the piece that is to be chamfered. This extra
significance is emphasized by a break in the arrow line. (The break is not necessary if the
designer has no preference as to which piece gets the edge treatment or if the piece to
receive the treatment should be obvious to a qualified welder.) Angle and depth of edge
treatment, effective throat, and separation at the root are described using the methods
discussed in the V-groove section.

U-Groove Weld
The edges of both pieces are given a concave treatment. Depth of edge treatment,
effective throat, and separation at the root are described using the methods discussed in
the V-groove section.

J-Groove Weld
The edge of one of the pieces is given a concave treatment and the other is left square. It
is to the U-groove weld what the bevel groove weld is to the V-groove weld. As with the
bevel, the perpendicular line is always drawn on the left side and the arrow (with a break,
if necessary) points to the piece that receives the edge treatment. Depth of edge treatment,
effective throat, and separation at the root are described using the methods discussed in
the V-groove section.

Flare-V Groove Weld
Commonly used to join two rounded or curved parts. The intended depth of the weld
itself is given to the left of the symbol, with the weld depth shown in parentheses.

Flare Bevel Groove Weld
Commonly used to join a round or curved piece to a flat piece. As with the flare-V, the
depth of the groove formed by the two curved surfaces and the intended depth of the weld
itself are given to the left of the symbol, with the weld depth shown in parentheses. The
symbol's perpendicular line is always drawn on the left side, regardless of the orientation
of the weld itself.

Common supplementary symbols used with groove welds are the melt-thru and backing
bar
symbols. Both symbols indicate that complete joint penetration is to be made with a
single-sided groove weld. In the case of melt-thru, the root is to be reinforced with weld
metal on the back side of the joint. The height of the reinforcement, if critical, is
indicated to the left of the melt-thru symbol, which is placed across the reference line
from the basic weld symbol.

When a backing bar is used to achieve complete joint penetration, its symbol is placed
across the reference line from the basic weld symbol. If the bar is to be removed after the
weld is complete, an "R" is placed within the backing bar symbol. The backing bar
symbol has the same shape as the plug or slot weld symbol, but context should always
make the symbol's intention clear.

Testing.

Plug and Slot Welds

Plug welds and slot welds are used join overlapping members, one of which has holes
(round for plug welds, elongated for slot welds) in it. Weld metal is deposited in the holes
and penetrates and fuses with the base metal of the two members to form the joint. (Note:
for the sake of graphical clarity, the drawings below do not show the penetration of the
weld metal. Recognize, however, that the degree of penetration is important in
determining the quality of the weld.) For plug welds, the diameter of each plug is given to
the left of the symbol and the plug-to-plug spacing (pitch) is given to the right. For slot
welds, the width of each slot is given to the left of the symbol, the length and pitch
(separated by a dash) are given to the right of the symbol, and a detail drawing is
referenced in the tail. The number of plugs or slots is given in parentheses above or
below the weld symbol. The arrow-side and other-side designations indicate which piece
contains the hole(s). If the hole is not to be completely filled with weld metal, the depth
to which it is to be filled is given within the weld symbol.