When welds are specified on engineering and fabrication drawings, a
cryptic set of symbols is used 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
published by the American
National Standards Institute and the American Welding 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 |
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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.
For more information, see ANSI/AWS A2.4, Symbols for Welding and
Nondestructive 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 round or curved parts. The intended depth of
the weld itself are 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.
For more information, see ANSI/AWS A2.4, Symbols for Welding and
Nondestructive 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.
For more information, see ANSI/AWS A2.4, Symbols for Welding and
Nondestructive Testing.
