The use of welding symbols enables a designer to indicate clearly to the welder, important detailed information regarding the weld.
The information in the welding symbol can include details for the weld such as length, depth of penetration, the height of reinforcement, groove type, groove dimensions, location, process, filler metal, strength, number of welds, weld shape, and surface finishing. All of this information would normally be included in the welding assembly drawings.
Welding symbols are a shorthand language for the welder. They save time and money and services to ensure understanding and accuracy. The American Welding Society has standardized welding symbols. Some of the more common symbols for welding are reproduced in this blog.
If more information is desired about symbols or how they apply to all forms of manual and automatic machine welding, these symbols can be found in the complete manual Standard Symbols for Welding, Brazing, and Nondestructive Examination, ANSI/AWS A2.4, published as an American National Standard by the American Welding Society.
The welding symbols and their meanings
The entire symbol, with all of its numbers and other symbols, is called the welding symbol. Welding symbols are used on drawings of parts and assemblies that are joined together by welding. A welding symbol may appear in any view on the drawing.
Whenever two or more pieces are joined by welding, the assembled item is called a weldment. When the pieces of a weldment are assembled, the lines along which their edges and surfaces come in contact are called joints.
The drawing of a weldment seldom shows how the edges are to be prepared or how the completed weld appears. The drawing shows only how the parts come together and what type of joint they form.
Occasionally, when an unusual or very complex weld joint is to be made, a detailed drawing of the joint is drawn, with the joint preparation and weld shape shown and dimensioned.
A complete welding symbol provides all the information needed to create a specific weld on a weldment.
A Welding symbol applies to only one joint and applies to that joint only until it changes direction. The welding symbol provides some or all of the following information to the welder:
- The type of weld to make.
- The edge preparation is required.
- Where to place the weld.
- The welding process to use.
- The size of the weld.
- The shape of the weld face.
- How to finish the weld surface after welding is completed.
The welding symbol provides much more information regarding the weld. Dimensions on a welding symbol may be in SI metric units or US Customary units of measurement.
Related Post: What is Welding?
The structure of the welding symbol
The foundation of the welding symbol is a reference line with an arrow at one end. The arrow points to the location of the weld. Instructions regarding the type of weld are indicated either above or below the reference line.
Also included is reference data such as the surface contour of the weld, the size of the weld bead, the length of the weld, how weld beads are to be finished, and often, what type of welding process is to be used.
All welding symbol data are indicated with geometric figures, numerical values, and abbreviations.
Weld Location
Welding symbols are applied to the reference line at the base. All reference lines have an arrow side (near side) and another side (far side). Accordingly, the terms arrow side, another side, and both sides are used to locate the weld with respect to the joint.
The reference line is always drawn horizontally. An arrow line is drawn from one end or both ends of a reference line to the location of the weld. The arrow line can point to either side of the joint and extend either upward or downward.
On the drawing of a welded part, the arrow of the welding symbol touches the line to be welded. The metal has two sides. The side of the metal that the arrow touches is always the arrow side. The opposite surface from the arrow is called the other side.
Because of the joint position on many weldments, there is no inside or outside, top or bottom, left or right.
To simplify identifying the location of the weld, the terms arrow side and other side are used. On the welding symbol, the arrow-side weld information is always shown below the reference line. The other-side weld information is always shown above the reference line.
It is not always possible to place the welding symbol on the side to be welded. The drawing is sometimes too crowded and complicated.
If the weld is to be deposited on the arrow side of the joint (near side), the desired weld symbol is placed below the reference line, Figure A. If the weld is to be deposited on the other side of the joint (far side), the weld symbol is placed above the reference line, Figure B.
When welds are to be deposited on both sides of the same joint, the same weld symbol appears above and below the reference line, Figures C and D.
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 is added to the basic welding symbol when it is necessary to designate the welding specifications, procedures, or other supplementary information needed to make the weld.
The notation placed in the tail of the symbol may indicate the welding process to be used, the type of filler metal needed, whether or not peeling or root chipping is required, and other information pertaining to the weld.
If notations are not used, the tail of the symbol is omitted. For joints that are to have more than one weld, a symbol is shown for each weld.
Basic Welding Symbols Charts
Weld symbols are used to indicate the welding processes used in metal joining operations, whether the weld is localized or “all-around”, whether it is a shop or field weld and the contour of welds.
These basic weld symbols (arc and gas weld symbols, resistance weld symbols, brazing, forge thermit, induction, and Flow Weld Symbols) are summarized below and illustrated.
Types of welds and their symbols
Each welding type 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.
1. Fillet welds Symbols
A fillet weld is approximately triangular in shape. It is used to join lap joints, tee joints, or corner joints where the joint is at an approximate right angle.
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.
2. Groove welds Symbols
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 welds 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 welds
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 welds
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 welds
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 welds
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.
3. Plug and slot welds Symbols
Occasionally, it is necessary to weld two pieces together at points that are not located on the edges. This is done by creating a hole in one piece and welding the two pieces together through this hole. The holes are usually round but can be any shape. Holes may be drilled, flame-cut, or machined.
Weld metal is deposited in the holes and penetrates and fuses with the base metal of the two members to form the joint.
If the hole is round, the weld is called a plug weld. A weld made in a hole that is not round is known as a slot weld.
The size of the plug is shown to the left of the weld symbol. In either a plug or slot weld, the sides of the hole may be counter-sunk (slanted). If a countersink is used, its angle is indicated beyond the weld symbol. The depth of the weld is shown inside the weld symbol.
A plug weld’s exact location on the weldment is shown on the assembly drawing. The length, width, and angle of the counter sink and the location and spacing of the slots for a slot weld are not shown on the basic weld symbol. These dimensions are shown on the assembly drawing. The depth of filling for a slot or plug weld is shown inside the weld symbol.
If there is a series of plug or slot welds, the pitch (P) or center-to-center distance is shown to the right of the weld symbol.
- The diameter or size is located to the left of the symbol (A).
- The angle of the sides of the hole, if not square, is given above the symbol (B).
- The depth of buildup, if not completely flush with the surface, is given in the symbol (C).
- The center-to-center dimensioning or pitch is located on the right of the symbol (D).
4. Spot welds Symbols
A spot weld is another method of joining two or more pieces together with a weld not at the edge of a part. To set up a spot weld, parts are overlapped, usually in a lap joint. A weld is made at the surfaces where the parts contact.
No hole or slot is cut into any of the parts. The weld can be made by resistance spot welding. The weld can also be made from one side by melting through the first panel and n1elting into the second panel.
The spot Weld symbol is a small circle. The circle may be on either side of the reference line, or it may straddle the reference line. If the weld is to be made from the arrow side, the weld symbol should be below the reference Line, as in all other welding symbols.
If the welding is to be done on both sides, as in resistance spot welding, the circle straddles the reference line. Projection welding, which requires projections (bumps) on one of the pieces of metal to be joined, is another process used to produce spot weld.
To indicate which piece has the projections on it, the circle is placed above or below the reference line. The information given for a spot weld is size, strength, spacing, and the number of spot welds.
The weld size is shown to the left of the spot weld symbol. If the weld strength is specified in the welding symbol, it is also shown to the left of the spot weld symbol. The weld strength is given in pounds or newtons per spot.
5. Seam Welds Symbols
A seam weld is another method of joining two or more pieces together. Parts are assembled in either a lap joint or a butt joint. No hole or slot is cut into any of the parts. The weld can be made by resistance seam welding.
The weld can also be made from one side by melting through the first piece and melting into the second piece. The weld symbol straddles the reference line if the joint is welded from both sides, as in resistance seam welding.
For other processes used for seam welding, the symbol can be placed above or below the reference line. This indicates from which side of the part the weld is to be made.
The process to be used is shown in the tail. The size (width) of the weld and strength of the weld are shown to the left of the weld symbol. The strength is given in pounds per linear inch or in new tons per millimeter. The length of the seam may be shown to the right of the weld symbol.
Field Weld Symbol
Welds to be made in the field (not in a shop or at the place of initial construction) are shown by a darkened triangular flag at the juncture of the reference line and arrow. The flag always points toward the reference tail of the line.
Surface Contour of Welds
When bead contour is important, a special flat, concave, or convex contour symbol is added to the welding symbol. Welds that are to be mechanically finished also carry a finish symbol along with the contour symbols.
Back Weld and Backing Weld Symbol
A back weld and a backing weld refer to a weld made on the opposite side of the regular weld. A back weld is made after the groove weld has been deposited. Back welds are occasionally specified to ensure adequate penetration and provide additional strength to a joint.
This particular symbol is included opposite the weld symbol. Backing welds are made before a groove weld is deposited to prevent excessive penetration of the weld metal. No dimensions of back or backing welds except the height of reinforcement are shown on the welding symbol.
Melt-Thru Weld Symbols
When complete joint penetration of the weld through the metal is required in welds made from one side only, a special melt-thru weld symbol is placed opposite the regular weld symbol. No dimension of melt-thru, except the height of reinforcement, is shown on the welding symbol.
Surfacing Weld Symbols
Welds whose surfaces must be built up by single- or multiple-pass welding are denoted by a surfacing weld symbol. The height of the built-up surface is indicated by a dimension placed to the left of the surfacing symbol. The extent, location, and orientation of the area to be built up are normally indicated on the drawing.
welding symbols chart
For more information, see ANSI/AWS A2.4, Symbols for Welding, and Nondestructive Testing.