Importance of Welding symbols:
Welding symbols are the integral part and the basic requirements for fabrication as they provide vital information for the joint location, weld size & length, weld type as well as quality requirements on the fabrication or construction drawing. The scheme for the symbolic representation of welds on engineering drawings used with the “third angle” method of projection around the globe. This is the method predominantly used in the United States.
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There has been always confusion between a welding symbol and weld symbol. A Welding symbol is different from a weld symbol; which is a graphic character connected to the reference line of a welded symbol specifying the joint geometry.
So basically, the weld symbol is a part of the welding symbol. A full welding symbol consists of an arrow line, reference line, welding symbol. A tail is an optional part of the welding symbol used to provide additional information which might be deemed necessary for the production of the welding joint. In welding symbol terminology, a clear understanding of the following three terms are very important:
- Primary Welding symbols
- Supplementary symbols
- Welding symbols placement
Figure 1 shows the master chart of the welding symbol showing the standard location of elements of a welding symbol.
As stated earlier, Weld Symbol is a term used explicitly to designate a specific type of weld. The pertinent types of welds considered under the governing AWS 2.4 specification for ‘Symbols for welding, brazing and non-destructive examination’ and the basic weld symbols are shown in the below figure 2.
Primary and Supplementary Welding Symbols
In contrast to weld symbol, Welding Symbol provides comprehensive information with respect to the geometry of preparation, fit-up, and welding of joints. It is composed of standards elements including a weld symbol, arrow line, reference line and uses any of the applicable supplementary symbols to effectively complement such information using the help of tail.
The important supplementary welding symbols are shown in below figure 2.
Understanding Welding symbols on Drawing
When welds are specified on engineering and fabrication drawings, combinations of lines and other geometry are used known as welding symbols for describing the type of weld, its size, and other processing and finishing information. Here you will learn to use the most common symbols and their meaning and their application. The complete set of symbols is given in a standard published by the American National Standards Institute (ANSI) and the American Welding Society (AWS): ANSI/AWS A2.4, Symbols for Welding and Nondestructive Testing.
The horizontal line also called the reference line on which other welding symbols are placed. The instructions for weld are written along the reference line. An arrow line connects the reference line to the joint that is to be welded. 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 detailed drawing, or any information that aids in the making of the weld that does not have its own special place on the symbol.
Arrow side or other side welding
We usually notice in drawing that there are two sides to the joint to which the arrow points, and hence two possible places for welding. For example, when two steel plates are joined together into a T shape, welding may be done on either side of the T joint as shown in the below figure.
The weld symbol differentiates 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 called the arrow side, and its weld is made according to the instructions given below the reference line. The other side of the joint is called the other side, and its weld is made according to the instructions given above the reference line. The simple rule is that below the line is the arrow side and above the line is the other side applies regardless of the arrow’s direction.
Fillet weld symbol
The length of the weld is given to the right of the symbol, while the size of the weld is specified on the left-hand side of the weld symbol always as we can see in the below figure.
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. Note that the spacing, or pitch, is not the clear space between the welds, but the center-to-center (or end-to-end) distance as shown in the below figure for intermittent fillet weld.
All around Welding Symbol
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.
Groove (Butt) Welds on drawing
A groove weld or butt weld is used when two parts come together in the same plane. These welds are applied in a butt joint and may have a preparation (e.g. V groove, U groove, etc.) or not (Square groove) before welding. Various types of groove welds and their welding symbols (add arrow line when drawing in a drawing) used on the drawing are shown in the below figure.
Dimensions of a groove weld
Flare V Groove and bevel groove weld Joint
Flare V Groove weld joints are 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 is 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.
Back, Backing weld, Surfacing weld
A back weld or backing symbol is the same for both, tail data to be checked for further information to distinguish between them.
A back weld is a weld made in the groove of a joint and followed by a weld, welded to the root side. This is most commonly used to ensure complete weld penetration on CJP grooves welds. The Back weld is welded after the root is grinded or gouged out to make sure that the weld from the face side is having thorough penetration.
A backing weld is made on the root side of a groove in order to ensure that the weld that is going to be made in the groove from the face side does not melt through the backside. This may also help ensure CJP weld.
Surfacing welds are made by single or multiple passes on components for a variety of reasons. These may include a buildup of worn material, hard-facing a part, or increasing part thickness by buttering. This symbol may be on the arrow side of a joint only. It is important that the arrow points specifically where the surfacing shall be added.
These welds may include a thickness of weld which will be located to the left of the weld symbol and may also show a length to the right of the symbol as shown in the below picture.
Example applications of Welding Symbols in actual parts
Various types of weld what you can encounter in welding drawings are shown in below picture with examples. Such simple fillet weld, weld with defined length, staggered weld, full penetration groove weld