How to understand welding symbols in steel detailing

How to understand weld symbols in steel detailing is a key part of we for welders, Inspectors & Engineers. Drawings contain special symbols to specify the weld location, type of joint, size and amount of weld metal to be deposited in the joint. The American Welding Society (AWS) has standardized them. 

A welder will see them whenever he or she performs a welding job from a set of prints. So, as a steel detailer we need to be familiar with all the elements of a standard welding symbol, location and meaning of the basic weld symbols. Previously, we have discussed about "Types of weld in steel structures".

To start learning, note that there are three main elements of a welding symbol:

• Arrow line
• Reference line
• And tail info

Fig 1: Standard welding symbols 

The reference line is a horizontal line which is heart of welding symbol that is used to indicate type of weld, size, and length etc. The arrow is used to point to the location of the weld, and the tail contains additional information about the weld. 

Fig 2: Standard weld symbol

The tail of the welding symbol is used only when necessary to include a process, specification, or other reference information. Weld symbols refer to the symbols for a specific type of weld, such as fillet, groove, butt, surfacing, plug, or slot.

Fig 3: Examples of weld applied to reference line of weld symbol. 

The weld symbol is only part of the information required in the welding symbol. When used to disseminate information, the term welding symbol refers to the total symbol, which includes all the weld symbols needed to specify the weld(s) required. How the weld symbol is applied to the reference line is as shown in Fig 3.

Fig 4: Example of specifying weld location 

Regardless of the direction of the arrow, all information applied to the reference line on a welding symbol is read from left to right. A listing of welding symbols is as shown in Fig 4.

Fig 5: location of elements of welding symbol 

The size, length, pitch (center-to-center spacing), groove angle, and root opening of a weld all have designated locations. These locations are determined by the side of the reference line on which the weld symbol is placed (See Fig 5).

Fig 6: Supplementary weld symbol

Besides the basic weld symbols, the welding symbol may include supplementary symbols (See Fig 6). Contour symbols show how the face is to be formed; finish symbols indicate the method to use to form the contour.

​Another supplementary symbol is the weld-all-around symbol. When this symbol is placed on a welding symbol, welds are to continue all around the joint. Yet another symbol on Snap 06 is the field weld symbol, a black flag that points toward the tail of the welding symbol. For welds that cannot be made in the shop, for size, transportation, constructability, or other reasons, this symbol directs the welder to make the weld in the field, which could be on site or filed.

Fig 7: Example of welding finish symbol 

A finish symbol (when used) shows the method of finish, C represents chipping, M means machining, and G indicates grinding, not the degree of finish. How contour and finish symbols are applied to a welding symbol is illustrated in Snap 07. This symbol indicates the weld is to be ground flush. Also, notice that the symbols are placed on the ​same side of the reference line as the weld symbol.

Conclusion

Achieving a training certificate of a professional welder is insufficient until you know how to read the draftsman’s drawing prior to welding. The sketch of welding symbols becomes a headache if you are not familiar with the basics of these symbols. This set of symbols simplifies communication between the planner and the workmen. Welding symbol is a very well-drafted language to master for better employment worldwide.