Subscribe to our newsletter to receive the latest news and events from TWI:

Subscribe >
Skip to content

A review of the application of weld symbols on drawings - Part 1


Weld symbols have been used for many years and are a simple way of communicating design office details to a number of different industrial shop floor personnel such as welders, supervisors, and inspectors. Subcontractors are often required to interpret weld symbols on engineering drawings, from perhaps the main contractor or client. It is essential that everyone should have a full understanding of weld symbol requirements to ensure that the initial design requirement is met.

There are a number of standards which relate to weld symbols including British, European, International and American (American Welding Society) standards. Most of the details are often similar or indeed, the same, but it is essential that everyone concerned knows the standard to be used. One of the first requirements therefore is:

Which standard?

The UK has traditionally used BS 499 Part 2. This standard has now been superseded by BS EN 22553, however in many welding and fabrication organisations there will be old drawings used that make reference to out of date standards such as BS 499 Pt 2.

BS EN 22553 is almost identical to the original ISO 2553 standard on which it was based. Therefore we can say, for at least this article's scope, there are no significant differences, but it is essential that the reader consults the specific standard. The American system is also similar in many respects but will not be covered here.

Basic requirements

All the standards have the same requirements in relation to the following items:

  • Arrow line and arrow head
  • Reference line

The arrow line can be at any angle (except 180 degrees) and can point up or down. The arrow head must touch the surfaces of the components to be joined and the location of the weld. Any intended edge preparation or weldment is not shown as an actual cross sectional representation, but is replaced by a line. The arrow also points to the component to be prepared with single prepared components. See Figs. 1-4.

Fig. 1.
Fig. 2.
Fig. 3.
Fig. 4.

Symbol types

To the basic set-up of the arrow and reference line, the design draughtsperson can apply the appropriate symbol, or symbols for more complex situations.

The symbols, in particular for arc and gas welding, are often shown as cross sectional representations of either a joint design or a completed weld. Simple, single edge preparations are shown in Fig. 5.

For resistance welding, a spot weld and seam weld are shown in Fig. 6:

Fig. 5.
Fig. 5.
Fig. 6.
Fig. 6.

Joint and/or weld shape

The above examples can be interpreted as either the joint details alone or the completed weld, however, for a finished weld it is normal to find that an appropriate weld shape is specified. Using the examples above, there are a number of options and methods to specify an appropriate weld shape or finish.

Butt welded configurations would normally be shown as a convex profile (Fig.7 'a', 'd' and 'f') or as a dressed-off weld as shown in 'b' and 'c'. Fillet weld symbols are always shown as a 'mitre' fillet weld (a right angled triangle) and a convex or concave profile can be superimposed over the original symbol's mitre shape. See Fig. 7.

Fig. 7.
Fig. 7.

Part 2 of this explanation of weld symbols covering more complex situations will appear in the next issue.

For more information please email: