Weld Symbols

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 This standard has now been superseded by BS EN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that make reference to out of date standards such as BS 499 Pt 2.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. 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.

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

A review of the application of weld symbols

on drawings - Part 2

Part 1 of this article which appeared in the May/June issue of Connect, dealt with the most basic weld symbols as they

appear on engineering drawings. As previously mentioned, it is essential that all concerned in any project are aware of

which Standard is being applied.

Weld sizing

In order that the correct size of weld can be applied, it is common to find numbers to either the left or to the right of the

symbol.

For fillet welds, numbers to the left of the symbol indicate the design throat thickness, leg length, or both design throat

thickness and leg length requirements. Figure 1 gives examples of symbols used in different Standards. Fig.1

For fillet welds:

Superseded BS499 Pt 2 gives

a = design throat thickness

b = leg length

ISO 2553/EN 22553 requirements

a = design throat thickness

z = leg length

s = penetration throat thickness

For butt joints and welds, an S with a number to the left of a symbol refers to the depth of penetration as shown in

Fig.2.

Fig.2

When there are no specific dimensional requirements specified for butt welds on a drawing using weld symbols, it

would normally be assumed that the requirement is for a full penetration butt weld ( Fig.3).