A review of the application of weld symbols on drawings

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Superseded BS499 Pt 2 gives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).

Fig.3

Numbers to the right of a symbol or symbols relate to the longitudinal dimension of welds, eg for fillets, the number of welds, weld length and weld spacing for non-continuous welds, as Fig.4.

Fig.4

On fillet welded joints made from both sides, a staggered weld can be shown by placing a 'Z' through the reference line ( Fig.5).

Fig.5

Supplementary symbols

Weld symbols indicate the type of preparation to use or the weld type. However, there may still be occasions where other information is required. The basic information can therefore be added to in order to provide further details as shown in Figs.6, 7 and 8.

Fig.6

Fig.7

Fig.8

Weld all round

For a Rectangular Hollow Section (RHS) welded to a plate, for example:

Weld in the field or on site

The box attached to the arrow can be used to contain, or point to, other information.

Welding process type

ISO 4063 gives welding processes specific reference numbers. As shown in Fig.9 the appropriate process number is placed in the tail of the arrow. Other processes are given a unique number. In this example, 135 refers to MAG welding.

Fig.9

There are a number of additional symbols given in the Standards ( eg ISO 22553) which refer to additional welding or joint requirements. Figure 10 shows the requirement for a sealing run.

Fig.10

Compound joints/welds

A compound weld could be a 'T' butt weld which requires fillet welds to be added to increase the throat thickness as shown in Fig.11.

Fig.11

The broken reference line

Fig.12

The main feature that distinguishes weld symbol standards is that for ISO 2553 and BS EN 22553, there is an additional feature of a broken reference line.
This method is used when a weldment or weld preparation needs to be specified on the 'other side' of the arrow as shown in Fig.12.
Any symbol that is used to show a joint or weld type feature on the other side of the arrow line is always placed on a dotted line.
BS 499 and AWS require symbols to be placed above the reference line (which indicate the other side) or below the reference line (indicating the arrow side).

Summary

Weld symbols are a very useful way of communicating welding requirements from the design office to the shop floor.
It is essential that the 'rules' of the standard used are correctly applied by drawing office personnel. However, it is also important that shop floor personnel are able to read and understand the details of weld symbols.
Much of this requirement can be met by reference to the standard being used within the organisation and by the drawing office personnel considering the needs of the end user such as the welders, welding supervisors, welding inspection personnel and welding engineers in order to minimise costly mistakes due to misinterpretation.
Training of all personnel in the correct use of weld symbol specifications also plays an important role in ensuring that weld symbols are both correctly applied and correctly read.
This article was written by Mark Cozens of Weld-Class Solutions.