The application of welding symbols to working drawings

The following notes are meant as a guide to the method of applying the more commonly used welding symbols relating to the simpler types of welded joints on engineering drawings. Where complex joints involve multiple welds it is often easier to detail such constructions on separate drawing sheets.

Each type of weld is characterized by a symbol given in Table 26.1 Note that the symbol is representative of the shape of the weld, or the edge preparation, but does not indicate any particular welding process and does not specify either the number of runs to be deposited or whether or not a root gap or backing material is to be used. These details would be provided on a welding procedure schedule for the particular job.

It may be necessary to specify the shape of the weld surface on the drawing as flat, convex or concave and a supplementary symbol, shown in Table 26.2, is then added to the elementary symbol. An example of each type of weld surface application is given in Table 26.3.

A joint may also be made with one type of weld on a particular surface and another type of weld on the back and in this case elementary symbols representing each type of weld used are added together. The last example in Table 26.3 shows a single-V butt weld with a backing run where both surfaces are required to have a flat finish.

A welding symbol is applied to a drawing by using a reference line and an arrow line as shown in Fig. 26.1. The reference line should be drawn parallel to the bottom edge of the drawing sheet and the arrow line forms an angle with the reference line. The side of the joint nearer the arrow head is known as the 'arrow side' and the remote side as the 'other side'.

The welding symbol should be positioned on the reference line as indicated in Table 26.4.

Sketch (a) shows the symbol for a single-V butt weld below the reference line because the external surface of the weld is on the arrow side of the joint.

Sketch (b) shows the same symbol above the reference line because the external surface of the weld is on the other side of the joint.

Table 26.1 Elementary weld symbols

From of weld

Illustration

BS symbol

Butt weld between flanged plates (the flanges being melted down completely)

Square butt weld

Single-V butt weld

Single-bevel butt weld

Single-V butt weld with broad root face

Single-bevel butt weld with broad root face

Single-U butt weld

Single-J butt weld

Backing or sealing run

Fillet weld

Plug weld (circular or elongated hole, completely filled)

Plug weld (circular or elongated hole, completely filled)

Spot weld (resistance or arc welding) or projection weld

Spot weld (resistance or arc welding) or projection weld

Butt Weld Symbol

Seam weld

Table 26.2 Supplementary symbols

Shape of weld surface BS symbol flat (usually finished flush)

Sketch (c) shows the symbol applied to a double-V

butt weld.

Sketch (d) shows fillet welds on a cruciform joint where the top weld is on the arrow side and the bottom weld is on the other side

The positioning of the symbol is the same for drawings in first or third angle projection.

Additional symbols can be added to the reference line as shown in Fig. 26.2. Welding can be done in the

Table 26.3 Some examples of the application of supplementary symbols

Form of weld

Illustration

BS symbol

Flat (flush) single-V butt weld

Convex double-V butt weld

Concave fillet weld

Flat (flush) single-V butt weld with flat (flush) backing run

Table 26.4 Significance of the arrow and the position of the weld symbol

Illustration

Graphic representation

Symbolic representation

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1 is the arrow line

2 is the reference line

3 is the symbol

Weld Symbol Definitions

Fig. 26.2 Indication of (a) site welds and (b) continuous welds factory or on site when plant is erected. A site weld is indicated by a flag. A continuous weld all round a joint is shown by a circle at the intersection of the arrow and the reference line. Note that if a continuous weld is to be undertaken at site then both symbols should be added to the drawing.

The introductory notes relating to welding processes are of a general nature. There are many specialized methods listed in BS 499. Each process is given an individual identification number and group headings are as follows; (a) Arc welding, (b) Resistance welding, (c) Gas welding, (d) Solid phase welding; Pressure welding, (e) Other welding processes, (f) Brazing, soldering and braze welding.

A welding procedure sheet will usually give details of the actual process to be used on a particular joint. On the drawing, a reference line with an arrow pointing

towards the joint at one end, will have a 'fork' added at the other containing the selected number. In the example given below, the figure 23 indicates that projection welding is the chosen method.

Useful standards for the draughtsman are as follows: BS 499-1 gives a Glossary for welding, brazing and thermal cutting. Includes seven sections relating to welding with pressure, fusion welding, brazing, testing, weld imperfections and thermal cutting. Information for welding and cutting procedure sheets is provided. BS 499-1 Supplement. Gives definitions for electrical and thermal characteristics of welding equipment.

European arc welding symbols in chart form are illustrated in BS 499-2C: 1999.

Symbolic Representation on Drawings for Welded, Brazed and Soldered Joints are illustrated in BS EN 22553. Welded and Allied Processes, Nomenclature of Processes and Reference Numbers are given in BS EN ISO 4063: 2000.

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