Weld symbols are standardised graphical symbols used on engineering drawings to indicate the type, size, and location of welds. They follow international standards such as ISO 2553 and are essential for communicating welding requirements in fabrication and manufacturing.
Quick Reference: The chart below shows the most common weld symbols used in engineering drawings based on ISO 2553, including fillet, groove, and supplementary weld symbols.
The British Standard for weld symbols was BS EN 22553 which has been superseded by BS EN ISO 2553:2019. When identification of the weld process is required as part of the weld symbol the relevant weld process code is listed in BS EN ISO 4063.
The weld symbol always includes
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Note: Weld symbols on the full reference line relates to welds on the near side of the plate being welded. Weld symbols on the dashed line relates to weld on the far side of the plate. If the welds are symmetrical on both sides of the plate the dashed line is omitted. If the dashed line is above the full line then the symbol for the nearside weld is drawn below the reference line and the symbol for the farside weld is above the dashed line. For example see sketch below Supplemetary symbols below.
ISO 2553 weld symbol numbering system:
The numbered elements in the diagram correspond to the following:
Welding.....Weld process numbers.
Supplementary weld symbols are used alongside primary weld symbols to provide additional information about the shape and finish of the weld surface. These symbols are not used on their own.
These symbols may be applied to both the near side and far side of the joint, depending on their position relative to the reference line.
The weld symbols below are used in addition to the primary weld symbols as shown above. They are not used on their own.
Example: The diagrams above show how supplementary symbols are applied to identify the weld surface profile on either the near side or far side of the joint.
Below is an example of the application of one of these symbol illustrating the identification of the location of the weld relative to the symbol.
Complementary weld symbols provide additional instructions related to welding operations and requirements.
These symbols are used to provide clarity on manufacturing requirements and ensure correct welding procedures are followed.
Note: Supplementary and complementary symbols are always used in conjunction with primary weld symbols to fully define the weld requirements.
Fillet welds are dimensioned using throat thickness (a), leg length (z), and weld length. The effective throat thickness is related to the leg length by the equation:
z = a × √2
Intermittent fillet welds are specified by the number of welds, weld length and spacing between welds. This is typically shown as:
Plug and slot welds are dimensioned by diameter or width, spacing and number of welds depending on the application.
A weld symbol chart shows the standard symbols used on engineering drawings to represent different weld types, sizes and positions according to ISO 2553.
The current standard for weld symbols is BS EN ISO 2553:2019, which defines the representation of welds on engineering drawings.
A weld symbol typically consists of an arrow line, a reference line, an optional dashed line, and a weld symbol indicating the type of weld.
The arrow side weld is applied to the side of the joint the arrow points to, while the other side weld is applied to the opposite side, usually indicated by a dashed reference line.
Weld symbol charts include fillet welds, groove welds, plug welds, slot welds and supplementary symbols such as contour and finish symbols.
Weld symbols provide a standardised way to communicate welding requirements, ensuring accuracy, consistency and clarity in fabrication and manufacturing.
A weld symbol chart is read by interpreting the symbol on the reference line, along with dimensions and supplementary symbols. The position of the symbol relative to the reference line indicates whether the weld is on the arrow side or the opposite side.
Fillet weld symbols represent triangular welds used in corner or lap joints, while groove weld symbols represent welds in prepared joints such as butt welds, where material edges are shaped before welding.
Numbers on a weld symbol indicate dimensions such as weld size, length and spacing. For example, values may define throat thickness, leg length, or the distance between intermittent welds.