Welding Symbols Explained: Complete List with Diagrams

1. Scope

This standard outlines the method of presenting welding symbols. It is applicable to both metal fusion welding and resistance welding.

2. Normative References

GB/T 5185 Designation of Metal Welding and Brazing Methods in Drawings; GB/T 12212 Technical Drawings – Dimension, Proportions, and Simplified Representation of Welding Symbols.

3. Basic Requirements

3.1 The welding symbol should clearly indicate the type of weld to be made and should not include excessive notes. The representation of the weld can be through the use of a weld graphic method or a weld symbol annotation method. The method of weld symbol marking is generally preferred, but if it’s unclear or if the graphical method is simpler, it can be used instead.

3.2 The welding symbol consists of a basic symbol and leader, and additional symbols such as an auxiliary symbol, supplementary symbol, and weld size symbol can be added if needed. The scale, size, and representation method of the graphic symbols should comply with GB/T 12212. For commonly used graphic methods in GB/T 12212, see Appendix C (normative appendix).

3.3 When professional standards specify the weld size and process, these should be indicated in the welding symbol. The welding method marked on the drawing should be in accordance with Appendix B (normative appendix). Any post-welding processing such as spading, grinding, or cutting should be indicated in the technical requirements.

I. Basic Forms of Weld Seam Overlap

1. Butt Joint

2. Overlap

3. Right Angle Connection

4. T-shaped Joint

5. Bevel Joint:

II. Basic Fracture Shapes of Weld Seams

No.	Schematic Diagram	Bevel Form	Welding symbols
1		I-shaped Groove
2		K-shaped Groove
3		V-shaped Groove
4		X-shaped Groove
5		Y-shaped Gap
6		X-shaped (with pure edge)
7		Oblique V-shaped Gap
8		Oblique Y-shaped Gap
9		Overlap (three-side weld)
10		U-shaped Gap
11		Single-sided U-shaped Break
12		Spot Welding
13		Irregular Break
14		Irregular Break
15		Irregular Break

III. Welding Symbols

1. Definition of Welding Symbols

These are symbols used to indicate welding methods, weld form, and weld size, among other technical content on a drawing.

2. Components of Welding Symbols

(1) Weld symbols:

1. Basic Symbols: Symbols representing the cross-sectional shape of the weld.

2. Supplementary Symbols: Symbols indicating the surface shape of the weld.

3. Additional Symbols: Symbols used to further explain certain characteristics of the weld.

(2) Reference Line:

Composed of an arrow line and a reference line.

(3) Weld Size Symbols:

Symbols indicating the dimensions of the weld shape.

3. Standard Position of Weld Symbols on Drawings

The standards specify clear rules for the placement of weld symbols, dimension symbols, and dimension values on the reference line. When creating welding diagrams, these rules must be strictly followed.

Symbols and numeric values are marked in seven zones, A~G, relative to the reference line. The positions of these zones relative to the reference line are fixed, regardless of changes in the direction of the arrow line, their position relative to the reference line will not change.

A Zone: Main functional area: Marks basic symbols, special symbols, backing strip symbols in supplementary symbols, and symbols for plane, convex, and concave in auxiliary symbols.

B Zone: Supplementary functional area: Located above or below the A Zone, marking the groove angle α, groove surface angle β, and root gap b in the weld size.

C Zone: On the left side of the basic symbol, marking the dimension symbols and values on the cross section of the weld, such as blunt edge p, groove depth H, weld angle size K, reinforcement h, effective weld thickness S, root radius R, weld width C, and fusion core diameter d.

D Zone: On the right side of the basic symbol, marking staggered weld symbols, and marking the longitudinal (length direction) size values of the weld, such as the number of weld sections n, weld length l, and weld spacing e.

E Zone: Marks the three-side weld symbols in supplementary symbols.

F Zone: Marks the field weld symbols and surrounding weld symbols in supplementary symbols.

G Zone: Marks the tail symbols in supplementary symbols. After the tail symbols, the number of identical welds N, welding method code, weld quality, and inspection requirements are marked.

4. Representation Codes of Common Welding Methods in Drawings

Refer to the table below (note: the table is not provided in the query).

5. For instance

(Example 1)

Indication: Weld height is 3, staggered welding, weld seam length is 50, interval is 30, site welding is required.

Example 2:

Statement: Spot weld diameter is 5, the number of spot welds is 10, and the interval is 30.

Example 3:

Indication: The weld height is 3, with full welding around. The joint is made using CO₂ gas shielded welding, with a total of 5 locations.

Example 4:

Indication: The weld height is 3, with a bevel V-groove, the weld surface is ground flat, the weld length is 30, in total 5 segments, and the welding is carried out using CO₂ gas shielded welding.

6. Basic symbols

The basic symbol represents the cross-sectional shape of the weld, as illustrated in Table 1.

Table 1 Basic Welding Symbols

Serial No	Symbol name	Sketch Map	Weld symbol
1	Rolled edge weld (fully melted rolled edge) Note: incompletely melted rolled edge weld is indicated by I-shaped weld symbol, and the effective weld thickness S is added, as shown in Table 7
2	I-shaped weld
3	V-shaped weld
4	Unilateral V-shaped weld
5	V-shaped weld with blunt edge
6	Single V-shaped weld with blunt edge
7	U-shaped weld with blunt edge
8	J-shaped weld with blunt edge
9	Sealing weld
10	Fillet weld
11	Plug weld or slot weld
12	Spot weld
13	Seam weld

7. Auxiliary symbols

1. Auxiliary welding symbols represent the shape characteristics of the weld surface and are shown in Table 2.

Table 2 Auxiliary Welding Symbols

Serial No	Symbol name	Sketch Map	Symbol	Explain
1	Plane symbol			The weld surface is flush
2	Concave symbol			Weld surface depression
3	Convex symbol			Raised weld surface

Note: Auxiliary symbols can be omitted if the surface shape of the weld does not need to be specified.

2. See Table 3 for application examples of auxiliary symbols.

Table 3 Application Examples of Auxiliary Symbols

Serial No	Symbol name	Sketch Map	Symbol
1	Plane V butt weld
2	Convex X butt weld
3	Concave fillet weld
4	V-shaped weld of flat back

8. Supplementary symbols

Supplementary symbols are used to add additional information about the characteristics of the welds. For examples of supplementary symbols, refer to Table 4.

See GB/T 5185 for symbols of welding process methods.

Table 4 Supplementary Symbols

Serial No	Symbol name	Sketch Map	Symbol	Explain
1	Symbol with backing plate			Indicates that there is a backing plate at the bottom of the weld
2	Three side weld			Indicates that there are welds on three sides
3	Peripheral weld			Indicates welding around the workpiece
4	Site Symbols			Indicates welding on site
5	Tail symbol			Mark welding process method

Table 5 Example of supplementary symbol application

Serial No	Sketch Map	Dimension example	Explain
1			Indicates that there is a backing plate at the bottom of the back of the V-shaped weld
2			There are welds on three sides of the workpiece, and the welding method is manual arc welding
3			It means welding around the workpiece on site

IV. Position of Welding Symbols on Drawings

1. Basic requirements

Complete weld representation methods consist of the basic symbol, auxiliary symbol, supplementary symbol, leader, dimension symbol, and data. The leader line is composed of an arrow leader line (also known as an arrow line) and a datum line, which can be either a solid line or a dotted line, as illustrated in Figure 1.

Fig. 1 Leader line

2. Relationship between arrow line and welding joint

Two terms are used to describe the relationship between the arrow lines and the joints:

a. Arrow side of the connector;

b. Non-arrow side of the connector.

Refer to Figures 2 and 3 for a description of these two terms.

(a) Weld seam on arrow side

(b) Weld seam is on the non arrow side

Fig. 2 T-joint with single fillet weld

Fig. 3 Cross joint of double fillet weld

3. Arrow position

Generally, there is no specific requirement for the position of the arrow line relative to the weld, as shown in Figures 4(a) and (b). However, when marking single-sided V-shaped, single-sided V-shaped with a blunt edge, and J-shaped welds, the arrow must point towards the workpiece with the groove, as shown in Figures 4(c) and (d). If necessary, bending the arrow line once is allowed, as shown in Figure 5.

4. Location of reference line

The dotted line of the reference line can be drawn either above or below the solid line of the reference line. The datum line must be parallel to the bottom edge of the drawing.

5. Position of datum mark relative to datum line

a. If the weld is on the arrow side of the joint, the basic symbol shall be marked on the solid line side of the datum line, as shown in Fig. 6 (a);

b. If the weld is on the non-arrow side of the joint, the basic symbol shall be marked on the dotted line side of the datum line, as shown in Fig. 6 (b);

c. When symmetrical welds and double-sided welds are marked, dotted lines may not be necessary, as shown in Fig. 6 (c) and (d).

Fig. 6 Position of basic symbol relative to reference line

V. Weld Size Symbol and Its Marking Position

1. Basic Dimensions and Related Concepts of Welds

1. Weld Toe:

The junction between the surface of the weld and the parent metal.

2. Weld Width (B):

The distance between the two weld toes on the surface of the weld.

3. Weld Thickness:

In the cross-section of the weld, the distance from the front of the weld to the back of the weld.

4. Leg Size:

The length of the right-angled side in the largest isosceles right-angled triangle drawn in the cross-section of the fillet weld.

5. Weld Leg:

In the cross-section of the fillet weld, the shortest distance from a weld toe on one right-angled surface to another right-angled surface.

6. Penetration Depth:

In the cross-section of the weld joint, the depth of melting of the parent metal or the previous weld seam.

7. Welding Form Factor:

The ratio of weld width B to calculated weld depth H on the single seam cross-section during fusion welding.

8. Reinforcement:

The maximum height of the weld metal that exceeds the line on the surface of the parent metal.

9. Weld Root:

The junction of the back of the weld and the parent metal.

10. Crater

During arc welding, a depression formed at the end of the welding path due to improper arc breaking or arc extinguishing.

11. Weld Pool

During fusion welding, under the influence of the welding heat source, the part of the metal on the workpiece that forms a certain geometric shape and becomes liquid.

12. Kerf Angle:

The angle between two kerfs;

13. Angle of groove surface:

The angle between the end face of the groove to be machined and the groove surface:

2. General requirements

2.1 If necessary, datum symbols can be provided with dimension symbols and data. See Table 6 for dimension symbols.

Table 6 Weld Size Symbols

Symbol	Symbol name	Example diagram	Symbol	Symbol name	Example diagram
δ	Workpiece thickness		e	Weld spacing
α	Groove angle		K	Fillet size
b	Root gap		d	Nugget diameter
P	Blunt edge		S	Effective thickness of weld
c	Weld width		N	Number of identical welds symbol
R	Root radius		H	Groove depth
L	Weld length		h	Surplus height
n	Number of weld segments		β	Groove face angle

2.2 The marking principles for the weld size symbol and data are illustrated in Figure 7.

a. The dimensions of the cross-section of the weld are indicated on the left side of the basic symbol;

b. The dimension in the length direction of the weld is indicated on the right side of the basic symbol;

c. The groove angle, groove face angle, and root gap dimension are indicated on the top or bottom of the basic symbol;

d. The number symbol for the same weld is indicated at the end;

e. When there are many dimension data to be marked and they are difficult to distinguish, corresponding dimension symbols can be added in front of the data for clarity.

2.3 See Table 7 for the example of weld size marking.

Table 7 Example of Weld Dimension

Serial No	Weld name	Sketch Map	Welding dimension symbol	Example
1	Butt weld		S: Effective thickness of weld
2	Crimping weld		S: Effective thickness of weld
3	Continuous fillet weld		K: Fillet size
4	Intermittent fillet weld		L: Weld length, excluding crater; e: weld gap ;n: number of weld segments
5	Staggered intermittent fillet weld		L: Weld length, excluding crater;e: weld gap;n: number of weld segments; K: weld fillet size
6	Plug weld or slot weld		L: Weld length, excluding crater; e: weld gap; n: number of weld segments; c: slot width.
			e: Weld clearance; n: number of weld segments; d: diameter of hole.
7	Seam weld		L: Weld length, excluding crater; e: weld gap; n: number of weld segments; c: weld width.
8	Spot weld		n: Number of weld segments; e: spacing; d: weld spot diameter.

3. Description of dimension symbols

3.1 The size for determining the position of the weld shall be indicated on the drawing rather than within the weld symbol.

3.2 If no marking is present on the right side of the basic symbol and no further information is given, it is assumed that the weld is continuous along the entire length of the workpiece.

3.3 If there is no marking on the left side of the basic symbol and no other information is given, it is assumed that the butt weld should be completely welded.

3.4 When the plug weld and groove weld have beveled edges, the size of the bottom of the hole should be marked.

VI. Example of Symbol Application

Appendix A

(Informative appendix)

Example of symbol application

A. 1 Application of basic symbols

See Table A.1 for examples of basic symbols.

A. 2 Basic symbol combination

See Table A.2 for application examples of basic symbol combination.

A. 3 Combination of basic symbols and auxiliary symbols

See Table A.3 for examples of the combination of basic symbols and auxiliary symbols.

A. 4 Special cases

See Table A.4 for the marks of flared weld, unilateral flared weld, stack weld and lock edge weld.

Table A.1 Application examples of basic symbols

Table A.2 Example of basic symbol combination

Table A.3 Examples of combination of basic symbols and auxiliary symbols

Table A.4 Marking of Special Welds

Appendix B

(Normative appendix)

Welding method and its name

B. 1 Marking of welding method in drawings

When various welding methods are marked on the drawings, Chinese characters shall be used instead of the codes specified in GB/T 5185.

B. 2 Common welding methods and their names

Common welding methods and their names are as follows:

a) Manual arc welding (coated electrode MIG welding);

b) Submerged arc welding;

c) MIG welding: Molten inert gas protection welding;

d) MAG welding: Molten non inert gas protection welding;

e) TIG: Tungsten inert gas welding.

f) Spot welding;

g) Oxygen acetylene welding;

h) Energy storage welding;

i) Flame brazing;

j) Induction brazing;

k) Soldering (tin).

Appendix C

(Normative appendix)

Graphic method

C. 1 General

When a simple representation of the weld is needed in the drawing, it can be shown through views, cross-sectional views, or cross-sectional drawings. This appendix provides a straightforward method commonly used by companies as outlined in GB/T 12212 for ease of use. For more information, refer to GB/T 12212.

C. 2 Views

C. 2.1 The drawing method of welds is shown in Fig. C.1 and Fig. C.2 (a series of fine solid line segments representing welds can be drawn by hand).

It is also allowed to use thick lines (2b ～ 3b) to represent welds, as shown in Fig. C.3.

However, in the same drawing, only one painting method is allowed.

C. 2.2 In the representation of the end face of the weld, a thick solid line is typically used to outline the contour of the weld.

If needed, a thin solid line can be used to depict the groove shape before welding, as depicted in Figure C.4.

C. 3 Sectional view or sectional view

In sectional or profile views, the metal fusion welding area of the weld is typically marked in black, as depicted in Figure C.5. If the groove shape needs to be indicated as well, the fusion welding area can also be represented as outlined in Clause C.2.2, as shown in Figure C.6.

VII. Welding Symbol Examples