1. Chapter 4 Welding Symbols
Weld Specification on Prints • Weld Joints • Weld Types • Welding Symbols • Edge Preparation • Brazing Symbols • Nondestructive Examination (NDE) Symbols

2. Object dimensions and welding symbols on a print convey fabrication information to the welder.
Object lines on the prints show the joint members before welding. Dimension lines are used to indicate the size and location of object features. Details provide additional information and show specific dimensions and features in a larger format for easier interpretation. Notes indicate additional fabrication information that may apply to a specific part or all parts on the print. The welding symbol indicates the location of the weld on the joint. See Figure 4-1. The completed weld, however, is not typically shown on the prints.

3. A weld is specified with a welding symbol and is completed by the welder using the specified process.
Weld specifications and locations are indicated on a print using welding symbols. A welding symbol is a graphic symbol that shows weld locations and specifications on prints. Welders interpret welding symbols and other weld joint information on a print to weld the part to required specifications. A welding symbol and other print information provide all information required to complete the specified weld using the required process in the shop or in the field. See Figure 4-2.

4. The five basic weld joints are the butt, lap, T, edge, and corner weld joints.
Weld joints are commonly specified by the engineer and are indicated on prints. Basic weld joints include butt, lap, T, edge, and corner joints. See Figure 4-3.

5. Weld types are classified by the cross-sectional shape of the weld.
The weld type specified for the weld joint is indicated by welding symbols on the prints. Weld types include groove, fillet, plug, slot, stud, spot, projection, seam, back, backing, surfacing, and edge welds. See Figure 4-4. Different weld types can be used with different weld joints as necessary in the fabrication process.

6. Groove welds are classified by the edge shape of the joint members.
The shape of a groove weld is determined by the edge shape(s) and the orientation of the joint members. See Figure 4-5. Groove welds are classified as square‑groove, V‑groove, bevel‑groove, U‑groove, J‑groove, flare‑V‑groove, and flare‑bevel‑groove, depending on the edge preparation performed.

7. Fillet welds are triangular in cross-sectional shape
Fillet welds are triangular in cross-sectional shape. They transfer loads to joint members positioned at 90° to one another.
Fillet welds are the most popular type of weld. They require little or no edge preparation. A single‑fillet weld is a fillet weld that has filler metal deposited on one side. Single-fillet welds are limited to smaller loads than double‑fillet welds. A double‑fillet weld is a fillet weld that has filler metal deposited on both sides. The weld on both sides provides additional strength. See Figure 4-6.

8. Plug and slot welds provide strength without affecting the edges of the joint members.
A plug weld is a weld type in the cross‑sectional shape of a hole in one of the joint members. A slot weld is a weld type in the cross‑sectional shape of a slot (elongated hole) in one of the joint members. Plug and slot welds are made through the opening of the hole or slot to the other joint member. The round hole, which is filled or partially filled with weld metal during the welding operation, becomes the plug weld. The elongated hole, which is filled or partially filled with filler metal during the welding operation, becomes the slot weld. See Figure 4-7.

9. Stud welds permanently join threaded fasteners to parts using heat and pressure.
A stud weld is a weld type produced by joining threaded studs with other parts using heat and pressure. During the welding process part of the stud is melted, providing weld reinforcement at the base of the stud. After welding, the stud is permanently joined to the part. See Figure 4-8.

10. The size of spot and projection welds is the diameter of the weld nugget. The size of seam welds is the diameter of the weld nugget and length of the weld.
Spot, projection, and seam welds are welds produced by fusion between or on joint members using heat and pressure. Electric current directed through the joint members is commonly used to produce the heat required. A weld nugget is formed where the fusion occurs. See Figure 4-9.

11. Back welds are deposited on the opposite side of the part after the groove weld is made. Backing welds are deposited on the opposite side of the part before the groove weld is made.
The difference between these two welds is based on when the weld is deposited. Back welds are deposited after the weld on the opposite side of the part. Backing welds are deposited before the weld on the opposite side of the part. See Figure 4-10.

12. Surfacing welds are commonly used to build up worn parts.
The filler metal can have the same or different characteristics as the base metal depending on the application. Surfacing welds are commonly used for building up worn parts or depositing abrasive‑resistant metals. Layers of filler metal are deposited with additional layers deposited 90° to the previous layer. See Figure 4-11.

13. Edge welds are commonly used on thin materials where filler metal is not required.
An edge weld is a weld in an edge joint, flanged butt joint, or flanged corner joint in which the weld fusion includes the full thickness of the joint members. See Figure An edge weld in an edge joint is when the joint members are parallel or nearly parallel. An edge weld in a flanged butt joint is when at least one of the joint members has a flanged edge shape at the joint. An edge weld in a flanged corner joint is when the butting joint member has a flanged edge shape at the joint. Edge welds are commonly used on light‑gauge metal. In some instances, part of the joint members may be melted and become part of the weld metal, which allows joining of the two joint members without the addition of filler metal.

14. Welding symbols provide standardized information regarding welding and examination requirements.
The weld location and specifications, including weld type, size, welding process, and examination procedures, can be specified on the welding symbol. Only information pertaining to the particular weld is included on the welding symbol. If welding requirements are the same on all welds on the print, a general note is included on the print. The parts of a welding symbol include the arrow, reference line, weld symbol, dimensions, and supplementary symbols. See Figure 4-13.

15. The arrow of the welding symbol points to the location of the weld specified.
The arrow is the part of the welding symbol that identifies the location where the welding operation is to be performed. The arrow points to the joint and the tip of the arrowhead touches the object lines on the print. The arrow includes an arrowhead and a leader line that connects to the reference line of the welding symbol. More than one arrow can be used to specify the same weld required at different locations. See Figure 4-14.

16. The reference line divides the welding symbol into the arrow side and the other side.
The reference line is the part of the welding symbol that identifies the side of the joint to be welded. It is a horizontal line attached to the arrow. Information regarding weld type and specification is divided by the reference line into two parts, the arrow side and the other side. The side nearest the observer is the arrow side. Weld information located on the arrow side indicates the weld information pertaining to the view side of the weld joint nearest the welding symbol. Weld information located on the other side of the arrow indicates the welding operation to be completed on the side of the weld joint furthest from the welding symbol. See Figure The arrow side or other side may also be called the near side or far side in the field.

17. Weld symbols on the welding symbol indicate the type of weld required.
Weld symbols are located on the reference line of the welding symbol. If there is no significance to which side the weld is made on, the weld symbol is centered in the reference line. Weld symbols with a vertical line always show the vertical line on the left side. More than one weld symbol may be required to specify a welding operation. See Figure 4-16.

18. Dimensions included in the welding symbol specify weld size and location requirements.
A dimension is the part of a welding symbol that specifies the weld size, number of welds, and weld location. The location of dimensions for welds varies depending upon the weld type, joint, and application. See Figure When no length dimension is specified on the welding symbol, the weld is continuous and extends the entire length of the joint.

19. Information in the tail of the welding symbol pertains to weld specification, weld process, or other reference.
The tail is the part of a welding symbol included when a specific welding process, specification, or procedure must be indicated. Special notations regarding detail and cross‑sectional drawings are also included in the tail. For example, the letters GTAW in the tail specify the weld is to be completed using the gas tungsten arc welding process. Welding and allied processes are abbreviated with letter designations. For quality control and production control, a manufacturer may include a weld identification number in the tail. The tail is omitted when no information is required in the tail of the welding symbol. See Figure 4-18.

20. Supplementary symbols provide additional information regarding the weld required.
A supplementary symbol is a symbol that further defines the welding operation to be completed. Supplementary symbols used on welding symbols include weld‑all‑around, field weld, melt‑through, consumable insert, backing, spacer, and contour. See Figure 4-19.

21. The arrow of the welding symbol is broken if a specific joint member requires edge preparation. If either joint member can be prepared, the arrow is not broken.
Edge preparation is indicated for weld joints that require weld reinforcement and/or access room to the weld area. The type of edge preparation required is determined by the engineer and is indicated by the welding symbol. The joint member requiring edge preparation is indicated on the welding symbol by a change in direction of the arrow. See Figure The arrow always points to the joint member to be prepared. Edge preparation of the joint members is specified in the welding symbol but is not shown on the print.

22. Brazing symbols show the brazing process designation in the tail.
A brazing symbol is a graphic symbol that shows braze locations and specifications on prints. Brazing symbols require no special symbols other than those used for specifying welds. See Figure The brazing process uses adhesion instead of fusion, as in the welding process. Adhesion is the joining together of metals by the bonding action of brazing filler metal through capillary action.

23. Nondestructive examination (NDE) symbols can be part of a welding symbol or a separate NDE symbol.
A nondestructive examination (NDE) symbol is a symbol that specifies examination methods and requirements to verify weld quality. The method of examination required can be specified on a separate reference line of the welding symbol or as a separate NDE symbol. See Figure 4-22.