Welding cannot take its proper place as an engineering tool unless means are provided for conveying the information from the designer to the workmen.
Welding symbols provide the means of placing complete welding information on drawings.
The scheme for the symbolic representation of welds on engineering drawings used in this manual is consistent with the “third angle” method of projection.
This is the method predominantly used in the United States.
The joint is the basis of reference for welding symbols.
The reference line of the welding symbol (fig. 3-2) is used to designate the type of weld to be made, its location, dimensions, extent, contour, and other supplementary information.
Any welded joint indicated by a symbol will always have an arrow side and an other side. Accordingly, the terms arrow side, other side, and both sides are used herein to locate the weld with respect to the joint.
The tail of the welding symbol is used to designate the welding and cutting processes and the welding specifications, procedures, or supplementary information to be used in making the weld.
If a welder knows the size and type of weld, he has only part of the information necessary for making the weld. The process, identification of filler metal that is to be used, whether or not peening or root chipping is required, and other pertinent data must be related to the welder.
The notation to be placed in the tail of the symbol indicating these data is to be established by each user. If notes are not used, the tail of the symbol may be omitted.
Elements of a Welding Symbol
A distinction is made between the terms “weld symbol” and “welding symbol.”
- The weld symbol (fig. 3-3) indicates the desired type of weld.
- The welding symbol (fig. 3-2) represents the weld symbol on drawings.
The assembled “welding symbol” consists of the following eight elements or any of these elements as necessary:
- Reference line
- Basic weld symbols
- Dimensions and other data
- Supplementary symbols
- Finish symbols,
- Process, or other references
The locations of welding symbol elements with respect to each other are shown in Figures 3-2 above.
Basic Weld Symbols
Weld symbols are used to indicate the welding processes used in metal joining operations, whether the weld is localized or “all around”, whether it is a shop or field weld, and the contour of welds.
These basic weld symbols (arc and gas weld symbols, resistance weld symbols, brazing, forge thermit, induction, and Flow Weld Symbols) are summarized below and illustrated in figure 3-3.
These symbols are used in many welding processes in congestion with welding symbols and are used as shown in figures 3-3.
Arc & Gas Supplementary Symbols
These welds are indicated by using a process or specification reference in the tail of the welding symbol, as shown in figure 3-4.
When the use of a definite process is required (fig. 3-5), the process may be indicated by one or more of the letter designations shown in tables 3-1 and 3-2.
Designation of Welding Processes by Letters
Letter designations have not been assigned to arc spot, resistance spot, arc seam, resistance seam, and projection welding since the weld symbols used are adequate.
Designation of Cutting Processes by Letters
When no specification, process, or other symbol, the tail may be omitted (fig. 3-6).
Other Common Weld Symbols
Figures 3-7 and 3-8 illustrate the weld-all-around and field weld symbol and resistance spot and resistance seam welds.
Weld All Around and Field Weld Symbols
Resistance Spot and Resistance Seam Welds
Read more: Seam and resistance spot weld symbols
Location Significance of Arrow
For Fillet, Groove, Flange, Flash, and Upset welding symbols, the arrow connects the welding symbol reference line to one side of the joint, and this side shall be considered the arrow side of the joint (fig. 3-9).
Arrow Side Fillet Welding Symbol
The side opposite the arrow side is considered the other side of the joint (fig. 3-10).
Other Side Fillet Welding Symbol
Projection Welding, Resistance Spot, Resistance Seam, Arc Seam, Arc Spot & Plug Welding Symbols
For these symbols, the arrow connects the welding symbol reference line to the outer surface of one member of the joint at the centerline of the desired weld.
The member to which the arrow points is considered the arrow side member.
The other joint member shall be considered the other side member (fig. 3-11).
Plug and Slot Welding Symbols
When a joint is depicted as an area parallel to the plane of projection in a drawing and the arrow of a welding symbol is directed to that area, the arrow side member of the joint is considered as the near member of the joint, following the usual conventions of drafting (fig. 3-11).
Near Side Welding Symbol
When a joint is depicted by a single line on the drawing and the arrow of a welding symbol is directed to this line, the arrow side of the joint is considered as the near side of the joint, following the usual conventions of drafting (fig. 3-12 and 3-13).
Arrow Side V-groove Welding Symbol
Other Side V-groove Welding Symbol
Location of Weld With Respect to Joint
Welds on the arrow side of the joint are shown by placing the weld symbol on the side of the reference line toward the reader (fig. 3-14)
Welds on the Arrow Side of the Joint
Welds on the other side of the joint are shown by placing the weld symbol on the side of the reference line away from the reader (fig. 3-15).
Welds on the Other Side of the Joint
Welds on both sides of the joint are shown by placing weld symbols on both sides of the reference line, toward and away from the reader (fig. 3-16).
No Side Significance
Resistance spot, resistance seam, flash, weld symbols have no arrow side or other side significance in themselves, although supplementary symbols used in conjunction with these symbols may have such significance.
For example, the flush contour symbol (fig. 3-3) is used in conjunction with the spot and seam symbols (fig. 3-17) to show that one member of the joint’s exposed surface is to be flush.
Resistance spot, resistance seam, flash, and upset weld symbols shall be centered on the reference line (fig. 3-17).
Spot Seam and Flash or Upset Weld Symbols
References and General Notes
Symbols With References
When a specification, process, or other reference is used with a welding symbol, the reference is placed in the tail (fig 3-4).
Symbols Without References
Symbols may be used without specification, process, or other references when:
- A note similar to the following appears on the drawing: “Unless otherwise designated, all welds are to be made in accordance with specification no….”
- The welding procedure to be used is described elsewhere, such as in-shop instructions and process sheets.
General notes similar to the following may be placed on a drawing to provide detailed information on the predominant welds. This information need not be repeated on the symbols:
- “Unless otherwise indicated, all fillet welds are 5/16 in. (0.80 cm) size.”
- “Unless otherwise indicated, root openings for all groove welds are 3/16 in. (0.48 cm).”
When the use of a definite process is required, the process may be indicated by the letter designations listed in tables 3-1 and 3-2 (fig. 3-5).
Symbol Without a Tail
When no specification, process, or other reference is used with a welding symbol, the tail may be omitted (fig. 3-6).
Weld All-Around and Field Weld Symbols
Welds extending completely around a joint are indicated by the weld-all-around symbol (fig. 3-7). Welds that are completely around a joint that includes more than one type of weld, indicated by a combination weld symbol, are also depicted by the weld-all-around symbol. The weld-all-around symbol also indicates welds completely around a joint in which the metal intersections at the welding points are in more than one plane.
Field welds are welds not made in a shop or at the place of initial construction and are indicated using the field weld symbol (fig. 3-7).
Extent of Welding Denoted by Symbols
Symbols apply between abrupt changes in the direction of the welding or the extent of hatching of dimension lines, except when the weld-all-around symbol (fig. 3-3) is used.
Welding on hidden joints may be covered when the welding is the same as that of the visible joint. The drawing indicates the presence of hidden members. If the welding on the hidden joint is different from that of the visible joint, specific information for the welding of both must be given.
Location of Weld Symbols
Weld symbols, except resistance spot and resistance seam, must be shown only on the welding symbol reference line and not on the drawing lines.
b. Resistance spot and resistance seam weld symbols may be placed directly at the locations of the desired welds (fig. 3-8).
Use of Inch, Degree & Pound Marks
Inch marks are used for indicating the diameter of arc spot, resistance spot, and circular projection welds, and the width of arc seam and resistance seam welds when decimal dimensions specify such welds.
In general, inch, degree, and pound marks may or may not be used on welding symbols, as desired.
Construction of Symbols
Fillet, bevel, J-groove, flare bevel groove, and corner flange symbols should always be shown with the perpendicular leg to the left (fig. 3-18).
In a bevel or J-groove weld symbol, the arrow shall point with a definite break toward the member, which is to be chamfered (fig. 3-19). In cases where the member to be chamfered is obvious, the break in the arrow may be omitted.
Information on welding symbols shall be placed to read from left to right along the reference line in accordance with the usual conventions of drafting (fig. 3-20).
For joints having more than one weld, a symbol should be shown for each weld (fig 3-21).
The letters CP in the tail of the arrow indicate a complete penetration weld regardless of the type of weld or joint preparation (fig. 3-22).
When the basic weld symbols are inadequate to indicate the desired weld, the weld shall be shown by a cross-section, detail, or other data with a reference on the welding symbol according to location specifications given in para 3-7 (fig. 3-23).
Two or more reference lines may be used to indicate a sequence of operations.
The first operation must be shown on the reference line nearest the arrow. Subsequent operations must be shown sequentially on other reference lines (fig. 3-24).
Additional reference lines may also be used to show data supplementary to welding symbol information included on the reference line nearest the arrow.
Test information may be shown on a second or third line away from the arrow (fig. 3-25).
When required, the weld-all-around welding symbol must be placed at the junction of the arrow line and reference line for each operation to which it applies (fig. 3-26). The field weld symbol may also be used in this manner.