Purpose of Welding Symbols

Welding symbols are found on construction drawings where metal-to-metal joints require welding. For each welded joint on the drawing there is a symbol, which is intended to provide the person performing the weld with all the information necessary to successfully complete the required weld. The information provided by the symbol includes, where necessary, such details as:

• The type of weld or welds required at the joint

• The exact location of the weld on the joint

• The size of the weld or welds

• The spacing of welds if more than one is used on a joint

• Special procedures or notes with respect to the weld

Weld symbols must be standardized in order to ensure they are consistently applied to engineering drawings. More importantly, though, these standard symbols allow welders to accurately interpret drawings and correctly produce the specified welds. In the USA, standard welding symbols were developed by the American Welding Society, adopted by the American National Standards Institute, and published as ANSI/AWS A2.4 Standard Symbols for Welding, Brazing and Nondestructive Examination. In Canada, the Canadian Standards Association identifies welding symbols in CSA W59 Welded Steel Construction Annex D. The CSA standard very closely follows the AWS standard with respect to welding symbols. The ASME and the National Board of Boiler Inspectors also endorse the use of these symbols.

The purpose of this chapter is to describe and explain basic welding symbols, using simple examples, and to define the associated terminology. The source AWS and CSA Standards should be consulted for more detailed studies.

Weld Joints and Weld Types

Since welding symbols relate directly to the types of welds, which are applied to specific types of joints, it is important to understand the various joint designs and weld types. Figure 1 shows the five basic joint types.

Groove Welds

Groove welds are used when the surfaces being joined are butted against each other in such a way that a groove is created. The weld is then deposited into the groove, so the weldment is contained in the groove. There are several standard groove shapes. These are created before welding by preparing the joining surfaces of one or both pieces, using grinding, flame cutting, or some other means. The welding symbol for a groove weld indicates the specific groove configuration.

Figure 2 shows the common configurations of butt joints, which require one or more groove welds. Each figure represents two pieces in cross-section, showing the shape of each joining surface and the corresponding name of that configuration.

a) V-Groove: The two surfaces are machined flat and smooth at an angle (called a bevel). When the two surfaces are placed together, they form a single “V” shape. In some cases the root of the “V” does not extend to the bottom surface of the material.

b) Double V-Groove: The edges are beveled from both sides. When placed together, the two pieces form a “V” on both sides. Both sides are then welded.

c) Bevel: One edge is beveled and the other is flat.

d) Square: Both edges are flat at 90 degrees. This creates a bottomless groove, formed by slight separation of the pieces.

e) U-Groove: Both edges are machined with a curvature that produces a “J” cross-section. When placed together they form a groove with a “U” contour.

f) Double U-Groove: Each piece is machined with a “J” contour from both sides. When brought together the edges form a “U” groove on each side. Welding is done on both sides.

g) J-Groove: One piece is machined from one side only with a “J” contour, while the other is flat at 90 degrees.

h) Scarf: The joining edges are machined flat, but at an angle. This design is common for braze welding.

i) Flare-V: Two surfaces with curved profiles are brought together to form a weld groove with curved sides.

j) Flare-Bevel: One edge has a curved profile while the other is flat at 90 degrees.

Figure 3 illustrates some of the features of typical V-groove welds, including common terms used on welding symbols.

a) Weld Root: the bottom edge of a weld or the deepest point of a weld.

b) Root Opening: the space intentionally left between joined surfaces before welding. The root opening is visible when the weld does not fully penetrate the material.

c) Weld Depth: the distance from the surface of the material to the root of the weld.

d) Reinforcement: the specified height of the weld above the surface of the material.

e) Melt through: the thickness of weld, measured from the root of the weld to the material surface, when the root extends beyond the surface. This is often intentional for the purpose of reinforcing the weld.

Fillet Welds

Fillet welds are used when the configuration of the joining pieces creates two weld surfaces, which are 90 degrees to each other. The fillet weld is deposited into the 90 degree joint and assumes a somewhat triangular cross-section.

Figure 4 shows four common applications of fillet welds, plus an illustration of fillet weld size.

a) A single fillet weld applied to a lap joint.

b) Fillet welds applied to each side of a T joint.

c) A single fillet weld used at a corner joint.

d) A continuous fillet weld, used to weld a vertical post to a flat plate. This is also called an all-around weld. Because it travels around corners it is also referred to as a box weld.

e) The size of a fillet weld is specified by the lengths of the legs of the weld, which is the perpendicular distance from the parent metal to the toe of the weld, as seen in the diagram. The legs of a fillet weld are usually the same length, but if the pieces being welded have different thickness the legs may be different.

Figure 5 shows two views of a T joint with staggered intermittent fillet welds on both sides of the vertical member. This technique is common where strength of the joint is not crucial or where complete sealing of the joint is not necessary. In order to successfully produce these welds, the welder must know the length of the individual welds and the pitch. As shown, pitch is the distance between the mid point of adjacent welds. In many cases the intermittent welds are not staggered, but directly across from each other, with identical length and pitch.

Plug and Slot Welds

As illustrated in Figure 6, plug and slot welding involves joining two relatively flat pieces with a series of small welds that are deposited into drilled plugs or machined slots in one piece. The piece with the slots or plugs is usually relatively thin and the sides of the holes may be perpendicular or bevelled. Information provided on the welding symbol will tell the welder how deep the welds must be within the plugs or slots.

Weld Symbols

Weld symbols are an integral part of welding symbols. They are tagged onto a welding symbol to tell the welder what type of weld to perform. In some cases, such as butt welds, the weld symbol also defines the preparation required of the surfaces before welding can begin.

Figure 7 shows the weld symbols for all weld types. In most cases, the shape of a weld symbol directly corresponds to a cross-section of its associated joint faces. The first row in Figure 7 shows groove weld symbols, while the second row shows various other types.

Some weld terms from Figure 7 not previously described are:

• Stud: A stud weld involves attaching a small stud, either perpendicular or at an angle, to a surface. An example would be studs on the outside of a tube to anchor refractory. The welding current flows directly through the stud, rather than a welding rod, causing the stud to fuse directly to the surface.

• Spot or Projection: To create a spot weld, two relatively thin surfaces are forced tightly together. Electrodes, directly across from each other and on opposite sides of the surfaces, send enough current through the materials to melt and fuse the metals at that spot. Projection welding is a variation of spot welding, in which one of the surfaces has small raised projections, which slightly separate the surfaces, but concentrate the welding heat and fusion at the projection points.

• Seam: Seam welding is used with relatively thin materials to produce a continuous weld where the materials butt or overlap to form a long seam. Electrodes, usually in the form of wheels, press the pieces together from opposite sides. The electrodes travel along the seam, applying current between them to melt and fuse the pieces together.

• Back or Backing: A back weld is applied to the back side (the root side) of a single-groove weld after the main weld has been completed. This reinforces the weld and fills in where the main weld did not fully penetrate the groove. A backing weld is applied to the back side (root side) of a single-groove weld before the main weld is started. Its purpose is to fill the root opening and prevent melt through of the main weld.

• Surfacing: A surfacing weld is simply laid down on a single surface for the purpose of strengthening or increasing the thickness of the surface. There is no joining of pieces. A common application is to replace metal that was lost due to corrosion or to intentionally thicken a surface in anticipation of corrosion.

• Edge: An edge weld is used to join two pieces along their adjacent, exposed edges. The weld is laid down along the join, with or without bevelling, where the two edges meet.

Welding Symbols

Welding symbols are a method of communication. To be fluent in this method of communication, it is necessary to know:

• the various elements of welding symbols,

• how welding symbols are constructed for various weld types, and

• how to interpret welding symbols when arranged on a construction drawing.

Each weld on a drawing has its own unique welding symbol, so the required weld is fully and accurately described.

Reference Line, Arrow, and Tail

Figure 8 shows three key elements of a welding symbol;

• the reference line,

• the arrow, and

• the tail.

Of these three, the reference line and the arrow are compulsory features of all welding symbols.

• The reference line is a straight, horizontal line. Its purpose is to contain, above or below it, any tags, symbols, notations that describe the type, dimensions, or location of the weld. The line has an arrow attached at one end and a tail at the other.

• The arrow joins the reference line to the joint at which the weld will be applied. The stem of the arrow should not be horizontal. It may be attached to the right end or left end of the reference line. The direction that the arrow points (up or down) is usually irrelevant. However, for some welds there is significance if the arrow has a crook in it, as in b), or it points back toward the reference line, as in d).

• The tail is attached to the opposite end of the arrow. The tail contains supplemental information to produce the specified weld. This additional information can not be shown on the reference line. For example, in Figure 8(c), “SMAW” is inserted in the tail to indicate the welding process is shielded metal arc welding. If no additional information is necessary, the tail may be left off, as in Figures 8(b) and 8(d).

Arrow Side vs. Other Side

The arrow and the reference line work together to indicate which side of a joint the weld must be applied to. Obviously, this is very important to a welder.

• The arrow points at (touches) one side of the joint. That side is called the arrow side. The opposite side of the joint is then referred to as the other side.

• The location of the information at the reference line determines whether the weld should be applied to the arrow side or to the other side. Any information below the reference line applies to the arrow side of the joint, while information above the reference line applies to the other side of the joint. In many cases, a joint will be welded from both sides, in which case there will be corresponding information both above and below the reference line.

Figure 9 shows some simple examples of arrow side and other side.

a) A butt joint is shown, with a V-groove symbol above the reference line, so the weld is made on the other side of the joint.

b) The symbol is shown below the line so the weld is made on the arrow side of the joint.

c) A V-groove symbol is both above and below the line, so a weld is applied to both sides of the joint.

d) A fillet joint is shown, with a fillet weld symbol above the reference line. The weld is made on the other side of the joint.

Supplemental Weld Symbols

Besides specific weld identifiers, there are other symbols that identify features of the weld procedure, not specific to the weld itself. These are shown in Figure 10 and described after the figure. The symbols are shown mounted on the reference line, as they would be.

• Melt Through: This was described earlier as root weld that extends beyond the surface at the bottom of a groove weld. It is an intentional process, so is shown on the welding symbol. Since it occurs on the back (other) side of the weld it is always shown above the reference line.

• Field Weld: A black flag, pointing away from the arrow direction, indicates a weld that cannot be performed in the construction shop, but must be performed at the final location (ie. in the field).

• Weld All Around: A circle at the end of the reference line indicates that the weld is to be continuous around one of the joint members. Figure 4(d) showed one example. Other examples include tube ends being welded to a tubesheet, or tube stubs welded to a header.

• Backing: Often a backing ring or plate is required at the back of a groove weld to prevent melt through. It is placed flush with the surface prior to welding. The root of the weld fuses with the backing, which normally remains in place after the weld.

• Spacer: A spacer is similar to a backing ring, except that it fits into the space between the members of a groove weld. It not only acts as backing, but keeps the joint root open during welding. Since the spacer extends through the weld, it is shown straddling the reference line.

• Consumable Insert: This refers to a filler material, which is added to the weld joint, usually to add strength.

• Contour Symbols: These symbols tell the welder how the face of a weld should be finished (flat or flush, concave, or convex). If the weld itself doesn’t produce the required contour, then machining or grinding must be used to shape the surface.

Groove Weld Symbols

In addition to the basic weld type symbol, which shows the cross-section of the weld joint, the reference line for groove welds usually contains additional, necessary information about the weld itself or the preparation of the joint. This includes specific sizing and shaping of the joint surfaces, depth of penetration, use of backing, thickness of melt-through, and others. Three basic examples are shown in Figure 11.

a) This weld symbol indicates a bevel joint, with bevels on both sides. The numbers in brackets to the left of the symbols indicate that the bevel on the arrow side is 7/8 inch deep and the bevel on the other side is 1/2 inch deep. For bevel joints, the perpendicular leg of the bevel symbol is always on the left. Also note that for bevel grooves the arrow is always slanted backwards to point toward the piece that is beveled.

b) The weld symbol in b) indicates a U-groove joint, welded from the arrow side. The depth of weld penetration is indicated to the left of the weld symbol. Penetration depth is measured from the top of the joint to the root (bottom) of the weld.

c) This symbol indicates a V-groove to be welded from the arrow side, with a melt through of 3/8 inch. Also note the contour symbol above the melt through symbol, telling the welder to finish the weld by grinding it flush.

Fillet Weld Symbols

The welding symbols for fillet welds indicate the location of the weld, size of the weld, and the surface finish required. Figure 12 shows some simple examples. Note that for the fillet weld symbol, the straight, vertical side is always on the left, regardless of the direction of the arrow or whether the symbol is above or below the reference line.

a) The welding symbol in (a) indicates that the T joint has a single fillet weld on one side only, the other side from the arrow. The size of the weld is shown to the left of the fillet weld symbol. Since there is only one dimension shown, the weld legs are required to be equal. For fillet welds, the contour tag is placed parallel to the slanted side of the symbol; in this case the line indicates that the weld face is to be flat. The method used to flatten is shown by the letter “G”, which stands for grinding.

b) In some cases, a fillet weld is required to have different leg lengths. The T joint in (b) has fillet welds on both sides of the joint. On the arrow side the weld is symmetrical with a leg of 3/8 inch. On the other side, the leg along A is 3/8 inch, but along B is 1/2 inch. This is indicated on the welding symbol by “3/8 × 1/2.” A note in the tail tells which leg is 1/2 inch. Note that the contour on the arrow side is convex, while on the other side it is flat.

c) The fillet welds in (c) are intermittent welds. On the left side of each weld symbol is the leg length. On the right side of each symbol is the length of each weld and the pitch. For example “2 – 6” means the welds are two inches long and are spaced 6 inches apart, center-to-center. If the welds on one side are staggered with the other side, the fillet symbols are offset on the welding symbol, as shown

1. Identify five fundamental pieces of information provided by welding symbols.

2. With regard to welding symbols, describe the relationship between the ANSI/AWS A2.4-98 and CSA W-59 standards.

3. Illustrate the five basic weld joint types.

4. Draw a weld symbol to match the following joint. The weld procedure stipulates GTAW.

5. Define the following terms, with the aid of simple illustrations:

(a) Root Opening

(b) Reinforcement

(c) Groove Angle

6. Under what circumstance would the joint indicated by the following weld symbol be used?

7. Draw the following weld symbols:

(a) single welded V-groove, other side

(b) double-welded bevel groove, ground flush on arrow side

(c) single welded V-groove, arrow side, with backing.

Self-Assessment

Question 1

The two fundamental weld joint categories are:

riveted and welded

fillet and groove

arc and gas

single sided and double sided

Question 2

The "flag" in the following weld symbol represents:

field weld

weld all around

shop weld

special surface preparation

Question 3

A proper weld symbol will not show:

the information pertinent to the welder performing the weld

the exact location of the weld

the identity of the welder performing the weld

the weld joint preparation

Question 4

In the following diagram, the "4" means:

total number of intermittent welds

length of weld on arrow side

four passes required to finish weld on arrow side

length of weld on other side

Question 5

The weld joint preparation indicated by the following weld symbol is:

SMAW

60 degree vee groove

60 degree double bevel groove

1/2" root pass