16.6 The Basic Elements of Welding Symbols
Cameron Kjeldgaard
If an engineer or designer would like welding to be carried out on a project they need a way to communicate that to the people (you) who are doing the welding. This information is often communicated via the blueprint. Welding can require a lot of specific information, for example: the type and size of the weld, the required weld groove preparation, the extent and location of the weld. Welding symbols provide a space-saving method for conveying all this, and more, information. There is a certain amount of explanation required to interpret a welding symbol properly. It is highly recommended that you read chapter 15, Weld Identification, before proceeding. The information provided in chapter 15 will be necessary to understand what types of welds and weld dimensions that will be discussed.
The Reference line, Arrow and Tail
The arrow serves the same function as a leader line. The arrow points to the weld joint, or surface, where the information on the weld symbol should be applied.
The reference line is where the bulk of information in the welding symbol is presented. It is important to note that the arrow may extend from either the left or right side of the reference line, it may also point to a place above or below the reference line. No matter the orientation or direction of the arrow the information on the reference line is always shown and read in the same order from left to right and top to bottom. This means that the pictogram of the weld is always in the center, while the size of the weld is always to the left, and length of the weld always to the right.
Whether the information is on the top or bottom of the reference line also has special significance. The arrow of the welding symbol will point to a weld joint, most weld joints have two sides to them. Information below the reference line refers to the arrow side of the joint, that is to the side of the joint the arrow is pointing at. Information above the reference line applies to the other side of the joint, opposite the side the arrow is pointing at.
The tail is always opposite from the arrow on the reference line. The tail is not always necessary, but serves an important purpose. The tail serves as a catch-all for any information that may need to be written out regarding the weld. If a specific weld process is required a note reading “GMAW”, “SMAW”, or “FCAW” may be placed here. Similarly if the weld in the symbol is to be applied multiple places a note reading “3 side” or “3 places” would be written. In some cases a single weld symbol may be used for many weld joints, the word “typical” or abbreviation “TYP” would be written in the tail.
Pictorial Elements of The Weld Symbol
There are a number of symbols, or small pictograms, used in welding symbols. Symbols that appear on the reference line indicate a a fillet weld or specific type of groove weld. For more information on fillet and groove welds see Chapter 15. These symbols indicating the type of weld are called weld symbols. Don’t confuse this with the term welding symbol which refers to the entirety of information conveyed on the reference line and by the arrow and tail. The picoral weld symbols are drawn so that their shape approximates that of the finished weld, or groove the weld will be deposited in. This helps to make the system more intuitive.
Groove Weld Symbols
Square: Two parallel dotted lines run horizontal and two parallel lines are square off of the top of the first dotted line. The same arrangement of lines squares off of the bottom dotted line. The symbol looks a like a 4-way intersection.
Scarf: Two parallel dotted lines run horizontal to the left of the first line, two diagonal parallel lines run off of the top line. On the bottom line, two parallel diagonal lines run from the bottom line.
V: Two parallel dotted lines run horizontal. A V shape rises off of the top line, and the same shape runs down from the lower line.
Bevel: Two parallel dotted lines run horizontal one straight line and one diagonal line are connected to each other at the center (forming a V with a straight edge and an angled edge) off the top line. The bottom line has the same marking, but the V shape angled down.
U: Two parallel dotted lines run horizontal. A straight line runs perpendicular in the center of the top line, and a curved U-shape sits on top of the straight perpendicular line. The same shape is repeated on the lower horizontal line extending below it.
J: Two parallel dotted lines run horizontal with a perpendicular straight line rising off of the top horizontal line. About ⅔ of the way up the perpendicular a line curves to the right. The same shape is repeated on the bottom horizontal line extending below it.
Flare V: Two parallel dotted lines run horizontal. About ⅓ of the way from the left of the top horizontal line, a short arced line curves to the left. About ⅓ of the way from the right on the top horizontal line, a similar arced line curves to the right. The same lines are repeated in the same distances, except upside down, on the lower horizontal line.
Flare bevel: Two parallel dotted lines run horizontal. About ⅓ of the way from the left of the top horizontal line is a perpendicular straight line. About ⅓ of the way from the right edge of the horizontal line an arced line curves to the right. These lines are repeated, pointed down, on the lower perpendicular horizontal line.
Other Wled Symbols
Fillet: Two parallel dotted lines run horizontal. On the top horizontal line, in roughly the center, a right triangle is depicted. The horizontal line forms the bottom edge of the triangle, while the hypotenuse is pointed to the right. The same marking appears on the second horizontal line, except the triangle is upside down.
Plug or slot: Two parallel dotted lines run horizontal. A rectangle, taking up all but the very edges of the horizontal line is centered on the line. The same drawing is repeated on the lower horizontal line, except the rectangle faces downward instead of up.
Spot or projection: Three parallel horizontal lines are pictured. A perfect circle is centered sitting on top of the top horizontal line. On the second horizontal line a circle is bisected by the line. In the third horizontal line, the circle appears below the line, but it is still touching the line.
Seam: Three parallel horizontal lines are pictured. A perfect circle is centered sitting on top of the top horizontal line. The circle is bisected at the top and bottom edges by solid horizontal lines. On the second horizontal line a circle is bisected by the line as well as two solid horizontal lines. In the third horizontal line, the circle appears below the line, but it is still touching the line. The third circle is also bisected at the top and bottom by two straight horizontal lines.
Back or backing: Two parallel dotted lines run horizontal. On the top line, an edge of a circle points downward. On the bottom horizontal line an edge of a circle points upwards.
Surfacing: One horizontal line is presented. Two half circles are attached to the line pointing down. The two circles meet int eh center.
Flange Edge: Two parallel dotted lines run horizontal. About ¼ of the way from the left edge of the top line, a J-shaped line is placed. About ¼ of the way from the right edge of the line, a backwards J-shaped line is placed. The same lines are repeated, upside down, on the lower horizontal line.
Flange Corner: The corner flange line is similar to the flange edge, however the left line is straight up and perpendicular to the horizontal line instead of curved.
Contour symbols are small symbols which appear directly above, or below, the weld symbol, indicating the desired contour of the weld face. If a contour symbol is not given then it should be assumed the weld is acceptable regardless how the weld face is contoured. A convex, concave, and flush contour symbol may be used. How strictly the contour of the weld must be shaped can be subject to welding code requirements.
If a contour symbol is used a finish designator may also be shown. Finish designators are letter designation that appear above, or below, the contour symbol. These letters designate what method should be used to shape the final weld:
- C- indicates chipping
- G- indicates grinding
- M- indicates machining
- R- indicates rolling
- P- indicates planishing
- U- indicates unspecified
Grinding and machining are the most common methods of achieving a given contour. If a U is present for unspecified, any method may be used. If no finish designator is shown, any method may also be used, or the weld may be acceptable without further finishing if the contour is correct.
There are two more pictorial elements to welding symbols. These are the field weld and weld all around symbols. Both these symbols are located at the junction of the arrow and reference line. The weld all around symbol is a circle centered on the junction of the lines, this symbol is useful when welding shapes with more than two distinct sides, such as an I-beam, pipe, or square tubing. If this symbol is present the weld should extend all around the joint. A field weld symbol is used to indicate welding should take place in the field rather than the shop. Many welding projects involve pre-fabricating part of a project in a controlled shop environment, with further assembly and welding required at the job site.
Attributions
- Figure 16.27: The Parts of a Welding Symbol © American Welding Society, illustration by Nicholas Malara (SBCTC Illustrator) Used with permission from the rightsholder, the American Welding Society.
- Figure 16.28: Arrow, Reference Line, Tail by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 16.29: Significance Of The “Arrow Side – Other Side” Parts Of The Welding Symbol Reference Line by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 16.30: Basic Weld Symbols by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 16.31: Contour Symbols by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 16.32: Field Weld and Weld All Around Symbols by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 16.33: The Significance Of The “Weld All Around” Weld Symbol by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
the entirety of information conveyed on the reference line and by the arrow and tail. Different from weld symbols, which are pictorial symbols that approximate the finished weld.