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Deciphering symbols

Every welder needs to be familiar with welding symbols, whether they find them frustrating or fun to decipher

Resembling some sort of hieroglyphics or old English runes, cryptic welding symbols would confuse any layperson looking at a drawing or blueprint. But no welder could do his job without knowing, at the very least, what the most common and important symbols indicate.

Engineering and fabrication drawings feature welding symbols that describe the type of weld, its size and other pertinent information. The need for consistency in welding led to the development of a system for indicating welding requirements. Originated by the American Welding Society in 1929, the latest version is AWS A2.4:2012 American National Standard Symbols for Welding, Brazing and Nondestructive Examination. Part A of this standard covers the complete set of welding symbols.

“Welders receiving a proper welding education should know welding symbols and how to read them,” says Charlie LaRiche, weld school instructor, CWI/CWE for The Lincoln Electric Co. “If they don’t know the symbols, they won’t know the type of weld, where to put it, how big it has to be and so on. Every welder should be familiar with the symbols, and they need to be to do their job.”

While memorizing all of the welding symbols in the AWS standard is nearly impossible, most welders become familiar with the ones they need fairly quickly.

“Depending on where you are working, some are more common than others,” LaRiche adds. “If you’re doing a lot in the construction area, like an ironworker, you do more groove welds, lap joints and T-joints. If you’re working in an area with a lot of resistance welding, those would be vastly different symbols.”

Symbol structure

An essential part of all welding symbols is the reference line, which is a straight horizontal line and the anchor for all other symbols. The instructions for making the weld are hung along the reference line (see Figure 1).

The other essential part of the welding symbol is an arrow that connects to the reference line and points to the location where a weld is required. The arrow may be connected to either end of the reference line and point up or down. The side of the joint to which the arrow points is the “arrow side” of the joint. The opposite side of the joint is the “other side” of the joint.

To minimize the number of welding symbols required, more than one arrow in a single symbol can be used if each joint to which an arrow is pointing is to be welded in the same way.

The tail of the welding symbol, which is not always required, is used to add any supplementary information about making the weld. The tail is drawn as a greater than (>) or less than (<) sign, connected at the end of the reference line opposite the arrow.

“The tail is a reference point to provide additional information,” LaRiche says. “Say you’re doing a fillet weld, the tail could include instructions to use GTAW welding. It could include the type of filler metal to use. It could include the X ray, ultrasound or other nondestructive method to use to test it. Or, the tail could say to see the legend for a breakdown of what is needed.”

Each type of weld has its own basic weld symbol (not to be confused with the entire welding symbol), which is typically placed near the center of the reference line – and above or below it, depending on which side the joint is located. If the symbol appears below the reference line, the weld is made on the arrow side of the joint. If the symbol appears above the reference line, the weld is made on the other side of the joint. If the symbol appears on both sides of the reference line, the weld is performed on both sides of the joint.

There are many weld symbols that represent the many different types of welds. Here are some of the most common ones with which welders are familiar.

Fillet welds

The fillet weld is used to make joints – lap joints, butt joints, corner joints, edge joints and T-joints. Metal is deposited in a corner formed by the fitup of the two members to form the joint. The fillet weld symbol is a triangular shape placed on the same side of the reference line with the vertical leg always placed to the left.

The size of the fillet weld is shown to the left of the weld symbol (no matter the orientation). It represents the length of the legs. If the two legs of the weld are to be the same size, only one dimension is given; if the weld is to have unequal legs, the size for each leg is given and there is an indication as to which leg is longer.

Fillet welds are often specified as intermittent welds rather than a single long weld. For an intermittent weld, the length for each weld segment is shown to the right of the weld symbol, followed by pitch dimension with a hyphen between the two. The pitch is the distance between centers of each weld segment (not the empty space between the segments; see Figure 2).

When intermittent welds are placed on both sides of a joint, they can be directly opposite each other (chain) or they can be offset (staggered). Intermittent welds are common on thin, heat-sensitive metals or for particularly long joints.

Groove welds

The groove weld is commonly used to make edge-to-edge joints. Metal is deposited within the groove and fuses with the base metal to form the joint. The groove weld symbol is placed on the same side of the reference line.

There are many ways to make a groove weld, as demonstrated by the variety of groove weld symbols. The type of groove weld used depends primarily on the geometry of the edges and parts to be joined.

The various types of groove welds include (see Figure 3):

  • Square groove
  • V groove
  • Bevel groove
  • U groove
  • J groove
  • Flare V groove
  • Bevel V groove

Common additional symbols used with groove welds are the melt through, backing bar, and back weld and backing symbols. In the case of melt through, the groove is reinforced with a weld on the back side of the joint welded from the opposite side. The melt-through shape is a black half circle (see Figure 4).

For support, a backing strip or bar can be welded onto the back side of the joint before the groove weld is performed. The backing can be removed after welding or left on to become part of the completed joint. Its rectangular-shaped symbol is placed across the reference line from the weld symbol. If the bar is to be removed after the weld is complete, an R is used (see Figure 4).

A back weld is when a weld is created on the back side of the joint after the groove weld is performed. A backing weld is applied to the root of a groove before welding the groove. Back welds and backing welds use the same symbol, which looks like an unshaded half circle (see Figure 4). Therefore, a note in the tail of the welding symbol may specify which type of weld is required or it may be specified in the legend.

Groove and fillet weld symbols are the most common, but there are many others, such as plug and slot, seam, spot, surfacing, edge and stud.

Numbers game

Numbers are also a big part of a welding specification, and there is much communicated above and below the reference line.

Each weld, with the exception of spot and plug welds, has a length component. The weld length may be the entire length of the joint or some portion thereof. The length is not given if the weld is to be the entire length of the joint. In most cases, the weld width (or diameter) is located to the left of the weld symbol, while its length is written to the right.

If a weld is required to make a change in direction, an additional symbol or a multi-arrow symbol should be used.

For a groove weld, in addition to the weld symbol, size, length and pitch, the symbol may include the depth of penetration, root opening, groove angle and degree of any beveling required on the base metal.

More to know

A weld-all-around circle indicates the fillet weld is to encircle the entire joint. The symbol consists of a circle that is placed over the intersection where the end of the reference line meets the arrow. In the case of a circular joint, the weld-all-around symbol is not required (see Figure 5).

A flagpole indicates a field weld, which simply means the weld is to be made on site, rather than in the shop. The symbol consists of a flag that is placed at the intersection where the end of the reference line meets the arrow. Any welding symbol that does not include a flag indicates that the weld is to be made in the shop (see Figure 6).

When a welding operation involves many steps, there may be multiple reference lines connected to the same arrow. Each line represents a separate operation and is performed in sequence beginning with the line closest to the arrow (see Figure 7).

Many other specifics are conveyed on engineering drawings and blueprints. Among the most common are finish and contour instructions, grinding or other machining, and consumables insert info.

The information presented here is just the tip of the iceberg when it comes to AWS welding symbols. Even for those familiar with welding symbols, it’s a good idea to have a reference chart that contains the symbols and the drawings of what the finished weld will look like.

LaRiche introduces welding symbols in about the 10th week of his course. “I have the students build a bucket tooth and use welding symbols, so that is where they start to pick them up,” he says. “Once you start learning, it can be a little difficult, but as you study and practice, it gets easier. But you must learn the basics. If you’re not ever going to get into resistance welding, there is no sense learning those symbols. But you have to know the symbols you are going to be seeing every day.”

For new hires without welding training, it’s up to the company to provide instruction on welding symbols. While the ideal hire would already have some knowledge of symbols, today’s shortage of welders makes that impractical. Luckily, reading welding symbols is a skill easily learned – and, for many, kind of fun.

The Lincoln Electric Co.


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