The Ultimate Guide To Welding Symbols
Welding symbols (not to be confused with weld symbols, which we’ll come onto later) are designed to show you exactly where to weld. Each welding symbol contains the following elements:
A reference line – This is a horizontal line which forms the foundation for all welding symbols. Everything else that you need to know extends from this line.
An arrow at the end of the leader line – In essence, the leader line is the shaft of the arrow, while the arrow refers to the actual point itself. This arrow points to the location that needs to be welded. More details are given by the weld symbols, which will be discussed in more detail later.
A tail – This sits at the opposite end of the reference line to the arrow, and forks out in a sideways ‘v’ shape. Don’t worry if you don’t see a tail like this on your welding symbol; it is optional and is only used in certain circumstances. A tail is usually included in cases where the designer wants to give special instructions that you can’t infer from the rest of the welding symbol, such as a particular type of welding to use.
A weld symbol – This is a series of short lines or a small geometric shape which can be found around the middle of the reference line, placed either directly above or below it.
The location of the weld symbol will tell you exactly where to place your weld. If it is sitting below the reference line, then the weld should be placed in the exact position that the arrow is pointing to (i.e. on the same side of the joint). If the weld symbol is sitting on top of the reference line, the weld should be placed on the opposite side of the joint to the arrow. If – on the other hand – the symbol is located on both the top and the bottom of the reference line, then you should weld on both sides of the joint. It is possible to have different symbols on the top and the bottom of the reference line, in which case two different types of welds should be performed on either side of the joint.
Resistance spot, resistance seam, flash and upset weld symbols bear no significance with regards to on which side of the reference line they are placed, or on which side of the joint they should fall. However, other symbols might appear alongside these symbols, but we’ll touch upon those later.
Below you’ll find some examples of the most common weld symbols you’ll come across, as well as their meanings.
Numbers and dimensions
You will probably find several numbers included on your welding symbol. These should give you an indication of the size that your weld should be. Unless otherwise stated, the unit of measurement is usually the inch.
A number located to the left of your weld symbol tells you the width of the weld, while a number on the right of the weld symbol indicates the length of the weld. If no length is given, then you should assume that it should continue for the entire length of the joint.
Sometimes these numbers may be contained within parentheses, in which case they indicate uneven fillet weld lengths.
Just as with the weld symbols, numbers below the reference line apply to welds on the same side of the joint as the arrow; numbers above the reference line apply to welds on the opposite side of the joint.
With regards to intermittent fillet welds, the pitch will be placed to the right of the weld symbol. For chain intermittent fillet welding, the dimensions will appear on both sides of the reference line: this is true for welds which line up, and those which are staggered.
Numbers placed to the right of arc spot and arc seam weld symbols indicate the distance that you should leave between the centers of each weld.
Certain symbols will have numbers in parentheses either above or below the symbol, which means that a specific number of those welds should be completed.
If you see a number placed within the actual weld symbol itself, this will refer to an angle between two beveled edges or the size of a root opening. If the number is written in a fraction format such as ‘1/8’, then this describes the size of the root opening. However, if you see a whole number (such as 45), this refers to the total angle between two beveled edges.
At the point where the reference line and the arrow join, you might see one of two symbols.
One possibility is a small flag symbol. In this case, the instruction is that you should perform the weld on-site, rather than doing it in a workshop.
The other alternative is a circle, which indicates that you should weld all the way around the joint. In other words, you should start and stop at the same point, just as a circle does.
If the leader line bends (in the case of bevel or J-groove welds), this means that the arrow is pointing to an area which should be chamfered.
At the face of the weld symbol, you may see a small arc or straight line. This is supposed to tell you the finish that your weld should be left with. A concave arc should result in a concave finish; a convex arc should result in a convex finish; a flat line should result in a flat finish.
If a small box or rectangle can be found on the opposite side of the reference line to the weld symbol, this suggests that a backing strip should be placed on the other side of the joint. Remember that this is different from a ‘back weld’, which is where a second line of welding is needed along the back of the first line of welding. If a back weld is needed, it will be indicated by a small semi-circle on the other side of the reference line to the weld symbol.
Flash and upset welds are depicted by a single vertical line crossing straight through the reference line.
A row of asterisks or stars indicates that resistance spot welds should be used; resistance seam welds are pictured with a pattern that resembles overlapping zigzag lines or a row of small diamonds.
If you see a flush contour symbol with one of these welds, then you should remember to make the exposed surface flush.
Projection welds are usually drawn with a break in the reference line, but with both ends of the break connecting to an ‘X’ symbol on either the top or the bottom of the line.
We’ve already touched upon the fact that the tail on the reference line is usually included to give specific instructions. For example, if a particular process or a type of welding is needed, then a short code is written inside the tail to indicate which process to use. A full list of the processes and their codes is included below.
- Torch brazing
- Twin carbon-arc brazing
- Furnace brazing
- Induction brazing
- Resistance brazing
- Dip brazing
- Block brazing
- Flow brazing
- Flow welding
- Flash welding
- Upset welding
- Percussion welding
- Induction welding
- Bare metal-arc welding
- Stud welding
- Gas shielded stud welding
- Submerged arc welding
- Gas tungsten-arc welding
- Gas metal-arc welding
- Atomic hydrogen welding
- Shielded metal-arc welding
- Twin carbon-arc welding
- Carbon-arc welding
- Gas carbon-arc welding
- Shielded carbon-arc welding
- Flux cored-arc welding
- Nonpressure thermit welding
- Pressure thermit welding
- Pressure gas welding
- Oxyhydrogen welding
- Oxyacetylene welding
- Air-acetylene welding
- Roll welding
- Die welding
- Hammer welding
- Automatic welding/cutting
- Machine welding/cutting
- Manual welding/cutting
- Semi-automatic welding/cutting
- Arc cutting
- Air-carbon-arc cutting
- Carbon-arc cutting
- Metal-arc cutting
- Oxygen cutting
- Chemical flux cutting
- Metal powder cutting
- Arc-oxygen cutting
- Complete penetration weld
Other things you might need to know
If there are welding symbols and numbers on both the top and bottom of the reference line, but they do not line up perfectly, then this indicates that the welds should be staggered along the length of the joint.
If you see a number (not a fraction) next to an arc spot weld, this refers to the strength of the weld itself. Remember that this is a minimum value; it is usually measured in pounds or newtons per spot weld.
Sometimes you will see a series of horizontal lines extending from the arrow’s leader line, which resembles the rungs of a ladder. These are used when the instructions are slightly more complicated, and a few more steps are needed with each weld. In these cases, each horizontal line indicates a separate step which needs to be completed. The closer the line to the point of the arrow, the earlier you should complete that step; the further away from the point of the arrow the instruction is, the later you should leave it.