AWS A2.4 weld symbol
Seam Weld Symbol
A seam weld symbol is a circle with a line through it, calling for a continuous fused seam between overlapping sheets — effectively a row of overlapping spot welds.
How to read the seam weld symbol
- For resistance seam welding the symbol is centred on the reference line, because the process has no side significance.
- For arc seam welding the symbol is placed on the arrow side or other side.
- The seam width, or the required strength per linear inch, is written to the left.
- The length of the seam is written to the right.
- Length and pitch together, such as 2-5, specify an intermittent seam.
Where the dimensions go
| Position | What it specifies |
|---|---|
| Left of the symbol | Width of the seam, or strength per linear inch |
| Right of the symbol | Length, and pitch if the seam is intermittent |
| In the tail | Process reference, for example RSEW |
Joint types
- Lap joint
- Butt joint
Practical notes
- Resistance seam welding uses wheel electrodes that roll along the joint, firing overlapping nuggets to form a continuous, leak-tight seam.
- It is the standard process for fuel tanks, drums, radiators and other pressure-tight sheet assemblies.
- An intermittent seam is faster and distorts less, but it is not leak-tight.
Seam Weld symbol — common questions
What is the difference between a spot weld and a seam weld symbol?
The spot weld symbol is a plain circle for a discrete nugget. The seam weld symbol is a circle with a horizontal line through it, calling for a continuous weld — in effect a row of overlapping spots.
Is a seam weld leak-tight?
A continuous seam weld is, which is why it is used on fuel tanks and pressure-tight containers. An intermittent seam, specified with a length and pitch, is not.
What does the number to the left of a seam weld symbol mean?
The width of the seam, or the required strength per linear inch of weld.
How is a resistance seam weld made?
Two wheel electrodes roll along the overlapping sheets while the machine fires a rapid series of resistance welds. Each nugget overlaps the last, producing one continuous fused seam.
Welding symbol anatomy
Every weld symbol attaches to the same framework. If any part of the diagram above is unfamiliar, the full guide to reading welding symbols walks through the whole system.
| Reference line | The horizontal backbone of every welding symbol. Everything else attaches to it, and it is always drawn horizontal on the drawing. |
|---|---|
| Arrow | The leader and arrowhead that connect the reference line to the joint. The side of the joint the arrow touches is the arrow side. |
| Weld symbol | The shape that says which kind of weld is required — triangle for a fillet, V for a V-groove, circle for a spot, and so on. |
| Arrow side (below the line) | A weld symbol drawn below the reference line calls for a weld on the side of the joint the arrow points to. This is the convention that catches people out most often. |
| Other side (above the line) | A weld symbol drawn above the reference line calls for a weld on the far side of the joint. |
| Both sides | Symbols drawn above and below the reference line call for welds on both sides of the joint. |
| Tail | An optional fork at the far end of the reference line, used to reference a specification, process or procedure such as GMAW or a WPS number. |
| Dimensions | Size is placed to the left of the weld symbol; length and pitch are placed to the right. |