— ● Seam weld
Seam weld · Soldadura en plano · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Continuous seam on bellows joint” states a seam weld requirement.
What controls
Continuous weld along a lap joint, normally produced with wheel electrodes that make overlapping spots until they form an uninterrupted line. The symbol is accompanied by the width of the seam and its length; if the seam is not continuous but alternates welded and unwelded segments, it is specified with length and pitch. Its distinguishing feature compared with spot welding is that it can produce a leak-tight joint, because the nuggets overlap one another.
How to verify
Seam width and length are checked with calipers and a tape measure. The actual continuity, which is what matters, is verified by leak testing when the joint must be leak-tight, and by macro-etch examination or destructive coupon testing to check the overlap between nuggets. Visual inspection only catches the obvious: misalignment, burn marks and incomplete travel.
Common mistakes when interpreting it
- Assuming every seam is leak-tight because it is continuous: leak-tightness must be tested, and it depends on the internal overlap between nuggets.
- Treating it as a series of independent spots during inspection: the acceptance criterion applies to the line, not spot by spot.
- Confusing a resistance seam weld with a continuous arc weld; neither the process nor the inspection criteria are the same.
How to get it in the workshop / if it comes out of tolerance
It is used where continuity is needed: sheet-metal tanks, bellows, enclosures that must be sealed. Wheel speed and pulse rate determine how much the nuggets overlap; if the overlap is lost, the seam is no longer leak-tight even though it looks like a continuous line from the outside. Cleanliness between the sheets is as important as with spot welding.
Leaks in a seam that looks correct mean insufficient overlap between nuggets: reduce wheel speed or increase the pulse rate. Burn marks or expulsion indicate current too high for that speed. If the sheet buckles in a wave along the seam, spread the heat input by welding alternate segments or cool the fixture.
Related symbols
Other symbols in Flat welding
Related tools
ISO fits
Calculates indicative ISO 286 tolerances for shaft and hole, H7/g6, H7/h6, H7/k6 and H7/p6 fits with clearance, transition and interference graph.
Inspection Plans
Upload a plan, extract dimensions and GD&T with AI and export your inspection guideline in PDF or CSV.
Shop trigonometry
Workshop trigonometry: right triangle, C chamfer, Z countersink, sine bar, taper and polar→X/Y for CNC operators.