Troubleshooting guide › Specialised welding › Seam welding

Seam welding problems: seam looks continuous but leaks, intermittent weld, wheel pickup, wrinkling and burn-through

A resistance seam weld is a row of overlapping spot nuggets made by two wheel electrodes while the sheet moves. For a leak-tight seam every nugget must overlap the one before it, which ties four settings together: current, weld time, cool time and wheel speed. Change one without the others and the seam looks fine on the outside and leaks on test. This page is for longitudinal and circumferential seam welders on tanks, drums, cans and ducting.

Covers: Longitudinal seam welders, circumferential seam welders, DuoFlex 20K spot and seam controller; mild steel, galvanised and stainless sheet 0.3-3 mm.

Reviewed by the Cruxweld technical team, October 2026. Settings are starting points to confirm on a test piece; acceptance is decided by the code or drawing the job is built to. Checks marked “call” are for our technical team.

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How the four settings fit together Faults, most likely first, and the fix for each Controller (DuoFlex 20K) notes Daily care Questions we get asked

Before you start: Switch off and unplug before touching electrodes, jaws, tips or any connection. Everything here is outside the cabinet; the inside is for our technical team. Wheels rotate under force: keep hands and sleeves clear. Never run without cooling water on the wheels and transformer. On the DuoFlex controller, run every new setting first in mechanical adjustment mode (no current) to check the stroke and the air circuit.

How the four settings fit together

Nugget spacing = wheel speed x (weld time + cool time). For a leak-tight seam the nuggets must overlap by about 25-50 %, so the spacing must be less than the nugget length. Raise the speed and you must shorten the cycle (or raise current to make bigger nuggets); lengthen the cool time and the nuggets separate. For a non-pressure-tight stitch seam the cool time can be long and the nuggets spaced.

Setting	Too low	Too high
Current (heat)	Small or no nuggets, seam peels	Expulsion, burn-through, pickup on the wheels
Weld time	Small nuggets	Overheating, indentation
Cool time	Continuous heating: wheels and sheet overheat, wrinkling	Nuggets separate: leaks
Wheel speed	Slow production, overheating	Nuggets separate, skipped welds
Force	Expulsion, pickup, inconsistent	Deep wheel tracks, thin seam

Faults, most likely first, and the fix for each

1Seam looks continuous but leaks on test

Nuggets not overlapping: speed too high for the cycle, cool time too long, current too low; or a gap in the overlap where the sheets were not in contact (fit-up).

Fix: Section a test seam and measure the overlap; reduce speed or cool time, or raise current; ensure the lap is tight and the sheets clean; test with a pressure or dye check before production.

2Intermittent weld, skipped nuggets

Wheel contact lost on a wavy or dirty sheet; wheel pickup insulating the face; controller in discontinuous mode when continuous was wanted; force too low.

Fix: Dress the wheels; clean the sheet; check the seam mode on the controller (continuous vs pedal-held); raise force.

3Metal pickup on the wheel electrodes

Current too high or force too low at the start of the seam; galvanised or dirty sheet; wheels dry (no cooling) or worn.

Fix: Lower current, raise force; dress the wheel face; cooling water on the wheels; on galvanised sheet expect to dress more often and use a slightly higher force.

4Sheet wrinkles or waves along the seam

Too much heat in a long seam: cool time too short, current too high, speed too low; thin sheet with no hold-down.

Fix: Longer cool time, lower current, faster speed; clamp the sheet both sides of the seam; on thin sheet reduce the wheel width.

5Burn-through, holes

Current too high; speed too low; sheets not in contact (gap) so the current concentrates; edge of the lap too narrow.

Fix: Lower current; raise speed; close the gap; lap of at least 8-10 mm on thin sheet.

6Deep wheel tracks, seam thinner than the sheet

Force too high; wheels too narrow; weld time too long.

Fix: Reduce force; wider wheel face; shorter weld time.

7Seam drifts off the lap

Guide not set; sheet feeding at an angle on a longitudinal machine; drum not concentric on a circumferential machine.

Fix: Set the guide and the lap width; align the fixture; check the mandrel.

8Start of seam good, end weak (long seams)

Wheels and transformer heating up; water flow low; mains sagging.

Fix: Check water flow; shorter seams per cycle; supply under load.

Controller (DuoFlex 20K) notes

Times are set in cycles of 20 ms (50 Hz): pre-pressure, squeeze, preheat, interval, weld, hold and rest each 0-999 cycles; heat as a conduction angle.
Seam modes: continuous (pedal once to start, once to stop) or discontinuous (welds while the pedal is held). The discharge timing (during preheat or while pressurised) and the sequence are selectable.
Run the first trial of any new setting in mechanical motion adjustment (no current) and in mould position adjustment to check electrode alignment, then a test weld on the same material and thickness; record the specification number.
Earth the controller housing; isolate and wait for the capacitors to discharge before any inspection; a wiring error can destroy the controller and the thyristor module.

Daily care

Wheels dressed to a flat, clean face; dressed again at the first sign of pickup.
Cooling water flowing to the wheels and transformer before the first seam.
Sheet edges clean and flat; lap width and guide set.
Section or leak-test a sample seam at the start of each batch.
Air pressure steady; FRL drained; controller clean and dry.

Questions we get asked

Longitudinal or circumferential machine?

Longitudinal for straight seams on open sheet and the side seam of a cylinder before it is closed; circumferential for the ends of drums, tanks and cans where the part rotates against the wheels. Many shops need both for a tank.

Can I seam-weld galvanised sheet?

Yes, with a little more current and force, frequent wheel dressing, and good extraction for the zinc fume. Expect more pickup on the wheels than with bare steel.

Models covered on this page

Longitudinal seam welderSpecifications →

Circumferential seam welderSpecifications →

DuoFlex 20K spot and seam welderSpecifications →

Open your model for its specifications; the spares page lists the consumables for it.

Welding or cutting problem rather than a machine fault?

If the machine runs but the weld or cut is wrong, the cause is usually settings, consumables or the material. Start here:

Spot welding problems →

Does the machine matter?

A seam welder needs a controller that times weld and cool cycles against wheel speed (the DuoFlex 20K sets pre-pressure, squeeze, weld, interval and hold in 20 ms cycles and stores them as specification numbers), water-cooled wheels and a drive that holds a constant speed. Longitudinal machines weld straight seams on open sheet; circumferential machines rotate a closed drum or tank end against the wheels.

Seam welders Find the right machine Cost calculator Order spares

Still stuck?

Send a photo of the weld or cut, your machine model, consumable and plate thickness. Our technical team replies on WhatsApp with the likely causes and the next checks to make.

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