Discontinuity
Spatter
Droplets of molten metal thrown out of the arc and stuck to the plate around the weld, mostly a cleanliness and coating problem but occasionally a source of local hard spots.
What it looks like
- Small rounded beads of metal fused lightly to the base metal beside the weld
- Ranges from a fine dusting to heavy globules that need a chisel to remove
- May leave small pits or discoloured marks on the plate when knocked off
- Heaviest on cellulosic electrodes, short circuit transfer, and out-of-tolerance settings
Causes
- Voltage or current settings outside the stable range for the transfer mode being used
- Excessive arc length or an erratic arc from a worn contact tip or poor wire feeding
- Damp or damaged electrodes and flux causing violent gas evolution in the arc
- Incorrect shielding gas composition or insufficient flow for the process
- Magnetic arc blow deflecting the arc and disrupting orderly metal transfer
Prevention
- Tune voltage and wire feed speed into the stable range for the chosen transfer mode
- Maintain contact tips, liners, and drive rolls so the wire feeds smoothly
- Use the correct shielding gas mixture and verify flow at the nozzle
- Apply anti-spatter compound sparingly to surfaces that must stay clean, and correct arc blow with lead placement
How it is found
- VT
- Spatter is entirely a surface condition, so direct examination and a hand over the plate identify it completely.
- MT
- Used after spatter removal to confirm that no small hard spot or crack was left where a globule fused to the plate.
- PT
- Checks the same removal areas on non-magnetic material, and confirms that grinding did not open a surface defect.
How inspectors think about it
- Spatter is usually judged on whether it interferes with a required finish, coating, or subsequent examination rather than on any structural effect.
- Heavy spatter still matters because a large globule fused to the plate behaves like a miniature arc strike, leaving a locally hardened spot beneath it.
- Excessive spatter is also read as evidence that the arc was not running correctly, which prompts a look at settings and consumable condition on the rest of the job.
General reasoning only. The accept/reject limits for your work come from the code or specification governing the job, which this site does not reproduce.
Related discontinuities
Arc strikeA small localised melted spot where the arc touched the base metal outside the joint, quenched instantly by the surrounding cold plate into a hard, brittle, crack-prone patch.UndercutA groove melted into the base metal at the weld toe and left unfilled by weld metal, reducing the section of the parent material and leaving a sharp notch exactly where stress concentrates.Uniformly scattered porosityRounded gas pockets frozen into the weld metal and spread fairly evenly through the deposit, rather than bunched together or lined up, showing that shielding or cleanliness was marginal for the whole pass.OverlapWeld metal that has rolled over the toe and sits on unmelted base metal, forming a lip with a sharp crevice underneath that carries no load and hides an unfused interface.
Can you name it on sight?
The gauge trainer's identification mode shows you a weld and four names. Reading about porosity and picking it out of a line-up are not the same skill.