Miscellaneous imperfections according to BS EN ISO 6520-1

Types of miscellaneous imperfections:

1. Stray arc (arc strike)



Local damage to the surface of the parent metal adjacent to the weld, resulting from arcing or striking the arc outside the weld groove. This results in random areas of fused metal where the electrode, holder or current return clamp have accidentally touched the work.

Causes:
• Poor access to the work
Prevention: Improve access (modify assembly sequence)
• Missing insulation on electrode holder or torch
Prevention: Institute a regular inspection scheme for electrode holders and torches
• Failure to provide an insulated resting place for the electrode holder or torch when not in use
Prevention: Provide an insulated resting place
• Loose current return clamp
Prevention: Regularly maintain current return clamps
• Adjusting wire feed (MAG welding) without isolating welding current
Prevention: Retrain welder

An arc strike can produce a hard HAZ which may contain cracks, possibly leading to serious cracking in service. It is better to remove an arc strike by grinding than weld repair.


2. Spatter



Globules of weld or filler metal expelled during welding adhering to the surface of parent metal or solidified weld metal.

Causes:
• High arc current
Prevention: Reduce arc current
• Long arc length
Prevention: Reduce arc length
• Magnetic arc blow
Prevention: Reduce arc length or switch to AC power
• Incorrect settings for GMAW process
Prevention: Modify electrical settings (but be careful to maintain full fusion!)
• Damp electrodes
Prevention: Use dry electrodes
• Wrong selection of shielding gas (100% CO2)
Prevention: Increase argon content if possible, however if too high may lead to lack of penetration

Spatter is a cosmetic imperfection and does not affect the integrity of the weld. However as it is usually caused by an excessive welding current, it is a sign that the welding conditions are not ideal so there are usually other associated problems within the structure, ie high heat input. Some spatter is always produced by open arc consumable electrode welding processes. Anti-spatter compounds can be used on the parent metal to reduce sticking and the spatter can then be scraped off.


3. Torn surface



Surface damage due to the removal by fracture of temporary welded attachments. The area should be ground off, subjected to a dye penetrant or magnetic particle examination then restored to its original shape by welding using a qualified procedure. Some applications do not allow the presence of any overlay weld on the surface of the parent material.


4. Additional imperfections


• Grinding mark
Local damage due to grinding.
• Chipping mark
Local damage due to the use of a chisel or other tools.
• Underflushing
Lack of thickness of the workpiece due to excessive grinding.
• Misalignment of opposite runs
Difference between the centrelines of two runs made from opposite sides of the joint.
• Temper colour (visible oxide film)
Lightly oxidised surface in the weld zone, usually occurs in stainless steels.