Solid foreign substances entrapped in the weld metal
SLAG
INCLUSIONS
Slag trapped during welding. The imperfection is an
irregular shape and thus differs in appearance from a gas pore.
Causes
Incomplete slag removal from underlying surface of
multi pass weld
Slag flooding ahead of arc
Entrapment of slag in work surface
Prevention
Improve inter-run slag removal
Position work to gain control of slag, Welder needs
to correct electrode angle
Dress/make work surface smooth
Comments
A fine dispersion of inclusions may be present
within the weld metal, particularly if the MMA process is used. These only
become a problem when large or sharp-edged inclusions are produced.
FLUX
INCLUSIONS
Flux trapped during welding. The imperfection is of
an irregular shape and thus differs in appearance from a gas pore. Appear only
in case of flux associated welding processes (i.e. MMA, SAW and FCAW).
Causes
Unfused flux due to damaged coating
Flux fails to melt and becomes trapped in the weld
(SAW or FCAW)
Prevention
Use electrodes in good condition
Change the flux/wire. Adjust welding parameters i.e.
current, voltage etc to produce satisfactory welding conditions
OXIDE
INCLUSIONS
Oxides trapped during welding. The imperfection is
of an irregular shape and thus differs in appearance from a gas pore.
Cause
Heavy mill scale/rust on work surface
Prevention
Grind surface prior to welding
Comments
A special type of oxide inclusion is puckering. This
type of defect occurs especially in the case of aluminium alloys. Gross oxide
film enfoldment can occur due to a combination of unsatisfactory protection
from atmospheric contamination and turbulence in the weld pool.
TUNGSTEN
INCLUSIONS
Particles of tungsten can become embedded during TIG
welding. This imperfection appears as a light area on radiographs due to the
fact that tungsten is denser than the surrounding metal and absorbs larger
amounts of X-/gamma radiation.
Causes
Contact of electrode tip with weld pool
Contact of filler metal with hot tip of electrode
Contamination of the electrode tip by spatter from
the weld pool
Exceeding the current limit for a given electrode
size or type
Extension of electrode beyond the normal distance
from the collet, resulting in overheating of the electrode
Inadequate tightening of the collet
Inadequate shielding gas flow rate or excessive wind
draughts resulting in oxidation of the electrode tip
Splits or cracks in the electrode
Inadequate shielding gas (e.g. use of argon-oxygen
or argon-carbon dioxide mixtures that are used for MAG welding)
Prevention
Keep tungsten out of weld pool; use HF start
Avoid contact between electrode and filler metal
Reduce welding current; adjust shielding gas flow
rate
Reduce welding current; replace electrode with a
larger diameter one
Reduce electrode extension and/or welding current
Tighten the collet
Adjust the shielding gas flow rate; protect the weld
area; ensure that the post gas flow after stopping the arc continues for at
least 5 seconds
Change the electrode; ensure the correct size
tungsten is selected for the given welding current used
Change to correct gas composition
Comments
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