3
Weld Quality Assurance
Regardless of the material to be welded,
there are a few basic precautions which must be taken to avoid
porosity in the weld and lack-of-fusion
defects. 1. The
material to be welded should be as clean as possible. All grease, oil, and other
lubricants should be removed.
For best quality welds, all scale, rust and other oxide coverings should be either
mechanically or chemically
removed. This is of extreme importance when welding aluminum.
2. When welding carbon steel plate,
use only the shielding gas- wire combinations recommended for the
specific variety of steel in use: killed,
semi-killed, or rimmed. See Chapter 5 for the recommended
combinations. 3.
Generally avoid welding conditions which result in the weld bead solidifying very
rapidly, such as very high travel
speeds. Gas which would normally be evolved from the weld metal during slower
cooling can be trapped,
thereby causing porosity. 4.
Maintain an adequate shielding gas flow (as shown in the welding condition tables)
and protect the welding
area from wind and drafts. 5.
Keep the welding wire centered in the shielding gas pattern. Wire curvature is
usually responsible for the wire
being off center. This can be corrected by using a wire straightening device on
the wire feeder. 6.
When welding from both sides of a plate and where there has been no penetration
of the first weld entirely
through the material, be sure that the second pass deeply penetrates the first.
When the first pass has
entirely penetrated, or where a root gap is used, it is common practice to grind
the back side to sound weld
metal before the second weld is made. This is mandatory when welding aluminum
and copper and where
x-ray quality welds are required in carbon and stainless steel.
7. Avoid welding conditions which allow
the molten weld metal to roll out in front of the arc. This is the main
cause for lack-of-fusion defects, in
particular, downhill welding. 8.
In multipass welding, grind to a flat surface all weld beads which appear to be
peaked and exhibit poor wetting.
9. Remove the small patches of oxide
slag found on the weld bead with a file or screwdriver if another weld
is to be made over it.
