If there is no melting of the edges of the base metal at the root face or on the side face or between the weld runs, then it is -

Explanation:

A fault is an imperfection in the weld which may result in failure of the welded joint while in service.

The following faults occur commonly in gas welding.

1. Undercut: A groove or channel formed in the parent metal at the toe of the weld is called undercut.

Cause: 

• When the current setting is too high
• When welding speed is too fast
• By overheating of the job due to continuous heating
• Due to faulty electrode motion
• When electrode angle is wrong

2. Incomplete Penetration: Failure of the weld metal to reach the root of the joint is known as incomplete penetration.

Cause:

• Too narrow edge penetration
• Excessive welding speed
• When the current setting is low
• When a larger diameter electrode is used
• Due to inadequate cleaning or gouging before depositing sealing run

3. Porosity or blow-hole:  A group of pin-holes in a weld (porosity) or a larger hole in the weld (blow-hole) are caused by the gas being entrapped.

Cause:

• Presence of contaminants on the job or electrode surface
• Presence of high sulphur in the job or electrode material
• Moisture trapped between joining surfaces
• Freezing of weld at a faster rate

4. Spatters: An unintentional deposit of weld metal, in the shape of small globules on the job surface along the weld is known as spatters.

Cause:

• A too high current setting
• Use of moisture affected electrode
• Wrong polarity
• Use of a long arc
• Arc-blows

5. Overlap: Metal flowing onto the surface of the base metal without fusing it.

Cause:

• Improper welding technique
• High welding current
• By using large electrodes

6. Lack of fusion: If there is no melting of the edges of the base metal at the root face or on the side face or between the weld runs, then it is called lack of fusion.

Cause:

• It occurs because of the low heat input
• Incorrect electrode and torch angle
• Low welding current
• High welding speed