There are varied types of discontinuities including:

• Cold lap – Here, the weld filler metal improperly fuses with the base metal.
• Porosity – Appearance of dark round or irregular spots singularly, in rows, or in groups on a radiograph. It arises due to entrapment of gas in the solidifying metal.
• Cluster porosity – It is similar to the porosity issue. But the spots will group together very closely on a radiograph.
• Slag inclusions – Appearance of dark, jagged asymmetrical shapes on a radiograph. It occurs due to entrapment of non-metallic solid material in weld metal or between base metal and weld.
• Incomplete penetration/lack of penetration – It is one of the most offensive flaws where the weld fails to penetrate the joint. This incomplete penetration leads to the occurrence of cracks.
• Incomplete fusion – Here, the weld filler improperly fuses with the base metal.
• Internal concavity or suck back – Here, the weld metal contracts as it cools and draws up into the root of the weld.
• Internal or root undercut – Here, the destruction of base metal occurs next to the root of the weld.
• External or crown undercut – Here, the destruction of base metal occurs next to the crown of the weld.
• Offset or mismatch – It occurs when two pieces to be welded together are not properly aligned.
• Inadequate weld reinforcement – Here, the thickness of the weld metal is less than the thickness of base material.
• Excess weld reinforcement – Here, weld metal is added excessively in an area of a weld.
• Cracks – It appears as jagged and very faint irregular lines.