The Nick-Break Test is useful for determining the internal quality of the weld metal. This test reveals various internal defects (if present), such as slag inclusions, gas pockets, lack of fusion, and oxidized or burned metal.
The test specimen shall be cut transversely to the welded joint and shall have the full thickness of the plate at the joint. The excess weld metal and penetration bead shall be left intact. Slots are sawed at each end of the specimen to be tested.
The specimen is then placed upright on two supports and the force on the weld is applied either by a press or blows of a hammer until a fracture occurs between two slots.
A visual inspection of the fractured surfaces is carried out in order to find defects. If any defect exceeds 1.5 mm in size or the number of gas pockets exceeds one per square cm, the piece has failed the test.