The nick-break test (notched fracture test) is a destructive test in which a specimen taken from a butt weld is notched in the weld and broken through the weld metal, so that the fracture surface can be examined visually. Its purpose is not to measure a value but to open up the weld and see its internal imperfections directly. FKT NDT provides nick-break testing of welded joints.
What Does the Nick-Break Test Show?
The notches make the specimen break in the weld metal rather than in the parent metal. The fracture surfaces are then examined for the presence, size and distribution of:
- Porosity and gas pores
- Slag and other solid inclusions
- Lack of fusion
- Lack of penetration
- Cracks
The test should not be confused with the Charpy impact test. The Charpy test measures toughness in joules; the nick-break test measures no energy and assesses the internal soundness of the weld by eye.
Where Is It Used?
- Pipeline welds: widely used in qualifying pipeline welding procedures and welders.
- Welder qualification: some standards accept it on butt welds as an alternative to bend testing or radiography.
- Production control: a quick check of internal weld quality after a change in welding parameters or when quality is in doubt.
A related approach for fillet welds and un-notched specimens is described on our fracture test page.
Standards
The nick-break test is commonly applied according to:
- ISO 9017: Destructive tests on welds in metallic materials – Fracture test
- API 1104: Welding of pipelines and related facilities (nick-break test)
- ISO 9606-1: use of the fracture test and its acceptance criteria in welder qualification
How the Test Is Performed
- Specimen preparation: the specimen is cut transversely from the butt-welded test piece. Notches are saw-cut or machined in the weld, at the edges and/or on the surface as defined by the standard, so that fracture occurs in the weld metal.
- Breaking: the specimen is broken through the weld by press, tensile machine or impact.
- Examination: both fracture faces are examined visually and, where needed, with a magnifier. The type and size of imperfections are recorded.
- Evaluation: findings are compared with the acceptance criteria of the applicable standard.
- Reporting: the report gives specimen identification, notch type, imperfections found on the fracture surface, their dimensions and the result. Photographs of the fracture faces can be added on request.
FAQ
What is a nick-break test?
It is a fracture test in which a weld is notched and broken so that the fracture surface can be checked for internal imperfections.
Is the nick-break test an alternative to radiography?
Some welder qualification standards accept a fracture test as an alternative to radiographic examination under certain conditions. However, the test only covers the cross-section where the specimen was taken, not the full weld length.
What if the specimen breaks in the parent metal?
The weld metal cannot then be examined, so the test is generally not valid. Depending on the standard, a new specimen may be needed.
How is the notch made?
The notch is usually cut with a saw or machined. Its position and depth are set by the applicable standard and the specimen thickness.
To arrange nick-break testing, contact us with the weld type and applicable standard, and we will prepare a quotation.