Summary of Non-Destructive Testing of Welds

Summary of Non-Destructive Testing of Welds

Method	Defects detected	Advantages	Limitations
Visual	Inaccuracies in size and shape. Surface cracks and porosity, under-cut, overlap, crater faults.	Easy to apply at any stage of fabrication and welding. Low cost both in capital and labour.	Does not provide a permanent record. Provides positive information only for surface defects.
Dye- penetrate	Surface cracks which may be missed by naked eye.	Easy to use. No equipment required. Low cost both in materials and labour.	Only surface cracks detected with certainty. No permanent record.

Method	Defects detected	Advantages	Limitations
Magnetic-particle	Surface cracks Which may be missed by naked eye. May give indication of sub-surface flaws.	Relatively low cost. Portable. Gives clear indication.	Only surface cracks detected with certainty. Can be used only on ferromagnetic metals. Can give spurious indications. No permanent record.
Radiography	Porosity, slag inclusions, cavities, and lack of penetration. Cracks and lack of fusion if correctly orientated with respect to beam.	Can be controlled to give reproducible results. Gives permanent record.	Expensive equipment. Strict safety precautions required. Better suited to butt joints -not very satisfactory with fillet-welded joints. Requires high level of skill in choosing conditions and interpreting results.
Ultrasonic	All sub-surface defects. Laminations.	Very sensitive can detect defects too small to be discovered by other methods. Equipment is portable. Access required to only one side.	Permanent record is difficult to obtain. Requires high level of skill in interpreting cathode-ray-tube indications.