According to a 2025 TWI technical report on NDT method selection for welded fabrications, ultrasonic testing (UT) and radiography (RT) are the two primary volumetric inspection techniques, but each has distinct strengths and limitations.
UT excels at detecting planar defects such as cracks, lack-of-fusion, and incomplete penetration. It is safer (no ionizing radiation), faster for thick sections, and can be performed in-service on hot or pressurized components. Modern phased-array UT (PAUT) adds imaging and sizing accuracy.
However, RT remains superior for volumetric defects like porosity, slag inclusions, and wall-thickness variations. RT provides a permanent film or digital image that is easier to interpret by non-specialists and is often required by code for critical pressure welds. UT requires skilled operators and surface preparation, and its results are highly operator-dependent.
The choice depends on defect type, material thickness, access, safety, and code requirements. A balanced NDT strategy uses both methods where appropriate.
Which NDT method do you rely on most for your critical welds?
Source: TWI, 2025