What are tests in welding ?

2. Radiographic test (RT)

When an accelerated electron hits a target of heavy metal, the radiation emanates. This radiation is a kind of electromagnetic wave. As its wavelength is shorter, its penetrative capacity becomes stronger. This penetrable capacity is used in the X-ray test to detect defects inside welds.

Weld zones can also be examined utilizing the radioactive isotopes (60Co; 192Ir, etc.) that emit γ -rays. These two methods using X-rays and γ -rays are called the radiographic test.

The extent of X-ray penetration varies depending on the kind and thickness of the test material. The radiation intensity changes at where there is a welding defect, reflecting a change in photosensitivity.

The radiation intensity becomes denser at most defects except for tungsten inclusions. Darker portions in the negative film indicate the existence of such defects as blowholes, lack of fusion, lack of penetration, slag inclusions, cracks, and undercut.

A brighter spot in the negative film indicates a tungsten inclusion, because tungsten absorbs the radiation at a high degree. In taking radiophotographs, an Image Quality Indicator (I.Q.I.) and contrast meter are used in order to confirm the quality of radiophotographs.