CEMP-E
TI 809-26
1 March 2000
5. RADIOGRAPHIC TESTING (RT).
a. Method Description. Radiographic Testing (RT) uses a radioactive source and, typically, a film
imaging process similar to X-ray film. The film provides a permanent record of the inspection. When a
weld is exposed to penetrating radiation, some radiation is absorbed, some scattered, and some
transmitted through the weld onto the film. Image Quality Indicators (IQIs) are used to verify the quality
and sensitivity of the image. Most conventional RT techniques involve exposures that record a
permanent image on film, although other image recording methods are also used. Real-time radiography
uses a fluoroscope to receive radiation, then presents an on-screen image for evaluation. The two types
of radiation sources commonly used in weld inspection are x-ray machines and radioactive isotopes.
(1) X-rays are produced by portable units capable of radiographing relatively thin objects. A large
2000 kV X-ray unit is capable of penetrating approximately 200 mm (8 in.) of steel, a 400 kV unit to 75
mm (3 in.), and a 200 kV unit to 25 mm (1 in.) of steel.
cobalt 60, cesium 137, and iridium 192. Cobalt 60 can effectively penetrate up to approximately 230 mm
(9 in.) of steel, cesium 137 to 100 mm (4 in.), and iridium 192 to 75 mm (3 in.) of steel.
b. Advantages and Disadvantages.
(1) RT can detect subsurface porosity, slag, voids, cracks, irregularities, and lack of fusion. See
Table D-5.
(2) Accessibility to both sides of the weld is required.
(3) RT is limited to butt joint applications by AWS D1.1. Because of the constantly changing
thickness for the exposure, RT is not effective when testing fillet welds or groove welds in tee or corner
joints.
(4) To be detected, an imperfection must be oriented roughly parallel to the radiation beam. As a
consequence, RT may miss laminations and cracks parallel to the film surface. Because they are usually
volumetric in cross-section, discontinuities such as porosity or slag are readily detected.
(5) The limitations on RT sensitivity are such that discontinuities smaller than about 1 percent of
the metal thickness may not be detected.
(6) The radiographic images provide a permanent record for future review, and aid in
characterizing and locating discontinuities for repair.
(7) RT is generally unaffected by grain structure, particularly helpful with ESW and EGW welds.
(8) RT is a potential radiation hazard to personnel, and strict safety regulations must be monitored
and enforced.
(9) The cost of radiographic equipment, facilities, safety programs, and related licensing is higher
than any other NDT process.
(10) There is usually a significant waiting time between the testing process and the availability of
results.
D-10
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