RT Radiographic testing (RT)
Radiographic testing (RT) · Inspección y ensayos · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “RT 100% category A joints per ISO 17636” states a radiographic testing (rt) requirement.
What controls
Volumetric test that produces an image of the inside of the part by passing ionizing radiation through it and recording the attenuation on film or a digital detector. It shows volumetric discontinuities (porosity, inclusions, shrinkage cavities) and missing material at a weld root very well, and it provides a permanent record that can be interpreted later. On the other hand, a planar defect oriented perpendicular to the beam may not be visible, and the technique does not tell you the depth of the discontinuity.
How to verify
Selection of source, distance and exposure time according to thickness and material, placement of the image quality indicator, exposure and interpretation by qualified personnel on a film viewer or calibrated monitor. Indications are identified, sized and compared against the applicable acceptance criterion. Each film or image is identified with the part, the joint and the position, and filed as a record.
Common mistakes when interpreting it
- Assuming that if nothing shows on the radiograph the part is necessarily sound, even for planar defects.
- Interpreting images in which the required image quality indicator is not visible.
- Not allowing for test time and radiation safety restrictions in the schedule.
How to get it in the workshop / if it comes out of tolerance
It affects scheduling for two reasons: radiation safety requires cordoning off areas or working in a shielded bunker, often on night shifts, and film processing and interpretation take time. Think about access: you need to be able to place the source and the detector on opposite sides, which is not always possible on an assembly that has already been put together. Image quality is demonstrated with image quality indicators placed in the exposure itself.
Image lacking contrast or with the image quality indicator not visible: the exposure is not valid and must be repeated, not interpreted with reservations. Planar defects suspected but not seen: the complementary test is ultrasonic testing, which is more sensitive to that type of discontinuity. If the geometry prevents correct placement of source and detector, change the technique before wasting exposures.
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