Radiographic Testing (RT): Industrial X-ray and Gamma Inspection is a volumetric nondestructive testing method that passes penetrating radiation through a component and records the transmitted intensity on film or a digital detector, revealing internal discontinuities that surface methods cannot detect. RT produces a permanent, reviewable image of a weld's or casting's internal structure, keeping it central to fabrication and in-service integrity programs.
An X-ray tube or a sealed gamma-ray source sits on one side of the part, with film or a detector on the opposite side. Denser regions, thicker sections, or a discontinuity attenuate the beam differently than sound material, so voids, cracks, and inclusions typically appear as darker regions on film or intensity variations on a digital image. A qualified technician interprets the radiograph against acceptance criteria in the governing code.
X-ray tubes generate radiation electrically, so the beam can be switched off and energy (kV) tuned to thickness; typical industrial tubes run roughly 100 kV to 450 kV, with linear accelerators used for very thick sections. Gamma sources, most commonly Iridium-192 and Cobalt-60, emit continuously and need heavy shielding. Ir-192 is designated for roughly 10 to 90 mm of steel (commonly applied around 12 to 65 mm); higher-energy Co-60 suits thicker sections, roughly 50 to 150 mm and beyond. Gamma sources suit field sites without power and confined geometries.
RT images flaws through the material thickness, not just at the surface. It is effective at detecting porosity and gas pockets, slag inclusions and lack of fusion in welds, lack of penetration at the weld root, internal shrinkage and cold shuts in castings, and wall thinning from corrosion where geometry permits.
RT is comparatively weak at detecting planar flaws perpendicular to the beam axis and fine surface-breaking defects, so it is routinely paired with surface methods, for example liquid penetrant testing or magnetic particle testing, to catch cracking a radiograph might miss.
Three recording technologies are in current use, each with different workflow and archival implications.
| Technique | Image capture | Typical relative sensitivity | Key characteristics |
|---|---|---|---|
| Film radiography | Silver halide film, chemically processed | Highest achievable resolution | Permanent record; needs darkroom processing |
| Computed radiography (CR) | Reusable phosphor plate, laser-scanned | Comparable to film | No chemical processing; plates reused many times |
| Digital radiography (DR) | Flat-panel or scintillator detector array | High, rapid availability | Near-instant image; enables tomography workflows |
CR and DR cut turnaround time versus film, though film retains a role where code or archival practice favors it.
Radiographic sensitivity, the smallest discontinuity reliably detectable, is verified using an Image Quality Indicator (IQI), also called a penetrameter. Wire-type IQIs (wires of decreasing diameter) are used widely under ISO and European practice; hole-type IQIs (a shim with drilled holes) are used widely under ASME practice. The IQI sits on the source side or film side per the governing procedure, and the radiograph must show the specified wire or hole before it is valid. Selection and exposure geometry are set by thickness and the applicable code.
RT uses ionizing radiation, so dose control is non-negotiable. Core controls include controlled areas barricaded to calculated dose-rate boundaries; ALARA practice (As Low As Reasonably Achievable), meaning shortest practical exposure time, maximum distance, and use of collimators or barriers; personal dosimetry, including a primary dosimeter (film badge or TLD/OSL badge) plus a secondary alarming rate meter; and source accountability, with gamma sources logged, stored under licensed conditions, and leak-tested on a defined schedule. Radiographers must be certified and radiation-safety trained, per national regulatory requirements.
ASME Boiler and Pressure Vessel Code, Section V, Article 2 covers radiographic examination requirements for pressure equipment fabrication and repair in North American practice, including technique, IQI selection, and film density. ISO 17636 (Part 1 covers film techniques; Part 2 covers digital detector techniques) is the primary international standard for radiographic testing of welded joints. Acceptance criteria come from a separate construction code, not the RT standard itself, so technicians apply both together.
RT is rarely used alone. A mature integrity program layers RT for volumetric coverage of welds and castings with complementary techniques, for example eddy current testing for surface and near-surface conductive flaws. Recording RT results, IQI sensitivity achieved, and interpreter findings alongside other NDT results in one maintenance record lets reliability teams trend degradation over time instead of treating each inspection as isolated. Fabrico ties inspection records and follow-up work orders to the same asset timeline as routine maintenance, so findings get actioned, not filed. Teams can book a Fabrico demo to see the workflow.
Yes, when controlled areas, shielding, and dosimetry procedures are properly implemented. The exposure zone is barricaded to a calculated boundary, exposure devices are checked before and after use, and radiographers carry both a primary and a secondary dosimeter. Unauthorized entry during exposure is the main hazard, which is why area control and radiation surveys are mandatory.
It depends on the source. X-ray tubes typically handle steel up to roughly 100 mm depending on energy, Ir-192 is designated for roughly 10 to 90 mm, and Co-60 or high-energy linear accelerators extend to roughly 150 mm and beyond. Thicker sections need longer exposure times, so technique selection is thickness-driven.
CR uses a reusable phosphor plate that is laser-scanned after exposure to produce a digital image, similar in workflow to film but without chemical processing. DR uses a digital detector array that produces an image almost instantly, enabling faster throughput and, in some configurations, real-time or computed tomography inspection.
No. RT is strong on volumetric and porosity-type flaws but can miss tight, surface-breaking cracks depending on orientation. Most quality programs pair RT with a surface method to catch both internal and surface-connected discontinuities.
Login
Blog