What is Radiography Testing?

What Is Radiography Testing?

Radiography Testing (RT) is a non-destructive testing technique that uses penetrating radiation — X-rays or gamma rays — to create images of the internal structure of solid components. When radiation passes through a material, it is attenuated (absorbed and scattered) by the material’s density and thickness. Variations in internal structure — voids, inclusions, cracks, thickness changes — produce local differences in radiation attenuation that are recorded on a detector (film, computed radiography plate, or digital flat panel) as contrast variations in the resulting image.

Radiography is one of the five fundamental NDT methods and is widely applied in weld inspection, casting quality evaluation, aerospace component certification, and pipeline integrity assessment across virtually every manufacturing and maintenance industry.

Physical Principles of Radiography

X-Ray Generation

X-rays are generated by accelerating electrons from a tungsten filament cathode and decelerating them abruptly at a tungsten anode — producing both characteristic X-ray lines and a continuous Bremsstrahlung spectrum. Industrial X-ray tubes operate at 20–450 kV — higher voltage produces more penetrating (harder) X-rays that can inspect thicker materials.

Gamma-Ray Sources

Gamma rays are produced by radioactive isotope decay — Ir-192 (average energy 340 keV, half-life 73 days) for steels up to 75 mm, Co-60 (average energy 1.25 MeV, half-life 5.27 years) for thick steel and concrete, and Se-75 (average energy 200 keV, half-life 120 days) for thin steel and aluminium. Isotope sources are compact and require no electrical power — enabling radiography in remote field locations and confined spaces where X-ray equipment is impractical.

Image Formation

Radiation passing through the test object exposes the detector proportionally to the transmitted radiation intensity. Defects with lower density than the surrounding material (voids, cracks) transmit more radiation — appearing as darker regions on film or brighter regions on digital detectors. Denser inclusions (metallic slag, tungsten) transmit less radiation — appearing lighter (brighter on film, darker on digital).

Radiography Methods

Film Radiography (Conventional RT)

The traditional method — radiation exposes silver halide film that is chemically processed to produce a permanent image. Film radiography provides excellent spatial resolution (to 0.1 mm) and permanent records. Film must be processed in a darkroom — turnaround typically 30–60 minutes. Governed by ASTM E94 and ASME Section V.

Computed Radiography (CR)

Photostimulable phosphor (PSP) imaging plates replace film. After exposure, the plate is scanned by a laser reader to produce a digital image — faster and more cost-effective than film, with reusable plates. Spatial resolution is slightly lower than film but adequate for most code requirements. Governed by ASTM E2033.

Digital Radiography (DR) — Flat Panel Detectors

Direct digital detection using amorphous silicon or amorphous selenium flat panel detectors provides real-time digital images within seconds of exposure — enabling immediate image review and manipulation. DR dramatically reduces inspection time and eliminates film processing chemistry. Governed by ASTM E2698.

Computed Tomography (CT)

Multiple radiographic projections at different angles are combined by reconstruction algorithms to produce three-dimensional volumetric images, as described in Blog 2 of Series 2. CT enables virtual cross-sectioning without physical specimen preparation.

Key Industrial Applications

Weld Inspection

Radiography is the standard volumetric NDT method for weld quality inspection in pressure vessels (ASME Section VIII), nuclear components (ASME Section III), pipelines (API 1104), and structural welds (AWS D1.1). It detects: porosity, slag inclusions, lack of fusion, incomplete penetration, and cracks — volumetric defects that are clearly imaged as contrast variations in the radiograph.

Casting Quality Evaluation

Casting radiography per ASTM E446 (steel castings) and ASTM E505 (aluminium castings) detects shrinkage voids, gas porosity, cracks, and inclusions — essential for aircraft engine castings, automotive engine blocks, and pressure-containing pump/valve bodies.

Aerospace Component Inspection

Composite aircraft structures, ceramic matrix composite (CMC) turbine components, and metallic aerospace forgings are radiographed during production for foreign object detection and internal defect identification per NAS 410 and AMS 2644.

Conclusion

Radiography Testing (RT) is one of the most powerful non-destructive testing methods for visualising the internal structure of materials without cutting or damaging them. By using X-rays or gamma rays, RT reveals hidden defects such as porosity, inclusions, cracks, and thickness variations that cannot be detected by surface inspection methods. With advancements from conventional film to computed and fully digital radiography, RT now offers faster inspection, real-time imaging, and improved data management.

Why Choose Infinita Lab for Radiography Testing?

At the core of this breadth is our network of 2,000+ accredited labs in the USA, offering access to over 10,000 test types. From advanced metrology (SEM, TEM, RBS, XPS) to mechanical, dielectric, environmental, and standardised ASTM/ISO testing, we give clients unmatched flexibility, specialisation, and scale. You’re not limited by geography, facility, or methodology—Infinita connects you to the right testing, every time.

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