Volumetric & Advanced NDT · RT
Radiographic Testing
A permanent photograph of everything inside the weld.
Radiographic testing (RT) images the interior of a component by passing X-rays or gamma rays through it onto film or a digital detector. Defects that absorb less radiation than the surrounding metal — pores, inclusions, lack of penetration — arrive as darker features on the image, producing a permanent, reviewable record of internal quality.
The explainer
Watch how it works.
Schematic · loops automatically
1Position source and detector
The source sits one side of the weld; film or a digital panel sits tight against the other, with IQIs placed on the job.
2Controlled exposure
Within a barriered exclusion zone, radiation passes through the component for a calculated exposure time.
3Thickness modulates the beam
Solid metal attenuates strongly; voids let more radiation through — the transmitted pattern carries the internal picture.
4The image develops
Film is processed (or the digital panel read): pores and lack of penetration print dark, dense inclusions light.
5Sentence against the standard
A qualified radiographer interprets the image, verifies IQI sensitivity, and sentences indications to the acceptance levels.
The physics
Radiation passing through matter is attenuated in proportion to the material’s density and thickness along each ray path. A void inside a weld is a short-cut: rays crossing a pore traverse less metal, arrive stronger, and expose the film more — printing the defect as a dark spot in the weld image. Dense inclusions do the opposite, arriving as light features.
Contrast and definition are engineered, not hoped for. Source selection (X-ray tube energy, or isotope — commonly iridium-192, selenium-75 or cobalt-60 for heavy sections), geometry, exposure and film class are all chosen to the standard’s requirements, and every radiograph carries an image quality indicator (IQI) — a set of graded wires whose visibility proves the achieved sensitivity on that exposure, not in theory.
Radiography’s defining strengths are the permanence and reviewability of the record — a third party can re-examine the film years later — and its excellence at volumetric defects. Its constraints are equally structural: radiation requires controlled areas and licensing, planar cracks oriented away from the beam can be missed, and defect depth is not directly measured. This is precisely the territory where phased array and TOFD have become accepted alternatives.
Where it earns its keep
Typical applications
- Pipework butt welds on process and utility systems
- Pressure vessel and boiler weld examination
- Castings and safety-critical components
- Welder and procedure qualification test pieces
Standards & schemes
| Designation | Covers |
|---|---|
| EN ISO 17636-1 / -2 | Radiographic testing of welds — film and digital techniques |
| EN ISO 10675-1 | Acceptance levels for radiographic testing of welds |
| EN ISO 19232 series | Image quality indicators and sensitivity classification |
Radiography is performed by certified radiographers under Metlab’s radiation safety procedures and statutory licensing, with interpretation by ISO 9712 Level 2/3 personnel.
Is radiography disruptive to a working site?
It requires controlled exclusion zones while the source is exposed, which is why site radiography is routinely scheduled for nights or shutdown windows. Where exclusion zones are impractical, phased array UT is the accepted alternative for many weld classes — we advise per contract.
Film or digital radiography?
Both are standardised (EN ISO 17636-1 film, -2 digital). Digital panels shorten exposure and give instant images and softcopy archiving; film remains widespread and contractually embedded. Sensitivity is proven the same way on both — by IQI wires visible on the actual image.
Why did radiography miss a crack that UT later found?
Radiographic detectability depends on the defect presenting a density difference along the beam; a tight crack at an unfavourable angle changes the path length almost nothing. Planar defects are UT territory — which is why critical welds often specify both, or an advanced UT technique with modelled coverage.
Delivered through
Testing · Inspection · Certification
Need RT on your asset?
Describe the component, the material and the question — a specialist confirms the technique, the standard and the turnaround.