Radiographic Testing (RT)

Radiographic Testing (RT) is an NDT method that uses X-rays or gamma rays to create a permanent image of the internal structure of a component on film or a digital detector, revealing porosity, cracks, inclusions, and other volumetric defects.

Definition

Radiographic Testing (RT) is a volumetric NDT method in which penetrating ionizing radiation — produced by an X-ray tube or a gamma source such as Ir-192 or Co-60 — passes through a test piece and exposes a film or digital detector on the opposite side. Variations in thickness or density produce contrast on the resulting radiograph, allowing inspectors to identify internal discontinuities.

Technical Context

Image quality is verified using an image quality indicator (IQI), and parameters such as geometric unsharpness, density, and sensitivity are tightly controlled. The source-to-film distance and exposure time are calculated from an exposure chart.

When It Is Used

Butt-weld inspection in pressure equipment and pipelines (per ASME Section V and API 1104)
Casting inspection for porosity and shrinkage
Aerospace structural verification

Related Standards

ASME Section V Article 2, ISO 17636, ASTM E94, EN 12668. Radiation safety follows ALARA principles under the supervision of a Radiation Safety Officer.

Synonyms

Also called radiography, X-ray testing, or gamma-ray testing. Modern variants include Computed Radiography and Digital Radiography.

How it works

Penetrating radiation passes through the component and is differentially absorbed on the way. What reaches the film or detector is a shadow image in which anything less dense than surrounding material — a void, a slag inclusion, missing weld metal — appears darker.

What it finds

Volumetric flaws with excellent clarity: porosity, slag, incomplete penetration seen along the beam, and geometry such as root condition. It yields a permanent image a third party can re-read years later, which is why owners and insurers still ask for it.

What it will not find

Tight planar flaws lying across the beam. A crack presenting a fraction of a millimetre of missing material along the radiation path may produce no discernible density change, and lack of fusion on a bevel face frequently escapes. This is the reason ultrasonic methods are specified alongside radiography for critical thick-section welds rather than instead of it.

How it is actually done

Technique selection sets source, energy, geometry and exposure; an image quality indicator placed on the source side proves sensitivity was actually achieved. Density or grey-level checks confirm the image is within the range where the eye can discriminate. Without the IQI, an image proves nothing about its own adequacy.

Governing codes and standards

ASME Section V Article 2 governs radiographic examination and defines IQI selection and placement; ISO 17636 covers radiographic testing of welds; API 1104 addresses pipeline girth welds with its own acceptance criteria.

Where it goes wrong

Accepting an image whose IQI hole or wire is not visible. That is not a marginal result — it is direct evidence that the required sensitivity was not reached, and any interpretation drawn from that image is unsupported.

Frequently asked questions

Why is a weld radiograph accepted by one code and rejected by another?

Because acceptance criteria live in the construction code, not in the examination standard. ASME Section V tells you how to take the radiograph; ASME Section VIII, B31.3 or API 1104 tells you what is acceptable in the image. The same film can pass under one and fail under another.

Is digital radiography accepted in place of film?

Increasingly yes, with conditions. Codes have added requirements for spatial resolution, contrast and archiving, because a digital image can be processed in ways film cannot. Where a specification predates those provisions, substitution needs written agreement.

Where Radiographic Testing fits in an inspection programme

A term is only useful when it connects to a decision. Radiographic Testing appears in written procedures, in technique sheets, and in the records an owner or accreditation body reviews afterwards — which means the way it is defined in your documentation has to match the way it is applied on site. Where the two drift apart, audits find it. Atlantis writes and reviews procedures against the governing codes, trains inspection personnel to apply them, and builds the record-keeping that makes the evidence retrievable years later. Procedure development and code consulting · NDT training and certification · Ask us about your programme.

Related terms

X-Ray Tube — An X-ray tube is an electrically powered radiation source that produces X-rays by accelerating electrons across a high-voltage gap and bombarding a tungsten target inside a vacuum envelope.
Gamma Source — A gamma source is a sealed radioactive isotope used in industrial radiography to produce penetrating gamma rays for inspecting thick or remote components without an external power supply.
Iridium-192 (Ir-192) — Iridium-192 is the most common industrial radiography isotope, providing gamma energies around 0.3–0.6 MeV and a 74-day half-life, suitable for inspecting steel between approximately 10 mm and 75 mm.
Image Quality Indicator (IQI) — An image quality indicator (IQI), also called a penetrameter, is a device placed on the source side of a radiographic test piece to verify image sensitivity and resolution by displaying known features such as wires or holes.
Computed Radiography (CR) — Computed Radiography (CR) replaces traditional X-ray film with a reusable photostimulable phosphor imaging plate that is scanned by a laser reader to produce a digital radiograph, reducing chemicals, time, and consumables.
Digital Radiography (DR) — Digital Radiography uses a flat-panel detector (amorphous silicon or amorphous selenium) to capture an X-ray image directly in digital form in real time, with higher signal-to-noise ratio and faster cycle time than CR or film.

More method terms

Ultrasonic Testing · Magnetic Particle Testing · Penetrant Testing · Eddy Current Testing · Visual Testing · Acoustic Emission Testing · Leak Testing · Thermography / Infrared Testing · Microwave Testing · Phased Array Ultrasonic Testing

Where this comes up in practice

Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.

Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.