What it finds

  • Volume flaws such as porosity, slag, inclusions and shrinkage in welds and castings.
  • Cracks and lack of fusion, when they line up with the radiation beam.
  • Assembly problems, such as missing parts, misplaced items or foreign objects inside something that cannot be opened.

How it works

A source of X-rays, or of gamma rays from a radioactive isotope, sits on one side of the part, and a detector on the other. Thicker or denser areas absorb more radiation, and voids absorb less, so the differences show as lighter and darker areas in the image.

The detector may be film, a reusable imaging plate read by a scanner (computed radiography, CR), or an electronic panel (digital radiography, DR). Computed tomography (CT) takes many images from different angles and builds a 3D model. An image quality indicator placed in the shot shows that the exposure was sensitive enough.

Where it is used

RT is used on pipeline and pressure vessel welds, on castings, on aerospace parts and on electronics and assemblies. See our guides to midstream pipelines, space and ships.

Limits

  • Radiation safety. Areas must be cleared or shielded, and work is often done at night or in a controlled bay. In the United States, radioactive sources are licensed by the Nuclear Regulatory Commission or an Agreement State, and trainees need radiation safety instruction before certification.
  • Tight cracks can hide. A crack at an angle to the beam may show nothing.
  • Depth is not obvious. A single image is flat, so it shows where a flaw lies across the part but not how deep it is.
  • Access and thickness. Most setups need access to both sides, and very thick or dense sections need stronger sources and longer exposures.
  • Cost and time. Setup, exclusion zones and film processing add time compared with many other methods.

Who is allowed to do this work is set by a certification scheme, with radiation rules on top. See How to Become an NDT Level I, II or III.

Frequently asked questions

Is a radiographed part radioactive afterwards?

No. Normal X-ray and gamma radiography does not make the part radioactive. The hazard exists only during exposure, or from the source itself.

Film or digital radiography?

Both can do the job. Digital gives quicker results and needs no chemical processing, while film remains widely accepted. The code, the customer and the procedure decide what is allowed.

What is the difference between RT and CT?

RT usually gives a flat image from one or a few directions. CT combines many images into a 3D model, which shows depth and internal geometry, but it costs more and suits parts that fit in the system.

How NDT LLC can help

Our team of Level IIIs helps with RT procedures, film and digital interpretation questions and program reviews, and we take on field NDT and inspection work. Contact us.

This article is general information for a business audience, not engineering, legal or regulatory advice. Always work to the current edition of the codes, standards, regulations and manufacturer data that apply to your equipment and contracts.

NDT LLC is an independent consulting firm. It is not affiliated with, endorsed by or sponsored by ASNT, ASME, ASTM International, the US Nuclear Regulatory Commission, or any other organization named in this article; names are used only to identify the organizations and documents referred to.