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X-Ray and Gamma Radiography

Radiography as a non-destructive test is exceptionally good at detecting volumetric flaws including voids, gas pores and solid inclusions, while ultrasonics (Phased Array) are recommended when measuring the thickness of the identified flaw.

The majority of industrial radiography is for the testing of welds on pressurised piping systems, pressure vessels, high-capacity storage containers, pipelines, and some structural welds.

Other tested materials include welder’s test coupons, machined parts, plate metal, or pipe wall corrosion.

For purposes of inspection, including weld inspection, there exist several exposure techniques.

  • Panoramic (SWSI) technique
  • SWSI arrangement
  • Exterior placement
  • Flat object
  • Super impose
  • DWDI technique

The process for radiography consists of positioning a source of ionising radiation close to one side of the test item with the radiographic film placed to the other. Radiation is partly absorbed during transmission with material thickness or absorption quality results being recorded as a full size image.

Both X-ray and gamma X-ray testing are available; the former being electrically generated by a high voltage X-ray tube, the latter by natural disintegration of nuclei in a radioactive isotope. Both processes are carried out under stringent safety measures.

Gamma radiation sources, most commonly iridium-192 and Selenium 75, are used to inspect a variety of materials. X-Ray equipment (electrically generated radiation) is also used, X-radiation provides a sharper image than gamma sources although it is not always possible to use x-ray generators due to the size, thickness or location of the item requiring inspection.

Our Inspection Equipment

Here at ITCL we are always looking for new inspection technology to assist us in providing the very best service. We currently use the following equipment and manufacturers for radiography equipment:

X-Radiography units: Xylon Smart 300 & 200KV generators

Gamma Ray projectors: Sentinel 880 projectors.

Radiography Consultancy Services

Project development:

Due to ITCL’s years of experience working with industrial radiography we able to provide a project development service, this is a bespoke service where a Level III technician will work one to one with your quality manager to work through the challenges of your project.

Once the solution has been identified they will write a procedure and provide technique sheets to enable the inspection to be carried out.

Radiographic Level Three Services:

ITCL offer a full range of Level III consultancy services, these include NDT Technique approval, writing and approval of NDT Procedures.

Learn more about the techniques and examples of Radiography (X-Ray & Gamma-Ray) here, read or download.

Alternatively contact a member of the ITCL team on 0151 356 7118 for more information.

 

Techniques Explained Further:

  1. Panoramic technique - one of the four single-wall exposure SWSI. This exposure is created when the radiographer places the source of radiation at the center of a pipe. Depending on the testing requirements, the radiographer would then place the film cassettes on the outside of the surface to be examined. This exposure arrangement is nearly ideal – when properly arranged and exposed, all portions of all exposed film will be of the same approximate density.
  2. Advantage -it takes less time than other arrangements since the source must only penetrate the total wall thickness (WT) once and must only travel the radius of the inspection item, not its full diameter.

    Disadvantage - the panoramic technique is that it may be impractical to reach the center of the pipe i.e. a pressurised or sealed system.

  3. SWSI arrangement - is an interior placement of the source in an enclosed inspection item without having the source centered up. The source does not come in direct contact with the item, but is placed a distance away, depending on the testing requirements.
  4. Exterior placement with similar characteristics as the SWSI arrangement.
  5. Flat objects - such as plate metal, and is also radiographed without the source coming in direct contact with the item. In each case, the radiographic film is located on the opposite side of the inspection item from the source.

 

In all four cases, only one wall is exposed, and only one wall is viewed on the radiograph.

Of the other exposure techniques, only the contact shot has the source located on the inspection item. This type of radiograph exposes both walls, but only resolves the image on the wall nearest the film.

This DWSI exposure technique takes more time than a panoramic exposure, as the source must penetrate the WT twice and travel the entire outside diameter of the pipe to reach the film on the opposite side.

Another is the super impose technique (wherein the source is placed on one side of the item, not in direct contact with it, with the film on the opposite side). This technique is usually reserved for very small diameter piping.

The last technique is DWDI the elliptical, in which the source is offset from the plane of the inspection item (usually a weld in pipe) and the elliptical image of the weld furthest from the source is cast onto the film.

The specimen to be inspected is placed between the source of radiation and the detecting device, usually the film in a light tight cassette, and the radiation is allowed to penetrate the part for the required length of time to be adequately recorded.

Lead is often placed behind the film to reduce the ‘back scattered’ radiation, which can lead to the film becoming over exposed.

Guidance

Before commencing any radiographic examination, it is always advisable to visually examine the component, to eliminate any possible external or internal defects.

After this visual examination, the operator will have a clear idea of the possibilities of access to the two faces of the weld, which is important both for the setting up of the equipment and for the choice of the most appropriate technique.

Our Inspection Equipment

Here at ITCL we are always looking for new inspection technology to assist us in providing the very best service. We currently use the following equipment and manufactures for Radiography equipment:

X-Radiography units: Xylon Smart 300 & 200KV generators

Gamma Ray projectors: Sentinel 880 projectors.

Contact a member of the ITCL team on 0151 356 7118 for more information.

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