Guide for Industrial Radiography Artefacts
All indications appearing in a radiograph are to be interpreted. Interpretation requires analysing the indication as to whether it is a true indication due to discontinuities or a false indication due to problems with film manufacturing, mishandling of film or poor storage. The interpreter should be able to distinguish a relevant discontinuity from a false indication.
No image in the area of interest must obscure the true indication. All false indications appearing in the area must be re-radiographed for interpretation. All true indications are interpreted and characterized.
In Industrial radiography, false indications are also called artifacts, which may form due to improper handling of film, lead screens or cassettes during any stage of the radiographic process. Common artifacts are described in below sections.
Static marks on Radiographs
Branchlike, jagged dark lines or irregular dark spots originating from rapid loading or unloading of film.
Pressure Marks
The major cause of pressure marks is poor film handling during the preparation of cassettes. Film maybe pinched in the cassette at some point in the handling process. An object dropped on the cassette can also cause pressure marks.
Chemical Strain Mark - Radiography Artifact
streaks on the film caused by inadequate removal of chemicals between processing stages or insufficient agitation of the film hanger.
Crimp Marks
Caused by abrupt bending of film; typically crescent shaped. • Water mark – circular pattern caused by water droplets drying on the film surface.
Radiograph Fog
Occurs when the film is stored too near a source of radiation, or when a film is inadvertently left in the exposure room during the exposure of another film;
Also, caused by storage of film in a faulty storage box or bin; leaving the lid off the box; exposure to white light in a faulty darkroom or to the use of the wrong type of safelight or too strong a bulb in the safelight, or to the use of a faulty film holder; it is usually local but may be overall fog;
Frilling of Emulsion
Loosening of the emulsion from the film base due to warm or exhausted fixer solution, high temperature of processing solutions or prolonged washing in warm water
Lead Screen Marks, Scratches
Caused by abrasive materials or rough handling, including fingernails. Damaged or reused cassette – may cause a false indication to reappear after processing if the same cassette is used. However, the indication will probably move slightly because cassette placement is usually not exact.
Conclusion
The above guide may not be complete and exhaustive. Radiography Film Artifacts are common while processing the films. As long as they do not interfere with interpretation they can be ignored. If the artifacts are masking the relevant flaw indications it is better to re-shoot the same spot radiography.
Artifacts are not only appear in manual processing. There are artifacts in automatic processing such as PI Lines due to scratched on the rollers.
Proper precautions can minimize the artifacts in Industrial Radiography service and may not be completely avoidable. Visit us to know more about NDT testing services