The tools used for film viewing include a film viewer and a densitometer. The film viewer is a variable light box which allows you to view film in different densities by utilizing a dimmer to adjust the lighting. The densitometer is a unit used to determine the specific darkness of a specific section within the film. A good x-ray film will have a specific density in the area of interest governed by the code or procedure being used for inspection. This density range is usually between a 1.0 – 4.0 depending on the procedure and type of defect sought. Both of these items are calibrated to ensure proper density verification. The densitometer is calibrated with a step wedge (piece of film with known density steps traceable to a known standard such as NIST ) and the film viewer is verified with a light meter.



The thickness of a given material which you can penetrate is dependent on the strength of your x-ray source. The generation of Industrial x-rays usually occur in one of two ways. From electrical machines which can be turned off (an X-ray tube) or a gamma ray source (an actual radioactive material) which cannot be turned off. X-ray tubes usually start at 100Kv small portable units and become enormous linear accelerators capable of producing MEv’s million electron volts capable of penetrating 11” + of Cast Steel. Sources are usually about the size of a pen tip and are extremely dangerous capable of penetrating 3-7” of Cast Steel. So for X-ray machines yes, size matters and space requirements are paramount when inspecting thick materials.

X-ray is a good process for surface and subsurface detection of flaws dependent on image sensitivity. Image sensitivity is affected by film selection, Source type or energy, part placement and orientation and part geometry. Sensitivity verification is usually accomplished with a penetrameter (aka penny) of the standard or wire variety. A good x-ray is one with appropriate contrast and latitude for the area of interest. For complex shaped parts it is common to have to examine one area with multiple pieces of film to ensure appropriate density coverage. The process of proper coverage is made easier with digital radiography which provides a quicker image than traditional film processes which take approximately 8 minutes for on piece of film to process and you get one image with a specific density. This point is important because the area of the film that is interpretable is dependent upon the density in that specific area. Digital radiography allows you to alter the density with a simple roll of the computer mouse.



Some of the downsides of radiography are
1. The danger of radiation.
2. Requires access to both sides of the part to take an x-ray shot.
3. The consumption of time and the cost of equipment required.
4. Training requirements on operators.
5. Film retention requirements.