تشریح رادیو گرافی جوش
INTERPRETATION OF WELD RADIOGRAPHS
Assessment and interpretation of radiographic images is widely used in industry for the quality control of weldments and castings. The purpose of this programme is to introduce the basic requirements for successful interpretation and to provide examples of weld defect types as revealed by radiography.
The requirements for satisfactory interpretation are that the interpreter must have adequate eyesight, whether corrected or uncorrected, and have the ability to recognise features in the image caused by various conditions. The standards usually quoted for eyesight require that personnel are able to read a minimum of the J2 level on the Jaeger eyesight chart with the chart at positioned a distance of 30.5 centimetres. Ability to recognise the features on a radiograph comes largely with experience.
Before viewing a radiograph the interpreter should have a basic knowledge of how the image was created and be aware of the radiographic technique used. The interpreter should have details of the weld configuration and should have some knowledge of the welding procedure used.
Viewing of radiographs should be carried out using a film viewer in a darkened room. When entering a darkened room from bright sunlight some time should be spent under darkroom conditions prior to commencing interpretation in order that eyesight can adjust to the low light level. Viewer screens should be cleaned before viewing and care must be taken to avoid marking or damaging the film. The area where films are viewed should be clean, work surfaces dry and the films handled by the edges to prevent fingerprints and damage to the film surfaces. Soft cotton gloves are often used by interpreters to limit the possibility of film damage.
Each radiograph is masked on the viewer so that stray light from around the film does not blind the interpreter. The film viewer can be activated by a foot switch when the film to be examined is in position. A dim side light can be used in order that notes can be made during the work.
Radiographs should be reviewed for film quality prior to interpreting the image for possible defects. Radiographs should be checked for identification, density and sensitivity and also for the presence of artefacts that may interfere with the assessment. Where film quality is unacceptable the area of weld covered by the film should be re-radiographed.
Manufacturers may have a method of radiographic identification which is linked to a quality system but the following is a guide to the normal requirements for details appearing on the radiograph.
The identification should include the manufacturer’s symbol, the component/item/weld number as appropriate, the location within the weld (such as location markers 1 to 2, B to C etc) and the date radiography was carried out.
The identification details usually appear in the image but sometimes a system of "flashing" the details on to the film before exposure is used. In all cases location markers which indicate the diagnostic length (extent of the weld on the film to be examined) must appear as radiographic images. The repair status of the weld should also be shown, usually by markers R1(repair), R2(second repair) etc. Identification details must not encroach on the weld area of interest - the length of weld and heat affected zone between the length markers.