Description

1. TASK 70-26-01-260-501 Radiographic Inspection Procedures

   

   WARNING

   RADIATION IS VERY DANGEROUS TO PERSONS, YOU MUST MAKE SURE THAT ALL SAFETY PRECAUTIONS AND INSTRUCTIONS, BOTH NATIONAL AND LOCAL, ARE OBEYED. THE MAXIMUM DOSAGES FOR PERSONS MUST NOT BE MORE THAN THE SPECIFIED LIMITS.

   

   WARNING

   YOU MUST NOT GO INTO AN AREA WHEN X-RAY EQUIPMENT IS IN OPERATION. PERSONS WHO ARE NOT APPROVED MUST NOT GO INTO AREAS WHERE X-RAY EQUIPMENT IS USED.

   

   WARNING

   ALL SAFETY DEVICES MUST BE EXAMINED BEFORE THEY ARE USED. THIS INCLUDES DOOR INTERLOCKS AND AUDIBLE AND VISUAL WARNING DEVICES.

   1. General

      1. Always do a test on the equipment, as specified by the manufacturer.

   2. Safety Precautions

   3. Preparation Procedure

      1. For full radiographic instruction, radiographic samples with related data sheet will be necessary together with photographs/drawings that show the positions of the film and part in relation to the radiation source. The data sheet must always specify the conditions that will be used to make the radiographic samples. These conditions are as follows:

         1. Dimensions of the equipment and source.

         2. Position of the radiation source in relation to the film/part to be examined.

         3. Angle of beam.

         4. Source to film distance (sfd).

         5. Kilovoltage.

         6. Tube current.

         7. Exposure time.

         8. Thickness and type of filters used.

         9. Thickness and type of screens used.

         10. Type of film used.

      2. Always make a record of the X-ray data. The completed radiograph must then agree with the data.

   4. Identification

      1. Before a radiographic inspection is made, make marks on all the parts to help with the identification. This is to make sure that each part is correctly identified on the completed radiographs.

      2. Where possible, lead markers that will show on the completed radiographs must be installed adjacent to the parts to be examined. Alternatively, where it is necessary, the markers must be installed on the surface of the part so that the position of the part on the radiograph can be found.

      3. Markers installed on the surface of a part, must be in a position where they cannot cause a shadow on the area to be examined.

   5. X-ray Equipment

      1. Only X-ray equipment that can make radiographs to the specified sensitivity and density standards (refer to steps Paragraphand Paragraph) for all the examined parts are permitted. In general, tube voltages of more than 150 KV are not necessary.

   6. Location of Film

      1. The films must be put as near as possible to the part and be accurately aligned. This is to make sure that the full area to be examined is included on the radiograph.

      2. There must always be a sufficient overlap between the films. Where this cannot cause be seen from the surface properties of the part lead markers must be used as specified in Paragraph

   7. Use of Multiple Film Procedures

      1. Multiple film procedures (that is the use of different films with different speed properties) can be used to examine parts of variable thickness.

      2. The exposure time must be calculated to record the thicker parts on the faster film and the thinner parts on the slower film.

      3. The exposure conditions will then be found from the thickest part to be examined.

      4. The difference in thickness must not be too much because it will cause decreased contrast on the thinnest parts.

   8. Use of Lead Screens

      1. Lead screens with the applicable thickness will usually be used for all exposures of 120 KV or more. They can also be recommended for use at lower exposures, to decrease the scatter when the front screen must not be more than 0.10 mm.

         1. With a radiation source of less than 100 KV, the use of a lead screen is usually only recommended to decrease radiation scatter. With a radiation source of between 100 and 400 KV, a screen thickness of less than 0.10 mm is recommended.

      2. In general, a lead or metal foil screen must be used for all exposures of 120 KV or more.

      3. Always make sure that the film touches the screen.

   9. Filters

      1. Filters can only be used they agree with the specified density and sensitivity requirements of this task. Refer to Paragraph and Paragraph.

   10. Radiation Scatter

       1. Radiation scatter can decrease the quality of the radiographs. Always try to decrease radiation scatter by the use of one or more of the devices that follow: Lead masks, diaphragms, cones or lead behind the film.

   11. Radiographic Sensitivity

       1. The Image Quality Indicator (IQI) sensitivity of a radiograph must be two percent or better for all the areas to be examined.

       2. An IQI must be used to prepare and do a procedure. It must then be used at such times, as is necessary, to keep the specified standard.

   12. Density

       1. A density of 1.5 to 3 is necessary.

   13. Image Quality Indicators (IQI)

       1. Approved image quality indicators (IQI) that agree with the specifications of British Standard 3971, DIN 54109 (ASME or MIL - STD 453), will usually be used. IQI's that do not agree with these specifications can be used but they must be calibrated and approved.

   14. Process the Films

       1. The films can be processed automatically or manually, but always make sure that the results are regular.

   15. Examine the Radiographs

       1. Always examine the radiographs in a room with a low ambient light level. The ambient light must not shine into the eyes from the radiograph.

       2. Noise and traffic in the room must be controlled to prevent distraction of the inspector when the radiographs are examined.

   16. Equipment Used to Examine the Radiographs

       1. The light source must always be sufficient to find the differences in film density on the radiographs. A controlled intensity light source, or a light box with different levels of light intensity can be used when necessary.

       2. The illuminators must be made to give a regular light level in the area where the radiographs are examined.

       3. There must also be a sufficient light mask in the area where the radiographs are examined.

   17. Control Checks

       1. Make checks at the start of each work time, to make sure the sensitivity and density standards are as specified in Paragraph and Paragraph. Make a record of all the checks.

       2. The density of a radiograph must be examined with a densitometer that is calibrated to be accurate to plus or minus 0.050 D.

   18. Radiographic Film Storage

       1. All radiographs must be kept as specified in the related contract.