Feature Reading Radiographs Here’s help in developing a systematic approach to reading radiographs The interpretation of radiographs may be divided into three major steps: • Determine the Quality • Analyze the Image • Report the Results Determine the Quality In this step, the quality of the radiograph itself is being assessed, not the quality of the specimen being radiographed. This requires an understanding of the applicable code requirements regarding the following items. Here are the procedures you must follow to determine the quality of the radiograph. Identification of the Radiographs. Verify that radiographs are properly identified with all required items. If any item of identification is missing from, or not clearly visible on, the radiographs, then they are not in compliance with the code. Image Quality Indicator (IQI). Verify that the proper Image Quality Indicator was used (or an acceptable alternative), and that it was positioned properly. Remember that in some cases, more than one IQI may be required so you must verify that the correct number of IQIs has been used. The IQI is the device used to judge the adequacy of the radiographic technique to produce a radiograph with the required sensitivity. The image of the IQI and the required hole (or required wire, if wire IQIs are used) are evidence that the radiographs have the required sensitivity. The IQI identification number must also be visible on the radiographs. Radiographic Density. Verify that all radiographs are within the specified density range. A calibrated densitometer should be used to verify density. The density should first be checked on the body of the IQI and 18 Inspection Trends / April 2011 then throughout the area of interest. When using wires, the IQI density should be taken near the essential wire. The density must fall within the specified range or the radiograph is not acceptable. Radiographic Technique. Verify that all technique parameters the radiographer used are in compliance with the code requirements. This includes the type of source used, energy level, source position, film type, type of screens, source-to-film distance, and geometric unsharpness (Ug). These items should all be reported by the radiographer on a technique sheet or the radiographic report. Remember that source-to-film distance (SFD) is used for exposure calculations, while source-to-object distance (SOD) is utilized for Ug calculations. Radiographic Coverage. The radiographer uses location markers (sometimes referred to as station markers) to indicate the area of the test specimen each film represents. Verify that location markers are displayed on each radiograph and that each radiograph in a series has adequate overlap to ensure the required coverage. This is especially important when film side markers are used on heavy-wall pipes. Film Processing. The method of film processing (i.e., manual or automatic) should be included in the information on the Radiographic Report. Verify that radiographs are free of film artifacts in the area of interest that might interfere with interpretation of the radiograph. Analyze the Image The next step in the film reading process is to analyze the image. This involves interpretation and classification of indications visible on the radiographs. Interpretation of indications involves determining the cause and classification of each indication. Remember that not all indications are caused by a discontinuity in the material; some indications are false indications, some are nonrelevant indications, and others are relevant indications, sometimes called true indications. Interpretation of Indications ASTM E 1316 may be referenced for standard terms and definitions used in radiography. It is important that we understand the standard terminology used in regard to radiographs. These terms include the following: Indication. A response, or evidence of a response, from a nondestructive examination (i.e., radiography) that requires interpretation to determine its relevance. An indication on the radiograph will appear as a change in the film density that may be either darker or lighter than the surrounding area. Interpretation. The determination of whether an indication is false, nonrelevant, or relevant. Discontinuities do not cause all indications; therefore, the interpretation will allow the Radiographic Interpreter (RI) to classify the indication as either false, nonrelevant, or relevant. False Indication. An indication caused by some condition other than a discontinuity in the test object, or by a change in the part geometry. In radiography, false indications are referred to as film artifacts and may be caused by improper handling of the film during loading and unloading of the cassettes. Failure to control film processing is also a major cause of artifacts.
Inspection Trends - April 2011 - Spring
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