1.1 These reference radiographs 2 illustrate various categories, types, and severity levels of discontinuities occurring in steel castings that have section thicknesses up to 2 in. (50.8 mm) (see Note 2 ). The reference radiograph films are an adjunct to this standard and must be purchased separately from ASTM International, if needed (see 2.2 ). Categories and severity levels for each discontinuity type represented by these reference radiographs are described in 1.3 . Note 1: The basis of application for these reference radiographs requires a prior purchaser supplier agreement of radiographic examination attributes and classification criterion as described in Sections 4 , 6 , and 7 of this standard. Note 2: Reference radiographs previously used for this thickness range carried the designation E71 , but included a now rarely used gamma source, that is, radium. The current document is also updated by inclusion of several recognized shrinkage or C categories and by elimination of the crack and hot tear categories except for one example of each of these discontinuity types. Reference radiographs for thicker sections may be found in Reference Radiograph standards E186 and E280 . Reference Radiograph standards E446 and E186 provide some overlap of severity levels for similar discontinuity categories within the same energy level range (see 4.2 , 5.1 , and 6.3 ). 1.2 These film reference radiographs are not intended to illustrate the types and degrees of discontinuities found in steel castings when performing digital radiography. If performing digital radiography of steel castings up to 2 in. (50.8 mm) in thickness, refer to Digital Reference Image Standard E2868 . 1.3 These reference radiographs consist of three separate volumes (see Note 3 ) as follows: ( I ) medium voltage (nominal 250-kV) X rays. ( II ) 1-MV X rays and Iridium-192 radiation, and ( III ) 2-MV to 4-MV X rays and cobalt-60 radiation. Unless otherwise specified in a purchaser supplier agreement (see 1.1 ), each volume is for comparison only with production radiographs produced with radiation energy levels within the thickness range covered by this standard. Each volume consists of six categories of graded discontinuities of increasing severity level and four categories of ungraded discontinuities. Reference radiographs containing ungraded discontinuities are provided as a guide for recognition of a specific casting discontinuity type where severity levels are not needed. Following is a list of discontinuity categories, types and severity levels for the adjunct reference radiographs of this standard: 1.3.1 Category A- Gas porosity; severity levels 1 through 5. 1.3.2 Category B- Sand and slag inclusions; severity levels 1 through 5. 1.3.3 Category C- Shrinkage; 4 types: 1.3.3.1 Ca-linear shrinkage- Severity levels 1 through 5. 1.3.3.2 Cb-feathery shrinkage- Severity levels 1 through 5. 1.3.3.3 Cc-sponge shrinkage- Severity levels 1 through 5. 1.3.3.4 Cd-combinations of linear, feathery and sponge shrinkage- Severity levels 1 through 5. 1.3.4 Category D- Crack; 1 illustration. 1.3.5 Category E- Hot tear; 1 illustration. 1.3.6 Category F- Insert; 1 illustration. 1.3.7 Category G- Mottling; 1 illustration. Note 3: The reference radiographs consist of the following: Volume I: Medium Voltage ( nominal 250 kVp ) X-Ray Reference Radiographs-set of 34 illustrations (nominal 5 by 7 in.) in a 15 by 17-in. ring binder. Volume II: 1-MV X Rays and Iridium-192 Reference Radiographs -Set of 34 illustrations (nominal 5 by 7 in.) in a 15 by 17-in. ring binder. Volume III: 2- MV to 4- MV X Rays and Cobalt-60 Reference Radiographs -Set of 34 illustrations (nominal 5 by 7 in.) in a 15 by 17-in. ring binder. Note 4: Although Category G-Mottling is listed for all three volumes, the appearance of mottling is dependent on the level of radiation energy. Mottling appears reasonably prominent in Volume I; however, because of the higher radiation energy levels mottling may not be apparent in Volume II nor Volume III. 1.4 The values stated in inch-pound units are to be regarded as the standard. SI values are shown for information only. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.