Methods of radiographic examination for steel castings valves
1 Scope
This standard specifies the general requirements and specific requirements for X-ray and γ-ray radiographic examination for carbon steel, alloy steel and stainless steel and castings valves, as well as the classification and evaluation methods of radiograph defects, the acceptance requirements, the radiographic examination records, the characteristic indexes of film systems, the key examination parts of radiogram, the method for determining the minimum distance (f) between the radiographic source and the steel casting, the periodic calibration method of nigrometer, the calculation method of focus size, the type and specification of special image quality indicator, and the position of overlapping mark.
This standard is applicable to the radiographic examination for steel castings valves (hereinafter referred to as castings). The radiographic examination of supporting pipe fittings, flanges and other compressed steel castings may also refer to this standard.
2 Normative references
The following documents contain provisions which, through reference in this text, constitute provisions of this standard. For dated references, subsequent amendments (excluding corrections), or revisions, of any of these publications do not apply to this standard. However parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition applies.
GB 11533-1989 Standard for logarithmic visual acuity charts
GB 16357-1996 Radiological protection standards for industrial X-ray detection
GB 18465-2001 Radiological protection requirements for industrial gamma defect detecting
GB 18871-2002 Basic standards for protection against ionizing radiation and for the safety of radiation sources
JB/T 7902-2006 Non-destructive testing - Image quality indicators (wire type) for radiographic testing
JB/T 7903-1999 Industrial radiographic illuminators
3 General requirements
3.1 Radiographic examination personnel
3.1.1 The radiographic examination personnel shall be trained in radiation safety knowledge before taking up their posts, and obtain the radiation worker certificate.
3.1.2 The uncorrected and corrected near vision and distant vision of the radiographic examination personnel shall not be less than 5.0 (decimal record value is 1.0) and the testing method shall meet the requirements of GB 11533. The eyesight of the film evaluator shall be checked once every year.
3.2 Radiographic film
3.2.1 Film systems are classified into four categories, i.e. T1, T2, T3 and T4. Category T1 is the highest and Category T4 is the lowest. See Annex A for the characteristic indexes of film systems. The film manufacturer shall conduct system performance test on the produced films and provide their categories and parameters. The film processing method, equipment and chemical agent used may be, according to the relevant requirements, tested and controlled with the test film which has been exposed beforehand and is provided by the manufacturer.
3.2.2 The film type shall be selected according to the casting thickness, ray sensitivity and intensifying method. Film of Category T3 or higher shall be adopted for Grade A and Grade AB radiographic examination techniques, and film of Category T2 or higher shall be adopted for Grade B radiographic examination technique. The fog density of the film background shall not be greater than 0.3.
3.2.3 When γ rays are used to examine materials with high crack sensitivity, film of Category T2 or higher shall be used.
3.3 Film viewing illuminator
3.3.1 The main properties of film viewing illuminators shall meet the relevant requirements of JB/T 7903.
3.3.2 The maximum brightness of film viewing illuminators shall meet the requirements of film evaluation.
3.4 Nigrometer (optical densitometer)
Foreword i
1 Scope
2 Normative references
3 General requirements
3.1 Radiographic examination personnel
3.2 Radiographic film
3.3 Film viewing illuminator
3.4 Nigrometer (optical densitometer)
3.5 Intensifying screen
3.6 Image quality indicator
3.7 Surface requirements and radiographic examination timing
3.8 Selection of radiographic examination technique grade
3.9 Radiation protection
4 Specific requirements
4.1 Ray energy
4.2 Minimum distance from radiographic source to object surface
4.3 Exposure
4.4 Exposure curve
4.5 Penetration arrangement
4.6 Application of image quality indicator
4.7 Shield of useless rays and scattered rays
4.8 Mark
4.9 Film processing
4.10 Film evaluation requirements
4.11 Quality of film
5 Classification and evaluation methods of defects on the radiograph
5.1 Classification and size measurement of defects
5.2 Defect levels of pores, sand inclusions and slag inclusions
5.3 Levels of shrinkage cavity defects
5.4 Comprehensive rating of defects
6 Acceptance requirements
7 Records of radiographic examination
Annex A (Informative) Characteristic indexes of industrial radiographic film system
Annex B (Normative) Key parts of radiographic examination for steel castings valves
B.1 Overview
B.2 Welded valves
B.3 Flanged valves
B.4 Others
B.5 Typical sections of castings subject to radiographic detection
Annex C (Normative) Method for determining the minimum distance from radiographic source to cast steel body (f)
Annex D (Informative) Periodic calibration method of nigrometer (optical densitometer)
D.1 General requirements for calibration of nigrometer
D.2 Procedures for calibration method of nigrometer
Annex E (Normative) Calculation method for focus size
E.1 Calculation of focus size
Annex F (Normative) Type and specification of special image quality indicator
F.1 Pattern of special image quality indicator
F.2 Type, specification and material of special image quality indicator
Annex G (Normative) Position of overlapping mark
Figure 1 Maximum allowable penetration tube voltage for different penetrated thickness
Figure 2 Eccentric inner radiography diagram
Figure 3 Concentric internal radiography diagram
Figure 4 Outer radiography diagram
Figure 5 Double-wall radiography diagram
Figure B.1 Gate valve body (Pressure seal bonnet)
Figure B.2 Y-shaped globe valve body (Pressure seal bonnet)
Figure B.3 Same type of bonnet for angle body (Pressure seal bonnet) and Y-shaped globe valve
Figure B.4 Lower elbow (Pressure seal bonnet)
Figure B.5 Gate valve body (Flanged bonnet)
Figure B.6 Globe valve body (Flanged bonnet)
Figure B.7 Disc valve body
Figure B.8 Plug valve body
Figure B.9 Disc cover slab
Figure B.10 Flat cover slab
Figure C.1 Nomogram for determining the distance from the focus to the object surface by Grade A and Grade B radiographic examination techniques
Figure C.2 Nomogram for determining the distance from the focus to the object surface by Grade AB radiographic examination technique
Figure E.1 Classification of focus shapes
Figure F.1 Basic pattern of special image quality indicator
Figure G.1 Plane castings
Figure G.2 Radiographic source-to-film distance f smaller than curvature radius of curved-surface object
Figure G.3 Curved-surface component with convex towards radiographic source
Figure G.4 Radiographic source-to-film distance f greater than curvature radius of curved-surface object
Figure G.5 Radiographic source at the curvature center of curved-surface object
Table 1 Material and thickness of intensifying screen
Table 2 Penetrated thickness range of γ-ray equipment or ray equipment with energy of 1MeV or above
Table 3 Brightness of film viewing illuminator
Table 4 Useful range of film density
Table 5 Grades of radiographic sensitivity
Table 6 Size of the evaluation zone and the maximum allowable number of pores
Table 7 Size of the evaluation zone as well as the maximum allowable number of sand inclusions and slag inclusions
Table 8 Number of single defects
Table 9 Maximum allowable size of defects without counting numbers
Table 10 Maximum allowable size of pores of Level I defects
Table 11 Maximum allowable size of sand inclusions and slag inclusions of Level I defects
Table 12 Maximum allowable length of stripy shrinkage cavity defects
Table 13 Maximum allowable area of dendritic shrinkage cavity defects
Table 14 Maximum size of shrinkage cavity defects exempt from evaluation
Table 15 Acceptable acceptance level of radiographic examination for steel castings
Table A.1 Main characteristic indexes of film system
