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NB/T 47013 consists of the following fourteen parts under the general title Nondestructive testing of pressure equipment:
——Part 1: General requirements;
——Part 2: Radiographic testing;
——Part 3: Ultrasonic testing;
——Part 4: Magnetic particle testing;
——Part 5: Penetrant testing;
——Part 6: Eddy current testing;
——Part 7: Visual examination;
——Part 8: Leak testing;
——Part 9: Acoustic emission testing;
——Part 10: Ultrasonic time of flight diffraction technique;
——Part 11: Standard practice for X-ray digital radiography;
——Part 12: Magnetic flux leakage testing;
——Part 13: Pulsed eddy current testing;
——Part 14: X-ray computed radiographic testing.
This is Part 14 X-ray computed radiographic testing of NB/T 47013.
This standard is developed in accordance with the rules given in GB/T 1.1-2009 Directives for standardization - Part 1: Structure and drafting of standards.
This part was proposed by and is under the jurisdiction of the National Technical Committee on Boilers and Pressure Vessels of Standardization Administration of China (SAC/TC 262).
This part is issued for the first time.
Nondestructive testing of pressure equipment - Part 14: X-ray computed radiographic testing
1 Scope
1.1 This part of NB/T 47013 specifies the technical and quality classification requirements for fusion welded joints of metal pressure parts of pressure equipment subjected to 450kV and below X-ray computed radiographic testing (hereinafter referred to as CR testing).
1.2 This part is applicable to CR testing of fusion welded joints of steel, copper and copper alloy, aluminum and aluminum alloy, titanium and titanium alloy, nickel and nickel alloy materials. The type of welded joint is butt weld of butt joint of plate or pipe (hereinafter referred to as "butt weld").
1.3 This part may also serve as a reference for CR testing on welded joint of other materials, supporting members and structural members of the pressure equipment.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB 11533 Standard for logarithmic visual acuity charts
GB/T 12604.2 Non-destructive testing - Terminology - Terms used in radiographic testing
GB 18871 Basic standards for protection against ionizing radiation and for the safety of radiation sources
GB/T 21356 Non-destructive testing - Qualification and long-term stability of computed radiology systems
GB/T 23901.5 Non-destructive testing - Image quality of radiographs - Part 5: Image quality indicators (duplex wire type) - Determination of image unsharpness value
GBZ 117 Radiological protection standards for industrial X-ray detection
JB/T 5075 Non-destructive testing - Metal intensifying screens for radiographic testing
JB/T 7902 Non-destructive testing - Image quality indicators (wire type) for radiographic testing
NB/T 47013.1 Nondestructive testing of pressure equipment - Part 1: General requirements
NB/T 47013.2-2015 Nondestructive testing of pressure equipment - Part 2: Radiographic testing
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 12604.2, NB/T 47013.1 and NB/T 47013.2 and the following apply.
3.1
imaging plate, IP
flexible board coated with photo-excited phosphorescent crystal and capable of storing information in the form of latent image after exposure and replacing film for radiography testing
3.2
X-ray computed radiography system, CRS
system consisting of IP, special laser scanner, computer hardware and special software, etc. and capable of converting the information on IP into digital images, which is referred to as "CR system"
3.3
object-to-IP distance, b
distance between the surface of the tested object (at the side of the radiation source) and the IP measured in the direction of the radiation beam
3.4
source-to-IP distance, F
distance between the radiation source and the IP measured in the direction of the radiation beam, i.e. the focal distance
3.5
source-to-object distance, f
distance between the radiation source and the surface of the tested object (at the side of radiation source) measured along the centerline of the radiation beam
3.6
contrast sensitivity, CS
sensitivity represented by gray difference of digital image caused by radiography thickness difference, which is generally expressed by line diameter or line diameter number of image quality indicator (wire type)
3.7
structure noise of IP
intrinsic noise of digital image caused by uneven structure of photosensitive layer and IP surface
3.8
grey level, GL
quantitative description for the brightness degree of black and white images, which is determined according to the number of bits of the system A/D converter (analog-to-digital converter). The higher of the number of bits of A/D converter, the higher of the grey level. For example, when the A/D converter is 12bit, the collected grey level is 212＝4 096
3.9
pixel
basic component units of an X-ray digital image. A X-ray digital image is composed of dots which are referred to as pixels
3.10
grey value, GV
value representing the brightness degree of pixels in a digital image
3.11
linearized grey value, GVlin
grey value proportional to the exposure of IP
3.12
basic spatial resolution of a CR system, SRb
ability of the digital image of a CR system to display the minimum details per unit length obtained according to standard test conditions when there is no tested object, which is referred to as "resolution of a CR system”
3.13
spatial resolution of a digital image, SRbi
ability of the digital image to display the minimum details per unit length obtained according to actual testing conditions when there is tested object, which is referred to as "resolution of a digital image”
3.14
signal-to-noise ratio, SNR
ratio of the average grey value to the standard deviation of the selected area in a digital image
3.15
normalized signal-to-noise ratio, SNRN
signal-to-noise ratio after normalization based on the resolution of a CR system SRb
3.16
effective length of a single exposure, Leff
effective testing length of a single exposure in conformity with the standard
3.17
scanning resolution
pixel geometry size of digital image determined by scanning, which depends on the line spacing of IP scanned by laser scanner and the ratio of the laser point scanning travel speed to the working frequency of analog-to-digital converter
3.18
digital image processing
methods and techniques of processing digital images by computer. Common processing methods of CR digital images include enlargement, reduction, grey scale transformation, contrast transformation and so on
4 General requirements
4.1 Testing personnel
4.1.1 Personnel engaged in CR testing shall meet the relevant requirements of NB/T 47013.1.
4.1.2 CR testing personnel shall be subjected to training on radiation safety knowledge, special CR theory and practical operation before taking up their posts, and obtain corresponding qualifications.
4.1.3 The uncorrected and corrected near vision and distant vision of CR testing 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. Personnel engaged in the evaluation of digital images shall be subjected to an eye test once a year.
4.2 Testing equipment and apparatus
4.2.1 Radiation source
X-ray machines with focus size, tube voltage range and rated power suitable for the tested objects and meeting the technical requirements shall be selected.
4.2.2 CR system
The appropriate CR system shall be selected based on the tested object and technical requirements. System performance testing conditions and methods shall be in accordance with the requirements of GB/T 21356. The system shall at least meet the following performance indexes:
a) the image geometric distortion shall be less than ±2%;
b) there shall be no jitter or slippage between the scanner and the imaging plate (IP), or the jitter shall be lower than the system’s noise level;
c) on the same horizontal line of the image, the background grey of the central area and the edge shall not exceed ±10%;
d) other performance indexes include: signal-to-noise ratio, laser beam function, shadow, image erasure, artifacts, and so on.
4.2.2.1 Imaging plate (IP)
The IP quality certificate shall include at least the main performance parameters such as IP type and specification, dynamic range, excitation response time, and chemical composition. Users shall use and preserve the IP under the temperature and humidity conditions recommended by manufacturers and avoid unnecessary radiation. For the less-thick tested objects, IP with slower ISO speed shall be selected, and for thick tested objects, IP with faster ISO speed may be selected.
4.2.2.2 Scanner
The quality certificate of the laser scanner shall include at least the main performance parameters such as specification, scan size, input voltage, scanning resolution, laser beam focus size, scanning step speed, etc., and its functions and performance shall meet at least the following requirements:
a) the scanner shall have scanning and erasing function, and the grey value of the residual latent image after erasing shall not be higher than 5% of the maximum grey value of the system;
b) the scanning laser power shall meet the requirements of signal acquisition;
c) the photomultiplier voltage or gain, and the scanning resolution of the scanner shall be adjustable;
d) the laser beam shall be free of vibration and such phenomena as artifact or scan line loss.
4.2.2.3 Display
It shall meet the following requirements:
a) the minimum brightness shall be 250cd/m2;
b) the grey level of the displayer shall be at least level 256;
c) the minimum light intensity ratio that can be displayed shall be 1:250;
d) it shall display at least 1M pixel with a pixel size less than 0.3mm.
4.2.2.4 System specific software
It shall at least cover the following functions:
a) measurement functions: including grey scale measurement, spatial resolution measurement, measurement of signal-to-noise ratio, measurement of signal-to-noise ratio, etc.;
b) adjustment functions: including gray scale transformation, contrast adjustment, image scaling, etc.;
c) marking function.
4.2.3 Image quality indicator (IQI)
4.2.3.1 IQI (wire type)
a) The IQI (wire type), which is used to determine the contrast sensitivity of digital images, is classified into general-purpose IQI and equal-diameter IQI, of which the model and specification shall meet the requirements of JB/T 7902.
b) The range of tested object materials, which are applicable to the material code and material of IQI (wire type) as well as Indicator (wire type) made of different materials, may be in accordance with those specified in Table 1; the absorption coefficient of the materials of IQI (wire type) shall be close to or identical with the absorption coefficient of the materials under test as much as possible and shall not be higher than the absorption coefficient of the materials under test in any case.
Table 1 Range of materials applicable to IQI (wire type) made of different materials
Material code of
IQI (wire type) Al Ti Fe Ni Cu
Material of IQI (wire type) Commercially pure aluminum Commercially pure titanium Carbon steel Nickel-chromium alloy 3# pure copper
Range of applicable materials Aluminum and aluminum alloy Titanium and titanium alloy Steel Nickel and nickel alloy Copper and copper alloy
4.2.3.2 IQI (duplex wire type)
a) The IQI (duplex wire type) is used to measure CR system resolution and digital image resolution.
b) The model and specification of IQI (duplex wire type) shall meet the requirements of GB/T 23901.5.
4.2.4 The functions and performance of the testing equipment and apparatus shall meet the requirements above and corresponding supporting documents shall be provided.
4.2.5 Calibration or operation verification
4.2.5.1 Geometric distortion, jitter, uniformity, laser beam function, shadow, artifact, etc. among the performance of the CR system shall be calibrated or checked at least once a year and recorded.
4.2.5.2 The in-service exposure curve shall be verified at least once every year. The exposure curve shall be redrawn in the case any important component of the X-ray machine is replaced or repaired.
4.2.5.3 Operation verification
The CR system shall be checked and recorded in the following cases. Refer to GB/T 21356 for the checking method :
a) in the case of system changes (including repair and replacement of each component as well as software upgrade, etc.);
b) where the system is reused after shutdown for over 3 months;
c) under normal use conditions, the user can specify the verification frequency in the process documents according to the product specifications and use frequency, and implement verification according to the regulations.
4.3 Testing technology level
4.3.1 The CR testing technology is classified into three grades: Grade A - low sensitivity technology; Grade AB - intermediate sensitivity technology; and Grade B - high sensitivity technology.
4.3.2 The grade selection for CR testing technology shall meet the requirements of relevant regulations, standards and design technical documents and meanwhile shall also meet other technical requirements agreed between the contracting parties. As for the butt weld of pressure equipment, it is recommended to adopt Grade AB testing technology in general. As for butt welds of important equipment and structures, as well as those with special materials and special welding process, Grade B testing technology may be adopted.
4.3.3 In case that certain testing conditions fail to meet the requirements of Grade AB (or Grade B) testing technology, as agreed between contracting parties, and under the premise that effective remedy measures (e.g. increase the exposure or adopt a system with higher signal-to-noise ratio) are taken, if the digital image quality meets the requirements of Grade AB (or Grade B) testing technology, then it can be considered that testing has been conducted in accordance with Grade AB (or Grade B) testing technology.
4.3.4 If the source-to-object distance f does not meet the requirements of 5.7, the provisions of 4.3.3 shall not apply.
4.3.5 In case that certain testing conditions fail to meet the requirements of Grade AB testing technology in the CR testing of in-service pressure equipment, as agreed between contracting parties, and under the premise that effective remedy measures (e.g. increase the exposure or adopt a system with higher signal-to-noise ratio) are taken, the Grade A testing technology may be adopted for testing, while other non-destructive testing methods shall also be adopted for supplementary testing.
4.4 Testing process documents
4.4.1 The testing process documents include process procedure and operating instructions.
4.4.2 In addition to meeting the requirements of NB/T 47013.1, the process procedure shall also specify the specific scope or requirements of the following related factors. If the changes of related factors exceed the provisions, the process regulations shall be re-compiled or revised:
a) applicable structure, material category and thickness;
b) energy range and focus size of the radiation source;
c) testing technology grade;
d) radiography mode;
e) IP type and model;
f) model of IQI (wire type) and IQI (duplex wire type);
g) type and thickness of metal screen;
h) model and parameter setting of scanner;
i) digital image displayer.
4.4.3 The operating instructions shall be prepared according to the process procedure and the testing requirements for the tested object. Its content not only shall meet the requirements of NB/T 47013.1, but also shall at least include:
a) testing equipment and apparatus: radiation source (focus size), IP, metal screen (type and thickness), IQI (type and model), backscattering shield lead plate, mark, scanner and observation equipment, etc.;
b) testing technology and process: the grade of testing technology used, radiography mode (relative position between the radiation source and the tested object and IP), parameter selection (radiation source, IP, exposure conditions), IQI and mark type and arrangement, etc.;
c) parameters of the scanner;
d) image processing technology;
e) digital image quality requirements: resolution, contrast sensitivity, normalized signal-to-noise ratio, mark, etc.;
f) acceptance criteria;
g) verification requirements for operating instructions.
4.4.4 Initially used operating instructions shall be subject to process verification so as to verify whether the digital image quality can meet the requirements specified in the standard. Verification may be conducted via special radiography test or the first batch of digital images of the product may be taken as the verification basis. The digital images verified shall be marked.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 General requirements
5 Testing process and its selection
6 Testing result evaluation and quality grading
7 Testing record and report
Annex A (Informative) Testing method for the minimum grey value
Annex B (Normative) Determination of spatial resolution
Annex C (Normative) Determination of normalized signal-to-noise ratio
