GB/T 40385-2021 (GB/T40385-2021, GBT 40385-2021, GBT40385-2021) & related versions
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Non-destructive testing of steel tubes -- Digital radiographic testing of the weld seam of welded steel tubes for the detection of imperfections
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GB/T 40385-2021
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GBT 40385-2021
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GB/T 40385-2021: PDF in English (GBT 40385-2021)
GB/T 40385-2021
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.20
CCS H 26
GB/T 40385-2021 / ISO 10893-7:2019
Non-destructive testing of steel tubes - Digital radiographic
testing of the weld seam of welded steel tubes for the
detection of imperfections
(ISO 10893-7:2019, Non-destructive testing of steel tubes - Part 7: Digital
radiographic testing of the weld seam of welded steel tubes for the detection
of imperfections, IDT)
ISSUED ON: AUGUST 20, 2021
IMPLEMENTED ON: MARCH 01, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 6
4 General requirements ... 7
5 Test equipment ... 8
6 Test method ... 9
7 Image quality ... 12
8 Image processing ... 18
9 Classification of indications ... 19
10 Acceptance limits ... 19
11 Acceptance ... 20
12 Image storage and display ... 20
13 Test report ... 21
Appendix A (Informative) Examples of distribution of imperfections ... 22
References ... 24
Non-destructive testing of steel tubes - Digital radiographic
testing of the weld seam of welded steel tubes for the
detection of imperfections
1 Scope
This document specifies the requirements for X-ray digital testing techniques of the
longitudinal weld seam or helical weld seam of automatic fusion arc-welded steel
tubes for the detection of imperfections, including the radiographic testing of
computed radiography (CR) or digital detector arrays (DDAs). This document also
specifies the acceptance levels and calibration procedures of digital radiographic
testing.
This document also applies to the testing of circular hollow sections.
Note: The digital radiographic testing method is used as an alternative of film-based
radiographic X-ray testing, as shown in ISO 10893-6 [8].
2 Normative references
The following documents are normatively referenced in this document and are
indispensable for its application. For dated references, only the version
corresponding to that date is applicable to this document; for undated references, the
latest version (including all amendments) is applicable to this document.
ISO 5576, Non-destructive testing - Industrial X-ray and gamma-ray radiology -
Vocabulary
ISO 9712, Non-destructive testing - Qualification and certification of NDT
personnel
ISO 11484, Steel products - Employer’s qualification system for non-destructive
testing (NDT) personnel
ISO 17636-2:2013, Non-destructive testing of welds - Radiographic testing - Part
2: X- and gamma-ray techniques with digital detectors
ISO 19232-1, Non-destructive testing - Image quality of radiographs - Part 1:
Determination of the image quality value using wire-type image quality indicators
ISO 19232-2, Non-destructive testing - Image quality of radiographs - Part 2:
Determination of the image quality value using step/hole-type image quality
indicators
ISO 19232-5, Non-destructive testing - Image quality of radiographs - Part 5:
Determination of the image unsharpness and basic spatial resolution value using
duplex wire-type image quality indicators
3 Terms and definitions
Terms and definitions determined by ISO 5576 and ISO 11484, as well as the
following, are applicable to this document.
3.1 Tube
Hollow elongated product, open at both ends, of any cross-sectional shape.
3.2 Welded tube
Tube (3.1) made by welding together adjacent edges of a flat rolled product. After
welding, it can be processed by cold working or hot working to obtain the final
dimensions.
3.3 Manufacturer
Organization that produces and manufactures products in accordance with relevant
standards and declares the conformity of the delivered products with all applicable
provisions of the standards.
3.4 Agreement
Contractual agreement between the manufacturer (3.3) and the purchaser at the time
of enquiry and order.
3.5 Signal-to-noise ratio
SNR
S/N
Ratio of the average value of the linearized grey values TO the standard deviation of
the linearized grey values (noise) in a given region in a digital image.
[Source: ISO 17636-2:2013, 3.10, modified: The symbol S/N is added.]
3.6 Spatial basic resolution of a digital detector
RbSdetector
The employer shall issue a testing (operation) authorization according to a written
procedure. The non-destructive testing (NDT) shall be authorized by a level 3 NDT
personnel approved by the employer.
Note: The definitions of levels 1, 2 and 3 personnel are shown in relevant standards
such as ISO 9712 and ISO 11484.
4.3 The tube under test shall be straight enough and shall be free of foreign matters,
so as to ensure the validity of the test. Surfaces of the weld seam and the adjacent
base material shall be free of foreign matters and surface irregularities, which may
interfere with the interpretation of the radiographic testing.
To gain an acceptable surface quality of the finished product, surface grinding is
permitted.
4.4 When the weld reinforcement is removed, markers (usually lead arrows) shall be
placed on both sides of the weld seam, so that the position of the weld seam can be
identified on the radiographic image; alternatively, an integrated automatic
positioning system can be used to identify the position of the weld seam.
4.5 Usually, the identification symbol, in the form of lead letters, shall be placed on
each part of the weld seam radiograph such that the lead letters are projected on the
radiographic image, so that the weld seam of each part can be clearly identified in
the radiographic image; alternatively, an integrated automatic positioning system can
be used to identify the position of the tube weld seam corresponding to each
radiographic image.
4.6 Marks shall be displayed on the radiographic images to provide accurate position
reference points for each radiographic image; alternatively, the automatic
measurement may be carried out on the digital image viewing screen by software to
achieve accurate positioning of the image.
4.7 When the size of the detector is smaller than the length of the penetrated weld
seam, the steel tube or the detector shall be moved in a step-by-step mode, and the
digital radiographic testing shall be performed when the steel tube is not moving.
Warning – Exposure of any part of the human body to X-rays can be highly
injurious to health. Wherever X-ray equipment is used, appropriate safety
measures shall be applied. National safety precautions shall be strictly applied.
5 Test equipment
The following digital imaging methods can be used instead of the radiographic film
testing:
a) Computed radiography (CR) using storage fluorescent material imaging plates
(such as EN 14784-1[21] or GB/T 21355[1], EN 14784-2[22] or GB/T 26642[2]);
b) Radiology using digital detector arrays (such as ASTM E2597-07[14] or GB/T
38240[4], ASTM E2698[15] or GB/T 35388[3]);
c) Digital radiographic testing method using image integration (such as EN
13068-1[18] or GB/T 23909.1[5], EN 13068-2[19] or GB/T 23909.2[6], EN
13068-3[20] or GB/T 23909.3[7]).
6 Test method
6.1 The digital radiographic testing technique specified in a) ~ c) of Chapter 5 shall
be used to inspect the weld seam.
6.2 According to the provisions of ISO 17636-2, the image quality classes shall be
divided into A and B:
a) Class A: basic technique;
b) Class B: enhanced technique.
Note: Class A imaging technique is used in most cases. Class B imaging technique is
used when enhanced sensitivity is required to visualize all imperfections
being detected.
The required image quality class should be specified in the relevant product
standard.
6.3 The digital-to-image display shall meet the technical requirements of Class A or
Class B.
6.4 During the testing, the beam of radiation shall be aimed at the center of the part
of the weld seam under test and shall be perpendicular to the steel tube surface at this
point.
6.5 Under the condition that the requirements of 6.9 and Chapter 7 are met, the
diagnostic length shall be determined according to the following requirements:
When the class B image quality is used, the penetrated thickness ratio at the end of
the effective diagnostic length of the radiographic image shall not exceed 1.1; when
the class A image quality is used, the penetrated thickness ratio at the end of the
effective diagnostic length of the radiographic image shall not exceed 1.2.
6.6 The single-wall penetration technique shall be used. When the single-wall
technique is not applicable due to the special size, the double-wall penetration
technique can be adopted by negotiation under the condition that the required
sensitivity is satisfied.
When using the detector-side image quality indicator for subsequent image
acquisition, the previous exposure parameter settings (including X-ray source,
detector and geometric arrangement) shall not be changed. For stable system and
process settings (such as automated testing systems using DDAs), it is sufficient to
verify the image quality once per shift as long as the steel pipe size, material and
inspection parameters remain unchanged. In this case, only the source-side image
quality indicator should be used to test the image quality.
The image unsharpness uim shall be measured using a duplex wire-type image
quality indicator conforming to ISO 19232-5.
The unsharpness is measured by the image of the duplex wire-type image quality
indicator in the digital radiation; the unsharpness value is the smallest wire pair
number (maximum wire diameter) when the modulation degree is less than 20%.
The duplex wire-type image quality indicator should be placed on the base metal at
about 5° to the pixel direction of the weld image, to avoid image aliasing.
7.2 The spatial basic resolution of a digital detector, RbSdetector, which is determined
by manufacturing parameters and hardware parameters, shall be measured by a
duplex wire-type image quality indicator placed in front of the detector; the RbSdetector
shall be calculated according to Formula (3).
Compensation principle:
Where the image quality indicators in Table 1 or Table 2 (wire type, hole type, and
duplex wire type) are used, if the detector system still does not meet the required IQI
sensitivity, the sensitivity of single wire image quality indicator can be increased to
compensate too high unsharpness values. The maximum limit of this compensation
shall be level 3.
Example: For class B image quality, 10 mm wall thickness, wire W14 and duplex
D11 are required. If D11 cannot be reached, compensation may be required: two
steps down from D11 to D9, but two steps up from W14 to W16.
For a given penetration distance and tube voltage, the image contrast sensitivity of
digital detectors depends on the penetration time and the tube current (mA), so, the
increase of exposure time and tube current (mA) can increase the sensitivity of the
single wire image quality indicator.
7.3 Two image quality classes are defined in Tables 1 and 2. For class A, the
minimum normalized signal-to-noise ratio (S/Nnorm) of the base metal should be
greater than 70. For class B, the minimum normalized signal-to-noise ratio (S/Nnorm)
of the base metal should be greater than 100. The normalized signal-to-noise ratio
9 Classification of indications
9.1 All indications found on radiographic image shall be classified as weld
imperfections or defects as defined in 9.2 and 9.3.
9.2 Imperfections refer to discontinuities of welds detected by the radiographic
testing method specified in this document, the size and/or distribution density of
which are within the specified acceptance limits, and have no practical impact on the
intended use of the steel tube.
9.3 Defects are imperfections whose size and/or distribution density exceeds the
specified acceptance limits. Defects may adversely affect or limit the intended use of
the steel tube.
10 Acceptance limits
10.1 Unless alternative requirements are specified in the product standards, the
acceptance limits specified in 10.2 ~ 10.6 are applicable to radiographic testing of
the weld seam.
10.2 Where cracks, incomplete penetration and lack of fusion are found in the
detection, the results shall be unqualified.
10.3 Individual circular slag inclusions and gas holes with a diameter not exceeding
3.0 mm or T/3 (whichever is the smaller, T is the nominal wall thickness of the steel
tube) found during the testing are acceptable.
Within any 150 mm or 12T (whichever is the smaller) weld length range, when the
spacing between individual inclusions is less than 4T, the maximum cumulative
diameter of all the above allowable individual imperfections shall not exceed 6.0 mm
or 0.5T (whichever is the smaller).
10.4 Individual elongated slag inclusions, with a length not exceeding 12.0 mm or T
(whichever is the smaller) or a width not exceeding 1.5 mm, found during the testing,
are acceptable.
Within any 150 mm or 12T (whichever is the smaller) weld length range, when the
spacing between individual inclusions is less than 4T, the maximum cumulative
length of all the above allowable individual imperfections shall not exceed 12.0 mm.
Note: For the limits specified in 10.3 and 10.4, refer to the figures in Appendix A.
10.5 Individual undercuts of any length, of which the maximum depth does not
exceed 0.4 mm and the minimum wall thickness meets the requirements, are
acceptable.
Individual undercuts within any 300 mm weld length, having a maximum length of
T/2 and a maximum depth of 0.5 mm, and not exceeding 10% of the nominal wall
thickness, are acceptable, provided that the number does not exceed two, and they
are ground.
10.6 Undercuts of any length and depth, which are coincident on the inside and
outside welds in the longitudinal direction, are acceptable.
11 Acceptance
11.1 Any tube not showing indications exceeding the corresponding acceptance
limits shall be deemed to have passed this radiographic testing.
11.2 Any tube showing indications exceeding the corresponding acceptance limits
shall be deemed suspect.
11.3 Suspect tubes shall be subjected to one or more of the following measures, and
shall meet the requirements of the product standard:
a) Grind the suspect area. Use magnetic particle or liquid penetrant to verify
whether the defect is completely removed; re-examine the ground area by
radiography. Adopt an appropriate method to measure the remaining wall
thickness, to verify compliance with the specified deviations.
b) Repair the suspect area by an approved welding procedure. Then, perform a
radiographic testing of the repaired area in accordance with the requirements
of this document and the corresponding product standard.
c) Cut the suspect area. Measure the remaining length of the tube, to verify
conformity with the specified length.
d) Reject the suspect tube.
12 Image storage and display
The original images delivered by the detector system shall be stored in full
resolution. Before storing the raw image, only the detectors related to image
processing shall be calibrated [e.g., offset calibration, gain calibration for detector
equalization and bad pixel calibration for detector images that provide no human
intervention (see ASTM E2597-07[14])]
The following minimum requirements shall be met when evaluating images:
a) minimum brightness of 250 cd/m2;
b) display of minimum 256 shades of grey;
......
| Standard ID | GB/T 40385-2021 (GB/T40385-2021) | | Description (Translated English) | Non-destructive testing of steel tubes -- Digital radiographic testing of the weld seam of welded steel tubes for the detection of imperfections | | Sector / Industry | National Standard (Recommended) | | Classification of Chinese Standard | H26 | | Classification of International Standard | 77.040.20 | | Word Count Estimation | 18,184 | | Date of Issue | 2021-08-20 | | Date of Implementation | 2022-03-01 | | Drafting Organization | Baoji Petroleum Steel Pipe Co., Ltd. (National Petroleum and Natural Gas Pipe Engineering Technology Research Center), Zhangjiagang Shagang Jinzhou Pipeline Co., Ltd., Pabo Testing Technology Service Co., Ltd., Metallurgical Industry Information Standards Research Institute, Zhejiang Jinzhou Pipeline Industry Co., Ltd. | | Administrative Organization | National Steel Standardization Technical Committee (SAC/TC 183) | | Proposing organization | China Iron and Steel Association | | Issuing agency(ies) | State Administration for Market Regulation, National Standardization Administration |
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