GB/T 43658.1-2024 Non-destructive testing - Radiographic inspection of corrosion and deposits in pipes by X and gamma rays - Part 1: Tangential radiographic inspection
1 Scope
This document specifies fundamental techniques of film and digital radiography with the object of enabling satisfactory and repeatable results to be obtained economically. The techniques are based on generally recognized practice and fundamental theory of the subject.
This document applies to the radiographic examination of steel pipes for service induced flaws such as corrosion pitting, generalized corrosion and erosion. Besides its conventional meaning, “pipe” as used in this document is understood to cover other cylindrical bodies such as tubes, penstocks, boiler drums and pressure vessels.
Weld inspection for typical welding process induced flaws is not covered, but weld inspection is included for corrosion/erosion type flaws.
The pipes can be insulated or not, and can be assessed where loss of material due, for example, to corrosion or erosion is suspected either internally or externally.
This document covers the tangential inspection technique for detection and through-wall sizing of wall loss, including with the source:
a) on the pipe centre line; and
b) offset from pipe centre line by the pipe radius.
ISO 20769-2 covers double wall radiography, and note that the double wall double image technique is often combined with tangential radiography with the source on the pipe centre line.
This document applies to tangential radiographic inspection using industrial radiographic film techniques, computed radiography (CR) and digital detector arrays (DDA).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements 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.
ISO 9712 Non-destructive testing - Qualification and certification of NDT personnel
Note: GB/T 9445-2015, Non-destructive testing - Qualification and certification of NDT personnel (ISO 9712:2012, IDT)
ISO 11699-1 Non-destructive testing - Industrial radiographic film - Part 1: Classification of film systems for industrial radiography
Note: GB/T 19348.1-2014, Non-destructive testing - Industrial radiographic film - Part 1: Classification of film systems for industrial radiography (ISO 11699-1:2008, MOD)
ISO 11699-2 Non-destructive testing - Industrial radiographic films - Part 2: Control of film processing by means of reference values
Note: GB/T 19348.2-2003, Non-destructive testing - Industrial radiographic films - Part 2: Control of film processing by means of reference values (ISO 11699-2:1998, IDT)
ISO 16371-1 Non-destructive testing - Industrial computed radiography with storage phosphor imaging plates - Part 1: Classification of systems
Note: GB/T 21355-2022, Non-destructive testing – Industrial computed radiography with storage phosphor imaging plates – Classification of systems (ISO 16371-1:2011, IDT)
ISO 19232-5 Non-destructive testing - Image quality of radiographs - Part 5: Determination of the image unsharpness value using duplex wire-type image quality indicators
Note: GB/T 23901.5-2019, Non-destructive testing - Image quality of radiographs - Part 5:Determination of the image quality unsharpness and basic spatial resolution value using duplex wire-type image quality indicators (ISO 19232-5:2018, IDT)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
actual wall thickness
tact
real thickness of the pipe wall which can differ from the nominal thickness
3.2
axial coverage
Ld
total axial extent of the evaluated section of the pipe radiograph measured on the detector (3.8)
3.3
axial coverage
Lp
total axial extent of the evaluated section of the pipe radiograph measured along the central axis of the pipe
3.4
basic spatial resolution
SRbdetector
smallest geometrical detail, which can be resolved in a digital image at a magnification equal to 1; corresponds to half of the measured image unsharpness in a digital image; corresponds to the effective pixel size (3.18) of the magnified image; and is determined from the smallest number of the duplex wire pair, which is not separable by visual inspection or from the smallest number of the duplex wire pair with less than 20 % modulation depth in a linearized profile
Note 1: For this measurement, the duplex wire IQI is placed directly on the digital detector (3.8) array or imaging plate.
Note 2: The measurements of SRbdetector and unsharpness are described in ISO 19232-5 And ASTM E2002.
3.5
basic spatial resolution
SRbimage
smallest geometrical detail, which can be resolved in a digital image at a magnification >1; corresponds to half of the measured image unsharpness in a digital image; corresponds to the effective pixel size (3.18) of the magnified image; and is determined from the smallest number of the duplex wire pair, which is not separable by visual inspection or from the smallest number of the duplex wire pair with less than 20 % modulation depth in a linearized profile
Note: The measurements of SRbimage and unsharpness are described in ISO 19232-5 And ASTM E2002.
3.6
comparator
C
reference object of defined dimension c and material for dimensional calibration of a radiographic image
3.7
computed radiography
CR
complete system comprising a storage phosphor imaging plate (IP) (3.23) and a corresponding read-out unit (scanner or reader), which converts the information from the IP into a digital image and the control software of the read-out unit
3.8
detector
D
detection device, consisting of a NDT film system (see ISO 11699-1) or a digital radiography system using a CR system or a DDA system
Note: Film systems and IPs can be used as flexible and curved detectors or in planar cassettes.
3.9
digital detector array
DDA
electronic device converting ionizing or penetrating radiation into a discrete array of analogue signals which are subsequently digitized and transferred to a computer for display as a digital image corresponding to the radiologic energy pattern imparted upon the input region of the device and the control software
3.10
imaged comparator dimension
c′
dimension of the comparator (3.6) measured on the detector (3.8)
3.11
imaged outside diameter
De′
nominal outside diameter of the pipe measured on the detector
3.12
maximum penetrated thickness
wmax
maximum thickness of material for a pipe which occurs for a tangent to the inner pipe surface
3.13
measured wall thickness
tmeas
thickness of the pipe wall as measured on the radiograph or digital image
3.14
nominal wall thickness
t
thickness of the pipe wall as given by the manufacturer, neglecting the manufacturing tolerances
3.15
normalized signal-to-noise ratio
SNRN
ratio of signal-to-noise, normalized by the basic spatial resolution, SRbimage, (3.5) as measured directly in the digital image and/or calculated from the measured SNRmeasured, by:
