GB/T 43658.2-2024 Non-destructive testing - Radiographic inspection of corrosion and deposits in pipes by X and gamma rays - Part 2: Double wall radiographic inspection
1 Scope
This document specifies fundamental techniques of film and digital radiography with the object ofenabling satisfactory and repeatable results to be obtained economically. The techniques are based ongenerally recognized practice and fundamental theory of the subject.
This document applies to the radiographic examination of pipes in metallic materials 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 double wall inspection techniques for detection of wall loss, including double wall single image (DWSI) and double wall double image (DWDI).
Note: That the DWDI technique described in this document is often combined with the tangential technique covered in ISO 20769-1.
This document applies to in-service double wall radiographic inspection using industrial radiographic film techniques, computed digital 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 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 systems1)
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 17636-2 Non-destructive testing of welds - Radiographic testing - Part 2: X- and gamma-ray techniques with digital detectors
Note: GB/T 3323.2-2019, Non-destructive testing of welds - Radiographic testing - Part 2: X- and gamma-ray techniques with digital detectors (ISO 17636-2:2013, MOD)
ISO 19232-1 Non-destructive testing - Image quality of radiographs - Part 1: Determination of the image quality value using wire-type image quality indicators
Note: GB/T 23901.1-2019, Non-destructive testing - Image quality of radiographs - Part 1: Determination of the image quality value using wire-type image quality indicators (ISO 19232-1:2013, 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 unsharpness and basic spatial resolution value using duplex wire-type image quality indicators (ISO 19232-5:2018, IDT)
ISO 20769-1 Non-destructive testing of welds - Radiographic inspection of corrosion and deposits in pipes by X and gamma rays - Part 1: Tangential radiographic inspection
Note: 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 (ISO 20769-1:2018, IDT)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20769-1 and the following apply.
3.1
digital detector array system
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
3.2
Double wall double image technique
DWDI
technique where the radiation source is located outside and away from the pipe, with the detector on the opposite side of the pipe and where the radiograph shows details from both the pipe walls on the detector and source sides of the pipe
Note: See Figure 3.
3.3
double wall single image technique
DWSI
technique where the radiation source is located outside the pipe and close to the pipe wall, with the detector on the opposite side of the pipe and where the radiograph shows only detail from the pipe wall on the detector side
Note: See Figure 1.
3.4
object-to-detector distance
b
distance between the radiation side of the test object and the detector surface measured along the central axis of the radiation beam
3.5
penetrated thickness
w
thickness of material in the direction of the radiation beam calculated on the basis of the nominal thickness
Note: For double wall radiographic inspection of a pipe, the minimum value for w is twice the pipe wall thickness. For multiple wall techniques (pipes in pipe or liners), the penetrated thickness is calculated from the nominal wall thicknesses t.
3.6
source-to-object distance
f
distance between the source of radiation and the source side of the test object measured along the central axis of the radiation beam
3.7
total effective penetrated thickness
wtot
total equivalent thickness of metallic material in the direction of the radiation beam calculated on the basis of the nominal thickness, with allowance for any liquid or other material present in the pipe and any insulation
4 Classification of radiographic techniques
The double wall radiographic techniques are divided into two classes:
——basic techniques DWA;
——improved techniques DWB.
The basic techniques are intended for double wall radiography of generalized and localized wall loss.
For the basic techniques, DWA, when using Ir 192 sources for pipes with penetrated thicknesses between 15 mm and 35 mm, the sensitivity for detection is high for imperfections, provided their diameters are greater than or equal to 2 mm and the material loss is typically greater than or equal to 5 % of the pipe penetrated thickness, in the absence of liquid or other products in the pipe. When using Se 75, the corresponding detection sensitivity is high for 2 mm diameter or larger imperfections with material loss greater than or equal to 4 % of the pipe penetrated thickness. The detection sensitivity is improved for flaws with larger diameters, whereas the presence of liquid or other products, and external insulation, can reduce the sensitivity for material loss depending on their properties. Different detection sensitivities may apply for penetrated thicknesses less than 15 mm and greater than 35 mm.
The presence of external corrosion product can reduce the techniques sensitivity to corrosion due to the increased radiation attenuation in the product, which can even exceed the reduced attenuation caused by the loss of steel. Build-up of internal solid material (e.g. scale) in pipes can similarly reduce sensitivity to internal degradation.
These techniques can also be used for detection of deposits inside the pipe.
The improved techniques should be used where higher sensitivity is required such as for radiography of fine, localized corrosion pitting.
Further improvements, beyond the improved techniques described herein, are possible and may be agreed between the contracting parties by specification of all appropriate test parameters.
The choice of radiographic technique shall be agreed between the concerned parties.
