GB/T 44845-2024 Low frequency electromagnetic testing method for pressure equipment
1 Scope
This document specifies the requirements of testing instruments, testing procedures and results evaluation methods for low frequency electromagnetic testing of pressure equipment.
This document is applicable to low frequency electromagnetic testing of surface and buried defects of pressure equipment made of conductive metal materials with wall thickness of 2mm to 20mm. During testing, the maximum lift-off height including coating thickness shall not be greater than 3 mm.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this standard. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.
GB/T5616 Non-destructive testing - Guidelines for application
GB/T12604.6 Non-destructive testing - Terminology - Terms used in eddy current testing
NB/T 47013 (All parts) Nondestructive testing of pressure equipments
3 Terms and definitions
For the purposes of this document, the terms and definitions given in NB/T47013.1 and GB/T12604.6 and the following apply.
3.1
low frequency electromagnetic excitation frequency
nominal frequency of low-frequency electromagnetic field excitation current
3.2
low frequency electromagnetic field
coupling field of eddy current and leakage magnetic field generated on the surface and inside of the tested object by using low-frequency AC current with an excitation frequency generally not higher than 300 Hz for excitation
3.3
defect equivalent
defect sizing given based on the obtained signal characteristics
3.4
orthogonal scan
scanning whose scanning directions are perpendicular to each other
4 Method summary
4.1 The basic principle of low frequency electromagnetic testing method is shown in Figure 1. The coil with low-frequency AC current excites low frequency electromagnetic fields on the surface and inside of the object being tested. The low frequency electromagnetic fields will be distorted at the defect location. By picking up the signal changes of the low frequency electromagnetic field through the testing element and analyzing and processing the signal, the testing of defects on the surface, near surface, and buried of the tested object can be achieved.
Key:
1——Magnetic core;
2——Testing element;
3——Excitation coil;
4——Tested object.
Figure 1 Schematic diagram of low frequency electromagnetic testing
4.2 For ferromagnetic materials, the low frequency electromagnetic excitation frequency is generally not greater than 30 Hz. For non-ferromagnetic materials, the low frequency electromagnetic excitation frequency is generally not greater than 300 Hz.
4.3 The magnetic core is mainly used to restrict the outward diffusion of the leakage magnetic field and improve the magnetic concentration ability.
4.4 According to different tested objects, the testing elements can be coils, Hall elements, etc.
Contents
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Method summary
5 Personnel qualification
6 Low frequency electromagnetic testing instrument
7 Low frequency electromagnetic testing procedure
8 Evaluation and processing of test results
9 Testing records and report
Annex A (Informative) Example of test area division and numbering
Annex B (Informative) Test records and reports
