Inspection of steam pipeline steel degradation by the coercimetric method

Speaker:
Uchanin, Valentyn; Karpenko Phisico-Mechanical Institute of National Academy of Sciences, Lviv; Ukraine

Authors:
Bezlyudko, G.; Special Scientific Engineering; Ukraine
Ostash, O.; Karpenko Phisico-Mechanical Institute of National Academy of Sciences; Ukraine
Uchanin, V.; Karpenko Phisico-Mechanical Institute of National Academy of Sciences; Ukraine

ID: ECNDT-0271-2018
Session: Materials Characterization - Magnetic Techniques 1
Room: J2
Date: 2018-06-14
Time: 14:30 - 14:50

The pipelines of power plants are operated under high pressure (up to 16 MPa) and elevated temperatures (up to 570º C). As a result of long-term operation the initial structural and phase state of materials are transformed with subsequent defects accumulation. These factors lead to changes in the mechanical characteristics of materials. To estimate these changes the information about the structural and stress-strain state of the material is needed. It is especially important for the areas of pipelines with high level of stress and strain concentration.
The objective of this study is to establish the regularities of changes in the coercive force for 12Kh1MF and 15Kh1M1F steels of the bends of steam pipelines after long-term operation depending on the phase composition and microdefects needed for development of the new methodology for prediction of the steam pipelines residual life.
The chemical and phase compositions, structural morphology, magnetic (coercive force) and mechanical properties of steel specimens cutout from the different areas of bends of steam pipelines after long-term operation (175–280·103h) were investigated. The possibility to evaluate the structural-mechanical states of the steels of steam pipelines after long-term operation by measuring their coercive force is shown. Coercive force was measured by KRM type device with an accuracy of ± 5 A/m. The device was preliminarily calibrated on standard specimens.
A methodology for estimation of the residual service life on the basis of the dependences of coercive force on the operating time and the number of startups and shutdowns of the steam pipelines was proposed. For this purpose the ultimate values of the coercive force of investigated steels, possible to be applied for prediction of the critical state of steam pipelines, were determined. It was shown that these ultimate values of the coercive force are close for static and cyclic loads and caused by the stress-strain state and the degree of the material microdamage.
Keywords: coercive force, thermal power plant, steam pipelines, heat-resistant steels, in-service degradation, mechanical characteristics, residual service life.