PSI - Issue 82

Valentyn Uchanin et al. / Procedia Structural Integrity 82 (2026) 288–294 Valentyn Uchanin et al. / Structural Integrity Procedia 00 (2026) 000–000

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1. Introduction Ferromagnetic structural steels (FSS) are widely applied in many long-term exploited structures, such as pipelines, rails, or bridges. That is why the development of new non-destructive testing (NDT) methods capable of ensuring their efficiency and safety is very important (Becker et al., 1997; Dobmann et al., 1997; Rummel, 2014). Electromagnetic NDT techniques based on the determination of magnetic hysteresis loop (MHL) parameters (coercive force (CF), remanence, etc.) allow the estimation of the structural integrity and stress state of FSS in many applications (Gilanyi et al., 1998; Gowindaraiu et al., 1997; Jiles, 2016; Kumar et al., 2010; Kwun, 1987; Uchanin and Ostash, 2019; Uchanin et al., 2020). It is known, that a MHL graphically represents the relationship between the magnetic field strength ( H ) and the magnetic flux density ( B ) of a FSS when the magnetic field is cyclically applied up to the point of magnetic saturation ( Н S , B S ), decreased back to zero, reversed to point (– Н S , – B S ), and go back to the starting point 0 (Fig. 1a). All MHL parameters are structure-sensitive and can be applied for structural health monitoring. For a long time, only the CF ( H c ) has been widely used for the evaluation of FSS (Gowindaraiu et al., 1997). Other MHL parameters did not receive wide application in NDT practice. The CF H c can be defined as the resistance of an FSS to changes in magnetization, and can be estimated as the magnetic field strength necessary to demagnetize the FSS preliminarily magnetized to the saturation state. Some knowledge about the factors that influenced the CF is known. In the FSS component subjected to cold working, the MHL form will be changed as it is sketched in Fig. 1b, and the CF H c will be increased. Any imperfections in FSS, such as dislocations or alloying elements, increase the energy loss required for the magnetization process and alter the corresponding MHL parameters (Jiles, 2016; Uchanin et al., 2020).

Fig. 1. (a) Typical MHL with related magnetic parameters, and (b) changes in the hysteresis loop for steel subjected to cold working or influenced by non-magnetic additions, shown for soft (1) and hardened (2) steels.

The tempering behavior of modified 9Cr–1Mo steel was studied using NDT methods in Kumar et al. (2010). The main conclusions were as follows: the magnetic parameters are in good agreement with the mechanical parameters. The application of magnetic methods for NDT of accumulated fatigue damage in FSS components in the nuclear industry is presented in Gilanyi et al. (1998). It was shown that MHL is changed with fatigue damage, and these changes correlated with microstructural alterations like dislocation density. In our study, a magnetic technique based on CF measurements was applied to evaluate the characteristics of degraded FSS in steam pipelines during long-term operation (Uchanin and Ostash, 2019; Uchanin et al., 2020). The fundamental difference of this study was related to the correlations between the CF and fatigue crack growth resistance characteristics. Another application focused on the distribution of stress along a ship’s load-bearing component under operational loading (Uchanin and Ostash, 2019). It was shown that the points of the maximum CF are related to stress concentration, and these points were applied for monitoring during service life. In recent years, increasing attention has been paid to the hydrogen influence on the mechanical behavior and fracture resistance of structural elements in hydrogen energy systems (Laureys et al., 2022). Hydrogen interacts with metals almost at all stages of production and operation (Barrera et al., 2018), emphasizing the need for NDT methods to assess material hydrogenation (Xie and Tian, 2018). The hydrogen concentration is a key factor determining structural