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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integrity (Dmytrakh et al., 2018, 2024). Existing laboratory techniques (Hanneken, 1999) are limited by specimen extraction and specialized equipment. Hydrogen uptake during production or service causes such degradation processes as hydrogen-induced cracking, embrittlement, fatigue strength reduction, and blistering (Dong et al., 2022). These phenomena significantly decrease the durability and reliability of pipeline systems (Bellahcene et al., 2012; Dmytrakh et al., 2022), especially under high pressure, temperature variations, and cyclic loading. During operation, the stress state of main pipelines (MP) made of FSS changes as a result of the action of abnormal force mechanical factors, such as soil movement of various origins (e.g., subsidence of soil in areas of crossings over transport highways), uneven clamping of the pipeline in different areas. So, NDT can be essential to prevent possible breakdowns. In principle, MHL parameters are also sensitive to changes in mechanical stress (Garikepati et al., 1988; Vourna, 2018). An equation derived from an early theoretical study by Garikepati et al. (1988) predicts a simple relationship between the applied stress and the bulk magnetic properties of steel. It was noted that the most useful application of the results would probably be in NDT of stresses in FSS. A method and instruments for determining residual stress in FSS, based on the measurement of magnetic differential permeability, were proposed by Vourna (2018). However, it was shown that these parameters also depend on the structural state of the FSS. In this case, the influence of the structural state and stress is difficult to distinguish. Methods based on magnetic anisotropy (MA) probes and the application of an alternating electromagnetic field can also be used for non-contact determination of operational and residual stresses in the surface layers of FSS, as reported by Abuku (1977), Kim et al. (2016), Langman and Mutton (1993), Yamada et al. (1985), and Yamada et al. (1989). This method is based on the Villari effect. It was shown that the parameters of MA have good sensitivity to stress and are invariant with respect to the structural state of inspected FSS (Uchanin et al., 2018). The EC technique based on MA evaluation has many advantages due to the possibility of measuring stresses through dielectric coatings, high productivity, and mobility. The first section of this review paper presents pioneering results on the hydrogen concentration effect on MHL parameters measured using the NDT technique with an attachable magnetic transducer. In the next sections, two applications of the MA method and related methodologies for stress determination are considered. 2. Results and discussion 2.1. Determination of hydrogen concentration by magnetic hysteresis loop parameters evaluation in ferrous steel Hydrogen influences the strength and service life of carbon steels by interacting with defects of various scales (Barrera et al., 2018; Dmytrakh et al., 2018, 2024; Dong, 2022), which are inherent to this material class. Even short term exposure to diffusible hydrogen causes irreversible structural changes and increases defect density. Therefore, hydrogen-charged steel exhibits physical and mechanical properties different from those of non-charged material. Prismatic specimens (10×20×75 mm) of ferrite-pearlite carbon steel with nominal composition 0.17–0.24 C, 0.17– 0.37 Si, 0.35–0.65 Mn, <0.04 S, balance Fe, were tested. Hydrogen charging was carried out electrochemically in an NS4 aqueous solution (Bellahcene et al., 2012) simulating neutral soil groundwater (pH 6.7) under galvanostatic conditions using a modified VoltaLab40 system. The hydrogen concentration was determined with a LECO DH603 analyzer. The KRM-C-MA magnetic analyzer with an attachable transducer (Uchanin and Ostash, 2019) was used to measure local MHL parameters in large FSS components (Fig. 2). The system consists of a U-shaped magnetization core that forms a closed magnetic circuit, magnetizing only a small surface area of the tested part. At low hydrogen concentrations ( C H ≤ 0.4 ppm), parameter scatter prevents reliable correlation. However, in the range of 0.4–8.5 ppm, distinct dependencies between hydrogen concentration and both CF ( H c ) and remanence ( B r ) were obtained (Fig. 3). The CF shows the highest response to hydrogen concentration, correlating with hardness, strength, toughness, and elastic modulus, as well as with microstructural features such as grain size and porosity. Remanence also exhibits high sensitivity, confirming its suitability for detecting hydrogen-induced microstructural changes. Thus, MHL characteristics – particularly CF and remanence – are effective indicators for NDT-based assessment of hydrogen concentration in carbon steels (Dmytrakh et al., 2025). These parameters enable indirect quantitative evaluation of hydrogen-related degradation and the detection of related FSS damage even through dielectric coatings.