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Fig. 3. The model for structural integrity analysis of boiler tubes exposed to hydrogen damage and hydrogen embrittlement: Zone | - "Safety" (KCVtor. (measurea) > KCVror. «); Zone 2 - "Critical" (KCVrtor. «) > KCVror. (easureay > KCVror. (critica) and Zone 3 - KCV ror, (Measured) < KCV ror. Critica and/or KCVp < KCVj. Two characteristic values of hydrogen concentration in a metal are Cy « and Cu iitican. Variation of the impact strength (KCVror.) and its crack propagation component (KCVp) and crack initiation component (KCV;) of Charpy specimens (S1-S6), as a function of the specimens mean hardness (hydrogen concentration, Cy).

Figure 3 The model for structural integrity analysis of boiler tubes exposed to hydrogen damage and hydrogen embrittlement: Zone | - "Safety" (KCVtor. (measurea) > KCVror. «); Zone 2 - "Critical" (KCVrtor. «) > KCVror. (easureay > KCVror. (critica) and Zone 3 - KCV ror, (Measured) < KCV ror. Critica and/or KCVp < KCVj. Two characteristic values of hydrogen concentration in a metal are Cy « and Cu iitican. Variation of the impact strength (KCVror.) and its crack propagation component (KCVp) and crack initiation component (KCV;) of Charpy specimens (S1-S6), as a function of the specimens mean hardness (hydrogen concentration, Cy).

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Fig. 1. Concept of a structural integrity model for prediction of hydrogen embrittlement and damage in steels: (1) Industrial component — TPP boiler tube; (2) Hydrogen damage of boiler evaporator tube unevenly saturated with hydrogen during exploitation; (3) Application of a structural integrity model - correlation between material macro-mechanical behaviour and simultaneously active HE micro-mechanisms (HELP+HEDE); (4) Assessment of hydrogen critical concentrations and (5) Predictive maintenance activities. ig. 1. Concept of a structural integrity model for prediction of hydrogen embrittlement and damage in steels: (1) Industrial component — T enhanced plasticity mediated mechanism (Robertson et al., 2015) can not only promote ductile behaviour and microvoid coalescence (MVC) modes of fracture in steels (Birnbaum and Sofronis, 1994), but also influence quasi- cleavage (QC) fracture (Martin at all., 2011) and the fracture pathway found on hydrogen-induced fracture surfaces from macroscopically brittle transgranular (TG) to intergranular (IG) failure mechanism (Wang et al., 2014). Recent molecular dynamics simulations of crack propagation in iron show that the various well-known HE phenomena can occur in the same material (Matsumoto et al., 2014), including HEDE and HELP, hydrogen-enhanced strain-induced vacancy model (HESIV) (Takai et al., 2008), adsorption-induced dislocation emission (AIDE) (Lynch, 2012) and the so-called defactant concept (Barnoush and Vehoff, 2010), depending on the boundary and the initial conditions. Recently, based on the special approach applied in subsequent post-mortem investigations of samples unevenly enriched with hydrogen and damaged during actual operation of industrial component, the simultaneous action of the HELP and the HEDE mechanisms were detected and confirmed to be active (HELP+HEDE), depending on the local concentration of hydrogen in the investigated low carbon steel (Djukic et al., 2015; Djukic et al., 2016). 1 1 % r m1 1 1
Fig. 1. Concept of a structural integrity model for prediction of hydrogen embrittlement and damage in steels: (1) Industrial component — TPP boiler tube; (2) Hydrogen damage of boiler evaporator tube unevenly saturated with hydrogen during exploitation; (3) Application of a structural integrity model - correlation between material macro-mechanical behaviour and simultaneously active HE micro-mechanisms (HELP+HEDE); (4) Assessment of hydrogen critical concentrations and (5) Predictive maintenance activities. ig. 1. Concept of a structural integrity model for prediction of hydrogen embrittlement and damage in steels: (1) Industrial component — T enhanced plasticity mediated mechanism (Robertson et al., 2015) can not only promote ductile behaviour and microvoid coalescence (MVC) modes of fracture in steels (Birnbaum and Sofronis, 1994), but also influence quasi- cleavage (QC) fracture (Martin at all., 2011) and the fracture pathway found on hydrogen-induced fracture surfaces from macroscopically brittle transgranular (TG) to intergranular (IG) failure mechanism (Wang et al., 2014). Recent molecular dynamics simulations of crack propagation in iron show that the various well-known HE phenomena can occur in the same material (Matsumoto et al., 2014), including HEDE and HELP, hydrogen-enhanced strain-induced vacancy model (HESIV) (Takai et al., 2008), adsorption-induced dislocation emission (AIDE) (Lynch, 2012) and the so-called defactant concept (Barnoush and Vehoff, 2010), depending on the boundary and the initial conditions. Recently, based on the special approach applied in subsequent post-mortem investigations of samples unevenly enriched with hydrogen and damaged during actual operation of industrial component, the simultaneous action of the HELP and the HEDE mechanisms were detected and confirmed to be active (HELP+HEDE), depending on the local concentration of hydrogen in the investigated low carbon steel (Djukic et al., 2015; Djukic et al., 2016). 1 1 % r m1 1 1
Table 1. Chemical composition of St.20 steel (wt.%) 4. Experimental concept and procedure
Table 1. Chemical composition of St.20 steel (wt.%) 4. Experimental concept and procedure
" Fig. 2. (a) Position of Charpy specimens and hardness measurements in the in the vicinity of the "window" type hydrogen damage; (b-e) SEM fractographs of the fracture surfaces of a particular Charpy specimen (S2-S5); (f) Mean hardness of the Charpy specimens.
" Fig. 2. (a) Position of Charpy specimens and hardness measurements in the in the vicinity of the "window" type hydrogen damage; (b-e) SEM fractographs of the fracture surfaces of a particular Charpy specimen (S2-S5); (f) Mean hardness of the Charpy specimens.
"Moderate drop; Sharp drop; ‘Sharp rise; ‘Predominate Table 2. Summary of active hydrogen embrittlement mechanisms and their effects on the decline in macro mechanical properties (hardness and impact strength) and ductile to brittle failure transition (DBT) in St.20 steel 5.1. A structural integrity model for prediction of hydrogen embrittlement and damage in steels
"Moderate drop; Sharp drop; ‘Sharp rise; ‘Predominate Table 2. Summary of active hydrogen embrittlement mechanisms and their effects on the decline in macro mechanical properties (hardness and impact strength) and ductile to brittle failure transition (DBT) in St.20 steel 5.1. A structural integrity model for prediction of hydrogen embrittlement and damage in steels
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Mechanical EngineeringMaterials ScienceCorrosion ScienceMechanical Behavior Of MaterialsFracture MechanicsMetallurgy and Materials EngineeringMechanical Behaviour of MaterialsFailure AnalysisMetallurgical and Materials EngineeringMechanical Testing of Materials
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