PSI - Issue 59

Myroslava Hredil et al. / Procedia Structural Integrity 59 (2024) 151–157 Myroslava Hredil, Oleksandr Tsyrulnyk, Ivan Shtoyko, Olha Zvirko / Structural Integrity Procedia (2024)

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A solution simulating water condensate inside the pipe has been used as an electrolyte. Its chemical composition in g/l is as follows: 14.44 Na + ; 0.129 K + ; 0.0025 Li + ; 0.052 NH 4 + ; 0.60 Ca 2+ ; 0.518 Mg 2+ ; 0.14 Ba 2+ ; 0.389 Sr 2+ ; 0.0003 Fe 2+ ; 0.0005 Mn 2+ ; 0.001 Al 3+ ; 25.40 Cl – ; 0.0036 F – ; 0.1 Br – ; 0.0021 I – ; 0.522 HCO 3 – ; 0.005 NO 3 – ; 0.005 SO 4 2 – ; 0.018 SiO 3 2 – ; 0.005 PO 4 3 – . To investigate the effect of molecular hydrogen on the intensity of electrochemical processes on pipe steels under the action of a model environment simulating condensate at the pipe's inner surface, a suitable laboratory method has been developed. It is introduced by Zvirko et al. (2023) and based on the measurement of electrochemical parameters of steel under conditions of gaseous hydrogen bubbling and it simulates operational conditions when hydrogen saturates a layer of condensate inside the pipe. An experimental setup is illustrated in Figure 1. An electrochemical response from the working electrode 1 (steel specimen) was measured using the potentiostat BioLogic SP-300 ( 5 ). Hydrogen bubbles were generated by water electrolysis according to the equation 2Н 2 О + 2е – = Н 2 + 2ОН – (1) at the platinum electrode 2’ located just under the spec imen using the power supply HPS305DF ( 6 ). The tested surface of the steel specimen was oriented vertically, so it was surrounded by the rising gas bubbles. A conjugated process of oxygen generation on the other electrode, connected to the power supply, was suppressed due to using a platinum anode with a ten times bigger surface area.

Fig. 1. Experimental setup: 1 – working electrode; 2 – counting electrode (Pt); 2' – cathode (Pt); 3 – reference electrode (Ag|AgCl); 4 – anode (Pt); 5 – potentiostat; 6 – power supply; 7 – magnetic stirrer; 8 – corrosive environment.

The main electrochemical parameter controlled was polarization resistance, obtained by the linear polarization resistance method. Polarization resistance of the working electrode was measured in the stationary environment, then under conditions of hydrogen bubbling, and also after the interruption of electrolysis to evaluate possible aftereffects of hydrogen on the corrosion activity of the steel (Sequence I, Figure 2).

Fig. 2. Experiment sequences: I – without mechanical stirring of electrolyte; II – involving a magnetic stirrer.