Dissolution Behaviors of Corrosion Products on 316LN Stainless Steel in Simulated Shutdown Acid-Reducing Water Chemistry

doi:10.1007/s40195-025-01932-z

Abstract

Abstract:

The dissolution behaviors of corrosion products on 316LN stainless steel (SS) in simulated shutdown acid-reducing water chemistry were investigated. The outer Fe- and Ni-rich corrosion products formed in borated and lithiated high-temperature water at 300 °C dissolved under the simulated shutdown acid-reducing water chemistry. NiFe₂O₄ began to dissolve at the initial stage of boration, but the dissolution of Fe₃O₄ mainly occurred at the low-temperature stage in shutdown acid-reducing phase. Low pH value and low-temperature conditions are conducive to the dissolution of the outer Fe-rich oxides. The potential-pH (E-pH) diagrams and solubility curves of spinel oxides at different temperatures were calculated. The possible dissolution mechanism of corrosion products was discussed.

Key words: 316LN stainless steel (SS), Acid-reducing water chemistry, Corrosion products, Potentiodynamic polarization, Thermodynamic diagrams

Yiran Xiong, Ziyu Zhang, Xinqiang Wu, Jibo Tan, Xiang Wang. Dissolution Behaviors of Corrosion Products on 316LN Stainless Steel in Simulated Shutdown Acid-Reducing Water Chemistry[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(12): 2289-2299.

Figures/Tables 13

Table 1 Compositions of 316LN SS investigated in the present work (wt%)

C	N	Cr	Ni	Mo	Mn	P	S	Si	Fe
0.015	0.12	16.92	12.92	2.08	1.37	0.018	< 0.003	0.35	Bal.

Table 2 Compositions of test solutions (ppm, by weight)

Test solutions	B (ppm)	Li (ppm)	T (°C)	pH_T
1	1500	2.3	300	6.83
2	3000	0	300	5.00
3	5000	0	300	4.84
4	3000	0	150	4.57

Fig. 1 SEM morphologies of the oxide films formed on 316LN SS after a pre-oxidized for 28 days in 1500 ppm B and 2.3 ppm Li solution at 300 °C, b pre-oxidized for 28 days and then exposed to 3000 ppm B solution at 150 °C for 14 days

Fig. 2 TEM observation and analysis of the oxide film formed on 316LN SS after pre-oxidized for 28 days. a Cross-sectional morphology of the oxide film, b element maps of Fe, Cr, Ni and O corresponding to a, c composition profile corresponding to the line shown in a, d, e HRTEM image and FFT image of the outer oxides in area 1, f, g HRTEM image and FFT image of the inner oxides in area 2

Fig. 3 TEM observation and element maps of the oxide film formed on 316LN SS after 28 days of pre-oxidation and then exposed to simulated shutdown acid-reducing water chemistry at 150 °C for 14 days. a Cross-sectional morphology of the oxide film, b element maps of Fe, Cr, Ni and O corresponding to a

Fig. 4 TEM observation and compositional analysis of the oxide film formed on 316LN SS after 28 days of pre-oxidation and then exposed to simulated shutdown acid-reducing water chemistry at 150 °C for 14 days. a Cross-sectional morphology of the oxide film containing undissolved outer oxide particle, b, c HRTEM image and FFT image of the outer oxides in area 1, d, e HRTEM image and FFT image of the inner oxides in area 2, f composition profile corresponding to the line shown in a, g EDS analysis of the dissolved outer oxide particle, h, i HRTEM image and FFT image of the dissolved outer oxide particle in g

Fig. 5 SEM morphologies of the oxide films formed on 316LN SS after 7 days of pre-oxidation and then exposed to borated and lithiated high-temperature water and different simulated shutdown acid-reducing water chemistry for 72 h. a 1500 ppm B and 2.3 ppm Li solution at 300 °C, b 3000 ppm B solution at 300 °C, c 5000 ppm B solution at 300 °C, d 3000 ppm B solution at 150 °C

Fig. 6 Potentiodynamic polarization curves of 316LN SS after 7 days of pre-oxidation and then exposed to borated and lithiated high-temperature water at 300 °C and different simulated shutdown acid-reducing water chemistry for 72 h

Table 3 Electrochemical parameters obtained from potentiodynamic polarization curves of samples in different water chemistry environments

Test solutions	OCP (V vs SHE)	E_corr (V vs SHE)	I_corr (μA cm⁻²)
1500 ppm B + 2.3 ppm Li, 300 °C	− 0.357 (± 0.010)	− 0.445 (± 0.007)	14.81 (± 0.364)
3000 ppm B, 300 °C	− 0.189 (± 0.022)	− 0.271 (± 0.016)	3.29 (± 1.004)
5000 ppm B, 300 °C	− 0.320 (± 0.018)	− 0.424 (± 0.012)	5.25 (± 0.244)
3000 ppm B, 150 °C	− 0.003 (± 0.002)	0.051 (± 0.008)	7.75 (± 1.072)

Fig. 7 E-pH diagrams of Fe-Cr-Ni-H2O system at 300 °C a and 150 °C b

Fig. 8 Solubility curves of NiFe2O4, Fe3O4, NiCr2O4 and FeCr2O4 at 300 °C a and 150 °C b

Table 4 Equilibrium equations used for the calculation of the solubilities of possible spinel oxides formed in high-temperature water in a wide pH value range

${\text{Fe}}_{3} {\text{O}}_{4}$
1	${\text{Fe}}_{3} {\text{O}}_{4} + 6{\text{H}}^{ + } + {\text{H}}_{2} = 3{\text{Fe}}^{2 + } + 4{\text{H}}_{2} {\text{O}}$
2	$2{\text{Fe}}_{3} {\text{O}}_{4} + 18{\text{H}}^{ + } = 6{\text{Fe}}^{3 + } + 8{\text{H}}_{2} {\text{O}} + {\text{H}}_{2}$
3	${\text{Fe}}_{3} {\text{O}}_{4} + 6{\text{CrO}}_{2}^{ - } + 6{\text{H}}^{ + } + {\text{H}}_{2} = 3{\text{FeCr}}_{2} {\text{O}}_{4} + 4{\text{H}}_{2} {\text{O}}$
4	${\text{Fe}}_{3} {\text{O}}_{4} + 2{\text{H}}_{2} {\text{O}} + {\text{H}}_{2} = 3{\text{HFeO}}_{2}^{ - } + 3{\text{H}}^{ + }$
${\text{NiFe}}_{2} {\text{O}}_{4}$
1	${\text{NiFe}}_{2} {\text{O}}_{4} + 2{\text{H}}^{ + } = {\text{Ni}}^{2 + } + {\text{Fe}}_{2} {\text{O}}_{3} + {\text{H}}_{2} {\text{O}}$
2	${\text{NiFe}}_{2} {\text{O}}_{4} + 6{\text{H}}^{ + } + {\text{H}}_{2} = {\text{Ni}}^{2 + } + 2{\text{Fe}}^{2 + } + 4{\text{H}}_{2} {\text{O}}$
3	${\text{NiFe}}_{2} {\text{O}}_{4} + {\text{H}}_{2} {\text{O}} = {\text{HNiO}}_{2}^{ - } + {\text{Fe}}_{2} {\text{O}}_{3} + {\text{H}}^{ + } { }$
${\text{FeCr}}_{2} {\text{O}}_{4}$
1	${\text{FeCr}}_{2} {\text{O}}_{4} + 2{\text{H}}^{ + } = {\text{Fe}}^{2 + } + {\text{Cr}}_{2} {\text{O}}_{3} + {\text{H}}_{2} {\text{O}}$
2	${\text{FeCr}}_{2} {\text{O}}_{4} + {\text{H}}_{2} = {\text{Fe}} + 2{\text{CrO}}_{2}^{ - } + 2{\text{H}}^{ + }$
3	${\text{FeCr}}_{2} {\text{O}}_{4} + {\text{H}}_{2} {\text{O}} = {\text{FeO}} + 2{\text{CrO}}_{2}^{ - } + 2{\text{H}}^{ + }$
4	$3{\text{FeCr}}_{2} {\text{O}}_{4} + 4{\text{H}}_{2} {\text{O}} = {\text{Fe}}_{3} {\text{O}}_{4} + 6{\text{CrO}}_{2}^{ - } + 6{\text{H}}^{ + } + {\text{H}}_{2}$
5	$2{\text{FeCr}}_{2} {\text{O}}_{4} + 3{\text{H}}_{2} {\text{O}} = {\text{Fe}}_{2} {\text{O}}_{3} + 4{\text{CrO}}_{2}^{ - } + 4{\text{H}}^{ + } + {\text{H}}_{2}$
${\text{NiCr}}_{2} {\text{O}}_{4}$
1	${\text{NiCr}}_{2} {\text{O}}_{4} + 2{\text{H}}^{ + } = {\text{Cr}}_{2} {\text{O}}_{3} + {\text{Ni}}^{2 + } + {\text{H}}_{2} {\text{O}}$
2	${\text{NiCr}}_{2} {\text{O}}_{4} + {\text{H}}_{2} {\text{O}} = {\text{NiO}} + 2{\text{CrO}}_{2}^{ - } + 2{\text{H}}^{ + }$

Table 4 Equilibrium equations used for the calculation of the solubilities of possible spinel oxides formed in high-temperature water in a wide pH value range

${\text{Fe}}_{3} {\text{O}}_{4}$
1	${\text{Fe}}_{3} {\text{O}}_{4} + 6{\text{H}}^{ + } + {\text{H}}_{2} = 3{\text{Fe}}^{2 + } + 4{\text{H}}_{2} {\text{O}}$
2	$2{\text{Fe}}_{3} {\text{O}}_{4} + 18{\text{H}}^{ + } = 6{\text{Fe}}^{3 + } + 8{\text{H}}_{2} {\text{O}} + {\text{H}}_{2}$
3	${\text{Fe}}_{3} {\text{O}}_{4} + 6{\text{CrO}}_{2}^{ - } + 6{\text{H}}^{ + } + {\text{H}}_{2} = 3{\text{FeCr}}_{2} {\text{O}}_{4} + 4{\text{H}}_{2} {\text{O}}$
4	${\text{Fe}}_{3} {\text{O}}_{4} + 2{\text{H}}_{2} {\text{O}} + {\text{H}}_{2} = 3{\text{HFeO}}_{2}^{ - } + 3{\text{H}}^{ + }$
${\text{NiFe}}_{2} {\text{O}}_{4}$
1	${\text{NiFe}}_{2} {\text{O}}_{4} + 2{\text{H}}^{ + } = {\text{Ni}}^{2 + } + {\text{Fe}}_{2} {\text{O}}_{3} + {\text{H}}_{2} {\text{O}}$
2	${\text{NiFe}}_{2} {\text{O}}_{4} + 6{\text{H}}^{ + } + {\text{H}}_{2} = {\text{Ni}}^{2 + } + 2{\text{Fe}}^{2 + } + 4{\text{H}}_{2} {\text{O}}$
3	${\text{NiFe}}_{2} {\text{O}}_{4} + {\text{H}}_{2} {\text{O}} = {\text{HNiO}}_{2}^{ - } + {\text{Fe}}_{2} {\text{O}}_{3} + {\text{H}}^{ + } { }$
${\text{FeCr}}_{2} {\text{O}}_{4}$
1	${\text{FeCr}}_{2} {\text{O}}_{4} + 2{\text{H}}^{ + } = {\text{Fe}}^{2 + } + {\text{Cr}}_{2} {\text{O}}_{3} + {\text{H}}_{2} {\text{O}}$
2	${\text{FeCr}}_{2} {\text{O}}_{4} + {\text{H}}_{2} = {\text{Fe}} + 2{\text{CrO}}_{2}^{ - } + 2{\text{H}}^{ + }$
3	${\text{FeCr}}_{2} {\text{O}}_{4} + {\text{H}}_{2} {\text{O}} = {\text{FeO}} + 2{\text{CrO}}_{2}^{ - } + 2{\text{H}}^{ + }$
4	$3{\text{FeCr}}_{2} {\text{O}}_{4} + 4{\text{H}}_{2} {\text{O}} = {\text{Fe}}_{3} {\text{O}}_{4} + 6{\text{CrO}}_{2}^{ - } + 6{\text{H}}^{ + } + {\text{H}}_{2}$
5	$2{\text{FeCr}}_{2} {\text{O}}_{4} + 3{\text{H}}_{2} {\text{O}} = {\text{Fe}}_{2} {\text{O}}_{3} + 4{\text{CrO}}_{2}^{ - } + 4{\text{H}}^{ + } + {\text{H}}_{2}$
${\text{NiCr}}_{2} {\text{O}}_{4}$
1	${\text{NiCr}}_{2} {\text{O}}_{4} + 2{\text{H}}^{ + } = {\text{Cr}}_{2} {\text{O}}_{3} + {\text{Ni}}^{2 + } + {\text{H}}_{2} {\text{O}}$
2	${\text{NiCr}}_{2} {\text{O}}_{4} + {\text{H}}_{2} {\text{O}} = {\text{NiO}} + 2{\text{CrO}}_{2}^{ - } + 2{\text{H}}^{ + }$

Fig. 9 Schematic of the dissolution model of the outer oxide film on 316LN SS during the shutdown acid-reducing phase. a Borated and lithiated high-temperature water at 300 °C, b the initial stage of boration at 300 °C, c low-temperature stage (150 °C) during the acid-reducing phase

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