Corrosion behavior and coating performance of carbon steel in HCl/NaOH thermal medium in wide temperature zone

doi:10.11949/0438-1157.20241260

Abstract

Abstract:

To address the corrosion problems in the distillation and solid caustic soda production processes of chlor-alkali industry, the corrosion behavior of Q235 carbon steel in hydrochloric acid and sodium hydroxide media, as well as the corrosion protection performance and mechanism of two types of hybrid epoxy resin organic coatings (EP-SiTiMg and EP-SiAlCa), were studied. The results show that the increase of HCl concentration and temperature will increase the hydrogen evolution reaction rate of Q235 and aggravate pitting corrosion. In the basic NaOH environment, when the temperature was less than 90℃, the carbon steel corroded initially and a passive film was formed on the surface, slightly reducing the corrosion rate. When the temperature was further increased, the passive film gradually dissolved, and the corrosion rate increased to 0.522 mg/(cm²·h), reaching the severe corrosion standard. EP-SiTiMg coating had excellent corrosion protectiveness in acidic environments, and could maintain a high impedance value of over 4×10⁹Ω·cm² at 150℃. It was suitable for long-term use in the distillation workshop. EP-SiAlCa coating had better corrosion protection effect in the alkaline environment at temperatures below 150℃. It reduced the corrosion rate by more than 52% compared to the carbon steel and was suitable for use in the solid caustic soda section at corresponding operating temperatures. When the temperature reached 150℃, the corrosion resistance of both coatings decreased slightly, and the impedance of the coatings remained around 10⁴Ω·cm², still providing corrosion protection for the carbon steel.

Key words: chlor-alkali industry, electrochemistry, corrosion, organic coating

摘要：

针对氯碱生产精馏与固碱工段的腐蚀问题，研究了Q235碳钢在盐酸、氢氧化钠介质中的腐蚀行为，以及两种掺杂型环氧树脂有机涂层（EP-SiTiMg及EP-SiAlCa）的腐蚀防护性能与作用机制。结果表明，HCl浓度和温度升高均会增大Q235的析氢反应速率，加剧点蚀。在NaOH碱性环境中，当温度≤90℃时，碳钢腐蚀初期表面会形成钝化膜，腐蚀速率略有减小；当温度进一步升高，钝化膜逐步溶解，腐蚀速率加快至0.522 mg/(cm²·h)，达到严重腐蚀标准。EP-SiTiMg涂层在酸性环境中防护性能优异，150℃时仍可保持4×10⁹ Ω·cm²以上的高阻抗值，适合精馏工段长期应用；EP-SiAlCa涂层在<150℃的碱性环境中防护效果更好，腐蚀速率较碳钢降低52%以上，适合在相应作业温度范围的固碱工段使用。当温度达150℃时，两种涂层防护效果均小幅下降，涂层电阻均保持在10⁴ Ω·cm²左右，但仍对碳钢有防护效果。

关键词: 氯碱工业, 电化学, 腐蚀, 有机涂层

CLC Number:

TQ 114.2

Jia KANG, Huan LIU, Haiyan LI, Maoliang LUO, Hong YAO. Corrosion behavior and coating performance of carbon steel in HCl/NaOH thermal medium in wide temperature zone[J]. CIESC Journal, 2025, 76(6): 2872-2885.

康佳, 刘欢, 李海燕, 罗茂亮, 姚洪. 宽温区HCl/NaOH热介质中碳钢腐蚀行为及涂层性能研究[J]. 化工学报, 2025, 76(6): 2872-2885.

Figures/Tables 17

Fig.1 Coating preparation process

Fig.2 XRD patterns of EP-SiAlCa and EP-SiTiMg coatings

Fig.3 Influence of changing concentration of corrosive medium on mass loss of Q235

Fig.4 Influence of changing concentration of corrosive medium on mass loss of two coatings

Fig.5 Mass loss curves in different corrosive environments

Table 1 Corrosion rate constants of Q235 at different temperatures

温度/℃	腐蚀速率K_L/(mg/(cm²·h))
温度/℃	HCl	NaOH
30	-0.308	-0.009
60	-0.825	-0.044
90	-6.852	-0.045
120	-11.262	-0.135
150	-21.721	-0.522

Fig.6 Mass loss curves of the two coatings in different corrosive environments

Table 2 Corrosion rate constants of the two coatings at different temperatures

温度/℃	腐蚀速率K_L/(mg/(cm²·h))
	HCl		NaOH
	EP-SiAlCa	EP-SiTiMg	EP-SiAlCa	EP-SiTiMg
30	-0.053	-0.043	-0.034	-0.048
60	-0.233	-0.109	-0.034	-0.066
90	-0.253	-0.146	-0.042	-0.065
120	-0.348	-0.198	-0.071	-0.076
150	-0.515	-0.236	-0.074	-0.086

Fig.7 Microstructure of the original sample and after corrosion at 90℃ and 150℃ of Q235, Ep-SiAlCa and EP-SiTiMg under acidic environment

Fig.8 Microstructure of original sample and after corrosion at 90℃ and 150℃ of Q235, EP-SiAlCa and EP-SiTiMg under alkaline environment

Fig.9 Changes of infrared functional groups of the two coatings after corrosion at different temperatures

Fig.10 Nyquist and Bode diagrams of electrochemical impedance spectra of Q235[(a)~(c)]， EP-SiAlCa[(d)~(f)] and EP-SiTiMg[(g)~(i)] in acidic environment

Fig.11 Equivalent circuit model

Table 3 Fitting results of electrochemical impedance spectra in acidic environment

样品		R_c/(Ω·cm²)	CPE_c/(F/cm²)	n₁
Q235	原始	1000.40	9.69×10^-4	0.77
	90℃	447.29	1.42×10^-2	0.69
	150℃	399.68	7.85×10^-3	0.64
EP-SiAlCa	原始	6.38×10⁹	1.10×10^-9	0.96
	90℃	1.63×10⁹	1.07×10^-9	0.96
	150℃	3.58×10⁵	1.15×10^-9	0.96
EP-SiTiMg	原始	6.94×10⁹	1.09×10^-9	0.96
	90℃	4.89×10⁹	1.09×10^-9	0.96
	150℃	4.26×10⁹	1.10×10^-9	0.96

Fig.12 Nyquist and Bode diagrams of electrochemical impedance spectra of Q235[(a)~(c)], EP-SiAlCa[(d)~(f)] and EP-SiTiMg[(g)~(i)] in alkaline environment

Fig.13 Equivalent circuit model

Table 4 Fitting results of electrochemical impedance spectra in alkaline environment

样品		R_c/(Ω·cm²)	CPE_c/(F/cm²)	n₁	R_ct/(Ω·cm²)	CPE_dl/(F/cm²)	n₂
Q235	原始	1000.40	9.69×10^-4	0.77	—	—	—
	90℃	110.24	3.15×10^-4	0.53	3075.71	12374×10^-3	0.73
	150℃	306.97	2.27×10^-3	0.84	—	—	—
EP-SiAlCa	原始	6.38×10⁹	1.10×10^-9	0.96
	90℃	1.02×10⁹	1.08×10^-9	0.96	—	—	—
	150℃	38978	1.02×10^-9	0.97
EP-SiTiMg	原始	6.94×10⁹	1.09×10^-9	0.96	—	—	—
	90℃	6.40×10⁸	1.13×10^-9	0.96	8.75×10⁹	2.65×10^-9	0.73
	150℃	53977.00	1.07×10^-9	0.97	1.01×10⁶	3.11×10^-5	0.82

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