Localized Corrosion and Service Life Prediction of Copper Heat Exchange Tubes in a Sodium Acetate Trihydrate Phase Change Thermal Energy Storage System

doi:10.11902/1005.4537.2025.283

Journal of Chinese Society for Corrosion and protection

2026, Vol. 46

Issue (4): 1045-1057 DOI: 10.11902/1005.4537.2025.283

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Localized Corrosion and Service Life Prediction of Copper Heat Exchange Tubes in a Sodium Acetate Trihydrate Phase Change Thermal Energy Storage System

MA Huanhuan¹^,², LV Shengdong³, QIAN Yixin², LIN Yong³, HAO Xiangping¹^,²(

), ZHANG Dawei², WANG Luning¹

^1.School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
^2.Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China
^3.Midea Group Co. Ltd., Foshan 528311, China

Cite this article:

MA Huanhuan, LV Shengdong, QIAN Yixin, LIN Yong, HAO Xiangping, ZHANG Dawei, WANG Luning. Localized Corrosion and Service Life Prediction of Copper Heat Exchange Tubes in a Sodium Acetate Trihydrate Phase Change Thermal Energy Storage System. Journal of Chinese Society for Corrosion and protection, 2026, 46(4): 1045-1057.

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Abstract

Sodium acetate trihydrate, as a storage substance is widely employed in water heater thermal storage systems due to its high phase change energy storage density and suitable melting point. However, as a corrosive medium for Cu, the sodium acetate trihydrate may cause corrosion of Cu-tubes in heat exchange systems, leading to reduced service life of heat exchange components. Therefore, investigating the corrosion behavior of Cu-tubes in the presence of phase change substances in service conditions and predicting their service life are essential. Herein, the corrosion behavior, corrosion morphology and corrosion products of Cu-tubes were studied by means of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). These Cu-tubes, set at different locations within a water heater, were suffered from corrosion induced by simulated operation in actual conditions for varying durations. Meanwhile, the morphology and depth of the corrosion pits were also assessed by confocal laser scanning microscopy. Furthermore, the service life of Cu-tubes set at different locations was predicted by means of a regression model. The corrosion observed on straight Cu-tubes, bent Cu-tubes, and welded joints manifested primarily as localized pitting corrosion. Notably, the bent Cu-tubes exhibited microcracks induced by tensile-compressive stresses, resulting in more severe corrosion compared to the straight tubes; It may be predicted that these tubes will fail due to corrosion perforation after 31 a. For the welded seams of Cu-tubes, there existed thermal cracks due to welding heat input and P element segregation, suffered from the most severe corrosion, while it may be predicted that they will fail due to corrosion perforation after 35 a. This evidence provides significant reference for understanding and mitigating the corrosion of Cu-components within water heaters.

Key words: sodium acetate trihydrate copper tube corrosion pitting corrosion corrosion mechanism life prediction

Received: 06 September 2025 32134.14.1005.4537.2025.283

ZTFLH:

TG174

Fund: National Natural Science Foundation of China(52201062);Guangdong Basic and Applied Basic Research Foundation(2021B1515130009)

Corresponding Authors: HAO Xiangping, E-mail: xphao@ustb.edu.cn

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	MA Huanhuan
	LV Shengdong
	QIAN Yixin
	LIN Yong
	HAO Xiangping
	ZHANG Dawei
	WANG Luning

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https://www.jcscp.org/EN/10.11902/1005.4537.2025.283 OR https://www.jcscp.org/EN/Y2026/V46/I4/1045

Fig.1 Typical heat exchange tube components: (a) copper straight tube, (b) copper bent tube, (c) copper welded bent tube

Fig.2 Macroscopic morphologyies of rusted copper straight tubes after test for 0 h (a), 500 h (b), 1000 h (c), 2500 h (d) and 4000 h (e)

Fig.3 Surface pit morphologies of the copper straight tube after 2500 h (a) and 4000 h (b) of service, with the corresponding CLSM on the right

Fig.4 Microscopic morphologies of copper straight tubes after testing for 0 h (a), 500 h (b), 1000 h (c), 2500 h (d) and 4000 h (e)

Fig.5 XRD pattern of the straight copper tubes after exposure for various durations

Fig.6 Macroscopic morphologies of rusted copper bent tubes after testing for 0 h (a), 500 h (b), 1000 h (c), 2500 h (d) and 4000 h (e)

Fig.7 Surface pit morphologies of the copper bent tube after 2500 h (a) and 4000 h (b) of service with the corresponding CLSM on the right

Fig.8 Microscopic morphologies of copper bent tubes after testing for 0 h (a), 500 h (b), 1000 h (c), 2500 h (d) and 4000 h (e)

Fig.9 XRD patterns of the copper U-bend tubes at different exposure durations

Fig.10 Macroscopic morphologies of rusted copper welded tubes after testing for 0 h (a), 500 h (b), 1000 h (c), 2500 h (d) and 4000 h (e)

Fig.11 Surface pit morphologies of the copper welded bent tube after 2500 h (a) and 4000 h (b) of service and the corresponding CLSM measurement

Fig.12 Microscopic morphologies of copper welded tubes after testing for 0 h (a), 500 h (b), 1000 h (c), 2500 h (d) and 4000 h (e)

Fig.13 Macroscopic morphologies of the copper tube weld joint (a) and microscopic defects (b, c) in the heat-affected zone

Fig.14 Element segregation in the heat-affected zone (a) and corresponding magnified micrograph (b) with elemental composition comparison

Fig.15 XRD patterns of the copper brazed joints acquired after exposure for various durations

Fig.16 Formation of the protective oxide layer on the copper tube surface (a), the doping of Cl elements into Cu₂O (b) and the degradation of the protective film (c)

Fig.17 Corrosion pit comparison of various copper tube components at different time intervals

Table 1 Corrosion pit data for various copper tube components at different time intervals

Fig.18 Life prediction fitting curves and corresponding fitting equations for copper straight tube (a), copper bent tube (b) and copper welded tube (c)

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