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Comportement en milieu salin de nouveaux échangeurs de chaleur en aciers inoxydables

Abstract : Heat exchangers are used in many sectors because they represent essential components for the development of industrial processes. Researches focusing on the development of innovative exchangers necessarily require a metallurgical study to determine the optimal alloy composition and design process. It is within this framework that the present study took place through an institutional project financially supported by Five's Cryogénics and the "Grand Est" region. The physicochemical study was undertaken to evaluate the resistance to aqueous corrosion in chloride media of new exchangers made of stainless steel of high purity and assembled by a brazing process performed at 1200°C. The objective was to acquire the best knowledge as possible of the fundamental corrosion processes that could affect the devices envisaged for specific service conditions. The objective of the first step was to characterize the microstructure of steels and brazing alloy before and after heat treatment (TH). The obtained results led to the determination of the microstructural transformation during heat treatment (HT). In particular, they showed that 316LTi steel is less subject to granular coarsening than 316L stainless steel. In addition, they evidenced the existence of Cr6Ni16Si7 remains controversial and that hinder the establishment of reliable thermodynamic models. The objective of the second step was to concentrate the investigations on the chemical reactivity in chlorinated aqueous media of the different intermetallic phases identified during the microstructural study. The electrochemical measurements have made it possible to characterize their resistance to corrosion and led to the following major results: i) the two stainless steels are susceptible to pitting corrosion and 316LTi substrate show higher performance that 316L alloy at 25 ° C but both exhibit identical performance at 60 ° C, ii) they are passivable and the passive layer produced at high temperature is particularly protective, iii ) the constitutive phases of the brazing alloy (before TH) and those appearing after heat treatment (post TH) are cathodic compared to both stainless steels and iv) they can protect them by playing the role of soluble anodes. The objective of the last step was to evaluate the behavior of different assemblies through immersion tests of several thousand hours. The obtained re.sults clearly show that after 2000 hours the tested devices are resistant to corrosion provided.
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https://hal.univ-lorraine.fr/tel-02558271
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Submitted on : Wednesday, April 29, 2020 - 2:20:27 PM
Last modification on : Thursday, February 25, 2021 - 11:04:18 AM

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  • HAL Id : tel-02558271, version 1

Citation

Mickaël Bolmont. Comportement en milieu salin de nouveaux échangeurs de chaleur en aciers inoxydables. Matériaux. Université de Lorraine, 2019. Français. ⟨NNT : 2019LORR0261⟩. ⟨tel-02558271⟩

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