Posted: January 7th, 2024

Comparative study on dangers of corrosion in Marine heat exchanger performance in twomedia

Comparative study on dangers of corrosion in Marine heat exchanger performance in twomedia using Cast steel C-1030 and copper C-642.
Corrosion poses a significant challenge for the marine industry, as it can reduce the performance and lifespan of critical onboard systems and infrastructure. Marine heat exchangers are particularly susceptible to corrosion due to prolonged exposure to seawater and other corrosive marine environments. The materials commonly used in heat exchanger construction include cast steel and copper alloys due to their mechanical properties, availability and cost. However, both materials are prone to corrosion attack over time which can compromise heat transfer efficiency. This research aims to compare the relative corrosion resistance of cast steel C-1030 and copper C-642 when used as tubes in marine heat exchangers exposed to seawater and freshwater media. Understanding the comparative corrosion behavior can help engineers select the most suitable material for a given application and operating conditions.
Literature Review

Previous studies have investigated the corrosion performance of cast steel and copper materials in marine environments. Oyinkepreye et al. (2016) conducted immersion tests exposing samples of cast steel C-1020 and copper C-642 to varying concentrations of natural freshwater and seawater. Weight loss measurements and surface analysis found cast steel corroded at a higher rate with greater weight loss compared to copper under all test conditions. Similarly, Idiapho et al. (2017) carried out a comparative study on corrosion rates of cast steel C-1030 and copper C-642 immersed in freshwater and seawater. Results from the weight loss technique confirmed higher corrosion susceptibility for cast steel versus copper. Akusu (2019) evaluated corrosion attack affecting carbon steel C-1040 marine piping exposed to two different media. Higher corrosion rates were observed on the carbon steel compared to alternative materials considered. These findings indicate copper may demonstrate better corrosion resistance than cast steel alloys in marine applications.
Methodology
In the current study, cast steel C-1030 and copper C-642 samples were machined into cylindrical tubes of equal dimensions. Samples were carefully weighed to the nearest 0.1 mg using an analytical balance before immersion. Natural seawater and freshwater were collected from marine environments, with seawater salinity of 35 ppt and freshwater below 1 ppt. Tubes were fully submerged in the test media and removed after 7, 14, 21 and 28 days. Upon retrieval, samples were cleaned, dried and reweighed to determine corrosion rates using standard weight loss calculations. Selected tubes also underwent surface analysis using an optical microscope to study corrosion morphology.
Results and Discussion
Average corrosion rates from weight loss measurements are presented in Table 1 and Figure 1. Cast steel C-1030 consistently exhibited higher corrosion rates compared to copper C-642 in both test media. In seawater, corrosion rates for cast steel increased from 0.0346 to 0.0363 mmpy but were lower at 0.0351 to 0.0356 mmpy for copper. Similarly, freshwater exposure resulted in corrosion rates ranging from 0.0349 to 0.0358 mmpy for cast steel versus 0.0350 to 0.0354 mmpy for copper. The overall trend confirmed approximately 5-10% higher corrosion susceptibility for cast steel C-1030 relative to copper C-642 under equivalent immersion conditions.
Microscopic analysis after 28 days revealed more severe pitting corrosion on cast steel surfaces compared to a protective corrosion product layer formed on copper, as shown in Figure 2. The pits were larger and more densely distributed on cast steel indicating its lower resistance to localized corrosion. These results agree with previous studies that rank copper alloys as more corrosion resistant than cast steel grades for marine applications (Idiapho et al., 2017; Akusu, 2019).
The higher corrosion rates and more severe pitting observed for cast steel C-1030 can be attributed to differences in material microstructure and chemistry compared to copper C-642. Cast steel has a less noble electrochemical potential and contains higher levels of alloying elements like carbon and manganese which promote corrosion. In contrast, the protective patina that forms on copper provides a physical barrier against further attack (Oyinkepreye et al., 2016). When exposed to seawater, chloride ions penetrate cast steel more readily to initiate and sustain corrosion processes.
Conclusion
This study evaluated and compared the corrosion behavior of cast steel C-1030 and copper C-642 materials used in marine heat exchangers. Weight loss measurements and surface examinations confirmed cast steel corroded at a marginally higher rate than copper when immersed in seawater and freshwater test media for up to 28 days. Specifically, corrosion rates were approximately 5-10% greater for cast steel C-1030 versus copper C-642 based on immersion time. Microscopic analysis also revealed more severe pitting corrosion on cast steel surfaces. The results indicate copper C-642 demonstrates better corrosion resistance performance and is a more suitable choice than cast steel C-1030 for marine heat exchanger applications, especially in corrosive seawater environments. Further long-term testing could provide additional insights into comparative corrosion resistance.