Evaluating the performance of Cu-Ni 90/10 alloy exposed to marine polluted seawater compositions

Description

The cupronickel (Cu-Ni) alloys 90/10 and 70/30 are widely used in heat exchanging applications in the offshore energy sector and shipping, mainly because of their excellent corrosion resistance, thermal conductivity, and antifouling ability in the natural seawater exposure environment compared to the contemporary alloys. However, in the complex seawater compositions developed over the year due immense human involvement not limiting to the aggressive marine pollutant factors, the rapid degradation in the corrosion resistance ability of Cu-Ni alloys has been a matter of great concern and challenge for offshore platforms. In this paper, the corrosion behavior of Cu-Ni alloy 90/10 exposed to the pollutant-rich harbor seawater conditions in the Arabian Sea region; containing higher levels of the corrosion-sensitive compounds has been investigated, by using coupons during the field experimental durations over 600 exposure days. The experimental corrosion losses were then compared to those observed in the clean natural seawater compositions in the nearest vicinity. Here, the corrosion losses and pit depths as functions of exposure durations were measured using the digital micrometry i.e., dimensional metrology (DM) method and the standard mass loss method. Furthermore, the corrosion products appeared on post-corrosion coupons were analyzed using the following analytical techniques: SEM, EDS, EDS mapping and Raman spectroscopy. The comparative results have shown extremely high corrosion rates (around 500 µm/yr) and pit depths (450–1100 µm within 665 days) on the coupon surface exposed to the polluted harbor seawater site, compared to the nominal corrosion rates (10-20 µm/yr) recorded in the natural seawater exposure site. Additionally, characterization results of the corrosion deposits in the polluted seawater conditions were found to complement the corrosion processes and bi-modal corrosion predicted models (aerobic and anaerobic corrosion phases) typically taking place in the similar exposure conditions. These elevated corrosion losses were found to reduce the useful life and reliability of Cu-Ni alloyed infrastructures significantly in the polluted seawater exposure conditions.

Institutions

• National University of Sciences and Technology

  Islamabad, Islamabad
• Queensland University of Technology

  Queensland, Brisbane

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