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05232 Corrosion Resistance of UNS NO4400 vs. Electroless Nickel in Simulated Marine Service

UNS N04400 cladding on steel valves can corrode during marine service.  The uniform corrosion rate of an EN coating in artificial seawater was measured by electrochemical impedance spectroscopy and was found to be less than that for N04400. The main conclusion is that an EN coating could be a viable solution to repair N04400-clad valves in-situ.

 

Product Number: 51300-05232-SG
ISBN: 05232 2005 CP
Author: Robert D. Klassen and Pierre R. Roberge, Royal Military College; Yueping Wang, DRDC Atlantic
Publication Date: 2005
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UNS N04400 cladding on steel valves can corrode during marine service, most seriously in the form of grooves or pits. Re-cladding of valves that are welded to the hull is very costly because of the processes of removal and re-attachment. There is then a need to develop techniques to repair these valves in-situ without removing them from the hull. The present work investigated the potential of plating with electroless nickel (EN) for repair. In this technique, a layer of about 90% nickel (the balance is phosphorous) is deposited chemically onto the damaged surface. A non-electrolytic cleaning technique was developed to allow EN to coat over the bottom of corrosion pits. The uniform corrosion rate of an EN coating in artificial seawater was measured by electrochemical impedance spectroscopy and was found to be less than that for N04400. Both N04400 and EN form a protective anodic layer in artificial seawater. The tendency towards pitting and crevice corrosion of an EN coating was also found to be better than that of N04400. The main conclusion from this work is that an EN coating could be a viable solution to repair N04400-clad valves in-situ.

Keywords: UNS N04400, electroless nickel, corrosion resistance, artificial seawater, electrochemical impedance spectroscopy

UNS N04400 cladding on steel valves can corrode during marine service, most seriously in the form of grooves or pits. Re-cladding of valves that are welded to the hull is very costly because of the processes of removal and re-attachment. There is then a need to develop techniques to repair these valves in-situ without removing them from the hull. The present work investigated the potential of plating with electroless nickel (EN) for repair. In this technique, a layer of about 90% nickel (the balance is phosphorous) is deposited chemically onto the damaged surface. A non-electrolytic cleaning technique was developed to allow EN to coat over the bottom of corrosion pits. The uniform corrosion rate of an EN coating in artificial seawater was measured by electrochemical impedance spectroscopy and was found to be less than that for N04400. Both N04400 and EN form a protective anodic layer in artificial seawater. The tendency towards pitting and crevice corrosion of an EN coating was also found to be better than that of N04400. The main conclusion from this work is that an EN coating could be a viable solution to repair N04400-clad valves in-situ.

Keywords: UNS N04400, electroless nickel, corrosion resistance, artificial seawater, electrochemical impedance spectroscopy

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