The question answered in this study is whether the demand on a cathodic protection system will change when the protected pipe material is changed from copper-nickel to alloy 625. Two piping mockups were designed to simulate a probable geometry for a cathodically-protected piping system. Each mockup consisted of a 20-foot (610-cm) length of nominal 2-inch (5-cm) diameter piping with a zinc anode for cathodic protection inserted in the discharge end of each. One mockup was made with 70-30 copper-nickel pipe and the other with alloy 625 pipe. Protection currents and potential profiles inside the pipes were measured over a six-month exposure period in natural seawater flowing at 7-ft/s (210-cm/s). The total protection current and sacrificial anode consumption for alloy 625 pipe was half that for copper-nickel pipe. This means that replacing copper-nickel pipe with alloy 625 pipe in areas close to cathodically-protected heat exchangers or hulls will result in a more conservative design for the cathodic protection system than was the case for the original copper-nickel piping.

Subject
Materials, Piping, Piping systems, Cathodic protection, Probes, Zinc anodes, Cathodic current, Wiring, Current measurements, Seawater, Tubing, Copper nickel alloys, Anodes
Keywords:
galvanic corrosion, cathodic protection, piping, alloy 625, copper-nickel, seawater, heat exchangers
© 1995 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1995
Association for Materials Protection and Performance (AMPP)
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