The cathodic polarization characteristics of the internal surfaces of 20-foot lengths of 1/2-in., 1-in., and 2-in. nominal I.D. pipes of Type 304 stainless steel, copper, and low carbon steel were studied. The basic study was conducted on pipes containing stagnant sea water, but the effect of flowing sea water on polarization was also determined. Cathodic protection was supplied by a single zinc anode attached internally at one end of each pipe.

All diameters of Type 304 stainless steel and copper pipes containing stagnant sea water were successfully cathodically protected to their extreme ends which were as much as 440 pipe diameters from the anode. Among the low carbon steel pipes containing stagnant sea water only the 2-in. nominal diameter pipe was protected to its extreme end. The nominal mean current density on the internal pipe surfaces decreased to 0.1 ma/sq-ft or less. The time required to achieve cathodic protection varied from less than 4 days to about 186 days and was dependent on the alloy and pipe diameter.

As expected, flowing freshly pumped sea water through the polarized pipes at a very slow flow rate resulted in marked loss of polarization. The distance remaining under cathodic protection was 6 feet or less depending on the alloy and pipe diameter.

Subject
Low carbon steel, Water, Piping, Cathodic protection, Tubes, Zinc anodes, Cathodic current, Current densities, Internal surfaces, Copper, Stainless steel, Polarization, Electrochemical potential
© 1973 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).
1973
Association for Materials Protection and Performance (AMPP)
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