Crevice corrosion of NiCrMo alloys 625, C-276, C-22, and Titanium (C.P. Grade 2) pipe and tube product was investigated in natural seawater (NSW) and seawater with chlorination concentrations of 1 mg/l and 85-90 mg/l. Exposures of up to one year duration were conducted in the three environments with all materials tested at two flow rates. Crevices were formed on the outside diameter of pipe and tube product by the application of vinyl (tygon) and Buna-N rubber sleeves as well as nylon compression fittings. Crevice corrosion resistance of the three NiCrMo alloys varied depending on environmental, crevice geometry and metallurgical factors.

Extensive testing of alloy 625 seamless pipe and tube product was conducted and crevice corrosion initiation and propagation are discussed in terms of seawater velocity, chlorination level, and test duration. It is shown that crevice corrrosion initiation of alloy 625 was not caused by metallurgical variables. Alloy 625 was aggressively attacked in 85-90 ppm chlorinated seawater (CSW), displaying crevice corrosion product within 24 hours of testing and substantial propagation after 60 days. Alloy 625 also showed susceptibility to crevice corrosion initiation in both natural seawater and 1 ppm chlorinated seawater. The degree of attack was similar in both environments and much less than that which occurred in 85-90 ppm chlorinated seawater. Crevice corrosion propagation continued with exposure time in both natural seawater and 1 mg/l chlorinated seawater, particularly for the specimens tested at higher flow rates.

Seam welded tube product of alloys 625, C-22 and C-276 were tested and the results are compared. Alloy C-276 was totally resistant in natural seawater while alloys C-22 and 625 exhibited crevice corrosion initiation. All three alloys were lightly etched in 1 mg/l chlorinated seawater and suffered the most corrosion in 85-90 mg/l chlorinated seawater. The inner diameter surfaces of the three NiCrMo seam welded alloys exhibited surface staining in 85-90 mg/l chlorinated seawater. In addition, alloys C-276 and C-22 showed some preferential etching along the weld seam whereas alloy 625 did not. The inner diameter surfaces of the three alloys were not attacked in either natural seawater or 1 mg/l chlorinated seawater.

Subject
Piping, Vinyls, Nickel based alloys, Chlorinated seawater, Tubes, Corrosion initiation, Natural seawater, Seawater, Crevices, Corrosion attacks, Crevice corrosion, Titanium alloys, Alloys
© 1989 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).
1989
Association for Materials Protection and Performance (AMPP)
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