Several stainless steels have been tested in the NACE solution at temperatures between 20° C and 150° C. The series includes austenitic stainless steels, highly cold-worked: first AISI types 301 and 316, and also special compositions as Cr 20 - Ni 25 - Mo 4.5 - Cu 1.5 (Uranus B6*), Cr 25 - Ni 25 - Mo 5 - Cu 1.5 (Uranus SB 8*), and a 4 % Si-bearing steel, Cu 17 - Ni 14 - Si 4 (Uranus S1*). Duplex stainless steels have also been tested, as cast, wrought, and highly cold worked products. Field experience is also discussed and documented.

Results at room temperature show that the duplex alloy is slightly more resistant when wrought, but becomes quite resistant when cold-worked, and this good resistant still prevails at 100° C and 150° C under a pressure of 5 to 15 bar of H2S. Conversely, hardening heat-treatments at temperature between 400° C and 900° C may in some cases impair significantly the resistance of the duplex steels.

The austenitic stainless steels, highly cold worked, are quite resistant at 20° C, except steel AISI 301. But steel AISI 316 becomes very prove to cracking when temperatures increases to 90° C, 100° C and 150° C, under 1 to 15 bar pressure of H2S, in which conditions it proves much inferior to the duplex compositions.

On the other hand the austenitic special alloys with 20 % to 25 % Cr, 25 % Ni, 5 % Mo and 1.5 % Cu are still quite resistant.

Cracking situations could usually be related to low values of the electrochemical potentiel (- 400 mV/SCE) while at - 100 to - 200 mV/SCE failures occured much more rarely.

As previously reported, the cracking processes operative in the duplex steels seem to be related to complex mechanical and electrochemical coupling between ferrite and austenite. In some circunstances, ferrite can initiate cracks by mechanical twinning. The twinning tendency of ferrite seems to be enhanced by hardening heat-treatments which cause complex precipitations in ferrite.

Conversely, cold work seem to retard these phenomena. These results lead to think that moderate-priced stainless steels can be used in oil and gas environments, provided the selection be correctly carried out. To that aim it would seem useful to better evaluate testing procedures.

Subject
Materials, Composition, Wiring, Stress cracking, Chloride solutions, Cracking resistance, Steel, Duplex stainless steel, Stainless steel, Ferrite, Electrochemical potential, Stress corrosion cracking, Chloride stress corrosion cracking
© 1983 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).
1983
Association for Materials Protection and Performance (AMPP)
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