Summary

The NACE T-1F-13 Task Group conducted a round robin program designed to evaluate the T-1F-9 proposed Test Method (TM), "Evaluation of Metals for Resistance to Sulfide Stress Cracking at Ambient Temperatures." A core program was conducted on four alloys according to either a constant load smooth tensile specimen or a constant deflection notched beam specimen as described in the proposed TM. An optional program included other materials, different sample geometries, and environmental variations. Eighteen companies participated in various phases of the program. Each laboratory was furnished test materials in rough form; they machined their own specimens, set up apparatus and tested independently.

The results showed that the tensile test was reproducible among laboratories, and that the sulfide stress cracking data were logarithmically related to time, i. e., σ = σ0-βlogt, where σ is stress, σ0 and β are material constants, and t is time. The notched beam test produced a relative ranking of materials within laboratories, but did not provide quantitative data suitable for ranking comparisons among laboratories. The primary problem was lack of agreement between laboratories in determining the yield deflection of the notched beam. In addition, scatter on a "deflection to failure" basis was also greater among laboratories than with the smooth tensile specimen. To rectify these problems, testing with the Shell Sc beam specimen and a similar smooth beam is being proposed with deflections to failure reported. Feasibility of testing with a fracture mechanics specimen is also to be examined.

Both the tensile and beam samples produced failures at stress levels well below the yield strength in materials which have given acceptable field service; quantitative performance criteria for sour service use is not indicated since this would depend on the specific service intended. Hydrogen blistering was encountered with very low strength steels normally considered immune to sulfide stress cracking failures and may present problems when using this test method. Microcracking parallel to the working direction and the applied stress was also observed in some instances. Use of the revised proposed TM is being recommended, however, and should result in improved communication between investigators of sulfide stress cracking.

Subject
Test methods, Water, Materials, Yield stress, Laboratory data, Tensile tests, Constants, Mechanical failure, Deflection, Steel, Stainless steel, Sulfide stress cracking, Yield strength
© 1975 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).
1975
Association for Materials Protection and Performance (AMPP)
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