Sulfide stress cracking (SSC) along with hydrogen embrittlement (HE) prevents the use of less expensive high strength carbon steel alloys in the recovery of fossil fuels in H2S containing ‘sour’ service environments that are commonly seen in deep well fossil fuel recovery efforts. High magnitude tensile stresses are generated by connection interferences created during power make-up of down hole tubular components. When subject to service loads the stresses are increased further providing the high tensile stresses necessary for SSC initiation. Because these alloys processed into high strength grades are not suited for fully saturated sour service environments, the current solution is to use or develop much more expensive alloys with increased corrosion-cracking resistance or limit their use to significantly weaker sour environments or higher operating temperatures.

Introduction of stable, high magnitude compressive residual stresses into less expensive carbon steel alloys alleviates the tensile stresses and mitigates SSC while also improving fatigue strength. This could allow the potential of using less expensive alloys in sour environments. Low plasticity burnishing (LPB) is highly effective when applied to metallic components using a proven reproducible process of producing deep, high magnitude compressive residual stresses in complex geometric components without altering the geometry, design or chemistry.

The LPB process, applied with advanced control systems, is presently being employed to treat components resulting in a substantial increase in service life through SSC mitigation and improved fatigue life. The benefits of LPB have been evaluated on full size specimens of uni-axial hoop stress loaded coupling blanks and C-ring specimens manufactured from quench and tempered API P110 grade steel with a yield strength of 132 ksi (910 MPa). Specimens were exposed to 100% NACE TM0177-Solution A at 1 bara H2S in both the LPB treated and untreated condition. The time to failure was documented along with the increase in life resulting from LPB treatment. LPB was successful in completely mitigating SSC in each test specimen up to 85% SMYS hoop tension; and in each case met or exceeded the 720-hour exposure time defined in NACE TM0177. At an applied fiber stress of 90% SMYS, the C-ring samples have exceeded exposures of 840 hours without failure. The initial results indicate that LPB processing of down hole tubular components may provide an alternative economical means of SSC mitigation and greatly reducing risk of component failure in sour environments.

Subject
Test methods, Materials, Compression, Sour environments, Couplings, Roughness, Stress, C ring stress corrosion testing, Mechanical failure, Tensile stress, Sulfide stress cracking, Alloys, Residual stress
Keywords:
low plasticity burnishing, sulfide stress cracking, fatigue, residual stress, sour service
© 2011 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).
2011
Association for Materials Protection and Performance (AMPP)
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