For investigation of the resistance of submerged arc welded (SAW) large-diameter pipes for application in sour service, a new full-size four-point-bend test method has been developed for performance of SSC tests on specimens of full pipe wall thickness. 45 specimen holders, designed for stressing specimens containing the original pipe curvature with a load up to 4 tons were machined. Specimens of 260 mm length, 25 mm width and up to 33 mm thickness were tested in solution A to NACE TM0177-96 at 0.1 MPa H2S and exposure times of 96 and 720 hours, respectively. The specimens had been machined from the pipes in 12 o'clock position and contained the original inner and outer pipe surfaces including the longitudinal welds. The specimens were loaded to stress levels between 72 % of the specified minimum yield strength and 110 % of the actual yield strength of the grade X65 pipe material with the inner surface in tension. Load application was monitored by strain gauges which were fixed close to the notch between the weld metal and the base metal. The investigations revealed that the pipe material was not susceptible to SSC under the present test conditions up to a load of 100 % of actual yield strength of the base metal. The results were confirmed by full scale H2S testing of two girth-welded pipe sections under internal pressure equivalent to a hoop stress of 72 % of the specified minimum yield strength of the same pipe material. The full-size four-point-bend test proved to be a usefill tool to evaluate the susceptibility of large-diameter pipes to SSC, particularly in case the weld area has to be tested. In contrast to four-point-bend testing of large-diameter pipe material on flat specimens, the new test method considers the real pipe geometry and a stress distribution close to service conditions.

Subject
Test methods, Pipe surfaces, Materials, Piping, Yield stress, Modeling, Internal stress, Base metals, Stress, Internal surfaces, Scale, Sulfide stress cracking, Yield strength
Keywords:
Sour service, SSC test, four-point-bend test, low alloy steel, large-diameter pipe, SAW, longitudinal weld
© 2004 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).
2004
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.