Intergranular stress corrosion cracks found in the weld heat affected zone of pipe in the Spent Fuel Pool piping system at Three Mile Island Unit No. 1 have been evaluated by a series of analytical tests. The intergranular nature of the cracks was identified by optical metallography and scanning electron microscopy. The presence of Cl− was observed by Energy Dispersive X-Ray Analysis and Auger Electron Spectroscopy (AES). Sulfur was observed by both EDX and AES both as particles and uniformly on the fracture surface.

Constant extension rate tests (CERT) performed on specimens removed from the pipe and containing the weld HAZ demonstrated that 15 ppm Cl− in a 1.3 wt% H3BO3 solution was sufficient to cause IGSCC when the original pipe surface was present. Removal of this surface resulted in 100% ductile (microvoid coalescence type) fracture for the same test condition. The association of cracks with grinding marks and surface defects in the as-received pipe also supports the conclusion that surface defects contributed to crack initiation.

Subject
Sulfur, Pipe surfaces, Water, Materials, Piping, Intergranular stress corrosion cracking, Fracture surfaces, Corrosion cracking, Intergranular cracking, Internal surfaces, Sensitization, Fracture, Grain boundary
© 1981 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).
1981
Association for Materials Protection and Performance (AMPP)
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