Metallurgical investigation's were performed on a cracked main steam isolation valve (MSIV) shaft from the Joseph M. Farley Unit #1 station and two MSIV shafts from the R. E. Ginna Station (only one shaft cracked). This investigation consisted of optical microscopy, chemical analysis, hardness testing, scanning electron microscopy and energy dispersive spectroscopy.

The shafts were manufactured from ASTM A276, Type 410 stainless steel in the quenched and tempered condition. The crack on the Farley shaft ran longitudinally and was approximately 16.7 cm (6.6 inches) in length. The crack on the Ginna shaft was approximately 7.6 cm (3 inches) in length and ran almost perpendicularly to the shaft's long axis. The second Ginna shaft had no visible cracks. Hardness measurements of the shafts revealed that the Farley shaft hardness values ranged between Rc 41-44.5, the cracked Ginna shaft values ranged between Rc 42.9-45, while the uncracked shaft's hardness was Rc 36-44.6. The cracks were intergranular and occurred on prior austenite grain boundaries. No evidence of corrosive species or fatigue contribution was seen. This cracking is considered to be an intergranular stress corrosion cracking phenomenon resulting from a high hardness/susceptible material in a pressurized water environment.

Subject
Water, Materials, Intergranular stress corrosion cracking, Valves, Analytical techniques, Hardness measurements, Intergranular cracking, Stainless steel, Fracture, Hardness, Cracks, Heat treatment, Stress corrosion cracking
© 1987 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).
1987
Association for Materials Protection and Performance (AMPP)
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