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Considering that use of cobalt alloys should be avoided as far as possible in PWR components, a programme aimed at establishing the performance of cobalt-free alloys was performed for valve applications, where cobalt alloys are mainly used. This report presents the work done in this field. Two types of cobalt-free alloys were selected: Ni-Cr-B-Si and Ni-Cr-Fe alloys. The behaviour of cobalt-free valves was evaluated in comparison with cobalt valves in a special PWR test loop. At the end of the loop test programme, which included endurance, thermal shock and erosion tests, cobalt-free alloys which are candidates to replace cobalt alloys are proposed for each valve type (globe valve and swing check valve). The following results were established: (i) Colmonoy 4-26 (Ni-Cr-B-Si alloy) and Cenium Z20 (Ni-Cr-Fe alloy) deposited by plasma arc process were found suitable for use in 3" swing check valves; (ii) for integral parts acting as guide rings, Nitronic 60 and Cenium Z20/698 were tested successfully; (iii) for small-bore components such as 2" globe valves, no solution can yet be proposed; introduction of cobalt-free alloys is dependent on the development of automatic advanced arc surfacing techniques applied to small-bore components.

Additional information

Authors: BENHAMOU C, Framatome, Paris (FR)
Bibliographic Reference: EUR 14568 EN (1992) 20 pp., FS, ECU 6
Availability: (2)
ISBN: ISBN 92-826-4964-4
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