Page 443 - Failure Analysis Case Studies II

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I Casing I

I!
Shaft

Original Design

I I Casing I

Shaft

New Design

Fig. 1. Original and new design of the first stage sealed area.

that the presence of copper components in the secondary cooling system of a NPP could affect the
integrity of the steam generator tubes [l]. Due to this possible contamination, the bronze bearing
was replaced by a sleeve and a bearing (Fig. 1). The sleeve was made of chromium-plated martensitic
stainless steel AIS1 416 and the bearing was made of graphite-nickel. The failure occurred with
this new design.

2. Visual inspection after the failure

Figure 2 shows the appearance of the shaft and the chromium-plated sleeve after the failure.
The marks existing in the sleeve indicate that both the upper part and the lower part of the sleeve
have been displaced from their initial position in the shaft. In the case of the upper part of the
sleeve this fact is clearly confirmed by the displacement existing in the screw footprint. The upper