Whiting Corp has alerted the US Nuclear Regulatory Commission to the risk of cracking on 20 single-failure proof cranes in US nuclear facilities.

In the alert, Whiting recommended the cranes, mostly capacities of 125 US tons (113t) be inspected and de-rated to 50% of load capacity until the cranes can be evaluated and/or upgraded. The recommended fix is to add one or two reinforcing plates.

Whiting alerted the NRC and the utilities operating the cranes with the affected design. Visual inspection after the notification did not reveal any cracks, Whiting president and CEO Jeff Kahn told Hoist.

Omid Tabatabai, NRC reactor systems engineer also said that no cracks or failures had been reported because of overstress conditions. But he added that the NRC does not require the results of the examinations to be formally reported.

The problem was noticed when Whiting was doing a design study for a recertification of a crane at a nuclear facility, Kahn said. ‘In our review, it was determined that the stress within a weld in the hoist equalizer structure could result in safety factors below the recommended value when the crane is used at full nameplate capacity.’ He said that the condition was unlikely to fail immediately, but after a ‘high number’ of load cycles might result in fatigue cracking.

He said that the analysis was probably not commonly done when the cranes and were installed in the 1960.