Corrosion Led to Failure in Heavy-Lift Crane Operation

In a report by the National Transportation Safety Board (NTSB), it was revealed that unnoticed corrosion and wear led to the snapping of a wire rope during the lifting of a wind turbine part on the Thorco Basilisk, a heavy lift vessel, last year. This incident caused damages estimated between $3 and $5 million.

The event unfolded on July 23, 2022, when a crane's wire rope on the Thorco Basilisk broke as it was unloading a 68-ton wind turbine nacelle at Greensport Terminal in the Houston Ship Channel.The nacelle plummeted onto the ship's tween deck in the cargo hold, and the crane's block smashed through the nacelle's top. Thankfully, there were no injuries or environmental harm reported, but the vessel and the nacelle suffered significant damage, amounting to $3-5 million.

According to investigators, the 1.5 inch wire rope was obviously corroded and worn externally. Approximately 60% of the rope sections on either side of the location where the rope had parted exhibited "significant levels of external corrosion”. Nevertheless, removing the grease from the rope allowed the visible signs of external corrosion to be seen. During relubrication maintenance ("slushing"), the crew left the old grease on their wire ropes, since removing the old dried-out lubricant would be impractical without special equipment. 

Despite being within its standard 10-year lifespan, the NTSB concluded that “the wire rope was near the end of its service life and probably should have been discarded.”

The NTSB noted, “Saltwater and humid ocean air cause corrosion of metals, presenting challenges for the maintenance of high-strength steel wire ropes on vessels. A deteriorated wire rope directly affects a crane’s ability to safely and reliably handle loads up to its rated capacity.”

In response to the NTSB's recommendations, Auerbach Marine, the vessel operator, revised its maintenance protocols, now mandating the replacement of crane wire ropes every five years.grcf