Undetected corrosion and wear led to an equipment failure on a cargo ship while offloading cargo last year in Houston, the National Transportation Safety Board (NTSB) said.
On July 23, 2022, the cargo ship Thorco Basilisk was offloading a wind turbine component at the Greensport Terminal on the Houston Ship Channel when the hoisting wire rope on one of the ship’s cargo cranes failed, causing the component to drop onto the vessel’s cargo hold tween deck.
No injuries were reported. Damages to the ship and cargo were estimated between $3-5 million.
An examination of the hoisting wire rope showed significant external corrosion and wear; however, the visible signs of external corrosion could not be fully seen until the grease on the rope was removed.
While annual surveys were performed on the wire ropes, the surveys primarily involved visual inspections to look for wear and would not have identified the underlying corrosion below the grease.
While the hoisting wire rope had been in use for 9 years, still within the standard 10-year period of use, a postcasualty examination found “the wire rope was near the end of its service life and probably should have been discarded.”
The operating company has since updated their planned maintenance system to require crane wire rope replacement every 5 years.
“Saltwater and humid ocean air cause corrosion of metals, presenting challenges for the maintenance of high-strength steel wire ropes on vessels,” the report said. “A deteriorated wire rope directly affects a crane’s ability to safely and reliably handle loads up to its rated capacity (safe working load). Therefore, diligent inspection, maintenance, and management of wire ropes are essential. Working wires should be changed at recommended intervals, or more frequently, depending on operating conditions and use.”