On 21 August 2023, the vessel FT Sturla was moored at the port of Genoa, Italy, to unload a low-sulfur fuel oil (LSFO) cargo. At 0700, the chief officer and the loading master held a ship-shore safety meeting. They agreed that the maximum pressure to be maintained at the vessel’s manifold throughout the unloading period would be 7.0 bar, reports the Marine Safety Investigation Unit.
About the incident
Following necessary checks and preparations, the unloading operation commenced at 1030. The cargo was pumped out from cargo tank nos. 5 port and starboard, through the common pipeline manifold valve on the starboard side. After confirming that everything was in order, the unloading pressure gradually increased to 6.8 bar at the vessel’s manifold.
However, at 1230, an able seafarer noticed an oil leak from the common pipeline on the port side and immediately notified the cargo control room (CCR) via his portable radio. He then pressed the emergency shutdown button at the port side manifold. The chief officer, who was in the CCR at that time, instructed the crew member at the vessel’s manifold to shut the starboard manifold valve. The master and the terminal were informed of the oil leak, and the general alarm was activated.
Oil Spill Containment
The master notified the vessel’s managers and relevant authorities, while the crew implemented oil spill contingency measures. An oil boom was rigged around the vessel to prevent the spread of oil in case any spilled overboard. Crew members also began containing and collecting the leaked oil on board. By 1300, representatives from a shore cleaning company boarded the vessel and assisted with the clean-up operation, which was completed by 2300. An estimated 500 liters of LSFO had spilled onto the vessel’s deck, all of which was contained on board.
Resumption of Cargo Unloading
At 0024 on 22 August, following approval from the classification society and local authorities, cargo unloading resumed.
Investigation of the Oil Spill Cause
During the investigation into the oil spill, it was discovered that one of the top cover bolts of a blind flange valve from cargo tank no. 5 starboard on the port side manifold had failed. The cargo being pumped out leaked from the top of the valve due to the fractured bolt. The bolt had fractured at the bottom threaded portion.
Laboratory Analysis of the Broken Bolt
The broken bolt was sent for metallurgical analysis. It was made from austenitic stainless steel grade AISI 304L, as per the valve’s specifications. The analysis involved various tests including visual inspection, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and a Vickers hardness test.
The fractured surface exhibited an irregular, faceted morphology, free from plastic deformation. Corrosion pits were observed on the side wall of the first thread near the fracture. Further, SEM and EDS analyses detected deposits of elements including oxygen, chlorine, and sulfur, indicative of corrosion.
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Source: Marine Safety Investigation Unit
