Unplanned release of 960 litres of hydraulic oil

A member has reported an incident which there was an unplanned release to the environment of 960 litres of hydraulic oil. The incident occurred during piling operations when a hydraulic hose parted from the hammer being used for the operations. After successfully installing a driven pile, the hammer was removed from the pile fast frame and the vessel transited to the next pile being installed. As per company procedure the hammer was raised 50 metres above the seabed and suspended on the vessel main crane. During the transit the ROV pilot noticed the main hammer supply umbilical line, which runs from deck to the hammer, tighten rapidly. An ‘all stop’ was called and on closer inspection by the ROV it was confirmed that oil was leaking from the umbilical. The piling contractor isolated the hose and oil tank supplying the hammer. Both the hammer and its supply umbilical were then recovered to deck.

Our member’s investigation found that the crane driver had unintentionally activated the crane controls resulting in the crane paying out the hook at 10 metres per minute. This caused the hammer to lower and in turn tightened the hose/umbilical running from the vessel to depth. The effect of the hammer being lowered caused the hose to tighten and part from the hammer at the coupling and also snapped the restraint chain in the process. This resulted in the loss of 960 litres of hydraulic oil.

The following mitigation measures were identified following the incident:

• Piling contractor to evaluate the use of biodegradable oil for future use;
• A standby switch for enabling crane controls to be activated when the crane was in prolonged periods of inactivity.

Supervisor to inform crane driver when crane is likely to be inactive for a long period; . During periods of crane inactivity random communications checks to be carried out with the crane driver; . A reminder circulated that hydraulic hoses should be immediately isolated in the event of a loss in pressure; . ROV to be effectively positioned to observe the hammer and hydraulic hoses; . Clear and robust communications system installed to the pile spread control cabin (VHF and telephone back up); . Pile spread supplier to investigate the use of a self-closing safety valve and alarm system; . A sensor in the oil supply tank set to minimise the loss of oil (vessel movement taken into account); . High-Vis tape/paint to be attached to the umbilical / hose to aid ROV visual identification.

Members may wish to refer to the following similar incidents (key words: release, spill, oil, hydraulic):

• Oil spill in port whilst discharging waste oil
• Ruptured hydraulic hoses