Hydraulic Oil Leak to Sea from Downline Fitting

What happened

During decommissioning, cutting work was being conducted using a diamond wire saw. A third-party supplier’s technician noticed a sudden drop in pressure, and it was discovered that 100 litres of hydraulic oil had been released to sea.

The downline was disconnected, recovered to deck and inspected. The leak was coming from a BSP fitting 40m from the diamond wire saw connection point.

Before the incident, the system had been deployed following deployment checks using a dedicated form for hydraulic checks. The downline was in a “figure 8” on deck and subsea as per procedure and risk assessment.

What was the cause?

Our member identified the following:

• Immediate Cause: the fittings became slack: It is not known when the fitting slackened. It is suggested that a combination of handling on deck, energising and de-energising were contributory factors;
• Underlying Cause: checks were omitted: Fittings were not checked for tightness when overboarding the diamond wire saw and downline;
• Root Cause: the checklist used did not prompt the check of all fittings for tightness, only visual checks.

Our member took the following actions

• Added additional supports on fittings attached to the tugger over and above existing controls;
• Ensured that physical checks for tightness were conducted;
• After a review of feasibility, the bight of the hydraulic hose was removed;
• Checklist was updated to include checks for the tightness of fittings;
• Incident was shared with other users of similar equipment.

Members may wish to refer to:

• LTI: diver injured during water jetting operations [threads came loose]
• Dropped object near-miss: Antenna parts worked loose and fell to deck
• Lightning Conductor Fell – Dropped Object Near Miss [The potential for the lightning conductor to become unscrewed was not recognised, and the connection is not easily visible during regular drops inspections]