Pollution Risk from Overboard Pipes Routed Through Fuel Oil Tanks
The West of England previously advised Members of a pollution incident involving the failure of a deck scupper drain pipe routed through a fuel oil tank. During bunkering, fuel entered the damaged pipe and escaped overboard through an undetected defect once the fuel level reached the height of the crack.
There have been two more pollution incidents arising from a similar arrangement. In both cases, an Oil Discharge Monitoring Equipment (ODME) overboard discharge pipe was routed through a bunker fuel tank before terminating at the ship’s side.
Although all three incidents involved tankers, the recurrence of this failure mode across unrelated vessels highlights a broader risk. The incidents demonstrate that seemingly isolated overboard piping can create a direct pathway between an oil-containing tank and the sea if the pipe loses integrity.
ODME Overboard Pipe Failures
In both recent cases, the section of ODME overboard discharge piping located within a bunker tank failed. Bunker fuel entered the pipe and escaped directly into the sea.
Importantly, the discharge occurred despite the ODME overboard valve being closed and the removable spool piece having been removed inside the vessel. These measures effectively isolated the inboard ODME system but did not isolate the section of pipe extending through the bunker tank to the vessel’s side.
The apparent causes of failure differed. In one case, corrosion and wastage were believed to be responsible. In the other, a crack developed along a welded seam from the vessel’s original construction.
While the causes differed, the outcome was the same. Once the pipe wall lost integrity inside the bunker tank, the pipe became an uncontrolled pollution pathway allowing fuel oil to escape directly overboard.
Why These Arrangements Warrant Attention
An overboard pipe routed through a bunker or cargo oil tank can create a single-point failure with potentially significant pollution consequences.
Depending on its location and service, the pipe may be exposed internally to water and externally to heated fuel oil. Corrosion, wastage, vibration, thermal cycling and local stress concentrations may all contribute to deterioration over time.
Inspection may also be challenging. Pipe sections located within fuel or cargo tanks can be difficult to access and examine effectively during routine inspections. There is also no practice of pressure testing of such pipe sections. As a result, corrosion, cracking or localised wastage may remain undetected until failure occurs.
The incidents highlight an important limitation of that piping arrangement. If a defect develops in a section of pipe located between the isolation overboard valve and the vessel’s shell, fuel oil may enter the pipe downstream of the closed valve and continue flowing directly overboard. Such a piping arrangement should not be assumed safe simply because the associated system has been isolated or is no longer in service because closing the overboard valve does not prevent pollution.
Recommended Actions
The West of England strongly recommends that Members and ship managers review the overboard piping arrangements across their fleets, giving particular attention to any overboard pipe that passes through a bunker or cargo oil tank and is capable of creating a direct route between a tank containing oil and the sea following loss of pipe integrity.
While the known incidents involved tankers, Members operating other vessel types may also wish to verify whether similar arrangements exist on board their vessels.
Members may wish to consider the following:
Identify Vulnerable Arrangements
Review piping diagrams, tank plans, construction drawings and onboard arrangements to identify any overboard pipe routed through a bunker or cargo oil tank.
Verify Pipe Condition
Inspection should cover the complete pipe length within the tank, including welded seams, joints, supports and areas susceptible to vibration, stress concentration or localised corrosion.
Assess Inspection Limitations
Consider whether the pipe can be effectively examined using routine visual inspection and thickness measurement techniques. Where access is restricted, alternative examination methods may be appropriate.
Review Isolation Arrangements
Confirm whether existing isolation measures effectively isolate the entire overboard pipe, including any section located downstream of the isolation point and upstream of the vessel’s shell plating.
Review Maintenance and Inspection Programmes
Planned maintenance systems should identify and specifically address concealed or difficult-to-access overboard pipework routed through oil tanks. Inspection frequency should take into account the pipe’s age, operating environment, material and accessibility.
Consider Alternative Pipe Routing
Where practical, overboard piping should be routed through void spaces or other non-oil compartments rather than through fuel or cargo oil tanks. For existing arrangements, Members may wish to consult their Classification Society regarding possible retrofit modification. Similar considerations should be addressed during the design and construction stages of newbuildings.
Report Defects to Class
Any identified cracking, defective welds, corrosion, wastage or other deterioration should be reported promptly to the vessel’s Classification Society. Repairs and modifications should be carried out under approval and supervision of Class.
Consider Interim Risk Controls
Where vulnerable arrangements remain in service, Members may wish to consider limiting maximum tank filling levels as an interim measure to reduce pollution risk.
Prepare Emergency Isolation Measures
Ship-specific contingency plans should address how leakage from an overboard pipe routed through an oil-containing tank can be stopped or controlled. Measures may include reducing tank levels, transferring oil to alternative tanks, sealing the external outlet where practicable and arranging temporary repairs under Classification Society oversight.
Emergency Response Considerations
Where leakage is suspected, prompt action is essential. The vessel should activate its shipboard pollution response procedures, notify the relevant parties, and take immediate steps to reduce or eliminate pressure acting on the damaged pipe.
During an active pollution incident, priority should be given to stopping or reducing the discharge. Operational concerns associated with fuel transfer, including compatibility considerations, should be balanced against the environmental consequences of allowing the leak to continue.
Any temporary plugging or sealing arrangement should be regarded as an emergency control measure only. Permanent repairs should be undertaken following safe tank preparation and in accordance with applicable Classification Society requirements.
Key Lessons
These incidents demonstrate how the failure of a single pipe section can bypass conventional pollution-prevention barriers when overboard piping passes through an oil-containing tank. A closed valve or disconnected spool piece may not prevent pollution if the defect develops downstream of the isolation point.
Where practical, eliminating the direct interface between oil-containing tanks and overboard piping remains the most effective long-term risk-control measure. Effective inspection, maintenance, emergency preparedness and appropriate piping arrangements all play an important role in preventing similar incidents.
Members requiring further information can contact the West of England Loss Prevention Department.