Lessons learned: Fuel oil tank vent pipes should be inspected regularly

by The Editorial Team

December 30, 2021

In its most recent Good Catch series, the American Club, provides lessons learned from corroded or damaged fuel oil vent pipes in cargo holds.

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The incident

A bulk cargo vessel experienced a serious problem when some of the clay cargo entered fuel oil tanks through holes in the fuel oil tank vent pipes located in the cargo holds.

The problem was first noticed by the engineers when the fuel oil filters became heavily clogged with what appeared to be cargo. After the engineers shifted to a different fuel oil tank, the problem stopped.                        

After offloading the clay and cleaning the cargo holds, the vent pipes were closely inspected in each cargo hold.

Probable cause

Several fuel oil vent pipes were found to have been holed by severe corrosion while others were so severely corroded and at risk of failure. The holes were found in locations that were not easily accessible. Analysis of fuel oil in the bunker tanks confirmed contamination from the cargo.

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The discovery of contaminated fuel and the holes in the fuel oil vent pipes necessitated an unscheduled repair period. The contaminated fuel had to be disposed of properly. The contaminated fuel oil tanks had to be cleaned and made safe for hot work. The corroded vent pipes had to be replaced. The vessel was out of service for over 2weeks.

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Luckily, the problem was discovered before any machinery was damaged. However, the cost to dispose of the contaminated fuel, clean the affected fuel oil tanks, make the necessary repairs and replace the contaminated fuel cost well in excess of $100,000 and the vessel was out for service for more than two weeks.

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While it may have been unlikely that this particular fuel contamination could have damaged machinery, rapid clogging of the filters could have unexpectedly shut down one or more engines. Had the cargo been soluble in fuel oil and of a highly abrasive nature, the fuel oil purifier and associated filters may not have been able to prevent the abrasive cargo from reaching and damaging the engines. Furthermore, had the cargo been sensitive to the fuel oil or fuel oil vapors, cargo damage could also have incurred.

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Lessons learned

• Fuel oil tank vent pipes should be inspected regularly and thoroughly to ensure that: the fuel is not contaminated by cargo; cargo is not contaminated by the fuel or fuel vapors; and fuel vapors do not enter spaces not designed for fuel vapors.

• Particular attention should be paid to fuel oil tank vent pipes that are: vulnerable to damage during cargo operations; or partially hidden or less visible, especially if corrosive or abrasive cargos are to be loaded or have been carried.

• A corroded fuel oil tank vent pipe in one cargo hold should immediately raise concerns about similar vent pipe problems in other cargo holds.