When a bulk carrier was at sea, high exhaust gas temperatures were noted and several piston rings were found broken after investigation. The rings were renewed and engine restarted. After some hours of running the main engine it malfunctioned once again and more broken rings weer found. The broken rings were again replaced, but then the engine failed to start and the vessel had to be towed to port. A considerable number of piston rings were broken. Excessive wear of liners and piston crown grooves were also found. The fuel oil used was suspected to be a probable cause, although the quality of it was not found abnormal according to the test report.
During investigations the air pipes leading through the cargo holds to the fuel oil tanks were found severely holed/wasted in places. Most of the affected pipes were found within the cargo holds and the damaged parts were fitted very close to the transverse bulkhead structure.
The vessel had carried different cargoes previously, and Alumina was one of them. Subsequent analysis of fuel oil samples from the tank confirmed a high percentage of Alumina (Al2O3) (bauxitt). As a result of the above all main engine liners and crowns were renewed and holed/wasted air pipes were replaced.
The Alumina has a very high hardness, and may act as grinding powder of various fineness when entering the fuel oil system. This can cause serious damage to the fuel oil system as well as to the pistons and cylinder liners.
The fuel oil separators are only designed to remove specific quantities of this type of substances in the fuel oil, not massive contamination. Thus the primary cause of the damage was suspected to have been abrasive cargoes entering the fuel oil system through the holed/wasted air pipes.
Routing of the air pipe close to the transverse bulkhead
Wasted air pipe
In a similar case upon examination of the main engine, certain parts were found to be heavily worn due to the presence of aluminum particles in the fuel. Samples taken from the engine itself showed contamination in the order of 200 ppm, while oil samples taken from the service tanks contained up to 2,000 ppm, whereas the engine manufacturers’ upper limit was 30 ppm. Aluminium particles have a highly abrasive effect on moving engine parts, and in this case severe damage was sustained by pistons, liners, fuel pumps etc.
In most cases where wastage has been found in air and sounding pipes passing through cargo holds, there is a risk of contamination of either the cargo, or as in this case the contents in the tanks to which the pipes belongs. Due to the fuel contamination the engine requires the fitment of many new parts under manufacturer supervision, while pipelines have to be flushed through and cleaned prior to departure. Fuel oil tanks should also be cleaned out.
In order to avoid occurrence of similar situations:
- During operation of the vessel owners and surveyors should pay due attention to examining (visual, UTM, hammer) air pipes in detail, in particular where it is located close to other structures like ship side, bulkheads etc.
- During the design phase of the vessel pipe runs should be placed at sufficient distance to other structure to provide easy inspection of the whole circumference of the pipe.
It should be kept in mind that in most cases where wastage has been found in air and sounding pipes passing through cargo holds, there is a risk of cargo contamination. However, as shown in the incident analysed above the reverse situation, the contamination of fuel oil tanks through damaged sounding pipes, is also possible and can cause serious problems.
Source: DNV
Officer of the Watch 
Leave a Comment