To,

The Superintendent Engineer

MV Alexa

ABC Pvt Ltd

Singapore

Subject: Report on Damage Suffered by Main Engine Exhaust Valves

Dear Sir,

I am writing to inform you about the premature failure of three exhaust valves in the main engine over the past four months. Below is a detailed report addressing the issue:

• The issue first became evident in Unit No. 3 of the main engine, where we observed a sudden increase in the exhaust temperature. The deviation was more than 70 degrees compared to the other units. This abnormality was confirmed by the local temperature gauge.
• Upon conducting a main engine performance analysis, it was noted that both Pcomp (compression pressure) and Pmax (maximum pressure) were lower than normal, suggesting a potential exhaust valve leak.
• During the next port call, we opened the exhaust valve of Unit No. 3 and discovered significant cracking and corrosion at the seating face. Subsequent inspections of the exhaust valves in Units 6 and 7 revealed similar issues, confirming a pattern of damage across multiple units.

• Recognizing that the damage might be due to the poor quality of fuel oil, particularly high levels of vanadium and sodium, we immediately reduced the engine's speed and load to lower the exhaust temperature and mitigate further hot corrosion.
• We conducted inspections of the exhaust valves in other units, replacing the affected valves with overhauled spares.
• The fuel oil in use was switched to an alternative tank with lower vanadium and sodium content, based on available laboratory analysis. Additionally, we sent samples of the recent oil (fuel that caused the issue) to a laboratory for testing, as the relevant report was missing from our files.

• The combustion of fuel oil containing high levels of vanadium and sodium can lead to the formation of sodium vanadate, which has a low melting point of around 450°C. These molten compounds are highly corrosive and can attack components such as exhaust valves and piston crowns.
• Fuel oil with a high asphaltene content may result in incomplete combustion, leading to increased deposits in the combustion chamber and exhaust gas system, further damaging exhaust valves and their seats.
• Scale deposits within the cooling pockets of the exhaust valves can reduce their cooling efficiency, leading to overheating, material degradation, and hot corrosion.
• Poor combustion timing or quality, such as late or incomplete combustion, can lead to higher exhaust temperatures, contributing to hot corrosion.

• Ensure the use of fuel with minimal vanadium, sodium, and asphaltene content. Laboratory analysis of bunker fuel should be carefully retained onboard for reference.
• Regular maintenance of fuel injection devices is essential to prevent late combustion and the associated rise in exhaust temperature.
• Adequate cooling of exhaust valve seats should be maintained through proper treatment of cooling water and regular cleaning of cooling pockets to prevent scale build-up
• When laboratory reports indicate high sodium and vanadium levels in the fuel, appropriate corrective actions should be taken before and during engine operation to prevent damage.

Please feel free to contact me for further discussion or clarification on the matter.

Yours sincerely,

[Your Name]

Second Engineer

MV Alexa