MARINE FUEL OIL,ITS ISO STANDARD,ANALYSIS AND CORRECTIVE ACTION

ISO 8217 specifies the requirement for petroleum fuels for use in marine diesel engines and boilers prior to appropriate treatment before use. There has been total of five editions of ISO 8217 till now.The most widely used specification is still ISO 8217:2005 i.e. the third edition. Fourth edition of ISO 8217 is ISO 8217:2010.

SALIENT FEATURES:-

• It provides for better fuel quality
• Improvement of the safety levels in shipboard operation 
• Reduced engine damage and consequential risks

It specifies 4 categories of distillate fuel,one of which is for diesel engines for emergency purpose, and 6 categories of residual fuel. 

New features added in distillate fuel are:-

• Lubricity:- Fuel has to possess lubricity if the sulfur content is less than 0.05% to avoid fuel pump wear down
• Oxidation stability:- This minimizes addition of bio-diesel to reduce storage risk on board vessel.

New features added in Residual fuel are:-

• CCAI:- It avoids uncharacteristic density viscosity relationship leading to ignition problem.
• Sodium: - It limits any sea water contamination and restrict high temperature corrosion.

New features added to both distillate and residue :-

• Acid number:- It minimizes damage to diesel engine fuel injection for high acidic compounds.
• H2S   :- Provides improvement margin for safety by reducing risk of exposure to ship board crew.

THIS H2S FEATURE HAS COME IN FORCE FROM 1ST JULY 2012. AND THIS BRINGS THE FIFTH EDITION OF ISO 8217 i.e. ISO 8217:2012. IT BECAME AVAILABLE ON 15TH AUGUST 2012. IT ADDS TEST METHOD FOR H2S CONTENT. 

Changes in 2010 edition from 2005 edition:-

• Some new grades were added where as some old were removed
• Sulfur limit was excluded as now they are controlled by statutory requirement
• Ash limit value for residual fuels were reduced
• Vanadium limit for RMG 380 increased
• Vanadium for all other grades were reduced
• Cat-fines limit was reduced from 80 to 60 ppm

Fuel analysis is carried out in shore laboratories. They check for all the characteristics as prescribed in the ISO standard. Following are some of the properties which can be found outside the limit and their corrective action:-

1. Density:- Max limit is 991 kg/m3 ( for RMG grade) and 1010 kg/m ( for RMK grade). Increased density will affect the centrifuge operation. It will be ineffective in water separation. It will affect the engine performance.

      If received bunker density is more than the specified limit inn RMG grade then its better to de-bunker it unless vessel has ALCAP purification system.

2. Viscosity:- At 50 deg Celsius common viscosity for residual fuel is 180 cst or 380 cst, but it can go up to 700 cst. It affects pump ability, preheating, settling/separation, atomization and combustion. Increased viscosity is not a problem unless vessel has got sufficient heating arrangements. Analysis report will state the correct amount of temperature to which the fuel should be heated to maintain the viscosity as prescribed the engine manufacturers. 

3. Sulfur:- It is now guided by the statutory requirements. If the value comes more than maximum specified by the regulation, bunkers will need to be debunkered.  However if the sulfur content comes too low then correct grade of CLO will have to be used to avoid cold corrosion or alkaline deposits on the piston top land.

4. Cat-fines:- Max limit is 60 ppm. The main problem with cat-fines are that they are not always evenly distributed and sometimes are accumulated in sediments. They are very difficult to remove as they are attracted to water droplets. To minimize the cat-fines key feature is to remove them by separation in separators. For that always maintain the purifiers according to manufacturer's recommendation. Ensure that separation is being carried out efficiently by minimizing the feed and optimizing the temperature. Never ever by-pass the fine filters given in the fuel line. It is better to keep one extra clean set and change them at regular interval. Keep the fuel at above 70 deg in the settling tank and drain settling and service tanks at regular intervals.

5. Water:- It is allowed up to  0.5% V/V for residual fuel and 0.3% for distillate fuel. Fresh water contamination will lead to corrosion damage to fuel pumps and injectors. How ever serious problems arises if the water content is sea water. It becomes more serious because of sodium content in sea water. Sodium along with vanadium in 1:3 can cause high temperature corrosion. It is recommended to remove the water content by centrifuge separation, giving sufficient setting time in settling tanks, Sufficient heating in settling tanks and by frequent draining of the settling/service tanks.

6. Ash:- Recommended value is 0.15% m/m for residual fuels. High ash content causes deposits on the piston surface, exhaust valves, turbocharger blades and boiler tubes. During combustion metal content is converted into solid ash which after certain temperature become partly fluid thus adhering to the all parts stated above causing corrosion problems. Ash removal is recommended by frequent cleaning of the parts. Turbochargers should be regularly dry washed or wet washed. Boilers should be frequently soot blown and cleaned with water.