This compatibility/stability test is a modified version of the ASTM D4740-94 method. The test methods list two separate procedures for predicting stability of residual fuel oil and the compatibility of residual fuel oil with a blend stock.
The Zematra test set consists of:
– sturdy case
– oven plus filterpaper holder
– magnetic stirrer plus heater
– Erlenmeyer 100 ml
– reference spot sheet ASTM D2781
– box of chromatographic paper
– electric digital thermometer
– pair of tweezers
Why test for compatibility and/or stability of fuel:
Stability of the fuel is very important as instable fuel can lead to separation in the bunker tanks, blocking of filters and separators and even can lead to a power failure. Also you will have a lot of slob discharge and the removal of this will cost a lot of money.
In earlier times, with a less demand of all kinds fuels and gasses the refining process was quite simple. Just heat up the crude oil and in the refining column you got separations of the fractions. On the top of the column the lightest ones going down for the heavier fractions. In this case you always received a straight run bunker with the required viscosity, so testing for stability was not really required. Now a days with the very larger demand the refinery process have changed a lot as even out of the heavier parts lighter parts are taken out by means of e.g. cat cracking. The bunkers you are receiving now a days are no straight runs anymore, but a mixture of very heavy residual fuel and lighter fractions to come to the ordered viscosity. There is a change that the mixtures received for getting the right viscosity are not stable which can lead to the above mentioned problems. To avoid this a simple test on stability can/will save you a lot of time, annoyance and money.
It is recommended not to put the fresh received bunker into a bunker tank with remaining fuels. When you have to do this a test for compatibility is necessary. The two fuels can be incompatible to each other which can lead to the above mentioned problems.
