New IMO-PAS "Publicly Available Specification" confirms risks of incompatibility when VLSFO is used.

ISO 8217 doesn`t regulate density and viscosity of VLSFO.

Since the new MARPOL 2020 sulfur cap regulations were published experts are warning to the risks of incompatibility when Very Low Sulfur Fuel Oils (VLSFO) are used.

The fears are:

1.)Blended VLSFOs are a mixture of minimum 2 different fuels like distillate and HFO with different densities and viscosities.

Due to these different densities and viscosities the blended VLSFO will fall apart during storage in the Tanks because the components of higher density and viscosity are bigger and heavier than the light and small distillate droplets. Due to force of gravity the bigger and heavier HFO components will separate and sink down to the bottom of the tanks.

2.) Recently a CEO of a leading Shipmanagement said in an interview:

" If your C/E puts a low sulfur fuel on top of another low sulfur fuel and they are incompatible you can have a catastrophic engine failure, you can have vessel breakdown at sea, you can have all sorts of huge problems"

Since it is impossible always to empty the Tanks before you refill them with new VLSFO it will happen that there will be a mixture of two different VLSFO supplies with different densities and viscosities in one tank.


These fears are now confirmed by recently published  IMO PAS 23263-2019.

In the PAS it is confirmed that the VLSFOs will be a blend of different fuels with a density of abt. 870kg/m³ and 997kg/m³.

It is also stated in the PAS under item 11:

" Already 100s of VLSFO samples have been tested and typically viscosity falls in the range of 10 to 380 cSt and density from 870 to 991 kg/m³.


This proves that the fears are founded that the delivered VLSFOs will be incompatible and that two different VLSFO in one tank will be incompatible as well.

The new ISO says that the supplied VLSFO must comply with the max. 0,5% sulfur content regulation but in the ISO 8217 specification the density and viscosity of the VLSFO are NOT regulated.

Therefore it is very likely that VLSFO of maybe 870kg/m³ will be mixed with existing VLSFO in the tanks with a density of 997kg/m³.

IMO and ISO says that the crew has to manage such problems.

These incompatibility problems easily can be solved if the VLSFOs are homogenized via S.I.T`s CD92 units.

If you want to hear how it works, please feel free to contact us. We will send more information material or visit you at your premises and do a technical presentation if requested.


Heino Stache, MD S.I.T GmbH


Skype: heinzicd92


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