"after all, we are talking about heavy fuel oil" begs a response. One of the main concerns with heavy fuel oils is contamination. That and quality. What was once acceptable nis increasingly less so.
The working assumption with engine fuel processing is that, between the refinery and the engine, contamination will occur. There are three types of problem here, one is with contamination as a natural result of the handling e.g. water, sea water etc. Another is unusual contaminants of unknown origin (reequiring expert analysis to track down the cause and source, such as polythenes) and then there are the acts of criminal adulteration such as using the fuel as a handy dumping ground for waste chemicals such as dry cleaning fluids.
Most fuel circuits are designed to handle the routinely expected contaminants but the unusual will cause problems.
I would suggest that since oil quality and its affect on engines is a hot topic in the industry that associations such as the IBIA (
offer advice. There are also the increasingly stringent problems of pollution control. Plus engines are changing all the time.
However, if the zinc coating is a commonly encountered situation then i would expect the engine manufacturers (via CIMAC working groups
may also have an informed opinion. Also laboratories such as Viswa