For marine work, we have tank and pipe to store & transfer oil. Now this topic will search about the effect of Zinc coating for tank and pipe in fuels oil. The concentration of zinc in a fuel was found depend upon the acidity of the fuel and upon the length / time of contact between fuel with zinc. In an investigation, the maximun concentration of zinc that might be found in a fuel stored for long time with typical tank proteced by zinc coating is in the order of magnitude of 20 milligrams per 100 millilitters ( about 230 parts per million ). It was conluded that the use of zinc coating should be avoid / prohibited for marine fuels.
The coating contain particacles of metallic zinc which are thought to act sacrificial electrodes. The zinc lost from such sacrificial electrodes may entre the fuel in this case. The fuel-soluble zinc compound can deposit in burner and engine ( injector ). Insoluble zinc compound can plug filter, strainer and other restricted openings. I either case, the presence of the zinc compound necessitates additional maintenance of the fuel system and could even result in operation casualties. Some fraction of these quantities would deposit in engine or boiler, restricting passages, leading to hot spots or valve burning and creating operating problem.
- Zinc coating are not suitable for use in fuel tank becasue zinc levels in the fuel can become appreciable.
- The amount of zinc in a fuel in contact with zinc coating reaches a maximun in 2 to 4 weeks and thereafter declines slowly to about 80% of its maximum value after 20 weeks.
- The rate of zinc acquisition by fuel in contact with zine coating: is increased in the presence of sea water; is increased by an increase in the acidity of the fuel; is increased by increase in the area of the coating in contact with the fuel; is lees when the fuel is in contact with an old coating that has been contacted with many batchs of fuel than it is in contact with a freshly applies coating.
- Zinc coating simultaneously in contact with both fuel and sea water tent to flake.
- Prohibit the use of inorganic zinc coating in fuel on new construction to eleminate a source of zinc compound deposits in boiler and engines and thus reduce maintenance and repair costs.
- If fuel must be stored in existing shipboard tank with zinc coating never allow the fuel to memain in the tank any longer than necessary.
- Keep the quantity of the free sea water in contact with the fuel asa small as possible with the available stripping system.
Breakdown of the fuel:
One of the most pressing issues with zinc within diesel fuel is the way it interacts with the fuel itself, causing it to break down more quickly than it would under normal conditions. If the temperature is kept stable at around 68 degrees F the fuel can remain stable for around 12 months or even longer, but the introduction of zinc within the fuel causes it to break down down faster. As diesel begins to age and break down it creates harmful sediments and a sticky substance known as gum which can then block the reaction of diesel with oxygen, thus affecting the overall efficiency of the engine and eventually leading to complete engine shutdown unless frequent filter changes occur.
When zinc is introduced to diesel fuel it begins to break down into unstable compounds which can then coat the various components and working surfaces of the engine, eventually covering the catalytic converter as well. Once this has happened the zinc becomes a catalyst contaminant which then transfers into the exhaust and out into the atmosphere, creating harmful vapors which can be poisonous if inhaled in large quantities. It is for this reason that there are regulations against zinc-plated fuel tanks and transportation tanks.
Fuel tank corrosion:
Zinc reacts differently than metals such as aluminum and steel to diesel fuel. Regardless of which type of tank diesel fuel is stored in, water from condensation will always enter the fuel and eventually settle to the bottom of the container. A barrier of bacteria then forms between the fuel and water, and those bacteria will use zinc as a food source, eventually penetrating the layer and corroding the walls of the tank far more quickly than steel or aluminum, since they do not create such a nutrient-rich environment for the bacteria to work with. Most modern tanks include filtration devices which allow for regular draining and filtering of the water from the tank to avoid corrosion build-up.