Marine Engine Q & A- Electrical-Nickel-Cadmium Battery Gassing, Topping up,

Gassing
The gases evolved during charging are oxygen (at the positive plates; and hydrogen (at the negative plates). Rate of production of gas increases in periods of overcharge. When hydrogen reaches a proportion of about 4% and up to 74% it constitutes an explosive mixture. Good ventilation of battery compartments is therefore necessary to remove gas. Equipment likely to cause sparking or arcing must not be located or introduced into battery spaces. Vent caps are non-return valves, as shown diagrammatically (Fig. 1.2) so that gas is released but contact by the electrolyte with the atmosphere is prevented. The electrolyte readily absorbs carbon dioxide from the atmosphere and deterioration results because of the formation of potassium carbonate. For this reason, cell vent caps must be kept closed
Topping Up
Gassing is a consequence of the breakdown of water in the electrolyte. This together with a certain amount of evaporation means that topping up with distilled water will be necessary from time to time. High consumption of distilled water would suggest overcharging.
Electrolyte
Potassium hydroxide solution is strongly alkaline and the physical and chemical properties of potassium hydroxide closely resemble those of caustic soda (sodium hydroxide). It is corrosive, so care is essential when topping up batteries or handling the electrolyte. In the event at skin or eye contact the remedy is to wash with plenty of clean water (for 15 minutes) to dilute and remove the solution quickly. Speed is vital to prevent burn damage; and water, which is the best flushing agent, must be readily available. Neutralizing compounds (usually weak acids) cannot always be located easily, although they should be available in battery compartments.
Specific of electrolyte in a Ni-Cd cell is about 1.210 and this does not change with charge and discharge as in lead-acid cells. However, over a period of time the strength f. the solution will gradually drop and renewal is necessary at about a specific gravity of 1.170


Containers
The electrolyte slowly attacks glass and various other materials. Containers are therefore of welded sheet t which is then nickel plated or moulded in high-impact polystyrene casings are preferred when batteries are subject to shock and vibration. Hardwood crates are used to keep the cells separate from each 2t and from the support beneath. Separation is necessary cause the positive plate assembly is connected to the steel casing.

Marine Engine Q & A- Electrical-Gas Emission,Topping up

Gas Emission
Towards the end of charging and during overcharge, the current wing into the cell causes a breakdown or electrolysis of water in electrolyte shown by bubbles at the surface. Both hydrogen and oxygen are evolved and released through cell vent caps into battery compartment. There is an explosion risk if hydrogen is allowed to accumulate (flammable range is 4% to 74% of hydrogen air). Thus regulations require good ventilation to remove gas and precautions against naked lights or sparks in enclosed battery compartments (see below)
Topping up
Batteries suffer water loss due to both gassing and evaporation, with consequent drop in liquid level There is no loss of sulphuric acid from the electrolyte (unless through spillage) checks are made to ensure that liquid level s above the top of the plates and distilled water is added as necessary. Overfilling will cause the electrolyte to bubble out of the vent.

MARINE ENGINE Q&A-MAIN ENGINE SAFETY GUIDE

Q: The purpose of Safety guide which definitions are generally followed in Marine Ship(Tanker).

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A: The following definitions are applied to Marine Ship (Oil & Chemical Tanker).

• Antistatic additive: A substance added to a petroleum product to raise its electrical conductivity above 100 pico siemens/metre to prevent accumulation of static electricity.
• Bonding: The connecting together of metal parts to ensure electrical continuity.
• Clingage: Oil remaining on the walls of a pipe or on the surfaces of tank interiors after the bulk of the oil has been removed.
• Cold Work: Work which can not create a source of ignition.
• Cathodic Protection: The prevention of corrosion by electro chemical techniques. On tankers it may be applied either externally to the hull or internally to the surfaces of tanks. At terminals, it is frequently applied to steel piles and fender panels.
• Entry permit:A document issued by a responsible officer permitting entry to a space or compartment during specific time interval.
• Flash Point: The lowest temperature at which a liquid gives off sufficient gas to form a flammable gas misture near the surface of the liquid.
• Inert Condition: A condition in which the oxygen content throughout the atmosphere of a tank has been reduced to 8 percent or less by volume by addition of inert gas.
• Inert Gas: A gas or a mixture of gases, such as flue gas, containing insufficient oxygen to support the combustion of hydrocarbon.
• Gas free: A tank, compartment or container is gas free when sufficient fresh air has been introduced into it to lower the level of any flammable, toxic, or inert gas to that required for a specific purpose, e.g. hot work,entry etc.
• Gas free certificate: A certificate issued by an authorized responsible officer confirming that at the time of testing a tank, compartment or container it was gas free for specific purpose.
• Pour point: The lowest temperature at which a petroleum oil will remain fluid.
• Toxic: Poisonous to human life.
• Topping off: The operation of completing the loading of a tank to a required ullage.
• Topping up: The introduction of inert gas into a tank which is already in the inert condition with the object of raising the tank pressure to prevent any ingress of air.