Stratification

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Definition - What does Stratification mean?

Stratification is the formation or deposition of layers, as of rock or sediments.

This chemical phenomenon occurs in lead-acid batteries. Stratification is a major concern in flooded batteries as well as in non-hybrid AGMs, leading to reduced capacity, active material shedding and grid corrosion.

Stratification causes tube failure in boilers as well as failure in stratified batteries. Fuel stratification in fuel tanks leads corrosion in fuel systems.

Corrosionpedia explains Stratification

Typical lead-acid batteries contain a mixture of water and acid with different concentration levels. Given that water and acid are of different densities, if a battery remains stationary and is rarely used (no charge or discharge), the mixture can separate itself — the water rises to the top while the denser acid sinks to the bottom. This is called stratification.

The effect of stratification has a great impact on battery life. The more concentrated and dense acid is found at the bottom, the more it accelerates the corrosion of the lower portion of the plates, therefore shortening the battery life.

Acid stratification occurs if the battery dwells at low charge (below 80 percent), never receives a full charge or has shallow discharges. Driving a car for short distances with power-robbing accessories contributes to acid stratification because the alternator cannot always apply a saturated charge. Large luxury cars are especially prone to acid stratification. This is not a battery defect per se but the result of use.

During periods of non-use of the battery, it is advisable to recharge at least once every month in order to mix the water and the electrolyte. Otherwise, a trickle charger can charge the battery at low power when it needs it, to keep the battery active.

Stratification can also cause tube failures in boilers. This most commonly occurs in sloped tubes located away from the radiant heat zone of the boiler, where heat input is low and positive circulation in the tubes may be lacking. The use of horizontal hairpin tube configurations with inadequate forced circulation of water through the tubes often permits stratification of steam and water. This often leads to steam blanketing or caustic corrosion problems.

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