PHOSPHORIC ACID CARGOES FROM INDIA

Published: January 1, 2017

There have been recent incidents where stainless steel cargo tanks of chemical tankers have been damaged following the carriage of phosphoric acid cargoes from the east coast of India.

The extent of the damage to the stainless steel cargo tanks ranges from mild pitting on the tank surface to more extensive corrosion, causing the tank surface to peel off as shown in the photographs on the right. Repairs can be labour intensive and time consuming and there is the additional risk of contamination of the cargo being carried. To minimise these risks, the following issues should be considered:

CREW KNOWLEDGE

It is important that the crew are familiar with the type of cargo being carried and the type of stainless steel within the ship’s tanks. Food grade phosphoric acid is not corrosive to stainless steel but fertilizer grade acid is far more aggressive. The crew must familiarise themselves with the Safety Management System (SMS) which should contain information on the dangers of carrying phosphoric acid and include guidance on the maximum temperature of the cargo to be loaded on board.

TANK RESISTANCE TABLES

The levels of fluoride and chloride, together with the cargo temperature, will influence the extent to which the cargo may react with the stainless steel cargo tanks. Cargo tank resistance tables, usually provided by the manufacturer, provide information on the safe temperature levels for carriage.

MAINTAIN A TEMPERATURE LOG ON LOADING

Cargo can sometimes be loaded at an excessive temperature. The crew should be aware of the location of temperature gauges and monitor the cargo temperature at the beginning and during loading. If the temperature is excessive, loading should be stopped.

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