Corrosion is one of the main causes of the failure of the storage tanks. In any plant, a
number of tanks are used to store and deliver a variety of liquids and gases. The
biggest problem is the corrosion of the bottom plate.
The complete network of plant consists of more than 100 tanks. These are used for
storing and distributing potable water, petrol, diesel and H.F.O. About 70 numbers of
Large Above Ground Storage Tanks (AST) are used for the storage of Heavy Fuel Oil
and water. During internal inspection of one of the tanks, bottom plates shown signs of
pitting corrosion of varying degrees and roof had numerous holes of varying sizes. But
they mainly centered on the locations where roof was touching rafters. Magnetic flux
leakage test (MFL) test indicated underside corrosion of bottom plates in number of
The paper presents and discusses the aspects involved with the corrosion of tank roof
and the bottom plates. An attempt has been made to discuss the inspection
methodology, the causes for corrosion, and methods of repair and refurbishment of the
tanks. It also describes the suitable Cathodic Protection system for the underside
corrosion protection of tank bottom plates.