WATER TANK INTERIOR CORROSION
The corrugated galvanized steel water storage tanks equipped with a flexible membrane
liner (liner) for water containment are designed to minimize corrosion of steel
components. The liner contains the water and prevents the water contact with the
corrugated galvanized steel tank wall sheets. However, there is always condensation
both on the outside tank walls and on the inside tank walls. When moisture is trapped
between two material layers the condensation may cause steel corrosion unless the
moisture has a route of escape from the area between the tank wall and the liner.
When flexible membrane liners in water tanks made their debut over 40 years ago, the
liners were installed either without a moisture wick or a cheaper flexible plastic was
installed in the tanks as a preliner. In the 1980’s we began to install geotextile material
preliners between the steel tank wall and the main water containment liner. This
geotextile material has nearly the same properties as the geotextile installed under the
pavement of highways. The geotextile serves as a wick to allow moisture to migrate
down the tank wall very quickly and allows for air circulation between the steel tank wall
and the liner. The geotextile is extremely strong and protects the main liner from
abrasion and potential punctures.
A CorGal tank installed near Seattle, Washington, in 1986, was inspected in 2006
during a routine replacement of the main liner. NO corrosion was observed of the
interior steel both due to the thickness of the hot dipped galvanized coating of the steel
and due to the use of the geotextile preliner inside of the tank structure.
Most steel tanks experience corrosion failure and leaks in the floor area of the tank. The
CorGal tank does not have a steel floor to corrode. The water containment liner rests on
a geotextile preliner installed onto the concrete tank foundation.
The underside of the galvanized steel roofs will experience moisture condensation but the
moisture will drain away which does not allow corrosion to be a problem.
National Storage Tank, Inc. Office: PO BOX 9580 Santa Rosa, CA. 95405 P: (707) 537-7433 F: (707) 5406045 Web: www.nationalstoragetank.com