Corrosion control systems used for the underside steel plates of above-ground storage tanks (ASTs) may not provide adequate protection in certain situations.
Specifically, severe corrosion of the chime area may lead to unplanned outages and could impact the tank’s structural integrity near the critical weld between shell plates and chime/floor plates.
Some design and construction practices may not address these factors that could promote severe corrosion of the asset.
Typical parameters that influence corrosion of soil-side bottom plates may include the following:
Volatile Corrosion Inhibitors (VCIs) for Corrosion Mitigation
Volatile Corrosion Inhibitors can be applied to the underside steel plates to mitigate corrosion of these areas; their application methods are summarized in Figure 1 below.
VCI Implementation Works for Various Tank Foundation Designs
The tank foundation design greatly affects the type of methodology used for VCI
implementation. Depending on the foundation, VCIs in dry powder form or VCIs
dissolved in a carrier, typically water, can be introduced to the soil side bottom
environment. The type of delivery system can be adapted to meet most tank
Types of Tank Foundation Designs Include:
Due to the wide variety of tank bottom foundation designs, application methods of
VCI, as a means of controlling corrosion effectively, should be discussed with a
VCI Effectiveness Proved Using Corrosion Rate Monitoring Techniques
Corrosion rate monitoring, using UT testing, weight loss coupons, electrical
resistance probes, UT probes, can be useful in determining VCI effectiveness and,
more importantly, the replenishment timelines or any substantial changes in the
corrosiveness of the environment beneath storage tank bottoms. As the number
and ages of storage tanks rise, corrosion rate monitoring and control may be of