Corrosion Control Systems for Various Tank Foundation Designs

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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:

  • Temperature Differential Aeration
  • Moisture Content Dissimilar Materials
  • Containment Levels Crevice Corrosion
  • 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
    foundation designs.

    Types of Tank Foundation Designs Include:

  • Asphalt/Bitumen
  • Concrete
  • Compacted Sand or Soil
  • Hard Pad
  • Double Bottom
  • Single Bottom
  • With Liner or Release Prevention Barrier (RPB)
  • Without a Liner or RPB
  • 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 professional.

    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
    increased necessity.