The Problem

Tank Bottom Corrosion Soil Side Bottom (SSB) corrosion of Aboveground Storage Tanks (ASTs) is a major cause of tank bottom failures. Such failures are often time-consuming and expensive to repair and may pose a potential hazard to the surrounding environment. Traditional Cathodic Protection (CP) methods are often utilized to prevent SSB corrosion, but these methods present their own restrictions and limitations. Such limitations include the resistivity of the underlying foundation, disruptions to the imposed current (either from environmental factors or tank construction) existing gap or void spaces, etc. The restrictions of traditional CP systems necessitate the option of additional means of corrosion protection.

 

Tank Bottom Corrosion Leads to Costly Repairs and Lost Revenue!

Maintenance Costs

• Purging and/or Cleaning
• Replacement of Bottom Plates
• Installation of Release Prevention Barrier (RPB) Liner
• Additional Inspections
• Opportunity Cost of Idle Tank

 

Operation Costs

• Downtime for Repairs or Replacements
• Environmental Concerns
• Revenue Loss
• Additional Inspections

 

The Solution

Zerust VCIs Zerust Vapor Corrosion Inhibitors (VCIs) Are A Cost-Effective Way to Control Corrosion

Corrosion of the underside surfaces of aboveground storage tanks is an ever-present drawback that can lead to costly environmental concerns because of product leakage.

Zerust’s Vapor Corrosion Inhibitors (VCIs), as stated in API 655, can be used for the protection of aboveground storage tank bottoms from soil-side corrosion and provide sufficient corrosion prevention to the soil-side bottom surfaces of steel storage tanks when applied correctly and analyzed regularly.

 

Benefits of Zerust IDS/VCI

• Provides the option for replenishment.
• Can be combined with simple monitoring procedures to ensure the effectiveness of the solution.
• Corrosion protection for voids and interstices that are impossible to protect with other methods.
• Protection for tank bottom plates and welds with little to no surface preparation.
• VCIs offer non-permanent corrosion protection at the molecular level that is safe and eco-friendly.
• Zerust’s methods of VCI dispersion ensure uniform distribution.
• Service life of tank bottom can be increased significantly at a minimal cost.
• Zerust IDS solutions are comprehensive and proven methods for protecting storage tanks with soil side bottoms.
• Zerust IDS solutions reduce overall costs to tank farm owners while increasing corrosion prevention efficacy.
• Tank operations do NOT need to be stopped during inspection or maintenance of the SSB solutions.

 

VCI and CP Compatibility

While DOT – PHMSA does not currently permit the use of VCI without Cathodic Protection (CP) for “break-out” tanks, most non-regulated tanks may use VCI without an active CP system, or for tanks where the use of CP is limited or not applicable as defined by API 651. VCIs serve as an alternate corrosion protection system in those scenarios.

 

API Standards for VCI use on AST Bottoms for Corrosion Protection (API 655 TR)

The American Petroleum Institute (API) has released its Technical Report (API TR 655) that discusses the use of Vapor Corrosion Inhibitors (VCIs) for the protection of aboveground storage tank bottoms from soil-side corrosion.

This technique provides effective corrosion protection to tank bottoms, comparable to existing cathodic protection (CP) systems, and a large body of client field results has been synthesized into API-655. For more information, click here. 

 

Implementing the Corrosion Solution

Every proposal for a Tank Bottom corrosion mitigation solution starts with custom-design work that thoroughly evaluates the construction details for a targeted asset. Based on those factors, an Inhibitor Delivery System (IDS) is selected for implementation. Zerust’s IDS were designed to allow for the application of our corrosion inhibitor compound to a variety of different environments and construction types. Zerust offers a variety of tank Inhibitor Delivery System (IDS) options that are detailed on the following pages.

 

Chime Ring Dry

Zerust’s patented Chime Ring Dry IDS solution is recommended for storage tanks with concrete or bitumen foundations. Zerust Oil & Gas has designed an innovative VCI/SCI (Soluble Corrosion Inhibitor) injection system to protect the tank bottom from corrosion. Perforated PVC pipe is installed around the entire annular chime area. The VCI dry sleeves are installed into the PVC pipe and the system is sealed to create an enclosure to contain the VCIs. The VCIs migrate and absorb onto the metal surface. The diffusion of VCIs provides corrosion protection in the critical 3 to 4 meters from the annular chime ring.

FOUNDATION(S): CONCRETE, BITUMEN, COMPACTED SAND OR SOIL.

 

Chime Ring Injection

Zerust’s patented Chime Ring Injection IDS solution is suitable for storage tanks with concrete, bitumen, or sand with liner foundations. Zerust Oil & Gas has designed an innovative VCI/SCI (Soluble Corrosion Inhibitor) injection system to protect the tank bottom from corrosion. The Chime Ring Injection IDS system features the same delivery installation as the Chime Ring Injection IDS solution. As the inhibitor slurry is pumped into the perforated PVC chime ring system, the VCIs migrate and absorb onto the metal surface. Meanwhile, the liquid inhibitor slurry works to neutralize any contaminants it may contact on either the bottom plates or the foundation. The combination of VCIs and SCIs works together to protect vulnerable areas of the tank bottom plates from corrosion.

FOUNDATION(S): CONCRETE, BITUMEN, COMPACTED SAND OR SOIL (ALL FOUNDATIONS MUST INCLUDE A LINER OR RPB).

 

Underside Injection

Zerust’s Underside Injection IDS solution is designed for tanks with compacted sand fill and Release Prevention Barriers (RPBs) , double bottoms with sand between the old and new floors, or tanks sitting on a hard pad such as concrete or asphalt.

The tank chime is sealed to prevent the ingress of moisture and contaminants. Low-viscosity inhibitor slurry is pumped through designated ring wall ports into the sand bed. As the slurry flows throughout the entire sand bed, the SCIs effectively neutralize contaminants on contact. Conversely, the VCIs emitted by the slurry migrate and absorb onto the metal surface.

The VCIs permeate the sand bed through capillary action and gravity, providing protection to the entire tank floor.

FOUNDATION(S): COMPACTED SAND OR SOIL (WITH LINER OR RPB), DOUBLE BOTTOM DESIGNS WITH COMPACTED SAND OR SOIL, HARDPADS

 

Internal Flood

The Internal Flood IDS solution is suitable for tank foundations of concrete, bitumen, or compacted sand with a liner. Low-viscosity inhibitor slurry is pumped into one or more temporary injection ports installed in selected locations through the tank floor. The VCIs emitted by the slurry migrate and absorb onto the metal surface. The SCIs work to neutralize any contaminants it may contact on either the bottom plates or the foundation. The multiple injection points allow for quick dispersion of the slurry across the entire tank bottom.

FOUNDATION(S): CONCRETE, BITUMEN, COMPACTED SAND OR SOIL (ALL FOUNDATIONS MUST INCLUDE A LINER OR RPB).

 

Dry Tube

The Dry Tube IDS system is designed to protect tank bottom plates during construction or new floor installation. This solution benefits tanks with concrete, bitumen, and compacted sand foundations with or without liners. Shallow trenches are cut into the foundation. Perforated, mesh-covered PVC pipes are placed within the trenches and the trenches are then filled with sand. The tank chime is sealed to prevent the ingress of moisture and contaminants, and dry mesh sleeves of VCI inhibitor are installed into each of the pipe tubes. The system is sealed to allow an enclosed area for the VCIs to rise from the sand in the tube channels, and the VCIs work to mitigate corrosion on the metal bottom plates of the tank.

FOUNDATION(S): CONCRETE, BITUMEN, COMPACTED SAND OR SOIL.

 

Underside Drip Tube

The Underside Drip Tube IDS is an innovative solution that protects tank bottom plates of single or double bottom tanks during construction or new floor installation. A network of perforated PVC pipes with mesh sleeves are installed in rings on top of the tank liner in the sand foundation. Inlet pipes penetrate the ring wall, allowing access points to the PVC pipe system. The tank chime is sealed, preventing the ingress of moisture and contaminants from entering the system. Low-viscosity inhibitor slurry is pumped into the designated ring wall port(s) into the sand bed, and the perforated PVC pipe network distributes the slurry evenly throughout the system. The VCIs are released from the sand bed, protecting the metal bottom plates of the tank. The SCIs in the inhibitor neutralize contaminants in the sand bed. The injection port(s) can be used for future inhibitor injections.

FOUNDATION(S): CONCRETE, BITUMEN, COMPACTED SAND OR SOIL (ALL FOUNDATIONS MUST INCLUDE A LINER OR RPB)

 

Corrosion Monitoring

ER Probes Electrical Resistance (ER) probes are inserted into the sand or soil foundation to measure the corrosivity of the underlying environment. Baseline corrosion rates are determined by monitoring the change in resistance over time detected by the ER probes. The vapors emitted from the VCI slurry protect the ER probes, demonstrating the effectiveness of the VCI. ER probe tubes are installed at various points to provide estimates of bottom plate corrosion. The ER probe cables are stored outside the ring wall to allow for ER probe readings to be taken while in service.

 

Zerust Solutions for Tank Bottom Protection

CASE STUDY: SSB INSTALLATION

The efficacy of Zerust Oil & Gas’ Underside Injection IDS solution was demonstrated at a recent installation. The IDS solution needed to be implemented without stopping tank operations, and the Underside Injection system was determined to be the most appropriate solution to suit the client’s needs. With this delivery system, liquid inhibitor slurry is introduced into the sand bed base under the tank through injection ports. The slurry spreads across the lined bottom of the sand bed, and the VCI will volatilize from the slurry to reach the entire soil side bottom of the tank.

The effectiveness of the Underside Injection IDS solution was determined by taking metal loss readings before and after injection using ER probes and a data logger. The metal loss readings were converted into corrosion rates for the time periods before and after corrosion inhibitor injection. A plot of ER Probe data from a field installation is shown below. Data from this installation shows a threefold reduction compared to the baseline corrosion rate.