Chemical storage tanks must withstand the products they hold, and the part of the tank that carries most of that load is the corrosion barrier. In FRP chemical storage tanks, this inner portion of the laminate is the first surface the stored chemical contacts. Belding Tank Technologies Inc. treats it as the most important feature of any fiberglass tank in corrosion service. This article explains how the corrosion barrier is built, why its thickness and internal finish matter, and which operating practices help protect it over the tank’s life.
People Also Ask
Does temperature affect sodium hypochlorite in storage?
Yes, Belding Tank states that higher temperatures contribute to the chemical decomposition of sodium hypochlorite.
Does every FRP chemical tank need a post cure?
No, Belding Tank’s tanks for ferric chloride, alums, and polymers require no post cure.
What the Corrosion Barrier Does Inside an FRP Tank
The corrosion barrier is the laminate’s chemical facing layer. Behind it sits the structural layer, and beyond that, the outside surface. Designing a corrosion barrier for chemical storage tanks starts with resin selection, and three resin systems show how the barrier carries the chemical resistance load:
- Economy: isophthalic polyester resin throughout the laminate.
- Standard: premium grade vinyl ester resin in the inner surface and interior layer, with isophthalic polyester in the structural layer and outside surface.
- Premium: premium grade vinyl ester resin throughout the laminate.
The standard option places the higher grade resin only where the chemistry makes contact. A corrosion barrier fiberglass tank designed this way separates the job of resisting the stored chemical from the job of carrying structural loads.
How the Inner Surface and Interior Layer Work Together
Together, the inner surface and interior layer form the corrosion barrier, with a glass content of 27% ± 5% by weight. The veil in this barrier changes with the chemistry:
- Sodium hypochlorite tanks use a two ply C-Glass or Nexus® synthetic veil.
- Sodium hydroxide tanks use a two ply Nexus® synthetic veil.
- Sulfuric acid tanks use a single C-Glass veil.
Cure systems vary too. On sodium hypochlorite tanks, a BPO/DMA catalyst system cures the corrosion barrier, while the structural layers use Co/MEKP. Sulfuric acid tanks also receive a hot air post cure for four hours at 180°F after assembly. In practice, the corrosion barrier for chemical storage tanks is specified chemical by chemical, not as one fixed recipe.
Why Barrier Thickness Affects Chemical Resistance
ASTM and ASME specify a corrosion barrier thickness of 96 mil, and Belding Tank builds all of its barriers to a minimum of 110 mil. Tank walls follow ASTM D3299 for filament winding and ASTM D4097 for contact molding, with ASME RTP-1 (design by rules) fabrication capabilities. Building above the published minimum adds chemical resistant material between the stored product and the structural layer that supports the tank. When you evaluate FRP chemical storage tanks, ask each supplier to state its minimum barrier thickness.
How a Resin Rich Finish Limits Contamination
A smooth interior starts with the mold. Building FRP chemical storage tanks on a male mold helps ensure a smooth, resin rich internal finish that aids corrosion resistance. Several related details support a clean interior:
- A unitized one piece bottom to sidewall construction removes the seam at that joint.
- A knuckle radius at the bottom corners makes cleaning easier.
- Internal baffles use the same resin and veil system as the tank, so added parts present the same chemical facing surface.
What Maintenance Preserves Barrier Integrity
Protecting the corrosion barrier for chemical storage tanks starts with correct use. Proper installation, correct usage, environmental conditions, and regular inspections all influence how long a tank lasts. The stored chemical also sets its own limits. With sodium hypochlorite, for example:
- The chemical must remain stable at a pH of 11 to 12, because instability leads to corrosion barrier attack. Using high quality sodium hypochlorite helps avoid degradation of the tank.
- For outdoor tanks, a white gel coat should be considered as an option.
Inspection frequency depends on the application and the stored material, and inspections should cover exteriors, fittings, and structural components. Tank repairs, inspections, and modifications are available as services, but contact the manufacturer before any repair, since unauthorized repairs and alterations void the warranty. Running within published limits, with regular inspection, keeps a corrosion barrier fiberglass tank within the service conditions its barrier was designed to handle.
To see how the barrier fits with resin selection, configuration, and sizing, read what to look for in FRP chemical storage tanks for industrial use. To specify FRP chemical storage tanks for your chemistry, contact Belding Tank Technologies Inc. now.
Frequently Asked Questions
Can FRP tanks handle extreme temperatures?
FRP tanks can be engineered to handle specific temperature ranges. Belding Tank advises avoiding rapid temperature changes to prevent structural stress and damage.
Which resins does Belding Tank use for sodium hypochlorite tanks?
Belding Tank uses Derakane 411, its bulk stored house resin, for dilute sodium hypochlorite up to 150°F. Higher temperatures call for Derakane 510A, B, or C. Concentrated solutions call for Derakane 510A only, kept below 100°F.
