In short: The corrosion barrier is the resin-rich inner layer of an FRP tank, pipe or duct that faces the chemical. A typical barrier is a 0.010–0.020 in (0.25–0.5 mm) veil-reinforced inner surface backed by chopped-strand mat, about 0.10 in (2.5 mm) in total. It is there to resist chemical attack and is left out of the strength calculation.
What is the corrosion barrier?
An FRP laminate for chemical service is built in layers. The inner surface is a thin, resin-rich layer reinforced with a light veil. Behind it is an interior layer of chopped-strand mat (CSM) with high resin content. Together these make the corrosion barrier. The structural layer goes on top: filament-wound roving or mat and woven roving. It carries pressure, vacuum and loads.
The barrier keeps the chemical away from the structural glass. If the chemical reaches the structural layer, it can attack the glass-resin bond and weaken the wall. For that reason, fabricators usually do not count the barrier toward structural thickness.
How thick is a typical corrosion barrier?
| Layer | Typical make-up | Typical thickness |
|---|---|---|
| Inner surface | Resin-rich layer with 1–2 surface veils (C-glass, ECR glass or synthetic) | 0.010–0.020 in (0.25–0.5 mm) |
| Interior layer | Chopped-strand mat, typically at least 3 oz/ft² total (often 2 plies of 1.5 oz) | About 0.08–0.10 in |
| Total barrier | Inner surface + interior layer | About 0.10–0.12 in (2.5–3.0 mm); thicker for aggressive service |
| Structural layer | Filament winding or contact-molded mat and woven roving | Set by design calculation |
These are typical values, not universal rules. The actual barrier must be stated on the drawing or data sheet for each order. ASTM C582 (contact-molded laminates) and the tank standards set laminate requirements, but your specification should still state the barrier construction you want.
Which surface veil should you choose?
- C-glass veil: a common default for many acids and general chemical service.
- Synthetic veil (e.g. polyester): often preferred where the chemical attacks glass, such as hydrofluoric acid, fluorides, and some strong alkalis or hypochlorite services.
- Carbon veil: used where the liner must be conductive, for example for static grounding, or as a spark-test target.
- Your resin supplier's chemical resistance guide: this is the final check. Veil choice depends on chemical, concentration and temperature together.
Which resin goes in the barrier?
The barrier resin is chosen for the chemical: often a vinyl ester, sometimes a premium polyester or a special resin for very hot or oxidizing service. The structural layer usually uses the same resin or a compatible one. See polyester vs vinyl ester vs phenolic resin, FRP temperature limits by resin type and the FRP chemical resistance guide.
How do you check a corrosion barrier?
- Thickness and construction: look for a cut-out coupon, a laminate sequence record or the inspection report.
- Cure: Barcol hardness on the inner surface, compared with the resin maker's value. See FRP quality control and Barcol hardness.
- Visual defects: no exposed glass fibers, dry spots, cracks or entrained air beyond the limits in the governing standard.
- Records: resin batch, veil type and the person who did the laminating, all traceable to the vessel.
How FIBROVX can help
Send us your service chemical, concentration, temperature and size, and we will propose a laminate and confirm what we can supply. Request a quote. Trade terms are CIF by default, FOB on request.
Common mistakes
- Vague "corrosion resistant" specs: state the barrier thickness, veil type and resin.
- Counting the barrier as structure: size the structural wall separately.
- Glass veil in fluoride service: check whether a synthetic veil is needed.
- Skipping post-cure checks: an undercured barrier can fail early even with the right resin.
Key terms
- Surface veil: a thin non-woven tissue that reinforces the resin-rich inner surface.
- CSM: chopped-strand mat, randomly oriented glass fibers held by a binder.
- Structural layer: the part of the laminate sized to carry loads.
- ECR glass: corrosion-resistant E-glass without boron.
FAQ
How thick is an FRP corrosion barrier? Typically about 0.10–0.12 in (2.5–3.0 mm): a 0.010–0.020 in veil-rich surface plus chopped-strand mat. Aggressive service may call for a thicker barrier.
Is the corrosion barrier part of the structural thickness? Usually not. Most fabricators and specifications leave it out of the strength calculation.
When should I use a synthetic veil instead of C-glass? When the chemical attacks glass, for example hydrofluoric acid and fluorides. Confirm with the resin supplier's guide.
Does a thicker barrier always last longer? Not always. The resin, cure quality and operating temperature matter as much as thickness.
Related guides
- FRP storage tanks guide
- FRP tank standards
- FRP chemical resistance guide
- FRP tanks for hydrochloric acid
- Request a quote
Sources
- A North American FRP manufacturer, Corrosion barrier selection
- ASTM C582, Contact-Molded Reinforced Thermosetting Plastic (RTP) Laminates for Corrosion-Resistant Equipment: https://www.astm.org/c0582-09r16.html
- ASTM D3299, Filament-Wound Glass-Fiber-Reinforced Thermoset Resin Corrosion-Resistant Tanks: https://www.astm.org/d3299-18.html