Steel vs FRP grating
When chemistry beats steel. Hot-dip galvanized steel grating is the industrial default, but FRP grating (fiberglass-reinforced plastic) wins in corrosive, electrically sensitive, or weight-critical environments.
Key takeaways
- Steel is 3× stiffer, 3× heavier, and 2.5–3× cheaper per m² than pultruded FRP.
- FRP corrodes in essentially nothing — acids, caustics, sea water, chlorides, hydrocarbons.
- Break-even is typically 7–10 years in pulp & paper, chlor-alkali, and wastewater, when steel replacement cycles are included.
- FRP is electrically non-conductive and non-magnetic: mandated in substations, MRI rooms, and cathodic-protection zones.
Side-by-side comparison
| Attribute | HDG steel grating | Pultruded FRP grating |
|---|---|---|
| Density (kg/m³) | 7,850 | 1,800–2,000 |
| Modulus E (GPa) | 200 | 17–28 (direction-dependent) |
| Allowable bending stress | 155 MPa (ASD) | 60–100 MPa (15–25% of ultimate) |
| Typical panel weight (m²) | 27 kg (30×3 mesh) | 11–13 kg (38 mm depth) |
| Corrosion resistance (neutral) | 10–40 years with zinc + paint | 25–30 years baseline |
| Acid / alkali resistance (pH 2–12) | Poor — coating failure | Excellent with vinyl-ester resin |
| Chloride / salt spray | Limited — chloride pitting | Excellent |
| Electrical conductivity | Conductive (must be grounded) | Insulator (>1012 Ω/sq) |
| Magnetic | Yes | No |
| Temperature range (°C) | −20 / +200 | −40 / +120 (polyester), +150 (vinyl-ester), +200 (phenolic) |
| Fire rating (ASTM E84 FSI) | Non-combustible (A1) | 25 (polyester), 15 (VE), <5 (phenolic) |
| Edge finish / fabrication | Cut, weld, field-modifiable | Cut with diamond/carbide; edges must be sealed |
| Relative cost (m²) | 1.0× baseline | 2.5–3.0× |
| Lifecycle maintenance | Zinc touch-up every 10–15 yr; replace at end of coating life | Essentially zero |
Where FRP beats steel
- Chemical plants — chlor-alkali, battery acid, acid tank farms, cooling-tower basins.
- Pulp and paper — bleach towers, white-water floors.
- Wastewater / desal — secondary treatment, screen houses, RO skids.
- Offshore oil & gas — splash zone walkways, phenolic FRP for fire-rated egress.
- Electrical / EMI sensitive — substations, transformer pits, MRI rooms, radar stations.
- Cathodic-protection zones — where steel would bypass the CP circuit.
- Remote / hand-carry — FRP is 3× lighter, installable without a crane.
Where steel wins
- Heavy vehicle loads — forklifts >3 t, H20 truck loads, loading docks — specify heavy-duty welded steel.
- High-temperature service — over 200 °C, thermal cycling, hot-work areas.
- Large open spans — where FRP deflection would exceed L/240 and would require deep I-bar profiles.
- Budget-led projects — dry, mild atmospheres where zinc alone reaches design life.
- Field-welded structural continuity — FRP cannot be welded in place.
Resin selection cheat-sheet (FRP only)
| Resin | Best for | Max temp | FSI (ASTM E84) |
|---|---|---|---|
| Isophthalic polyester | General industrial, neutral pH, walkways | ~120 °C | ~25 |
| Vinyl-ester | Chemical, pH 1–14, chlor-alkali, wastewater | ~150 °C | ~15 |
| Phenolic | Offshore, fire-rated egress, transport infrastructure | ~200 °C | <5 |
| Halogen-free fire-retardant polyester | Tunnels, mass transit, public buildings | ~120 °C | ~10 |
Frequently asked questions
- When does FRP beat steel on total cost?
- When avoided maintenance and replacement cycles exceed the 2.5–3× material premium. Typical break-even is 7–10 years in pulp & paper, chlor-alkali, wastewater, and coastal oil & gas.
- Is FRP weaker than steel?
- Stiffness yes (E ~20 GPa vs 200 GPa). Deflection typically governs FRP spans. At walkway loads (5 kPa, 1.2 m span) pultruded FRP 38 mm deep is a drop-in replacement for steel 25×3.
- Can FRP handle forklift traffic?
- Pultruded heavy-duty FRP (I-bar, 50–75 mm deep) supports 2 t rubber-tired forklifts at 1.0 m span. For steel-wheeled traffic or H20 loads switch to heavy-duty welded steel.
- Does FRP burn?
- Polyester ~FSI 25–35, vinyl-ester 15–25, phenolic <5 with near-zero smoke. Specify phenolic in egress routes and offshore modules.
- Is FRP electrically non-conductive?
- Yes — surface resistivity >1012 Ω/square and non-magnetic. Specified around high-voltage substations, MRI rooms, transformer pits, and cathodic-protection zones.
- What about UV degradation?
- Exposed FRP develops surface "fiber bloom" after 5–10 years of UV. A synthetic veil + UV inhibitor in the resin extends cosmetic life to 25+ years; this is standard in our FRP grating.
Steel or FRP? Tell us the chemistry.
Send environment (atmosphere, chemicals, temperature, electrical requirements) and load — we'll return a material recommendation and a quote.