Mild steel (MS) and galvanised (GI) gratings have been the default for industrial walkways, platforms and trench covers for decades. In many plants they are also the part of the structure that corrodes first. FRP (fibreglass reinforced plastic) gratings were developed for exactly those locations. This guide compares the two on the points that matter to plant engineers and buyers, using the comparison in Rawji's FRP/GRP grating specification sheet.
The short answer
- Choose FRP where gratings face chemicals, effluent, salt air, constant wetness, or electrical hazards, or where heavy steel panels are hard to handle and replace.
- Steel can still be the right choice in dry, non-corrosive areas, at high temperatures, or where very heavy wheeled loads must cross long spans and the structure is designed around steel.
How they compare
From the material comparison in Rawji's grating specification sheet:
- Corrosion resistance: FRP high; steel low.
- Strength: both high.
- Weight: FRP low; steel high.
- Electrical conductivity: FRP low (non-conductive); steel high.
- Thermal conductivity: FRP very low; steel high.
- EMI/RFI transparency: FRP yes; steel no.
- Fabrication: both easy to cut and fit.
- Life-cycle cost: FRP low; steel moderate.
1. Corrosion: the main reason plants switch
Steel gratings depend on paint or galvanising. Once that coating is damaged, rust starts, and in chemical plants, ETPs and STPs, electroplating shops and coastal sites that can happen quickly. FRP gratings do not rust. The resin system decides how much chemical exposure they can take:
- Type I / Type IFR (isophthalic polyester): industrial-grade corrosion resistance. IFR adds fire retardancy (ASTM E84 Class 1, flame spread 25 or less).
- Type V (vinyl ester): superior corrosion resistance for continuous acid, alkali or solvent exposure, also fire retardant (Class 1, 25 or less).
- Type P (phenolic): low smoke and superior fire retardancy (Class 1, 5 or less), for enclosed areas.
For acid and caustic areas, see chemical-resistant FRP walkway gratings.
2. Weight and handling
FRP gratings are much lighter than steel panels of a similar size. Panels can usually be carried and placed by hand without lifting equipment, which makes installation and replacement in congested plant areas quicker and safer.
3. Electrical and thermal safety
FRP is electrically non-conductive and has very low thermal conductivity, so it is used near electrical equipment, in power plants and substations, and in areas where a steel surface would get hot or cold to the touch. It is also transparent to radio and electromagnetic signals (EMI/RFI), useful near telecom and instrumentation equipment.
4. Slip resistance
Molded FRP gratings have a concave meniscus top surface that gives natural slip resistance, and a gritted (carborundum) surface is available for oily or very wet areas. See anti-slip trench and drain gratings.
5. Load and span
Steel is stiff, and FRP is designed to the span. For FRP, check the manufacturer's load table for your clear span between supports. Rawji's molded SM 38 panel (38 mm deep, 38 × 38 mesh), for example, has a maximum recommended uniform load of 4,500 kg/m² at a 600 mm span. Pedestrian walkways are typically designed for 250–300 kg/m². For longer spans, pultruded GRP gratings are much stiffer in the bar direction, and the 38 mm I-15 series is rated up to 1,600 mm spans. Full tables are on the molded FRP gratings page.
When steel may still be the better fit
- Areas with sustained high temperatures, beyond what the chosen resin system is rated for. Ask our technical team.
- Very heavy wheeled loads over long spans where the structure is already designed for steel.
- Dry, covered, non-corrosive areas where a steel grating will last and cost is the only concern.
Replacing steel gratings with FRP
FRP panels are cut to fit existing steel support structures. Measure the clear span between supports, the panel sizes and the bearing direction, and tell us what the area is exposed to. We will recommend a molded or pultruded panel and resin grade. Fix the panels with SS 316 clips. See our installation and clamping guide.
See the full FRP gratings range or the FRP grating price list.
