FRP Trench Cover Grating for Drainage Channels

Each 1.2 m panel ships with two SS316 lifting loops (stainless steel bearing), optional gas strut for panels >1.2 m, and 304 key lock. Edge frame is hot-dip galvanized steel or FRP angle 75×75 for chemical zones. See also FRP profiles and molded grating.

Trench covers are simply supported panels over a channel. The governing limit is deflection under a pedestrian point load (1.0 kN) or wheel load. For pedestrian trenches, #38 molded over 500–900 mm span is standard. For cart traffic, pultruded I 50×10 over 750 mm span carries 10 kN/m². Edge angle is required on both sides to spread the point load into the channel wall.

Channel width vs cover type

Resin selection by trench content

For floor drainage (water, detergent), isophthalic is sufficient. For chemical sumps (acid, alkali, solvent), vinylester is required. For hydrocarbon-containing trenches, phenolic resin may be specified for fire resistance. See molded grating resin options.

Every trench cover ships with two SS316 lifting loops, cast into the panel edge. For panels wider than 1.2 m, we add a gas strut (pneumatic stay) to hold the panel open during cleaning. Locking options: 304 key lock (standard), or SS316 bolt-down for permanent installations. Edge frames are hot-dip galvanized steel for dry areas, or FRP angle 75×75 for chemical zones. The frame is cast into the concrete channel wall during construction.

Odor control

For H₂S-containing trenches (sewage, wastewater), we supply a neoprene gasket that sits under the cover edge, reducing odor escape by 90%. Combined with locking, this prevents unauthorized access and odor complaints from neighboring areas.

Glass-fiber reinforced polymer (GRP / FRP) grating has become the default choice for industrial walkways, platforms and trench covers. The reason is not aesthetics — it is total cost of ownership. Painted steel grating requires scraping and repainting every 3–5 years in chemical and marine environments. Galvanized steel lasts 10–15 years before corrosion attacks the bars. Aluminum corrodes in alkaline washdown areas. Stainless 316 is the only comparable metal, but at 3× the cost of vinylester GRP and still prone to pitting at the waterline.

FRP does not rust, does not need painting, and carries a 25-year design life. It is 70% lighter than steel, which reduces the structural steel subframe, lowers shipping cost, and makes manual installation feasible without heavy equipment. It is non-sparking and non-conductive, which is why it dominates refinery, offshore and substation applications. It also has a lower coefficient of thermal conductivity than aluminum, so barefoot areas stay cool in sunlight.

Total cost of ownership comparison

The numbers tell the story: vinylester GRP is 55% lower total cost than either steel or stainless over a 25-year horizon. Add the safety benefits (non-sparking, non-conductive, anti-slip wet), and the engineering case is clear.

FRP grating is famously low-maintenance. But "low maintenance" does not mean "no maintenance". For a 25-year service life, we recommend the following inspection schedule. Annual visual inspection: walk every 12 months, look for broken bars, missing clips, UV chalk on the top surface. Clips: re-torque every 3 years — thermal cycling loosens bolts slightly. Cleaning: wash with high-pressure water 200 bar; for chemical residue, use pH-neutral detergent. Do not use solvent-based cleaners on the gel coat — they can craze the surface.

UV chalk: after 8–10 years outdoors, the gel coat may show faint surface chalk. This is normal and does not affect structural strength. If appearance matters, apply a coat of UV-stabilized clear gel coat, available from us as a touch-up kit. Repairs: a broken bar can be spliced with a FRP repair kit (resin + mat) in 30 minutes; the panel remains in service. Full panel replacement takes 15 minutes for two workers — no hot work, no welding.

Safety in installation

Cutting FRP generates dust. Wear P100 respirator, eye protection, gloves. Dust is silica-glass, not toxic but irritates lungs. Wet cutting suppresses dust. Do not cut near open flame — resin is combustible, though self-extinguishing per ASTM E84.

When specifying GRP grating for a new project, three variables dominate: panel thickness, resin type, and surface finish. Thickness carries the load. Resin determines chemical and temperature resistance. Surface finish determines slip resistance. Get these three right and the rest follows.

Panel thickness guide

Resin selection

Isophthalic is the default for atmospheric and light chemical service. Vinylester for marine, chemical splash, hot water. Phenolic for high temperature and low-smoke requirements. We provide a chemical resistance chart for 200+ chemicals on request — if your media is not listed, send us the concentration and temperature, and our engineering team will recommend the right resin.

Surface finish

Smooth top for indoor dry areas. Carborundum grit (aluminum oxide F24) for wet and slip-prone areas. Double grit (top and bottom) for marine and washdown. The grit is cast into the gel coat, not glued on — it will not peel.