What happens inside a cooling tower

A cooling tower transfers heat from circulating water to air, and the interior stays warm, wet and chemically treated. Water evaporates from the fill, droplets are carried out as drift, and components dry out during shutdowns and maintenance. Grating walkways, fan decks and access routes sit in this environment, carrying load while enduring repeated wetting and drying.

Unlike an ordinary outdoor platform, the tower is close to saturated, warm all year and carries biocide, scale inhibitor and corrosion inhibitor. These chemicals affect both metals and resins, and compatibility depends on the type and concentration; the words cooling water are not enough to describe the duty.

Grating here is rarely process equipment; it is the access for maintenance and operation: fan service platforms, fill replacement routes, valve operating platforms. Failure is usually not a sudden break but surface ageing, corroded fasteners and distorted supports that eventually make the platform unsafe.

Wet-dry cycling and resin hydrolysis

The ester bonds in polyester resin hydrolyse under heat and water, showing up as blistering, whitening and exposed fibre. Wet-dry cycling is harsher than continuous immersion, because each drying cycle shrinks the surface layer and the next wetting drives water into the microcracks; the more cycles, the more visible the degradation.

Resin choice is the first line of defence. Isophthalic polyester resists hydrolysis better than orthophthalic, and vinyl ester is usually better still; a surface veil and resin-rich layer can block water entry, but only if the resin is fully cured and free of bubbles and dry spots. Under-cured resin will hydrolyse within months even when the grade is correct.

Confirm temperature against the actual duty. Cooling tower water is usually at tens of degrees Celsius, but local spots may be hotter, especially near hot water inlets or steam discharge. The resin's heat distortion temperature and long-term service temperature need margin; do not select from short-term laboratory data. Chemical resistance is compared in the chemical-resistant FRP grating guide

Algae, biofilm and cleaning

Warm, damp, sunlit grating grows algae and biofilm. Biofilm carries no load, but it makes the surface slippery, hides cracks and loose fasteners, and leaves difficult stains when it dries. Walkways and platforms that are rarely cleaned lose slip resistance noticeably.

Design for drainage and cleanability: grating should not hold water, platforms should fall to a drain, and corners should not form traps; where cleaning is frequent, the surface should wash easily, and a grit surface, though slip-resistant, holds more dirt.

Cleaning chemicals must be compatible with the resin and coating. Chlorinated disinfectants, strong alkalis and some biocides can attack the resin or fade pigments; confirm concentration and contact time, and test a small area first. Cleaning also raises the risk of slips, so plan shutdowns and protection.

Ultraviolet light and surface ageing

Cooling towers often stand outdoors or on roofs, and the top surface of the grating takes continuous UV. UV breaks resin molecular chains, showing as chalking, loss of gloss, colour fade and a brittle surface. Moisture accelerates the process, because water vapour and UV together do more damage than either alone.

UV stabilisers, pigments and surface veils are the usual defences. Dark elements run hotter and often age faster; light elements reflect more sun but still need weather-resistant pigments. A gelcoat gives a thicker protective layer, though local repairs show a colour difference.

Inspection should look at the top surface, not the sides. The top takes the sun and holds water; widespread chalking or visible fibre texture means the surface layer has thinned, and the question is structural condition, not appearance alone.

Walkways, fan decks and maintenance loads

Loads on a cooling tower platform are not only people. Maintenance brings tools, fan blades, bearings and fill, sometimes as temporary lifting loads; operation brings vibration and wind pressure. Check permanent load, live load, maintenance point load and wind separately, and use the worst combination.

The deflection limit usually decides panel depth before strength does. Too much walkway deflection is uncomfortable to walk on and can reverse drainage falls; a fan deck also has to meet equipment level tolerances. Span is the clear distance between supports, and support beam width and position belong on the layout drawing.

Handrails and toe boards matter as much. FRP handrails are less stiff than steel, so posts need to be closer; fixing the rail to the structure is more stable than fixing it to the grating and keeps horizontal load out of the panel. Platform edges, ladder openings and lifting holes need toe boards or kerbs to stop tools falling. Span and load are covered in the FRP grating load capacity guide

Supports, fixings and vibration

Tower supports may be concrete, steel beams or FRP sections. Different materials expand differently, so the fixing must allow some relative movement; clamping all four edges rigidly makes the panel arch as it warms and cracks at the fasteners.

Use stainless fasteners and select the grade for the environment; in wet or chloride-bearing air, carbon steel fasteners rust first and the rust stains the grating. Do not over-tighten clamps. FRP has low compressive strength, and over-tightening starts cracks at the hole edge.

Fan vibration travels through the structure into the grating, and long-term vibration loosens fasteners and wears clamps. Lock washers or thread-locking compound can help at critical points, but these accessories must also resist corrosion; add a fastener check to the maintenance schedule.

Moulded, pultruded and structural form

Moulded grating carries load in two directions and suits irregular platforms with many openings; pultruded grating is strong along its load bars and suits long spans and walkways. The two carry load differently and cannot be compared by weight or unit price alone.

Pultruded load bars must run across the supports; laid the wrong way, the panel deflects noticeably under design load. Moulded grating has a stronger direction, which should span the shorter distance; where cutting is needed, keep cuts clear of load bars and seal them with the matching resin.

Platforms in a cooling tower often need site openings, edge cuts and extra supports. Complex shapes can be prefabricated as panels and assembled on site with stainless connectors; every site cut must be sealed, or water wicks along the fibres and damages the panel from inside.

Selection, spares and maintenance

For an inquiry, give the location, ambient temperature and humidity, contact media and chemicals, span, load type, deflection limit, panel size, colour, surface, fire requirement and fixing method. For tower chemicals, give the composition or the safety data sheet directly.

Keep spares for vulnerable locations such as fan deck edges, frequently removed access covers and areas near the hot water inlet. Spares from the same batch and resin system make colour and performance easier to match.

The maintenance plan should cover periodic washing, fastener and clamp checks, cut-edge sealing and surface chalking, and assessment of handrail and support distortion. Recording inspection results is cheaper than replacing panels after obvious damage. More industry practice is in the FRP grating applications by industry

• Choose resin by temperature and chemicals, not by price.
• Fall the platform to a drain; avoid standing water and algae.
• Run pultruded load bars across supports; seal every cut.
• Check fan decks for maintenance point load and vibration.