Steel Corrodes at 3 to 5 Times the Standard Rate Inside Cooling Towers. FRP Does Not Corrode at All.
- Aug 7
- 12 min read
A cooling tower is one of the most corrosive secondary infrastructure environments in UK industry. Continuous hot water contact at 40 to 60°C, biocide treatment for Legionella control, chlorine dosing, scale inhibitors, and persistent wetting and drying cycles combine to attack galvanised steel structural members at 3 to 5 times the rate of standard outdoor atmospheric exposure. UK regulations require every cooling tower to be registered with the local authority under the Notification of Cooling Towers Regulations 1992 and to maintain a documented Legionella risk assessment and water treatment programme. The structural and access infrastructure of that cooling tower must perform in those conditions across its full design life. FRP is the material that was built for exactly this environment.
Published by Reinforce Technology | 1 August 2026
Cooling towers are among the most widely distributed pieces of industrial infrastructure in the UK. They cool process water in power stations, petrochemical plants, pharmaceutical facilities, food and beverage processing operations, and — increasingly — in the data centres that are being built across the UK at a pace the sector has never seen before. London's installed data centre capacity was 2.45 GW in 2025, projected to reach 5.16 GW by 2031 at a 13% compound annual growth rate, with AI-driven hyperscale facilities requiring the most intensive cooling systems of any data centre generation (Mordor Intelligence, 2026). Each of those facilities requires cooling towers or equivalent heat rejection infrastructure that operates continuously, in a persistently wet and chemically aggressive environment, for 25 to 30 years.
The UK's regulatory framework for cooling towers is specific and demanding. The Notification of Cooling Towers and Evaporative Condensers Regulations 1992 requires every operator to register their cooling tower with the local authority and to notify when towers are no longer in use. The Health and Safety Executive's Approved Code of Practice L8 requires a documented Legionella risk assessment, a written scheme of control, and a monitored water treatment programme as the minimum standard for every operational cooling tower. The combination of regulatory compliance requirements and the inherently aggressive chemistry of an operational cooling tower creates a secondary infrastructure specification environment where the material of the structural frames, walkways, fan decks, and access systems determines both the operational safety and the maintenance cost of the installation across its designed service life.
FRP is the material of choice for cooling tower structural and access infrastructure in the most demanding industrial applications globally. Its corrosion immunity in hot water, biocide, and chlorine environments, its non-porous surface that does not harbour the biofilm that promotes Legionella growth, its lighter weight that reduces structural loading on cooling tower basins and rooftop installations, and its maintenance-free performance across 25 to 30-year design lives make it the specification that the cooling tower environment demands and that galvanised steel demonstrably cannot match.
Why the Cooling Tower Environment Is Uniquely Destructive to Steel
The corrosion environment inside an operating cooling tower is the product of four simultaneous and reinforcing attack mechanisms that together produce the fastest corrosion rates encountered in any industrial secondary infrastructure application.
The first is hot water chemistry. Cooling towers circulate water at temperatures typically between 25 and 45°C in the cold water basin and 40 to 60°C in the hot water distribution zone. At these temperatures, the electrochemical corrosion rate of steel approximately doubles for every 10°C increase in temperature, following the Arrhenius equation for temperature-dependent reaction kinetics. The hot water zones of a cooling tower therefore drive steel corrosion at rates two to four times higher than the same steel would experience at ambient temperature in the same water chemistry.
The second is biocide and chemical treatment. UK Legionella control regulations require the maintenance of effective biocide concentrations in cooling tower water to control bacterial populations. Oxidising biocides — chlorine, chlorine dioxide, and bromine-based compounds — are the most commonly used and most effective Legionella control agents, and they are also the most aggressive to galvanised steel coatings. Chlorine at the concentrations required for effective Legionella control reacts directly with zinc coatings, forming zinc chloride compounds that dissolve from the coating surface and progressively deplete the protective zinc layer. The combination of elevated temperature and oxidising biocide chemistry is the primary mechanism by which galvanised steel coatings inside cooling towers fail within 2 to 4 years, far shorter than the same coating's life in standard outdoor atmospheric exposure (Unicomposite, 2026).
The third is wetting and drying cycling. Cooling tower structural members experience continuous wetting from the water distribution system and intermittent drying from the airflow through the tower. This wetting and drying cycle concentrates dissolved salts, scale-forming minerals, and chemical treatment agents at the metal surface during drying, creating locally concentrated corrosive conditions at precisely the points where corrosion is already proceeding most rapidly. Scale deposits on steel structural members create crevice corrosion cells beneath the scale where dissolved oxygen is depleted and local acidification accelerates base metal corrosion further.
The fourth is the biological dimension. Biofilm formation on steel surfaces inside cooling towers provides both a habitat for Legionella growth and a mechanism for microbiologically influenced corrosion (MIC), in which bacterial metabolic products including organic acids and hydrogen sulphide directly attack the metal surface beneath the biofilm. MIC on steel cooling tower internals is well-documented in the corrosion engineering literature and represents a corrosion mechanism that biocide treatment alone cannot fully address once biofilm is established on a roughened or corroded steel surface.
The Legionella Dimension: Why FRP Is Not Just About Corrosion
Legionella pneumophila, the bacterium responsible for Legionnaires' disease, thrives in the warm, moist conditions of cooling towers. The UK Health and Safety Executive's L8 Approved Code of Practice identifies cooling towers as the highest-risk category of water system for Legionella amplification and aerosol release, because the combination of water temperatures in the optimal growth range for Legionella (20 to 45°C), the large surface area of fill media in contact with circulating water, and the mechanical aerosol generation of the cooling tower fan creates conditions that can produce infectious aerosol concentrations rapidly if bacterial populations are not controlled.
Corroded steel surfaces inside cooling towers are a specific Legionella risk amplifier. Corrosion products on steel structural members create rough, pitted surface textures that provide ideal attachment sites for the biofilm communities in which Legionella grows preferentially. Iron oxide corrosion products also serve as nutrients for iron-oxidising bacteria that create the anaerobic microenvironments within biofilm that support Legionella growth even at biocide concentrations that would kill planktonic bacteria in the bulk water. A cooling tower with corroding steel structural internals is, by the specific mechanism of corrosion product biofilm nucleation, a cooling tower with higher Legionella risk than an equivalent tower with non-corroding internals.
FRP structural components and grating in cooling tower internals provide a smooth, non-porous surface that does not corrode, does not produce iron oxide or zinc oxide deposits, and does not create the rough surface texture that promotes biofilm attachment and Legionella colonisation. GRP resins formulated to BS 6920 and verified under microbiological growth tests do not support Legionella pneumophila growth in direct contact (Vistech Cooling, 2023). The UK Health and Safety Executive's guidance on Legionella risk management explicitly addresses the importance of material selection in cooling tower design as a component of the risk control programme, alongside chemical treatment and monitoring. Specifying FRP structural and access components in cooling tower internals is a Legionella risk reduction measure as well as a maintenance cost reduction measure (HSE, L8).
Where FRP Is Specified in Cooling Tower Infrastructure
1. Structural Profiles — Columns, Crossbeams, and Frame Members
The primary structural frame of a cooling tower, including the vertical columns, horizontal crossbeams, and diagonal bracing members that carry the loads of the fan assembly, fill media, water distribution system, and access platforms, operates in direct hot water contact in the worst corrosion zone of the cooling tower. Pultruded FRP structural profiles for cooling tower primary frames provide structural sections that carry design loads across a 25-year service life without the corrosion section loss that causes galvanised steel structural members to fail prematurely in the hot water and biocide environment of the cooling tower interior.
The structural design of FRP cooling tower frames accounts for the lower modulus of elasticity of FRP compared with steel, typically using deeper section sizes to achieve equivalent deflection performance at equivalent span. The significantly lower density of FRP, approximately 75% lighter than steel, means that the increased section depth does not necessarily result in a heavier structure, and in rooftop cooling tower installations where structural loading on the building below is a design constraint, FRP primary framing can enable higher cooling capacity from a given building structure than equivalent steel framing would permit (IntechOpen, 2022).
2. Fan Deck Grating and Maintenance Walkways
The fan deck of a cooling tower — the horizontal platform at the top of the tower structure supporting the fan motor assembly and providing maintenance access — is the most directly challenged secondary infrastructure in the cooling tower. It is continuously wet from drift and fan-generated water contact, exposed to the UV environment of the tower top, subject to the vibration loads of the fan motor assembly during operation, and required to provide safe anti-slip access for maintenance personnel in wet conditions.
FRP moulded grating for cooling tower fan decks must satisfy two simultaneous requirements: anti-slip surface performance on continuously wet surfaces, and flame-retardant (FR) rating for grating adjacent to fan motor assemblies and electrical drive components where ignition risk from heat and electrical arc must be managed. Standard cooling tower fan deck grating specifications call for 38 to 50mm depth panels with a concave anti-slip surface or gritted anti-slip surface in FR-grade formulations tested to ASTM E84 Class 1 or equivalent. The FR rating is not optional for fan deck applications where proximity to ignition sources makes standard combustible grating a fire risk (Unicomposite, 2026).
Internal maintenance walkways at lower levels of the cooling tower, providing access to the fill media, water distribution headers, and basin for inspection and maintenance, operate in the most concentrated corrosion environment of the tower — direct hot water contact, biocide splash, and the warm, humid atmosphere of the tower interior. FRP moulded grating for internal cooling tower walkways provides corrosion-immune anti-slip access that does not require replacement due to corrosion section loss, does not require recoating maintenance interventions that would necessitate tower shutdown, and does not produce iron oxide contamination of the water below that would contribute to biofilm nucleation on the fill media and basin surfaces.
3. Water Distribution Headers and Lateral Support Brackets
The hot water distribution system of a cooling tower delivers water from the incoming feed to the spray nozzles above the fill media, distributing heat load uniformly across the tower cross-section for maximum cooling efficiency. The pipe support brackets and header support angles that secure the distribution piping to the tower frame operate in direct contact with the distribution water at the highest temperature zone in the tower, in the most aggressive combination of temperature and biocide chemistry encountered anywhere in the installation.
FRP pultruded angle sections and channel sections for distribution system support brackets provide corrosion-immune structural fixings that do not contaminate the distribution water with corrosion products, do not require periodic replacement due to corrosion section loss, and maintain the distribution system's flow characteristics by preventing the sag and displacement that corroded and weakened steel brackets introduce over time. Each sub-header and lateral pipe is secured to the tower wall with FRP angles and stainless steel U-bolts, providing a corrosion-resistant fixing assembly throughout the distribution system support structure (TEI, 2015).
4. Basin and Sump Infrastructure
The cold water basin at the base of the cooling tower collects the cooled water after it has passed through the fill media and returns it to the process via the recirculation pump. The basin operates as a permanently wet sump at ambient air temperature, with the full concentration of the cooling water chemistry including biocides, scale inhibitors, and the accumulated contamination from the cooling process. Access grating for basin maintenance, structural supports for sump pump connections, and any bunding or secondary containment around the basin perimeter operate in continuous water contact with the full cooling water treatment chemistry.
FRP basin grating and structural supports provide corrosion-immune access and containment infrastructure that does not contaminate the basin water with corrosion products, does not require removal and recoating during basin maintenance and cleaning operations, and provides the non-sparking property relevant in cooling tower basin areas where hydrogen accumulation from corrosion reactions or biological activity could create a flammable atmosphere in enclosed basin spaces.
The Data Centre Cooling Tower Pipeline
The most significant new market for cooling tower infrastructure in the UK is the data centre sector. London's installed data centre capacity is growing from 2.45 GW in 2025 to a projected 5.16 GW by 2031, with AI-optimised hyperscale facilities requiring cooling systems that handle thermal densities of 30kW per rack and above. The shift from air cooling to water-based cooling systems — cooling towers, dry coolers, and liquid cooling infrastructure — for AI data centres means that more cooling tower capacity is being installed in the UK's data centre estate than at any previous point in the sector's development.
Data centre cooling towers face the same Legionella regulatory requirements as industrial cooling towers under the Notification of Cooling Towers Regulations 1992 and L8, with the additional constraint that data centres operate as Critical National Infrastructure requiring continuous availability with no acceptable downtime for structural maintenance. A data centre cooling tower whose galvanised steel structural frame requires partial replacement at year 8 due to corrosion section loss faces a maintenance programme that is incompatible with the continuous availability requirement of the facility it serves. FRP structural frames and access infrastructure eliminate that maintenance programme entirely, providing the same 25-year maintenance-free structural performance in the data centre cooling tower environment as in any other industrial application.
The Lifecycle Cost Position
The lifecycle cost case for FRP in cooling tower applications is among the most straightforward available for any industrial secondary infrastructure. The corrosion rate of galvanised steel in the cooling tower environment is documented, the coating life is 2 to 4 years before base metal exposure begins, and the cost of each maintenance intervention in an operational cooling tower is amplified by the requirement for tower shutdown, water draining, surface preparation, coating application, and the production or process interruption that follows. An unplanned structural replacement during peak cooling demand, when tower shutdown means immediate production interruption for the process facilities the tower serves, is the cost consequence that most procurement teams underestimate when specifying cooling tower structural material by upfront unit cost rather than total owner cost (Unicomposite, 2026).
FRP cooling tower structures, grating, and access components provide corrosion-immune performance across 25-year design lives without the coating maintenance cycle that galvanised steel requires. A peer-reviewed lifecycle cost analysis found approximately 50% lifecycle cost savings for GFRP versus steel over long study periods (Younis, Ebead and Judd, 2018). In the cooling tower environment, where the corrosion rate is 3 to 5 times the standard outdoor rate and each maintenance event requires tower shutdown, the break-even point at which FRP's lower lifecycle cost offsets its higher purchase price falls earlier than in any other industrial secondary infrastructure application.
Cooling towers are among the most chemically aggressive secondary infrastructure environments in UK industry. Steel corrodes at 3 to 5 times the standard outdoor rate. Coatings last 2 to 4 years before base metal exposure begins. Corroded steel surfaces amplify Legionella risk by providing biofilm nucleation sites. UK regulations require documented risk assessment and control for every operating tower. FRP structural profiles, grating, and fan decks provide corrosion-immune, non-biofilm-supporting, maintenance-free cooling tower infrastructure across 25-year design lives in the environments where steel accumulates its fastest and most consequential maintenance liabilities.
Reinforce Technology FRP Products for Cooling Tower Applications
Reinforce Technology supplies FRP moulded grating, pultruded structural profiles, and structural angle and channel sections for cooling tower structural frames, fan decks, internal walkways, water distribution supports, and basin access infrastructure. Available in polyester and vinyl ester resin systems, with flame-retardant formulations tested to fire performance classifications required for fan deck and motor proximity applications. All products are corrosion-immune in the hot water, biocide, and chlorine chemistry of UK cooling tower water treatment programmes across 25-year design lives.
Contact us to discuss your cooling tower project and the correct FRP specification for your specific water chemistry, temperature, regulatory requirements, and operational horizon.
Final confirmation of suitability for any specific cooling tower application, including structural loading assessment, fire performance classification, and compatibility with specific water treatment chemistry, remains the responsibility of the appointed project engineer. Reinforce Technology provides technical guidance and material recommendations based on information supplied to us, but specification sign-off should always sit with the qualified professional responsible for the design. Operators are reminded that Legionella risk management under L8 remains the responsibility of the competent person appointed by the duty holder.
References
HSE (2013) Legionnaires' Disease: The Control of Legionella Bacteria in Water Systems. Approved Code of Practice and Guidance (L8). 4th edn. Sudbury: HSE Books. Available at: https://www.hse.gov.uk/pubns/books/l8.htm [Accessed: 1 August 2026]. [Cooling towers highest-risk water system category; risk assessment; written scheme of control; water treatment programme requirements; material selection as risk control component].
IntechOpen (2022) 'Fibre-Reinforced Polymer (FRP) in Civil Engineering', in IntechOpen Engineering Series. Available at: https://www.intechopen.com/chapters/84203 [Accessed: 1 August 2026]. [75% lighter than steel; corrosion-immune in aggressive chemical environments; non-sparking; 25-year design life].
Mordor Intelligence (2026) United Kingdom Data Center Market
. Available at: https://www.mordorintelligence.com/industry-reports/united-kingdom-data-center-market [Accessed: 1 August 2026]. [London installed capacity 2.45 GW in 2025; projected 5.16 GW by 2031 at 13.21% CAGR; AI-linked hyperscale facilities driving demand].
NACE International (2016) International Measures of Prevention, Application and Economics of Corrosion Technology (IMPACT). Houston, TX: NACE International. Available at: http://impact.nace.org/economic-impact.aspx [Accessed: 1 August 2026].
ScienceDirect (2025) 'Sustainable composites for metal replacement: Environmental assessment and material selection of fiber-reinforced polymer across industries', ScienceDirect, doi: 10.1016/S2667-3789(25)00051-3. Available at: https://www.sciencedirect.com/science/article/pii/S2667378925000513 [Accessed: 1 August 2026]. [Pultruded GFRP manufacturing emissions approximately 60 to 70% lower per tonne than primary steel, cradle-to-gate].
TEI (2015) Suggested Cooling Tower Specifications. Available at: https://www.tei-usa.com/wp-content/uploads/2015/09/Intl_DW_FRP_Structure_Ceramic_Fill.doc [Accessed: 1 August 2026]. [FRP structural shapes for drift eliminator supports; 0.61m wide FRP grating maintenance walkways; FRP angles and stainless steel U-bolts for distribution piping support].
Vistech Cooling (2023) Insight into GRP Lining for Cooling Towers. Available at: https://www.vistechcooling.co.uk/knowledge-centre/articles/an-insight-into-grp-lining/ [Accessed: 1 August 2026]. [GRP resins to BS6920; microbiological growth tests confirming no Legionella pneumophila growth in direct contact; fire retardant to BS476].
Younis, A., Ebead, U. and Judd, S. (2018) 'Life cycle cost analysis of structural concrete using seawater, recycled concrete aggregate, and GFRP reinforcement', Construction and Building Materials, 175, pp. 135-144. doi: 10.1016/j.conbuildmat.2018.04.183.
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