In this latest case study, North Ridge Pumps explains how a self-priming seawater intake pump was specified to resolve ongoing reliability issues in a demanding coastal cooling application.
The client had originally installed submersible pumps for seawater cooling but experienced persistent operational problems. They approached us for expert guidance on the most effective and cost-efficient solution for their seawater abstraction system.
Seawater abstraction is the process of drawing water from the sea for large-scale industrial cooling, power generation or processing. In many systems, seawater is returned to the ocean after use, sometimes at a higher temperature.
More generally, abstraction refers to taking water from natural sources such as rivers, streams or groundwater for agriculture or potable use. Offshore water and open ocean environments act as vast, stable and naturally cold heat sinks. This provides significantly improved energy efficiency and reduced operating costs compared to conventional closed-loop or evaporative cooling systems.
For UK coastal manufacturing plants, process facilities and energy sites, seawater cooling systems offer a highly efficient, cost-effective and environmentally responsible alternative to traditional cooling methods, particularly where deep cold-water sources are accessible.
The client’s installation comprised three seawater intake pumps, with two operating in duty and standby configuration and a third acting as back-up.
The pumps were suspended from a pier within a port and immersed in 6 m to 7 m of seawater. An integrated inverter controlled the units to ensure the required cooling capacity was maintained. Seawater was pumped vertically to the main pier and then transferred several hundred metres horizontally through pipework into the production plant.
Although the design met the required hydraulic duty, the submersible pumps were suffering extensive wear and frequent maintenance issues.
One of the primary issues with submersible pumps in corrosive environments is seal failure, either at the pump or the motor. Exposure to saline conditions accelerates component wear and increases the risk of water ingress.
Long periods of downtime were also encountered due to limited spare part availability. Additionally, problems similar to those seen in flammable liquid handling applications can arise, sometimes only becoming apparent after installation.
Submersible pump motor casings are typically available in a limited range of materials. Stainless steel casings offer excellent corrosion resistance but can be expensive or restricted to specific models. As a result, many submersible motors are manufactured from cast iron or mild steel, which is less suitable for long-term seawater exposure.
The cable entry point is one of the most vulnerable elements in submersible pump design.
If pumps are not handled correctly, the cable may be used inadvertently as a lifting point, damaging the cable or casing joint. This can lead to water ingress and motor failure.
In this installation, the cable gland passed through a mild steel outer casing prone to corrosion. As corrosion progressed, clearances increased, making it progressively harder to maintain an effective seal and prevent moisture reaching the motor windings.
The motor casing is oil-filled for cooling and to protect the windings from moisture. However, following maintenance and reinstallation, leakage via the cable gland can occur. This necessitates draining, rewinding and refilling the motor with oil before restart, a labour-intensive and costly process that significantly increases downtime.
Submersible pumps located on seabeds are frequently exposed to sediment movement caused by tidal action and bow thrusters from offshore support vessels.
Sand, stones and debris become agitated and can enter pump inlets. This results in accelerated casing corrosion, mechanical seal damage and cavitation. Over time, this severely impacts reliability and whole life cost.
Another major challenge with submersible pump systems is spare parts availability. Many designs rely on bespoke components supplied only by the original manufacturer.
In contrast, industrial centrifugal pumps often use standardised motors and couplings available globally. This significantly reduces downtime risk in critical process applications where pump failure can halt production.
In this case, the motor casings were constructed from mild steel, a material not compatible with prolonged seawater exposure.
To mitigate corrosion, sacrificial anodes made from reactive alloys such as zinc or aluminium were installed. These provide cathodic protection by corroding preferentially to protect the steel casing.
While effective, sacrificial anodes require replacement every three months to ensure ongoing protection. Because the pumps were suspended from a pier, they had to be removed using a crate system to access and replace the anodes.
This added further maintenance cost, labour and operational disruption.
To overcome these challenges, we specified an electric high-flow self-priming pump manufactured from duplex stainless steel to replace the submersible seawater intake pumps.
Duplex stainless steel combines approximately equal proportions of austenite and ferrite. This delivers high mechanical strength and superior corrosion resistance in chloride-rich marine environments. It allows reduced wall thickness, lower weight and long-term reliability in harsh offshore and coastal conditions.
The pontoon-mounted self-priming pump provides a 5 m to 6 m suction lift and delivers in excess of 240 m³/h, drawing seawater via a baseplate-mounted priming pump.
To protect against salt spray and aggressive atmospheric conditions, the pump was coated with a C5 marine coating system. This high-performance industrial protective coating is classified under ISO12944 for use in extremely corrosive high-salinity coastal and offshore environments.
Unlike submerged systems, the self-priming configuration removes many of the risks associated with underwater motor casings, cable gland ingress and difficult maintenance access. It also simplifies inspection, reduces maintenance frequency and improves overall system resilience.
For industrial facilities across the UK that rely on seawater cooling pumps, selecting the correct pump type and materials of construction is critical. Corrosion resistance, maintainability, spare parts availability and lifecycle cost must all be considered at specification stage.
At North Ridge Pumps, we are not limited to one pump technology. With over 25 years of experience across industrial pumping applications, we specify the most appropriate and cost-effective solution for each project brief.
If you have a seawater abstraction or marine cooling application that requires a rethink and need expert, impartial advice, speak to North Ridge Pumps to see how we can help optimise reliability, reduce downtime and improve long-term performance.
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