Heat exchanger coating: why it can really make a difference

The technique of heat exchanger coating currently offers one of the most effective ways to improve some key performance factors of these devices, such as efficiency, duration and reliability.

In sectors related to power generation, oil & gas, refineries, refrigeration plants and chemical processes, heat exchangers (especially shell and tube models) constitute critical components which are continuously exposed to:

• harsh operational conditions;
• aggressive fluids;
• sea water or industrial liquids with high impurity levels.

The introduction of advanced coating systems, such as those using epoxy or epoxy-phenolic resins can bring significant improvements in the plant’s performance and lifespan.

A daily problem: corrosion, deposits and system blockages

To understand the importance of the coating, we can observe what happens inside a shell and tube heat exchanger during use.  Its surfaces are in continuous contact with sea water, industrial liquids or aggressive processing fluids.

Sediments, biological organisms and carbonate compounds are rapidly deposited, reducing thermal transfer capacity and at the same time creating the ideal conditions for the formation of corrosion and deposits.

These are not marginal effects; even a single hole in a tube can cause an immediate system stoppage, as in the case of condensers serving turbines or in refrigeration circuits, where a micro-perforation can cause the loss of large amounts of refrigerant gas and a consequent interruption of service.

It is in exactly that scenario that heat changer coating can play a strategic role.  Protecting the surfaces means preventing issues which, if allowed to persist, can lead to high costs and chronic inefficiency.

How the coatings work and why they make a difference

Over the last few decades, industry has developed coating techniques using epoxy and epoxy-phenolic resins, which are able to protect metallic surfaces from the combined effects of corrosion, erosion, cavitation and fouling.

These substances are applied to the tube plate, the inside of the tubes and inside the water boxes.  Their efficiency is due to their ability to create a homogenous, resistant barrier, which can cope with operational temperatures of up to 180°C and resist highly aggressive fluids.

Thanks to patented systems with internal sensors which spray the resin uniformly, a film of controlled, even thickness is obtained; an essential condition to ensure long term protection and performance.

Protection from corrosion alone justifies the use of the coating in heat exchangers, but there are also many other advantages.  One of the most interesting discoveries of recent years relates to the capacity of these coverings to reduce deposit adhesion, a crucial factor in maintaining a high level of thermal exchange efficiency.

Laboratory studies have analysed the effect of these construction techniques on stainless steel, Cu-Ni and tin-aluminium tubes, simulating real conditions with sea and river water.  The coated surfaces showed less roughness, reduced wettability and greater uniformity.

Tests using an electron microscope revealed a clear difference between treated and untreated surfaces, while prolonged immersion for up to 28 weeks confirmed reduced adhesion of carbonate deposits and a reduction in biofilm formation.

In some cases, a cell count on the stainless steel tubes showed values up to sixty times greater on uncoated surfaces compared to coated ones.  This means that an adequate coating not only protects, but also contributes directly to improving thermal efficiency, keeping the exchanger cleaner and enhancing its performance over time.

It is also important to emphasise that the validity of the coatings has been established not by sporadic observation but through a rigorous testing and checking process.  The formulations undergo regular testing during which they are exposed to saline mist for up to 2000 hours, as well as immersion testing in compliance with ISO 2812 and other specific checks designed to guarantee stability, resistance and consistant performance.

The systematic gathering of data obtained from their use in the field also enables applicational techniques to be updated and optimised, ensuring the tangible, continuous improvement of the proposed solutions.

When protection makes a difference: a case study

A good example of the process described above is a key oil & gas site in Libya, where eight coated tube plates were installed in 2013.  Considering that similar untreated exchangers had previously encountered serious short term issues related to corrosion and fouling, the decision was made to apply a complete epoxy cycle to the inside of the tubes and a dense coating to the tube plate.

After four years of use, a visual inspection and an endoscopy showed that the coated areas were in much better condition compared to the untreated areas.  Almost no corrosion was present, deposits were minimal and the coating was still perfectly intact.

This is clear confirmation of what laboratory tests had already indicated: this approach enables a real reduction in deterioration issues, thereby extending the equipment’s working lifespan and ensuring a more efficient and stable operation over time.

The adoption of a specific coating for heat exchangers therefore enables companies to obtain a dual benefit.  Firstly, costs and maintenance work are reduced, cleaning is less frequently required and potentially serious breakdowns are avoided, while at the same time energy efficiency is improved and the internal surfaces are kept clean for longer, ensuring optimal thermal transfer.

It also offers the opportunity to use cheaper base materials and avoid the need for highly resistent and therefore more expensive alloys.  The coating becomes not only a protection, but a strategic element in the design and optimisation of the system itself.

Consequently, in an industrial context where efficiency and reliability are key, the coating of heat exchangers can be considered a wise decision, backed by tangible data.

It offers protection and extends the useful life of the equipment, reduces fouling and improves energy performance.  It is a consolidated technology, validated by decades of experience and continues to evolve thanks to ongoing research and experimentation.

For companies wishing to increase operational continuity, reduce costs and improve the performance of their systems, investing in these high quality solutions represents a major step towards more efficient, sustainable management.