A shell & tube heat exchanger.

Heat-cured phenol coatings

This article looks at the use of heat-cured phenol coatings to provide safe corrosion protection for heat exchangers. Some case studies are examined and cost-saving advantages in both lifecycle costs and maintenance are pointed out.
 
^ A shell & tube heat exchanger.

Article By Daniël Eras, Commercial Manager, Heat-Cured Phenol Specialist, CP Phenolics, The Netherlands
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Phenol heat-cured coatings are used to provide corrosion protection, and baked phenol coating technology offers a safe protection and security for industrial processes. 

Over the past sixty years this coating material, and the accompanying process technology, has been developed to provide reliable corrosion protection. It prevents, for example, dangerous incrustations and fouling in tube bundles, air coolers, heat exchangers, and other types of coolers. Today, the coatings are used worldwide. In addition, they are also used to protect equipment such as valves, process vessels, ship coolers, ISO tank containers, (cooling water) pipelines, and plate heat-exchanger plates, etc. One-component thermally hardening coatings, also called baked phenol or heat-cured coatings, are applied in a multilayer process and cured in special polymerization ovens at temperatures no higher than 230°C. Every layer gets an oven treatment for a different length of time at an appropriate temperature schedule. It is a technology proprietary to CP Phenolics B.V.

The heat treatment in the polymerization oven forms homogeneous, hard, flexible, non-porous, and chemically very resistant protective layers. Moreover, they are not sensitive to strong temperature fluctuations because the coating layers are cross-linked with each other at a molecular level.

Heat-cured phenol coatings can be divided into two groups: 

(1) Phenol-formaldehyde-based coatings; 

(2) Epoxy-phenol-based coatings.

A ‘diffusion-resistant’ type is available for both the phenol-formaldehyde base and the epoxy-phenol base.

In this way it is possible to protect against media in the acidic as well as in the alkaline spectrum and for situations where protection at a higher ΔT is required.

It is further inadmissible for some applications that static charging can occur. For these cases it is possible to use an electrically conductive phenol-formaldehyde coating. In most cases, the phenol heat-cured coatings are electrically insulating, which is especially important in protecting against galvanic corrosion when using different base metals. In this way, baked phenol coatings can be used not only to protect coolers, but can also be used to protect semi-precious metals against corrosion, caused by sacrifice in the immediate area. The most widely used application, and therefore the most known, is that of the direct protection of heat exchangers against cooling water or other aggressive media. These can affect heat exchangers in such a way that their lifespan and their heat transfer and/or cooling capacity can be negatively affected. Reduction of the total cost of ownership through a heat-cured phenol coating treatment is the most important reason for a treatment. Moreover, a lot of money can be saved on maintenance and purchase costs when high-quality protection against corrosion is opted for. 

Various sources have for years drawn attention to the problems caused by fouling in refineries. For example, in one year alone the worldwide costs for so-called ‘crude oil preheat trains’ were of the order of $ 4.5 billion. 

Applying a phenol heat-cured coating can help solve these problems when it comes to corrosion protection. 

A good example is that of a heat exchanger that was designed for a capacity of 800 W/mK. After operating for approximately two months, the capacity had already been reduced to 600 W/mK as a result of fouling and incrustations that had build-up in the tubes of the heat exchanger. After approximately twenty months of use and high-pressure cleaning, the heat transfer further decreased to 350 W/mK. As a result, the heat exchanger was taken out of service. 

An alternative solution would have been to provide the heat exchanger with an internal heat-cured phenolic coating, over the tube side. Under the same conditions, this would have had a lower capacity resulting from the new installation, and a heat transfer of 625 W/mK. This heat transfer capacity corresponds to an uncoated heat exchanger that has been in operation for approximately two months. However, the heat transfer remained constant over a thirty-six-month period without maintenance or cleaning. Therefore, in addition to extending the service life, there was also the advantage in the cost of the material. Carbon steel is an excellent material for providing an optimal adhesion profile for a heat-cured phenolic coating. Moreover, when choosing a complete surface treatment, a barrier is also created against any uncoated parts that should not be affected by negative effects of galvanic corrosion.

Air coolers 

Heresite baked phenol coating

Through a specialized pouring process, coolers with a very compact finned pack are thoroughly and precisely coated. The phenol heat-cured Heresite coating is ideally suited for the treatment of: 

• Finned air coolers 
• Radiators 
• Cooler coils 
• Charge-air coolers 

In environments with salty sea air and industrial environments, Heresite’s heat cured phenol coatings will provide excellent protection, but can also withstand exposure to a wide range of corrosive and chemical vapors and condensate. 

Less than 1% loss of cooling capacity 

Because these products are efficient thermal conductors, applied in very thin films, HVAC-R and process equipment coil OEMs have indicated that no additional heating or cooling surface is required due to the presence of the modified baked phenolic coating. The cutting edge of slats are often the most vulnerable parts that are sensitive to corrosion. The heat-cured phenol coating of Here site is precisely designed to provide maximum protection for those parts against these extreme influences.
 

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