Why coat rotating equipment?

An exhaustive overview of rotating equipment, plus how and why it should be protected by coating and/or lining.

Rotating equipment operating in severe and aggressive environments, such as industrial manufacturing, chemical processing, waste incineration and power plants, is often subjected to the attack of corrosive media. These range from aggressive exhaust gases at high temperatures of 200 °C, which form sulfuric acid (H₂SO₄), hydrogen sulfide (H₂S), hydrofluoric acid (HF) and hydrochloric acid (HCl) when condensing, to water saturated with chemicals from exhaust filtration and other process media, i.e. water from the coking process or liquids being recirculated for chemical cleaning.

Turbines: protection required against fume condensate, furnace gases and other corrosive media

An example of turbines and turbine housings requiring protection through coating or lining is in the iron ore/steel manufacturing industry, where blast furnaces are used. The typical composition of blast furnace gases includes approximately 45-60% nitrogen (N), 20-30% carbon monoxide (CO) and carbon dioxide (CO₂) with 2-4% hydrogen (H).

The hydrogen element in particular can cause severe aggressive corrosion (hydrogen-induced cracking corrosion) when in contact with cast iron used for larger housings, even at relatively low temperatures of 40-60 °C, as the presence of acidic condensate, carbonic acids, etc. further accelerates corrosion.

Similar scenarios occur in waste incineration plants, such as energy-from-waste (EfW) or energy-recovery facilities (ERF), where the composition of flue gases may differ in conjunction with higher temperatures. In these instances, surfaces must withstand temperatures from 200 °C to 130 °C and lower, where condensation occurs. The resulting condensation often contains sulfuric acid (H₂SO₄), hydrogen sulfide (H₂S), hydrofluoric acid (HF) and hydrochloric acid (HCl).

High-quality coating systems that guarantee both chemical resistance and thermal shock resistance are therefore necessary to ensure long-lasting protection of turbine components.

How SÄKAPHEN can help: coating solutions for turbines in corrosive environments

SÄKAPHEN’s heat-cured phenolics have become the market standard for coating turbines.

Typically, specific parts of a turbine are coated, including shafts and turbine blades, depending on customer requirements. A tried and tested product and a proven process are both critical, as it is essential that the protective coating forms a thin, uniform protective layer that only adds minimal additional mass to the treated structure, thus reducing potential balancing issues during commissioning and operation. Its enhanced adhesion to the substrate also ensures it is not affected by high centrifugal forces.

For special requirements, e.g. when heat-cured coating is not possible for practical reasons, cold-cured coatingproductsare also available. In that case, due to the nature of the size and weight of a typical turbine or turbine housing installed in the iron ore/steel manufacturing industry, the application of SÄKAPHEN’s protective coatings is preferably carried out on-site.

Impellers: protection required against chemical attacks

Impellers are used to increase the pressure and flow of numerous mediums. They are especially installed inside ducts in all industries, including refineries, power plants, petrochemical facilities, chemical processing plants and general industrial processing facilities, where exhaust gases can reach temperatures of 200 °C. These aggressive gases, combined with high moisture levels, lead to condensation in periods of inactivity between cycles, during shutdowns or when general maintenance is carried out. This causes acids and other chemically active substances to condense on the impeller surfaces.

How SÄKAPHEN can help: protective coatings for impellers in aggressive operating environments

SÄKAPHEN linings or coatings are unaffected by temperature fluctuations and offer temperature resistance up to 200 °C, depending on the medium. A key advantage is the excellent adhesion to the substrate, which remains unaffected even under dynamic loads. At the same time, these coatings add only minimal additional weight to the component, preventing imbalance and ensuring energy-efficient operation.

Pump wheels and housings: protection required against corrosion and incrustation in severe operational conditions

In addition to being found within industrial exhausts and extraction systems, coated impellers can also be installed in (centrifugal) pump systems to pump aggressive mediums, including, for example, chemically saturated water caused by the exhaust filtration process, water from the coking process or liquids recirculated for chemical cleaning.

For instance, in quenching towers, the coke is extinguished with water as the last step of the coking process to prevent burning. Such water is then collected and pumped for further treatment. The pump wheels installed in the centrifugal pumps are relatively small (e.g. 400 mm diameter x 50 mm width) but are required to pump large volumes. Operating at temperatures of +100 °C, the water stream contains wide-ranging chemicals that can include ammonia (NH₃), carbon dioxide (CO₂), sulfides and chlorides with trace amounts of phenols, as well as a considerable level of ferric ferrocyanide, which is not only abrasive but can cause clogging of the pump due to incrustation.

How SÄKAPHEN can help: efficient protection for pumps under extreme process conditions

SÄKAPHEN has set the standard in producing and applying bespoke coatings and linings in the field of pumps. Some years ago, a customer of ours was experiencing incrustation and corrosion issues causing its pumps to be out of action every 3 weeks. Coating them with SÄKAPHEN’s ceramic-filled heat-cured epoxy-phenolic product extended this period to 2 years. The coating developed on that occasion, Si 570 AR (Abrasion Resistance), is now also applied on heat exchangers.

Scraped surface heat exchangers: protection required against corrosion and friction

Scraped surface heat exchangers are used in many applications, including de-waxing, oil separation and manufacturing of fatty acids, to ensure continuous mixing of liquid and semi-solid products while cooled or heated. Within these systems, spring-loaded blades are connected to a central shaft to scrape and remove highly viscous media. Simultaneously, any fouling is also removed from the surface.

How SÄKAPHEN can help: protective solutions for scraped surface heat exchangers

Under such challenging operating conditions, SÄKAPHEN’s heat-cured phenolic linings and coatings provide outstanding corrosion protection and exceptional chemical resistance, as well as being non-porous and non-stick. SÄKAPHEN linings and coatings have a surface tension between 28 mN/m and 35 mN/m, compared with carbon steel, with a surface tension of >56 mN/m. Additionally, their surface roughness is approximately 0.89–1.59 microns compared with 30–50 microns of untreated steel, and thus they can be classified as hydrophobic.

The components of scraped surface heat exchangers, including shafts, shaft centralizers, scraper blades, spider wheels and scraper blade holders, can all be coated with our heat-cured phenolics.

Re-lining and re-coating rotating equipment: NDT/NDE integrity

Rotating equipment, especially turbines and impellers operating at high revolutions, is often susceptible to severe material stress, which can negatively affect the material integrity of the metal substrates. That is why they are regularly inspected for structural integrity, with particular attention paid to weld seams. In cases where the turbine or impeller is coated, the applied product may have to be removed, as any residual deposits may hinder the NDT/NDE. Especially in processes based on magnetic powders or ultrasound, coating residues can distort the results. Therefore, existing coatings are removed by abrasive blasting so that the base material is exposed without damaging the substrate.

How SÄKAPHEN can help

Although SÄKAPHEN linings and coatings are robust and provide excellent resistance against thermal and chemical stresses, they can be easily removed by abrasive blasting should the need arise for NDT / NDE.

Once maintenance and inspection are complete, the rotating equipment can be transported to either the SÄKAPHEN site in Gladbeck, Germany or one of our international authorized applicators to conduct the necessary re-lining and re-coating operations.

This coordinated approach optimally combines operational reliability, inspection quality, and long-term protection.

SÄKAPHEN’s solutions: our best 4 coatings for rotating equipment

We offer a vast range of products, from heat-cured phenolics / epoxy-phenolics to cold-cured epoxies, Novolac vinyl esters and epoxy vinyl esters, depending on the type of equipment and operating conditions.

In particular, the SÄKAPHEN heat-cured phenolic and epoxy-phenolic range guarantees protection against strongly acidic and alkali media, especially at high temperatures, in addition to exceptional chemical resistance in conditions of increased media concentration. Cold-cured epoxies are often an excellent choice for large pieces of equipment operating at lower temperatures.

Our 4 best coating and lining solutions for turbines, impellers, pump wheels and similar devices are:

• Si 14 E: the original and still the best. It is a single-component phenolic-based thermosetting product with excellent chemical resistance to organic and inorganic acids, salt solutions, aliphatic and aromatic hydrocarbons, fume gases, alcohols and cooling water and exceptional hydrophobic properties, preventing caking, fouling and incrustation.
• Si 17 N: a single-component phenolic-based thermosetting product that is chemically resistant to metal oxychlorides (VOCL3), 40% hydrofluoric acid, organic and inorganic acids, fume gases, chlorinated aromatic and aliphatic hydrocarbons, oils and greases and forms an exceptionally smooth film.
• HR 60 Extra G (Red): a two-pack cold-cured epoxy lining with exceptional resistance to temperature fluctuations, chemicals, and all types of water including brackish, river and sea water, as well as deionized water.
• SÄKATONIT Extra AR: a superior two-pack epoxy that stands out for being hydrophobic, mechanically durable, resistant to various substances and abrasion- and impact-resistant. It contains an ultra-high solid volume (wt.%) of 95% or more and even withstands extreme weather conditions.

Get in touch with SÄKAPHEN

Contact us and let’s discuss how to protect your critical rotating equipment.