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AkzoNobel Aerospace Coatings supports full refinish of a historic KC-135 aerial refuelling aircraft
6 Analysis
40 years of performance testing on the Hutton TLP, investigating the impact of highly-loaded lamellar glassflake in offshore coatings, and reimagining longlife corrosion protection for offshore atmospheric exposure
22 Spotlight
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Publisher: Andrew Deere andrew.deere@mpigroup.co.uk
UP FRONT
HISTORIC AIRCRAFT REPAINT
AkzoNobel Aerospace Coatings supports full refinish of a historic KC-135 aerial refuelling aircraft.
ABoeing KC-135 Stratotanker, one of the world’s longest-serving aerial refuelling aircraft, has received a full coatings upgrade and new heritage tail design using AkzoNobel Aerospace Coatings’ high-performance systems. The new design was unveiled at the beginning of July at the 128th Air Refueling Wing of the USA’s Wisconsin Air National Guard, based at Milwaukee Airport.
The coatings refurbishment, including the fuselage, wings and tail assembly, brings new life to this important aircraft, known for enabling long-range operations by transferring fuel mid-air to other aircraft. The addition of a heritage-inspired tail design connects the 128th Air Refueling Wing with the city of Milwaukee and the pride felt by the unit’s members.
Each feature of the design was carefully chosen to represent the unit’s mission, identity and ties to the city. The SAC stripe, with star constellations and the Wing’s shield running across the fuselage, honours the unit’s legacy under Strategic Air Command. The tail features a flying beer stein, a symbol dating back to 1963, which reflects the Wing’s nickname, ‘Brew City Tankers’. The bold ‘Milwaukee’ tail flash highlights local pride, while the barley detail pays tribute to the city’s rich brewing heritage.
Long-term durability
To ensure long-term performance and durability, the aircraft was coated using AkzoNobel’s militaryqualified aerospace products, including an epoxy primer for superior corrosion protection and Aerodur 5000 Camouflage topcoat – a two-component polyurethane military aircraft camouflage finish with exceptional chemical and weather resistance.
The paint scheme on the tail incorporates Aerodur 5000 Flat colours in blue and yellow donated by AkzoNobel’s distributor AIS. The yellow is a bespoke colour developed by the AkzoNobel team to represent the unit’s shield, the Milwaukee flag and the Milwaukee Brewers.
“The major elements of this design help to connect the 128th Air Refueling Wing, the city of Milwaukee, and the hometown pride felt by unit members,” said Master Sgt Elizabeth Cywinski, 128ARW Structural Maintenance Specialist and Command Jet Repaint Lead Coordinator.
“A display as prominent as the stein on the tail helps to amplify pride and dedication – not only for the maintainers and aircrew, but for all personnel across the base that make the mission possible,” said Cywinski. “It has become a symbol; it motivates, binds, and connects the
members, rallying and driving us toward mission accomplishment and the delivery of exceptional airpower.”
The heritage design and its application were completed by the unit’s airmen, making the aircraft not just a symbol of tradition but also a reflection of the skill and commitment of those who serve at the 128th Aerial Refueling Wing.
“The KC-135 Aerial Stratotanker has a rich history in global aerial refuelling, supporting
global flight operations for nearly seven decades,” said Ted Wiesner, Air Defense Segment Manager at AkzoNobel Aerospace Coatings. “We are pleased to support the unit with this latest update, which reflects its legacy and the continued importance. Our highperformance coating will help protect an aircraft that carries not just fuel, but decades of history, craftsmanship, and community identity for years to come.” ■
40 YEARS OF PERFORMANCE
Hutton TLP case study and the impact of highly loaded lamellar glassflake in offshore coating, carried out by International Paints, part of AkzoNobel.
Illustration of water permeability
High water permeability
Low aspect ratio glass particles
Substrate
Low water permeability
High aspect ratio glass pigment
EXECUTIVE SUMMARY
In the offshore environment, both for oil & gas (O&G) and wind energy sectors, there is an increasing need to extend the lifetime of assets to 40 years or more. The main drivers of this change are to reduce the need for expensive and hazardous maintenance in difficult-to-reach offshore locations and to minimise the environmental impact these assets have over their lifetime.
Currently, there are no recognised industry standards for accelerated testing beyond 30 years. This leaves paint manufacturers with the critical question: “How do we prove our coatings can last beyond 40 years?”
AkzoNobel’s approach to answering this question involves examining long-standing real-world examples of assets and utilising both existing and new testing methods to determine the expected durability of our coatings.
Two recognised accelerated testing approaches used in the industry to determine the lifetime expectation of a coating system for splash zone and immersed areas are Water Immersion and Corrosion Creep at the Scribe.
A. Water immersion
Long-term water immersion tests and cathodic disbondment tests form part of recognised standards such as ISO 12944 and Norsok M-501. Newer standards such as ISO 24656:2022 provide guidance for long-term durable coating systems for both immersed and partly-immersed areas offshore and recommend the use of epoxy coatings with highly loaded lamellar glassflake (>20%) for the longest durability.
B. Corrosion creep at the scribe
Accelerated corrosion tests such as ISO 12944 and Norsok M-501 utilise corrosion creep at the scribe along with set pre-qualification criteria. These methods measure the performance
once the coating has been artificially damaged and once the steel is exposed, it will start to corrode, and the coating’s role is to slow down the expansion and spread of the corrosion due to under-film corrosion.
The main function of a coating in the splash zone or immersed area is to ensure appropriate barrier protection and to prevent the external environment from causing steel metal loss. One way to achieve this is to ensure that the coating remains intact for as long as possible, thereby ensuring and prolonging low permeability and high barrier properties.
In this paper, we explore the durability of Interzone® 1000 when varying the loadings of lamellar glassflake. The loading of lamellar glassflake was varied then subjected to a range of performance tests to ascertain a comparison versus the standard commercially available product.
In addition, a review of how a commercially available product performed in an offshore realworld environment via a 40-year case study, evaluating visual appearance, adhesion, crosssectional optical microscopy, and electrical impedance spectroscopy (EIS).
GLASSFLAKE CONTENT
STUDY – PART 1
Introduction
Interzone 1000 is one of the longest-serving products within the International® range of protective coatings. It is designed for the most aggressive offshore environments, such as underdeck areas, splash and tidal zones, and sub-sea areas. Interzone 1000 offers an excellent combination of corrosion protection and resistance to mechanical damage in both atmospheric and immersed environments. It boasts an extensive track record, including 40-year performance testimonials, which is unmatched in the industry.
Coating Category I II
Related Standard and Code categories
N/A
DNVGL RPB401 Cat I DNVGL RPB401 Cat II
12944-9 lm4
NORSOK M-501 7B
RPB401 Cat II1
12944-9 CX lm4
M-501 7A
micronised > 20% by weight Minimum number of coats 1 1
NDFT (μm) ≥ 20 ≥ 250 ≥ 350 ≥ 600 ≥ 1000
1. Some of the codes and standards referenced in Table D.1 allow the use of zinc-rich primers. In this standard zinc-rich primers are not recommended for use in the immersed, tidal and splash zones.
In these aggressive environments, Interzone 1000 typically utilises high Dry Film Thickness (DFT) combined with a high loading of glassflake. Interzone 1000 contains >30% corrosion and chemically resistant lamellar structure glassflake in the cured film. This glassflake significantly contributes to the high barrier against moisture ingress and reinforces the dry film, providing excellent resistance to mechanical damage such as impact and abrasion.
Furthermore, the ISO 24656:2022 standard (Cathodic Protection of Offshore Wind Structures) recommends a high-build, glass-flake epoxy or polyester material containing at least 20% nonmicronised glassflake for the longest service life. This recommendation has led to questions about the glassflake loading level in Interzone 1000, with some competitors claiming that the >30% lamellar structure glassflake level is excessive.
The aim of Part 1 of this study is to investigate the impact and abrasion resistance of Interzone 1000 when compared to variants with reduced levels of lamellar structure glassflake. The data from this work will show whether this reduction significantly affects the impact and abrasion resistance.
Test programme
Variants of Interzone 1000 were formulated with glassflake levels varying from 20% down to 0% in the dry film. These were tested alongside the control formulation – Interzone 1000 – with its >30% loading level in the dry film.
2. The use of any of the coating systems in Table D.1 demands that all coatings, surface prepAration, application, inspection and testing has been carried out in full accordance with all relevant parts of the referenced related codes and standards.
This resulted in the following four variants being tested:
1. Interzone 1000 (standard product with glassflake loading at >30%)
2. Interzone 1000 (reduced glassflake loading to 20%)
3. Interzone 1000 (reduced glassflake loading to 10%)
4. Interzone 1000 (No glassflake loading – 0%)
There are numerous methods for assessing the abrasion resistance of a coating system. The most extensively used is the Taber Abrasion test. However, there are concerns that this test does not provide an accurate gauge of a coating’s abrasion resistance.
In Part 1 of this study, the focus has been to evaluate performance in the following tests:
. Shear Box (BS1377 Part 7: Method 5)
. Gardner Impact (ASTM D2794)
In addition, the mechanical properties, such as tensile strength and elongation, were investigated for the formulation variants to ascertain whether this data correlated with the abrasion resistance. The Cyclic Ageing Test (ISO 12944-9) was also included in the test programme to understand whether the reduction in glassflake has a detrimental effect on corrosion at a scribe. Results from this study will be released in future parts.
Extract from ISO 24656
Illustration of
Measure Damage Visually and Immerse Panels
Test X9 (shear box)
■ Cargo eg: coal, iron ore
■ Coated steel panel
Test results
Shear Box (BS1377 Part 7: Method 5
Abrasive cargoes such as bauxite, iron ore, and coal are placed in a shear box, which is then positioned onto a coated steel panel with a set pressure ranging from 300 kPa to 1,200 kPa. The panel is dragged under the cargo at a set rate (up to 1.1 mm/min) while the pressure is applied. The coating loss or damage is then measured and categorised as either cohesive damage (damage within the coating) or damage down to the steel substrate (where the underlying steel is exposed to atmospheric conditions).
This test has been shown to differentiate coatings in a manner similar to in-service conditions and has been used for cargo settling and icebreaker coating assessments. It was originally derived from civil engineering purposes for the classification of soils and clays (BS 1377 Part 7: Method 5).
Since Interzone 1000 sustains minimal damage, particularly down to the underlying steel substrate (which could lead to corrosion), the test parameters were slightly modified to investigate the coating’s endurance and to differentiate the various loading levels of lamellar glassflake:
. The cargo chosen was iron ore, the most aggressive cargo available for this test method.
. The pressures were significantly increased from 300 kPa to 900 kPa and to a maximum of 1200 kPa.
. In addition to the standard scheme thickness (2x 500μm DFT), a single scheme thickness was investigated.
. Repeats of the test were carried out on panels to determine whether a second run would significantly impact the abrasion resistance, given the likely DFT loss from the first run.
Cargo under Pressure (300-600 KPa)
31,000-62,000 kg/sqm
Panel “Dragged” under cargo
The typical scheme thickness for Interzone 1000 is 1,000μm (two coats at 500μm per coat).
Reducing the scheme thickness to 1 x 500μm increases the likelihood of abrasion damage reaching the underlying steel substrate thus being able to better visually correlate performance across the glassflake loading levels.
Duplicate panels were prepared as a singlecoat scheme (1 x 500μm DFT). Half of these panels were tested using iron ore at 900 kPa, and the remaining panels were tested at 1,200 kPa before being assessed for abrasion damage. The Graph 1 shows how the coatings performed at the two different pressures.
The most critical performance parameter is the damage down to the steel substrate, as this could lead to corrosion of the structure. The damage down to steel was plotted against the glassflake loading.
The test at 900 kPa shows a significant difference between the highest and lowest loading levels of glassflake; the damage down to the steel substrate ranges from 0% to almost 1% when the glassflake is removed in the standard Interzone 1000 formulation. The damage to the 10% and 20% glassflake loading level is so low that there is no significant difference between these coatings.
The test carried out at an increased pressure of 1,200 kPa shows a much more obvious trend in terms of abrasion resistance and glassflake loading level. In this instance, the only coating with no damage down to the steel substrate is the standard Interzone 1000 with >30% lamellar glassflake. The level of damage increases as the level of glassflake loading decreases.
Shear box testing at single thickness (1 x 500micron DFT)
■ 900 KPa Iron Ore ■ 1200 KPa Iron Ore
Gardner Impact (ASTM D2794)
The Gardner Impact test assesses the resistance of a coating to rapid deformation following the impact of a specified falling weight from a specified height. This test method uses a metal cylindrical weight with a hemispherical indenter housed within a vertical tube. The tube, graduated in centimetres, guides the indenter as it falls due to gravity towards the test panels. The height (h) from which the weight is released is directly proportional to the impact energy, calculated using the equation: E = mgh where (m) is the weight of the drop -tup and (g) is the gravitational acceleration.
The aim of Gardner testing is to find a drop height at which 50% of the tested specimens will crack. This height can then be converted to the impact energy that causes the coating to break down. Several impacts need to be performed to identify the impact damage energy.
The result of the impact testing is shown in the table below (Table 2). The table provides the highest energy each coating variant can withstand and to what degree of success. According to the Gardner test results, the impact resistance of the coating decreases in line with the decrease in glassflake content.
Graph 1: Comparative results from shear box testing
Table 2: Comparative results from Gardner Impact testing
SCR
Findings
Within the scope of the testing carried out, the results from the Shear Box and Gardner Impact testing indicate a reasonable correlation between the loading of lamellar glassflake content and the abrasion and impact resistance of the coating. This in turn, within the scope of the testing carried out, demonstrates that a >30% lamellar glassflake content, combined with the epoxy technology used in Interzone 1000, provides the most robust performance.
HUTTON TLP 40-YEAR CASE STUDY
Introduction
In the previous section we have given some evidence as to why Interzone 1000 would perform well over extended periods of time, now we will show what that looks like in a realworld example.
From 1982 a new design for offshore oil and gas production using a tension leg platform (TLP)[3] was being used allowing for exploration in deeper waters. A TLP is a vertically moored floating structure normally used offshore in the production of oil or gas and is particularly suited for water depths greater than 300 metres (about 1,000 ft) and less than 1,500 metres (about 4,900 ft).
The platform is permanently moored by means of tethers or tendons grouped at each of the structure’s corners where a group of tethers is called a tension leg. A feature of the design of the tethers is that they have relatively high axial stiffness (low elasticity), such that virtually all vertical motion of the platform is eliminated. This allows the platform to have the production wellheads on deck (connected directly to the subsea wells by rigid risers), instead of on the seafloor. This allows a simpler well completion and gives better control over the production from the oil or
gas reservoir, and easier access for downhole intervention operations.
TLPs have been in use since the early 1980s, with the first built for Conoco Philips for the Hutton field in the North Sea in the early 1980s. The hull was built in the drydock by Highland Fabricators, Scotland, with the deck section built nearby at McDermott’s yard at Ardersier. The two parts were then combined in the Moray Firth in 1984.
The Hutton TLP was originally designed for a service life of 25 years in the North Sea and at the time of construction Conoco Phillips coating engineers decided to use a coating that was loaded with high levels of lamellar glassflake to maximise service life. The coating system selected for the jacket included a blast holding primer followed by three coats of a high build epoxy pigmented >30% by weight of lamellar glassflake in the dry film followed by an epoxy finish.
Specification:
1. Abrasive blast clean to SSPC SP10 near white metal with sharp angular profile of 75-100 microns (3-4 mils)
2. Epoxy blast primer 25 microns (1 mil)
3. Interzone 1000 500 microns (20 mils)
4. Interzone 1000 500 microns (20 mils)
5. Interzone 1000 500 microns (20 mils)
6. Epoxy finish 75 microns (3 mils)
Production on the Hutton field began in August 1984[4] and the field was retired in the summer of 2001. During its lifetime the Hutton TLP was exposed to 25-metre waves and 100 mile per hour winds. After this period the Hutton TLP had a nomadic life as the platform was removed for re-use outside the UK.
In early 2009 the hull section of the former Hutton TLP was relocated in the Cromarty Firth, Scotland where it remained on station.
In 2011 a visual inspection was carried out on the condition of the coating system and reported [5] to be in excellent condition. After nearly 30 years in service the highly loaded glassflake epoxy is still performing very well on the painted tubular splash zone sections of the Hutton TLP hull with an estimated corrosion of less than 1% over the coated immersed and splash/tidal zone. The jackets remained at Cromarty until 2022 when the asset was subsequently purchased for decommissioning at Invergordon, thus effectively completing its lifecycle close to the place where it was constructed.
The Hutton TLP jacket has three separate environmental zones including atmospheric and splash/tidal zones being protected by the coating system and the submerged zone which was protected using a combination of coating and sacrificial anode cathodic protection (SACP). Interestingly the submerged zone only had the full coating system applied to approximately 10 metres below the waterline.
Experimental procedure
In early 2022 we were approached by Nerida Limited, who were responsible for the final decommissioning of the Hutton TLP jackets, with regard to the coatings applied. During conversations with Nerida it was agreed to provide test plates from the Hutton jacket for detailed inspection as to the condition of the coating system.
A coating inspection company was tasked with providing independent witnessing of the inspection and provided a report [6] on the results which are discussed in detail below.
Visual appearance
The general coating system appeared to be in excellent condition with no visible signs of cracking, flaking, blistering or corrosion even under 30x magnification.
Optical microscopy
The steel plate was cut to expose the coating system and reveal the cross section which was examined using digital microscopy at 300x magnification to look at the number of coats and typical thickness of each layer. From the cross section the coating system consists of five distinct layers:
1. A buff primer layer typically 25 microns (1 mil) in thickness which is epoxy polyamide based and pigmented with inert pigments.
2. Layers 2-4 consist of Interzone 1000 typically ranging from 300-600 microns per coat (12-24 mils) in thickness. Each layer is pigmented with high amounts of lamellar glassflake as can be seen below as thin plate-like particles well aligned throughout the coating.
3. Top layer consists of a yellow topcoat of typically 75 microns (3 mils) thickness based on an epoxy polyamide finish coat.
The total dry film thickness measured on test plates ranged between 1,200-1,400 microns (48-56 mils) consisting of the holding primer
followed by three layers of Interzone 1000 and finally an epoxy finish coat.
The epoxy topcoat on the sample plates generally appeared in good condition. However, on closer observation some areas of the jackets had indeed suffered from signs of chalking and even complete removal of the topcoat due to long term exposure to the damaging effects of UV irradiation. Some areas were more affected than others. This can be explained by the protection initially given to the jackets by the topside whilst in service.
Once the topside was removed, some areas were generally more shaded than others depending on their position in relation to the sun. As expected, areas subjected to higher levels of UV will have chalked and eroded more, exposing the glassflake epoxy undercoat. In general terms the epoxy topcoat has performed well.
with ISO 4624[7] using a self-aligned pneumatic adhesion tester. A total of six dollies were fixed to the coating system using two separate test plates. The adhesion values were of a high value with averages of 11.68MPa (1,694 psi) and 13.69MPa (1,986 psi) respectively with failures typically occurring cohesively within the glassflake epoxy layer with no adhesive failures to steel, confirming the excellent performance of the coating system even after 40 years exposure.
Infrared spectroscopy
A flake sample from the Hutton TLP was subjected to infrared spectroscopy. The glassflake epoxy layer was compared to a recently manufactured batch of Interzone 1000 and showed to be a very good match.
Electrochemical impedance spectroscopy
(EIS) can be used as a non-destructive technique to determine a coating’s barrier properties and potentially indicate substrate corrosion processes under the film. Intact coating locations (each with an area 12.55 cm2) were measured to assess the barrier properties that are representative of the overall bulk coating. EIS measurements[8] were performed using a sinusoidal signal of 200 mV applied at open circuit potential in the frequency range 10,000 – 1 Hz. As the EIS measurements were carried out in the field, values were obtained using a two-electrode system, in which the working electrode is the coated steel substrate, and the counter electrode is a stainless-steel casing in a 3.5 wt.% NaCl(aq) electrolyte which is kept in contact with the measurement area (12.55 cm2) using a magnetic cell. The electrodes were attached to the test plate for 48 hours to ensure total saturation of the sample area prior to scanning.
Results of the EIS scans demonstrated that the coating had excellent barrier properties even after 40 years exposure and were comparable with a freshly applied sample of the coating material.
Findings
Conoco Philips decided to use an epoxy, pigmented with a high loading of lamellar glassflake, to provide corrosion protection for the jackets of the Hutton TLP with a design life of 20-25 years in the harsh North Sea environment. At the time of writing the jackets have been exposed for a total of 40 years in various offshore locations and an opportunity to inspect the condition of the coating system was realised. It is clear from the inspection of the test plates that the performance of the coating system has been impressive.
The visual inspection of the coating showed no signs of blistering, cracking, flaking or corrosion and appeared in excellent condition in all environmental zones on the jackets.
Significantly, using electrochemical spectroscopy it was found that the barrier properties of the 40-year old epoxy coating system was essentially unchanged from the initial barrier properties of a virgin coating sample. This correlated well with the observations reported in 2011, that after 30 years of exposure there was less than 1% corrosion on the Hutton jacket across the submerged (Im4), splash/tidal (Im4/CX) and atmospheric (CX) zones.
The adhesion values of the coating were of a very high order of typically more than 10MPa and only demonstrated cohesive failure within the glassflake epoxy with no adhesive failure to the steel substrate indicating the coating still had good overall strength.
The use of optical microscopy highlighted five layers in total consisting of a blast primer, three layers of high build epoxy each pigmented with high loadings of lamellar glassflake and an epoxy finish coat.
Due to the high loading of glassflake the coating system has exhibited excellent abrasion resistance minimising mechanical damages and providing a tortuous path for salts and moisture through to the substrate, (i.e. stifling external corrosion), and thus resulting in the overall low corrosion observed on the jackets.
Table 3: Adhesion testing results
Electrochemical impedance spectroscopy fresh sample vs 40 year field aged samples
Poor Coating Barrier
The examination of the Hutton jacket shows that it is possible to have a maintenance-free coating system that can last up to 40 years, and potentially beyond, in highly corrosive environments including submerged zone (Im4), splash/tidal zone (Im4/CX) and atmospheric zone (CX) based on epoxies pigmented with a high loading of lamellar glassflake. Therefore, the latter coatings would be an ideal solution for offshore assets for the protection of foundations and transition pieces for extended life to first major maintenance.
The excellent performance of the coating system on the Hutton jackets supports the recommendations offered in a recently released ISO standard for offshore wind assets, ISO 24656:2022 ‘Cathodic Protection of Offshore Wind Structures[2].’ Part of this standard covers coating selection and includes breakdown rates per year for both the splash and submerged zones. The standard describes the coating type with the lowest corresponding annual breakdown rates per year as having >20% lamellar glassflake by weight in the dry film.
Acknowledgement
We would like to offer thanks to Jonathan Townley of Nerida Decommissioning for supplying the test plates for inspection.
Conclusion
Considering the data gathered in the glassflake Content study and in view of the results of the real world 40-year case study, demonstrates that the 33% loading of lamellar glassflake in
Interzone 1000 provides excellent protection to assets for extensive durations, ensuring the lifetime of assets are met and exceeded.
References
Name of standard or report (latest revision), “Title of Standard or Report” (City of publisher, State of publisher: Name of publisher).
1. ISO 12944-9:2018, “Paints and varnishes –Corrosion protection of steel structures by protective paint systems – Part 9:Protective paint systems and laboratory performance test methods for offshore and related structures”.
2. ISO 24656:2022, “Cathodic protection of offshore wind structures”.
3. Our World of Energy “What is a TLP and how has this technology been used in offshore production?” Newsletter 2016-01-26.
4. R. D’Souza and R. Aggarwal “The Tension Leg Platform Technology – Historical and Recent Developments,” 2013 Offshore Technology Conference Brazil, Paper #24512 29-31 October, 2013.
5. Case history:2011, “Hutton TLP after 29 years”, International Protective Coatings, AkzoNobel.
6. Element Materials, inspection report N100253, 2023.
7. ISO 4624:2016, “Paints and varnishes – Pulloff test for adhesion”.
8. ISO 16773-2:2016, “Electrochemical impedance spectroscopy (EIS) on coated and uncoated metallic specimens – Part 2: Collection of data”. ■
Extending the service life of an offshore wind turbine tower brings value to the owner and reduces environmental impact. Zincrich primers provide essential corrosion protection that extends service life, with organic epoxy or urethane mid- and/ or topcoats being the prevailing additional components comprising the corrosion protection system, explains Kristen Blankenship from Carboline in St Louis, Missouri.
Figure 1: The Missouri Department of Transportation’s Dorsett/Lindbergh overpass in suburban St Louis was coated with IOZ/IO
In recent years, silicate topcoats made without zinc have entered the market to create a two-coat inorganic system that testing demonstrates can offer superior corrosion protection. But the implications of adopting two-coat inorganic coating systems for offshore atmospheric exposures transcend improved performance: Important cost, application, and long-term environmental benefits also emerge. This article explores a two-coat inorganic corrosion-resistant coating system, its function, application, and how it extends the service life of wind towers by inhibiting corrosion for decades.
Offshore environments: The most severe service
Offshore environments have always posed a special challenge for protective coatings. Today, wind towers newly contribute to a coastal tapestry once only dotted by offshore oil rigs. While the offshore exposure environment remains consistent, the demands on protective coatings for these two assets are unique: Offshore asset protective coatings must comply with ever more stringent standards for health and environmental impact, while also protecting the asset against the more aggressive exposure to saltwater, wind, and wind-driven rain, snow and ice.
ISO 12944-9 and parts of NORSOK M-501 address the atmospheric tower. These standards were the basis of testing, summarised below, which demonstrates improved corrosion protection performance with wide-reaching and consequential implications.
Corrosion protection of atmospheric wind towers
Above sea level, various coating systems may be used, again, predominantly governed by ISO 12944-9 and NORSOK M-501. Zinc primers, both organic and inorganic, are the foundation for corrosion protection. Organic zinc-rich primers, based on epoxy resins, are resilient against moisture and salts but not UV light. As a result, these primers should be protected by a midcoat and/or topcoat. This coating scheme relies on film build and more resilient chemistry against UV degradation, namely polyurethanes or polysiloxanes. But regulatory trends put in doubt the resilience of this scheme. For example, in the EU, polyurethanes are becoming increasingly more challenging to use due to licensing requirements when using systems that need isocyanates.
The other type of zinc-rich primer is based on inorganic resin chemistry. Ethyl silicates cure via hydrolysis followed by condensation reaction. The final coating film consists of zinc metal in a matrix of siloxane (Si-O-Si-O). Importantly, these bonds are stronger than terrestrial UV light. Because inorganic zinc (IOZ) primers are inert to UV degradation, they do not require the use of a topcoat. Singlecoat inorganic coating systems have been highlighted as a cost-effective and competitive approach to corrosion protection for steel –especially bridges.
Single-coat inorganic zinc (SIOZ) primers were tested for 10 years in the US state of Florida, a warm, humid subtropical region known for its corrosive environment, most acutely at and near its coasts. No corrosion
was visible on the test panels. This type of single-coat inorganic system also shows excellent performance in lab-simulated salt fog testing. Very little corrosion is observed after 70,000 hours of ASTM B 117.
Why do single-coat inorganic zinc-rich coatings perform so well? It is theorised that while zinc metal participates in cathodic protection of bare steel, at a cut or damaged area, it is actually the reaction of zinc with corrosives at the air-coating interface which ultimately builds barrier protection against corrosion. The reaction of zinc with atmospheric oxygen, carbon dioxide and water forms zinc salts that fill surface pores, further increasing the barrier protection provided by SIOZ coatings.
In fact, in coastal exposures, salt catalyses the polymerisation of unreacted silicic acid groups, increasing the molecular weight and thus protection by the silicate matrix. Ethyl silicate resins cure with atmospheric moisture, creating a film that is notably more porous than traditional organic-based coatings. This porosity is far from a disadvantage. Instead, it allows for cure but also allows for the zinc near the air-coating interface to react with atmospheric oxidizers. This is why topcoating IOZ with organic, less porous materials typically shows lesser performance.
Two-coat inorganic finish system
Adding a topcoat to SIOZ isn’t necessary but is sometimes desired for aesthetics. An inorganic topcoat also based on ethyl silicate resins may be used. The topcoat has no zinc, so various colours beyond grey are possible. Crucially, the inorganic topcoat maintains the permeability necessary for proper moisture curing of the primer and topcoat, as well as allowing for corrosives in the air to travel through the film to the outer layers of zinc, reinforcing its barrier protective properties.
Figure 1 shows images of a bridge in the US state of Missouri coated in 2019 with a two-coat inorganic system. State departments
of transportation across the US have shown increasing interest in updating their protective coating specifications owing to the clearly improved performance of two-coat inorganic systems vs conventional three-coat zinc/ epoxy/urethane systems, and the resulting overall reduction in maintenance cycles and the traffic disruptions these always cause.
Inorganic coatings can reduce carbon footprint
Long-life coatings reduce environmental impact because they eliminate painting cycles. But this benefit is somewhat offset even for the highestperforming organic-based coatings because, as these degrade on offshore assets like wind towers, fine particulates enter the sea and may be considered microplastics. In the case of an inorganic coating system, degradation will be very slow and result only in the eventual accumulation of something akin to sand.
Also consider the embodied carbon of the primary resins used in two coating systems: 1) an organic zinc-rich primer based on a BPA epoxy, and 2) an ethyl silicate-based inorganic zinc-rich primer. The BPA epoxy has 3.8 kg CO2 eq/kg resin (according to RER, system model version of the ecoinvent database) and the tetraethyl orthosilicate resin has 2.6 kg CO2 eq/ kg resin (according to the GLO system model of the ecoinvent database version 3.9). The ethyl silicate resin has 32% less embodied carbon.
Utilising inorganic primers and finishes on assets offshore reduces environmental impact through both extending service life and a reduction in embodied carbon.
Experimental procedure
ISO 12944-9 assesses the corrosion performance of coating systems in atmospheric exposure in offshore environments, such as for wind turbine towers.
Exterior exposure testing is the best way to assess how a coating system performs. Real world weathering is the most representative approach, but obviously this takes time. The
Table 1: ISO 12944-C5 High neutral salt spray of two-coat IO system
E 10 2(S4) Ri0 0(S0) 0(S0) 0.19
*Estimated scribe creep, coating not removed as test was ongoing
**Stained from edge rust or grit contamination
best compromise is the use of accelerated testing. The ISO 12944 standard is well recognised for understanding a coating system and the ability it has to protect against corrosion. ISO 12944-6 C5-M (now known as C5 High) requires 1,440 hours neutral salt spray. A single coat of inorganic zinc passes this test.
A two-coat inorganic system was tested (Table 1). This system was composed of an inorganic zinc primer with an inorganic finish.
. The ISO 12944-9 Annex B Cyclic Ageing Test is designed to study coatings exposed in extreme environments such as offshore. Coating systems were applied over carbon steel with an SSPC- SP 10 or better surface prep and a 25-75 micron (1-3 mil) profile.
The systems studied included:
. System A: Inorganic zinc primer B, 50-75 microns (2-3 mils)/Experimental inorganic finish, 75-125 microns (3-5 mils)
. System B: Inorganic zinc primer A, 50-75 microns (2-3 mils)/Inorganic finish, 75-125 microns (3-5 mils)
. System C: Galvanizing, 75-100 microns (3-4 mils)
. System D: Thermal spray metallizing, 300350 microns (12-14 mils)
. System E: Thermal spray metallizing/ Polyurethane clear, total of 450-550 microns (18-22 mils)
Results
Results of ISO 12944-6 testing show that both the single inorganic zinc coating (SIOZ) along with a two-coat inorganic system both pass at C5 High exposure. This indicates that both systems offer excellent corrosion protection in high- to severe corrosion environments including coastal areas for at least 15-25 years.
Results of the ISO 12944-9 testing suggest that two-coat inorganic finishes perform as well as galvanizing or thermal spray metallizing. The results in Table 2 are after 4,200 hours.
The rusting seen with galvanizing is possibly due to application issues (thin film in some areas). This does suggest that traditional spray-applied coatings offer an ease of application and robustness that can prevent premature failures. Images of the panels after 4,200 hours are shown in Figure 2.
A two-coat inorganic finish passes the ISO 12944-9 cyclic test for CX corrosive environments, including offshore, indicating performance beyond 25 years. But just how far beyond? What results would be observed if the test was run a second time? A third?
Scientists in Carboline’s Research, Development and Innovation laboratory in St Louis, Missouri, ultimately ran the test panels through four ISO 12944-9 Cyclic Ageing Test cycles, or 16,800 hours total hours of exposure. Following this fourth cycle, the panels were inspected and achieved passing results. System Panel ID
Figure 2: ISO 12944-9 test panels after 4,200 hours exposure
It is important to note that ISO has so far not defined a minimum service life for any coating system passing four successive ISO 12944-9 test cycles. But the condition of the IOZ primer/inorganic finish coat system after a staggering 16,800 hours of exposure in those test conditions suggests the system is capable of extremely high performance with little to no maintenance for the entire design life of an offshore wind asset.
Conclusion
Coating structures for offshore use is complex. Considerations of exposure environment affect the corrosion mechanism scheme.
For atmospheric protection on wind towers, a two-coat inorganic coating system provides longer service life, reduced maintenance, lower embodied carbon and the elimination of microplastic accumulation in oceans. Coatings based on ethyl silicate resin technology offer ultra-long-lasting corrosion protection, are essentially inert to UV degradation (strong Si-O bonds) and have lower embodied carbon than standard epoxy resins used in organic zinc-rich primers. A two-coat inorganic system offers an array of colour options beyond the grey found in IOZ primers.
The science is clear. More proof of field performance emerges every day.
As society and economy each embrace their obligation to minimise ecological damage while optimising the performance of their
Coatings based on ethyl silicate resin technology offer ultra-longlasting corrosion protection, are essentially inert to UV degradation and have lower embodied carbon than standard epoxy resins used in organic zinc-rich primers.
most essential assets and infrastructure, good stewardship compels the rapid adoption of high-performance two-coat inorganic corrosion protection systems. ■
Figure 3: ISO 12944-9 Inorganic zinc primer/ Inorganic finish test panels after 12,600 hours exposure (three successive test cycles)
ANAEROBIC DIGESTER REPAIRS
Corroless Eastern recently carried out repairs and relining on two anaerobic digesters in the UK: one in Lincolnshire and one in Cornwall.
The anaerobic digester in Lincolnshire had previously been lined internally with a membrane system that extended over the top of the tank walls. Unfortunately, hydrogen sulfide-rich gas had been able to enter under this membrane, allowing biogenic sulfuric acid to form beneath, resulting in attack and degradation of the tank structure.
The intricate nature of wastewater treatment and its degradation processes pose significant challenges to the surrounding infrastructure. The rate of chemical attack is determined by a range of factors related to both the wastewater and its environmental conditions. These factors can even lower the pH level below 1 in extreme cases. Uncoated concrete is particularly susceptible to so-called biogenic sulfuric acid corrosion (BSA). BSA corrosion is caused by bacteria present in wastewater. These bacteria metabolize hydrogen sulfide (H2S) into sulfuric acid. The sulfuric acid then deposits directly onto the concrete, causing chemical attack. This attack is particularly aggressive because the sulfuric acid lowers the pH of the concrete, making it more susceptible to corrosion. The resulting erosion of the concrete surface can be rapid and damaging.
Concrete removal
Corroless Eastern proposed the removal of defective concrete followed by reinstatement and protection with a suitable tank lining system. The company proposed a choice of tank lining systems depending on the climatic conditions that might have been present at the time of application (February/March).
Due to the prevailing climatic conditions, the most suitable and cost-effective tank lining system was Sikagard M790. This material can be applied in ambient and substrate temperatures as low as 5°C. By contrast, other systems proposed required a minimum ambient temperature of 10°C.
Sikagard-7000 CR is a durable protective coating engineered for the preservation of concrete structures in water management applications, particularly water supply infrastructure and tanks within wastewater treatment facilities. It is based on the unique Xolutec Technology. By optimising the intermolecular interactions between the resin building blocks, it forms an enhanced cross-linked polymer network (XPN). This material is an excellent solution for aggressive
The anaerobic digester had previously been lined internally with a membrane system that extended over the top of the tank walls
wastewater and digestion environments as it offers excellent chemical resistance and crack bridging, with an expected service life in excess of 20 years.
Preparation
Initially, the heavily-degraded thickened sections on the precast concrete tank panel externals were isolated using diamond saws. They were then broken off using vibrationdamped breakers.
Termination points for the concrete repairs on the top of the tank wall were also made using the diamond saws prior to the removal of degraded concrete by means of high-pressure water jetting (10,000 psi).
All areas to be repaired were primed using Sika MonoTop 1010, applied using a slurry brush to work the material into the substrate. Sika MonoTop 612 was then laid ‘wet on wet’ into this bonding bridge for maximum adhesion. The tank internals were then prepared using water-entrained abrasive blasting. The precast concrete panels are extremely hard, with a compressive strength greater than 70N/mm, meaning that this was the best method to raise a surface profile for the tank lining to adhere to.
During the preparation works we discovered that the concrete had been stained through its service. To remove this staining required the degradation of the concrete surface that would necessitate further repairs before the tank lining could be applied. To confirm if this was necessary, areas were blasted to a point that sufficient surface profile was present for adhesion of the tank lining but not removing the engrained staining. Sample areas of Sikagard P770 primer were then applied.
Once cured, pull-off test dollies were bonded in place and adhesion tests conducted. This confirmed that the staining was not detrimental to the adhesion of the tank lining, with all test results exceeding 3N/mm2
This standard of preparation was then continued across all areas where the tank lining was to be applied. Some localised areas were treated using Sika TopSeal 586 cementitious fairing coat to provide a surface suitable for a tank lining to be applied to.
Prior to coating works commencing and during application, the climatic conditions were tested and recorded as part of Corroless Eastern’s standard tank lining quality assurance to ensure compliance with the manufacturer’s recommendations.
Termination points for the concrete repairs on the top of the tank wall were made using diamond saws prior to the removal of degraded concrete by method of high-pressure water jetting
The tank internals were then prepared using water entrained abrasive blasting
Prior to coating works commencing and during application, the climatic conditions were tested and recorded
Application
All surfaces were primed using Sikagard P770 applied by brush and roller at a practical coverage rate of 0.4kg/m2. Sikagard P770 is extremely damp-tolerant and has no substrate moisture content limitations, making it extremely versatile.
Once cured overnight, the first coat of Sikagard M790 was applied in a contrasting red colour to a minimum wet film thickness of 400 microns.
This was again allowed to cure overnight, prior to the application of a second coat of Sikagard M790 in a contrasting grey colour. This was applied at the same application rate as the previous coat. The reason that contrasting colours are used as per best tank lining practice is to aid identification during application and ensure full coverage.
Wet film thickness readings were taken throughout the application to ensure that the correct thicknesses were achieved.
As part of Corroless Eastern’s standard tank lining quality assurance, the applied tank lining was tested for porosity by high-voltage spark
testing – called DC Holiday testing. By running a copper brush earthed to a non-coated area, any breaks in the coating are identified. This is essential in an aggressive environment such as that found in an anaerobic digester, as a single pinhole will allow the attack of the concrete to recommence in these areas.
CORNISH DIGESTER RELINING
Upon opening the anaerobic digester to remove grit, Corroless Eastern’s client found that the existing tank lining was in a very poor condition. Extensive blistering and breaks had allowed the concrete to be attacked and degraded because of exposure to hydrogen sulfide/biogenic sulfuric acid.
Again, Corroless Eastern proposed the removal of the existing failed tank lining and application of Sikagard-7000 CR tank lining, which is particularly suitable for use in an anaerobic digester environment.
Initially, the failed lining and degraded concrete were removed using ultra-highpressure water jetting. This dust-free method of surface preparation not only removed the failed coating and concrete but also perfectly textured the concrete substrate in readiness to receive concrete repair materials.
Application
SikaCem -133 S Gunite was then spray-applied by Corroless Eastern’s sprayed concrete subcontractor GSSL. This was sponge-float finished to provide a mechanical profile for the subsequent tank lining to adhere to.
As per the manufacturer’s recommendations, the concrete repair materials were protected with polythene sheeting to ensure proper curing. Once the concrete curing regime had been achieved, the sheeting was removed and the concrete repairs cleaned using high-pressure washing to remove any dust contamination.
The moisture content of the concrete was then tested and recorded as part of Corroless Eastern’s standard tank lining quality assurance. However, this is not strictly required when using the Sikagard-7000 CR system as the primer Sikagard P770 can be applied to extremely damp substrates and has no substrate moisture content limitations. This was the reason that this tank lining system was selected for this application, as the client had an extremely tight programme of works and could not afford any delays whilst waiting for the concrete to hydrate.
Once cured overnight the first coat of Sikagard M790 was applied in a contrasting red colour to a minimum wet film thickness of 400µ (top), prior to the application of a second coat in a contrasting grey colour (bottom)
The existing tank lining was in a very poor condition, with extensive blistering and breaks
The first coat of Sikagard M790 was applied by brush and roller in a red colour at a practical coverage rate of 0.6Kg/m2
The climatic conditions were tested and recorded prior to and during tank lining application.
All surfaces were primed using Sikagard P770 using brush and roller at a practical coverage rate of 0.4kg/m2. The Sikagard-7000 CR system does not have any relative humidity restrictions, making it very versatile and flexible tank lining material.
The first coat of Sikagard M790 was applied by brush and roller in a red colour at a practical coverage rate of 0.6kg/m2. This was allowed to cure overnight prior to the application of the second coat in a contrasting grey colour as per best tank lining practice, in the same manner and application rate as the previous coat. Wet film thickness readings were taken throughout the application process to ensure that the correct thicknesses were achieved.
Once cured, the applied tank lining was tested for porosity using a DC Holiday spark tester to check for pinholes. In an aggressive hydrogen sulfide-rich environment such as an anaerobic digester a single pinhole is all that is required for attack of the concrete substrate to recommence.
Any pinholes found were marked with chalk prior to touching in using the same material applied by brush. ■
A second coat of Sikagard M790 was applied in a contrasting grey colour as per best tank lining practice
A look at the more technical aspects of paints & coatings, corrosion investigation & prevention
INFLUENCE OF OVERPROTECTION ON AC CORROSION: Analysis of a real case
The risk of AC corrosion has always been linked to the parallelisms of underground pipelines with HVAC lines, especially in those geographical areas where the morphology of the territory creates obligatory so-called ‘technological corridors’ and therefore forces the coexistence of different services over long distances.
Recently, the greater diffusion of AC-powered railway networks has further increased the AC interfering sources, while the use of more performing coatings on underground pipelines has on the one hand increased their insulation from the surrounding soil, and on the other has increased the risk of overprotection compared to old, less performing, or more degraded coatings.
This paper, starting from a real case found in a gas distribution network, will present the normative criteria to be used to keep the AC corrosion risk under control, and will highlight how the simultaneous presence of cathodic overprotection may result in an autocatalytic cycle leading to accelerated AC corrosion, in which monitoring becomes essential in order to be able to carry out on time the appropriate corrective actions, explains Ivano Magnifico, Corrosion Protection Specialist at Automa Srl, Ancona, Italy.
Interference mechanisms
There are several mechanisms through which an AC source can interfere with a metal structure (Figure 1): by inductive coupling, as an effect of the magnetic field generated with respect to an underground structure; by capacitive coupling, in the case of an aerial structure; by conductive coupling in presence of a fault current in the ground, in the case of an underground pipeline.
In the case of underground pipelines, under normal operating conditions, the mechanism that can generate AC interference is inductive coupling: normally the interference effect is greater as larger the length of the sections where the pipeline and the AC source (high voltage AC lines, railways operated in AC) follow a parallel path.
AC corrosion protection criteria
International industry standards specify which electrical parameters shall be monitored and their maximum allowed values. The standard ISO 18086:2019 “Corrosion of metals and alloys – Determination of AC corrosion – Protection criteria” [1] indicates two steps for the verification of permissible AC interference levels (Figure 2):
The first step relates to a safety criterion for maximum permissible touch voltage (15V threshold) and does not have a direct rule in AC corrosion risk assessment. This value considers a hand to hand or hand to foot resistance for an adult male human body of
1500Ω, yielding a current flow of 10mA when 15V is applied. [2]
The criterion is based on current density measurements carried out through a coupon whose surface is defined by the standard to be 1cm², connected to the structure. Both AC current density and DC current density must be measured, as the level of cathodic protection can affect the AC corrosion phenomenon.
NACE standard SP21424-2018 “Alternating Current Corrosion on Cathodically Protected Pipelines: Risk Assessment, Mitigation, and Monitoring” [3] expresses similar values, where depending on the measured DC current density value, different levels of AC current density are allowed:
. If J.dc > 1A/m2 then J.ac < 30A/m2; or . if J.dc < 1A/m2 then J.ac < 100A/m2
This standard imposes a maximum AC current density limit even if the DC current density is less than 1A/m², while the coupon surface of 1cm² is indicated as generally used but not mandatory.
The Spread Resistance is the ohmic resistance through a coating defect towards remote earth and controls the DC or AC current passing through a defect at a given voltage:
. Uac = Rs Iac or Uac = Rs J.ac . where Rs is the normalised Spread Resistance expressed in Ω·m2
Figure 1: AC interference mechanism
Figure 2: AC corrosion risk assessment according to ISO 18086
On coating defects, where cathodic protection current reaches the steel surface, cathodic reactions occur involving oxygen reduction and hydrogen evolution. Both reactions generate hydroxide ions (OH-) leading to increased pH at the interface and alkalinity.
Since Spread Resistance depends [4] on both defect size (decreases as surface decreases) and pH value at the interface (decreases as pH increases), the DC current density reaching the defect affects it:
. Lower current density leads to decreased pH value and increased Spread Resistance . Higher current density leads to increased pH value and decreased Spread Resistance
This is where overprotection can have an effect on AC corrosion:
. presence of a very electronegative IR-free potential (due to high DC current densities);
. decrease in the Spread Resistance value; . possibility of significant AC current density even with low measured AC voltage.
Regarding the choice about which size of coupon to use, increasing the surface area of the coupon results in a lower average current density since the Spread Resistance increases linearly with increasing defect diameter and the current density decreases linearly with surface area. Therefore, the current density is typically underestimated when the surface area of the coupon is chosen to be larger than the maximum defect size on the structure: for this reason, in the case of AC corrosion, the standards indicate the use of a 1cm2 coupon.
AC corrosion mechanism in the presence of overprotection [3]
For pipelines with applied cathodic protection, AC corrosion development requires simultaneous coexistence of: Induced AC, Excessive cathodic protection, Small coating defects. Under these conditions:
1. Induced alternating current leads to alternating current discharge on coating defects.
2. AC current density is regulated by alternating voltage and Spread Resistance associated with the coating defect, through Ohm’s Law.
3. Spread Resistance depends on:
a. coating defect size
b. soil resistivity near the defect
c. soil chemistry
d. cathodic protection current density in the coating defect.
As shown in Figure 3, the AC current density can lead to the depolarisation of the defect: this requires a higher DC current density to maintain a certain cathodic protection potential. Increasing the level of cathodic protection to mitigate AC corrosion, in this case, has the opposite effect: the increase in DC current density further decreases the Spread Resistance at the coating defect due to the production of OH- ions (alkalinisation). Through high levels of cathodic protection, the Spread Resistance decreases, thus increasing the density of alternating current, restarting the cycle: this scenario results in an autocatalytic cycle leading to AC corrosion. It therefore becomes clear that, to leave this cycle, it is necessary to control both the AC current density and the DC current density.
Analysis of a real field case
The case that will be shown has been detected on a measurement point of the distribution network of a large European city, with the following features:
. An extensive cathodic protection system forming a ring around the city centre with radiating offshoots
. Multiple crossings with DC powered railways and surface metro
Figure 3: Autocatalytic Nature of AC Corrosion on Cathodically Protected Pipelines described by SP21424
. Multiple parallels with the HVAC network
. Cathodic Protection guaranteed by two T/Rs.
The analysed measuring point (MP):
. Located in a CP system area with several km of parallelism with HVAC line
. Local soil resistivity between 25 and 50Ωm
. Equipped with permanent CSE reference electrode with integrated 10cm² coupon (measured current density is underestimated compared to 1cm² coupon)
. Equipped with a G4C-PRO remote monitoring device capable of performing instant-off measurements on coupon and current density measures.
The measurements shown in Figure 4 correspond to daily reports calculated on measurements performed continuously at a frequency of 1Hz (1 measure per second) for each measuring channel. The minimum, average and maximum daily values are shown over a period of four days:
. Eon.dc: ON potential (DC) expressed in V CSE
. Eon.ac: ON potential (AC) expressed in V
. Eoff: instant-off on coupon, equivalent to IR-Free potential (measured, every second,
after a 1ms wait from switch opening and over a 20ms interval) expressed in V CSE
. mIon: DC polarisation current of the coupon expressed in mA; as the coupon size is 10cm2 the shown value corresponds to the current density in A/m2
. mIon.ac: AC polarisation current of the coupon expressed in mA; as the coupon size is 10cm2 the shown value corresponds to the current density in A/m2 (note: the current density value measured on a 1cm2 coupon would be significantly greater than that measured on the 10cm2 coupon)
In the absence of coupons, the only available measures would be Eon.dc and Eon.ac, and, on these values, the only possible evaluation would be that relating to the first step of ISO 18086, which would be absolutely respected considering that the highest AC average value along the four days shown (0,424V) is well below the indicated threshold of 15V.
Generally, such a low AC voltage value would never suggest a real risk of AC corrosion, but as can be detected from the DC and AC current densities, we are faced with unacceptable interference levels:
. mIon: between 15A/m2 and 17A/m2:
. greater than the threshold of 1A/m2 for which (according to ISO 18086) the AC current density value would be indifferent
. mIon.ac: between 35A/m2 and 39A/m2:
. greater than the threshold of 30A/ m2 indicated by ISO 18086 and NACE SP21424.
The explanation for this situation is given precisely by the significant level of cathodic overprotection present, represented by IR-Free potential values more negative than -1.3 V CSE and very high DC current density values, being the MP in a site suffering cathodic DC interference generated by metro and railway systems.
This results in a reduction of the Spread Resistance value, up to the point of generating an AC current density higher than the allowed limits even in the presence of a very low AC voltage.
The main evidence of the dependence of this condition on overprotection has been clearly shown when, due to a malfunction, one of the two T/Rs protecting the Cathodic
Figure 4: Daily reports of the MP analysed
Figure 5: Daily reports of the MP analysed
Protection system did shut down, changing the values measured on the Measurement Point as in Figure 5.
On day 21/01 the shutdown of one of the two T/Rs obviously brought a reduction of the DC protection current, with the result that, at a positive shift of the IR-Free potential from -1,3 V CSE to -1,06 V CE, AC current density has become less than half, from average daily values of 28A/m2 to values of 12A/m2 possibly again compatible with the acceptance criteria expressed in ISO 18086 and NACE SP21424. (It should be remembered that being the measure made on a 10m2 coupon, the result is certainly underestimated compared to the use of a 1cm2 coupon as required by the aforementioned standards).
The trend is also evident in Figure 6, which shows the evolution of the daily average values in the two weeks when the switching off of the T/R happened:
In correspondence to the decrease of the cathodic current density (J.dc) there is obviously a simultaneous positive shift of the values of the IR-Free potential measurement (Eoff): this leads to the reduction of the values
of the AC current density (J.ac) to permissible values (and a slight increase in the AC voltage values in terms of absolute value, which is almost three times compared to the values measured under overprotection conditions).
Unfortunately, from a cathodic protection system management point of view, this presents some critical issues that, from a global perspective, do not allow for an easy management of the problem by simply reducing the current supplied by the T/Rs, since this would lead to problems in reaching protection levels in other areas of the system. For this reason, solutions were evaluated to locally mitigate the AC interference, the installation of which is currently being managed.
It is interesting to note that, even in the long term, this behaviour is confirmed (Figure 7):
. as long as the IR-Free potential remains in protective values, but without overprotection, the AC current density remains within the allowed limits; . as soon as the value of the IR-Free potential returns to overprotection values, the AC current density also exceeds the
Figure 6: Trend of the daily average values measured on the analysed MP in correspondence with the malfunctioning of the T/R
Figure 7: Trend of the daily average values measured on the analysed MP over a period of 19 months
eligibility limits thus confirming the strong influence that overprotection has on AC corrosion.
Conclusions
As also verified in the real field situation, in the presence of alternating interference, an overprotection condition is able to significantly accelerate the phenomenon of alternating current corrosion: an increased cathodic protection current density increases alkalinity at the defect interface and lowers its Spread Resistance value.
A too low Spread Resistance value, in the presence of alternating interference, may lead to average AC current density values higher than the allowed limit values, even in the presence of AC voltage values much lower than the threshold indicated by the first verification step of ISO 18086 (Vac = Rs * Jac).
For this reason, even if it turns out to be the driving force, it is not possible to establish a reliable criterion based only on the value of the AC voltage, since the process is driven by the value of the Spread Resistance and therefore will be dependent on the size of the defect, the type of soil and the local change of alkalinity
The use of coupons is fundamental to monitor both overprotection and DC and AC current densities.
generated by the DC current density that arrives on the defect coupon.
The use of coupons is fundamental to monitor both overprotection and DC and AC current densities, and for this reason a remote monitoring device that allows a continuous monitoring of all these electrical parameters simultaneously becomes necessary, especially if it may allow managing two coupons simultaneously: the one with variable size (e.g.: 10cm2) for the verification of protection and overprotection levels and DC current density, and the 1cm2 one for the verification of AC current density.
Bibliography
[1] ISO 18086:2019 “Corrosion of metals and alloys – Determination of AC corrosion –Protection criteria”.
[2] NACE SP0177-2019 “Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems”.
[3] NACE SP21424-2018 “Alternating Current Corrosion on Cathodically Protected Pipelines: Risk Assessment, Mitigation, and Monitoring”.
[4] L.V. Nielsen, M.B. Petersen, L. Bortels, J. Parlongue; “Effect of Coating Defect Size, Coating Defect Geometry, and Cathodic Polarization on Spread Resistance: Consequences in relation to AC Corrosion Monitoring”; Proceedings CEOCOR Congress 2010, Bruges, Belgium. ■
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Epoxy passive fire protection over galvanized steel
Epoxy Passive Fire Protection (EPFP) systems are safety-critical installations that are installed in high-hazard facilities. Their requirement is often driven by legislation and of life-safety importance. Hot-dip galvanizing is often specified for long-term corrosion control of steel which is not required to be protected by EPFP, and its acceptance for use under thick-film EPFP systems will be driven by the quality of its installation and adds a degree of risk, explains Chris Fyfe at International Paints.
This article will argue that the best practice is the direct application of EPFP paint systems to properly prepared steel substrates and a correct EPFP system installation will give a comparable corrosion-free life expectancy. Therefore, galvanizing should only be considered as a substrate for EPFP when there are no other design options available, and even then, only with additional (stringent) quality control measures that may go beyond typical industry/project expectations. This article will explore the inherent risks – including excessive thickness, metallurgical defects, and inadequate repair methods – that can compromise the adhesion and ultimately could detract from the EPFP safety-critical function.
Application is critical
Epoxy Passive Fire Protection (EPFP) is designed to insulate critical steel structures in a fire event. This safety-critical insulation function reduces the temperature rise in the structure and maintains the steel loadbearing or pressureretaining integrity, giving time for emergency shutdown, inventory blowdown, and safe abandonment. Therefore, the correct application of the EPFP is critical, and the entire system is only as strong as its foundation. When the EPFP is applied to a galvanized surface, the galvanizing itself becomes that foundation. If it fails, then the EPFP will be compromised and only offer a limited degree of protection.
Hot-dip galvanizing creates a metallurgical bond between zinc and steel. When executed correctly on a properly prepared surface, this bond is incredibly robust. However, several factors in the galvanizing process can create a weak and unreliable substrate that may be unsuitable for supporting a safety-critical EPFP system. It is crucial to understand that these issues are not restricted to EPFP alone; they are a fundamental concern for all high-build coating systems that rely on strong adhesion to function under stress.
Galvanizing challenges
The ability of a galvanized coating to support an EPFP system can be severely impaired by several influencing factors.
. Excessive galvanizing thickness: The primary source of impairment.
. Metallurgical defects: Inclusions and weak layers formed during the galvanizing process. . Poor bonding: Inadequate surface preparation leading to a weak initial bond.
. Surface passivation: Post-galvanizing treatments that can impair adhesion.
The ‘Thicker is Better’ concept
Standard galvanizing specifications like ISO 1461 and ASTM A123 are written for corrosion protection alone; they do not consider any additional thick-film coating or system. They often imply that exceeding the minimum required thickness is not a cause for concern. However, for EPFP applications, this is a dangerously misleading statement.
Experience has shown that as a galvanized coating thickness increases, its cohesive strength decreases. The primary drivers for this excessive growth are the chemical composition of the steel – typically its silicon (Si) and phosphorus (P) content – and the thermal mass of the steel section.
. High silicon and phosphorus content:
Steel with high levels of silicon (particularly in the range of 0.04% to 0.14%, known as the ‘Sandelin range’) and phosphorus accelerates the growth of the zinc-iron alloy layers (eta, zeta, and delta).
. Uncontrolled growth: Rapid growth results in a thick, brittle, and often friable zeta layer. Instead of a dense, tightly bonded coating, there is an increasing likelihood that a coarse, crystalline structure which is inherently weak results.
Therefore, a galvanized coating that is too thick – for example, exceeding 250μm (microns) – may not be as robust when coated with thick EPFP coatings. It may have micro-cracks and have a high degree of internal stress resulting in voids and weak layers. When the EPFP is applied over this type of surface, the galvanized layer itself can delaminate due to stress imparted by the EPFP or thermal shock in fire or cryogenic liquid exposures.
Setting strict limits
Therefore, a robust well-written project specification should always override standard galvanizing norms. The following limits are critical:
. Upper galvanizing limit: The galvanizing thickness must be strictly controlled. Any measurements exceeding 250μm should trigger a formal integrity assessment. Sections with thicknesses greater than 300-350μm must be rejected. There is no reliable method to salvage a coating this thick for EPFP service.
. Mill Test Certificates: Engineers and specifiers should always review the steel’s Mill Test Certificate (MTC) at the design stage. An MTC (specifically a Type 3.1 certificate as per ISO 10474) provides a detailed chemical breakdown. If the silicon and phosphorus levels are high, excessive galvanizing growth could be considered predictable, and the required additional inspection protocols can then be implemented at the galvanizer’s facility.
Defects which could impair performance
Defects within the galvanizing layer that may create immediate points of failure.
Process factors which could impair performance
Properties at the surface of the galvanizing layer that may create immediate points of failure.
. Passivation and quenching: Post-treatment of galvanized surfaces with chromates or water quenching is common. Water quenching creates a thin, weak layer of zinc oxides and hydroxides on the surface. Chromate treatments are often used for aesthetics. This layer is completely unsuitable for coating adhesion and should be prohibited in the project specification. Any steel that has been water-quenched should be rejected before a EPFP application.
. Use of cold spray repair compounds:
repair compounds have been used should be rejected prior to EPFP system application.
High film builds: A closer look at the implications
When a thick-film material like EPFP is applied over a cohesively weak galvanized layer, several critical issues could materialise.
. Internal stress: The EPFP can induce stress in brittle/weak, over thick zinc-iron alloy layers from curing and temperature cycling, leading to cracking and delamination.
. Adhesion failure: The primer for the EPFP system cannot achieve a proper bond to a galvanized surface which is contaminated with weak oxide layers or has incompatible treatments applied. The failure point is within the incompatible treatment in the case of cold spray repair compounds or between the primer and the galvanized steel.
. Fire performance or cryogenic liquid exposure performance compromised: During a fire, the thick, weak galvanized layer may fracture and delaminate.
Remedial actions: No half measures
When non-conformances are found, the remedial actions need to be appropriate to the EPFP system application. The goal is not to ‘repair’ the galvanizing in the traditional sense, but to create a sound substrate for the EPFP.
. Reject: For issues like water quenching or thickness exceeding 300-350μm, the section should be rejected. There is no reliable site-based correction.
. Thorough blasting with appropriate media: For sections with excessive thickness (250-300μm) or surface defects like ash, the only acceptable method of repair is to aggressively abrasive blast. The goal of a ‘sweep blast’ is not merely to create a profile; it is to remove the defective and friable outer layers of the galvanizing until a sound adherent zinc layer is exposed. If this means blasting through to harder alloy layers in some areas, then the lifetime expectation is met by the application of the EPFP system. This must be brought to the client’s attention, as it fundamentally changes the specification requirement.
. Stop inadequate repairs: Standard galvanizing repair methods, such as cold spray repair compounds detailed in standards like ASTM A780, or the use of zinc-based solders, should not be accepted
for surfaces receiving EPFP. These repairs do not possess the cohesive strength or compatibility with the EPFP system and could create a point of failure.
All galvanized steel specified for EPFP application should always be sweep blasted to remove surface contaminants and the weak oxide layer, providing an angular profile of 50-75μm for the EPFP system to function adequately in service and during accidental release scenarios. This should be stated clearly in the specification.
Conclusion: A call for best practice
The industry must shift its mindset. Applying EPFP over hot-dip galvanizing introduces significant, unnecessary risk to a facility’s most critical safety system. The default specification should always be EPFP applied directly to appropriately primed mild steel prepared to the EPFP manufacturer’s requirements. When galvanizing is unavoidable, it must not be treated as a finished product, but as a substrate in need of quality control and further preparation for the EPFP system.
To achieve a safe and reliable outcome, the following actions should be considered essential.
. Specify correctly: Write a detailed coating specification that explicitly prohibits water quenching, surface treatments and defines strict lower and upper thickness limits for the galvanizing coating.
. Early intervention: Review Mill Test Certificates at the project’s outset to identify reactive steels and plan for heightened inspection.
. Mandatory surface preparation: Mandate that all galvanized surfaces receive an aggressive sweep blast to remove weak layers and create a suitable surface profile before priming.
. Consult the experts: Engage the EPFP manufacturer at the design stage to assist with specifications and inspection test plans (ITPs).
By prioritising the integrity of the substrate, we can ensure that these vital safety systems perform as designed, protecting assets, the environment, and, most importantly, lives. ■
Author: C J (Chris) Fyfe CSci FICorr
RESTORING STEEL WITH A GENTLE TOUCH: Why Bristle Blasting is the Smart Choice for the Maritime Sector
drs. JF (Frits) Doddema, CEO of Monti Group
In the world of marine maintenance, time is money – and surface preparation is everything. Whether you’re a superintendent overseeing drydock schedules, a ship captain responsible for operational uptime, a corrosion engineer aiming for maximum longevity, or a maintenance engineer tasked with rust removal, you understand how critical it is to prepare steel surfaces the right way.
At Monti Group, we’ve spent decades pioneering a surface preparation method that is comparable to conventional ‘sand’ blasting: the Bristle Blaster. Today, it is the only power toolbased technology in the world that achieves visual cleanliness and an uniform anchor profile comparable to loose abrasive blasting, without the operational complexity and environmental challenges that come with loose media such as grit.
THE PROBLEM WITH TRADITIONAL BLASTING METHODS
WHY SURFACE PREPARATION MATTERS
Before diving into what sets the Bristle Blaster apart, it’s worth re-emphasizing a universal truth: Coating Performance is only as good as the substrate preparation. Even the highest-grade epoxy, polyurethane, or antifouling system will fail prematurely if applied over poorly prepared steel. This is particularly true in maritime applications where steel is constantly under attack – from saltwater, UV radiation, cargo residues, and changing humidity.
Traditionally, grit blasting has been seen as the gold standard for removing corrosion and old coatings. But is it always the best – or even the most practical – option? We believe the answer is often ‘no’. Let me explain why.
Loose abrasive media blasting requires infrastructure: compressors, hoses, containment systems, recovery equipment, and highly trained operators. On a drydock, that might be manageable. But when your vessel is at anchor, on a voyage, or docked in a port with environmental restrictions, grit blasting becomes a logistical headache – and sometimes entirely prohibited.
Moreover, grit blasting generates enormous volumes of waste – spent abrasive, old coatings, rust, and often contaminated dust. This not only poses environmental challenges but also raises disposal costs and can delay maintenance.
Then there’s the issue of surface accessibility. Tight corners, vertical bulkheads, flange edges, ballast tanks, or container undersides aren’t always accessible with large blasting equipment. Crews need a more mobile, controllable, and precise solution.
THE BRISTLE BLASTER ADVANTAGE:
BLASTING WITHOUT GRIT
Our patented Bristle Blaster bridges the performance of grit blasting with the practicality of hand tools. It is the only power tool in the world that is comparable to ISO 8501-1 Sa 2½ to Sa 3 visual cleanliness and generates a surface roughness of up to 120 µm (4.7 mils) – ideal and crucial for bonding a coating and adhesives. Here’s how it works: the tool features specially hardened bristle tips that rotate at high speed and are dynamically tuned to strike the steel surface at an optimal angle. The result is simultaneous corrosion removal and micro-anchoring, all in one step – without the need for blasting media or secondary clean-up.
Let’s break down the real-world benefits:
1. Mobility and Accessibility
From ballast tanks to deck edges to inside of containers, the Bristle Blaster allows your crew or maintenance contractor to access confined or vertical spaces where blasting rigs simply cannot reach. Whether you’re working at sea, on deck, or in port, our compact tools operate reliably from a power outlet or pneumatic source – no compressors or containment tents needed.
2. Environmental Stewardship
As a captain or superintendent, you know how strict port regulations have become. Many jurisdictions now restrict or ban abrasive blasting unless fully enclosed systems are used. The Bristle Blaster produces no abrasive waste, no airborne media, and minimal dust, making it ideal for environmentally sensitive locations or in-transit maintenance. The bristles remain clean!
3. Lower Cost and Faster Deployment
Grit blasting setups can take hours to assemble and require multiple operators and cleanup crews. In contrast, the Bristle Blaster is plug-and-play, allowing rapid mobilisation and deployment – even during a port call or cargo turnaround. This drastically reduces labour, consumables, and downtime costs.
4. Verified Coating Compatibility
Our surface profile has been validated by leading coating manufacturers across the marine and offshore sector. We routinely test Bristle Blaster surfaces with coating partners and independent laboratories to verify pull-off adhesion, edge retention, and longterm corrosion resistance. In some cases, coatings have performed better on Bristle Blasted surfaces due to cleaner, sharper anchor patterns with fewer contaminants and therefore for a longer coating
window flash-rust free in marine environments.
5. Safety and Control
Grit blasting is inherently hazardous – flying media, pressurized hoses, visibility issues, and confined space risks. The Bristle Blaster offers a controlled, operatorfriendly alternative that significantly reduces noise, dust, and risk of injury. It is also safer for surrounding crew and equipment, especially on active vessels.
USE CASES FROM THE FIELD
We have seen Bristle Blaster used across all classes of vessels: bulkers, tankers, offshore platforms, ferries, and containerships. One major liner operator recently used it during a mid-voyage coating spot repair on deck fittings – saving a planned drydock intervention.
In another case, a container leasing company deployed Bristle Blasters across its global refurbishment hubs, drastically cutting abrasive consumption and enabling local teams to work without permits or special waste disposal.
CLOSING THOUGHTS: FUTURE-PROOFING YOUR MAINTENANCE STRATEGY
The maritime industry is evolving under increasing pressure: environmental regulations, tighter schedules, and aging fleets demand agile, efficient, and sustainable maintenance tools. The Bristle Blaster is not here to replace grit blasting in every case, but to give you a valuable and certified alternative – one that is cleaner, more precise, and better suited to modern marine operations.
As CEO of Monti Group, I can confidently say we’re committed to solving real-world maintenance challenges for real-world people. We work with your coating suppliers, your technical managers, your shipyards, and your classification bodies to ensure every application of our technology meets the highest performance standards.
If you haven’t experienced the Bristle Blaster yet, I encourage you to try it. Because in the end, what matters isn’t just cleaning steel – it’s preserving value, reducing downtime, and extending asset life. That’s what we’re here for.
FOCUS
A COPPER-FREE ANTIFOULING SOLUTION IN
PPG helps ship operator and shipyard with sustainability targets.
Sylt Express is a Ro-Ro passenger ship operated by FRS Syltferry and sails between Havneby on the Danish island of Rømø and the German island resort List on Sylt. The parent company FRS (formerly Förde Reederei Seetouristik) is an international ferry operator based in the north of Germany with around 75 vessels. The company carried 5.7 million passengers and 1.5 million vehicles on its numerous national and international shipping lines in 2023. The Sylt Express is not only responsible for transporting tourists to and from List on Sylt but also for the island’s access to food, infrastructure and more.
The docking took place at Esbjerg Shipyard, Denmark, in collaboration with the applicator MMT Group and industrial equipment supplier Mouritsen A/S. Mouritsen supported the shipyard and PPG with the equipment needed to ensure that the application went smoothly.
The challenge
One of FRS’s guiding principles is corporate social responsibility. It is always looking for innovative, sustainable solutions that are geared towards long-term business goals and sustainable strategies with the intent of reducing its ecological footprint.
Esbjerg Shipyard is always looking for innovations that can help it reach its sustainability goals and minimise its
environmental footprint. “Operating a shipyard in the middle of a national park also brings obligations to think of more environmental and sustainable products to be used for maintenance and repair of ships,” explains Brian Mose, the yard’s Sales Supervisor.
The solution
For many years, PPG has invested in developing sustainably advantaged products, helping shipowners reach their sustainability targets. Investing in advanced hull coatings helps owners cut fuel use, lower GHG emissions and comply with IMO regulations. By reducing drag, these coatings boost efficiency and support sustainable, cost-effective operations.
One example is PPG Sigmaglide 2390, a fouling release silicone-based coating that is 100% biocide free, along with PPG Nexeon 810, which is a copper-free antifouling with reduced photodegradable biocides. These two products are unique not only due to being sustainably advantaged, but they are also suitable for electrostatic application. This spraying technique significantly reduces coating overspray and waste, minimising the loss factor, resulting in less paint needed.
To support the customer’s needs, PPG proposed PPG Nexeon 810 as an ultra-lowfriction hull coating for the ferry. As it is 100% copper-free, PPG could ensure that no copper
would be released into the marine environment in relation to the coating. This ultra-low friction product also delivers immediate power and emissions savings, compared with traditional antifouling coatings, thereby reducing environmental impact.
As stated above, PPG Nexeon 810 is suitable for electrostatic coating application, a technology that has an increased paint transfer efficiency compared to airless spraying. Using an electrostatic spray gun, the charged paint droplets are drawn to the grounded hull surface like a magnet. This technique not only creates a uniform, ultra-smooth, longlasting film layer but also significantly reduces overspray and waste. It also minimises the need for masking the vessel and cleaning the dock post-application, saving time, materials and costs.
PPG Nexeon 810 helps to improve vessel performance by delivering up to 25% emissions savings due to reduced drag, maintaining higher speeds while staying CII compliant.
The result
Relying on PPG as a trusted partner, FRS Syltferry and Esbjerg Shipyard took significant steps towards achieving their sustainability ambitions, whilst not compromising on aesthetics and performance. PPG Nexeon 810 helps to improve vessel performance by delivering up to 25% emissions savings due to reduced drag, maintaining higher speeds while staying CII compliant, and improving speed by 0.5 knots, compared with traditional antifouling coatings.
The electrostatic spraying technique also greatly reduced overspray around the shipyard and contamination in the surrounding waters. ■
RESICOAT RISES TO THE CHALLENGE
Epoxy powder coating aces long-running valves and fittings test.
Back in 2000, as the new millennium dawned, plans were afoot to carry out a long-term test involving more than 10 companies – and AkzoNobel was one of them.
Conducted in Bad Bentheim, Germany by an industry association and water board, the test involved AkzoNobel’s Resicoat powder coatings. Now, after more than two decades, the results – verified by the MPA Hannover testing institute – are in.
The Resicoat epoxy powder coating has become one of the first products of its kind to complete a 25-year real-world study to prove its ability to protect valves and fittings and provide long-term anticorrosion protection for drinking water supply systems.
Valves and fittings
As part of the test, fully operational test valves and fittings coated with Resicoat were installed in a drinking water pipe before it was buried two metres underground – the standard depth for water pipes worldwide.
When the pipeline was unearthed, it showed no leaks, water flowed freely and Resicoat’s epoxy coatings displayed no delamination or cracking. With no impacting signs of corrosion, the results showed that the integrity of the pipeline had been preserved.
“Epoxy powder coatings make water supply systems more reliable and help reduce maintenance costs,” explains Yidong Meng, Global Functional Segment Manager at AkzoNobel’s Powder Coatings business.
“They’re more dependable than ‘traditional’ paint or enamel coatings and consequently help minimise water wastage due to leaks and floods. Ultimately, this ensures a reliable, sustainable source of clean drinking water for millions of people around the world.”
Drinking water
The Resicoat R series is a high-quality thermosetting epoxy powder coating specifically designed for the protection of cast iron or steel valves and fittings used in water distribution networks. It is applied in one layer on a pre-heated surface by fluidised bed or electrostatic spray application.
The research was carried out by industry association GSK (Quality Association HeavyDuty Corrosion Protection of Valves and Fittings with Powder Coating e.V.) and the Wasserbeschaffungsverband Obergrafschaft Bad Bentheim (Water Supply Association of Upper County Bad Bentheim and Surrounding Areas).
“This comprehensive study provides the market with important, independent and irrefutable proof of the value of epoxy powder coatings in safeguarding the integrity of potable water supplies,” says Lars Walther, General Manager GSK.
“It will give even greater confidence to water suppliers that one of the most challenging of issues to their pipes and associated infrastructure has a credible, long-term solution.”
PCE October - December 2025 Issue
The Leading Protective Coatings Magazine
SPECIAL EDITORIAL FEATURES:
• Metallisation
• Petrochemical
• Floor Coatings
• Polyurea/Polyurethane
Focus – Marine
PCE will continue to showcase its regular features; Lifting the Lid, Upfront and Spotlight, as well as featuring the latest news and developments in marine and offshore coatings
PCE International is published quarterly by MPI Group
Peel house, Upper South View, Farnham, Surrey. GU9 7JN. UK
To advertise in the magazine, on the website and /or newsletter contact Nick Carugati: nick@pce-international.com
BEYOND EPOXY
Why polyurea is the future of protective coatings is explained by Darren Hull, Director of Marketing at Ultimate Linings.
For decades, epoxy coatings have been the industry standard for protecting infrastructure, industrial assets and commercial surfaces. Their mechanical strength and chemical resistance made them a reliable choice across sectors. However, as performance demands increase and downtime becomes more costly, epoxy is showing its limitations. A new generation of coatings is stepping in to meet these challenges: polyurea.
The decline of epoxy
Epoxy coatings, while robust, are inherently rigid. In environments where substrates expand, contract or shift, epoxy can crack and fail. Recent laboratory testing has revealed that a commonly used epoxy coating offered a tensile strength around 925 psi and elongation at break of just 13%. This limited flexibility makes them vulnerable to stress, impact and substrate movement.
Epoxy also suffers from long cure times. Depending on conditions, full cure can take up to 14 days. In fast-paced industrial settings, this delay can disrupt schedules and increase costs. Additionally, epoxy coatings are more prone to wear in high-traffic environments, with abrasion resistance values significantly higher than polyurea alternatives.
Polyurea:
A highperformance alternative Polyurea coatings are engineered for speed, strength and adaptability. In recent controlled testing, a pure polyurea system demonstrated tensile strength exceeding 3,200 psi and elongation rates over 200%. This combination of strength and flexibility allows polyurea to absorb impact and accommodate substrate movement without cracking.
Components exposed to corrosive chemicals had previously failed under epoxy and polyurethane coatings on industrial mixing shafts. Polyurea provided a chemicallyresistant barrier that cured in under 48 hours and has maintained operational efficiency ever since
A chemical facility facing cracked concrete in its containment areas applied polyurea as a seamless membrane
Polyurea also excels in abrasion resistance, tear strength and impact durability. It cures within seconds and reaches full strength in 24 hours, allowing for rapid return to service. These properties make polyurea ideal for environments where downtime must be minimised and long-term performance is critical.
Real-world applications and cost savings
Across multiple sectors, polyurea has replaced epoxy and delivered measurable benefits:
. Parking decks: In elevated and ground-level structures, polyurea systems have provided waterproofing, UV resistance and durability under heavy traffic. Unlike epoxy, which often cracks under thermal expansion, polyurea’s flexibility has extended the life of these assets and allowed foot traffic within hours of application.
. Secondary containment: A chemical facility facing cracked concrete in its containment areas applied polyurea as a seamless membrane. The result was long-term chemical resistance and structural integrity, with minimal downtime.
. Sewage treatment tanks: In Denmark, two large wastewater tanks were recoated with polyurea and returned to service within 24 hours. Five years later, the coating remains intact with no failures.
. Industrial mixing shafts: Components exposed to corrosive chemicals had previously failed under epoxy and polyurethane coatings. Polyurea provided a chemically-resistant barrier that cured in under 48 hours and has maintained operational efficiency ever since.
These examples highlight how polyurea has prevented premature failures, reduced maintenance costs and extended asset lifecycles, often saving projects large sums of money in long-term expenses.
Application matters
While polyurea offers superior performance, its success depends on three critical factors:
1. Trained professionals who understand the nuances of polyurea application.
2. Proper surface preparation to ensure adhesion and long-term durability.
3. High-quality materials formulated for the specific demands of each project.
Polyurea is not just a coating, it is a system. When applied correctly, it transforms infrastructure from vulnerable to resilient.
Ultimate Linings is driving innovation and growth in the polyurea coatings industry with a clear commitment to technological advancement and scalable production. This vision is embodied in the company’s new 302,000-square-foot facility in Lebanon, Tennessee, which integrates corporate offices, an advanced manufacturing unit and a dedicated innovation centre.
Purpose-built for efficiency and expansion, the facility positions Ultimate Linings as a key player in North America’s protective coatings market. With a production capacity exceeding 300 million pounds (136 million kilograms) annually, the company is uniquely equipped to meet large-scale demands with speed, reliability and consistency, delivering highperformance solutions backed by decades of expertise. ■
News from the Corrodere Academy in partnership with PCE Magazine
Corrodere Academy provides globally recognised accredited training and qualifications to the protective coatings and corrosion control industry. Their aim is to raise standards throughout the industry worldwide and help students learn, discover and succeed.
JMK training news
Corrodere Academy is delighted to announce that JMK Training has become the official Global Support Partner for Australia.
JMK Training were already a trusted Affiliate Training Provider, but with this expanded role they now deliver the full suite of Corrodere Academy courses — including Train the painter, inspection, and specialist programmes.
We spoke with JMK Training about what this development means for the industry and for training across Australia.
1. What led to JMK Training taking on the role of Global Support Partner for Australia?
JMK Training has joined the Corrodere Academy as a Global Support Partner to expand training opportunities in Australia for industrial blast, paint, and inspection. The industry in Australia faces challenges related to course flexibility and local accessibility. Through collaboration with Corrodere Academy, JMK Training aims to offer flexible and online training options, enabling both employers and employees to access skills development within the sector, and supporting the training of qualified blasters, painters, and inspectors across the country.
2. How do you see Corrodere Academy’s training fitting into the Australian market?
The industry in Australia is exploring alternative training options to enhance flexibility and affordability in course offerings. Through this partnership, programmes are available with both classroom and online delivery formats, supported by experienced trainers nationwide to ensure local coverage. This provides clients and students with various options when selecting their training pathways.
3. What approach will you take to introducing these courses across Australia?
Further course options will be introduced across Australia, targeting industries experiencing growth and requiring skilled blasters and painters. Programmes will be available nationwide and can be tailored to meet specific project requirements of each client, ensuring that training adheres to relevant specifications and industry standards.
4. In what way does the Corrodere Academy programme connect with Australia’s Certificate III qualifications?
The Train the painter programme has been acknowledged by the PCCP as recognition of prior learning for the Australian Certificate III in Engineering – Fabrication Trade (Surface Finishing). JMK Training is collaborating with several industry associations to explore incorporating Train the painter as an additional option to the current Certificate III within relevant standards and specifications.
The partnership between Corrodere Academy and JMK Training marks an exciting development for the Australian surface preparation and coatings industry. By expanding access to world-class training, this collaboration will help equip the workforce with the skills and qualifications needed to meet current and future industry demands.
We’re delighted to announce José Sahagún as our July Student of the Month! José achieved an outstanding 100% on the exam for our Corrosion Under Insulation course – a fantastic accomplishment that reflects his commitment and expertise.
José, who works as a PFP Manager at AkzoNobel, shared his thoughts on the course:
“I found the Corrodere course and training extremely valuable, especially when facing reallife scenarios. It offers a wealth of information and references, making the learning experience truly enjoyable.”
Huge congratulations José from everyone here at the Corrodere Academy!
Congratulations José from everyone at the Corrodere Academy!
Celebrating 5 Years with Taziker
We’re proud to announce that Taziker has renewed as a Registered Company of Train the painter for the fifth consecutive year.
It’s a pleasure to continue working with the Taziker team and their Approved Trainer, Nigel Rose, as they deliver firstclass training and uphold the highest standards in the coatings industry.
Thinking about registering your own company? Become part of our internationally renowned Train the painter programme and empower your team with industry-leading training.
Corrodere Academy launch new Ethics module
Corrodere Academy has launched a brand-new Ethics Module, available as an optional online add-on to all Train the painter inspection and specialist courses. While not mandatory, this module is available to all students and designed to provide valuable insight into working ethically within the protective coatings industry. Covering key topics such as responsible project management, best business practices, and the importance of ethical decision-making, it supports individuals and organisations who want to raise standards and operate with integrity.
Narus represent Train the painter at SENIPA
Recently our brilliant Train the painter training provider Narus took part in the SENIPA conference, engaging with industry leaders on asset preservation, corrosion challenges, and the value of professional training across Brazil.
Richard Forster Bayer from Narus commented: “SENIPA Manaus showed the importance of addressing anticorrosion challenges across Energy, Oil & Gas, Mining, and waterway transport. For us at NARUS it is very important to participate in these itinerant seminars to understand regional demands and challenges across Brazil’s diverse climates.”
Narus continue to champion Train the painter nationwide.
Corrodere Academy Announces Charity Partnership with Challengers
Corrodere Academy is proud to announce a new charity partnership with Challengers, a Guildford and Farnham-based charity providing inclusive play opportunities for disabled children and young people.
The team recently met with Chris McIsaac, Corporate Engagement Manager at Challengers, who shared the impact of the charity’s work: “The amazing support from Corrodere has already made such a big difference to our families.” Through this partnership, Corrodere Academy will be supporting Challengers with fundraising, awareness, and events, helping to ensure more families in the local community benefit from the charity’s vital services.
PPG & Corrodere Academy – successful audit renewal
Since 2010, Corrodere Academy has proudly developed and supported a bespoke training platform for PPG, enabling the delivery of accredited IMO PSPC Coating Inspection training to staff worldwide.
Last week, the platform successfully underwent another ABS Hellas audit, resulting in a renewed ABS certificate and excellent feedback. Marta Lourenço, Global Field Technical Service Standards and Data Manager at PPG, commented: “The recent ABS Hellas audit was completed with outstanding results, reflecting the strength and effectiveness of the well-structured quality management system.”
Congratulations to PPG on this achievement — we are delighted to continue supporting their training journey.
PSI Global Training expands course offering with Powder Coating Application
PSI Global Training, one of our trusted train the painter affiliate providers, has added the Powder Coating Application course to its portfolio. To deliver the practical element, PSI has partnered with Advanced Coatings & Fabricators, whose specialist facility provides students with essential hands-on training alongside expert guidance. This new course complements the existing suite of train the painter programmes already delivered by PSI, including Protective Coating Application, Spray Painting, Abrasive Blast Cleaning, and Thin Film Intumescent Coating Application.
Corrodere Academy Registered Companies and Affiliate Providers
Advanced Polymer Coatings (APC) has completed a tanker recoating contract for Spanish-headquartered shipping line Marflet Marine.
APC applied its industryleading MarineLINE protective tank coating to the Panagia Thalassini after the previous successful coating of Marflet Marine’s Santiago 1.
The recoating work for the Madrid-based shipping group took place at the IMC Shipyard (Zhoushan) in China where APC operates a team of specialist heat-curing engineers and inspectors to support customers.
The deal is the latest in a raft of contracts secured by APC throughout 2025 as it continues its global growth journey.
The MRII chemical and oil product tankers Panagia Thalassini and Santiago 1 were
both built in Croatia. Santiago 1 was completed in 2022 and Panagia Thalassini is five years older.
Operating since 1957, Marflet Marine is one of the oldest and highly regarded privately-owned Spanish shipping companies.
The MarineLINE coating system was chosen by Marflet because of its superior chemical resistance properties, ease and speed of cleaning, and the reduced risk of contamination from previous cargoes. MarineLINE is designed to carry specialist heated and challenging free fatty acid cargoes. Both vessels are modern designs fitted with the latest technology to ensure efficient cargo operations, including the coating.
“We have built a good working relationship with
Marflet and it found the case for MarineLINE compelling when it came to this recoating work,” says Peter Stoyles, APC European Sales Manager. “Switching easily between cargoes was very important here, together with faster cleaning times which can free up sailing days, improving the earning ability of the vessel. Plus, faster cleaning time means fewer emissions.
“This is because unlike other epoxy coatings, our unique technology means significantly less fuel is required to heat vast quantities of hot water for cargo tank cleaning, for ships using MarineLINE.”
MarineLINE is rigorously tested at APC’s R&D facility in Avon, Ohio to ensure it can provide protection against thousands of highly aggressive chemicals.
NETWORK RAIL CORROSION PROTECTION
A newly-certified protective coating system from German manufacturer Steelpaint GmbH is gaining attention across the UK rail sector following successful demonstration and approval by Network Rail.
Steelpaint’s Stelcatec three-layer moisturecured urethane coating, distributed by Recoat UK, is now formally listed under Network Rail’s specification XM92/M24 and offers rail contractors a faster, simpler and more flexible approach to corrosion protection and steel maintenance.
Approved in January 2025, Stelcatec is engineered for in-field applications, allowing for full protection of steelwork without the logistical burden of multi-component coatings or other corrosion-prevention solutions.
In a demonstration held in March at Specialist Painting Group’s facility in Peterborough, Stelcatec was applied to three ‘gingered’ steel samples manually cleaned to St3 standard, under realistic ambient conditions of 13°C. The full three-coat system was applied within four hours using only rollers. Pull-off adhesion testing later confirmed the system’s performance on marginally-prepared substrates.
“This isn’t about just meeting the spec,” said Andreas Engert, Technical Director at Steelpaint. “This is about optimising steel protection, application process and cost efficiencies. Stelcatec was formulated with all these requirements in mind.
Hempel A/S has appointed Gosha Kolton Executive Vice President & Head of Marine
Applicators were surprised at how easily they could finish a job in one shift, not three.”
The event was attended by representatives from Network Rail and several leading painting contractors and consultants. Their participation not only validated the product’s technical capability but demonstrated industry appetite for alternatives to traditional multi-pack systems, which often require site-specific mixing, tight environmental controls and extended drying times.
Recoat UK, which has worked closely with Steelpaint over the past two years to introduce the product to the British market, sees the certification as a commercial turning point.
“It’s a rare opportunity when something comes along that saves time, reduces risk, and performs to the highest standards,” said Perry Poppelaars, Director at Recoat. “Stelcatec ticks all those boxes.”
Unlike traditional epoxy coating systems, Stelcatec does not require complicated mixing or the use of hazardous hardeners. As a onecomponent moisture-curing polyurethane, it is applied directly from the can, cures rapidly even in high humidity, and provides strong adhesion on manually-prepared steel –a crucial feature when blast cleaning is not practical.
NEW EVP MARINE FOR HEMPEL
Hempel A/S has appointed Gosha Kolton Executive Vice President & Head of Marine, effective from the beginning of January 2026.
“I am delighted to
welcome Gosha to Hempel,” said Michael Hansen, Group President & CEO at Hempel, commenting on the appointment. “Her international perspective, leadership experience and passion for innovation will be invaluable as we continue to strengthen our position in the marine coatings industry. Her commitment to building strong teams and customerfocused strategies will also help us deliver value for our stakeholders.”
Kolton brings extensive international experience in strategic and operational leadership across both developed and emerging markets. Her experience in leading complex transformations and delivering customer value aligns perfectly with Hempel’s strategic priorities and ambitions for the marine segment.
“I am excited to join Hempel and the Marine team, and I look forward to working together to deliver outstanding value for Hempel’s customers and drive sustainable growth,” she says.
A Polish national, Kolton joins Hempel from her role as EU Vice President of Packaging Adhesives, Coatings and Sealants at German multinational Henkel. In that position, she successfully steered one of the company’s largest regional businesses through volatile market conditions and transformations over the last five years, consistently delivering strong results across Europe.
SEA LOCK CORROSION BREAKTHROUGH
Steelpaint has delivered a decisive breakthrough in the renewal of Wilhelmshaven’s Great Sea Lock, applying corrosion protection to some 26,000m2 of steel on one of the world’s largest sluice gates.
At 60m long, 20m high and with a depth of 10m, the 1,700t gate provides access to Germany’s only deepwater port for naval vessels, commercial ships and energy carriers. The completion of the main coating work marks a significant step forward in a challenging project that started in 2018.
Steelpaint’s Stelpant coating system was selected after a two-component epoxy system from another supplier was found to be incompatible with an autumn/winter application, when freezing temperatures and nearsaturated humidity can make epoxy coatings unusable.
Muehlhan Germany GmbH, which worked together with Hermann Maschinenbau GmbH in a working group for port authority WNA Hannover & WSA Weser-Jade-Nordsee, opted for Steelpaint’s singlecomponent polyurethane system Stelpant, which can cure at temperatures down to
-5°C with a relative humidity up to 98%. Its use allowed the coating application work to continue through winter, ensuring the gate could be floated back into position and reinstalled for interim use.
The coating package consisted of a 75μm zinc-rich primer of Stelpant-PU-Zinc followed by two 225μm coats of Stelpant-PUCombination 300. Together, the layers provide advanced corrosion protection against saltwater, abrasion and mechanical stress in one of Europe’s harshest marine environments.
The zinc primer provides cathodic protection and excellent adhesion, while the polyurethane intermediate and topcoat delivers abrasion resistance, flexibility and durability even under aggressive marine exposure. The system is certified by the Federal Waterways Engineering and Research Institute in Karlsruhe for use in hydraulic steel structures and for environments from Im1 to Im3 under DIN EN ISO 12944-5.
“This was one of the largest and toughest projects we have been involved in in the last few years, but it showed exactly what our technology can do,” said
Fynn Baumfalk, Key Account Manager at Steelpaint. “The schedule slipped again and again and even now some areas remain unfinished, yet our coatings went on when and where they were needed and performed exactly as intended. Our market presence in Wilhelmshaven is growing more and more. First the Jade-Weser-Port, now the gate refurbishment and currently in progress is the refurbishment of sluice Hooksiel”.
The main corrosion protection on the refurbished gate is complete, though minor rework is required and some hot work also needs to be redone before recoats.
Baumfalk confirmed that the Stelpant coating system will also be used in these areas, with full commissioning of the gate expected in 2026.
The Wilhelmshaven Sea Lock sits at the mouth of the Jade, where the river meets the North Sea. Its location exposes it to salt corrosion, tidal erosion and abrasive silt, demanding the highest levels of protection.
The success of the Stelpant coating could see Steelpaint selected for further phases of JadeWeserPort dock’s wider renewal. Three entirely new dock gates are being
discussed for commissioning towards the end of the decade. A feasibility study updated in 2019 confirmed the economic viability of a second container terminal 2km north of the existing one.
CO2-SLASHING PAINT SHOP
Dürr has built a paint shop designed to slash CO2 emissions at one of the Volkswagen Group’s largest manufacturing facilities. The plant in Puebla, Mexico, was inaugurated in January 2025. The turnkey project includes two identical painting lines that are particularly environmentally friendly due to their electrified equipment, such as the electric drying system. Dürr is also implementing key components of its new ‘Paint Shop of the Future’ concept with a highbay warehouse and driverless transport systems.
Since January 2025, the Puebla Volkswagen plant paints 90 vehicle bodies of different models per hour. Dürr was awarded the contract in 2022. The innovative paint shop is engineered to seamlessly accommodate additional models and emerging future technologies.
Two identical painting lines feature 170 sealing and painting robots, with the corresponding application technology for sealing and coating the different Volkswagen models in the future. This encompasses EcoRS Clean F, a prime example of Dürr’s efforts to bolster system technology to equip it for growing model diversity. It combines the thorough, gentle cleaning prowess of a feather roller system with the high flexibility inherent to a robotic setup. This makes it perfect for lines that paint many body
variations with complex contours.
The contract scope also includes the complete paint and PVC supply and software solutions with AI applications from Dürr’s proprietary DXQ product family.
NEW POWDER COATING COLLECTION
AkzoNobel has launched the Interpon D2525 Trends Collection, designed to offer designers and architects a striking selection of colours and finishes that complement the unique architectural style and natural beauty of the Middle East.
Building on the success of the Interpon D Futura powder coatings collection, a favourite of the architectural industry for more than 20 years, the Trends Collection includes three curated colour palettes: Desert Sands, Shimmering Mirage and Arabian Nights.
Inspired by the rich tones of the desert and the avantgarde architectural styles of the Middle East, the Trends Collection blends effortlessly with both modern and traditional regional designs to bring fresh, lasting appeal to a building’s facade, windows and doors.
AkzoNobel’s Trends Collection is backed by an Environmental Product Declaration (EPD), meaning the collection’s raw materials, manufacturing processes and transportation have been thoroughly assessed for their sustainability. This provides important assurances to architects and designers that their choice of powder coating is environmentally responsible and contributes to a building’s environmental rating.
The Superdurable Interpon D2525 collection also boasts exceptional durability, as well as offering superior gloss retention, colour stability and UV resistance. With a 25-year warranty and certifications such as Qualicoat Class 2 and GSB Master, the Trends Collection is built to withstand the test of time, making it ideal for demanding climates.
HEMPEL REAFFIRMS CLIMATE AMBITION
Hempel has updated its Scope 3 emissions target, approved by the Science Based Targets initiative (SBTi), reaffirming its commitment to reducing emissions in line with climate science, while supporting the company’s continued business growth.
The new target underscores Hempel’s dedication to responsible business practices while ensuring its sustainability goals remain aligned with its evolving business.
The updated target shifts from a 50% absolute reduction to a 55% reduction in the intensity of Scope 3 emissions per euro value added (GEVAGreenhouse Gas Emissions per Value Added). By measuring emissions across the value chain against the financial value created, Hempel’s approach provides a more accurate reflection of its growing business, while staying firmly aligned with the 1.5°C pathway.
“Our ambition is as strong as ever,” says Emilie Barriau, Executive Vice President and Chief Technology Officer at Hempel. “We remain firmly
committed to reducing emissions in line with climate science, and this updated target ensures our goals stay both relevant and reflective of our evolving business.”
Scope 3 emissions are those generated indirectly across a company’s value chain, such as from raw materials, packaging and transport. According to SBTi, companies must revalidate their targets at least every five years or when significant changes occur.
“Since setting our original target in 2021, we’ve reshaped our business and sustainability landscape through acquisitions and divestments, alongside updated emissions data and an expanded value base,” Barriau explains. “These shifts made recalibrating our Scope 3 baseline both necessary and timely.”
Shifting to a financial intensity target ensures that profitability and sustainability are closely aligned. It emphasises Hempel’s commitment to innovate and deliver solutions with higher sustainable value for its customers while lowering the joint environmental footprint.
AIRLESS SPRAYING TECHNOLOGY REDEFINED
Elcometer, a global leader in coating inspection, surface preparation and spray equipment, has launched Elcometer Tornado Airless Pumps, a breakthrough in high-performance airless spraying technology.
Developed by spray painters for spray painters, the Elcometer Tornado redefines industry standards with superior quality, reduced maintenance and extended operational lifespan, ensuring unmatched durability and precision for the industrial and marine protective coatings industries.
The Elcometer Tornado Airless Pumps are the result of an exhaustive three-year development process, which included more than 13 million pump cycles and over 3,600 hours of extensive laboratory and field trials.
Tested across a wide range of marine and protective coatings, in temperatures from -3°C to 52°C (27°F-126°F), the pump proved its ability to deliver consistent,
high-performance spraying which withstands harsh environments and resists wear and tear.
Engineered to tackle heavy-duty coating applications, the Tornado is available in two models:
• Tornado 71 (71:1) – Max outlet pressure of 425 bar (6,164 psi)
• Tornado 43 (43:1) – Max outlet pressure of 260 bar (3,771 psi). ■
Join the Train the painter programme to deliver fully accredited coating applicator courses to your team.
• Train a trainer to deliver courses internally
• Demonstrate a commitment to high quality workmanship
• Internationally accredited and approved training material and qualifications
• Affordable and flexible
• Available in multiple languages
• Monitor staff progress with the Train the painter log book app
