The economic stakes in the region are enormous. According to a 2011 study cited by the authors, the total cost of corrosion in Qatar was estimated at approximately 7.8 billion US dollars, representing roughly 4.6 percent of the country’s nominal GDP, slightly above the 3.4 percent global GDP cost of corrosion estimated in 2016. Saudi Arabia and the United Arab Emirates spent roughly 24.8 and 14.3 billion dollars respectively. These figures underscore why accurately predicting how long a coating will remain effective matters so much: service-life predictions drive maintenance schedules, budgeting, and asset management decisions for buildings, bridges, pipelines, and industrial facilities across the Gulf Cooperation Council region.

The research team, led by Alexander Saul and Qingyang Liu along with Monir Aljaradli and Brahim Aissa, prepared flat carbon steel panels of grade HA250 and applied four distinct commercial coating systems. System A combined a zinc-rich epoxy primer, an epoxy intermediate layer, and an acrylic polysiloxane topcoat. System B paired a zinc-rich epoxy primer with a thick polyurethane topcoat. System C used a dual-epoxy base and intermediate topped with a thin polyurethane, while System D consisted of a polyamine-cured epoxy base coat with an acrylic polyurethane topcoat. Each system was applied according to manufacturer specifications for nominal dry film thickness, surface cleanliness, and curing conditions, with three independent panels prepared per exposure condition.

The laboratory regime followed ISO 12944-9, the cyclic aging standard widely used for coatings destined for C5 or CX corrosivity environments. It consists of 25 cycles totaling 4,200 hours, alternating 72 hours of ultraviolet and condensation exposure with 72 hours of neutral salt spray in a 5 percent sodium chloride brine, followed by 24 hours at low temperature. Meanwhile, the field samples were mounted at a 45-degree angle facing south on a wooden test rack in Doha, approximately nine kilometers from the sea. Although the site’s carbon steel mass loss classified it as C2 corrosivity under ISO 9226, the panels endured summer daytime temperatures frequently exceeding 40 degrees Celsius, nocturnal humidity often above 70 percent, and annual solar irradiance on the order of 2,000 to 2,200 kilowatt-hours per square meter.

The team deployed a battery of assessment techniques, and the contrasts between them proved to be the study’s most striking finding. Visual inspection under ISO 4628 showed almost no visible defects on unscribed samples in either environment, yet this apparent perfection masked serious underlying damage. Corrosion creep measurements around artificial scribes told a very different story: after 4,200 hours of laboratory aging, creep values ranged from about 3.3 to 21.6 millimeters, compared with roughly 0.6 to 15.1 millimeters after two years in the field. Under the ISO 12944-9 qualification criteria, all coatings except System A would have failed, despite looking pristine to the naked eye. The authors note that visual assessment evaluates only the visible symptoms of failure, long after water uptake and swelling have begun beneath the surface.

Perhaps the most counterintuitive result came from pull-off adhesion testing. Conventional wisdom holds that adhesion should decline as coatings weather, yet for three of the four systems, adhesion tensile strength actually increased over time in both laboratory and field samples, a behavior the researchers attribute to post-curing effects beyond the typical 24 to 72 hour window. Only System B showed the expected decline, plummeting from 8.3 megapascals after one year in the field to below 3.4 megapascals after two years, with failure analysis revealing 100 percent adhesive failure at the coating-substrate interface. Scanning electron microscopy of cross-sections confirmed a continuous air gap and cracks along the interfaces in System B, validating interfacial debonding as its dominant degradation mechanism.

Electrochemical impedance spectroscopy, increasingly favored as a non-destructive, time-resolved technique, also delivered a sobering lesson. All samples, regardless of exposure environment, maintained low-frequency impedance above 10 to the ninth power ohm-square centimeters, the threshold conventionally associated with excellent barrier protection, with many values approaching the potentiostat’s own measurement ceiling near 10 to the eleventh power. Yet System B, which retained high impedance, had failed catastrophically in the mechanical tests. The explanation lies in what EIS actually measures: the dielectric properties of an intact film area, which remains blind to interfacial delamination and localized breakdown at scribes. A coating can lose its mechanical integrity entirely while still behaving as a superb electrical barrier over undamaged regions.

The statistical analysis quantified this decoupling with unusual precision. The Pearson correlation coefficient between corrosion creep and pull-off adhesion was a near-zero 0.04, demonstrating that a strong bond does not guarantee resistance to lateral delamination and rust creep from defects. EIS correlated weakly with adhesion at 0.39 and, counterintuitively, showed a moderate positive correlation of 0.55 with corrosion creep, meaning systems with higher bulk film resistance were actually associated with greater scribe-driven degradation. Dry film thickness correlated moderately with bulk properties but negatively with creep, suggesting that interfacial chemistry rather than simple film build governs resistance to underfilm corrosion. Fourier-transform infrared spectroscopy added a chemical dimension, showing that laboratory aging induced more aggressive oxidative changes in polyurethane topcoats than natural weathering did, indicating that accelerated cycling may not faithfully reproduce field degradation mechanisms at all.

The overall performance ranking that emerged, from best to worst, was System A, followed by D, then C, then B. System A, with its zinc-rich primer, epoxy intermediate, and acrylic polysiloxane topcoat, showed the lowest creep at approximately 3.2 to 3.3 millimeters, strong adhesion, and stable high impedance. System C presented a particularly instructive paradox: it retained the highest impedance values and adhesion strength exceeding 20.7 megapascals, yet exhibited the worst corrosion creep, confirming that high scores on individual metrics can coexist with poor protection of the underlying steel. The authors caution that performance differences reflect the complete system, including layer architecture, number of coats, primer chemistry, and application quality, not binder chemistry alone.

For engineers and asset managers, the practical message is clear but nuanced. Accelerated testing under ISO 12944-9 proved genuinely useful as a screening tool, reliably identifying the poorer performers, Systems B and C, and producing more severe scribe degradation than the field for all four systems. However, it was overly conservative for the durable systems, A and D, which performed considerably better in real-world exposure. The authors conclude that laboratory hours cannot be converted directly into years of field service, and that qualification of coatings for high-value or safety-critical infrastructure should combine accelerated testing with representative field exposure. Crucially, no single performance indicator, whether impedance, adhesion strength, or visual rating, should determine acceptance. A multi-parameter assessment that probes bulk barrier performance, interfacial integrity, and defect-driven degradation together offers the only reliable path to service-life prediction in the world’s most aggressive climates, and the two-year Doha dataset now provides a rare, quantified foundation for building that integrated approach.

Subject of Research: Predicting the field durability of protective anti-corrosion coatings by comparing accelerated laboratory weathering with two-year atmospheric exposure in Qatar

Article Title: From lab to field: case study of predicting the capability of accelerated weathering for protective coatings in Qatar

Article References: Saul, A., Aljaradli, M., Aissa, B., & Liu, Q. (2026). From lab to field: case study of predicting the capability of accelerated weathering for protective coatings in Qatar. Results in Engineering, 32, Article 113290. https://doi.org/10.1016/j.rineng.2026.113290

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113290

Keywords: protective coatings, corrosion, accelerated weathering, ISO 12944-9, electrochemical impedance spectroscopy, pull-off adhesion, corrosion creep, Qatar, service life prediction, atmospheric corrosion, coating durability, field exposure testing

Low-carbon steel, containing no more than 0.2 percent carbon, is the workhorse metal of the global construction industry, prized for its mechanical strength and low cost. But it is also notoriously vulnerable to atmospheric corrosion, the electrochemical process by which thin films of moisture on a metal surface react with oxygen and dissolved salts to form rust. In coastal zones, airborne chloride particles delivered by breaking waves dramatically accelerate this process, which is why seaside structures so often deteriorate decades before their inland counterparts. Ecuador’s coastline, with enormous building potential and a historically sparse network of corrosion monitoring stations, offered the researchers an ideal natural laboratory to quantify just how aggressive such an environment can be.

The team, led by Juan Carlos Guerra and Francisco Corvo, established six exposure sites along roughly a kilometer of shoreline in the Manabí province, each fitted with wooden racks mounted three meters above the ground and angled at 45 degrees toward the prevailing west-northwest wind. At each site, dry cloth devices captured airborne salt for monthly chloride measurements, while polished steel coupons, degreased in n-hexane and pickled in hydrochloric acid, were exposed to track mass loss over time. Meteorological data on relative humidity, temperature, and wind speed came from the nearby Portoviejo station operated by Ecuador’s National Institute of Meteorology and Hydrology. The study ran from July 2021 through June 2022, spanning both the dry and rainy seasons of Ecuador’s coastal climate.

The environmental readings painted a picture of remarkable atmospheric stability. Relative humidity averaged 82 percent with a coefficient of variation of just 2.7 percent, temperature held near 25 degrees Celsius, and wind speed averaged 1.59 meters per second. That persistent humidity is critical: it means a water film essentially never dries from metal surfaces, sustaining the wetness conditions under which corrosion proceeds continuously. The moderate temperature, hovering around the level at which stable electrolyte films form most readily, combined with high humidity to create nearly ideal conditions for electrochemical attack. Yet the low variability of these parameters may itself have tempered the corrosion rates, since other studies have linked strong temperature fluctuations to higher corrosivity.

The chloride numbers were striking. Annual average deposition rates measured by the dry cloth devices exceeded 126 milligrams per square meter per day, which converts to more than 300 milligrams per square meter per day under the wet candle equivalent used by the ISO 9225 standard. That places the atmosphere firmly in the S3 category, the highest chloride deposition class, spanning 300 to 1500 milligrams per square meter per day. No previous corrosion study in Ecuador’s coastal zones, whether from the last century or recent work across Manabí’s cantons, had reported monthly chloride values this high. Deposition also spiked during the January-to-April rainy season, adding a seasonal signature to the salt record.

Multiple linear regression analysis revealed which meteorological forces drove the salt delivery. Relative humidity emerged as the dominant factor, with positive correlation coefficients above 0.61 and statistically significant p-values at every site. The researchers attribute this to the formation of larger, heavier salt particles in saline solution form within the breaking wave zone, which settle at very short distances from the coastline. Wind speed mattered too, but only above a threshold. The data suggested a critical wind speed of roughly 1.5 meters per second, below the transition between what the modern Beaufort scale calls a Ventolin and a Weak Breeze. That threshold is among the lowest ever recorded worldwide; comparable studies in Brazil, Australia, Spain, and Cuba found thresholds near 3 meters per second, while sites in Russia and Bangladesh reported values above 5.5 meters per second. The implication is sobering: even gentle onshore winds in Crucita are enough to load the air with corrosive salt.

Then came the surprise. When the team correlated monthly chloride deposition with monthly corrosion rates, the relationship was consistently negative, with correlation coefficients as strong as −0.96 and p-values well below 0.05 across all six sites. Linear models fitted to the data, such as the averaged equation relating corrosion rate to chloride deposition with a coefficient of determination of 78 percent, confirmed that months with less salt deposition saw more steel loss. The proposed explanation lies in oxygen chemistry. When chloride concentrations in the aqueous layer on the steel surface become extremely high, the solubility of dissolved oxygen drops, suppressing the cathodic oxygen reduction reaction, the essential electron-accepting step that drives atmospheric corrosion. In essence, the salt load becomes so concentrated that the corrosion reaction is partially starved of the oxygen it needs.

This mechanism, though statistically grounded here, echoes earlier observations elsewhere. A study at the Cabo Vilano wind farm in Spain found higher steel corrosion at a sheltered site with lower salt deposition than at an unsheltered one, and laboratory work has shown that corrosion of low-carbon steel in immersion conditions decreases once sodium chloride concentrations exceed about 10 grams per liter. The researchers are careful to note that their interpretation rests on statistical analysis alone; electrochemical techniques such as polarization curves, impedance spectroscopy, and direct dissolved oxygen measurements would be needed for definitive confirmation. Still, the consistency of the inverse relationship across all six sites lends the finding considerable weight.

Scanning electron microscopy of the rust layers added further texture to the story. The one-year corrosion products revealed amorphous ferrihydrite, grass-like lepidocrocite, hummock-shaped maghemite, and ring-shaped magnetite, the latter two forming under oxygen-deficient, chloride-rich conditions and driving cracking and exfoliation of the oxide layers. Energy-dispersive X-ray spectroscopy confirmed elevated chloride and oxygen mass fractions in many samples, and numerous embedded salt particles were visible across most specimens. Notably absent was akaganeite, a phase often found in severely chloride-contaminated rust, which the authors attribute to the lack of the accelerated internal drying that elevated temperatures would normally provide. Bird-beak-shaped feroxyhyte and rosette-shaped goethite completed the mineralogical inventory, a suite consistent with a high-salinity tropical atmosphere.

For engineers, the practical takeaway is a formal corrosivity classification. All six exposure sites earned a Very High (C5) rating for low-carbon steel, confirmed visually by the deteriorated specimens, and ISO-based modeling predicted that this classification would hold across exposure periods from 2 to 20 years. That is paradoxically less severe than the Extreme (CX) category the team had anticipated given the sites’ extreme proximity to the surf, likely for the same oxygen-solubility reasons that suppressed monthly corrosion peaks. Previous Ecuadorian studies had capped out at C4 or found C5 and CX only at isolated near-shore locations. By demonstrating that the highest salt loads do not automatically translate to the fastest metal loss, the Crucita study gives coastal planners in Ecuador and similar tropical environments a more nuanced, and ultimately more reliable, foundation for specifying materials and protection strategies before the first concrete is poured.

Subject of Research: Atmospheric corrosion of low-carbon steel and chloride deposition in a high-salinity tropical coastal environment

Article Title: Chloride deposition and atmospheric corrosion behavior of low-carbon steel in a high-salinity tropical coastal environment

Article References: Guerra, J. C., Corvo, F., Pech, I., Gorety, M., Castañeda, A., & Bastidas-Arteaga, E. (2026). Chloride deposition and atmospheric corrosion behavior of low-carbon steel in a high-salinity tropical coastal environment. Case Studies in Construction Materials, 25, Article e06546. https://doi.org/10.1016/j.cscm.2026.e06546

Image Credits: AI Generated

DOI: Not provided

Keywords: atmospheric corrosion, low-carbon steel, chloride deposition, coastal environment, Ecuador, corrosivity category, relative humidity, wind speed threshold, rust morphology, ISO 9223, marine aerosols, infrastructure durability