Chrysanthemum Extract Shields Pipeline Steel From Acid Corrosion

A flower long prized in traditional Chinese medicine for its soothing teas and anti-inflammatory properties is now showing an entirely different kind of healing power: the ability to protect one of the world’s most important pipeline steels from aggressive acid attack. In a study published in Discover Electrochemistry, researchers from Suez Canal, Tanta, and Mansoura Universities in Egypt report that a simple methanol extract of Chrysanthemum indicum flowers can suppress the corrosion of API 5L X70 carbon steel in sulfuric acid by more than 91 percent, offering a biodegradable, plant-based alternative to the synthetic corrosion inhibitors that have long dominated the industry.

Carbon steel is the workhorse of the petrochemical world. It is inexpensive, strong, and durable, which is why it carries oil and gas through pipelines, lines storage tanks, and forms the backbone of boilers, reactors, and heat exchangers. But wherever steel meets acid, trouble follows. In sulfuric acid, iron atoms at the metal surface lose electrons and dissolve as ferrous ions, while hydrogen ions consume those electrons at cathodic sites to evolve hydrogen gas. The result is gradual thinning, pitting, and eventual failure of equipment, with enormous economic and environmental costs. The standard defense has been organic inhibitor molecules rich in nitrogen, oxygen, or sulfur heteroatoms, which adsorb onto the metal and block the reactive sites. Concerns about the toxicity and environmental persistence of many synthetic inhibitors, however, have pushed corrosion scientists toward greener chemistry.

Chrysanthemum indicum seemed like a promising candidate. Phytochemical analyses of its flowers have revealed volatile compounds such as eucalyptol, alpha-pinene, and germacrene D, along with abundant flavonoids and glycosides including quercitrin, myricetin, and luteolin-7-glucoside. These molecules carry electron-rich oxygen and nitrogen atoms and aromatic pi-systems, exactly the structural features that allow inhibitors to anchor themselves to iron surfaces through donor-acceptor interactions. The Egyptian team collected flowers from the Daqahlia Governorate in June 2023, dried and powdered them, and extracted 200 grams of material in 800 milliliters of methanol for 48 hours before concentrating the crude extract under vacuum.

The researchers then tested the extract at concentrations from 200 to 400 parts per million in 0.5 molar sulfuric acid, using a battery of complementary techniques. Weight-loss measurements on polished steel coupons, performed according to the ASTM G31-72 standard, showed that mass loss fell steadily as extract concentration rose. At the optimum dose of 400 ppm and 25 degrees Celsius, the inhibition efficiency reached approximately 91.53 percent, the highest value recorded in the study. When the temperature was raised to 45 degrees Celsius at the same dose, efficiency dropped to 78.28 percent, a decline that carries important mechanistic information.

That temperature dependence, combined with Arrhenius analysis, told the team that the extract binds to steel largely through physical adsorption. The apparent activation energy of the corrosion process increased with inhibitor concentration, a signature of weak electrostatic interactions between adsorbed molecules and the charged metal surface that weaken as heat disrupts them. Thermodynamic parameters reinforced the picture: the adsorption was exothermic, with negative enthalpy values, while positive entropy changes reflected the displacement of adsorbed water molecules as inhibitor species attached to the surface. The adsorption data fit the Langmuir isotherm almost perfectly, with slopes near one and high correlation coefficients, indicating that the phytochemicals form a monolayer on the steel. Free energies of adsorption fell between the classic thresholds for physisorption and chemisorption, suggesting that both mechanisms contribute, with electrostatic attraction dominating and chemical coordination adding strength.

Electrochemical measurements told a consistent story. Potentiodynamic polarization curves showed that the extract suppresses both the anodic dissolution of iron and the cathodic hydrogen evolution reaction, with corrosion current density falling sharply as concentration increased. Because the corrosion potential shifted by only about 4 millivolts, far below the 85-millivolt threshold, the extract qualifies as a mixed-type inhibitor. The Tafel slopes barely changed with dose, meaning the adsorbed film simply reduces the active surface area rather than altering the fundamental corrosion mechanism. Electrochemical impedance spectroscopy added quantitative depth: charge-transfer resistance jumped from roughly 4.5 ohm-square centimeters in bare acid to about 31.1 ohm-square centimeters at 400 ppm, while double-layer capacitance plunged from about 425 to 108 microfarads per square centimeter, evidence that bulky organic molecules were displacing hydronium ions and thickening the interfacial layer.

Surface imaging provided the most visually striking confirmation. Scanning electron micrographs of steel immersed in uninhibited acid for 24 hours revealed severe roughness and widespread pitting, the classic scars of acidic attack. The surface treated with 400 ppm of the extract, by contrast, appeared smooth and largely free of pits. Energy-dispersive X-ray analysis detected nitrogen and sulfur signals on the protected surface, chemical fingerprints of adsorbed organic constituents, alongside a stronger iron signal indicating suppressed dissolution. Atomic force microscopy quantified the transformation: average roughness fell from 647 nanometers on corroded steel to just 84 nanometers on protected samples, a nearly eightfold smoothing that directly reflects the uniformity of the protective film.

Fourier-transform infrared spectroscopy then identified which functional groups do the anchoring. The free extract shows a broad band at 3237 per centimeter from O-H and N-H stretching; after adsorption this band shifts to 3214 per centimeter, indicating that hydroxyl and amine groups participate in binding through hydrogen bonding and coordination with iron. A carbonyl band at 1635 per centimeter shifted to 1653 per centimeter, consistent with oxygen lone pairs donating electron density into the empty d-orbitals of iron atoms, while C-O and C-N bands near 1032 per centimeter also changed position and intensity. Together, these shifts sketch a mixed-mode mechanism in which electron-rich donor atoms coordinate directly with iron while weaker van der Waals and hydrogen-bonding forces add coverage.

The practical significance is considerable. API 5L X70 steel is a high-strength grade used in long-distance oil and gas transmission pipelines, and acidizing operations, pickling, and industrial cleaning all expose such steels to corrosive acids. An inhibitor derived from an abundant, biodegradable flower, effective at just 400 parts per million, could reduce both the environmental footprint and the health risks associated with conventional formulations. The authors note that this is the first reported use of Chrysanthemum indicum extract for protecting this particular steel grade in sulfuric acid, and they acknowledge that direct comparisons with other plant-based inhibitors remain a task for future work.

The convergence of evidence is what makes the study compelling. Weight loss, polarization, impedance, microscopy, elemental analysis, and spectroscopy all point to the same conclusion: molecules in the chrysanthemum extract spontaneously assemble into an adherent organic film that starves the corrosion reactions of active sites. As industries worldwide face mounting pressure to replace hazardous chemicals with sustainable alternatives, the humble chrysanthemum, already valued for centuries in medicine and ornament, may find a new career guarding the steel arteries of the global energy economy.

Subject of Research: Plant-derived green corrosion inhibitors protecting carbon steel in acidic media

Article Title: Chrysanthemum indicum extract as a sustainable inhibitor for acid-induced corrosion of API 5L X70 steel

Article References: Chrysanthemum indicum extract as a sustainable inhibitor for acid-induced corrosion of API 5L X70 steel. (n.d.). https://doi.org/10.1007/s44373-026-00170-x

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00170-x

Keywords: Chrysanthemum indicum, corrosion inhibition, green inhibitor, API 5L X70 steel, sulfuric acid, Langmuir isotherm, electrochemical impedance spectroscopy, potentiodynamic polarization, adsorption mechanism, plant extract, carbon steel, sustainable chemistry