Grass Extract Blocks Chloride Corrosion in Duplex Stainless Steel

A humble grass that grows wild in the alluvial soils of northern India may soon help protect the steel pipelines that carry the world’s oil and gas. In a new open-access study published in the Journal of Materials Science: Metallurgy, researchers at the Rajiv Gandhi Institute of Petroleum Technology report that an extract of munj grass (Saccharum munja) shields duplex stainless steel 2205 from the aggressive chloride-driven corrosion that plagues process industries in brine-laden environments. The work, led by Swati Chaudhary and Deepak Dwivedi, combines electrochemistry, surface science and quantum-mechanical modelling to demonstrate that a simple biomass extract can deliver up to 87 percent inhibition efficiency at a modest 5 percent volume concentration, offering an eco-friendly alternative to the toxic synthetic compounds that currently dominate corrosion control.

The economic stakes are enormous. Corrosion costs the world an estimated 2.5 trillion US dollars every year, roughly 3.4 percent of global gross domestic product, with the oil and gas sector among the hardest hit. Steel pipelines transporting crude oil and natural gas routinely carry produced water dominated by sodium chloride brine, and the chloride ions in that brine attack the protective magnetite layer on steel surfaces, triggering localized pitting that can escalate into leaks, structural failures and safety incidents. Conventional wisdom holds that better corrosion management could save between 15 and 35 percent of these costs, equivalent to hundreds of billions of dollars annually, and the search for inhibitors that are both effective and environmentally benign has become one of the most active frontiers in materials chemistry.

Duplex stainless steel 2205 was the test subject for good reason. With its balanced microstructure of ferrite and austenite phases, DSS 2205 combines exceptional mechanical strength with strong resistance to chloride stress corrosion cracking, making it a mainstay of petrochemical plants, offshore platforms and underwater engineering. Yet even this robust alloy is not immune: chloride ions adsorb onto and infiltrate the passive film, initiating pitting corrosion that has caused significant economic losses. Earlier studies have shown that solution annealing temperature, hydrogen exposure and alternating dry-wet marine conditions all influence how badly 2205 pits, but comparatively little work had explored sustainable, biomass-derived inhibitors specifically for this alloy in brine media, and the molecular details of how such inhibitors bond to the steel’s protective oxide film remained poorly understood.

The Indian team turned to munj grass, a fast-growing plant long used in Ayurvedic medicine for its diuretic, cooling and anti-inflammatory properties, and recognized as the One District One Product of Amethi in Uttar Pradesh, where its stems are woven into baskets, mats and decorative handicrafts. Crucially, munj is rich in phytochemicals including phenolics, saponins, flavonoids and tannins, molecules packed with heteroatoms and aromatic rings that can adsorb onto metal surfaces and block chloride-induced attack. The researchers harvested leaves from the RGIPT campus, dried and ground them, and refluxed 10 grams of powder in 0.2 molar sodium hydroxide solution for two hours at 105 degrees Celsius. After filtration and drying, the process yielded 2.3 grams of extract, a 23 percent extraction yield, which was then dosed into 3.5 percent sodium chloride solution, a standard simulation of seawater salinity, at concentrations ranging from 1 to 5 percent by volume.

Electrochemical testing told a compelling story. Using electrochemical impedance spectroscopy and linear polarization resistance on a three-electrode cell with a platinum counter electrode and Ag/AgCl reference, the team measured polarization resistance rising from just 131 ohm square centimeters in the blank brine to a maximum of 1670 ohm square centimeters at 5 percent extract, corresponding to an efficiency of about 92 percent by the impedance route. Nyquist plots showed a single capacitive semicircle whose diameter, a direct proxy for charge transfer resistance, grew steadily with inhibitor concentration, indicating that the extract does not change the underlying corrosion mechanism but simply erects an increasingly effective barrier. The double-layer capacitance fell from 2.95 to 0.87 microfarads per square centimeter, consistent with inhibitor molecules displacing water at the interface and thickening the protective dielectric layer.

Potentiodynamic polarization confirmed the picture over immersion periods stretching from one hour to 96 hours. Corrosion current density at the one-hour mark dropped from 0.227 microamperes per square centimeter in uninhibited brine to 0.027 microamperes per square centimeter with 5 percent extract, and the same monotonic decline appeared at every time point tested. The corrosion potential shifted by less than 85 millivolts with inhibitor addition, classifying munj extract as a mixed-type inhibitor that suppresses both anodic metal dissolution and cathodic reactions. Efficiency climbed during the first 24 hours as adsorbing molecules gradually built their film, dipped slightly at 48 hours in what the authors attribute to partial desorption or competitive chloride adsorption, and recovered again by 96 hours as a more stable adsorption equilibrium established itself on the surface, with a headline inhibition efficiency of 87 percent.

Surface and structural analyses corroborated the electrochemical findings. X-ray diffraction verified the duplex ferrite-austenite microstructure and showed that uninhibited exposure weakened diffraction peak intensities through chloride-driven dissolution, while samples protected with 3 and 5 percent extract retained peak sharpness essentially matching the unexposed alloy, with no new crystalline corrosion products detectable. Field-emission scanning electron microscopy revealed severe pitting and rough, corroded morphology on unprotected coupons, whereas inhibited samples stayed comparatively smooth, with the extract visibly coating and shielding the surface. Energy-dispersive spectroscopy of the pit regions showed iron depletion in uninhibited specimens and recovered iron content in inhibited ones, and Fourier-transform infrared spectroscopy of the extract identified O-H, C-H, C-O-C and C=C functional groups characteristic of polyphenols, carboxylic acids and oligosaccharide-linked sapogenins.

Gas chromatography-mass spectrometry pinpointed the chemistry behind the protection. The extract’s major constituents included gamma-sitosterol at nearly 30 percent, the fatty amide 13-docosenamide, also known as erucamide, at 21 percent, phytyl linoleate at about 9 percent, along with methyl stearate, squalene, tetracontane-1,40-diol and hexacontane. Docosenamide, a long-chain amide already valued in the oil and gas industry as a corrosion-inhibiting additive, emerged as the likely workhorse molecule, donating its polar CONH2 head group to anchor onto oxidized steel while its hydrocarbon tail adds hydrophobic shielding.

To probe that anchoring at the atomic scale, the team ran density functional theory calculations using plane-wave pseudopotential methods in Quantum ESPRESSO, adsorbing the CONH2 fragment onto the (110) surfaces of hematite and chromia, the dominant oxides in the passive film. The results were strikingly surface-dependent: chemisorption on Fe2O3 (110) was strongly exothermic, at 7.72 electronvolts for the FCC form and 4.27 electronvolts for the trigonal form, while Cr2O3 (110) adsorbed more weakly at 3.59 electronvolts, and the Fe2O3 (100) surface was energetically unfavorable altogether. Under-coordinated iron atoms on the (110) plane, the authors argue, act as Lewis acid sites that bind the amide’s nitrogen and oxygen, meaning that inhibitor performance is governed not just by molecular structure but by which oxide phases and crystallographic faces the passive film actually exposes.

Beyond the laboratory, the findings carry real sustainability weight. Munj grows on infertile land with little water, its extract is non-bioaccumulating and non-polluting, and the study’s authors frame the work as a direct contribution to United Nations Sustainable Development Goals 9, 12 and 14 on industry, responsible production and life below water. If amide-rich plant extracts can protect even a premium alloy like DSS 2205 at percent-level dosages, the door opens to greener pipeline treatments across the energy sector, and to a rural Indian grass playing an unlikely starring role in the trillion-dollar fight against corrosion.

Subject of Research: A plant-extract green corrosion inhibitor protecting duplex stainless steel 2205 in chloride-contaminated brine solutions.

Article Title: Anti corrosion and anti-pit resistant munj extract inhibitor for DSS 2205 in chloride contaminated solutions

Article References: Chaudhary, S., Mylapilli, S. V. P., Pandey, S., Kumar, V., & Dwivedi, D. (2026). Anti corrosion and anti-pit resistant munj extract inhibitor for DSS 2205 in chloride contaminated solutions. Journal of Materials Science: Metallurgy, 1(1), Article 21. https://doi.org/10.1007/s44492-026-00022-0

Image Credits: AI Generated

DOI: 10.1007/s44492-026-00022-0

Keywords: corrosion, green inhibitor, duplex stainless steel 2205, munj grass, Saccharum munja, chloride pitting, electrochemical impedance spectroscopy, docosenamide, density functional theory, biomass extract, brine solution, sustainable materials