Self-formation of protective layer on carbon steel surface in 1 M HCl solution containing Barringtonia acutangula leaf extract

•Barringtonia acutangula leaf extract (BALE) exhibited a great corrosion inhibitor for carbon steel in aggressively acidic environment.•Ilexosapogenin A, arjunic acid, taraxerol, tormentic acid and α-amyryltetracosanoate as the main chemical components were isolated from BALE.•The major compounds form a solid protective layer on the carbon steel surface.•The work suggests a novel process for precisely characterizing the chemical constituents in plant extracts.