Two 8-Hydroxyquinoline-based piperazine, 7-((4-(4-chloro phenyl)piperazin-1-yl) methyl) quinolin-8-ol (CPQ) and 7-((4-methyl piperazin-1-yl) methyl)quinolin-8-ol (MPQ) were prepared, identified and investigated as corrosion inhibiting additives of C35E steel in HCl electrolyte using experimental and theoretical tools. All outcomes findings confirm that CPQ and MPQ significantly improved anti-corrosion properties of C35E steel and CPQ performed better than MPQ and their inhibition efficiency depends on the temperature, the amount, and the chemical structure of the inhibitor. The ηmax of CPQ and MPQ reaches as much as 91.5% and 86.3% at 10−3 M, respectively. EIS outcomes revealed that the corrosion of C35E steel is controlled by only one charge transfer mechanism and the adsorbed CPQ and MPQ molecules decreased the steel dissolution by developing a pseudo-capacitive film on the steel surface. Both additives revealed mixed-type inhibitory activity, lowering of cathodic and anodic corrosion reactions rate, as proposed from the polarization investigation. The UV–Visible spectra suggest the existence of strong interaction between iron cations and 7-(4-alkylpiperazinylmethyl)-8-Hydroxyquinolines molecules. The 7-(4-alkylpiperazinylmethyl)-8-Hydroxyquinolines were chemisorbed on the C35E steel surface in accordance with Langmuir adsorption isotherm. Temperature influence studies of CPQ and MPQ adsorption behavior, as well as estimated thermodynamic magnitudes, are consistent with a physisorption process. The computational correlations (DFT, Monte Carlo, and Molecular Dynamic simulations) justify the experimental observations.