Studies on corrosion inhibition of 18% Ni M 250 grade maraging steel under welded condition in acidic media

Abstract

The corrosion behaviour of 18% Ni M250 grade maraging steel under welded conditions in two different acid media, namely, hydrochloric acid and sulphuric acid in various concentrations and temperatures have been studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The corrosion rate in the sulphuric acid medium was higher than in the hydrochloric acid medium. The effect of corrosion inhibition on welded maraging steel was carried out by using five inhibitors, n a m e l y , 2,5-Bis (3,4,5-trimethoxy phenyl)-1,3,4-oxadiazole (BTPO), 1-Phenyl-4-(4-nitrophenyl) thiosemicarbazide (PNPT), 3,4,5-Trimethoxy benzoicacid(3,4,5-trimethoxy-benzylidene) hydrazide (TBTBH), 2-(5-Chloro-1Hbenzoimidazol-2-yl) phenol (CBP), 2-(4-Methoxy-phenyl)-benzo[d]imidazo[2,1-b] thiazole (MPBIT). The results pertaining to the corrosion inhibition studies of five inhibitors in two different acid media at different temperatures in the presence of varying concentrations of inhibitors are reported in the thesis. Activation parameters for the corrosion of the alloy and thermodynamic parameters for the adsorption of the inhibitors have been calculated and the results have been analysed. The adsorption of all five inhibitors on the alloy was through both physisorption and chemisorption, with predominant physisorption in both the media. The adsorption of all the five inhibitors on alloy surfaces follows Langmuir adsorption isotherm. The inhibition efficiencies of all five inhibitors decrease with the increase in temperature and increase in concentration of acidic media.