Corrosion inhibition study of carbon steel A515 in sour water at 75⁰C

Dissertant

Nur, Rana Sohaib

Thesis advisor

Anai, Rana Afif Majid
Hafiz, Muhammad Hliyil

University

University of Technology

Faculty

-

Department

Department of Materials Engineering

University Country

Iraq

Degree

Master

Degree Date

2013

English Abstract

This thesis includes study of corrosion inhibition of carbon steel (which is used in Al-Durra refinery at vacuum distillation unit as body of separating vessels) in sour medium which contains H2S and ammonium using electrochemical technique by Potentiostat/Galvanostat instrument at heat temperature of 75oC.

Four sour media have been obtained from light and heavy naphtha units and then selected the medium which has the highest electrical conductivity and the most contents of H2S and NH4+.

Four amines were selected as corrosion inhibitors; two liquids aliphatic amines: dibutylamine (DBA) with four concentrations (0.0237, 0.0356, 0.0475 and 0.0593M); and cyclohexylamine (CHA) with four concentrations (0.0349, 0.0523, 0.0698, and 0.0872M), and two solid aromatic amines: diphenylamine (DPA) and phenylenediamine (PDA) with four concentrations of each one of them (1x10-5, 1x10-4, 1x10-3 and 1x10-2 M).

Corrosion parameters have been measured such as corrosion potentials Ecorr and corrosion current densities icorr, in addition to cathodic and anodic Tafel slopes bc&ba by Tafel extrapolation method, corrosion rates also are calculated in mm/y.

The data showed that the presence of these amines shifted, in general, corrosion potential toward noble direction and corrosion current density values became lower.

The data of Tafel slopes indicate that aliphatic amines behave as mixed inhibitor type, while aromatic amines are anodic inhibitors.

Protection efficiencies P% were calculated and the results showed that all selected amines are acting as good inhibitors, and there are best concentration of each amine which gives the best efficiency as follow: Inhibitor Conc.0.0237M DBA 0.0872M CHA 1x10-3M PDA 1x10-2M DPA P% 92.28 > 90.78 > 90.45 > 85.81Cyclic polarization curves have been recorded and their results were agreement with the results of linear polarization obtained from galvanodynamic tests for the current in the range of -15 to +15 mA.

From cyclic polarization curves it can be seen the decreasing in hysteresis loop compared with the test in the absence of inhibitors, or disappear of hysteresis loop which indicates the decreasing of chances of the occurrence of pitting and crevice corrosion.

FTIR spectra has been used to explain the role of inhibitive action of selected amines, where indicats the decreasing in N—H stretching band of amine in the film formed on the steel surface due to adsorption of amine on the metallic surface and suggests that nitrogen of amine group is coordinated with Fe2+ on the anodic sites of the metal surface to form Fe2+—N—complex, in addition to the reduction of broad band which appears in the absence of inhibitor due to H—bonded between the iron ions and the water molecules from medium.

This bonding may be due to solvation of metallic ions at electrical double layer.

Optical and scanning electron microscopes support the results of electrochemical measurements and FTIR spectra.

Flakes which show corrosion products are observed in the micrographs.

The micrographs revealed that the surface has been strongly damaged owing to corrosion in absence of the inhibitor, but in the presence of the inhibitor, the damage on the surface seemed to be smaller.

This is attributed to the formation of a good protective film on the low carbon steel surface.

The selected amines obeyed Langmiur isotherm type.

The negative values of Gibbs free energy ΔGoads indicate the spontaneous adsorption of four inhibitors.

Large values of Kads imply more efficient adsorption and hence better inhibition efficiency.

The negative sign of the change of enthalpy ΔHoads in sour medium indicates that the adsorption of inhibitor molecules is an exothermic process.

The negative values of the change of entropy ΔSoads are indicating that amines retained the mobility of metal ions and reducing the dissolution of carbon steel.

Main Subjects

Engineering & Technology Sciences (Multidisciplinary)

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-418350