Eco-friendly 2-Thiobarbituric acid as a corrosion inhibitor for API 5L X60 steel in simulated sweet oilfield environment: Electrochemical and surface analysis studies

Abstract

The corrosion inhibition efficiency of 2-Thiobarbituric acid (TBA) for metal substrate (API X60 steel) in 3.5% NaCl solution saturated with CO₂ gas was probed using various techniques namely, LPR (linear polarization resistance), EIS (electrochemical impedance spectroscopy), and PDP (potentiodynamic polarization). The effects of TBA concentration (25-100 ppm), solution pH (4 and 6), temperature (25-80 °C), and immersion time (2-72 h) on the inhibition efficiency were examined. SEM (scanning electron microscopy) and XPS (X-ray photoelectron spectroscopy) were deployed to explore the corrosion retardation mechanism. TBA exhibited protection efficiencies exceeding 90% for all experimental conditions considered. The excellent anticorrosion performance by TBA was retained up to 72 hours of immersion time. PDP results exhibited that TBA behaved as a mixed type inhibitor. Results from kinetics and thermodynamics analyses indicate that TBA chemically adsorbed on the steel surface following Langmuir isotherm model. The composition of the adsorbed TBA film has been analyzed by XPS.

Figure 1

Chemical structure of 2- Thiobarbituric acid (TBA).

Figure 2

Variation of open circuit potential with time for API 5 L X60 mild steel in CO₂ saturated 3.5% NaCl in the absence and presence TBA at (a) pH 4 and (b) pH 6.

Figure 3

Variation of corrosion rate and inhibition efficiency against concentration for API 5 L X60 mild steel in CO₂ saturated 3.5% NaCl in the absence and presence TBA at pH 4 and 6 from LPR measurements.

Figure 4

EIS Spectra for the behavior of API 5 L X60 mild steel in 3.5% CO₂ saturated NaCl with and without TBA at 25 °C (a) Nyquist plot; pH = 4 (b) Nyquist plot; pH = 6 (c) Bode plot; pH = 4 and (d) Bode plot; pH = 6.

Figure 5

Equivalent circuit diagram used to fit impedance data (a) Blank and (b) presence of inhibitor.

Figure 6

Potentiodynamic polarization curves for X60 mild steel in 3.5% CO₂ saturated NaCl without and with 50 ppm TBA at pH 4, 25 °C and 2 h immersion.

Figure 7

EIS plots for API 5 L X60 steel in CO₂ saturated 3.5% NaCl with and without 50 ppm TBA at 25 °C and pH 4 (a) Nyquist for blank (b) Nyquist for 50 ppm TBA (c) phase angle for blank (d) phase angle for 50 ppm TBA at different immersion times.

Figure 8

EIS Nyquist Spectra for the behavior of API 5 L X60 mild steel in 3.5% CO₂ saturated NaCl (a) without and (b) with 50 ppm of TBA at different temperatures.

Figure 9

(a) Arrhenius and (b) Transition state plots for API 5 L X60 steel in 3.5% NaCl in the absence and presence of 50 ppm TBA.

Figure 10

Langmuir adsorption isotherm of API 5 L X60 mild steel in 3.5% NaCl saturated with CO₂ containing TBA at 25 °C and pH 4.

Figure 11

SEM images for API 5 L X60 mild steel in (a) before immersion, (b) after immerstion in CO₂ –saturated 3.5% NaCl and (c) immersion in CO₂ –saturated 3.5% NaCl with 50 ppm TBA.

Figure 12

Survey scan of XPS spectra for API 5 L X60 mild steel surface product obtained after 24 h immersion in 3.5% NaCl at 25 °C and pH 4 without and with 50 ppm TBA.

Figure 13

High Resolution XPS Spectra for API 5 L X60 mild steel after 24 h immersion at 25 °C and pH 4 in CO₂ - saturated 3.5% NaCl: (a) Fe2p (b) O1s (c) C1s (d) S2p and (e) N1s.

Figure 14

High Resolution XPS Spectra for API 5 L X60 mild steel after 24 h immersion at 25 °C and pH 4 in CO₂ - saturated 3.5% NaCl with 50 ppm TBA: (a) Fe2p (b) O1s (c) C1s (d) S2p and (e) N1s.