Effect of Acid Hydrolysis on Inhibition Performance
assessed using the weight-loss and electrochemical methods. The results obtained are summarised in the following sections.
Gravimetric Measurements
The performance of diamine corrosion inhibitors before and after acid hydrolysis was evaluated using the weight-loss method. The effect of corrosion inhibitor concentration and type and acid concentration were also considered.
Table 1 shows the effect of inhibitor concentration on the protection of mild steel in 1M HCl solution at 60°C for six hours. The results show that inhibition efficiency is a function of inhibitor concentration: as the inhibitor concentration was increased, the inhibition efficiency also increased. All diamine inhibitors before and after acid hydrolysis exhibited significant improvement in their inhibition efficiency compared with the starting material (1,12-dodacanediamine), as shown in Table 1. This is attributed to the introduction of substituents with pi-cloud that enhanced the adsorption of derivatives to steel surfaces.
At the lowest-examined inhibitor concentration (50ppm), diamine-B after acid hydrolysis exhibited the highest protection for mild steel (88.4%). This might be attributed to the presence of triple-bond substituent that allowed this compound to polymerise, forming a protective layer.16,17 The same compound at the same concentration (50ppm) before acid hydrolysis had an inhibition efficiency of only 66.9%. As inhibitor concentration was increased to 400ppm, the effect of acid hydrolysis diminished for all of the compounds examined.
The effect of acid concentration was investigated for diamine-A. Table 2 shows the corrosion protection of mild steel coupons in HCl solutions at concentrations of 1, 4.1 and 7.7M, inhibited by diamine-A (400ppm) at 60°C for six hours. The results showed that the inhibition performance of diamine-A decreased as the acid concentration was increased.
Electrochemical Methods (Tafel Plots) Table 3 shows the corrosion rates for diamine synthesised corrosion inhibitors at 200ppm obtained by Tafel plots at the end of six hours’ exposure time at 60°C in 1M HCl.
The percentage inhibition was calculated using the following equation: Percent Inhibition = 1-
CR1 CR0
x100 (4)
CR0 is the corrosion rate in acid alone and CR1 is the corrosion rate in inhibited acid.
The results obtained from the Tafel plots (see Table 3) are comparable to those obtained by the gravimetric method (see Table 2). The results
1. Frenier WW, et al., Oilfield Review, 1989;1(2):15–21. 2.
Effect of Acid Hydrolysis—Weight Loss Versus Linear Polarisation
The effect of acid hydrolysis of formylated corrosion inhibitors on inhibition efficiency was investigated using the gravimetric weight-loss method and linear polarisation technique. In linear polarisation tests, a concentration of 200ppm was used for all diamine inhibitors and the tests were conducted at 60°C for six hours.
Figure 2 shows the corrosion rate of triallyl diamine (diamine-A) before and after acid hydrolysis. There was no significant change in corrosion-inhibiting activity after hydrolysis. Before hydrolysis, this compound showed slightly better inhibition efficiency. This result is in agreement with that obtained using linear polarisation (see Figure 3). Diallyl propargyl diamine (diamine-B) showed slightly better inhibiting activity after acid hydrolysis. This result is indicated by both weight
The most effective types of corrosion inhibitor for well stimulation are film-forming amines and their salts.
loss and linear polarisation techniques. For diallyl benzyl diamine compound (diamine-C), the same result as with diamine-A was obtained. The weight loss and linear polarisation are in agreement in showing that there was a slight decrease in inhibitory activity after acid hydrolysis. Overall, there was no significant effect of acid hydrolysis on inhibitor activity to protect mild steel in 1M HCl, especially at high inhibitor concentration.
Conclusions The effect of acid hydrolysis on inhibitor activity to protect mild steel in HCl solutions was found to be a function of inhibitor type and concentration. The introduction of multiple adsorption centres into diamine derivatives improves their corrosion inhibition for mild steel in HCl solution compared with the starting material, 1,12-dodacanediamine. This is attributed to the π-electrons present in aromatic and multiple-bond substituents. The weight-loss results are in good agreement with the electrochemical results before and after acid hydrolysis. The results obtained in these tests are very promising and suggest that diamine derivative inhibitors can be used in acid formulations used to acidify oil wells. This means some of these corrosion inhibitors have a good potential to be used in oil/gas well acid stimulation or in pickling treatments. n
Abayrathna D, et al., Inhibitor Evaluations Using Various Corrosion Measurement Techniques in Laboratory Flow Loops, Available at:
www.onepetro.org/mslib/servlet/onepetropreview?id= NACE-00021&soc=NACE (accessed 30 September 2010).
3. Fontana MG, Corrosion Engineering, National Association of Corrosion Engineers, 1986.
4. Schauhoff S, et al., Material Performance, 1999;51(3):141–6.
5. Frenier WW, et al., Corrosion, 1989;440(1):440. 6.
Frenier WW, Presented at the International Symposium on Oilfield Chemistry, 8–10 February 1989.
7. Raicheva N, et al., Corrosion Sci, 1993;34:343. 8. Braun RD, et al., Corrosion Sci, 1993;34:125–7. 9. Du T, et al., Corrosion Journal, 1997;32:301–3. 10. Popova A, et al., [Original in Russian], Khimia i industri, 1988;2:72. 11.
Popova A, et al., [Original in Russian], Khimia i industri, 1987;6:275. 12. Luo H, et al., Corrosion, 1998;54(9):721–31.
13. Rozenfeld I, New York, McGraw-Hill, 1981. 14. Gardner G, Corrosion Inhibitors, NACE, Houston, TX, 1973;156–72. 15. Antopove L, A correlation between the kinetics of corrosion and the mechanism of inhibition by organic compounds, Corrosion Sci, 1967;9:607–20.
16. Mengoli G, et al., Corrosion Sci, 1991;32:743–53. 17. Frenier WW, et al., Mechanisms of Corrosion Inhibitors Used in Acidizing Wells, paper SPE 19042-PA, SPE Production Engineering, 1988;3(4):584–90.
also showed that all synthesised corrosion inhibitors exhibit significant improvement in their inhibition efficiency compared with the starting material (1,12-dodacanediamine).
EXPLORATION & PRODUCTION – VOLUME 9 ISSUE 1
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