3Uchinchi renessansyosh olimlari: zamonaviy vazifalar,
innovatsiya va istiqbol Young Scientists of the Third Renaissance: Current Challenges, Innovations and Prospects
THE EFFECT OF SODIUM BENZOATE ON THE CORROSION OF CARBON STEEL IN GROUNDWATER
Sh. Orzikulova
assistant, Jizzakh Polytechnic Institute. shohsanamtalant@gmail.com. Uzbekistan.
Carbon steel, the most widely used engineering material, accounts for approximately 85%, of the annual steel production worldwide. Despite its relatively limited corrosion resistance, carbon steel is used in large tonnages in marine applications, nuclear power and fossil fuel power plants, transportation, chemical processing, petroleum production and refining, pipelines, mining, construction and metal-processing equipment. There are many methods to reduce corrosion in steel structures. They are coatings, corrosion inhibitors and cathodic protection. Corrosion is a fundamental process which plays an important role in economics and safety. Apparently, corrosion cannot be avoided, but its severity can be prevented. Inhibitors have always been considered to be the first line of defense against corrosion. Several corrosion inhibitors are available today. Corrosion inhibitors offer corrosion protection that is similar to coatings as they act as a barrier between the oxidizing agents and the metal surface. The inhibitor adsorbs on to the steel surface and slows down or eliminates one or more of the electrochemical reactions by blocking the reaction site. The degree of protection that a corrosion inhibitor provides is heavily dependent on the properties of the inhibitor, the properties of the steel and the fraction of the steel surface that is blocked by the inhibitor.
Experiments were carried out for 110 days in the presence of atmospheric oxygen to study the effect of inhibitor sodium benzoate concentrations obtained in the laboratory on the corrosion of carbon steel in groundwater on the basis of local raw materials. It was determined in experiments that the corrosion of carbon steel in the heating fluid has the lowest value when the pH value is pH = 8. For this purpose, working solutions with inhibitor concentrations of 0.1-0.5% were prepared and tested without changing the value of the pH of the solution medium, is when pH = 8. The experimental results are presented in Table 1.
The data in Table 1 show that sodium benzoate at a concentration of 0.1-0.5% is an effective inhibitor of carbon steel in distilled water as well as in groundwater. In distilled water, the protective effect of sodium benzoate in groundwater was found to be p = 0,0008 - 0,0005 g / m2-day higher than other heating liquids. The same inhibitor
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Table 1. Effect of sodium benzoate (inhibitor) on corrosion of carbon steel (St.3) (t=20±50C; ©=0 cycles/min; x= 110 days in the presence of atmospheric
oxygen
№ Solution Soluti on mediu m pH Concentr ation of inhibitor, % P> g/m2 • day Post-experimental appearance of the sample surface
1 2 3 4 5 6
1 H2O (dist.) 8 0,1 0,0008 Very little corrosion, there is less brown corrosion product on the surface of the steel sample
2 groundw ater 8 0,1 0,0007 Very little corrosion, there is less brown corrosion product on the surface of the steel sample
has been found in experiments to be an effective inhibitor for carbon steel (St.3) in groundwater as well.
Data on the protective effect of the inhibitor are given in Table 2 Experimental results showed that when the concentration of sodium benzoate was 0.1% and the pH was 8, the rate of corrosion under inhibitory conditions was several times lower than under non-inhibitor conditions. The data in Table 2 show that the protective effect of the inhibitor is good.
When the inhibitor concentration is 0.3% and the pH is 8, the corrosion rate is significantly reduced in inhibitory conditions than in non-inhibitor conditions, and the protective effect of the inhibitor is effective.
The inhibitor concentration is 0.5% and the corrosion rate is the same in all solutions even when the pH is 8, and the corrosion rate in groundwater is 0.0005 g/m2-day. In this case, the protective effect of the inhibitor was found to be 85 in experiments.
The inhibitor concentration is 0.5% and the corrosion rate in groundwater is 0.0005 g/m2-day even when the pH value is 8. Experiments have shown that the protective effect of the inhibitor is 75. Thus, experimental results showed that sodium benzoate can be used as an effective inhibitor when the pH value is 8 for aqueous solutions of groundwater at concentrations of 0.1-0.5%.
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3 H2O (dist.) 8 0,3 0,0007 Very little corrosion, there is less brown corrosion product on the surface of the steel sample
4 groundw ater 8 0,3 0,0006 Very little corrosion, there is less brown corrosion product on the surface of the steel sample
5 H2O (dist.) 8 0,5 0,0006 Very little corrosion
6 groundw ater 8 0,5 0,0005 Very little corrosion
Table 2. Protective effects of sodium benzoate at different concentrations
Consantratio p, without p, with
Solution pH n of inhibitor, inhibitor inhibitor
% g/m2 • day g/m2 • day
H2O (dist.) 8 0,1 0,013 0,0008
Groundwater 8 0,1 0,06 0,0007
H2O (dist.) 8 0,3 0,013 0,0006
Groundwater 8 0,3 0,06 0,0005
H2O (dist.) 8 0,5 0,013 0,0006
Groundwater 8 0,5 0,06 0,0005
After experimental work we can conclude that in groundwater, carbon steel is very aggressive with a pH less than 7 (pH = 3-5), and steel samples corrode very dangerously at pH values (pH = 3J5) in the same solution.
The corrosion rate is much slower at much higher values of pH (pH = 7.5) and the surface of steel samples is better preserved when pH = 8. As pH value is higher than 8, corrosion rate of the steel samples decreases.
It was found that the small values of the corrosion rates of steel samples in groundwater were pH = 8.
When sodium benzoate is used as an inhibitor, good results are obtained at small concentrations of corrosion of carbon steel in natural aqueous solution at a concentration of 0.1-0.3% at pH = 8.
Thus, the corrosion rate of carbon steel in groundwater was found to have the lowest value when the inhibitor concentration was 0.1-0.3% and the pH = 8.
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The corrosion process of carbon steel samples in groundwater has high velocities in the solution medium - pH values below 8, the corrosion rate decreases with increasing pH value and the surface of carbon steel samples is much better preserved.
When sodium benzoate is used as an inhibitor, the corrosion of carbon steel in groundwater is very minimal. The corrosion of carbon steel in groundwater is so great at all values of pH less than 8 that the specimens become completely unusable.
At values of pH 6-7.5, flat corrosion occurs on the surface of carbon steel samples. When the pH value is 8, the corrosion process is sharply reduced when sodium benzoate is added as an inhibitor at concentrations of 0.1-0.5%. Therefore, in order to slow down the corrosion process of carbon steel in groundwater, it is necessary to keep the value of the medium - pH in the range of 7.5-8. In order to further reduce the corrosion process of carbon steel, the corrosion rate can be further reduced by adding 0.1-0.5% sodium benzoate as an inhibitor when the pH value is 8.
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5. Corrosion engineering. Mars G. Fontana. 2018.
6. Elsener B: "Mixed-in Inhibitors", in "COST 521: Corrosion of Steel in Reinforced Concrete Structures. Prevention - Monitoring - Maintenance", Final Report (Ed. Weydert R), Final Workshop 18-19 February, Luxembourg, 2002, pp 43-55. 8
7. Groundwater .R.AllanFreze, John cherry. 1979by Prentice -Hall.
8. Gatos H 1-rd Symposium European Les Inhibiteuos De Corrosium Universita Degli Stady De Ferrara, 1961, p257.
9. Sukhotin A. M., Kartasheva K. M. "Protection of metals", 1969, vol. 5, no. 5, p. 575. 19.
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