Evaluation of the efficiency of corrosion inhibitors for pipe steels in hydrogen-sulfide-containing media
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EVALUATION OF THE EFFICIENCY OF CORROSION INHIBITORS FOR PIPE STEELS IN HYDROGEN-SULFIDE-CONTAINING MEDIA R. M. Yurkevych
UDC 620.194
About one third of newly explored gas fields in the Ukraine contain at most 1 vol.% of hydrogen sulfide. For gas fields with relatively low contents of hydrogen sulfide, the application of materials with elevated resistance to hydrogen-sulfide stress-corrosion cracking (HSSC) and hydrogen-induced cracking leads to unreasonably high costs spent for the equipment of gas fields. At the same time, the application of insufficiently resistant materials may lead to failures of the equipment with unpredictable consequences [1–3]. Thus, it is most reasonable to use steels with relatively low resistance to HSSC in combination with inhibitors. For the protection against hydrogen-sulfide corrosion, it is proposed to use various domestic and foreign inhibitors [4–6]. They decrease the rate of general corrosion but not always serve as reliable protectors of steel against stress-corrosion cracking. Until recently, the gas-processing equipment of the Lokachyn Gas Field has been protected against possible corrosion failures by the Naftokhim-3 corrosion inhibitor produced by the “Galychyna” Enterprise (Drohobych) or by the DODICOR inhibitor (Germany) with similar properties [7]. At that time, the Naftokhim-8 inhibitor was not commercially produced. Its testing was originated in June 2005, parallel with testing of the Naftokhim-3 and DODICOR inhibitors. In view of these facts, the development of highly efficient commercially available domestic inhibitors and the analysis of their protective action under the conditions close to operating is a quite urgent problem. Materials and Methods of Investigations The influence of the Naftokhim-8, Naftokhim-3, and DODICOR inhibitors on the retardation of the general corrosion of 20 pipe steel and steel of the hardness group K (Table 1) were studied gravimetrically according to to the degree of protection Z and the coefficient of corrosion inhibition γ (principal criteria of the efficiency of inhibitors) in a NACE solution (5% aqueous solution of NaCl + 0.5% CH3 COOH saturated with H2 S; pH 3–4; 23 ± 3°C) [8]. The mechanism of protective action of the Naftokhim-8 and DODICOR inhibitors was studied by the electrochemical method based on measuring the stationary potential (for 24 h) and recording polarization curves on specimens of low-alloy K steel in the NACE solution. The working area of each specimen was 1 cm2 . The electrochemical characteristics were measured with a P-5827M potentiostat in the potentiodynamic mode. The rate of changes in the potential was equal to 1.67 mV / sec. As a reference electrode, we used a saturated silver–silver-chloride electrode (ϕ = 0.2 V) connected with the investigated electrode by using a bridge and a Lugin capillary. Karpenko Physicomechanical Institute, Ukrainian National Academy of Sciences, Lviv, Ukraine; e-mail: [email protected]. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 45, No.
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