Laboratory assessment of corrosion inhibitors efficiency at oilfield pipelines of West Siberia region II. Tests in a U-cell

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1 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, Lortory ssessment of corrosion inhiitors efficiency t oilfield pipelines of West Sieri region II. Tests in U-cell I. S. Sivokon, 1 D. B. Vershok 2 nd N. N. Andreev 2* 1 OJSC Trnsenergostroi, Derenevsky n. 7, ldg. 10, Moscow, Russin Federtion 2 A. N. Frumkin Institute of Physicl Chemistry nd Electrochemistry, Russin Acdemy of Sciences, Leninskii pr. 31, Moscow, Russin Federtion *E-mil: n.ndreev@mil.ru Astrct This pper is continution of series of pulictions relted to lortory ssessment of the performnce of cron dioxide corrosion inhiitors for oilfield pipelines in the West Sierin region. The test results otined in U-shped glss cells re considered. The effects of temperture, cron dioxide content, test durtion, specimen surfce condition, presence nd volume of hydrocron phse, nd inhiitor concentrtion on the corrosion kinetics nd protective properties of wide rnge of industril inhiitors re nlyzed. Recommendtions re given on specific inhiitor test conditions to e used for ssessment of inhiitor suitility for the protection of wter pipelines nd oil pipelines with low wtercut. Key words: corrosion inhiitors, corrosion tests, oilfield pipelines. Received: Novemer 5, doi: / Introduction Corrosion inhiitors testing in glss U-shped cell is populr test [1, 2] tht simultes the conditions of internl corrosion development in wter lines nd oil pipelines with low wtercut [3]. However, the rnge of the opertionl conditions in these pipelines is quite rod [3]. Simulting ll of them in ech series of the l tests increse the work scope mny times nd mkes the inhiitors testing more expensive. In view of this, the purpose of this pper is to develop methodology for ssessment of inhiitor performnce in glss U-cell under the criticl conditions in terms of corrosion nd pipeline filure rte. The uthors set the following ojectives: to nlyze the effect of model conditions on steel corrosion kinetics nd efficiency of protection y inhiitors sed on tests in glss U-shped cell; to select the simplest test conditions convenient for inhiitor rnking tht would simulte criticl opertion modes of wter lines nd oil pipelines with low wtercut.

2 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, These tsks were ddressed y the exmple of commercil inhiitors produced in Russi nd interntionlly. References to the commercil nmes of the inhiitors re omitted since the key purpose of this series of pulictions is optimiztion of the test methods on rel chemicls rther thn choice of inhiitors for specific oilfield pipelines. Insted, the inhiitors re mrked with numers from 1 to 7. Informtion out their chemicl nture is scrce. Inhiitors No. 3, 4 nd 7 re qulified y the mnufcturers s imidzolines; No. 5 is ttriuted to quternry mmonium ses. No. 1 is mixture of quternry mmonium ses nd imidzoline derivtives. It is only known out inhiitors No. 2 nd 6 tht they re mine compounds. Experimentl procedure The test method uses mesurement of the corrosion rtes in steel specimens exposed to flow of corrosive fluids circulting in U-shped glss cell [1 3]. The fcility consisted of glss cell supplied with jcket connected to thermostt, propeller stirrer tht ensures circultion of the fluid inside the cell, hermetic drive, n electric motor, nd rck (Fig. 1). Fig. 1. Fcility lyout [5]. 1 rck se; 2 rod; 3 cse; 4 electric motor; 5 hydrulic power drive; 6 power toggle switch; 7 fixtor; 8 stirrer; 9 U-shped cell with thermostt jcket; 10 specimen holder with specimens; 11 choke for fluid/gs dmission; 12 cell mount.

3 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, The queous solution simulting the formtion wter of West Sieri fields /4/ nd two-phse model fluids on its sis hve een selected s the corrosive fluids. The queous solution simulting the corrosion conditions in wter lines ws prepred in volumetric flsks filled with wter y 85 90%. The following compounds were dded, g/l with respect to the finl volume: NCl; 0.76 MgCl 2 6H 2 O; 2.99 СаCl 2 ; 0.08 FeCl 3 6H 2 O; 0.33 N 2 CO 3, while рн of the solution ws djusted to with concentrted HCl. The inhiitor ws dded to the solution s required, the volume ws djusted to the mrk, nd the fluid ws stirred. In simulting the corrosion sttus t oil pipelines with smll wtercut, two-phse fluid ws used fter the following preprtion. White spirit or hexne ws dded to the ove solution contining no inhiitors t rte of 5 prts (y volume) to 95 prts of the solution nd then the inhiitor ws dded s required. The resulting fluid ws stirred for 1 h to ensure equilirium distriution of the inhiitor nd poured to seled continer. No more thn 2 h efore the corrosion tests, the model fluids were plced in sturtor vessel, deerted y mens of nitrogen or rgon uling, nd sturted with cron dioxide. At lest three prllel experiments were mde in ech test fluid. The mss losses normlly used [6,7] to define the corrosion rtes (K) nd the inhiitor protection cpcity (Z) for the metls were estimted t lest in four specimens for ech test. The specimens were mde of steel 20. Their surfces were treted with snd pper, degresed with cetone, nd then dried in the ir. After tht, the specimens were wrpped in filtering pper, plced into desicctor with clcinted СCl 2, kept there for 24 h, nd weighted to within g on n nlytic lnce. To simulte the ctive stte of pipeline steel, the specimens were immersed for 2 min into 5% H 2 SO 4 solution nd wshed strem of distilled wter for 30 seconds. The time tht the wshed specimens styed in the ir did not exceed 1 min. Blnk specimens similr to those used in the tests were pplied to estimte the mss loss during cid pickling. Before the tests, the fcility ws dismounted in complince with its opertion guidelines [5]. The prts contcting the test fluid were wshed with detergent, then with distilled wter, rinsed with lcohol, nd dried. After tht, the cell ws re-instlled on the rck, nd the specimens prepred for the test were fstened to the holder. The cell ws purged for 10 min with strem of n inert gs to remove oxygen. To keep the required temperture, the jcket of the cell ws connected to thermostt. The model fluid (0.5 liters) prepred for the tests ws forced over y n inert gs flow to the test cell. After tht, liquid circultion inside the cell nd in the jcket ws strted. The flow rte of the corrosive fluid during the test ws 1 mps. The test time ws mesured from the moment the cell ws filled with the simultion fluid. After the tests, the specimens were recovered from the holders nd inspected. Further, in order to remove the corrosion products, they were plced into solution (880 ml distilled wter, 66 ml concentrted H 2 SO 4 of 1.83 g/cm 3 density, 100 g citric cid, nd 10 g thioure) for s, wshed in tp wter nd then in distilled wter, wiped with filtering pper, nd plced for 24 h into desicctor with CCl 2. The specimens treted in this wy

4 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, were gin weighted on the nlytic lnce. After removl of corrosion products y pickling, the specimen mss losses were estimted using witness specimens similr to the corroded specimens in terms of shpe, mteril nd size. Unless otherwise specified in the text, the tests lsted for 24 hours nd the О 2 content in the model fluids ws mg/l. Results nd discussion Effect of temperture, dissolved О 2 concentrtion, specimens ctivtion nd test durtion on steel corrosion rte (K) in uninhiited model fluids. With temperture (t) increse from 8 to 45 C, the K vlue increses (Fig. 2). In the tests simulting the opertionl conditions of wter lines (model queous solution), t growth from 8 to 25 C results in K increse from 1.6 to 7.4 nd 11.6 g m 2 dy 1 for ir-oxidized nd cidctivted specimens, respectively. Fig. 2. Effect of t on K in uninhiited model queous solution (а) nd two-phse fluid (). In simultion of the opertionl conditions of oil pipelines with low wtercut (twophse model fluid contining white spirit), similr t growth modified the K vlues to smller extent from 2.0 to 3.6 for ir-oxidized steel nd from 2.7 to 2.9 g m 2 dy 1 for ctivted steel. Heting of the model fluid y dditionl 20 C strongly intensified corrosion. The corrosion rte incresed nerly 7-fold for oth types of specimens. An increse in О 2 concentrtion in the model queous solution from to mg/l t t = 25 C cused n pprent increse (from 7.4 to 23.2 g m 2 dy 1 ) in the K vlue for ir-oxidized steel (Fig. 3). An increse in О 2 content to mg/l lso cuses corrosion rte increse to 27.5 g m 2 dy 1. An increse in the durtion of the test in the model queous solution from 6 to 24 h t t = 25 C incresed the K vlue for oth ir-oxidized (from 3.7 to 7.4) nd ctivted specimens (from 7.4 to 11.6 g m 2 dy 1 ). Activtion of specimens y cid pickling stimulted corrosion in short-term tests. For exmple, in 6-hour tests t 25 C, ir-oxidized specimens corroded in the model queous

5 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, solution t nerly 2 times smller rte thn ctivted specimens (3.7 vs g m 2 dy 1 ). If the durtion of the tests ws incresed, these differences relted to decomposition of the primry oxide film leveled off. In fct, in 24 hour tests under the sme conditions, the K vlues differed y out 30% (7.4 versus 11.6 g m 2 dy 1 ). Fig. 3. Effect of oxygen concentrtion on corrosion rte in ir-oxidized specimens t 25 C in uninhiited queous solution. In the tests tht utilized the model queous solution t lower temperture, t = 8 C, or in the tests with two-phse fluid, the differences in the corrosion ehvior of differently treted specimens ctully did not exceed the dt sctter. The ddition of hydrocrons into the model fluid t the first stge (up to 5 vol.%) slowed down the corrosion (Fig. 4). Thus, in 24 hour tests on ir-oxidized specimens in queous solution t 25 C, the K vlue ws 7.4 g m 2 dy 1. In the sme fluid contining 5% hexne, K = 4.0 g m 2 dy 1, nd if hexne is sustituted y white spirit, K = 2.5 g m 2 dy 1. A further growth of the hydrocron content in the model fluid incresed its corrosivity which chieved mximum in the fluids contining 30% of hydrocron phse. If this concentrtion ws exceeded, the K of steel decresed gin. Fig. 4. Effect of the presence of hydrocrons on the corrosion rte of ir-oxidized specimens t 25 C in model fluids.

6 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, The tested inhiitors reduce the K of steel in most cses, though exceptions from this rule were lso oserved (Tle 1). Thus, ddition of 50 mg/l chemicl No. 3 into the model fluid stimulted the corrosion of ir oxidized specimens t t = 25 C. Addition of 50 mg/l of chemicl No. 2 slightly ccelerted the corrosion of ctivted specimens under the sme conditions. Tle 1. Protective cpcity of inhiitors under vrious test conditions. Inhiitor No. Model fluid C in, mg/l t, C Specimen preprtion Z, % Aqueous solution 10 8 Oxidized 63 1 Sme 25 8 Sme 64 1 Sme 50 8 Sme Sme 50 8 Activted 64 1 Sme Oxidized 27 1 Sme Sme 73 1 Sme Activted 74 1 Sme 50 8 Oxidized 45 1 Two-phse fluid 50 8 Activted 51 1 Sme Oxidized 66 1 Sme Sme 90 1 Sme Activted 71 1 Sme Oxidized 88 1 Sme Sme 95 1 Sme Sme 97 1 Sme Activted 88 2 Aqueous solution 50 8 Oxidized 75 2 Sme 50 8 Activted 5 2 Sme Oxidized 57 2 Sme Activted 72 2 Two-phse fluid 50 8 Oxidized 18 2 Sme 50 8 Activted 34 2 Sme Oxidized 38 2 Sme Activted < 0 2 Sme Oxidized 53 2 Sme Activted 20 3 Aqueous solution 50 8 Oxidized 80

7 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, Inhiitor No. Model fluid C in, mg/l t, C Specimen preprtion Z, % 3 Sme 50 8 Activted 50 3 Sme Oxidized 47 3 Sme Activted 66 3 Two-phse fluid 50 8 Oxidized 53 3 Sme 50 8 Activted 62 3 Sme Oxidized < 0 3 Sme Activted 10 3 Sme Oxidized 43 4 Aqueous solution 10 8 Sme 42 4 Sme 25 8 Sme 63 4 Sme 50 8 Sme Sme 50 8 Activted 62 4 Sme Oxidized 45 4 Sme Sme 78 4 Sme Activted 74 4 Two-phse fluid 50 8 Oxidized 70 4 Sme 50 8 Activted 43 4 Sme Oxidized 66 4 Sme Sme 85 4 Sme Sme 79 4 Sme Activted 48 4 Sme Oxidized 91 4 Sme Sme 97 4 Sme Sme 95 4 Sme Activted 91 5 Aqueous solution 50 8 Oxidized 76 5 Sme 50 8 Activted 45 5 Sme Oxidized 71 5 Sme Sme 83 5 Sme Activted 73 5 Sme Sme 81 5 Two-phse fluid 50 8 Oxidized 45 5 Sme Sme 85 5 Sme Activted 66

8 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, Inhiitor No. Model fluid C in, mg/l t, C Specimen preprtion Z, % 5 Sme Oxidized 91 5 Sme Activted 78 6 Aqueous solution 50 8 Oxidized 53 6 Sme 50 8 Activted 48 6 Sme Oxidized 23 6 Sme Activted 77 6 Two-phse fluid 50 8 Oxidized 76 6 Sme 50 8 Activted 50 6 Sme Oxidized 65 6 Sme Sme 74 6 Sme Sme 89 6 Sme Sme 83 6 Sme Sme 88 6 Sme Activted 74 7 Aqueous solution 50 8 Oxidized 65 7 Sme 50 8 Activted 46 7 Sme Oxidized 30 7 Sme Activted 74 7 Two-phse fluid 50 8 Oxidized Sme 50 8 Activted 64 7 Sme Oxidized 67 7 Sme Activted 53 7 Sme Oxidized 73 7 Sme Sme 97 7 Sme Sme 99 7 Sme Activted 94 Comprison of Z vlues otined in the model electrolyte t t = 25 C during 24 hour test demonstrtes tht in most cses, the efficiency of the inhiitors improves long with n increse in their concentrtion (C in ) from 10 to 50 mg/l. This is perfectly demonstrted y the exmple of inhiitors No. 1, 4 nd 5 for ir-oxidized specimens nd No. 5 for ctivted specimens. Inhiitors No. 2, 3, 6 nd 7 re less efficient t C in =50 mg/l, so they were not nlyzed t C in = 10 or 25 mg/l. The dependencies cquired in the model fluid contining white spirit re more complicted. In cse of ir-oxidized specimens t 25 C, the protective effect of inhiitors

9 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, No. 1 nd 6 incresed with increse in C in from 25 to 50 mg/l. However, the Z vlues of inhiitor No. 4 decresed somewht under these conditions from 85% to 79%. At elevted temperture, t = 45 C, prllel growth of C in nd Z ws oserved for inhiitors No. 1, 6 nd 7, wheres the concentrtion plot of the protective effect for inhiitor 4 pssed through n extremum nd chieved mximum vlue, Z = 97%, t C in = 25 mg/l. The effect of T on Z vlues differs for different model fluids. In queous solution, t growth from 8 to 25 C reduced the protective cpcity for ir-oxidized specimens nd incresed Z for ctivted specimens. This is confirmed y the dt otined for ll chemicls t C in = 50 mg/l (Fig. 5). Fig. 5. Effect of temperture on the protective cpcity of inhiitors (50 mg/l) for ir-oxidized (а) nd ctivted () specimens in model queous solution. In two-phse model fluid, the Z increse ws prllel to the t vrition for specimens of oth types (Fig. 6). Inhiitors No. 3, 2 nd 6 mke n exception. For chemicl No. 3 t C in = 50 mg/l, trnsition from 8 to 25 C on ir-oxidized specimens chnged the effect from corrosion inhiition to some stimultion. In cse of chemicl No. 2, temperture growth decresed Z of ctivted specimens, while t 25 С corrosion of ctivted steel ws stimulted. In the cse of chemicl No. 6, heting of the system from 25 to 45 C hd lmost no effect on the protection of ir-oxidized steel.

10 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, The effect of oxygen concentrtion on the protective effect ws tested on chemicl No. 1 nd ir-oxidized specimens in model queous solution t t = 25 C in 24-hour test (Fig. 7). The protective effect decresed with n increse in О 2 content in the model electrolyte. A decrese in Z ws lso demonstrted for other inhiitors in cse of poor seling of the cell nd uncontrolled ir ccess into it. The effect of test durtion on Z ws studied t t = 25 C in the model queous solution on ir-oxidized nd ctivted specimens t C in = 50 mg/l. The results demonstrte tht Z increses for ll inhiitors in cse of the test prolongtion from 6 to 24 h (Fig. 8), which is cused y quite slow formtion of the protective inhiitor film on the steel surfce. Fig. 6. Effect of temperture on inhiitor protective cpcity (50 mg/l) for ir-oxidized (а) nd ctivted () specimens in two-phse model environment.

11 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, Fig. 7. Effect of oxygen concentrtion on the protective cpcity of inhiitor No. 1 (50 mg/l) for ir-oxidized specimens in model queous solution t 25 C. Fig. 8. Effect of test durtion on inhiitor protective cpcity (50 mg/l) for ir-oxidized (а) nd ctivted () specimens in model queous solution. The effect of specimen ctivtion on the protective effect of the inhiitors ws tested in the model queous solution t t = 25 C in 6- (Fig. 9) nd 24-hour tests t О 2 concentrtions of mg/l. Activtion of the specimens either increses or nerly does not ffect the protective properties of the inhiitors. The trend of Z increse is oserved most clerly in short tests. Adding white spirit (two-phse model fluid) into the system cuses reverse effect, nmely, ctivtion of the specimens decresed the Z vlues. The effect of the hydrocron phse on the protective effect depended on the inhiitor composition (Fig. 10). Comprison of the Z vlues otined for the inhiitors in the model electrolyte nd in the two-phse model fluid demonstrted tht the Z vlues could increse,

12 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, decrese, or sty the sme, depending on the chemicl selected nd on the specimen preprtion. Upon replcement of the model queous solution to the two-phse fluid, the Z vlue incresed for oxidized specimens nd for chemicls No. 1, 6, nd 7. A decrese in Z ws oserved for chemicls No. 2 nd 3. In the cse of inhiitors No. 4 nd 5, ddition of hydrocrons did not chnge the protective efficiency. For ctivted specimens, no Z increse ws oserved upon ddition of white spirit. Fig. 9. Effect of steel ctivtion on the Z of inhiitors (50 mg/l) in model queous solution (а) nd two-phse fluid (). Durtion of the tests is 6 hours. Anlysis of the ove dt exhiits tht the key focus in inhiitor rnking should e mde on the highest temperture mode in the simulted pipelines. Under these conditions, even the est inhiitors ensure reduction in corrosion rte to the level pproching tht in n uninhiited electrolyte t t = 8 C. Therefore, the protective cpcity of the inhiitors t low tempertures is not likely to produce strong effect on the protection sttus of simulted pipelines where the filure rte is defined y the opertion modes nd the sections with elevted tempertures. In inhiitor rnking, one should lso py ttention to the О 2 content in the system. As its concentrtion grows, the corrosion rte increses nd the protective effect of the inhiitors declines. The protective cpcity of inhiitors t low О 2 content would not ffect the protection of wter lines since their filure rte is defined y enhnced ertion levels. On the other hnd, the mximum О 2 levels reported in [3] modifies the corrosion

13 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, mechnism. This gives distorted ide of the efficiency of inhiitors. We elieve tht the tests should e crried out in electrolytes nd model fluids tht contin mg/l of О 2. Fig. 10. Protective effect of inhiitors (50 mg/l) in model queous solution (fluid 1) nd twophse fluid (fluid 2) t 25 C for ir-oxidized () nd ctivted () specimens. Inhiitor testing in U-cell should est e performed using 24-hour tests (the mximum continuous opertion time of commercilly ville equipment of this type). The inhiitor film does not hve enough time to develop in the recommended 6 hours [1, 2] nd the results of the test provide n incorrect ide of the protection efficiency. With this in mind, simultion of wter line opertion (model queous solution) primrily focused on t = 25 C. Under these conditions t C in = 50 mg/l, none of the tested inhiitors provided Z > 83%. For ir-oxidized specimens, the est three inhiitors in terms of protective cpcity form the series: No. 5 (83%) > No. 4 (78%) > No. 1 (73%). The worst performnce for these conditions ws demonstrted y inhiitors No. 6 (23%) nd No. 7 (30%) (Fig. 11).

14 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, Fig. 11. Protective effects of inhiitors (50 mg/l) in model queous solution t 25 C for iroxidized () nd ctivted () specimens. For specimens ctivted y cid pickling, the est performnce ws demonstrted y inhiitors No. 5 nd No. 6. The third position ws shred y No. 1, No. 4, nd No. 7. Accordingly, the series of est performnce ws s follows: No. 5 (81%) > No. 6 (77%) > No. 1 = No. 4 = No. 7 (74%). The worst results were provided y No.3 (66%). Inhiitors No. 5, 4 nd 1 re common for oth top lists. In rnking of inhiitors during simultion of oil pipelines with low wtercut, the key ttention ws given to the tests t t = 45 C. In this cse, the top list of inhiitors for iroxidized specimens ws s follows (Fig. 12): No. 7 (99%) > No. 1 (97%) > No. 4 (95%). It is the sme s the top list for ctivted steel specimens: No. 7 (94%) > No. 1 (91%) > No. 4 (88%). The worst results were delivered y compounds No. 2 nd 3.

15 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, Fig. 12. Protective effects of chemicls (50 mg/l) in two-phse model fluid t 45 C for iroxidized () nd ctivted () specimens. Conclusions 1. During the tests, one should mke sure tht the tested inhiitor is not hzrdous nd does not stimulte corrosion t smll concentrtions. 2. The key focus in the ssessment of inhiitor protective properties should e mde on the mode with the highest tempertures in the simulted pipelines. The Z vlues of inhiitors mesured t low tempertures does not ffect the pipeline protection. 3. The oxygen content in the system should e tken into ccount when testing inhiitors in U-shped glss cell. The tests must e crried out in electrolytes nd model fluids tht contin mg/l О The inhiitor film does not hve enough time to develop within the time period recommended y GOST , nd the results of the test provide n incorrect estimte of the protection efficiency. The durtion of the tests should e 24 hours (the mximum continuous opertion time of commercilly ville equipment of this type). 5. U-cell tests llow us to recommend inhiitors No. 5, 4, nd 1 for protection of wter lines nd inhiitors No.7, 1 nd 4 for oil pipelines with low wtercut. Inhiitor No.3 is the worst choice for oth types of pipelines. 6. The top lists for ir-oxidized nd ctivted specimens re nerly the sme, so the esier tretment of specimens tht does not require cid pickling cn e used for the tests.

16 Int. J. Corros. Scle Inhi., 2012, 1, no. 2, References 1. Metodicheskie ukzniy po ispytniyu ingiitorov korrozii dly gzovoi promyshlennosti (Recommended prctice for testing of corrosion inhiitors for gs industry), Moscow, RAO GAZPROM (in Russin). 2. GOST (USSR Stte Stndrd) , Ediny sistem zshchity ot korrozii i streniy. Ingiitory korrozii metllov v vodno-neftynykh sredkh. Metody opredeleniy zshchitnoi sposonosti (Unified system of corrosion nd geing protection. Corrosion inhiitors of metls in wter-petroleum environments. Methods of protective ility evlution), Moscow, Stndrds pulishing house, 1988 (in Russin). 3. I. S. Sivokon nd N. N. Andreev, Int. J. Corros. Scle Inhi., 2012, 1, no. 1, 65. doi: / V. V. Zv ylov, Prolemy ekspluttsionnoi ndezhnosti truoprovodov n pozdnei stdii rzrotki mestorozhdenii (Prolems of pipelines opertionl reliility t rownfield stge), Moscow, OJSC VNIIENG, 2005 (in Russin). 5. Ustnovk dly otsenki zshchitnoi sposonosti ingiitorov korrozii grvimetricheskim metodom. Psport i tekhnicheskoe opisnie (SNPKh-GPR-05) (Fcility for inhiitors protective ility ssessment y grvimetricl method. Specifictions nd technicl description), Kzn, OJSC NIIneftepromkhim, 2010 (in Russin). 6. I. L. Rozenfeld, Ingiitory korrozii (Corrosion Inhiitors), Moscow, Khimiy, 1977 (in Russin). 7. J. I. Bregmn, Corrosion Inhiitors, Mcmilln, 1963.