2008 real time corrosion monitoring to assess the corrosivity of oil water mixtures and the kinetics

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Paper No.

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08286

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CORROSION 2008 '=:-=)I'/lRENCE &

REAL TIME CORROSION MONITORING TO ASSESS THE CORROSIVITY OF OIL WATER

MIXTURES ANO THE KINETICS OF THE RESPONSE TO IMIOAZOLlNE BASEO CORROSION

INHIBITORS

WVillamizar

Corrosión y Protección Ingeniería, S.C.

Rio Nazas 6, Col. Vista Hermosa , Cuernavaca , Morelos , Mexico , CP 62290

wvillamizar@corrosionyproteccion .com.mx

C. S. Magaña PEMEX. Marina Nacional Torre PEMEX Piso 23 , México , D.F ., México, CP 01000 H. Chow PEMEX Exploración y Producción.

Boulevard Adolfo Ruiz Cortines 1202, Villahermosa, Tabasco, Mexico, CP 86030 G. Gonzalez Rodríguez

Centro de Investigación en Ingeniería y Ciencias Aplicadas UAEM

Universidad 1001 , Cuernavaca, Morelos , México , CP 62210

M. Casales

Instituto de Ciencias Físicas , UNAM

Universidad 1001 , Cuernavaca , Morelos , Mexico , CP62210

L. Martinez Gómez

Instituto de Ciencias Físicas, UNAMI Corrosion y Protección Ingenieria Universidad 1001 , Cuernavaca, Morelos , México, CP 62210 ABSTRACT In this paper , we report experiences assessing real time corrosion inhibitors performance employing corrosion inhibitors currently used in the field in the Gulf of Mexico. The onset of the corrosion inhibitor performance in reducing the corrosion rate was clearly monitored in seven minutes intervals after the inhibitor application. By controlling the inhibitor concentration in the range of 5 to 100 ppm, corrosion rates are determined in time evolution from over 150 mpy to less than 1 mpy in the best performing chemical treatments. The real time corrosion monitoring equipment which includes several techniques : linear polarization resistance (LPR) , harmonic analysis (HA) , and electrochemical noise (EN).

Environments include 3 % NaCI solution with and without 10 % diesel , saturated with CO 2 at 50°C. 80th, LPR and HA techniques had a quick answer, within 7 minutes, however, HA showed big fluctuations although similar trend in the corrosion rate to those given by the LPR technique . On the other hand , regarding localized type of corrosion , the results given by the EN and HA techniques , as

Copyrigh t 1\.)2008 by NACE Intemalional. Requesls for perm issi on lO pu bli sh thi s man uscn pl m an" I·orm. In pan or In ",hale must be in writing lO NAC E Intemali ona l, Copyri gh l Di vi sion. 1440 Soulh creek Drive. Houslon , Te.\a5 777084 The mal erial prese l1 led and Ihe views exp ressed in Ihis pa per are solel)' Ihose ol' the aU lhor(s) and are nOI necessari h' endo rsed b) the ,",ssocial lon. Pnnled In Ihe USA

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measured by the pitting factor, were dissimilar too regardless of the used solution, because the pitting factor values increased as son as the inhibitors were words:

electrochemical

harmonic analysis, on-line, pitting factor.

INTRODUCTION The Injection of corrosion inhibitors is a standard in the oil and gas production to control internal corrosion of carbon steel structures. has shown to be very successful and cost The of a treatments chemicals tor a field application would typícally undergo a rigorous laboratory evaluatíon programmed followed by field assessment. A traditional and widely used method of corrosíon monitoring is the evaluations of coupons of corrosion. They yield information on mass loss corrosion rate, extent and distributíon of localized corrosíon, but the blQoe:st drawback is that provide time average data can not be utilized for real time or on - line corrosion monitoring. The importance of on - line monitoring of corrosíon ís recognized from the fact that many techniques are being adopted and new techniques are explored. In general, the most common methods of assessment of corros ion behavior are usually by linear "",I",,,·.,.,,,t.,,,n resistance (LPR) and electrical resistance It is that there are limitations in the selection of chemical by simply basing the decision on the results of LPR. Wider possibilities are by electrochemical techniques based on non - linear measurements.

Harmonic is based on perturbatíon with AC sígnal and the analysis of the response nonlinear ín the on this basis allow extraction of the required of kinetic of the envíronments when corrosíon process. HA and LPR well ín aqueous corrosíon ís occurring. The maín advantage of HA is that the measurements of corrosion rate not employ values for the Tafel slopes, and measurements can be undertaken ín a of the time conventional methods. HA has been applied in various studies of corrosion and under a variety of conditions '.2.3 noíse performs well not only in aqueous environments but also in mixed hydrocarbon and low conductivity environments in both stable and unstable condítíons. EN monitoring real time corrosíon which provides ínformation both on the level of corrosíon activity in a and the dominant corrosion mechanism 4. 6. This data can be used to efficiently evaluated corrosíon ínhibitors effectíveness and to optimize rates 7.8. The pitting factor and higher order statistícal measures and are potentially applícable to the their 9 Although the monitoríng corrosíon, however further work ís needed to electrochemical techniques as EN y HA are wider within the monitoring corrosion and plant operation communitíes, a more succinct method of analyzíng and the results of EN Y HA data is need.

The present research was undertaken to ascertaín if LPR. HA Y EN in combinatíon are suítable for the study of performance ofcorrosion inhibitors under a variety of conditions for example in the absence and presence of hydrocarbons and corrosíon sweet. In our previous works, the studies of different types of imidazolines like as corrosion inhíbitors based on theoretícal study and electrochemical using curves and electrochemícal impedance spectroscopy was reported 10,11.

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EXPERIMENTAL SmartCETTM (1) equipment was used for on-line monitoring of LPR, EN and HA The equipment measured on a 7 minutes and 10 seconds Linear polarization resistance measurements invo/ve 25mV at 10 mHz) sinusoidal the measurement of the current response to a small amplitude polarization of the electrodes under potentiostatic control.

Harmonic distortion ís a measure of the non-linear current distortion measurement. The data is (using Fast Fourier Transform to of the corrosion current, and to an on-line calculation of the Tafel and

during the LPR a measurement constants.

nrr.\llnIQ

Efectrochemical nolse refers to the f1uctuations in current or potential that occurs on the surface of a metal at the free corrosion. The pitting factor is derived the electrochemical noise and the harmonic data. The Pitting Factor has a value between O and 1. As the value approaches 1, the system will be in a pitting regime rather than a regime of general corrosion. The calculation for PF is as follows: PF = (EN) / (A icorrHA) EN A icorrHA

(1 )

Current noise (standard deviations)

Electrode surface area,

Corrosion current from harmonic analysis, Alcm 2

Electrodes test AII the electrochemical corrosion tests were performed using a standard three identical "finger­ electrode" with a triangular configuration identícal in surface area and made of the same material (1018 mild Before the electrode was with 600 silicon carbide emery paper and then cleaned with alcohol, acetone, and dístilled water.

solutions Six types of commercial imidazolines like a corros ion inhibitors were used in this study Table 1.).

The inhibitors were dissolved in a solution to 10 % of 2-propanol and the concentration of the inhibitor used in this work was 20 ppm.

A basíc solution of 3 wt % NaCI and a mixtu re which consisted of 90 % vol. of th is solutions + 10 % vol. diesel were used as testing solutions. The solutions were saturated with CO 2 for 2 h before testíng and was kept kept under a CO 2 atmosphere during testing. For all experiments, the systems of both solutions was 4.2. The solution was further stirred constants at 50 ± 2 oC. The continuously. The working electrode was pre-corroded in the corrosive electrolyte for 2 h before the ínhíbítor was introduced.

RESUL TS ANO OISCUSSION

Figs. 1 and 2 show the on-line corrosion rate measurements with the LPR technique in both, 3 NaCI solution wíthout and with diesel alter a two period at 50 ± 2 oC with 20 ppm of the three of imidazolines: hydroxyethyl imidazoHnes 81, HEI-12 and HEI-18), amíno-ethyl imidazolines AEI-18b) and amido-ethyl imidazoline (AMEI-18), during 20 hours of testing.

1 shows that the corrosion rate values in the solution without diesel decrease rapídly with time, 7­ 21 minutes after the addition of the ímidazolines, reaching a stable and the time to reach this stable value for e'!l~h imidazoline, taking several hours in each case.

SmarCETTM is a trade mark of Honeywelllnternatlonallnc, Morristown, NJ, USA

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1 shows that the two amino-ethyl imidazolines AEI-18a and AEI-18b, together with the hydroxyethyl imidazoline HEI-181 show the lowest corrosion rate values within the first minutes alter adding them, Hydroxyethyl imidazoline HEI-12, being the most hydrophilíc molecule, does not seem to be the most efficient inhibitor in this solution, which could indicate that the carbon chain has a just as established in the literature , On the other hand, the presence of the oily phase, i.e. diese!. seems to increase the efficiency of the inhibitors, (Fig. 2) since the time to decrease the corrosion rates are much shorter than those when since, the corrosion rate by AEI-18a, AEI-18b and amido imidazoline AMEI-18, were there is no decreased to values closer than 1 mpy alter 7 minute, 14 minutes AMEI-18 and 21 minutes for AEI-18b imidazoline. It is important to emphasize that the response time tor the equipment is approximately 7 minutes, The most hydrophilic the hydroxyethyl imidazolines 81, HEI-12 and HEI-18) took longer times to decrease the corrosion rate values than 1 mpy, The corrosion rates obtained by the HA technique followed a similar tendency to those obtained by the LPR one (Figs. 3 and 4) but with much more instabilities, One have to note that the corrosion rates obtained by the HA technique are than one half values obtained by the LPR technique. This is due to the that tor the HA technique, the anodic and cathodic Tafel are obtained by a linear whereas for the LPR measurements, the equipment uses a analysis in each one of the cathodic and anodic Tafel slopes, Le 120 mV/decade respective/y.

The above results show an apparent interaction between the inhibitor surface and the carbon chain group, improving the hydrophobic properties and the film inhibitor adherent, as it has been shown Víllamizar et al. 11, 12. We must say that the addition of the imidazolines to the 3% NaCI + diesel solutíon tended to produce dispersion, producing some oíly drops, and these drops could be adsorbed on the meta! surface. in 3% NaCI so!ution without Figs. 5 and 6 show the pitting factor (PF) obtained tor 1018 carbon and with diese! and the addition of 20 ppm of the different imidazolines alter 2 hours of at 50 ± 2 oC during 20 These show that, tar the solutions without inhibitor, the PF value líes in the intervals 0.01 0.001 and decreasing with time until it reaches constant values lower than 0.001 during the first 30 minutes. According to these PF values, the type of corrosion that 1018 carbon steel undergoes in these condítions is unifarm or general. On the other hand, as soon as the inhibitors are added to either solution, the PF values abruptly increase reaching values several orders of magnitude, between 3 and 4, higher than those obtained wíthout inhibítors. For the solutions with the HEI-1 which had a PF value of 0.1, For the the PF values lied between 0.1 and 5, 3 NaCI solution, only the HEI-181 and AEI-18a inhibitors had PF values higher than 0,1. A particular case is the HEI-181 hydroxyethyl imidazoline, since it has the lowest PF values in presence of diese!. but when diesel is added, it has one of the highest PF values together with the AEI-18a amido-ethyl imidazoline. the specimens were observed in an electronic microscope, and none of them Alter the corrosíon showed any evidence of any type of localized corrosíon, despite the PF values that predicted that they should suffer from localized attack. One possible explication is that the HA measurements are very instable under these conditions and that currents fluctuate around zero. This produce hígh, wrong, PF values, predícting localized type of corrosion, even when the metal surface ís undergoing a uniform type of corrosion.

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CONCLUSIONS

Our results confirm that the LPR and HA techniques are very useful for monitoring corrosion rates.

Both techniques respond very quickly to any change in the environmental tested conditions, allowing us to use several techniques in short time periods, making them powerful on-line monítoring techniques.

When using the electrochemical noise be taken when usíng the factor (PF) since it of corrosíon undergoing by the The PF values but a surface analysis did not show any evidence of such damage,

ACKNOWLEDGEMENTS We thank the valuable support of Anselmo Gonzalez for hís support for the laboratory work, as well as y Javier Lara Arnulfo Manriquez Lara and Ivonne M Salazar de la Cruz of PEMEX Produccíon, Activo Poza Rica Altamira.

REFERENCES 1.

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Mészaros L., G., and Lengyel B. J. Electrochem. Soc., Vol. 141 No. 8 (1 p: 2068 - 2071 Pirnat A., Mészaros L., and Lengyel B. Corrosion Science Vol. 37 No. 6 (1995) p: 963 - 973 Durnie W., De Marco R., Jefferson a., and Kinsella B. Corrosion Science Vol. 44 (2002) p: 1223 - 1221 Gareth J., and Rothwell N., CORROSION 2002, Paper No., 02337, (Houston NACE International, G. E. C., L. M., and Lawson K., CORROSION 2000, No., 00412, (Houston NACE International, Teevens p J., CORROSION 98, Paper No" 388, (Houston NACE International, 1998).

Ryder J. C., Pickin N, J., and Wooding G. P., CORROSION 2001, Paper No., 01293, (Houston NACE International, 2001).

Barr E. E., Greefield A H., and Pierrard l., CORROSION 2001, Paper No., 01 (Houston NACE International, 2001, Bagley G" CoUis R. A., and Laycock p, J., CORROSION Paper No., 191, (Houston NACE International, 1999) Luz Maria Rodríguez-Valdez, W. M. J.G. González-Rodríguez, Alberto L. Daniel Glossman-Mitnik., Science Vol. 48 (2006) p: 4053 - 4064 W. Villamizar, M. J. G. L. Materials and Vol. No. 9 , (2006) p: 696 704.

W. Villamizar, M. J. G. and L. Martínez., J Solid State Electrochem Vol. 11 p: 619 - 629 Jovancícevíc V., Ramachandran S. and Prince P., Corrosíon 55 (1999): p, 449

TABLE 1

IMIDAZOLlNE TYPES

Product

Alkyl chain (derivative)

Chemical Name HYOROXYETHYL IMIOAZOLlNES 1H-imidazole-1-ethanol, 4,5-dihydro ,-2­ C 1S- 17 unsaturated alkyl derivatives 1H-imidazole-1 ethanol. 4,5-dihydro ,-2-nor coco alkyl derivatives 1H-imidazole-1ethanol, 2-Heptadecyl-4,5­ Dihydro AMINOETHYL IMIDAZOLlNES Fatty acids , tall oil compounds with diethylene triamine tall oil fatty acid reactions products Fatty acids, tall oil reactions products compounds with diethylene tria mine AMIDOETHYL IMIDAZOLlNES 9-0ctadecenamide N­ [2-[2-[(8­ Heptadecenyl) 4,5-Dihyd ro-1 H-Imidazole­ 1-Y]Ethyl-]

HEI-181 HEI-12 HEI-18

AEI-18a AEI-18b

AMEI-18

CH (Tall Oil) C 12 (Cocunut) C 7 ' (Stearic) C 17 (Tall Oil)

CH (Tall Oil)

CH (Tall Oil)

210 180

Addtion of inhibitor

/

150 ~

NaCI3%

- - HEI-181

- 6 - - HEI-12

<;>­ HEI-18

a.

E 120

~ ~

e o ¡¡;

e o

u

-<-

90 60 30

o

o

200

400

600

800

1000

1200

t (min)

FIGURE 1 - Change in the corrosion rate (mpy) with time for 1018 carbon steel exposed to 3 % NaCI solution with the different types of imidazolines.

6

/

140

Addtion 01 inhibitor

120

100

- - :-

2

NaCI3°o~ D ies,,1

HEI -1 8J

E 80

----<>---- HEJ-J2

'"

----<>- AEJ- J8u ----+- AEI-18

~HEJ-18

~ 60 e

O

l. ~ "'E'- '"

'i/;

2 40

6

u

20

f\

.¡¡';ÍÍ\I'Íl!Z!!

O

o

200

400

600

800

1000

1200

t(min)

FIGURE 2 - Change in the corrosion rate (mpy) with time obtained by the LPR technique for 1018 carbon steel exposed to 3 % NaCI + diesel solution with the different types of imidazolines

180 150

Additlon 01 inhibitor

~~ AEI-18a

1;: 120

- --c'­

g Q)

~

- . - NaCI3% -- ~ HEI-181 -o---- HEI-12 - 0 - ' HEI-18

~,

90

AEI-18b AMEI-18

c::

o

éii

g

60

o

o

30

o o

200

400

600

800

1000

1200

t (min )

FIGURE 3 - Change in the corrosion rate (mpy) with time obtained by the HA technique for 1018 carbon steel exposed to 3 % NaCI solution with the different types of imidazolines

7

160 - ' - HEI-12 - l > - HEI-18 --<>- AEI-18a - :- AEI-18b -é-- AMEI-18 NaCI3%+ i

140 120

>: o.

100

a.>

80

-S § e

O

üi

e

o

o

I~~,' ,'~I . !J\j'I

60 40 20

o o

200

400

600

800

1000

1200

t(min)

FIGURE 4 - Change in the corrosion rate (mpy) with time obtained by the HA technique for 1018 carbon steel exposed to 3 % NaCI + diesel solution with the different types of imidazolines

~

o

0.1

t3 ro

LL

Ol

e

:e

0.01

o::

1E-3

o

200

400

600

800

1000

1200

t (min )

FIGURE 5 - Change in the PF data with time for 1018 carbon steel exposed to 3 % NaCI solution with the different types of imidazolines

8

10~-------------------------------,

o

tí

0.1

ro

l.!..

,

"

--c.- HEI-'2 ""-,- HEI-18 ", '" AEI-18a AEI-18b "v-'" AMEI-l B

001

1E-3

a

200

400

600

sao

1000

1200

t (min)

FIGURE 6 in the PF data with time for 1018 carbon steel exposed to 3 % NaCI + diesel solution wíth the dífferent of

9