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Corrosion Inhibitors for the Protection of Oil Production Equipment
a report by
Ruslan Vagapov
Lead Researcher, Laboratory of Inhibitor Protection, Scientific Research Institute of Natural Gases and Gas Technologies
In the oil production industry, economic losses and ecological refinement, transportation and processing.
1
Prominent among them
Engineering & Construction
damage caused by corrosion stem from the very large amounts of are nitrogen-containing compounds with a diphilic structure, i.e.
metal equipment and structures that come into contact with highly colloidal cationic surfactants. Because of their inherent hydrophilic
aggressive media. The most important tasks in the development of an protonated amino and imino groups or a quaternary (charged)
oilfield are reliable operation and long life of equipment and pipeline nitrogen atom, they can firmly adsorb on the negatively charged
systems. The presence of corrosive components in transported fluids steel surface, while a hydrophobic substituent – e.g. alkyl chains
negatively affects metal in oil production, refinery, transportation and composed of 12 or more carbon atoms – orientates the inhibitor
processing operations. The degree of corrosive damage to oil during adsorption to form a polymolecular barrier layer that reliably
production equipment is determined by the degree of heterogeneity screens the metal from the corrosive medium.
of the extracted fluid, the content of corrosive gases (carbon dioxide
[CO
2
] and/or hydrogen sulphide [H
2
S]), the degree of mineralisation The corrosive media used in the oil industry are different. In all of
in the aqueous phase and the variability of the corrosion activity of the cases discussed below, steel equipment and pipelines can be
technological media in the course of exploration of a given deposit. effectively protected by corrosion inhibitors.
Under such conditions, a technically justified and efficient method of Corrosion Inhibition in Stratal Water
protection is the use of inhibitors that adsorb as protective films on Corrosion of downhole equipment and pipelines can be intensified
a metal to prevent its corrosion. At the same time, inhibitor when the produced hydrocarbons are characterised by increased
protection seems to be one of the most appropriate and cost- watering. The corrosiveness of the produced oil depends on the
efficient ways to address this problem. The inhibitors applied during aggressiveness of the stratal water, which can be mineralised
the operation of oil equipment and pipelines should satisfy a number and can contain acidic gases (CO
2
and/or H
2
S). Laboratory tests
of engineering requirements: they should be soluble or dispersible in in the two-phase H
2
S-containing electrolyte (non-aqueous
water or brine, they should pass to an organic phase in insignificant capillary electrophoresis [NACE] solution) plus hydrocarbon (white
amounts only, they should not create emulsions in water and spirit) system show that the corrosion rate reaches values of
condensates, they should be easily separable, they should ensure a 0.1–0.15mm/year in static and mixing conditions and at different pH
highly protective effect, they should prevent the formation of values (see Figure 1). This is the case for media that contain CO
2
pitting, they should prevent the hydrogenation of steel (in the case together with H
2
S. As can be seen from Table 1, the corrosion rate
of the presence of H
2
S), they should be non-toxic and they should of stratal water with different degrees of mineralisation and with or
have strong after-effects. without H
2
S can be even higher – 0.3–1.57mm/year – especially at
elevated temperatures.
Along with strong protective properties, another important
requirement for inhibitors is that their foaming and emulsifying Most inhibitors that were created to protect metals from corrosion
abilities should be low, since foaming and emulsification may impair under hydrocarbon production conditions are effective only in the
the operating process of oil treatment: a corrosion inhibitor might presence of H
2
S. However, a lot of stratal water contains H
2
S only in
cause a working solution to foam, which would disturb the operation small quantities or does not contain H
2
S at all. Stratal water itself is a
of the system. Systems for complex oil treatment for transportation highly corrosive medium (see Figure 2), and even effective inhibitors
separate hydrocarbons–water liquid mixtures to isolate an oil fraction. cannot ensure a high protective level at low concentrations of H
2
S.
2,3
The corrosion inhibitors used to protect equipment and pipelines Tests of more than 20 inhibitors in stratal water (see Table 1)
should not decelerate the separation of the oil–water mixture. demonstrated that no inhibitor can be effective in all types of water.
Some inhibitors can protect steel only at low mineralisations and low
Modern sanitary, hygienic and ecological requirements make it concentrations of H
2
S, while others can protect steel only in media
imperative to replace toxic corrosion inhibitors with equally effective with high mineralisation levels in the presence or absence of H
2
S.
inhibitors that are safe in terms of their production and application.
In addition, it is vital to produce inhibitors from less expensive raw It is known that in acidic media H
2
S stimulates steel corrosion and
materials. In this context, the development of ecologically safe and accelerates hydrogenation, causing the steel to become brittle and
highly effective organic compounds with simple synthesis from widely crack. The hydrogen concentration after exposure to H
2
S-containing
available raw materials remains a matter that must be addressed. solutions increases over time, reaching 8cm
3
/100g steel. In the
presence of H
2
S, corrosion inhibitors should prevent absorption of
Various corrosion inhibitors have long been used successfully for hydrogen by steel. A lot of inhibitors effectively decrease the
the protection of steel equipment and pipelines in oil production, corrosion rate, but they do not affect the hydrogenation of steel.
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© TOUCH BRIEFINGS 2009
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