WO1998033953A1 - Corrosion inhibition through the use of a quaternary pyridine salt-hydrocarbon combination - Google Patents

Abstract

A method for inhibiting corrosion of a surface of carbon steel exposed to an aqueous medium in which the method includes forming a layer having a corrosion-inhibiting amount of a quaternary pyridine salt and a water-immiscible organic component on the surface by incorporating into the medium a composition containing the salt, the organic component and a surfactant. The surfactant is present in the composition in an amount sufficient to solubilize a sufficient amount of the organic component in the aqueous medium so as to permit formation of the protective layer. The organic component is most often a hydrocarbon and can be a single hydrocarbon, but is more likely to be a mixture of hydrocarbons. The surfactant can be cationic, non-ionic, amphoteric or anionic.

Description

Corrosion inhibition Through The Use Of A Quaternary Pyridine Salt - Hydrocarbon Combination

Field of the Invention

The present invention relates to the inhibition of corrosion of iron and other metal surfaces exposed to an aqueous medium, as in the oil and gas industry. In particular, this invention features the introduction of an inhibitor, including a quaternary pyridine salt in combination with a hydrocarbon, into the aqueous medium in order to bring the inhibitor into contact with the surface to be protected.

Background of the invention In the oil and gas industry, it is common for fresh water or brine to be produced along with the desired hydrocarbon material. Corrosion of iron surfaces exposed to such an aqueous component is a problem in the industry. The present invention is addressed to the problem of corrosion of the internal surfaces of oil and gas pipelines and vessels associated with these systems. Many approaches to the problem of internal corrosion are already known, including the use of inert lining materials, resistant alloys and the introduction of chemical inhibitors to produced fluids. All of these approaches are employed to varying degrees in the industry, but the use of chemical corrosion inhibitors appears to be the most widespread. Many pipeline systems were built before such options as linings and alloys were considered feasible. The costs and the sometimes poor reliability of these other materials do not always make retrofitting these systems attractive. The costs of chemical inhibitors are generally met from operational budgets, not capital budgets as this reduces start-up expenditures and the costs of chemical inhibition are suspended whenever a well is shut-in, for example.

There is a wide range of conditions to which a pipeline interior might be exposed. Pipeline environments typically fall in the ranges given below:

pH 3 to 7, usually 3.5 to 5.5

Temperature 0 to 100°C, typically 20°C to 70"C

Water content 0 to 100 weight percent

Chloride content (of water) 0 to 20 weight percent H₂S partial pressure 0 to 100% of total pressure (typically 0 to 30%)

C0₂, partial pressure 0 to 100% of total pressure (typically 0 to 20%)

The interplay of these parameters largely determines the corrosivity of a given system but understanding the influence of the various factors and the effect of their inter-relationships is mostly empirical. Generally, however, systems containing C0₂ with less than about 1000 ppm H₂S are often called "sweet" , whereas those with greater than 1000 ppm H₂S are called "sour".

Systems in which the partial pressure of either C0₂ or H₂S are very high are thought to be the most corrosive. For example, other parameters being equal, the corrosion rate of carbon steel is known to increase with increasing C0₂ pressure by about a two-thirds power [C. De Waard and D.E. Milliams, Corrosion, 31, No. 5, pp 177-181 (1975)]. Similarly, the higher the mole fraction of H₂S in the produced gas, the higher the internal corrosion rate will usually be.

In the case of oil, brine is sometimes co-produced. The brine is sometimes in the form of an emulsion, or sometimes the water forms an immiscible phase separate from the oil, depending on factors such as temperature, production pressure, pressure gradients, wellhead and pipeline velocities and the chemistries of the aqueous and oil components themselves. It is generally true that if oil and brine are co-produced as an emulsion, then the corrosivity of the mixture will increase with increasing water volume fraction. For a given environment, turbulence, pressure changes, high velocities and low temperatures all tend to favor emulsion formation and stabilization, while low velocities and high temperatures tend to favor phase separation of the oil and aqueous components.

Oil is sometimes produced in the form of a water-in-oil or oil-in-water emulsion, the resolution of which into separate immiscible phases requires heating and/or the injection of a chemical demulsifier. Hard to break, or "tight'' emulsions, with high oil volume fractions and high pipeline velocities often require little or nothing in the way of chemical corrosion inhibition.

On the other hand, "loose" emulsions, or two-phase systems, especially those being transported at low velocities, often require chemical treatment to reduce internal corrosion and hence lower the risk of structural failure of the pipeline. While it is clear that the flow characteristics of a system affect internal pipeline corrosion, the determination of such characteristics is rarely straightforward, complicating the prediction of effectiveness for any given inhibition program.

For example, it is possible, where full or partial phase separation of a produced emulsion occurs, for an aqueous layer to form at the bottom of a pipeline. This can lead to a corrosion failure at the so-called six o'clock position of the pipeline. Corrosion problems can arise when there is a "hold up" of brine at the bottom of an incline where the flow velocity in the pipeline is insufficient to carry the water up and over a pipeline gradient. One can thus see that it is possible for localized internal corrosion to create problems in pipelines carrying oil, even if there is a relatively small amount of water in the system. Natural gas wells also co-produce water, even if it is only water of condensation due to the drop in temperature and pressure of the system as the gas is produced from the formation. Gas wells can additionally produce brine independently of the water of condensation. Further, light hydrocarbons can condense throughout the well and gathering pipes, resulting in a three phase flow system which is difficult to model, understand and predict. It can still be said that the corrosivity of the aqueous phase will increase as the flow rate and pH fall, and as the chloride level and as the amount of dissolved acid gases increases.

The corrosion inhibition properties of certain quaternary pyridine salts, "quats" have been known for a long time. For example, in United States Patent No. 4,672,118, (Fisk et al., issued June 9, 1987), the specification of which is incorporated herein by reference, describes N-(hydrophobe aromatic)pyridinium compounds useful as corrosion inhibitors. Novel quaternary pyridinium salts with improved corrosion inhibition properties are disclosed. United States Patent No. 5,132,093 (Hettiarachchi etal., issued July 21 , 1992), the specification of which is incorporated herein by reference, describes synergistic corrosion inhibitors, based on compounds that are N- aryl or N-alkyl substituted pyridinium halides. United Sates Patent No. 5,368,774 (Borgard etal., issued November 29, 1994), the specification of which is incorporated herein by reference, discloses refinery inhibitors which use quaternary pyridinium salts in combination with organosulfur compounds.

United States Patent No. 5,336,441 (Shah etal., issued August 19, 1994), the specification of which is incorporated herein by reference, describes apparent improvements obtainable by a combination of certain cationic surfactants with quats. Particularly, in Example 1 , Shah etal. report studies involving inhibition of the steady-state corrosion rate of a carbon steel electrode immersed in 900 ml of a stirred fluid made up of one part isopar-M and two parts water (35 ppm CI^" solution at a pH of 3). It was found that inclusion of the cationic surfactant cetyl trimethylammonium bromide (CTAB) at an overall concentration of 31.3 ppm in such a solution containing 50 ppm of a benzyl chloride quat effected an 81% reduction in the observed corrosion rate. Compounds such as CTAB, in addition to possessing surfactant properties, are also quaternary ammonium compounds known to have corrosion inhibition properties [see for example, United States Patent No. 5,272,346 (Kaplan etal., issued December 21 , 1993) and United States Patent No. 5,200,096 (Williams etal., issued April 26, 1993) the specifications of which are incorporated herein by reference]. Additionally CTAB has apparently been described as able to form a bilayer on metal surfaces, and it was suggested by Shah et al. it is this ability of CTAB which is important to the observed reduction in corrosion. This interpretation by Shah et al. is consistent with their reported observation that separation of the aqueous and organic phases of the system in their Example 1 was clean, with no discoloration of either phase. As a hydrophilic surfactant, CTAB would be expected to solubilize hydrophobic elements in the aqueous layer. In other words, the cloudy appearance that would be expected to be observed if CTAB were acting as a surfactant, by forming an organic emulsion in the aqueous phase (oil-in-water), was not reported by Shah et al.

Summary of the Invention According to the present invention, the corrosion rate of an iron surface exposed to an aqueous environment can be reduced by the incorporation of a quaternary pyridinium salt and an organic component into the aqueous environment. According to one aspect of the invention, such incorporation of the organic component involves the formation of an emulsion by a suitable surfactant in the aqueous milieu of the system being treated. According to another aspect, if the system being treated is sufficiently turbulent, emulsification of the organic component in the aqueous phase can occur without the need for a surfactant, that is through a shear stabilized emulsion.

A first embodiment of the invention thus includes a method for inhibiting corrosion of a surface of carbon steel exposed to an aqueous medium in which the method includes forming a layer comprising a corrosion-inhibiting amount of a quaternary pyridine salt and a water- immiscible organic component on the surface by incorporating into the medium a composition containing the salt, the organic component and a surfactant. According to the method, the surfactant is present in the composition in an amount sufficient to solubilize a sufficient amount of the organic component in the aqueous medium so as to permit formation of the protective layer. The organic component is most often a hydrocarbon and can be a single hydrocarbon, but is more likely to be a mixture of hydrocarbons. The hydrocarbon can be aliphatic, aromatic or a mixture. The hydrocarbon component can thus have a single boiling point or it can boil over a range. Usually, the boiling range is within 70°C and 400 °C, meaning that 10% of the component is boiled off when the temperature is raised to about 70°C and about 90% of the component is boiled off when the temperature is raised to about 400°C. More typically, boiling ranges are between 100°C and 400°C, 100°C and 300°C, 150°C and 400°C, 150°C and 300°C and 150°C and 250°C. A particularly preferred organic component has been found to be what is known in the industry as high boiling reformate, which is a mixture of relatively high molecular weight aromatic hydrocarbons having a boiling range of 153°C to 235°C. Others described in specific examples below, are PCP solvent (50% recovered at 290°C and 90% recovered at 345°C) and Cyclosol 63 (10% recovered at 160°C and 90% recovered at 170°C).

The surfactant of the first embodiment of the invention is a hydrophilic surfactant capable of emulsifying the organic component of the mixture in the aqueous medium of the system being treated. The surfactant can be cationic, non-ionic or anionic and particular surfactants are described in the description of preferred embodiments.

The quats of the present invention are conventional, but this is not to say that improved quats not currently known could not just as well be incorporated into the present invention. The quat and hydrocarbon component can be present in the composition in a relative salt.hydrocarbon component molar proportion of from about 1 :1 to about 1 :14; 1 :2 to about 1 :14; 1 :2 to about 1 :12; 1 :4 to about 1 :9; 1 :5 to about 1 :7; or simply 1 :7. These molar ratios are based on results obtained using heavy reformate, examples of which are given below. It must be borne in mind that the precise optimum ratio of particular components to be used in particular conditions varies, but instructions for the choice or components and their relative proportions are given below.

The hydrocarbon component can be between about 10% and 80% (by volume) of the composition, or it can between 25% and 65%, or more preferably between about 35% and 50% of the composition. Typically, the amount of surfactant is between about 0.1 % and 10 % of the weight of the composition and more typically is between about 1% and 10% of the weight of the composition. It can also be between about 1% and 5%, or between about 1% and 3% of the weight of the composition.

Where the organic component is a hydrocarbon solvent, it is thought that the surfactant can be typically present in the composition at a level of between about 0.1 and 10% by weight of the amount of the hydrocarbon solvent, but that a level of between about 1 and 10% by weight of the amount of the hydrocarbon solvent is more likely to be preferred.

The pH of the medium being treated would generally be between about 3 and 7 although a pH range of between about 3.5 and 5.5 is more common. The chloride content of the aqueous medium can be anywhere between about 0% and 20% by weight although content ranges between about 5% and about 15% or between 1% and 8% are more common. The temperature of the aqueous medium can be between about 0°C and about 80°C, but temperatures between about 20°C and 70°C, or between about 40°C and 70°C are generally more common. The system to be treated can be a pipeline, production equipment tubing, vessel, orvalving, or the like— -i.e., is of similar metallic materials exposed to similar conditions. Fluid of the system may or may not have a hydrocarbon component in addition to the aqueous component. The system being treated may be a natural gas pipeline.

The system can include H₂S and the partial pressure of H₂S can be greater than about 0.1 % of the total pressure. The system can include C0₂ and the partial pressure of the H₂S can be greater than about 0.1 % of the total pressure up to about twice the partial pressure of the C0₂.

The composition can also include a co-surfactant for retaining the composition as a single phase in storage prior to incorporation into the medium. The co-surfactant can include an alcohol having between about 3 and about 8 carbons and can be butanol. Also, to stabilize the composition prior to use, as for shipment and/or storage, the composition can also include one or more tying agents such as nonylphenols, particularly ethoxylated nonylphenols, and/or dodecylbenzenesulphonic acid.

It may also be desirable to lessen the corrosivity of the concentrated inhibitor mixture itself, to include a base for adjustment of the pH of the composition for storage of the composition prior to incorporation into the medium. The pH could typically be adjusted to about 9, say, and the base could be, for example, an organoamine such as monoethanolamine or diethylamine.

If the mixture is to be used in a cold climate, it might be desirable, and it is possible to obtain compositions, which are pourable at low temperatures, say down to -35°C, or even lower. It would thus be desirable for a liquid composition to be pourable over a temperature range of from about -35°C to about 50°C, but more typically, a desirable range might be from about -20°C to about +20°C.

A particular embodiment of the invention is thus a method for inhibiting corrosion of an iron surface exposed to an aqueous medium which includes contacting the exposed surface with a corrosion-inhibiting amount of a quaternary pyridine salt and a water-immiscible organic component by incorporating into the medium a liquid composition comprising the salt, the organic component and a surfactant, the surfactant being present in the composition in a sufficient amount to stabilize an emulsion containing the organic component in the aqueous medium. Another aspect of the invention is a method for inhibiting corrosion of a surface of carbon steel exposed to a turbulent aqueous medium, the method including the step of incorporating into the medium a corrosion-inhibiting amount of a quaternary pyridine salt and a water-immiscible organic component so as to form a corrosion-inhibiting layer comprising the salt and organic component on the surface. As with the previously described embodiment, it might be desirable to include as part of a composition an agent for retaining the composition as a single phase for storage and shipping prior to incorporation into the medium.

Another embodiment of the invention is an additive composition suitable for inhibiting corrosion of a surface of carbon steel exposed to an aqueous environment. The composition includes a quaternary pyridine salt, a water-immiscible organic component and a surfactant. The composition preferably also includes an agent for maintaining the composition in a single phase. The agent is typically an alcohol having from about 3 to 8 carbon atoms, say butanol. The organic component can be a hydrocarbon liquid, as described above.

In another aspect, the invention is a method of manufacturing an additive composition for inhibiting corrosion of a surface of carbon steel exposed to an aqueous environment, the method comprising, combining a quaternary pyridine salt, a water-immiscible organic component and a surfactant for solubilizing the organic component in the aqueous environment upon addition thereto. The method can include combining an agent as part of the composition for maintaining the composition in a single phase. Such agent can be an alcohol having from about 3 to 8 carbon atoms, say butanol. The method can include combining a hydrocarbon liquid as the organic component. The method can include combining into the composition other components described above.

Brief Description of the Drawings

Preferred embodiments of the invention are described below, reference being made to the accompanying drawings wherein: Figure 1 shows inhibition of corrosion of test coupons (mgs lost) as a function of concentration (ppm) of IC10 (ψ) and Composition A (o);

Figure 2 shows inhibition of corrosion of test coupons (mgs lost) for a number of inhibitor formulations: 1) Composition A, without CTAB and without heavy reformate; 2) Composition B; 3) Composition B plus 5.6% heavy reformate; 4) Composition B plus 12.4% heavy reformate; 5) Composition B plus 21.4% heavy reformate; 6) Composition B plus 33.3% heavy reformate; 7) Composition B plus 50.0% heavy reformate; 8) Composition A. The quat concentration was 500 ppm for all experiments;

Figure 3 shows inhibition of corrosion of test coupons (percent protection) observed for inhibitors containing various surfactants: 1) Composition A; 2) Composition A with an equivalent amount of CPC substituted for CTAB; 3) Composition A with an equivalent amount of LA 230 (an ethoxylated (23 mole) alcohol) substituted for CTAB; and 4) Composition A with an equivalent amount of NP-9 (an ethoxylated (9 mole) alcohol) substituted for CTAB;

Figure 4 shows inhibition of corrosion of test coupons (percent protection) observed for inhibitors containing various hydrocarbons: 1) Composition A with a similar concentration of xylene substituted for heavy reformate; 2) Composition A; 3) Composition A with a similar concentration of Isopar M (an aliphatic solvent boiling from about 215° to 280°C) substituted for heavy reformate; 4) Composition A with a similar concentration of PCP solvent (a blend of aromatic and aliphatic hydrocarbons) substituted for heavy reformate; and 5) Composition A with a similar concentration of Cyclosol 63 (heavy petroleum naphtha, hydrotreated) substituted for heavy reformate. The overall inhibitor concentration for this series of experiments was slightly lower than that used for the experiments summarized in Figure 3;

Figure 5 shows inhibition of corrosion of test coupons (percent protection) as a function of the total volume of the hydrocarbon kerosene (μl). Compositions were obtained by the addition of an inhibitor having the same composition as that of Composition A, except for the presence of kerosene in place of heavy reformate; and

Figure 6 shows inhibition of corrosion of test coupons (percent protection) observed under static (+) and dynamic (□) conditions for various inhibitor formulations: 1) Composition A; 2) Composition A with NP6 substituted for CTAB; 3) Composition A with equal amounts of NP6 and CTAB substituted for the usual total amount of CTAB; and 4) Composition A with equal amounts of NP6 and NP40 substituted for the usual total amount of CTAB. The quat concentration was 500 ppm for all experiments.

Description of Preferred Embodiments

It has been found that the corrosion rate of iron surfaces exposed to certain aqueous environments can be reduced by the incorporation of a quaternary pyridinium salt and a hydrocarbon into the aqueous environment. Normally such incorporation involves the formation of an emulsion in the aqueous component of the system being treated. It has been found that the hydrocarbon element can be incorporated into the aqueous component through emulsion formation by a suitable hydrophilic surfactant, i.e, a surfactant stabilized emulsion. If the system to be treated is sufficiently turbulent, emulsification of the hydrocarbon in the aqueous phase might occur without the need for a surfactant, i.e., a shear stabilized emulsion. In either case however, it is thought that the emulsified hydrocarbon is brought into contact with the surface to be protected and is incorporated into the protective quat coating to enhance the protection afforded by the quat layer. Mixtures of quats, obtainable by the reaction of a pyridine and a quaternization agent such as an alkyl halide, have been used for many years as corrosion inhibitors for mild steel pipelines. A typical commercial inhibitor contains 20 to 40 percent quat, and is used at an overall concentration of between about 10 and 1000 ppm.

The raw pyridine bases used for quaternization and blending into corrosion inhibitor formulations are generally complex mixtures and often contain hundreds of compounds. There are at least four commercial sources: i) by-products from the manufacture of nicotinic acid. (A mixture of formaldehyde, acetaldehyde and ammonia is reacted under pressure at high temperature. Beta-picoline is distilled out of the mixture, then oxidized to nicotinic acid. The remainder contains a mixture of picolines, lutidines, collidine, etc., as well as alkylanilines and non- nitrogenous aldol products.); ii) by-products of the manufacture of vinylpyridine for making polymers. The process is very similar to (i), but propionaldehyde is used instead of, or together with, acetaldehyde; iii) coal tar distillate; and iv) alkylpyridines produced for the purpose of making corrosion inhibitors. The patent literature provides many examples of quats, as set out for example in the specification of Shah et al., which describes mixtures having higher quat concentrations than those typically used. Although tests and experiments involving the present invention used particular quats, as described below, it is believed that the protection offered by other quats that provide corrosion inhibition, conventional or otherwise, can also be enhanced through the present invention. It should be mentioned that the mechanism by which quats inhibit the corrosion of iron surfaces is not completely understood, but it is known that an adequate concentration of inhibitor must be maintained in the aqueous phase (the "residual" level) in order to maintain corrosion protection.

A pyridine salt used as part of the present invention may be a quaternary salt obtained from a pyridine-containing composition and a compound of the formula R-X wherein R is selected from the group consisting of alkyl and aryl groups of up to about 16 carbon atoms and X is a halide. More preferably, R has up to about to about 10 or about 7 carbon atoms. R can be a benzyl group.

A list of potentially useful quats which could be enhanced through application of the present invention are listed in Table One. These could be used alone or in combination with each other.

^*= UVCB Although the present invention may be used as a "batch" treatment, for example to coat the internal surface of a pipe, its preferred application is as a "continuous" inhibitor. In other words the inhibitor is preferably added (as by injection at a suitable location) directly to fluid flowing through a pipeline needing protection against corrosion, injection would normally be continuous, or at least sufficiently often to maintain the minimum effective concentration in the aqueous phase, and hence the integrity of the protective layer.

As far as the hydrocarbon component of the present invention is concerned, the enhanced corrosion protection has been observed with a number of different hydrocarbons. As illustrated in the examples below, high boiling aromatic materials such as heavy reformate have been found to be particularly suitable. Other hydrocarbons that have been found to reduce corrosion under test conditions, as exemplified below, are kerosene, diesel, xylene and blends of aliphatic hydrocarbons such as Isopar M available from Exxon Chemicals. Other high-boiling, substituted benzenes of various boiling ranges that have been found to enhance corrosion protection under laboratory conditions include Cyclosol 53, 63 and PCP solvent, available from Shell Chemicals. Other examples are Aromatic 100 and 150 available from Exxon.

Hydrocarbons tested with the commercially available quats composition known as IC10 were found to enhance the corrosion inhibition afforded by these quats. This was particularly true of those hydrocarbons having boiling points above 100°C, such as toluene and xylene, or boiling ranges which start above 100°C, such as kerosene. For example, the boiling point range of Isopar M is 215 to 280°C, for Cyclosol 63 it is 184 to 206°C and for PCP Solvent it is 210 to 365°C. For application of the invention in natural gas pipelines, in which relatively volatile hydrocarbons might be more prone to being stripped away by passing gases, hydrocarbons having relatively high boiling points and boiling ranges are the most suitable. While it is believed that just about any hydrocarbon which meets these boiling point and boiling range criteria would offer some degree of enhanced protection, the laboratory testing described in the pertinent examples given below has identified those currently believed to be most preferable.

A list of potentially useful hydrocarbons are given in Table Two. This list is illustrative and not complete. A useful hydrocarbon can include any petroleum naphtha, distillate, refined solvent, gas oil or extract; light or heavy; catalytic reformed, cracked, straight run or dewaxed; aromatic, naphthenic or aliphatic that successfully performs in the test outlined below. These can be used alone or in combination with each other.

The question of the amount of a particular hydrocarbon to use with respect to a unit amount of quat is a complex one, best illustrated by example. It has been found that the performance enhancement increases steadily with the hydrocarbon volume fraction, however, for an inhibitor that includes a surfactant (as opposed to an inhibitor which relies on system turbulence for emulsification) the potential exists for the formation of a Winsor "Type III" microemuision. Type III microemulsions are well known in the industry for reducing the surface tension between oil and water phases, usually by several orders of magnitude, and this property has been exploited successfully during microemuision flooding to enhance the removal of crude oil from porous rock formations. However, we have found that the formation of a Type III system in a pipeline carrying a multi-phase fluid attenuates, rather than enhances, the corrosion inhibiting properties of quat- based formulations. The formation of a Type III microemuision depends upon the overall composition of the corrosion fluids, including the inhibitor, and the thermodynamic conditions, such as temperature, pressure and pH of the system. As the relative proportions of hydrocarbon, surfactant, and quat are controlled during the formulation of a corrosion inhibitor of the present invention, formation of a Type 111 system can usually be avoided. The best way known to the inventors to determine the relevant parameters is by developing an active formulation using the instructions given below, which guide the selection of materials, including the hydrocarbon phase, and the choice of relative proportions. This "stock" inhibitor is then optimized by testing formulations with both lesser and greater proportions of the chosen hydrocarbon phase under the corrosive conditions of interest, ensuring the realization of the enhanced performance offered by the invention and confirming that the in situ formation of a Winsor Type III system has been avoided. By following such a procedure, the inhibitor described as "Composition A" has been found preferable for the following set of conditions:

pH of brine 3.5 to 5.5

Temperature 20°C to 70°C

Water content Low water content gas lines

Chloride content (of brine) 1 to 15 weight percent

H₂S partial pressure >0.1 % of total pressure, >2x C0₂ pressure C0₂ partial pressure <50% of total H₂S pressure

Using the example of the IC10 quat (75% active material, 25% methanol, 1.044g cm^"3 @ 60°F) and heavy reformate (100% active material, 0.878g cm^"3 @ 20°C), testing suggests that no significant enhancement in corrosion protection occurs until the hydrocarbon:quat ratio (volume/volume) exceeds about 1 :1. Thereafter it was found to improve steadily until the ratio was above 5:1 , with little or no further improvement being observed beyond 6:1. The desired range of the ratio of IC10 to heavy reformate (vol/vol) is therefore between about 1 :1 and 1 :10, more preferably between 1 :3 and 1 :8, and most preferably from 1 :5 to 1 :7. For different combinations of quats and hydrocarbons, particularly those of different activities and specific gravities, these ratios would likely vary. In the majority of applications in which the present invention is likely to be applied, the pipeline fluids will not provide sufficient turbulence for the hydrocarbon component to be emulsified into the aqueous part of the system. As previously mentioned, in such cases, a surfactant should be used to ensure the formation of an "oil-in-water" emulsion.

A surfactant which is sufficiently hydrophilic to stabilize an emulsion of the chosen hydrocarbon phase in brine is chosen for this purpose. Surfactants found to be suitable include cationics, such as quatemized ammonium and pyridinium salts with a long carbon chain (>C12) alkyl substitutions; non-ionics such as those of nonylphenol-xEO series, where x is generally >6, and ethoxylated linear alcohols; and zwitterionics, such as betaines or sultaines. Anionic surfactants such as sulphates, ether sulphates, sulphonates, phosphate esters and the like, have been found to produce the desired effect, but seem less likely to be as preferable because of potentially unfavorable interactions with the cationic quat component of the inhibitor.

There are a great many surfactants, cationic, non-ionic, anionic or amphoteric, which could be employed depending on their ability to stabilize the emulsion of the chosen hydrocarbon along with the corrosion inhibitor quat and co-surfactant. A list of classes and subclasses of cationic, anionic, nonionic and amphoteric surfactants potentially useful for the process described herein are listed below. Classes and Subclasses of Cationic Surfactants:

Quaternary Ammonium Salts Sulfate Quats Imidazolinium salts Amine Salts

Classes and Subclasses of Nonionic Surfactants:

Alkyl Phenol Ethoxylates Alcohol Ethoxylates

Ethylene oxide - Propylene oxide Copolymers Alkyl Amine Ethoxylates

Alkyl Acid Ethoxylates

Alkyl Acid Ethylene oxide - Propylene oxide Copolymers Alkanoiamides Alkanolamides Ethoxylates Carboxylic Acid Ester Ethoxylates

Glycerol esters

Polyethylene Glycol Esters

Sorbitan esters

Sorbitan ester ethoxylates Ethylene and diethylene glycol esters

Propanediol esters

Natural fat and oil ethoxylates Carboxylic Acid Esters

Classes and Subclasses of Anionic Surfactants: Carboxylic Acids and Salts

Sulfonic Acids and Salts

Alkyl benzene sulfonates Alkyl benzene sulfonates, polymerized Alkylaryl sulfonates Alkylaryl sulfonates, polymerized

Alpha-sulfonated fatty acids Sulfonated fatty acids Sulfonated fatty esters Sulfonates with ether, ester or amide groups Mono & Di-ester sulfosuccinates

Sulfosuccinamates Naphthalene sulfonates

Alkyl naphthalene sulfonates Alkyl naphthalene sulfonates, polymerized Alkyl naphthalene/formaldehyde condensate polymer sulfonates Petroleum sulfonates ϋgnosulfonates Other sulfonates Sulfuric Acid Esters and Salts Alkyl sulfates Alcohol sulfates

Alcohol ether sulfates Alkyl phenol ether sulfates Fatty amide sulfates Fatty amide ether sulfates Fatty acid sulfates

Fatty ester sulfates Alpha-olefin Sulfates Alpha-sulfated fatty esters Natural Fat and Oil sulfates Phosphoric and Polyphosphoric Acid Esters and Salts Phosphated alkyoxylated alcohol and salts Phosphated alkyoxylated phenol and salts Other phosphoric and polyphosphoric acid esters and salts Phosphonates

Classes and Subclasses of Amphoteric Surfactants:

Betaines Sultaines Carboxylated Imidazolines

A partial list of specific surfactants for each class which can be used in the present invention are listed in Table Three. These can be used alone or combination with each other.

Ranking the effectiveness of various surfactants for their corrosion inhibition properties has not been attempted. One must bear in mind in any case that "effectiveness" in the laboratory, by whatever measure, is only one consideration in choosing a surfactant for use in a particular field situation. In practical terms, other factors must also be taken into account, such as cost, availability, environmental acceptability, etc. As illustrated by the examples however, both CTAB and ethoxylated nonylphenols NP-15 have been shown to be effective surfactants in the laboratory and would be expected to improve quat performance under similar conditions of temperature and composition.

This being said, it is relatively straightforward for a person skilled in the art to choose a suitable surfactant, i.e. one that will emulsify the chosen hydrocarbon phase in brine. A few drops of a surfactant are added to a 10 ml sample of the intended hydrocarbon phase. If the 0.5 to 10% solution formed in this way is not cloudy, the proposed surfactant is too hydrophobic, i.e. too miscible with the hydrocarbon. Further discrimination is possible by adding a sufficient amount of the cloudy surfactant hydrocarbon mixture to a test brine, enough to form a 1 to 2% solution. The emulsion which is formed on shaking should settle only slowly on standing, i.e. it should not settle in less than five minutes, and preferably in not less than fifteen or more minutes. If the test fails, a surfactant which is either more hydrophilic or more compatible with the hydrocarbon phase could then be tried. The selected surfactant should be used at a level of between 1 and 10% (by weight) of the amount of hydrocarbon in the formulation.

For practical purposes, it is preferable that the inhibitor as a whole, i.e. the inhibitor with all components combined, have particular characteristics. It is preferable that the combined components remain in a single phase (the emulsion should be stable and the hydrocarbon should not phase separate) and remain pourable for convenient use over a wide range of temperatures, preferably as low as -35°C. The inhibitor itself should not itself be corrosive to mild (carbon) steel. As a person skilled in the art will appreciate, obtaining a stable mixture using the elements disclosed above has inherent difficulties, since hydrophilic and hydrophobic components are being combined. One or more co-surfactants can thus be used to ensure that the concentrated inhibitor components remain in a single phase. The preferred cosurfactants are short-chain (C3 to C8) alcohols, with butanol having been found to be particularly suitable.

A list of potentially useful co-surfactants are listed in Table Four. The choice of a co-surfactant depends on the combination of hydrocarbon, quat and surfactant used. Suitable combinations and proportions can be obtained using procedures given above. A particular co- surfactant can be used alone or in combination with one or more other co-surfactants.

If an aromatic hydrocarbon phase, such as heavy reformate, is being used, around 25% (on a volume/volume basis) is likely required. A method to determine the exact proportions is to form a two phase mixture of the quat, surfactant and hydrocarbon phase, according to the guidelines given above, and then add the desired co-surfactant until the mixture forms a single phase at room temperature. If desired, freeze stability can then be ensured by adding progressively more co-surfactant until the single phase inhibitor concentrate does not phase separate when placed in a freezer at -35 °C for 48 hours.

Other elements can also be used, if necessary, to stabilize the mixture. For example, when incorporating an aliphatic hydrocarbon with a quat, "tying agents" such as oxyalkylated nonylphenols or dodecylbenzenesulphonic acid (DDBSA) can be used as part of the inhibitor blend. Amines such as monoethanolamine or diethylamine are often added to inhibitor concentrates in the amount of 2 to 5% to adjust the acidity of the formulation. It is desirable to adjust the acidity such that a 1 % concentrate of the solution (1 gm of solution added to 99 gm of water) has a pH of above 9 to ensure tolerance to the mild steel vessels in which such materials are commonly transported and stored. At more acid pH's, concentrated inhibitors can themselves be corrosive to carbon steel. The amine itself has not been observed to affect the performance of the blend.

It should be noted that these other additives, such as solvents, co-surfactants and amines can be treated as solutes, and cease to be important in terms of performance once the inhibitor is added to a pipeline.

All of the laboratory tests described below were carried out with a brine having the following composition:

MgS0₄-7H₂0 1.41 g litre^"1

MgCI₂-6H₂0 4.69 g litre"¹ CaCI₂-2H₂0 4.70 g litre^"1

NaHC0₃ 6.43 g litre"¹

NaCI 86.89 g litre^"1

Corrosion rates can be assessed in the laboratory through the use of mild steel test coupons exposed to the corrosive conditions over a period of time. The data which follow were obtained in tests in which coupons had been fashioned from a 6" wide, 0.008" thick roll of shimstock (carbon steel) by cutting it into strips approximately V-≥ wide.

A suitable volume of brine, having the composition given above, was purged for four hours with a pre-blended mixture of 80% H₂S and 20% C0₂. Each corrosion inhibitor to be tested was added, at the concentration indicated, to a 350 ml glass bottle, together with 100 ml of brine and a cleaned pre-weighed shimstock test coupon. The headspace in each bottle was purged with the H₂S/C0₂ gas mixture to remove oxygen. The bottles were sealed and spun slowly for 7 days at 60°C, after which period the coupons were reclaimed, cleaned by immersion in inhibited hydrochloric acid, xylene and methanol, and then re-weighed. In one set of tests described below, in which inhibitors were tested under "static" conditions, the bottles were not spun, but were left on their sides in a stationary position.

The weight loss from each coupon (referred to as "mg lost") was sometimes used as a measure of the amount of corrosion of test coupons. Alternately, a "percent protection", or "%P" value was calculated using weight loss from a blank experiment (i.e. one in which no chemical inhibitor was added to the brine), according to the following equation:

₀/₀p _ Weight loss from "blank" coupon - weight loss from "test" coupon _x <ιoo%

Weight loss from "blank" coupon

Another commonly reported parameter related to the amount of corrosion on the coupons is the "mils per year", or simply mpy. Corrosion rate, or mpy data, allow comparisons to be made between different experiments, inhibitors and systems more easily, as they are not distorted by abnormal results from "blank" experiments. For test coupons with this geometry, the corrosion rate in mpy is given by the following equation:

442ΔW ^{mpy "} (test hours) (12.55M + 0.619)

where: ΔW is the weight loss from the coupon in milligrams M is the mass of the coupon in grams

A second step in assessing corrosion is a visual inspection of the test coupons. Under modest magnification (say x16), localized corrosion is often apparent, even on coupons whose overall weight loss is minimal. Failure of pipelines through pitting attack is common in the industry, and an assessment of the extent and type of pitting damage on mild steel coupons is useful in determining the potential effectiveness of an inhibitor formulation. An advantageous aspect of the preferred embodiment of present invention is its ability to reduce localized corrosion on test coupons under laboratory conditions. This lack of pitting has also been observed in field tests.

Examples

The effectiveness of composition A relative to IC10 determined under laboratory conditions is illustrated by Figure 1 in which the amount of material lost from test coupons is plotted as a function of the amount of each inhibitor present in the test solution. As can be seen, at quat concentrations below 1500 ppm the inhibitor composition A is more effective than IC10 at inhibiting loss of material from test coupons. IC10 alone provides an equivalent degree of protection at a concentration of 2500 ppm of quat.

Turning to Figure 2, points 2 through 8 show the effect of varying the concentration of the heavy reformate component of Composition A on corrosion inhibition, point 1 being for the composition lacking both CTAB and heavy reformate. The overall quat concentration was 500 ppm for ail of the experiments. As can be seen, at concentrations of heavy reformate between about 12 and 21% (points 4 and 5), the amount of corrosion increases, but eventually corrosion inhibition is enhanced in the presence of heavy reformate (points 6 through 8). The decreased protection observed at points 4 and 5 is presumably due to the formation of a Winsor Type III microemuision, as discussed above. Figure 2 thus illustrates how the expected performance of an inhibitor can be established once the quat, surfactant and hydrocarbon components have been selected.

Figure 3 shows the effect on % protection of inhibitors containing cationic and non- ionic surfactants in place of CTAB. At similar surfactant concentration, the inhibition observed was comparable to that observed for Composition A.

Figure 4 shows the effect on % protection of inhibitors containing other hydrocarbon solvents in place of heavy reformate. At similar solvent concentration, the inhibition observed was comparable to that observed for Composition A. Of the hydrocarbons illustrated, both aliphatic and aromatic solvents were tested. Heavy reformate was preferred for being more readily formulated into a stable, single-phase and freeze resistant concentrate than the others. Figure 5 shows the effect of the total volume of hydrocarbon, in this case kerosene, on corrosion inhibition. In other respects the inhibitor formulation was the same as Composition A. As can be seen, the degree of protection against corrosion was found to increase with increasing volume of the hydrocarbon component.

Figure 6 shows the performance of four inhibitor formulations, which differ in surfactant component, under "static" and "dynamic" conditions. Dynamic conditions are simply those used in all other experiments in which the test bottles were spun for the duration of the test period. In experiments described as taking place under static conditions, the test bottles were maintained in a stationary position, on their sides, for the duration of the test period. As can be seen, inhibition of corrosion was observed under both static and dynamic conditions for all of the formulations tested, although the fourth inhibitor formulation did not perform as well under static conditions. When NP6 was used in conjunction with a more hydrophilic surfactant, e.g. CTAB or NP40, both the dispersion of the hydrocarbon phase in the brine and the lifetime of the emulsion were improved but the observed performance did not appear to be significantly improved.

Generally speaking, using the methods described above, it is possible to obtain inhibitors in accordance with the present invention to provide enhanced corrosion protection under a set of conditions selected from a broad range.

These ranges include temperatures between about 20°C to about 70°C; pressures between about 14 and 2100 psig, but more typically between 140 and 700 psig; and a pH between about 3 and 7, but more typically between about 3.5 and 5.5. Water content may be at any level, from very "dry" pipelines containing only water of condensation to pipelines with those with larger volumes of brine and containing little or no hydrocarbon. The chloride level can be up to 20% (200,000 ppm) of the aqueous layer, but more typical levels would be between about 1000 and 150,000 ppm. Acid gas partial pressures may be anywhere from 0 to 100% for both H₂S and C0₂ but they would more typically be in the range of 0 to about 20% for C0₂ and 0 to about 80% for H₂S.

Particular circumstances in which inhibitors of the present invention are useful include:

1. There is little or no naturally produced hydrocarbon in the liquid phase. For example water source wells or gas wells containing only water of condensation or brine. 2. Dry pipelines downstream of water traps, separators, knock-outs and other mechanical equipment, present to lower the water volume fraction in the line. 3. A pipeline containing one or more regions in which the brine present is either stagnant (dead-legs, very low flow rates, etc.) or is "held up" by features such as inclines, pipeline diameter changes, etc. 4. The volatility of the inhibitor is a concern, for example, a pipeline carrying a wet, high velocity gas.

5. The acid gases associated with the produced hydrocarbon are extremely sour, i.e. the partial pressure of H₂S is high with respect to both the C0₂ content (>1 :1) and the total pressure (>1%).

6. The system being treated contains significant amounts of particulate sulfur, which is known to exacerbate the corrosion of carbon steel.

Composition A has been tested in a gas line section under field-type conditions. The section was relatively dry with a high gas velocity, significant amounts of particulate sulfur were present, and the section had an elevation change. Laboratory testing indicated that conventional inhibitors would not provide adequate protection except at extremely high concentrations, but that composition A should provide corrosion protection at a treatment rate of 6000 ppm. Pitting corrosion was detected when the conventional inhibitors were used and the inhibitors were shown to be prone to gunking. Inhibitor deposits were thought responsible for some of the observed corrosion. Composition A was tested on a fresh section under comparable conditions. Monitoring failed to indicate a corrosion rate above 2.8 mpy and after several months a detailed inspection of the interior showed the section treated with Composition A to be in excellent condition.

A "threshold" effect in the observed corrosion inhibitory effect of Composition A was observed and this is typical, as far as the inventor is aware, of quat-based inhibitors.

Protection rises gradually with concentration until a certain threshold value is reached, whereupon a further small increase improves the inhibition dramatically. At that point, further improvement in protection against corrosion usually does not occur with increasing concentration, i.e., there is a plateau in performance. It might be that there is a dynamic between adsorbed and solvated inhibitor molecules which gradually increases the surface coverage with concentration until a protective layer is formed, at which point a very significant decrease in the corrosion rate is observed.

For a given set of conditions meeting the broad criteria above, it should usually be possible to obtain an inhibitor according to the present invention that is effective at a concentration of less than 1 %, based on the volume of brine. Concentrations of thousands of ppm are usually considered high, but the current invention can be suited to relatively dry systems, making the economics reasonable. In any case, in such systems it possible to obtain inhibitors according to the present invention which are effective to a degree not possible with conventional inhibitors at comparable concentrations. As described above, a principle of the current invention is to incorporate a condensed (liquid phase) hydrocarbon component into the aqueous phase of fluid material contained in a pipeline or other enclosure constructed from mild (carbon) steel, in which a quat component is used as an inhibitor against corrosion of an iron, for example, ferrous surface by the aqueous phase. This is because it has been found that incorporation of the hydrocarbon with the protective quat layer enhances the protection provided by the quat. Quats are water soluble, but hydrocarbons generally are not, hence the requirement to somehow induce or direct the hydrocarbon into the aqueous phase so as to bring it into contact with the protective quat layer for incorporation therewith. A person skilled in the art would thus understand that factors which affect the phase behavior of the hydrocarbon are likely to affect the performance of a hydrocarbon as a corrosion inhibitor in combination with a quat. Generally speaking, in relatively static systems, there is the need for a surfactant to draw the hydrocarbon into the aqueous layer.

The experiments reported above demonstrate that it is possible to select inhibitor components and proportions to optimize corrosion protection under particular circumstances. This being said, the inventor does not wish to be limited by theories described herein, although certain observations can be described in terms of phase behavior. Particularly, the observation that corrosion initially increases upon addition of smaller amounts of heavy reformate to an inhibitor containing a quat and a surfactant. In this case, it might be that when the composition forms a Winsor Type III microemuision (three immiscible phases, oil, water and a surfactant rich "middle phase") a low surface tension between the organic components and the aqueous phase reduces the ability of the system to deposit a corrosion inhibiting layer on the metal surface. As the proportion of hydrocarbon increases, a Winsor Type I microemuision (immiscible brine and hydrocarbon phases, with the surfactant partitioned to the aqueous phase) predominates, which permits the desired film formation.

List of Definitions and Abbreviations

IC10 A blend of benzyl alkyl pyridinyl quaternary ammonium chloride (73 to 77%) and methanol (23 to 27%), available from P-Chem Inc., Latexo, Tx.

CTAB Cetyltrimethyl ammonium bromide.

CPC Cetylpyridinium chloride. Heavy A heavy aromatic naphtha containing 15-40% dimethyl benzene,

Reformate available from Shell Chemicals, code number 646-250.

Cyclosol An aromatic hydrocarbon solvent available from Shell Chemicals, code number 646-200. PCP Solvent An aromatic hydrocarbon solvent available from Shell Chemicals, code number 645-900. NP-x Nonylphenol derivatives in which x designates the number of moles of ethylene oxide incorporated in each mole of NP material. The higher the value of x, the more hydrophilic the surfactant. These non-ionic surfactants are available from Rhone-Pouienc Canada Inc., under the trade name Alkasurf NP-x

LA230 An ethoxylated linear alcohol containing twenty three moles of ethylene oxide per mole of alcohol. Available from Alkaril Chemicals Ltd. of Mississauga, Ontario, Canada under the trade name Alkasurf LAN-23. Composition A IC10 9.3%; CTAB 2.2%; monoethanolamine 2.1%; heavy reformate

61.9%; butanol 17.0%; methanol 5.1 % and water 2.4% (by weight).

Composition B Composition A without any heavy reformate Preferred embodiments of the invention having been described, the scope of the invention is defined by the claims which follow.

Claims

1. A method for inhibiting corrosion of a surface of carbon steel exposed to an aqueous medium, comprising the step of: forming a layer comprising a corrosion-inhibiting amount of a quaternary pyridine salt and a water-immiscible organic component on the surface by incorporating into the medium a composition comprising the salt, the organic component and a surfactant, the surfactant being present in the composition in a sufficient amount to solubilize a sufficient amount of the organic component in the aqueous medium so as to permit formation of said layer.

2. The method of claim 1 wherein the organic component has a boiling range above about 70°C.

3. The method of claim 2 wherein the organic component has a boiling range above about 100°C.

4. The method of claim 2 wherein the boiling range is between about 70°C and about 400°C.

5. The method of claim 4 wherein the boiling range is between about 100°C and about 300°C.

6. The method of claim 5 wherein the boiling range is between about 150°C and about 300°C.

7. The method of claim 4 wherein the boiling range is between about 150°C and 400^βC.

8. The method of claim 7 wherein the boiling range is between about 150°C and 250°C.

9. The method of claim 1 wherein the organic component is selected from the group consisting of 2-methyl butane; hexane; dimethyl benzene; 1-methylethyl benzene; kerosine; Stoddard solvent; light alkylate naphtha; heavy catalytic reformed naphtha; hydrotreated middle distillates; hydrotreated light distillates; hydrotreated heavy naphtha; hydrotreated light naphtha; light aliphatic solvent naphtha;, heavy aromatic solvent naphtha; light aromatic solvent naphtha; normal C5 - 20 paraffins; diesel fuels; hydrotreated, dicyclopentadiene-rich, aromatic distillate; C6 - 10, acid treated, neutralized aromatic hydrocarbons; C9 - 17 aromatic hydrocarbons; C6 - 8, naphtha- raffinate pyrolyzate-derived aromatic hydrocarbons; C8, o-xylene-lean aromatic hydrocarbons; C9 - 11 , aromatic hydrocarbons; C12 - 20, aromatic hydrocarbons; or a combination thereof.

10. The method of claim 1 wherein the organic component is a hydrocarbon liquid.

11. The method of claim 1 wherein the organic component is an aromatic liquid.

12. The method of claim 11 wherein the aromatic liquid has a boiling range which is within the range from about 100° to 300°C.

13. The method of claim 1 wherein the surfactant is a cationic surfactant.

14. The method of claim 13 wherein the surfactant is selected from the group consisting of: N, N, N - trimethyl - 1 - hexadecanaminium bromide; 1-dodecyl pyridinium chloride; 1-hexadecyl pyridinium chloride; 1-decyl pyridinium chloride; 1-tetradecyl pyridinium chloride; 1 -phenylmethyl pyridinium chloride; 1-(2,4 dinitrophenyl) pyridinium chloride; 1-[2-oxo-2-[[2-[(1-oxododecyl) oxy] ethyl] amino] ethyl] pyridinium chloride; 1-[2-oxo-2-[[2-[(1-oxooctadecyl) oxy] ethyl] amino] ethyl] pyridinium chloride; 1 -dodecyl pyridinium chloride; 1- (2-hydroxyethyl)- pyridinium chloride; dicoco alkyldimethyl quaternary ammonium chloride compounds; 1 - benzyl -4,5- dihydo-1 - (hydroxyethyl) -2-norcoco alkyl imidazolium chloride compounds; N-tallow alkyltrimethylenediamines; N-coco alkyltrimethylenediamines; 1-[2- [[2-cyano-3- [4- (dimethylamino) phenyl] -1-oxo-2-propenyl] oxy] ethyl] pyridinium chloride; benzyl -C12-16- alkyldimethyl quaternary ammonium chloride compounds; N,N¹-bis[3- (dimethylamino)propyl]- urea, polymer with 1 ,1¹- oxybis [2-chloroethane]; or a combination thereof.

15. The method of claim 13 wherein the surfactant is cetyl trimethylammonium bromide.

16. The method of claim 1 wherein the surfactant is an anionic surfactant.

17. The method of claim 16 wherein the surfactant is selected from the group consisting of: N, N, N - trimethyl -1 - hexadecanaminium bromide; 1 -dodecyl pyridinium chloride; 1-hexadecyl pyridinium chloride; 1-decyl pyridinium chloride; 1-tetradecyl pyridinium chloride; 1 -phenylmethyl pyridinium chloride; 1-(2,4 dinitrophenyl) pyridinium chloride; 1-[2-oxo-2-[[2-[(1-oxododecyl) oxy] ethyl] amino] ethyl] pyridinium chloride; 1-[2-oxo-2-[[2-[(1-oxooctadecyl) oxy] ethyl] amino] ethyl] pyridinium chloride; 1 -dodecyl pyridinium chloride; 1- (2-hydroxy ethyl)- pyridinium chloride; dicoco alkyldimethyl quaternary ammonium chloride compounds; 1 - benzyl -4,5- dihydo-1 - (hydroxyethyl) -2-norcoco alkyl Imidazolium chloride compounds; N-tallow alkyltrimethylenediamines; N-coco alkyltrimethylenediamines; 1-[2- [[2-cyano-3- [4- (dimethylamino) phenyl] -1-oxo-2-propenyl] oxy] ethyl] pyridinium chloride; benzyl -C12-16- alkyldimethyl quaternary ammonium chloride compounds; N,N¹-bis[3- (dimethylamino)propyl]- urea, polymer with 1 ,1¹- oxybis [2-chloroethane]; or a combination thereof.

18. The method of claim 1 wherein the surfactant is a non-ionic surfactant.

19. The method of claim 18 wherein the surfactant is selected from the group consisting of: oxirane, methyl-, polymer with oxirane; poly (oxy -1 ,2- ethanediyl), alpha-(nonylphenyl)- omega - hydroxy-; poly (oxy -1 ,2- ethanediyl), alpha-[(1 ,1 ,3,3-tetramethylbutyl) phenyl)- omega -hydroxy-; poly (oxy -1 ,2- ethanediyl), alpha-(4-nonylphenyl)- omega -hydroxy-; fatty acids, tall-oil, ethoxylated; amines, N-tallow alkyltrimethylenedi-, ethoxylated; amines, coco alkyl, ethoxylated; alcohols, C12-15, ethoxylated; poly (oxy -1 ,2- ethanediyl), alpha-(nonylphenyl)- omega -hydroxy-, branched; alcohols, C12-14, ethoxylated; amides, coco N,N-bis (hydroxyethyl); fatty acids, tall-oil, esters with triethanolamine; or a combination thereof.

20. The method of claim 1 wherein the surfactant is an amphoteric surfactant.

21. The method of claim 20 wherein the surfactant is selected from the group consisting of: 1 - hexadecanaminium, N - (carboxymethyl) -N, N- dimethyl-, hydroxide, inner salt; 1 - propanaminium, 3-amino-N- (carboxymethyl) -N, N- dimethyl-, N-coco acyl derivs., hydroxides, inner salt; 1 H- imidazole, 4,5-dihydro-, 2-nortall-oil alkyl derivs.; 1 H- imidazole-1 -ethanol, 4,5- dihydro-, 2-norcoco alkyl derivs.; 1H- imidazole-1 -ethanol, 4,5- dihydro-, 2-nortall-oil alkyl derivs.; 1- propanaminium, N-(3- aminopropyl)-2-hydroxy -N,N- dimethyl-3-sulfo-, N-coco acyl derivs., hydroxide, inner salts; coco, N - [3- (dimethylamino) propyl] amides; imidazolium compounds, 1 - (carboxymethyl) -4,5- dihydro-1 -(hydroxyethyl)-2-norcoco alkyl, hydroxides, monosodium salts; 1 H- imidazole-1 -ethanamine, 4,5- dihydro-, 2-nortall-oil alkyl derivs.; 1 H- imidazole-1 - ethanamine, 4,5- dihydro-, 2-noraphthenyl derivs.; imidazolium compounds, 1-[2- (carboxmethoxy)ethyl]-1 -(carboxymethyl) -4,5-dihydro-2-norcoco alkyl, hydroxides, inner salts, disodium salts; 1- propanaminium, N-(3- aminopropyl)-2-hydroxy -N,N- dimethyl-3-sulfo-, N-coco acyl derivs., hydroxide, inner salts, sodium salts; imidazolium compounds, 2-C7-17-alkyl-1-(2- carboxyethyl) -4,5-dihydro-3-(hydroxyethyl), hydroxides, inner salts; decanoic acid, reaction products with 2-[(2-aminoethyl) amino] ethanol, acrylic acid alkylated (1 :2), disodium salts; octanoic acid, reaction products with 2-[(2-aminoethyl) amino] ethanol, acrylic acid alkylated (1 :2), disodium salts; coco, N- [3- (dimethylamino) propyl] amides, alkylation products with sodium 3- chloro-2-hydroxypropanesulfonate; 1- propanaminium, 3-butoxy-2-hydroxy -N- (2-hydroxy-3- 5 sulfopropyl) -N,N- dimethyl-, hydroxides, inner salt; 1- propanaminium, 3- [(2-ethylhexyl) oxy]-2- hydroxy -N- (2-hydroxy-3-sulfopropyl) -N,N- dimethyl-, hydroxides, inner salts; or a combination thereof.

22. The method of claim 1 wherein the quaternary pyridine salt is selected from the group consisting of 1 -ethyl pyridinium chloride; 1-decyl pyridinium chloride; 1 -dodecyl pyridinium chloride; 0 1-tetradecyl pyridinium chloride; 1-hexadecyl pyridinium chloride; 1 -phenylmethyl pyridinium chloride; 1-(2-phenylethyl) pyridinium chloride; 1-(2,4 dinitrophenyl) pyridinium chloride; 1-(2 hydrazino-2-oxoethyl) pyridinium chloride; 1-[[(3-nitrophenyl)methoxyy]methyl] pyridinium chloride; 1 -(carboxymethyl) pyridinium chloride; 1-[2-(ethylphenylamino)ethyl] pyridinium chloride; 1-(2- hydroyethyl) pyridinium chloride; 1-[2-[ethyl(3-methylphenyl)amino]ethyl] pyridinium chloride; 1-[[(1- 5 oxohexadecyl) amino] methyl] pyridinium chloride; 1-[2- [[2-cyano-3- [4- (dimethylamino)phyenyl] - 1-oxo-2-propenyl] oxy] ethyl] pyridinium chloride; 1-[2-oxo-2-[[2-[(1-oxododecyl) oxy] ethyl] amino] ethyl] pyridinium chloride; 1-[2-oxo-2-[[2-[(1-oxooctadecyi) oxy] ethyl] amino] ethyl] pyridinium chloride; 1 ,2 dimethyl pyridinium chloride; 1-hexadecyl, 2 methyl pyridinium chloride; 1- phenylmethyl, 2 methyl pyridinium chloride; 1-hexadecyl, 3 methyl pyridinium chloride; 1- 0 phenylmethyl, 3 methyl pyridinium chloride; 1-tetradecyl, 4 methyl pyridinium chloride; 1- hexadecyl, 4 methyl pyridinium chloride; 1 -phenylmethyl, methyl pyridinium chloride; 1-methyl, ethyl, methyl derivs., pyridinium chloride; 1 -phenylmethyl, ethyl, methyl derivs., pyridinium chloride; 1 -phenylmethyl, C7-8 alkyl derivatives., pyridinium chloride; 1 -phenylmethyl, alkyl derivs., pyridinium chloride; 1 -phenylmethyl, 3 carboxy pyridinium chloride; 1 -phenylmethyl, 3 carboxy 5 pyridinium chloride, sodium salt; 1 -phenylmethyl, 3-(aminocarbonyl) pyridinium chloride; 1-(2, 4- dinitrophenyl), -4-phenyl pyridinium chloride; 1 -phenylmethyl, 3-ethoxycarbonyl pyridinium chloride; 1 -phenylmethyl, 3-[(1-methylethoxy) carbonyl] pyridinium chloride; 1-(2-hydroxyethyl, 4- [2- [4- [ethyl (phenylmethyl) amino] phenyl] ethenyl] pyridinium chloride; 1-(4-morpholinylcarbonyl) 3- (aminocarbonyl) pyridinium chloride; 1-(formylhydroxymethylphenyl), 3-carboxy pyridinium

30 chloride; l-(oxiranylmethyl), 2-amino pyridinium chloride; 1-[2-[(cyanoacetyl) oxy] ethyl] pyridinium chloride; 1 -phenylmethyl, ethyl pyridinium chloride, mixed with 1 -phenylmethyl, methyl chloride; 1 ,2 dimethyl, 5-ethenyl pyridinium chloride, polymer with 5-ethenyl -2- methylpyridine; 1-methyl, 3- ethenyl pyridinium chloride, polymer with 5- ethenyl -2- methylpyridine; or a combination thereof.

23. The method of claim 1 wherein the quaternary pyridine salt is a pyridine-HCI salt.

35 24. The method of claim 1 wherein the pyridine salt is a quaternary salt of a pyridine-containing composition and a compound of the formula R-X wherein R is selected from the group consisting of alkyl and aryl groups of up to about 16 carbon atoms and X is a halide.

25. The method of claim 24 wherein R has up to about 10 carbon atoms.

26. The method of claim 25 wherein R has up to about 7 carbon atoms. 40

27. The method of claim 25 wherein R is a benzyl group.

28. The method of claim 10 wherein the quaternary pyridine salt and the hydrocarbon liquid are present in the composition in a relative salt:hydrocarbon liquid molar proportion of from about 1 :1 to about 1 :14.

29. The method of claim 28 wherein the quaternary pyridine salt and the hydrocarbon liquid are 5 present in the composition in a relative salthydrocarbon liquid molar proportion of from about 1 :2 to about 1:14.

30. The method of claim 29 wherein the quaternary pyridine salt and the hydrocarbon liquid are present in the composition in a relative salthydrocarbon liquid molar proportion of from about 1 :2 to about 1 :12.

10 31. The method of claim 30 wherein the quaternary pyridine salt and the hydrocarbon liquid are present in the composition in a relative salthydrocarbon liquid molar proportion of from about 1 :4 to about 1 :9.

32. The method of claim 31 wherein the quaternary pyridine salt and the hydrocarbon liquid are present in the composition in a relative sal hydrocarbon liquid molar proportion of from about 1 :5

15 to about 1 :7.

33. The method of claim 32 wherein the quaternary pyridine salt and the hydrocarbon liquid are present in the composition in a relative salthydrocarbon liquid molar proportion of about 1 :7.

34. The method of claim 10 wherein the hydrocarbon liquid is between about 10% and 80% by volume of the composition.

20 35. The method of claim 34 wherein the hydrocarbon liquid is between about 25% and 65% by volume of the composition.

36. The method of claim 35 wherein the hydrocarbon liquid is between about 25% and 50% by volume of the composition.

37. The method of claim 1 wherein the amount of surfactant is between about 0.1% and 10 % of 25 the weight of the composition.

38. The method of claim 37 wherein the amount of surfactant is between about 1 % and 10% of the weight of the composition.

39. The method of claim 38 wherein the amount of surfactant is between about 0.5% and 8% of the weight of the composition.

30 40. The method of claim 39 wherein the amount of surfactant is between about 1 % and 5% of the weight of the composition.

41. The method of claim 405 wherein the amount of surfactant is between about 1 % and 3% of the weight of the composition.

42. The method of claim 10 wherein the surfactant is present in the composition at a level of 35 between about 0.1 and 20% by weight of the amount of the hydrocarbon liquid.

43. The method of claim 42 wherein the surfactant is present in the composition at a level of between about 0.1 and 10% by weight of the amount of the hydrocarbon liquid.

44. The method of claim 43 wherein the surfactant is present in the composition at a level of between about 1 and 10% by weight of the amount of the hydrocarbon liquid.

40 45. The method of claim 1 wherein the aqueous medium has a pH of between about 3 and 7.

46. The method of claim 45 wherein the aqueous medium has a pH of between about 3.5 and 5.5.

47. The method of claim 1 wherein the chloride content of the aqueous medium is between about 0% and 20% by weight.

5 48. The method of claim 47 wherein the chloride content of the aqueous medium is between about 5% and about 15% by weight.

49. The method of claim 47 wherein the chloride content of the aqueous medium is between about 1% and 8% by weight.

50. The method of claim 1 wherein the temperature of the aqueous medium is between about 0°C 0 and about 80°C.

51. The method of claim 50 wherein the temperature of the aqueous medium is between about 40°C and 70°C.

52. The method of claim 1 wherein the aqueous medium is present in a pipeline, production equipment tubing or valving, or the like, and is part of a fluid system having a hydrocarbon 5 component.

53. The method of claim 52 wherein the aqueous medium is located in a natural gas pipeline.

54. The method of claim 52 wherein the aqueous medium and hydrocarbon component are present in separate phases.

55. The method of claim 52 wherein the system includes H₂S. 0

56. The method of claim 55 wherein the partial pressure of H₂S is greater than about 0.5% of the total pressure.

57. The method of claim 52 wherein the system includes CO_z and the partial pressure of the H₂S is greater than about 0.1 % of the total pressure and is up to about twice the partial pressure of the

C0₂. 5 58. The method of claim 57 wherein the partial pressure of the H₂S is greater than about 0.5% of the total pressure.

59. The method of claim 1 further comprising a co-surfactant for retaining the composition as a single phase in storage prior to incorporation into the medium.

60. The method of claim 59 where the co-surfactant is selected from the group consisting of 1- 30 propanol; 1 -butanol; 1-pentanol; 1-hexanol; 1-heptanol; 1-octanol; fusel oil; 2-ethyl-1-hexanol; alpha-dimethyl-alpha benzenemethanol; or a combination thereof.

61. The method of claim 59 wherein the co-surfactant includes an alcohol having between about 3 and about 8 carbons.

62. The method of claim 1 further comprising one or more tying agents.

35 63. The method of claim 62 wherein said one or more tying agents is selected from the group consisting of nonylphenols and dodecylbenzenesulphonic acid.

64. The method of claim 1 further comprising a base for adjustment of the pH of the composition for storage of the composition prior to incorporation into the medium.

65. The method of claim 64 wherein the base is an amine.

40 66. The method of claim 65 wherein the amine is a non-aromatic organoamine.

67. The method of claim 66 wherein the amine is selected from monoethanolamine and diethylamine and combinations thereof.

68. The method of claim 64 wherein the pH of the composition is about 9 when diluted to 1% (w/w) in water.

5 69. The method of claim 64 wherein the base is an organoamine.

70. The method of claim 1 wherein the composition is a liquid at room temperature.

71. The method of claim 70 wherein the liquid is pourable over a temperature range from about - 35°C to about 50°C.

72. The method of claim 71 wherein the liquid is pourable over a temperature range from about - 10 20°C to about +20°C.

73. The method of claim 70 wherein the liquid is pourable down to a temperature of about -35°C.

74. A method for inhibiting corrosion of an iron surface exposed to an aqueous medium, comprising contacting the exposed surface with a corrosion-inhibiting amount of a quaternary pyridine salt and a water-immiscible organic component by incorporating into the medium a liquid

15 composition comprising the salt, the organic component and a surfactant, the surfactant being present in the composition in a sufficient amount to stabilize an emulsion containing the organic component in the aqueous medium.

75. The method of claim 74 wherein the composition includes an agent for retaining the composition as a single phase for storage and shipping prior to incorporation into the medium.

20 76. The method of claim 75 wherein the organic component is an aromatic hydrocarbon having a boiling range above about 100°C.

77. A method for inhibiting corrosion of a surface of carbon steel exposed to a turbulent aqueous medium, comprising the step of incorporating into the medium a corrosion-inhibiting amount of a quaternary pyridine salt and a water-immiscible organic component so as to form a corrosion-

25 inhibiting layer comprising the salt and organic component on the surface.

78. The method of claim 77 wherein the quaternary pyridine salt and the organic component are included as part of composition which includes an agent for retaining the composition as a single phase for storage and shipping prior to incorporation into the medium.

79. An additive composition suitable for inhibiting corrosion of a surface of carbon steel exposed to 30 an aqueous environment, the composition comprising, a quaternary pyridine salt, a water- immiscible organic component and a surfactant for solubilizing the organic component in the aqueous environment upon addition thereto.

80. The additive composition of claim 79, further comprising an agent for maintaining the composition in a single phase.

35 81. The additive composition of claim 80 wherein the agent is an alcohol having from about 3 to 8 carbon atoms.

82. The additive composition of claim 81 wherein the organic component is a hydrocarbon liquid.

83. The additive composition of claim 82 wherein the hydrocarbon liquid is an aromatic liquid having a boiling range above about 100°C.

40 84. The additive composition of claim 80, including an agent for maintaining the basicity of the composition, when diluted to 1% in water (w/w) at a basic pH.

85. The additive composition of claim 84, wherein the agent for maintaining the basicity is an amine, optionally and organoamine, optionally a non-aromatic organoamine, or optionally monoethanol amine or diethylamine or a mixture thereof. 5

86. The additive composition of claim 85 wherein the pH is between about 7 and about 10.

87. The additive composition of claim 86 wherein the pH is between about 8 and about 9.

88. A method of manufacturing an additive composition for inhibiting corrosion of a surface of carbon steel exposed to an aqueous environment, the method comprising, combining a quaternary pyridine salt, a water-immiscible organic component and a surfactant for solubilizing the organic

10 component in the aqueous environment upon addition thereto.

89. The method of claim 88 further comprising the step of combining an agent as part of the composition for maintaining the composition in a single phase.

90. The method of claim 89 wherein the agent is an alcohol having from about 3 to 8 carbon atoms.

15 91. The method of claim 90 wherein the organic component is a hydrocarbon liquid.