Treatments for controlling liquid and vapor phase corrosion with film-forming compounds

Abstract

Treatments are described for inhibiting corrosion in aqueous systems having metal surfaces that are in contact with water in a liquid phase and a vapor phase. The treatment includes adding a film-forming amine to the water and adding an additional film-forming compound that includes at least one of (i) an ethoxylated alkyl amine, (ii) an alkyl bis amide, and (iii) a fatty acid, an ester of the fatty acid, or an alkoxylated product of the fatty acid.

Description

TREATMENTS FOR CONTROLLING LIQUID AND VAPOR PHASE CORROSION WITH FILM-FORMING COMPOUNDSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the earlier filing date benefit of U.S. Provisional Application No. 63 / 736,949, filed on December 20, 2024, the entirety of which is incorporated by reference herein.BACKGROUND

[0002] Film-forming amines ("FFA") are used to inhibit corrosion in industrial water systems for boiler water, steam treatments, and other high temperature corrosive environments. FFAs are particularly useful in water systems where it is desired to inhibit corrosion in a condensate system because the FFAs are somewhat volatile and can be transferred from the liquid to vapor state with steam. The FFAs can provide corrosion protection when the steam is condensed on equipment surfaces of the water system.

[0003] By way of example, boilers generate power by elevating water temperature while limiting the escape of the steam, which generates higher pressure that further increases the boiling point of the water. The application of FFAs such as octadecyl amine, oleyleamine, or N- olyelpropane-l,3-diamine can create a barrier along the metal in the condensate circuit that prevents the escape of the corrosion byproducts, decreases the solubility of dissolving iron, and thereby inhibits corrosion. The FFAs are generally added to the water system so that enough of the material residual is present in the system to develop the film.

[0004] FFAs are known to provide good protection against corrosion for metal surfaces that are in contact with either the vapor or liquid phase. However, a residual amount of FFAs in the water are necessary to maintain the protective film on the metal surface. As the residence time of the FFAs in the system increases, the high temperatures and pressures will cause the FFA residuals to oxidize to form organic acid byproducts. The organic acids can contaminate the system because they contribute to cation conductivity and interfere with the detection of corrosive analytes such as chlorides and sulfates. The deterioration of the protective film also increases iron residuals in the water that can build up in equipment and create corrosive conditions.SUMMARY

[0005] In accordance with one aspect, this disclosure provides a method of treating an aqueous system that has corrodible metal surfaces in contact with water in a liquid phase and a vapor phase. The method includes combining with the water (a) at least one filmforming amine ("FFA") having a primary amine group and an aliphatic hydrocarbon group having 5 to 40 carbon atoms, and (b) at least one additional film-forming compound that is selected from (i) an ethoxylated alkyl amine having an ethoxy-substituted amine group and an aliphatic hydrocarbon group having from 5 to 40 carbon atoms, wherein the ethoxylated alkyl amine has from 1 to 25 ethoxy groups; (ii) an alkyl bis amide having at least two aliphatic hydrocarbon groups having 5 to 40 carbon atoms; and (iii) a fatty acid compound that includes at least one carboxylic acid group and an aliphatic hydrocarbon group having from 5 to 40 carbon atoms, an ester of the fatty acid compound, or an alkoxylated product of the fatty acid compound. The at least one FFA and the at least one additional film-forming compound are added to the water in a relative weight ratio that is in a range of from 1 : 10 to 10: 1.

[0006] In accordance with another aspect, this disclosure provides a method of treating a boiler system that includes a boiler that generates steam by heating liquid water and operates a temperature in a range of from 100 to 500°C and a pressure of from 100 to 4,000 psig. The method includes combining with the water (a) at least one FFA having a primary amine group and an aliphatic hydrocarbon group having 5 to 40 carbon atoms, and (b) at least one additional film-forming compound that is selected from (i) an ethoxylated alkyl amine having an ethoxy-substituted amine group and an aliphatic hydrocarbon group having from 5 to 40 carbon atoms, wherein the ethoxylated alkyl amine has from 1 to 25 ethoxy groups; and (ii) an alkyl bis amide having at least two aliphatic hydrocarbon groups having 5 to 40 carbon atoms. In this embodiment, the FFA and the additional film-forming compound are combined with the water so that they are present in the liquid water at a combined concentration that is in a range of from 20 ppb to 20 ppm, and are added to the water at a relative weight ratio that is in a range of from 1 :2 to 2: 1.

[0007] In accordance with another aspect, this disclosure provides a liquid composition that includes (a) from 40 wt.% to 99 wt.% of water or other solvent, (a) from 0.1 to 10 wt.% of at least one FFA having a primary amine group and an aliphatic hydrocarbon group having 5 to 40 carbon atoms, (b) from 0.1 to 10 wt.% of an additional film-forming compound that is selected from at least one of (i) an ethoxylated alkyl amine having an ethoxy-substituted amine group and an aliphatic hydrocarbon group having from 5to 40 carbon atoms, wherein the ethoxylated alkyl amine has from 1 to 25 ethoxy groups; (ii) an alkyl bis amide having at least two aliphatic hydrocarbon groups having 5 to 40 carbon atoms; and (iii) a fatty acid compound that includes at least one carboxylic acid group and an aliphatic hydrocarbon group having from 5 to 40 carbon atoms.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig. l is a schematic diagram illustrating a boiler system;

[0009] Figs. 2A and 2B are graphs of the impedance spectroscopy of metal samples treated with corrosion inhibitor compositions in a flow-through boiler system;

[0010] Figs. 3 A and 3B are graphs of the corrosion rate over time of the metal samples treated with corrosion inhibitor compositions in the flow-through boiler system;

[0011] Figs. 4A and 4B are graphs showing percentage change of the corrosion rate over time for the metal samples treated with corrosion inhibitor compositions in the flow- through boiler system;

[0012] Fig. 5 is a graph showing the corrosion rate over time for metal samples that are tested in an LPR autoclave; and

[0013] Figs. 6A and 6B are graphs showing the degradation rate of a protective film formed on metal samples treated with corrosion inhibitor compositions.DETAILED DESCRIPTION OF EMBODIMENTS

[0014] The methods and compositions discovered in connection with this invention provided improved corrosion inhibition performance in aqueous systems in which metal surfaces are exposed to both liquid phase and vapor phase.

[0015] Treatment Methods

[0016] The methods of inhibiting corrosion according to aspects of the invention include combining a chemical treatment to water that is present in an aqueous system to form a film on (i) a metal surface that is in contact with the liquid phase, and (ii) a metal surface that is in contact with the vapor phase. The chemical treatment includes at least one FFA and at least one additional filming compound that is selected from (i) an ethoxylated alkyl amine having from 1 to 20 ethoxy groups and an aliphatic chain that has from 5 to 40 carbon atoms;(ii) an alkyl bis amide that includes an aliphatic chain having from 5 to 40 carbon atoms; and(iii) a fatty acid having an aliphatic chain that has from 5 to 40 carbon atoms, or an ester of the fatty acid, or an alkoxylated product of the fatty acid. In some embodiments, two or more of these additional filming compounds can be used with the at least one FFA, e.g., at leastone from each of groups (i), (ii), and (iii), at least one from each of groups (i) and (ii), at least one from each of groups (i) and (iii), or at least one from each of groups (ii) and (iii). Likewise, multiple compounds from each of the aforementioned groups can be used.

[0017] As explained in connection with the examples below, as compared to conventional treatments that employ FFAs alone, the chemical treatments described herein have been found to form a persistent film on surfaces that contact the liquid and vapor phase, and provide excellent resistance against corrosion. Without intending to be bound by theory, it is believed that FFAs form a protective film on a metal surface by attaching themselves to the metal in a monomolecular layer, which imparts strong water repellence to the surface of the metal to improve corrosion. And since the FFAs are volatile, they can transfer to the vapor phase and can condense on the metal surface with any condensed water to form a protective film on metal surfaces that are exposed to the water vapor. It is believed that the additional filming compounds improve corrosion inhibition performance by interlocking with the FFA molecules to provide a tighter film that is more tenacious. The additional compounds may also work by initially interacting with the metal surface to decrease the polarity or charge on the metal surface, which allows for the FFA to more readily approach the surface and form the protective film. Additionally, at least the ethoxylated alkyl amine component is typically less soluble than the FFA, which may better hold the film to metal surface. The ethoxlyate fragment of the ethoxylated alkyl amine may also oxidize to an acid over time, which creates another functional group that binds to the metal surface and may provide a relatively long-lasting protective film.

[0018] The combination of the FFA and the at least one additional film forming compound enables the development of a more thermally stable and tenacious film that develops quickly and requires a lower feed rate to develop the film. In turn, this reduces iron residuals from the metal surface that can build up in equipment such as evaporator tubes. It also reduces the amount organic acid byproducts in the water, which reduces the cation conductivity (after ion exchange) that the treatment contributes. For example, whereas a conventional FFA-only treatment may add about 20 microsiemens of cation conductivity to the water, based on treatments described herein the protective film can be formed by using amounts of FFA that add less than 12 microsiemens of cation conductivity, such as from 5 to 10 microsiemens.

[0019] FFA component:

[0020] The FFAs that are used are volatile, higher molecular weight amines with a surfactant type structure. The FFA includes at least one unsubstituted primary amine group,and an aliphatic hydrocarbon group that may be straight chained, branched, saturated or unsaturated, substituted or unsubstituted. The hydrocarbon group can include 5 to 40 carbon atoms, 10 to 30 carbon atoms, or 15 to 25 carbon atoms. The FFA may have a molar mass in the range of 150 to 400 g / mol, from 200 to 350 g / mol, or from 225 to 300 g / mol. Suitable FFAs may include octadecyl amine, oleyleamine, N-olyelpropane-l,3-diamine ("OLDA"), or combinations thereof, for example.

[0021] Ethoxylated alkyl amine component:

[0022] The ethoxylated alkyl amine includes at least one ethoxy-substituted amine group. The ethoxylated alkyl amine can include a total number of ethoxy groups that is in a range of from 1 to 25, from 2 to 15, or from 2 to 5, for example. Typically, the at least one ethoxy-substituted amine group is a terminal -NH2 group in which both of the hydrogen atoms are substituted with one or more ethoxy groups. The ethoxylated amine includes a branched or unbranched, substituted or unsubstituted, saturated aliphatic hydrocarbon group having 5 to 40 carbon atoms, 10 to 24 carbon atoms, or 14 to 20 carbon atoms. Examples of the ethoxylated amine include polyoxyethylene oleyl amine, polyoxyethylene tallow diamine, polyoxy ethylene-N-tallow-l,3-diaminopropane.

[0023] Alkyl bis amide compound:

[0024] The alkyl bis amide may be a long chain alkyl bis amide including at least two branched or unbranched, substituted or unsubstituted, saturated aliphatic hydrocarbon groups having 5 to 40 carbon atoms, 10 to 24 carbon atoms, or 14 to 20 carbon atoms. In one embodiment, the long chain alkyl bis amide includes at least two unsubstituted alkyl groups, and in another embodiment the at least two unsubstituted alkyl groups are unbranched. The alkyl bis amide may have a chemical structure represented by the following formula (I):

[0025] In formula (I), R1and R3may independently be a branched or unbranched alkyl group having 5 to 40 carbon atoms, 10 to 26 carbon atoms, or 14 to 22 carbon atoms; and R2may be a branched or unbranched, substituted or unsubstituted, alkyl group having 1 to 22 carbon atoms, 2 to 10 carbon atoms, or 2 to 6 carbon atoms. R1and R3may be the same or different. Suitable alkyl bis amides may include bis-stearamides (e.g., ethylene bisstearamide ("EBS")), bisoleamides, bispalmitamides, and bislinoleamides.

[0026] Fatty acid compound:

[0027] The faty acid compound includes at least one carboxylic acid group and a branched or unbranched, substituted or unsubstituted, saturated aliphatic group having 5 to 40 carbon atoms, 10 to 24 carbon atoms, or 14 to 20 carbon atoms. The fatty acid compound can also include (i) esters of these fatty acids such as a Cl -CIO, or C1-C4 ester of the fatty acid; or (ii) alkoxylated products of these fatty acids, including those formed by reacting ethylene oxide or polyethylene glycol with the fatty acid (e.g., polyethylene glycol monostearate).

[0028] The FFA and additional filming compound can be combined with the water together or separately. The weight ratio of the amount of FFAs added to the water system to the amount of the aforementioned additional filming compounds added to the water system can be in a range from 1 : 10 to 10: 1, from 1 :4 to 4: 1, from 1 :2 to 2: 1, or from 1 : 1.5 to 1.5: 1, for example.

[0029] The FFA and the additional filming compound may be dosed so that the combined concentration of these compounds in the liquid phase is in the range of, for example, from 20 ppb to 20 ppm, from 50 ppb to 5 ppm, from 100 ppb to 1 ppm, and from 250 ppb to 750 ppb. In practice, these treatment chemicals can be dosed into the water system continuously, periodically, or intermittently, e.g., in response to a determination that the concentration of either or both of the FFA and additional filming compound are below a threshold limit.

[0030] Other chemicals can also be added to the water system such as pH adjusting agents (e.g., ammonia), neutralizing amines (e.g., monoethanolamine), and / or chemical oxygen scavengers, for example.

[0031] The chemical treatment is effective to form films on metal surfaces of equipment and conduits in the aqueous systems, and in particular, iron-containing metal surfaces in these systems such as those made of mild steel. The chemical treatment should also be effective to form protective films on aluminum surfaces and yellow metal surfaces such as copper and brass. The aqueous system can be a closed industrial system that includes liquid water and water vapor, including a steam generating system, such as a boiler system. The aqueous system can also be a hydrostatic system such as hydrostatic cooker or hydrostatic sterilizer, for example. The chemical treatment can be added to these systems in any location that will distribute the film-forming compounds to the metal surfaces that are prone to corrosion. For example, in the case of boiler systems, the film-forming compounds can be added to the boiler feedwater, steam header, etc.

[0032] The water in the aqueous systems can be heated and can have a temperature in a range of from 30°C to 500°C, such as from 35°C to 95°C in the case of hydrostatic systems, or from 100°C to 450°C or from 250°C to 375°C in the case of boilers. Boilers are also operated at high pressures such as from 100 psig to 4,000 psig, from 500 psig to 3,000 psig, or from 1,000 psig to 2,500 psig, for example. The water can have a pH that is in the range of 8 to 11, 8.5 to 10.5, or 9 to 10, for example.

[0033] The methods according to one aspect of this disclosure are described in Fig. 1 in connection with a boiler system 200. Corrosion is a problem caused by water in the boiler. Corrosion can be caused by dissolved oxygen, corrosion currents due to heterogeneities on metal surfaces, or by the water directly attacking iron in the boiler. Corrosion may occur in the feed-water stream as a result of low pH water and the presence of dissolved oxygen and carbon dioxide. Corrosion is also a problem in the condensate return, which is typically composed of mild steel piping and equipment, and occasionally copper alloys. Corrosion in the condensate system is often in the form of pitting which can cause failure of the equipment if not monitored.

[0034] Fig. 1 illustrates a typical boiler system 200, where the boiler 220 heats water to provide steam for a heat exchanger 225 or other process. Condensate from the heat exchanger is collected in a condensate tank 230 that is fed to a deaerator or feedwater tank 240 before being directed back to the boiler 220. The deaerator can remove oxygen and carbon dioxide to low levels in the boiler feedwater. Makeup water stream 215 is directed to tank 240 as needed to ensure that the amount of water in the system remains constant. The make water stream can be metered into tank 240 with a water meter that can be controlled based on, e.g., a water level sensor in the boiler. The boiler also has a continuous and bottom blow down 255 to remove water from the boiler.

[0035] A treatment composition including the FFA and the additional filming compound can be introduced at port 210 into the return water stream 212 where the treatment composition is pumped as needed to provide adequate corrosion protection in the system. The treatment composition could similarly be supplied directly to the boiler water or to the makeup water stream 215. To determine the residual concentration of FFA and / or the additional filming compound, water from the condensate tank 250 can be sampled and assayed at monitoring station 250 using any known techniques. The monitoring station 250 may communicate with a pump or valve of port 210 via feedback control loop 260 to control the amount of the treatment composition that is introduced to the boiler based on the results from monitoring station 250.

[0036] Treatment Compositions

[0037] This disclosure also provides novel liquid compositions in which the filmforming components are included together to allow for convenient dosing when treating water. Thus, the compositions can include a combination of the FFA described above together with at least one of the additional filming compounds described above, i.e., (i) the ethoxylated alkyl amine compounds; (ii) the alkyl bis amide compounds; and (iii) the fatty acid compounds. The FFAs can be present in an amount of from 0.1 wt.% to 15 wt.%, from 1 wt.% to 10 wt.%, or from 2 wt.% to 5 wt.%, for example. The additional filming compounds can similarly be present in an amount of from 0.1 wt.% to 15 wt.%, from 1 wt.% to 10 wt.%, or from 2 wt.% to 5 wt.%, for example. The weight ratio of the amount of FFAs to the amount of the additional filming compounds can be in a range from 1 : 10 to 10: 1, from 1 :4 to 4: 1, from 1 :2 to 2: 1, or from 1 : 1.5 to 1.5: 1.

[0038] The liquid compositions can include water or another solvent in a total amount of from 40 wt.% to 99.5 wt.%, from 75 wt.% to 99 wt.%, or from 90 wt.% to 98 wt.%, for example.

[0039] Other components can be included in the compositions to stabilize the composition such as emulsifiers, thickening agents, etc. Acid reagents can also be added to solubilize the components if necessary. In this regard, ethoxylated alkyl amines with lower degrees of ethyoxylation have a lower solubility in water, and acid can be added to dissolve the ethoxylated amine.

[0040] EXAMPLES

[0041] The following corrosion inhibitor compositions were prepared and tested for corrosion inhibition and film-forming properties.

[0042] Comparative Example: An aqueous solution that includes 5 wt.% OLDA.

[0043] Example 1 : An aqueous solution that includes 2.5 wt.% OLDA and 2.5 wt.% of a polyoxyethylene tallow diamine with 15 total ethoxy groups.

[0044] Example 2: An aqueous solution that includes 2.5 wt.% OLDA and 2.5 wt.% of a polyoxyethylene oleyl amine with 5 total ethoxy groups.

[0045] Example 3: An aqueous solution that includes 2.5 wt.% OLDA and 2.5 wt.% of a polyoxyethylene oleyl amine with 2 total ethoxy groups. Formic acid is added to solubilize the polyoxyethylene oleyl amine.

[0046] Example 4: An aqueous solution that includes 2.5 wt.% OLDA, 2.5 wt.% of a micronized ethylene bisstearamide, and 5 wt.% of a polyoxyethylene stearate.

[0047] Research Boiler Experiment

[0048] The inhibitor compositions in the examples and comparative examples were added to the feedwater of a research boiler system. The research boiler system has a feedwater setup that has a purge system to maintain dissolved oxygen at a specific concentration and provides injection points for adding chemicals (e.g., pH adjusting agents or the example compositions). The feedwater setup feeds water to an autoclave with a preheater and an autoclave chamber. The autoclave chamber has a standpipe so that after filling halfway, the water flows out the standpipe. The water flowing out the standpipe goes through a sample cooling system.

[0049] During this experiment, the boiler feedwater was set to a flowthrough rate of 25 ml / min, and the boiler was maintained at 348.8°C, 2400 psi, a pH of 10.0 (monoethanolamine), and a dissolved oxygen level of less than 10 ppb. The boiler was stirred at 100 rpm. For each experiment, one of the examples were dosed in amounts corresponding to 250 ppb of OLD A, and the comparative example was dosed in an amount corresponding to 500 ppb of OLDA. Two mild steel coupons were mounted below the water level and two mild steel coupons were mounted above the water level. The boiler was maintained with the aforementioned concentrations of filming compounds and at the stated conditions for 18 hours while the inhibitor compositions formed films on the coupons.

[0050] The coupons were then removed from the research boiler and placed in electrochemistry glassware that is filled with 200ppm solution of NaCl at room temperature and a pH of about 10. Electrical impedance spectroscopy (EIS) was performed for 15 minutes and linear polarization resistance immediately followed.

[0051] The EIS test results are shown in Figs. 2A and 2B. Fig. 2A shows the EIS results on the coupons submerged in water and Fig. 2B shows the EIS results on the coupons exposed to vapor. EIS measures capacitance which indicates the film depth that is formed on the coupons from the treatment compositions. In the figures, the film thickness is proportional to the area under the curve such that a larger area under the curve indicates a thicker film. It can be concluded from these figures that Examples 2 and 3 had the thickest film in the liquid phase coupons, and that Example 2 had the thickest film in the vapor phase coupon. It can also be seen that using both an FFA compound and a film forming promoter compound generally provided better film thicknesses in the liquid phase than a comparable amount of the FFA compound alone.

[0052] As soon as the EIS was completed, linear polarization measurements (LPR) began and continued for 18 hours. The LPR results are shown in Figs. 3 A (liquid phasecoupons) and 3B (vapor phase coupons). These LPR measurements show that the corrosion rates (in mpy) for all treatments started off at similar values, particularly in the vapor phase. Over time and in the absence of filming residuals in the electrochemical cell, the films begin to deteriorate. As shown in Figs. 3 A and 3B, the example compositions exhibit comparable or improved corrosion performance as compared to the comparative composition that includes only OLDA. In some cases, the improvement over 18 hours was significant, which indicates that regardless of film depth, the example films are much more persistent and dissolve more slowly than films made from OLDA alone. The improvements in the vapor phase corrosion performance were even higher than the liquid phase, which indicates that the films are thicker in the liquid phase and thinner in the vapor phase. Figs. 3 A and 3B also show that corrosion performance can be significantly improved even though the amount FFA is reduced and replaced with one of the above-identified additional filming compounds.

[0053] Figs. 4A and Figs. 4B show the percentage change of the corrosion rate for some of the coupons over time. The corrosion rate was measured once per hour for 18 hours and the percentage change refers to the change from the prior measurement. Once the coupons are removed from the autoclave and placed into the electrochemistry cell they will begin to dissolve off the surface. Figs. 4A and 4B show the relative persistence of the films. As can be seen, some of the examples form films that dissolve quickly on the liquid phase coupon, but are more persistent on the vapor phase coupon, and vice-versa.

[0054] LPR Autoclave Experiment

[0055] In this experiment, the comparative example and examples were tested for corrosion rates (mpy) in an LPR autoclave where the electrochemistry can be measured while filmer residuals are present. 500 ml RO water with 200 ppm NaCl is added to the autoclave and the pH is adjusted to 10.0 with ammonium hydroxide. The system is purged with nitrogen for 30 minutes to remove oxygen. The temperature is maintained at 180°C, the pressure is maintained at 145 psig, and the contents are stirred at 500 rpm. The example compositions and comparative example composition are each dosed at 20 ppm, which is the equivalent of 500 ppb OLDA for the examples and 1 ppm OLDA for the comparative example. Linear polarization resistance measurements are taken every 15 minutes for four hours. The results are shown in Fig. 5. As can be seen, the example treatments were more effective in inhibiting corrosion as the comparative example, even though the comparative example included twice as much of the FFA.

[0056] Film Degradation Experiment

[0057] In this experiment, the corrosion inhibitor compositions of the Comparative Example, Example 3, and a nonamine treatment (also for comparison purposes) were tested to determine how quickly the protective film degrades once formed. Mild steel coupons were exposed for 18 hours to water having 100 ppb of the active filming agent. Mild steel coupons were also exposed to water without any active filming agent (a “blank”). In all cases, the pH of the water was adjusted to 10 with ammonium hydroxide and maintained at 350 °C and 2400 psig. For each test, mild steel coupons were mounted both below and above the water level. After this experiment, the coupons were placed in salt water without any filmer treatment, and the corrosion rate was measured after 4 h, 8 h, 12 h, and 16 h.

[0058] Fig. 6A illustrates the degradation rate of the film on the coupons in the liquid phase and Fig. 6B illustrates the degradation rate of the film on the coupons in the vapor phase. The results are reported as a percentage of improved corrosion inhibition relative to the blank. As can be seen, the formulation corresponding to Example 3 appears to have developed a protective film somewhat slower than the nonamine treatment, but once the film was formed the Example 3 film degraded at a significantly slower rate than either the nonamine treatment or the standard FFA treatment of the Comparative Example.

[0059] Total Iron Field Study

[0060] The total iron (ppb) was measured at several locations in a Heat Recovery Steam Generator (HRSG) system to determine the reduction in iron during a unit start, the HRSG had been treated for 3 months with the corrosion inhibition composition of Example 3. The HRSG includes a low pressure drum acting primarily as a feedwater heater to an intermediate pressure drum and a high pressure drum. After an outage of the HRSG, the total iron (ppb) was measured 8 h after start-up and 24 h after start-up in the low pressure drum, the intermediate pressure drum, the high pressure drum, and the condensate. The results are shown in the Table below.

[0061] These results show that 24 hours after the unit was started, the iron levels at each of the locations were substantially reduced, and that at least the high pressure drum and condensate were at or below acceptable limits.

[0062] It will be appreciated that the above-disclosed features and functions, or alternatives thereof, may be desirably combined into different systems or methods. Also, various alternatives, modifications, variations or improvements may be subsequently made by those skilled in the art, and are also intended to be encompassed by the following claims. As such, various changes may be made without departing from the spirit and scope of this disclosure as defined in the claims.

Claims

WHAT IS CLAIMED IS1. A method of treating an aqueous system having corrodible metal surfaces that are in contact with water in a liquid phase and a vapor phase, the method comprising: combining with the water (a) at least one film-forming amine ("FFA") having a primary amine group and an aliphatic hydrocarbon group having 5 to 40 carbon atoms; and (b) at least one additional film-forming compound selected from the group consisting of:(i) an ethoxylated alkyl amine having an ethoxy-substituted amine group and an aliphatic hydrocarbon group having from 5 to 40 carbon atoms, wherein the ethoxylated alkyl amine has from 1 to 25 ethoxy groups;(ii) an alkyl bis amide having at least two aliphatic hydrocarbon groups having 5 to 40 carbon atoms; and(iii) a fatty acid compound that includes at least one carboxylic acid group and an aliphatic hydrocarbon group having from 5 to 40 carbon atoms, an ester of the fatty acid compound, or an alkoxylated product of the fatty acid compound, wherein the at least one FFA and the at least one additional film-forming compound are added to the water in a relative weight ratio that is in a range of from 1 : 10 to 10: 1.

2. The method of claim 1, wherein the additional film-forming compound includes the ethoxylated alkyl amine.

3. The method of claim 1, wherein the additional film-forming compound includes the alkyl bis amide.

4. The method of claim 2, wherein the ethoxylated alkyl amine has from 2 to 15 ethoxy groups.

5. The method of claim 2, wherein the ethoxylated alkyl amine has from 2 to 5 ethoxy groups, and the aliphatic hydrocarbon group of the ethoxylated alkyl amine has from 10 to 24 carbon atoms.

6. The method of claim 3, wherein the alkyl bis amide as a structure corresponding to Formula (I) below:wherein R1and R3are independently a branched or unbranched alkyl group having 10 to 26 carbon atoms, and R2is a branched or unbranched alkyl group having from 2 to 10 carbon atoms.

7. The method of claim 1, wherein the at least one additional film-forming compound includes the alkoxylated product of the fatty acid compound, and wherein the fatty acid compound has from 10 to 24 carbon atoms.

8. The method of claim 1, wherein the water is heated to a temperature in a range of from 100°C to 400°C and has a pressure of from 1,000 psig to 3,000 psig.

9. The method of claim 1, wherein the water has a pH that is in a range of from 8 to 11.

10. The method of claim 1, wherein the at least one FFA and the at least one additional film-forming compound are added to the water in a relative weight ratio that is in a range of from 1 :4 to 4: 1.

11. The method of claim 1, wherein the FFA and the additional film-forming compound are combined with the water so that they are present in the liquid phase of the water at a combined concentration that is in a range of from 20 ppb to 20 ppm.

12. The method of claim 1, wherein the FFA and the additional film-forming compound are combined with the water so that they are present in the liquid phase of the water at a combined concentration that is in a range of from 50 ppb to 1 ppm.

13. The method of claim 1, wherein the metal surfaces are mild steel.

14. A method of treating a boiler system that includes a boiler that generates steam by heating liquid water and operates a temperature in a range of from 100 to 500°C and a pressure of from 100 to 4,000 psig, the method comprising: combining with the water (a) at least one film-forming amine ("FFA") having a primary amine group and an aliphatic hydrocarbon group having 5 to 40 carbon atoms; and (b) at least one additional film-forming compound selected from the group consisting of:(i) an ethoxylated alkyl amine having an ethoxy-substituted amine group and an aliphatic hydrocarbon group having from 5 to 40 carbon atoms, wherein the ethoxylated alkyl amine has from 1 to 25 ethoxy groups; and(ii) an alkyl bis amide having at least two aliphatic hydrocarbon groups having 5 to 40 carbon atoms, wherein the FFA and the additional film-forming compound are combined with the water so that they are present in the liquid water at a combined concentration that is in arange of from 20 ppb to 20 ppm, and are added to the water at a relative weight ratio that is in a range of from 1 :2 to 2: 1.

15. The method according to claim 14, wherein the FFA and the additional filmforming compound are added to the water at a relative weight ratio that is in a range of from 1 : 1.5 to 1.5: 1.

16. The method according to claim 14, further comprising combining with the water a fatty acid compound that includes at least one carboxylic acid group and an aliphatic hydrocarbon group having from 5 to 40 carbon atoms, an ester of the fatty acid compound, or an alkoxylated product of the fatty acid compound.

17. The method according to claim 16, wherein the fatty acid compound is an ethoxylated product of the fatty acid compound.

18. The method according to claim 14, wherein the boiler system includes a first surface that is made of mild steel that contacts the liquid water and a second surface made of mild steel that contacts the steam, and wherein the at least one FFA and the at least one additional film-forming compound form a film on the first surface that inhibits corrosion and form a film on the second surface that inhibits corrosion.

19. A liquid composition that includes:(a) from 40 wt.% to 99 wt.% of water or other solvent;(a) from 0.1 to 10 wt.% of at least one film-forming amine ("FFA") having a primary amine group and an aliphatic hydrocarbon group having 5 to 40 carbon atoms;(b) from 0.1 to 10 wt.% of an additional film-forming compound selected from the group consisting of:(i) an ethoxylated alkyl amine having an ethoxy-substituted amine group and an aliphatic hydrocarbon group having from 5 to 40 carbon atoms, wherein the ethoxylated alkyl amine has from 1 to 25 ethoxy groups;(ii) an alkyl bis amide having at least two aliphatic hydrocarbon groups having 5 to 40 carbon atoms; and(iii) a fatty acid compound that includes at least one carboxylic acid group and an aliphatic hydrocarbon group having from 5 to 40 carbon atoms.

20. The liquid composition of claim 19, wherein the composition includes from 1 wt.% to 5 wt.% of the at least one FFA and from 1 wt.% to 5 wt.% of the at least one additional film-forming compound.

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