WO2020174607A1

WO2020174607A1 - Method for providing corrosion protection to a water-steam circuit

Info

Publication number: WO2020174607A1
Application number: PCT/JP2019/007560
Authority: WO
Inventors: Wolfgang Hater; Andre De Bache; Patrick Kraft
Original assignee: Kurita Water Industries Ltd
Current assignee: Kurita Water Industries Ltd
Priority date: 2019-02-27
Filing date: 2019-02-27
Publication date: 2020-09-03
Anticipated expiration: 2021-08-27
Also published as: JP2022532692A

Abstract

The present invention relates to a method for providing corrosion protection to a water-steam circuit having both internal surfaces made of aluminium or aluminium alloy and internal surfaces made of steel, which method comprises operating the water-steam circuit with water having a pH value, measured at 22°C, in the range of pH 8.8 to 10.0, in particular in the range of pH 9.0 to 9.6, especially in the range of pH 9.2 to 9.6 and containing a film forming amine.

Description

Method for providing corrosion protection to a water-steam circuit

The present invention relates to a method for providing corrosion protection to a water-steam circuit having both internal surfaces made of aluminium or aluminium alloy and internal surfaces made of steel.

The use of aluminium and aluminium alloys in the construction of power plants, in particular in the construction of water-steam-circuits (hereinafter WSC), is gaining in importance. For example, aluminium and aluminium alloys are increasingly used in the construction of tubes in air cooled condensers such as Heller towers and jet spray coolers. Not least due to their low specific weight, the use of aluminium and aluminium alloys offers both construction and economic benefits.

However, aluminium and aluminium alloys are more sensitive to corrosion than steel or non-ferrous metals which are commonly used in the construction of components of WSC. Therefore, the means conventionally taken for corrosion protection of conventional WSC constructed of steel cannot be transferred one to one to WSC having components made of aluminium or aluminium alloys. In fact, the means for corrosion protection have to be adequately adapted in order to meet the requirements of aluminium and aluminium alloys. What is more, corrosion products of aluminium may distribute in the WSC and form deposits on the turbine blades. Further complicating the matter is the fact that other components of water-steam-circuits such as boilers may still require to be made of steel for construction reasons, which have other requirement with regard to the optimum corrosion protection.

Aluminium is an amphoteric metal. International standards, such as standards of the International Association for the Properties of Water and Steam (IAPWS) require that WSC having components made of aluminium or aluminium alloys are operated at pH levels of approximately pH 8.0, e.g. in the range of pH 7.7 to 8.0 (see IAPWS Technical Guidance Document 3 10(2015)). In such WSC corrosion protection is usually achieved by oxygen treatment (OT) at these pH levels. While oxygen treatment at pH 8.0 and a stationary oxygen concentration of about 50 ppb may provide sufficient protection of both the aluminium and the steel components of WSC during continuous operation, steel components will suffer corrosion under these conditions during shutdown or cycling mode operation, because it is not possible to achieve a stationary oxygen concentration under these conditions. Therefore, WSC made of steel components are usually subjected to an all-volatile treatment (AVT) at elevated pH level, e.g. at pH of above pH 8.7, preferably at least pH 9.2 and up to 10, according to the VGB guideline VGB-S-010-T00 or IAPWS Technical Guidance Document 3 10(2015), in order to avoid corrosion of the steel surfaces, especially when the plant, and thus the WSC, is operated in cycling mode. For power plants operated under OT conditions, VGB-S-116-00-2016-04-EN “Conservation of Power Plants” recommends an AVT treatment at elevated pH of 9.2 - 9.5 prior to a wet conservation. Following this regime under cycling mode conditions would mean a frequent change of operating modes which would be extremely difficult to realize, if possible at all.

It is apparent that cycling mode, i.e. discontinuous operation with frequent short-term stand-by periods (off periods), will lead to difficult challenges for plant operators, because every time the WSC is turned off and on, the boiler, steam lines, turbine and auxiliary components go through unavoidably large thermal and pressure stresses, which may cause damage. These challenges will become even more serious, if the WSC comprises both components made of steel and components made of aluminium, in particular because of the different demands of aluminium components and the steel components to the quality of the circulating water.

Film forming amines have been suggested as feed water additives for providing improved corrosion protection of WSC made of steel or copper components. Film forming amines, i.e. long chain alkyl fatty amines and long chain oligoalkylamine fatty amines adsorb to the interior surfaces of WSC components and form a tight protective barrier against corrosive agents. There are numerous studies on film forming agents and their use for corrosion protection. For example, Voges et al., Power Plant Chemistry 2010, 12(3), pp. 132-138 describe the distribution ratio and average surface coverage of film forming amines in steam generator plants. W. Hater et al., Power Plant Chemistry 2014, 16(5), pp. 284-292 describe dry lay-up of steam generators by using a formulation containing a film forming amine and a volatile organic alkalising amine. The corrosion inhibition properties of film forming amines in closed cooling/heater water systems have been investigated by C. Foret et al., Power Plant Chemistry 2014, 16(5), pp. 284-292 using electrochemical impedance spectroscopy. A. Bursik et al., Power Plant Chemistry 2015, 17(6), pp. 342-353 describe an all-volatile treatment in WSC of Fossil and Combined Cycle/HRSG power plants with film forming amine.

So far, the corrosion protection effects of film forming amines have been investigated only at almost neutral pH values of approximately pH 8.0-8.5. It was found that film forming amines provide a certain corrosion protection at these pH levels. However, it is strongly recommended to keep the pH level in this range in order to avoid corrosion of aluminium - see e.g. IAPWS Technical Guidance Document 8 16(2016). One reason for this is that solubility of aluminium oxide increases dramatically at increased pH levels. What is more, aluminium oxide/hydroxide has a significant volatility in steam and thus may transport into the steam turbine and deposit on the turbine blade surfaces. Further complicating the matter is the fact is the low solubility of aluminium oxides/hydroxides which makes it impossible or at least very difficult to remove these deposits chemically. Therefore, just slight corrosion of aluminium parts may cause more severe problems than slight corrosion of other materials of the WSC. Moreover, it is expected that film forming amines may increase volatility of aluminium oxides/hydroxides thereby furthering the undesired transport of aluminium and the formation of deposits.

Detailed description of Invention

It is apparent from the foregoing that there is a strong need for efficient corrosion protection of WSC, having both internal surfaces made of aluminium or aluminium alloy and internal surfaces made of steel because of the different needs of these materials.

Surprisingly, it was found that film forming amines sharply increase the protection of aluminium against corrosion at elevated pH levels of at least pH 8.8, e.g. at pH 8.8 to pH 10, in particular at least pH 9.0, e.g. pH 9.0 to 9.6, which is similar to the protection level at neutral or almost neutral pH of approximately pH 8.0. At these pH levels the steel parts are almost inert to corrosion because of an insoluble magnetite layer formed on the surface of the internal steel parts. Surprisingly, no noticeable transport of aluminium is observed under these conditions.

Therefore, the present invention relates to a method for providing corrosion protection to a water-steam circuit having both internal surfaces made of aluminium or aluminium alloy and internal surfaces made of steel, which method comprises operating the water-steam circuit with water having a pH value, measured at 22°C, in the range of pH 8.8 to 10.0, in particular in the range of pH 9.0 to 9.6, especially in the range of pH 9.2 to 9.6 and containing a film forming amine.

The method is associated with several benefits. First of all, the method allows for efficient prevention or reduction of corrosion of the internal surfaces of components made of aluminium or aluminium alloy under conditions which are also beneficial for the corrosion protection of the internal surfaces of components made of steel. Therefore, the method of the present invention facilitates corrosion protection of water-steam circuits containing both components made of steel and components made of aluminium or aluminium allows. Apart from that, the method of the invention also provides efficient corrosion protection of those components, which are made of non-ferrous metals, such as e.g. copper or copper alloys, such as brass, and nickel base alloys. Moreover, no significant transport of aluminium salts of formation of aluminium containing deposits within the water-steam cycle is observed under these conditions. Therefore, the process of the invention can be broadly applied to water-steam circuits under different operating conditions, i.e. under continuous operation but also under cycling mode conditions or for preparing a lay-up for shut down.

The term “internal surfaces” is understood as those surfaces of the water-steam circuit, which get into contact with the water or the steam circulating in the water-steam circuit und thus are principally subjected to conditions which may cause corrosion.

Typical components of water-steam circuits, which have internal surfaces, include but are not limited to steam generators, also called boilers, condensers, coolers and pipes connecting the different components. As further components, they may also include feed water tanks, deaerating heaters for removing corrosive gases from the feedwater, economizers and flash tanks. If the water-steam circuit is part of a power plant it will also have one or more turbines for driving generators. Furthermore, a water-steam circuit may also include a pretreatment system for adjusting quality parameters of the water used for operating the water-steam circuit, such as concentration of salts and pH value.

While steam generators and turbines are frequently made of steel, other components, such as condensers or coolers and pipes may be made of aluminium or aluminium alloys.

The type of steel or aluminium alloy will depend from the type of component and the constructional demands thereof. Steels types frequently used for the construction of components of water-steam circuits may be high alloy steels or low-alloy steels and include, but are not limited to, e.g. martensitic steels, in particular martensitic steels having a chromium content of 9 - 14 %, such as the martensitic steels T/P92 and VM12/VM12-SHC, austenitic steels and ferritic steels, e.g. low alloy ferritic steels such as T/P24, but also nickel base alloys. Typical aluminium materials include in particular pure aluminium having an aluminium content of > 99 % and aluminium alloys such as aluminium-magnesium alloys, aluminium-magnesium-silicon alloys and aluminium-zinc alloys.

In order to ensure sufficient corrosion protection of the internal surfaces of the water-steam circuit, the average concentration of the film forming amine in the water used for operating the water-steam circuit is preferably in the range from 0.01 to 5.0 mg/kg, in particular in the range from 0.05 to 2.0 mg/kg and especially in the range from 0.1 to 1.5 mg/kg. For this, the film forming amine is dosed to the water used for operating the water-steam circuit in such an amount that at least during operation of the water-steam circuit the above concentrations are achieved.

In this context, the term “average concentration” is understood as a time average of the concentration, which means that during the operation time of the water-steam circuit the concentration of the film forming amine in the water used for operating the water-steam circuit is on average within the above ranges. In fact, the concentration of the film forming amine in the water must not necessarily be in the above range at every point of time, when the water-steam circuit is operated. Rather, it is possible that the concentration may be outside the above ranges for a certain period of time. However, any period where the concentration of the film forming amine is outside the above ranges will usually not exceed 4 h, in particular 2 h. Moreover, during these periods the concentration will usually not exceed 2 times of the upper limit given above and it will not or only shortly, preferably for not more than 4 h, drop to zero.

Here and in the following the terms “pH level” and “pH value” are used synonymously.

The concentration ranges given above refer to the concentration of the film forming amine in those parts of the water-steam circuit, where the water used for operating the water-steam circuit is in the liquid state. A skilled person will also understand that the concentration of the film forming amine in the water used for operating the water-steam circuit may vary within the water-steam circuit to a certain extent and not be the same at each and every point of the water-steam circuit. However, the deviation will not be very high and generally the average concentration ranges given above are maintained in any part of the water-steam circuit where the water is in the liquid state.

Suitable film forming amines for use in the method of the present invention are hydrophobic amines having at least one long chain hydrocarbon radical having preferably from 12 to 22 carbon atoms. Examples include fatty amines and oligoamines wherein at least one long chain hydrocarbon radical having preferably from 12 to 22 carbon atoms is attached to one nitrogen atom of the oligo amine. In addition to the long chain hydrocarbon radical the film forming amines may bear hydroxyalkyl or oligoalkylenoxide groups attached to the nitrogen atom(s). Compounds, which are suitable as film forming amines are the compounds of the following formula (I) and mixtures thereof:

R¹-(NR³-R²)_n-NR⁴R⁵ (I)

wherein
n is 0, 1 or 2;
R¹ is a linear or branched, acyclic hydrocarbon group having 12 to 22 carbon atoms, in particular 16 to 20 carbon atoms;
R² is C₂-C₄-alkanediyl, in particular 1,2-ethandiyl or 1,3-propandiyl;
R³, R⁴, R⁵ are identical or different and independently selected from the group consisting of H, C₁-C₄ alkyl and -(C_mH_2m-2O)_p-H, wherein m is 2, 3, or 4, in particular 2, and p is = 1, 2, 3 or 4.

In the context of formula (I), R¹ is preferably a linear, i.e. straight chain, hydrocarbon group having 12 to 22 carbon atoms, in particular 16 to 20 carbon atoms, in particular a saturated linear hydrocarbon group having 12 to 22 carbon atoms, in particular 16 to 20 carbon atoms, or an unsaturated linear hydrocarbon group having 12 to 22 carbon atoms, in particular 16 to 20 carbon atoms, and 1, 2 or 3 C=C-double bonds, in particular 1 or 2 C=C-double bonds. In particular, R¹ is a straight chain hydrocarbon group having 16 to 20 carbon atoms, especially a saturated straight chain hydrocarbon group having 16 to 20 carbon atoms or an unsaturated straight chain hydrocarbon group having 16 to 20 carbon atoms and 1 or 2 C=C-double bonds. Especially, R¹ is a straight chain hydrocarbon group having 18 carbon atoms, especially a saturated linear hydrocarbon group having 18 carbon atoms or an unsaturated straight chain hydrocarbon group having 18 carbon atoms and 1 C=C-double bond, especially preferred R¹ is an unsaturated straight chain hydrocarbon group having 18 carbon atoms and 1 C=C-double bond.

Examples of groups R¹ include, but are not limited to lauryl (n-dodecyl), myristyl (n-tetradecyl), cetyl (n-hexadecyl), margaryl (n-heptadecyl), stearyl (n-octadecyl), arachidyl (n-eicosanyl), behenyl (n-docosenyl), palmitoleyl (9-hexadecen-1-yl), oleyl(9-hexadecen-1-yl), 11-octadecen-1-yl, 9,12-octadecadien-1-yl and 9,12,15-octadecatrien-1-yl and mixtures thereof, such as tallowalkyl (mixture of linear alkyl which mainly consists of linear C₁₆/C₁₈ alkyl), and cocoalkyl (mixture of linear alkyl, which mainly consists of C₁₂-C₁₈-alkyl). In a very special embodiment, R¹ is oleyl, which means an unsaturated C₁₈H₃₅-radical.

In the context of formula (I), C₂-C₄-alkanediyl is understood to mean a saturated hydrocarbon group having 2, 3 or 4 carbon atoms, which may be linear or branched and which is preferably linear. Hence, R² is ethanediyl, propanediyl or butanediyl, in particular 1,2-ethanediyl, 1,3-propanediyl or 1,4-butandiyl, and especially 1,3-propanediyl.

In the context of formula (I), C₁-C₄-alkyl denotes a linear or branched alkyl radical comprising from 1 to 4 carbon atoms, for example CH₃, C₂H₅, n-propyl, CH(CH₃)₂, n-butyl, CH(CH₃)-C₂H₅, CH₂-CH(CH₃)₂ and C(CH₃)₃.

In the context of formula (I), R³, R⁴ and R⁵ are preferably hydrogen or -(C₂H₄O)_p-H.

In the context of formula (I), n is preferably 0, 1 or 2. In particular, the film forming amines are compounds of the formula (I), where n is 1 or 2, or mixtures comprising at least 80 % by weight, based on the total amount of film forming amine, of one or more compounds of formula (I), where n is 1 or 2. In particular, the film forming amines consist to at least 80 % by weight, based on the total amount of film forming amine, of one or more compounds of formula (I), where n is 1 or 2. Preferably, the amount of compounds of formula (I), where n is 0 does not exceed 20 % by weight of the total amount of film forming amine.

More preferably, the film forming amines consist to at least 80 % by weight of compounds of formula (I), where n is 1 or 2, and where
R¹ is a straight chain hydrocarbon group having 16 to 20 carbon atoms, especially a saturated straight chain hydrocarbon group having 16 to 20 carbon atoms or an unsaturated straight chain hydrocarbon group having 16 to 20 carbon atoms and 1 or 2 C=C-double bonds.
R² is 1,2-ethanediyl, 1,3-propanediyl or 1,4-butandiyl, and especially 1,3-propanediyl
R³, R⁴ and R⁵ are preferably hydrogen or -(C₂H₄O)_p-H.

In a particular group of embodiments, R³, R⁴ and R⁵ are hydrogen. Examples of particular amines of formula (I) with n being 0 and R³, R⁴ and R⁵ being hydrogen are octadecylamine, oleylamine and tallowamine. Examples of compounds of formula (I) with n being 1 or 2 and R³, R⁴ and R⁵ being hydrogen include but are not limited to N-oleyl-1,3-diaminoethane, N-tallow-1,3-diaminopropane, 1-cocoalkyl-1,3-diaminopropane, stearyl-1,3-diaminopropane, N-[3-(cocoalkylamino)propyl]propane-1,3-diamine (=cocoalkyldipropylentriamine), N-[3-(tallowalkylamino)propyl]propane-1,3-diamine (=tallowalkyldipropylentriamine), N-[3-[3-(cocoalkylamino)propylamino]-propyl]propane-1,3-diamine (= cocoalkyltripropylentetramine) and N-[3-[3-(tallowalkyl-amino)propyl-amino]propyl]propane-1,3-diamine (= tallowalkyltripropylentetramine). Examples of commercial compositions of film forming amines, which contain at least 80 % by weight, based on the total weight of the film forming amine, of compounds of the formula (I) with n being 1 or 2 are the Duomeen(trademark) brands of AkzoNobel, such as Duomeen(trademark) T, Duomeen(trademark) O and Duomeen(trademark) C, the Triameen(trademark) brands of AkzoNobel, such as Triameen(trademark) T and Triameen(trademark) C, the Dinoram(trademark) brands of Archem, such as Dinoram(trademark) O, and Inipol(trademark) DS. Examples of commercial compositions of film forming amines, which contain at least 80 % by weight, based on the total weight of the film forming amine, of compounds of the formula (I) with n being 3 and R³, R⁴ and R⁵ being hydrogen are the Tetrameen(trademark) brands of AkzoNobel, such as Tetrameen(trademark) T.

In another particular group of embodiments, at least one of R³, R⁴ and/or R⁵ are -(C_mH_2m-2O)_p-H while the others of R³, R⁴ and R⁵ are hydrogen. These amines are also termed alkoxylated fatty amines. In this group of embodiments m is preferably 2. In this group of embodiments, n is preferably 0, 1 or 2. Preference is given to alkoxylated fatty amines which contain at least 80 % by weight of compounds of the formula (I), where n is 1 or 2. Preferably the total number of repeating units C_mH_2m-2O, in particular of groups CH₂CH₂O, per molecule, is in the range from 2 to 15, in particular in the range from 2 to 6. A skilled person will immediately understand that alkoxylated fatty amines may be mixtures of compounds of the formula (I) having a different number of repeating units C_mH_2m-2O, in particular of groups CH₂CH₂O. Hence, the total number of repeating units C_mH_2m-2O, in particular of groups CH₂CH₂O is understood as the number average of these groups in the alkoxylated fatty amines.

Alkoxylated fatty amines are known and commercially available. They can be prepared by common methods, e.g. by reacting a compound of the formula (I), where R³, R⁴ and R⁵ are hydrogen, with at least one C₂-C₄-alkylene oxide, in particular with ethylene oxide. When compounds of formula (I) are employed in the alkoxylation, where R³, R⁴ and R⁵ are hydrogen, at least one of the hydrogens R³, R⁴ and R⁵ is replaced by polyether chains -(C_mH_2m-2O)_p-H in the resulting product compound. Frequently all of the hydrogens R³, R⁴ and R⁵ are replaced by polyether chains -(C_mH_2m-2O)_p-H in the resulting product compound.

In a particular group of embodiments, a fatty amine or fatty amine mixture based on natural fatty amines is employed for alkoxylation. In these compounds n is 0. Amines based on vegetable or animal fat typically comprise a mixture of at least one of the following amines: oleic amine, palmitic amine, stearic amine, myristic amine, linoleic amine, oleyl amine, decyl amine, undecyl amine, dodecyl amine, tridecyl amine, tetradecyl amine, hexadecyl amine, octadecyl amine. Examples of fatty amine mixtures based on natural fatty amines are fatty amines derived from tallow, coconut oil, sunflower oil, rape oil, soybean oil or palm kernel oil. Suitable fatty amines of formula (I) with n = 0 are commercially available, e.g. cocoamine as Ethomeen C/12, Ethomeen C/15, Ethomeen C/25, Berol 398 or tallowamine as Ethomeen T/12, Ethomeen T/12 LC, Ethomeen T/15, Ethomeen T/25, Ethoduomeen T/13, Ethoduomeen T/22, Ethoduomeen T/25 or oleylamine as Berol 302, Ethomeen O/12, Ethomeen O/12 LC, Ethomeen OV/17, Ethomeen OV/22. Suiatable alkylene oxides for alkoxylation are ethylene oxide (EO), propylene oxide (PO), 1,2-butylene oxide, 2,3-butylene oxide and mixtures thereof.

A further particular group of embodiments relates to compound mixtures of formula (I), where n = 0 and least one of R³, R⁴ and/or R⁵ are -(C_mH_2m-2O)_p-H, in particular 2-hydroxyethyl, while the others of R³, R⁴ and R⁵ are hydrogen. Examples include ethoxylated fatty amines selected from ethoxylated tallow amine, ethoxylated coco amine, ethoxylated soya amine, ethoxylated oleyl amine, ethoxylated decyl amine, ethoxylated dodecyl amine, ethoxylated tridecyl amine, and ethoxylated tetradecyl amine with preference given to ethoxylated tallow amine with 3 to 15 EO, ethoxylated coco amine with 3 to 15 EO, ethoxylated oleyl amine with 3 to 15 EO, ethoxylated dodecyl amine with 3 to 15 EO, ethoxylated tridecyl amine with 3 to 15 EO, ethoxylated tetradecyl amine with 3 to 15 EO, ethoxylated hexadecyl amine with 4 to 15 EO, ethoxylated octadecyl amine with 3 to 15 EO, and mixtures thereof. Examples of particular amines of formula (I) with n being 0 and R³, R⁴ and R⁵ are hydroxyethyl are commercially available as the Ethomeen T series from Akzo Nobel, such as Ethomeen C/12, Ethomeen C/15, Ethomeen C/25, Ethomeen T/12, Ethomeen T/12 LC, Ethomeen T/15, Ethomeen T/25, Ethomeen O/12, Ethomeen O/12 LC, Ethomeen OV/17, Ethomeen OV/22.

A further particular group of embodiments relates to compound mixtures, consisting to at least 80 % of compounds of formula (I), where n is 1 or 2 and least one of R³, R⁴ and/or R⁵ are -(C_mH_2m-2O)_p-H, in particular 2-hydroxyethyl, while the others of R³, R⁴ and R⁵ are hydrogen. Preferably the total number of repeating units C_mH_2m-2O, in particular of groups CH₂CH₂O, per molecule, is in the range from 3 to 15, in particular in the range from 3 to 6. Particular examples include ethoxylated tris(2-hydroxyethyl)-N-tallowalkyl-1,3-diaminopropane, ethoxylated N-oleyl-1,3-diaminoethane, ethoxylated N-tallow-1,3-diaminopropane, ethoxylated 1-cocoalkyl-1,3-diaminopropane, ethoxylated stearyl-1,3-diaminopropane, ethoxylated N-[3-(cocoalkylamino)-propyl]propane-1,3-diamine (=ethoxylated cocoalkyldipropylentriamine), ethoxylated N-[3-(tallowalkylamino)-propyl]-propane-1,3-diamine (=ethoxylated tallowalkyl-dipropylenetriamine), ethoxylated N-[3-[3-(cocoalkylamino)propylamino]-propyl]propane-1,3-diamine (=ethoxylated cocoalkyltripropylentetramine) and ethoxylated
N-[3-[3-(tallowalkyl-amino)propyl-amino]propyl]propane-1,3-diamine (=ethoxylated tallowalkyltripropylentetramine). In the aforementioned compounds the degree of ethoxylation, i.e. the sum of p is preferably in the range from 3 to 15 and in particular from 3 to 6. These compound mixtures are commercially available as the Etoduomeen T series from Akzo Nobel, such as Ethoduomeen T/13, Ethoduomeen T/22, Ethodumeen T/25.

Preferred examples of film forming amines for use in the method of the invention include oleyl amine, N-(3-aminopropyl)oleyl amine, mixtures of oleyl amine and N-(3-aminopropyl)oleyl amine, ethoxylated N-(3-aminopropyl)oleyl amine, and mixtures of ethoxylated N-(3-aminopropyl)oleyl amine and ethoxylated oleylamine.

In the context of the present invention, particular preference is given to film forming amines, which comprise at least 80 % by weight, based on the total amount of film forming amine, of one or more compounds of the formula (I), wherein
n is 1 or 2,
R¹ is a straight chain hydrocarbon group having 16 to 20 carbon atoms, especially a saturated straight chain hydrocarbon group having 16 to 20 carbon atoms or an unsaturated straight chain hydrocarbon group having 16 to 20 carbon atoms and 1 or 2 C=C-double bonds, and
R² is 1,3-propandiyl;
R³, R⁴ and R⁵ are hydrogen or at least one of R³, R⁴ and/or R⁵ are -(C_mH_2m-2O)_p-H, in particular -(C₂H₄O)_p-H, while the others of R³, R⁴ and R⁵ are hydrogen, where the total number of p, is either 0 or 3 to 15 especially 3 to 6.

Even more preference is given to to film forming amines, which comprise at least 80 % of compounds of the formula (I), where n is 1,
In the context of the present invention, particular preference is given to film forming amines, which comprise at least 80 % by weight, based on the total amount of film forming amine, of one or more compounds of the formula (I), wherein
n is 1,
R¹ is a straight chain hydrocarbon group having 18 carbon atoms,
R² is 1,3-propandiyl;
R³, R⁴ and R⁵ are hydrogen or all of R³, R⁴ and R⁵ are -(C₂H₄O)_p-H, where the total number of p, is either 0 or 3 to 15 especially 3 to 6.

In order to monitor the concentration of the film forming amine and to keep it in the above ranges, the concentration of the film forming amine is usually determined periodically or continuously in at least one point of the water-steam-circuit in particular in at least two points of the water-steam-circuit. In this regard, further reference is made to point 8.2 of the IAPWS Technical Guidance Document 8 16(2016) and the references cited therein. Suitable points for determining the concentration of the film forming amine are in particular those, where the water is in the liquid state. Preferred points for controlling the concentration of the film forming amine include e.g.
- the feed water, i.e. the water which is fed from the feed tank to the water-steam circuit;
- the condensate water and
- the water of the steam drum, i.e. the water contained in the steam generating part of the boiler.

For monitoring the actual concentration of the film forming amine, usually a sample is taken and the concentration of the film forming amine in the sample is determined by a standard method, e.g. the British standard BS 2690: Part 117:1983, by photometrical methdos as described by K. Stiller et al. Power Plant Chemistry 2011, 13(10), pp. 602-611, M. Lendi et al., Power Plant Chemistry 2014, 16(1), pp. 4-11, EP 562210, or by the colorimetric method described in GB 994 051. Of course, it is also possible to determine the concentration of the film forming amine by inline measurements, e.g. by passing a portion of the water used for operating the water-steam circuit through a bypass having a flow-through sensor or flow-through measuring cell e.g. by the methods of M. Lendi et al. Power Plant Chemistry 2015, 17(1), pp. 8-13, or B. Hoock et al. Power Plant Chemistry 2015, 17(5), pp. 283-293. In this regard, further reference is made to point 8.4 of the IAPWS Technical Guidance Document 8 16(2016) and the references cited therein.

In order to keep the concentration of the film forming amine in the above ranges, any film forming amine which is consumed will be replenished in such amounts that the film forming amine is present in the concentration ranges given above. For this, the film forming amine is dosed to the water used for operating the water-steam circuit in such an amount that at least during operation of the water-steam circuit the above concentrations are achieved.

To maintain a proper concentration of the film forming amine in the water used for operating the water-steam circuit the film forming amine may be added in portions or continuously. The amount or rate of addition will of course depend from the the concentration of the film forming amine determined in the control measurements. In case the water-steam circuit was previously operated without the film forming amine, it is preferred that the amount of film forming amine which is initially added will result only in a low concentration which is close to the lower limit given above and that further additions will be made in order to achieve a preferred concentration range. In particular, an initial overdosage should be avoided.

For this, the film forming amine can principally added at any point of the water-steam circuit, in particular at a point, where the water is present in liquid form. Suitable points for addition of the film forming amine are principally known to a skilled person, e.g. from A. Bursik et al., Power Plant Chemistry 2015, 17(6), pp. 342-353 and from IAPWS Technical Guidance Document 8 16(2016), point 8.5 and the references cited therein. Suitable points include any point between the feed water tank and the boiler, such as feedwater pump inlet of the boiler, the deaerating heater (deaerator), in particular the deaerator outlet, the economizer, in particular the feedpump inlets of the low pressure or high pressure economizer circuits, the condenser and into the pipeline to an air cooled condenser, condensate extraction pump and/or drum. It is preferred to add at least a portion of the film forming amine into the condensate, in particular at the condensate discharge pump.

In order to ensure high corrosion protection of both internal surfaces made of aluminium or aluminium alloy and internal surfaces made of steel, the pH level of the water used for operating the water-steam circuit is in the range from pH 8.8 to pH 10 and in particular in the range from pH 9.0 to pH 9.6. In this context, the pH ranges given here refer to the pH value as determined at 22°C. The pH is usually determined by an electrochemical method, e.g. by using a commercially available pH meter, which usually includes a glass electrode or a combination thereof with a reference electrode. The procedures for measuring the pH are known and described e.g. in DIN EN ISO 10253:2012-04 (see also point 3.1.3 of IAPWS Technical Guidance Document 2 09(2015)). It is apparent for a skilled person that in some cases it may not possible to measure the pH at 22°C. However, it is not necessary to measure the pH level at exactly 22°C because a skilled person is familiar with the temperature dependence of pH level. Therefore, it is possible to measure the pH level at a temperature different from 22°C and making proper corrections. Modern pH measurement equipment usually have temperature compensation means. Frequently, the pH level will be measured in samples which have a temperature in the range from 20 to 27°C in order to minimize temperature effects.

During the operation time of the water-steam circuit the pH value of the water used for operating the water-steam circuit is on average within the above ranges. In fact, the pH value of the water must not necessarily be in the above range at every point of time, when the water-steam circuit is operated. Rather, it is possible that the pH value may be outside the above ranges for a short period of time. However, any period where the pH level is outside the above ranges will usually not exceed 1 h, in particular 30 min. to avoid an increase of corrosion. Moreover, during these periods the pH level will usually not deviate by more than 0.2 pH units, in particular not more than 0.1 pH units of the limits given above.

A skilled person will also understand that the pH level of the water used for operating the water-steam circuit may vary within the water-steam circuit to a certain extent and not be the same at each and every point of the water-steam circuit. However, the deviation will not be very high and generally the above average pH levels are maintained in any part of the water-steam circuit where the water is in the liquid state.

In order to monitor the pH level of the water used for operating the water-steam circuit and to keep it in the above ranges, the pH level is usually determined periodically or continuously in at least one point of the water-steam-circuit in particular in at least two points of the water-steam-circuit. Suitable points for determining the pH level are in particular those, where the water is in the liquid state. Preferred points for controlling the pH level include e.g.
- the feed water, i.e. the water which is fed from the feed tank to the water-steam circuit;
- the condensate water and
- the water of the steam drum, i.e. the water contained in the steam generating part of the boiler.

For monitoring the actual pH level of the water used for operating the water-steam circuit, a sample may be taken and the pH of the sample is determined according a standard procedure as described above, in particular according to the procedure described in DIN EN ISO 10253:2012-04. Of course, it is also possible to determine the pH value by inline measurements, e.g. by passing a portion of the water used for operating the water-steam circuit through a bypass having a flow-through measuring cell equipped with a pH meter.

In order to keep the pH level in the above ranges, it will usually be necessary to adjust the pH by addition of a base. While the film forming amine itself is a base, it may not be sufficient to rely for pH adjustment on the addition of the film forming amine and the addition of a further base is usually required. Suitable further bases include sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium phosphate, ammonia, volatile amines such as cyclohexylamine, N,N-diethylamino ethanol, 2-aminoethanol (= monoethanolamine), morpholine, methoxylpropylamine, thrmethylamine, trimethylamine, diglycolamine, aminomethylpropanole, iospropoxypropylamine and mixtures thereof. For this, the base can principally added at any point of the water-steam circuit, in particular at a point, where the water is present in liquid form. Suitable points for addition of the base art those mentioned above for the addition of the film forming amine and include e.g. the feedwater tank, any point between the feed water tank and the boiler, such as feedwater pump inlet of the boiler, the deaerating heater (deaerator), in particular the deaerator outlet, the economizer, in particular the feedpump inlets of the low pressure or high pressure economizer circuits, the condenser and into the pipeline to an air cooled condenser, condensate extraction pump and/or drum.

To maintain a proper pH level of the water used for operating the water-steam circuit the further base may be added in portions or continuously. The amount or rate of addition will of course depend from the outcome of the pH measurements.

Furthermore, it has been found beneficial to keep the conductivity of the water used for operating the water-steam circuit at a level of at most 30 μS/cm, in particular at most 20 μS/cm or at most 10 μS/cm. The conductivity values given here refer to the specific conductivity of a sample of the water used for operating the water-steam circuit as determined at 22°C. The conductivity can be determined by standard procedures as described e.g. in DIN EN 27888:1993-11. It is apparent for a skilled person that in some cases it may not possible to measure the pH at 22°C. However, it is not necessary to measure the conductivity at 22°C because a skilled person is familiar with the temperature dependence of conductivity. Therefore, it is possible to measure conductivity at a temperature different from 22°C and make proper corrections. Modern conductivity meters usually have temperature compensation means. Frequently, the conductivity is measured in samples which have a temperature in the range from 20 to 27°C in order to minimize temperature effects.

During the operation time of the water-steam circuit the conductivity of the water used for operating the water-steam circuit is on average below the above limits. In fact, the conductivity of the water must not necessarily below the above limits at every point of time, when the water-steam circuit is operated. Rather, it is possible that the conductivity may be slightly higher than the above limits for a short period of time. However, any period where the conductivity is higher than the above limits will usually not exceed 4 h, in particular 2 h. Moreover, during these periods the conductivity will usually not exceed 50 μS/cm, in particular not exceed 30 μS/cm or 20 μS/cm.

A skilled person will also understand that the conductivity of the water used for operating the water-steam circuit may vary within the water-steam circuit to a certain extent and not be the same at each and every point of the water-steam circuit. However, the deviation will not be very high and generally the above limits of conductivity are maintained in any part of the water-steam circuit where the water is in the liquid state.

In order to monitor the conductivity of the water used for operating the water-steam circuit and to keep it in the above ranges, the conductivity is usually determined periodically or continuously in at least one point of the water-steam-circuit in particular in at least two points of the water-steam-circuit. Suitable points for determining the conductivity of the water used for operating the water-steam circuit are those, where the water is in the liquid state. Preferred points for controlling the pH level include e.g.
- the feed water, i.e. the water which is fed from the feed tank to the water-steam circuit;
- the condensate water and
- the water of the steam drum, i.e. the water contained in the steam generating part of the boiler.

For monitoring the actual conductivity of the water used for operating the water-steam circuit, a sample may be taken and the conductivity of the sample is determined according a standard procedure as described above, in particular according to the procedure described in DIN EN 27888:1993-11. Of course, it is also possible to determine the conductivity value by inline measurements, e.g. by passing a portion of the water used for operating the water-steam circuit through a bypass having a flow-through measuring cell equipped with a conductivity meter.

In order to keep the conductivity below the above limits, it may be necessary to remove ions causing the conductivity from the water. For this, the water circulating in the water-steam circuit may be conducted through a bed of an ion-exchange resin, in particular a mixed bed of an cation exchange resin and an anion exchange resin to remove any ionic impurities. These units are also termed polishing units. Preferably, the condensate is conducted through the polishing unit.

The method of the present invention may be applied principally to any water-steam circuit having internal surfaces made of steel and internal surfaces made of aluminium. The method of the present invention is particularly suitable for fulfilling the high demands of water-steam circuits, which are part of a power-plant, including water-steam circuits of fossil power plants, such as coal fired power plants and gas turbine power plants, of biogas power plants, of nuclear power plants and the like. The method of the present invention is especially suitable for fulfilling the high demands of water-steam circuits, which are part of a power-plant, that are operated in cycling mode.

In contrast to continuous mode, cycling mode is understood as discontinuous operation with frequent short-term stand-by periods (off periods). In a power plant cycling mode is understood similarly and means the operation of electric generating units at varying load levels (power demand), including on/off and low load variations, in response to changes in system load (demand) requirements. The method of the invention allows for efficient and economic corrosion protection under these challenging conditions.

The following figures and examples shall further elucidate the present invention.

Figure 1a shows a Nyquist plot of an electrochemical impedance measurement of an aluminium electrode in deionised water containing 0.2 g/L of NaCl at pH 9.2 and 50°C according to example 1 after a treatment time of 8 h. The polarization resistance derived from the plot is 3.0 kΩcm² indicating insufficient formation of a corrosion protection layer. Figure 1b shows a Nyquist plot of an electrochemical impedance measurement of an aluminium electrode in deionised water, containing 0.2 g/L of NaCl and 4 ppm of a film forming amine consisting mainly of N-(3-aminopropyl)oleyl amine, at pH 9.2 and 50°C according to example 1 after a treatment time of 8 h. The polarization resistance derived from the plot is 6.85 kΩcm² indicating formation of a corrosion protection layer. Figure 1c shows a Nyquist plot of an electrochemical impedance measurement of an aluminium electrode in deionised water, containing 0.2 g/L of NaCl and 4 ppm of a film forming amine consisting mainly of ethoxylated N-(3-aminopropyl)oleyl amine (3 EO), at pH 9.2 and 50°C according to example 1 after a treatment time of 8 h. The polarization resistance derived from the plot is 6.10 kΩcm² indicating formation of a corrosion protection layer.

Examples

Example 1: Electrochemical Impedance Measurements

For electrochemical impedance measurements the following equipment was used
- rotating disc Hach EDI 101 with speed control unit CTV101 (500 rpm);
- potiometer Autolab PG Stat 12 controlled by nova 1.11 software (Methrom):
- Working electrode: Aluminium rod (purit > 99.999 %) having a diameter of 5 mm and a tip surface of 0.196 cm²;
- counter electrode: Radiometer platinum;
- Origalys Ag/AgCl reference electrode;
- 600 mL beaker;
- Heating plate;
- pH-meter Knick Portamess with temperature compensation unit and a SE102N electrode;
- Pt 100 thermometer for temperature control.

The working electrodes were prepared by grinding the Al electrode tip at 150 rpm using a grinder and silicon carbide grinding paper with a grit of P4000 until a plane surface is accomplished. This metal surface is polished to a so called “mirror effect”.

Test solutions were prepared as follows:
Blank solution: 0.2g (+/- 0.005g) of NaCl p.a. was weighed into a 1L volumetric flask and filled up to 1 L with deionized water. The pH was adjusted with 0.05 mol/L NaOH or 0.05 mol/L HCl depending of the target pH (8.2, 9.2 or 9.7).
Sample with film forming amine: A solution of the film forming amine in deionized water having a concentration of the film forming amine of 1000 ppm was prepared. From this solution 4 mL were added to the blank water to the total volume of 1 L. The pH was adjusted with 0.05 mol/L NaOH or 0.05 mol/L HCl depending of the target pH (8.2, 9.2 or 9.7).

The following film forming amines were used:
Film forming amine 1 (FFA 1): A commercial product formulation, wherein the film forming amine essentially consists of N-(3-aminopropyl)oleyl amine.
Film forming amine 2 (FFA 2): A commercial product formulation, wherein the film forming amine essentially consists of ethoxylated N-(3-aminopropyl)oleyl amine having a total of three hydroxyethyl groups per molecule.

Test setup:
400 mL of the test solution mentioned above were filled into 600 mL beaker and the pH was adjusted to the target pH value. In case of test at 50°C the solution was heated up to this temperature on a heating plate. During the trial the temperature was maintained by the heating plate and controlled via a Pt-100 thermometer. The rotating disk working electrode with the aluminum electrode tip, the Pt-reference electrode and the Ag/AgCl reference electrode were placed into the solution as follows: Going from the electrode tip in the middle: 0.03 cm to the left the counter electrode was placed and 4.5 cm on the right the reference electrode was placed. The electrode tip was placed about 90% deep into the solution and the other electrodes are placed about the same height into the solution.

The test was started within 2 minutes after the electrode tip had been grinded to avoid any oxidation on the surface and to guarantee the reproducibility of the test.
The speed control unit of the rotating disk was started with a rotation speed of 500 rpm.

The measurement is started with an open circuit potential (OCP). For this, the voltage of the working electrode is measured against a reference electrode in order to set a start potential for the actual measurement. The actual potentiostatic measurement is conducted by a frequency scan with frequency response analyzer (FRA). All key parameters of the OCP and FRA are mentioned below.

Test - parameters:
- Current range: 1mA,
- OCP determination max 120 sec.,
- Detection limit: 10^-6,
- Amplitude: 0,01,
- Logarithmic,
- Frequencies: 65000 Hz to 0,005 Hz (72 frequencies total),
- Integration time: 0.125 sec.,
- Automatic current range: from 100 nA to 100mA,
- Wave type: single sine;

For a standard test 5 repetitions every 20 minutes are made and for the long term 11 measurements at the following time intervals: 0 h, 0.5 h, 1 h, 2 h, 4 h, 8 h, 12 h , 18 h, 24 h, 36 h and 48h.

From the observed parameters (frequency ω, excitation signal E_t, response signal I_t and the phase shift Ф), the impedance Z(Ф) was calculated, which is a complex number having a real part Z’ and an imaginary part Z’’ which are shown as a Nyquist plot: -Z´´ vs Z´ or Bode plot. Further reference is made to C. Foret et al., Power Plant Chemistry 2014, 16(5), pp. 284-292, in particular to equations (1) to (4) on page 364. The evaluation of the data can be done either graphical or calculated via nova software or Excel. The results of the measurements are converted with the metal surface value of 0,196cm² in order to get the actual results in Z´´ vs Z´ (Ω*cm²). From the Nyquist plot, the polarization resistance R_p can be calculated as from the intercept of the Nyquist plot with the X axis at low frequency Z’(ω→0) and the intercept at high frequency Z’(ω→∞) according to the following equation R_p= Z’(ω→0) - Z’(ω→∞). Possible fittings for determining the polarization resistance R_p are made by nova software. The higher the polarization resistance R_p the better the corrosion resistance. For practical reasons it is sufficient to calculate polarization resistance R_p by the following equation:
R_p= Z’(ω = 0.32 Hz) - Z’(ω = 63 kHz).

The results of the measurements and the measurement conditions are given in the following table 1:

From the data it can be seen that the addition of film forming amine results in an increased polarization resistance R_p and thus in a better the corrosion resistance. Surprisingly, even high pH values of 9.2 and 9.7 are tolerated by aluminium even at elevated temperature. The R_p data at pH 9.7 show a decrease for the blank solution with time, indicating corrosion, whereas the values for the FFA1 strongly increase with time. Apparently, at this pH the corrosion protection by FFA1 takes more time.

Example 2: Investigation of FFA induced Carry-Over of Aluminium Salts

For evaluating whether film forming amines further the carry over of aluminium salts the following experiment was conducted in a so-called First Condensate Corrosion apparatus (FFC apparatus). The FFC apparatus includes a 3-neck 4 L round bottom flask equipped with a nitrogen inlet in one of the sideward necks, a vertical heating tube with a heating mantle connected to the central neck of the round bottom flask, a condenser at the distal end of the heating tube, a return line equipped with a mantle cooler and having means for discharging condensate probe downstream of the mantle cooler and a nitrogen outlet downstream the means for discharging condensate (condensate sampling unit), the return line being connected to the other sideward neck of the round bottom flask. The FFC apparatus also includes a heating bath for heating the round bottom flask.

Blank Trial:
3 L of ultrapure water and approx. 5mg/L aluminum (as aluminium sulfate) were filled into the 4 L round bottom flask. After 5 min of stirring a sample was taken in order to determine the actual concentration of aluminium in the flask, which was 5.6 mg/L. Then the solution was heated up with maximum heating rate (heating mantle + heating bath). The solution was stirred at 250rpm. After the first condensate flew back into the flask, every hour a sample of the condensate was taken (4h sampling time in total) from the condensate sampling unit and the aluminium concentration in the condensate was determined. No aluminium was found in the condensate. The concentration of aluminium in the flask was still 5.6 mg/L.

Trial 1: With 5 ppm Al and 4 ppm Film Forming Amine 1:

In a first step, the FFC apparatus was conditioned by heating an aqueous solution of the film forming amine (10 mg/L) at maximum heating rate for 8 h. The solution was discharged from the FFC apparatus.

In a second step, 3 L of ultrapure water, approx. 5 mg/L aluminum (as aluminium sulfate) and 4 mg/ ml were filled into the 4l round bottom flask. After 5 min of stirring a sample was taken in order to determine the actual concentration of aluminium and film forming amine in the flask, which was 5.6 mg/L for aluminium and 4.06 mg/L for FFA 1. Then the solution was heated up with maximum heating rate (heating mantle + heating bath). The solution was stirred at 250rpm. After the first condensate flew back into the flask, every hour a sample of the condensate was taken (4h sampling time in total) from the condensate sampling unit and the aluminium concentration and the concentration of FFA1 were determined in this condensate. No aluminium was found in the condensate. The concentration of aluminium in the flask was still 5.6 mg/L. The concentration of FFA1 in the condensate was < 0.05 ppm, which is close to the detection limit. The concentration of FFA1 in the flask was still 3.11 mg/L.

Trial 2: With 5 ppm Al and 4 ppm Film Forming Amine 1:
The test conditions and procedure were equivalent to Trial 1. However instead of adding the aluminium sulfate (approx. 5mg Al/l) in the beginning together with FFA1 into the round bottom flask, it was added after 2h, when FFA1 was already detectable in the condensate at the condensate sampling unit. The heating was continued for 70 hours and samples were taken 1 h, 2 h, 3 h, 4, h, 20 h, 24 h, 48 h and 70 h after the addition aluminium sulfate from the condensate sampling unit.
The results are summarized in the following table 2:

The results of trial 2 show a slight loss of aluminium which may be ascribed to initial loss during dosage. No significant carry over could be observed.

The concentration of aluminium in samples was determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

The concentration of the film forming amine was determined by the Bengalrose method described in K. Stiller et. al. Power Plant Chemistry 2011, 13(10), pp. 602-611

Claims

A method for providing corrosion protection to a water-steam circuit having both internal surfaces made of aluminium or aluminium alloy and internal surfaces made of steel, which method comprises operating the water-steam circuit with water having a pH value, as determined at 22°C, in the range of pH 8.8 to 10.0 and containing a film forming amine.
The method of claim 1, wherein the average concentration of the film forming amine in the water used for operating the water-steam circuit is in the range from 0.01 to 5.0 mg/kg.
The method of any of the preceding claims, wherein the water used for operating the water-steam circuit has a pH value, as determined at 22°C, in the range of pH 9.0 to 9.6.
The method of any of the preceding claims, wherein during operation of the water-steam cycle the pH value of the water contained in the water-steam cycle is controlled and maintained in the range of pH 8.8 to 10.0, in particular in the range of pH 9.0 to 9.6, as determined at 22°C.
The method of claim 4, wherein the pH of the water is controlled at least in one of the following points of the water-steam-circuit:
- the feed water,
- the condensate water and/or
- the water of the steam drum.
The method of any of the preceding claims, wherein during operation of the water-steam cycle the concentration of the film forming amine in the water contained in the water-steam cycle is controlled and maintained in the range from 0.01 to 5.0 mg/kg.
The method of claim 6, wherein the concentration of the film forming amine in the water is controlled at least in one of the following points of the water-steam-circuit:
- the feed water,
- the condensate water and/or
- the water of the steam drum.
The method of any of the preceding claims, wherein during operation of the water-steam cycle the water the water contained in the water-steam cycle has a conductivity of at most 30 μS/cm as determined at 22°C.
The method of any of the preceding claims, wherein the water-steam circuit is part of a power-plant.
The method of claim 9, wherein the power plant is operated in the cycling mode.
The method of any of the preceding claims, wherein the film forming amine is selected from compounds of the formula (I), including mixtures thereof:

R¹-(NR³-R²)_n-NR⁴R⁵ (I)
wherein
n is 0, 1 or 2
R¹ is a linear or branched, acyclic hydrocarbon group having 12 to 22 carbon atoms;
R² is C₂-C₄-alkanediyl;
R³, R⁴, R⁵ are identical or different and independently selected from the group consisting of H, C₁-C₄ alkyl and -(C_mH_2m-2O)_p-H, wherein m is 2, 3, or 4 and p is = 1, 2, 3 or 4.
The method of claim 11, wherein R¹ in formula (I) has 16 to 20 carbon atoms.
The method of claim 11 or 12, wherein R¹ in formula (I) is a saturated straight chain hydrocarbon group or an unsaturated straight chain hydrocarbon group having 1, 2 or 3 C=C double bonds.
The method of any one of claims 11 to 13, wherein R³, R⁴ and R⁵ in formula (I) are hydrogen or -(C₂H₄O)_p-H.
The method of any one of the preceding claims, wherein the film forming amine is selected from oleyl amine, N-(3-aminopropyl)oleyl amine, mixtures of oleyl amine and N-(3-aminopropyl)oleyl amine, ethoxylated N-(3-aminopropyl)oleyl amine, and mixtures of ethoxylated N-(3-aminopropyl)oleyl amine and ethoxylated oleylamine.