WO2000046423A1

WO2000046423A1 - Cleaner composition and method of use thereof

Info

Publication number: WO2000046423A1
Application number: PCT/US2000/000513
Authority: WO
Inventors: Roger John Arthur Tippett; Terrence Patrick Small
Original assignee: Betzdearborn Inc.
Priority date: 1999-02-05
Filing date: 2000-02-02
Publication date: 2000-08-10
Also published as: JP2002536545A; AU2962400A; EP1153160A1; CA2361606A1; KR20010094757A

Abstract

Methods and compositions for removing iron oxide scale from metal surfaces. A combination of ethoxylated mercaptan and/or oxidized ethoxylated mercaptan and 1-hydroxyethylidene-1,1-diphosphonic acid is added to an aqueous system, such as a steam generating system, to remove scale from the metal surfaces.

Description

CLEANER COMPOSITION AND METHOD OF USE THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of Application No. 09/245,440, filed February 5, 1999, the disclosure of which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to cleaner compositions useful for removing scale from metal surfaces. The present invention also relates to cleaner compositions that have reduced base metal loss without inhibiting or significantly inhibiting scale removal from metal surfaces. More particularly, the present invention provides for cleaner compositions for removing magnetite containing scale from metal surfaces, especially in steam generating equipment.

BACKGROUND OF THE INVENTION

In steam boilers, feed water heaters, piping and heat exchangers where water is circulated and heat transfer occurs, water insoluble salts deposit on the metallic interior surfaces. The nature of the deposits, such as magnetite (Fe₃O ) deposits, can vary from a tightly adherent low porosity scale to loosely adherent sludge piles.

Excess scale must be removed periodically to ensure proper functioning of the scale suffering system. Previously, scale removing compositions have been employed. Inorganic acids such as hydrochloric and phosphoric acid as well as organic acids have been used to dissolve iron oxide scale. Alkali metal and amine salts of alkylene polyamine polyacetic acids have also been used to remove iron oxide deposits from ferrous metal surfaces.

Steam generators in pressurized water reactor (PWR) nuclear power plants are heat exchangers transferring heat from a primary coolant (pressurized water) system to a secondary coolant system. In the secondary side of PWR nuclear steam generators, magnetite deposits form over time on both the Inconel® 600 heat transfer surfaces and the mild steel support structures. This causes problems associated with loss of heat transfer efficiency and corrosion of system metallurgies through denting and pitting mechanisms.

These deposits are removed on an infrequent basis using either off-line chemical or mechanical methods. In general, the mechanical methods are less efficient and more costly than the chemical methods. The industry accepted chemical cleaning method utilizes a 10 to 25% diammonium EDTA cleaning solution at a solution pH of 7.5 or higher. The mild-steel corrosion inhibitor employed is an alkylthiopolyimino-amid with a low sulfur content, which is advantageous in that this lessens the stress corrosion cracking of Inconel© tubes. The cleaning process is typically scheduled to coincide with a refueling outage, and often requires the use of auxiliary heaters to maintain the temperature of the steam generator water at 200°F to 290°F. The present inventors have discovered a cleaner composition that avoids these difficulties inherent in the earlier processes. It has been discovered that the new composition will remove iron-containing deposits at lower temperatures than EDTA-based cleaners. The cleaner solution is less aggressive to the base metal being cleaned and will work at a neutral pH. Additionally, the cleaner composition does not contain halogen ions and has a lower sulfur content, as well as being of lower toxicity and easier to handle.

SUMMARY OF THE INVENTION

The present invention provides for compositions comprising 1 -hydroxy-ethylidene- 1 , 1 - diphosphonic acid (HEDP) and ethoxylated mercaptan and/or oxidized ethoxylated mercaptan, especially for removing iron oxide containing deposits from ferrous metal surfaces, especially in steam generators.

In one aspect the present invention provides a method for cleaning iron oxide containing scale from a metal surface, comprising contacting the metal surface with an aqueous composition containing 1-hydroxyethylidene- 1,1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan. In another aspect the present invention provides a cleaning composition comprising

1-hydroxyethylidene 1,1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan.

The ethoxylated mercaptan can have the formula: H-(-O-CH₂-CH₂.)_n-S-R, wherein R, is a hydrocarbyl group, n is 1 to 100, preferably 4-20, more preferably 4-12, and the oxidized ethoxylated mercaptan can comprise oxidized derivatives thereof.

The ethoxylated mercaptan can be prepared from at least one mercaptan having the formula of R,SH, wherein R,SH comprises at least one of benzyl mercaptan, cyclohexyl mercaptan, dipentene dimercaptan, ethyl mercaptan, ethylcyclohexyl dimercaptan, ethylthioethanol, isopropyl mercaptan, n-butyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, n-propyl mercaptan, pinanyl mercaptan-2, s- butyl mercaptan, t-butyl mercaptan, t-dodecyl mercaptan, t-nonyl mercaptan, 1,2 ethanedithiol, 2- ethylhexyl-3-mercaptopropionate, 2-mercaptoethanol, and 3-mercapto-l-propanol.

R, can preferably have up to 30 carbon atoms, and can be C, to C₃₀ alkyl or substituted alkyl, the alkyl or substituted alkyl can be branched, or straight chained. The ethoxylated mercaptan can comprise ethoxylated tertiary dodecyl mercaptan, such as ethoxylated tertiary dodecyl mercaptan having about 6-10 moles of ethoxylation per mole of mercaptan. or about 8 moles of ethoxylation per mole of mercaptan. The ethoxylated mercaptan can comprise ethoxylated n-dodecylmercaptan, such as ethoxylated n-dodecylmercaptan having about 4.9 or 8.2 moles of ethoxylation per mole of mercaptan. The ethoxylated mercaptan can comprise ethoxylated 2-phenylethyl mercaptan, such as ethoxylated 2-phenylethyl mercaptan having about 6.7 moles of ethoxylation per mole of mercaptan.

The metal surface can be ferrous metal, and the metal surface can be in contact with an aqueous system.

The metal surfaces can be in a nuclear steam generator system. The 1 -hydroxyethylidene- 1 , 1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan can be contained in an aqueous solution.

The aqueous composition can be contacted with the metal surface while off-line, the composition can remain in contact with the metal surface for up to 10 days, or up to 7 days.

The 1-hydroxyethylidene- 1,1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan can be separately added to the aqueous system.

The 1-hydroxyethylidene- 1,1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan can be added as a neat composition of 1-hydroxyethylidene- 1,1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan to the aqueous system. The aqueous system can comprise from about 0.1 parts to 50,000 parts solution in the system of at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan and from about 1 to 200,000 parts HEDP per million parts solution in the system. The aqueous system can comprise from about 0.1 to 20,000 parts ethoxylated mercaptan per million parts of solution in the system, and from about 5,000 to 100,000 parts HEDP per million parts of solution in the system. The aqueous system can comprise from about 500 to 10,000 parts ethoxylated mercaptan per million parts of solution in the system, and from about 20,000 to 80,000 parts HEDP per million parts of solution in the system. The aqueous system can comprise from about 1,000 to 5,000 parts ethoxylated mercaptan per million parts of solution in the system. The aqueous system can comprise about 2,500 parts ethoxylated mercaptan per million parts of solution in the system, and about 43,500 parts HEDP per million parts of solution in the system.

The weight ratio of 1-hydroxyethylidene- 1,1 -diphosphonic acid to at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptans can range from about 4: 1 to about

200:1, more preferably from about 4:1 to about 80:1, and even more preferably from about 4:1 to about 50:1.

The aqueous composition can further comprise at least one of reducing agents, anionic polymers, surfactants, hydrotropes and corrosion inhibitors. The at least one reducing agent can comprise at least one of L-ascorbic acid, hydroquinone, sodium sulfite, diethylhydroxylamine, hydrazine, erythorbic acid and carbohydrazide.

The pH of the aqueous system can range from about 5 to 12, more preferably about 6 to 12, even more preferably about 6-8. Also, the pH of the aqueous system is at least about 5, at least about 6, and at least about 6.5. The temperature of the aqueous composition can range from about 70°F to 250°F.

The at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan can comprise ethoxylated mercaptan, oxidized ethoxylated mercaptan, or mixtures thereof.

DESCRIPTION OF THE RELATED ART

U.S. Pat. No. 5,614,028, Rodzewich, teaches methods for cleaning and passivating a metal surface by incorporating a corrosion inhibitor into an acid cleaner. The corrosion inhibitor is ethoxylated tertiary dodecyl mercaptan.

U.S. Pat. No. 4,810,405, Waller et al., teaches methods for removing iron oxide deposits from iron or steel metal surfaces with a composition comprising a phosphonate such as HEDP, a reducing agent and a corrosion inhibitor exemplified by azoles. U.S. Pat. No. 4,666,528, Arlington et al, teaches methods for removing iron and copper containing scale from a metal surface using a composition comprising an aminopolycarboxylic acid such as EDTA and a phosphonic acid or salt thereof. Frost et al., U.S. Pat. No. 3,854,996, discloses methods for removing magnetite scale from metal substrates by contacting the metal with an aqueous solution of a polyphosphonic acid or salt thereof such as HEDP. U.S. Pat. No. 3,806,459, Petrey, Jr., teaches on stream cleaning of iron oxide deposits using a composition comprising HEDP and an aminoacetic acid. U.S. Pat. No. 4,637,899, Kennedy, Jr., teaches a corrosion inhibiting composition which can be used to remove rust from metal surfaces. The composition comprises an aliphatic pyridinium or quinolinium salt and a sulfur-containing compound.

DETAILED DESCRIPTION OF THE INVENTION Unless otherwise stated, all percentages, parts, ratios, etc., are by weight.

Unless otherwise stated, a reference to a compound or component includes the compound or component by itself, as well as in combination with other compounds or components, such as mixtures of compounds.

Further, when an amount, concentration, or other value or parameter, is given as a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of an upper preferred value and a lower preferred value, regardless whether ranges are separately disclosed.

The present invention relates to methods and compositions for cleaning iron oxide containing deposits from metal surfaces comprising contacting the surfaces with a composition comprising 1 -hydroxy-ethylidene- 1,1 -diphosphonic acid (HEDP) and ethoxylated mercaptan(s) and/or oxidized ethoxylated mercaptan(s).

The ethoxylated mercaptan generally has the formula: H-(-O-CH₂-CH₂-)_n-S-R, wherein R, comprises a hydrocarbyl group, and n is 1 to 100, more preferably n is 4 to 20, and even more preferably n is 4 to 12.

As used herein, the term "hydrocarbyl" is understood to include "aliphatic," "cycloaliphatic," and "aromatic." The hydrocarbyl groups are understood to include alkyl, alkenyl, alkynyl, cycloalkyl, aryl, arylalkyl, and alkaryl groups. Further, "hydrocarbyl" is understood to include branched and unbranched compounds, and both non-substituted hydrocarbyl groups, and substituted hydrocarbyl groups, with the latter referring to the hydrocarbon portion bearing additional substituents, besides carbon and hydrogen.

The number of carbon atoms in R, can vary. Without wishing to be bound by theory, R, should have a sufficient number of C atoms to provide activity in the aqueous system to provide corrosion inhibition without significantly inhibiting scale removal. Moreover, the number of C atoms is preferably maintained at an upper limit taking at least into consideration compound expense and/or the ability of the compound to be maintained in a useful state in the aqueous system, such as ensuring sufficient solubility of the compound in the aqueous system. Preferably, the hydrocarbyl group contains less than 30 carbon atoms.

Preferably, R, is an alkyl or substituted alkyl, preferably containing C, to C,₀, more preferably C₆ to C,₈, and even more preferably C₈ to C₁₄, which can be branched or straight chain, and the substitutions can preferably include hydroxy, sulfonate, phosphate, amino and aromatic groups.

In general, ethoxylated mercaptans can be prepared from a reaction of ethylene oxide and mercaptan of the form R,SH, wherein R, is defined as above. Examples of R,SH include, but are not limited to, benzyl mercaptan, cyclohexyl mercaptan, dipentene dimercaptan, ethyl mercaptan, ethylcyclohexyl dimercaptan, ethylthioethanol, isopropyl mercaptan, n-butyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, n-propyl mercaptan, pinanyl mercaptan-2, s-butyl mercaptan, t-butyl mercaptan, t-dodecyl mercaptan (such as Sulfole®120 available from Phillips Specialty Chemicals, Bartelsville, OK), t-mix mercaptan (such as Sulfole®100 available from Phillips Specialty Chemicals, Bartelsville, OK), t-nonyl mercaptan (such as Sulfole®90 available from Phillips Specialty Chemicals, Bartelsville, OK),

1,2 ethanedithiol, 2-ethylhexyl-3-mercaptopropionate, 2-mercaptoethanol, and 3-mercapto-l- propanol.

Preferably, the ethoxylated mercaptan includes, but is not limited to, ethoxylated alkyl mercaptans, most preferably ethoxylated alkyl mercaptans having about 4 to 12 moles of ethoxylation per mole of mercaptan, including ethoxylated tertiary dodecyl mercaptans, such as those having 6 moles of ethoxylation per mole of mercaptan, e.g., ALCODET 260 available from Shibley Chemicals, Elyria, OH, and manufactured by Rhone-Poulenc, those having 8 moles of ethoxylation per mole of mercaptan, e.g., ALCODET SK available from Shibley Chemicals, Elyria, OH, and manufactured by Rhone-Poulenc, and those having 10 moles of ethoxylation per mole of mercaptan, e.g., ALCODET 218 available from Shibley Chemicals, Elyria, OH, and manufactured by Rhone-Poulenc; and ethoxylated n-dodecylmercaptan, such as those having about 4.9 or about 8.2 moles ethoxylation per mole of mercaptan. Burco TME, which is available from Burlington Chemicals, Burlington, N.C., is a particularly preferred ethoxylated alkyl mercaptan. Ethoxylated 2-phenylethyl mercaptans having about 6.7 moles ethoxylation per mole of mercaptan are also preferred.

Preferably, oxidized ethoxylated mercaptans are utilized in the composition according to the present invention. In particular, it noted that oxidized ethoxylated mercaptans provide exceptional corrosion inhibition without inhibiting scale removal from metal surfaces. Thus, while ethoxylated mercaptans have been found to provide exceptional corrosion inhibition combined with very low levels of metal loss when utilized in conjunction with HEDP, it was further discovered that oxidized ethoxylated mercaptans provide an even greater corrosion inhibition when utilized in conjunction with HEDP

The ethoxylated mercaptan can be oxidized utilizing various procedures, and one having ordinary skill in the art would be able to oxidize ethoxylated mercaptans following the guidance provided herein. For example, methods such as disclosed in "Advanced Organic Chemistry" by Jerry March, 3rd Edition, pages 1089-1090, 1985, published by John Wiley & Sons, which is incorporated by reference in its entirety.

For example, without limiting the manner of oxidizing the ethoxylated mercaptans, the ethoxylated mercaptans can be oxidized using hydrogen peroxide. Thus, as an example of oxidization of ethoxylated mercaptans according to the present invention, the ethoxylated mercaptans can be reacted with hydrogen peroxide, such as by utilizing an aqueous solution of hydrogen peroxide preferably containing about 1 to 70 wt%, more preferably about 30 to 50 wt%, at a temperature of preferably about 25°C to 100°C, more preferably about 40°C to 60°C, for a sufficient period of time to oxidize the ethoxylated mercaptan, preferably about 30 minutes to 8 hours, more preferably about 1 to 2 hours.

Residual hydrogen peroxide can be removed utilizing any method for removing the hydrogen peroxide which is not detrimental or which is substantially non-detrimental to the oxidized ethoxylated mercaptan. For example, residual hydrogen peroxide can be removed by raising the pH of the reaction composition that contains the oxidized ethoxylated mercaptan and the residual hydrogen peroxide, or a catalyst for hydrogen peroxide can be added to reaction composition. Thus, for example, the pH of the reaction composition can be raised to at least about 10 and/or a catalyst, such as at least one of platinum, palladium, ferric chloride, cobalt chloride, and cupric chloride can be added to the reaction composition. While there is no upper limit to the pH, preferably the pH is maintained below about 14, with a preferred range being about 10-12.

Without wishing to be bound by theory, it is believed that the sulfur component of the ethoxylated mercaptan is oxidized in the oxidation reaction to sulfoxide. Moreover, it is believed that at least some of the sulfoxide is further oxidized to sulfone. Thus, it is believed that the oxidized ethoxylated mercaptan contains sulfoxide and/or sulfone groups. For pu oses of the present invention, the term ethoxylated mercaptan can include a mixture of one or more ethoxylated mercaptans, and the term oxidized ethoxylated mercaptan (also alternatively referred to herein as "derivatives of ethoxylated mercaptans") can include mixtures of one or more oxidized ethoxylated mercaptans. Moreover, according to the present invention, there can be mixtures of ethoxylated mercaptans and oxidized ethoxylated mercaptans.

The cleaning composition of the present invention is typically added to steam generating systems, heat exchangers and other high pressure vessels where heat transfer to an aqueous medium occurs. These systems often have ferrous metal surfaces where magnetite scaling can occur. The cleaning composition is preferably employed in the secondary side of Pressurized

Water Reactor nuclear steam generators which contain bundles of metal tubes held in place by tube sheets and support plates.

The cleaning composition may be added to systems, such as the above-noted systems, as an active recirculating system, e.g., where the system is undergoing operation to at least partially, and preferably substantially completely or completely achieve usual system performance such as by being on-line. The cleaning composition may also be preferably added off-line, such as adding the cleaning composition to an off-line nuclear steam generator. Off-line addition includes static cleaning wherein the cleaning composition is not moving or substantially non- moving, such as wherein the cleaning composition is added to a container and/or a pipe and not circulated therein. Moreover, off-line addition includes scale removal wherein the cleaning composition is caused to flow, such as by being agitated, such as by bubbling with an inert gas, such as nitrogen, or by being circulated, such as by a pump and/or gravity. When added off-line, the cleaning composition may be left in contact with the metal surface for extended periods of time, such as long as 7 days, even as long as 10 days, or longer. This period of time will vary depending upon the temperature of the water and the extent and amount of magnetite scale on the surfaces contained therein. In particular, the lower the temperature, the longer the contact time required to removal the scale. For example, at temperatures of about 25°C to 100°C, in a static cleaning system, the cleaning composition can be contacted with the surface to be cleaned for about 3 hours to 10 days. Typically, the cleaning composition is added as an aqueous solution. The individual components of the composition may be added separately or together depending upon the particular system treated. Additionally, the cleaning composition may be added neat to the system to be treated. The total amount of cleaning composition to be added to the system will vary depending upon the amount of magnetite scale and the temperature of the water. The cleaning composition may be added to the system to be treated in an amount ranging from about 0.1 to about 50,000 parts ethoxylated mercaptan per million parts of solution in the system, more preferably about 0.1 to about 20,000 parts ethoxylated mercaptan per million parts of solution in the system, more preferably from about 500 to 10,000 parts ethoxylated mercaptan per million part of solution in the system, even more preferably from about 1,000 to 5,000 parts ethoxylated mercaptan per million part of solution in the system, with one preferred value being about 2,500 parts ethoxylated mercaptan per million part of solution in the system. Moreover, the cleaning composition may be added to the system to be treated in an amount ranging from about 1 to

200,000 parts HEDP per million parts of solution in the system, preferably 5,000 to 100,000 parts HEDP per million parts of solution in the system, even more preferably 20,000 to 80,000 parts HEDP per million parts of solution in the system, with one preferred value being about 43,500 parts HEDP per million parts of solution in the system. The weight ratio of HEDP to at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan will range from about 4 to 1 to 200 to 1 , more preferably from about 4 to 1 to 80 to 1, even more preferably from about 4 to 1 to 50 to 1, with one preferred weight ratio being about 17 to 1.

The inventive cleaning composition may be added to the system to be treated with additional chemicals serving other purposes in the system. This holds true whether the chemical is added with the cleaning solution or is already present in the aqueous system.

These other chemicals typically can be reducing agents such as L-ascorbic acid, hydroquinone, sodium sulfite, diethylhydroxylamine, hydrazine, erythorbic acid or carbohydrazide; anionic polymers such as carboxylates (e.g. polyacrylic acid, polymethacrylic acid and copolymers thereof) poly(alkenyl)phosphonic acids; surfactants such as phosphate esters, polyethylene oxide, polypropylene oxide and copolymers thereof, fatty acid amides and ethoxylated alcohols; hydrotropes such as sodium xylene sulfonate ; and corrosion inhibitors, such as copper corrosion inhibitors such as benzotriazoles and tolyltriazole. For purposes of the present invention, this list is merely representative and not meant to be exclusive. Moreover, it is once again noted, as indicated above, that the compositions and processes of the present invention can include other corrosion inhibitors in addition to the ethoxylated mercaptan and/or oxidized ethoxylated mercaptans of the present invention. The cleaning composition of the present invention can be employed at pH's at least about 5 or above, more preferably at least about 6 or above, with a preferred range of about 5 to 12, more preferably about 6 to 12, and even more preferably about 6 to 8. The pH of the cleaner composition can be adjusted, preferably to a pH greater than about 5, more preferably to a pH greater than about 6, and more preferably to a pH of about 6 to 8, using various materials that can raise the pH of the system, preferably by using alkali metal hydroxide salts such as NaOH or KOH, organic amines, or ammonia.

Besides the ability to remove magnetite deposits from ferrous metal surfaces, particularly the secondary side of PWR nuclear steam generators, the present inventors anticipate that the cleaning composition will be effective in pre-operational boiler cleaning in fossil fuel systems, off-line and on-line boiler cleaning, cleaning of closed and open loop cooling systems and heat exchangers.

The invention will now be described with respect to certain examples which are merely representative of the invention and should not be construed as limiting thereof.

EXAMPLES

The invention is illustrated in the following non-limiting examples, which are provided for the purpose of representation, and are not to be construed as limiting the scope of the invention. All parts and percentages in the examples are by weight unless indicated otherwise.

Acronyms utilized in the examples for ingredient utilized in the examples are defined in Table 1, with one column in Table 1 providing the common name of the ingredient and one column providing how the ingredient was obtained, such as by denoting its source or indicating how the chemical compound was prepared.

Mild steel corrosion and iron oxide dissolution studies were performed in a three-neck 250 mL glass flask. This flask is referred to as the process vessel. The vessel surface was prepared by rinsing with several aliquots of acetone followed by deionized water. Magnetite

(0.5555 grams, nominal 80 micron size particles, Strem Chemical, Newburyport, MA) and deionized water (1 mL) were then introduced to the process vessel forming a slurry.

The test cleaner solutions were prepared separately. The components of the cleaner solution were added to deionized water (100 mL) in a 250 mL Pyrex beaker. The cleaner solution was then titrated to pH indicated in the examples with ammonium hydroxide. The beaker volume was increased to 199 mL with deionized water and the solution was heated to the temperature of usually 140°F, or as indicated.

When the cleaner reached temperature, the process vessel containing the magnetite was positioned on the heater and the cleaning solution was slowly poured into the process vessel, and heated to usually 140°F, or as indicated. The resultant solution contained 2000 ppm magnetite as

Fe and the cleaner solution at the desired concentration. A 1010 mild steel coupon of surface area 18.704 cπr was placed horizontally into the vessel such that it was fully immersed in the cleaning solution. The metal coupons were obtained from Metal Samples Inc., Mumford, AL. Prior to use, the metal coupons were sonicated in acetone for ten minutes at room temperature. The coupon surface was prepared with a pumice buff followed by thorough deionized water rinses and drying with compressed nitrogen. The initial coupon weights were recorded. After the coupon was added to the process vessel, the thermometer, air lock and sealed glass adapter were inserted into the process vessel. The date and initial conditions (time, pH, and temperature) were recorded. The solution was then maintained at temperature for the prescribed cleaning time.

After the cleaning time, the temperature, dried filter weight, and time were recorded. The coupon was removed from the process vessel with loose oxides gently rinsed back in the process vessel. The coupon surface was immersed into an inhibited acid for 10 minutes and then rinsed and dried with a nitrogen stream. A final coupon weight was then taken. Dissolution performance was determined by filtration of the hot processed cleaner solution through a dried and pre-weighed 0.2 um filter using a vacuum pump set to 10 psig. The used filter paper was dried and reweighed . A sample of the filtrate of the cleaner solution was taken for iron analysis by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP) and for determination of the final solution pH. Cleaner performance was evaluated using the coupon and filter weights in the equations below. Note that all weights are expressed in grams Dissolution (%)

((initial oxide weight - final oxide weight )/initial oxide weight) x 100

Metal Loss (microns)

((initial coupon weight - final coupon weight) x 1000 x 0.9799)/14.37)

Corrosion Inhibition (%)

((metal loss[no inhibitor] - metal loss [with inhibιtor])/metal loss [no inhibitor]) x

100

Table 1 describes the materials utilized in the examples.

TABLE 1

TABLE 1. continued

*Manufactured by Rhone-Poulenc

Table 2 illustrates Comparative Examples 1-4 including EDTA (ethylenediamme tetraacetic acid), CCI-801 (alkylthiopolyamino-amid) and hydrazme

These test results demonstrate that the combination of EDTA and CCI-801 (alkylthiopolyimino-amid) does not perform well at lower temperatures. However, HEDP was found to dissolve magnetite at these temperatures. These HEDP solutions were found to be somewhat aggressive to the metal surface.

Further testing was performed using 4.35 wt% aqueous solutions of HEDP. These results are presented in Table 3 for examples according to the invention and comparative examples.

TABLE 3- 4.35 wt% HEDP in presence of corrosion inhibitors (0.25 wt%) at

140°F and pH of 7.1 for 24 hours

Total Iron (Magnetite) = 2,000 ppm Fe as Fe₃O₄

TABLE 3, continued

As demonstrated in Table 3, the inventive composition proved more effective at inhibiting base metal loss without significantly reducing magnetite dissolution than a combination of HEDP and propoxylated mercaptans. At 140°F, the addition of CCI-801 to the HEDP resulted in a reduction in corrosion but also a reduction in the dissolution of magnetite. Further, dibutylthiourea was also effective but contains 17%> sulfur by weight and is a suspected carcinogen. Burco TME, for example, only contains 5%_> sulfur by weight and is easier to handle. Still further, Table 4 demonstrates the even further increase in corrosion inhibition/reduced metal loss and excellent dissolution when utilizing oxidized ethoxylated mercaptans as compared to ethoxylated mercaptans.

TABLE 4- 4.35 wt% HEDP in presence of corrosion inhibitors (0.25 wt%) at

140°F and pH of 7.1 for 24 hours

Total Iron (Magnetite) = 2,000 ppm Fe as Fe₃O₄

Still further, Table 5 demonstrates uses of pH's other than 7.1. It is noted that several examples include hydrazine.

Table 5 - 4.35 wt% HEDP in presence of corrosion inhibitors (0.25 wt%) at 140°F for 24 hours using various pH's

Total Iron (Magnetite) = 2,000 ppm Fe as Fe₃O₄

While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.

Claims

Having thus described the invention, what we claim is:

1. A method for cleaning iron oxide containing scale from a metal surface, comprising contacting said metal surface with an aqueous composition containing 1-hydroxyethylidene- 1,1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan.

2. The method as claimed in claim 1 wherein said ethoxylated mercaptan has the formula:

H-(-O-CH₂-CH₂N-S-R, wherein R, is a hydrocarbyl group, n is 1 to 100, and said oxidized ethoxylated mercaptan comprises oxidized derivatives thereof.

3. The method as claimed in claim 2, wherein the ethoxylated mercaptan is prepared from at least one mercaptan having the formula of R,SH, wherein R,SH comprises at least one of benzyl mercaptan, cyclohexyl mercaptan, dipentene dimercaptan, ethyl mercaptan, ethylcyclohexyl dimercaptan, ethylthioethanol, isopropyl mercaptan, n-butyl mercaptan, n-decyl mercaptan, n- dodecyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, n-propyl mercaptan, pinanyl mercaptan-2, s-butyl mercaptan, t-butyl mercaptan, t-dodecyl mercaptan, t-nonyl mercaptan, 1,2 ethanedithiol, 2- ethylhexyl-3-mercaptopropionate, 2-mercaptoethanol, and 3-mercapto-l-propanol.

4. The method as claimed in claim 2, wherein R, is tert dodecyl.

5. The method as claimed in claim 2, wherein R, is tert nonyl mercaptan.

6. The method as claimed in claim 2, wherein R, is C, to C₃₀ alkyl or substituted alkyl.

7. The method as claimed in claim 6, wherein said alkyl or substituted alkyl is branched.

8. The method as claimed in claim 6, wherein said alkyl or substituted alkyl is straight chained.

9. The method as claimed in claim 6, wherein n is 4 to 20.

10. The method as claimed in claim 9, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

11. The method as claimed in claim 9, wherein n is 4 to 12.

12. The method as claimed in claim 11, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

13. The method as claimed in claim 2, wherein R, has up to 30 carbon atoms.

14. The method as claimed in claim 13, wherein n is 4 to 20.

15. The method as claimed in claim 14, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

16. The method as claimed in claim 14, wherein n is 4 to 12.

17. The method as claimed in claim 16, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

18. The method as claimed in claim 2, wherein ethoxylated mercaptan comprises ethoxylated tertiary dodecyl mercaptan.

19. The method as claimed in claim 18, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

20. The method as claimed in claim 18, wherein said ethoxylated tertiary dodecyl mercaptan has about 6-10 moles of ethoxylation per mole of mercaptan.

21. The method as claimed in claim 20, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

22. The method as claimed in claim 20, wherein said ethoxylated branched mercaptan has about 8 moles of ethoxylation per mole of mercaptan.

23. The method as claimed in claim 22, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

24. The method as claimed in claim 2, wherein said ethoxylated mercaptan comprises ethoxylated n-dodecylmercaptan.

25 . The method as claimed in claim 24, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

26. The method as claimed in claim 24, wherein said ethoxylated n-dodecylmercaptan has about 4.9 or 8.2 moles of ethoxylation per mole of mercaptan.

27. The method as claimed in claim 2, wherein said ethoxylated mercaptan comprises ethoxylated 2-phenylethyl mercaptan.

28. The method as claimed in claim 27, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

29. The method as claimed in claim 27, wherein said ethoxylated 2-phenylethyl mercaptan has about 6.7 moles of ethoxylation per mole of mercaptan.

30. The method as claimed in claim 1 , wherein said metal surfaces are ferrous metal.

31. The method as claimed in claim 1 , wherein said metal surfaces are in a nuclear steam generator system.

32. The method as claimed in claim 2, wherein said metal surfaces are in a nuclear steam generator system.

33. The method as claimed in claim 15, wherein said metal surfaces are in a nuclear steam generator system.

34. The method as claimed in claim 18, wherein said metal surfaces are in a nuclear steam generator system.

35. The method as claimed in claim 19, wherein said metal surfaces are in a nuclear steam generator system.

36. The method as claimed in claim 24, wherein said metal surfaces are in a nuclear steam generator system.

37. The method as claimed in claim 27, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

38. The method as claimed in claim 1 wherein said 1-hydroxyethylidene- 1,1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan are contained in an aqueous solution.

39. The method as claimed in claim 1, wherein said metal surface is in contact with an aqueous system.

40. The method as claimed in claim 39 wherein said 1-hydroxyethylidene- 1,1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan are contained in an aqueous solution.

41. The method as claimed in claim 2 wherein said aqueous composition is contacted with the metal surface while off-line.

42. The method as claimed in claim 41 wherein said composition remains in contact with the metal surface for up to 10 days.

43. The method as claimed in claim 42 wherein said composition remains in contact with the metal surface for up to 7 days.

44. The method as claimed in claim 39 wherein the 1 -hydroxyethylidene- 1 , 1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan are separately added to said aqueous system.

45. The method as claimed in claim 39 wherein the 1 -hydroxyethylidene- 1 , 1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan are added as a neat composition of 1-hydroxyethylidene- 1,1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan to said aqueous system.

46. The method as claimed in claim 39 wherein said aqueous system comprises from about 0.1 parts to 50,000 parts solution in said system of at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan and from about 1 to 200,000 parts HEDP per million parts solution in said system.

47. The method as claimed in claim 46, wherein said aqueous system comprises from about

0.1 to 20,000 parts ethoxylated mercaptan per million parts of solution in the system, and from about 5,000 to 100,000 parts HEDP per million parts of solution in the system.

48. The method as claimed in claim 47, wherein said aqueous system comprises from about 500 to 10,000 parts ethoxylated mercaptan per million parts of solution in the system, and from about 20,000 to 80,000 parts HEDP per million parts of solution in the system.

49. The method as claimed in claim 48, wherein said aqueous system comprises from about 1,000 to 5,000 parts ethoxylated mercaptan per million parts of solution in the system.

50. The method as claimed in claim 49, wherein said aqueous system comprises about 2,500 parts ethoxylated mercaptan per million parts of solution in the system, and about 43,500 parts HEDP per million parts of solution in the system.

51. The method as claimed in claim 1 wherein the weight ratio of 1-hydroxyethylidene- 1,1 -diphosphonic acid to at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptans ranges from about 4:1 to about 200:1.

52. The method as claimed in claim 51 wherein the weight ratio of 1-hydroxyethylidene- 1,1 -diphosphonic acid to at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptans ranges from about 4: 1 to about 80:1.

53. The method as claimed in claim 52 wherein the weight ratio of 1-hydroxyethylidene- 1,1 -diphosphonic acid to at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptans ranges from about 4: 1 to about 50:1.

54. The method as claimed in claim 1 wherein said aqueous composition further comprises at least one of reducing agents, anionic polymers, surfactants, hydro tropes and corrosion inhibitors.

55. The method as claimed in claim 1 wherein said aqueous composition further comprises at least one reducing agent.

56. The method as claimed in claim 55 wherein said least one reducing agent comprises at least one of L-ascorbic acid, hydroquinone, sodium sulfite, diethylhydroxylamine, hydrazine, erythorbic acid and carbohydrazide.

57. The method as claimed in claim 39 wherein the pH of said aqueous system ranges from about 5 to 12.

58. The method as claimed in claim 57 wherein the pH of said aqueous system ranges from about 6 to 12.

59. The method as claimed in claim 39 wherein the pH of said aqueous system ranges from about 6-8.

60. The method as claimed in claim 39 wherein the pH of said aqueous system is at least about 5.

61. The method as claimed in claim 39 wherein the pH of said aqueous system is at least about 6.

62. The method as claimed in claim 39 wherein the pH of said aqueous system is at least about 6.5.

63. The method as claimed in claim 1 wherein the temperature of the aqueous composition ranges from about 70°F to 250°F.

64. The method as claimed in claim 1 wherein the at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan comprises ethoxylated mercaptan.

65. The method as claimed in claim 1 wherein the at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan comprises oxidized ethoxylated mercaptan.

66. The method as claimed in claim 1 wherein the at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan comprises mixtures of ethoxylated mercaptan and oxidized ethoxylated mercaptans.

67. A cleaning composition comprising 1-hydroxyethylidene 1,1 -diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan.

68. The composition as claimed in claim 67 which is in the form of an aqueous solution.

69. The composition as claimed in claim 68 further comprising a compound selected from the group consisting of a reducing agents, anionic polymers, surfactants, hydrotropes and corrosion inhibitors.

70. The composition as claimed in claim 69 further comprising at least one reducing agent.

71. The composition as claimed in claim 70 wherein said least one reducing agent comprises at least one of L-ascorbic acid, hydroquinone, sodium sulfite, diethylhydroxylamine, hydrazine, erythorbic acid and carbohydrazide.

72. The composition as claimed in claim 67 wherein said ethoxylated mercaptan has the formula:

73. The composition as claimed in claim 62, wherein the ethoxylated mercaptan is prepared from at least one mercaptan having the formula of R,SH, wherein R^H comprises at least one of benzyl mercaptan, cyclohexyl mercaptan, dipentene dimercaptan, ethyl mercaptan, ethylcyclohexyl dimercaptan, ethylthioethanol, isopropyl mercaptan, n-butyl mercaptan, n-decyl mercaptan, n- dodecyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, n-propyl mercaptan, pinanyl mercaptan-2, s-butyl mercaptan, t-butyl mercaptan, t-dodecyl mercaptan, t-nonyl mercaptan, 1,2 ethanedithiol, 2- ethylhexyl-3-mercaptopropionate, 2-mercaptoethanol, and 3-mercapto-l-propanol.

74. The composition as claimed in claim 72, wherein R, is tert dodecyl.

75. The composition as claimed in claim 72, wherein R, is tert nonyl.

76. The composition as claimed in claim 72, wherein R, is C, to C₃₀ alkyl or substituted alkyl.

77. The composition as claimed in claim 76, wherein n is 4 to 20.

78. The composition as claimed in claim 77, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

79. The composition as claimed in claim 77, wherein n is 4 to 12.

80. The composition as claimed in claim 79, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

81. The composition as claimed in claim 72, wherein R, has up to 30 carbon atoms.

82. The composition as claimed in claim 81 , wherein n is 4 to 20.

83. The composition as claimed in claim 82, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

84. The composition as claimed in claim 82, wherein n is 4 to 12.

85. The composition as claimed in claim 84, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

86. The composition as claimed in claim 72, wherein ethoxylated mercaptan comprises ethoxylated tertiary dodecyl mercaptan.

87. The composition as claimed in claim 86, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

88. The composition as claimed in claim 72, wherein said ethoxylated mercaptan comprises ethoxylated n-dodecylmercaptan.

89. The composition as claimed in claim 88, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

90. The composition as claimed in claim 72, wherein said ethoxylated mercaptan comprises ethoxylated 2-phenylethyl mercaptan.

91. The composition as claimed in claim 90, wherein the ethoxylated mercaptan is oxidized ethoxylated mercaptan.

92. The composition as claimed in claim 67 wherein the weight ratio of 1 -hydroxyethylidene- 1 , 1 -diphosphonic acid to at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptans ranges from about 4: 1 to about 200:1.

93. The composition as claimed in claim 92 wherein the weight ratio of 1 -hydroxyethylidene- 1 , 1 -diphosphonic acid to at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptans ranges from about 4:1 to about 80:1.

94. The composition as claimed in claim 93 wherein the weight ratio of 1-hydroxyethylidene- 1,1 -diphosphonic acid to at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptans ranges from about 4:1 to about 50:1.

95. The composition as claimed in claim 67 wherein the at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan comprises ethoxylated mercaptan.

96. The composition as claimed in claim 67 wherein the at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan comprises oxidized ethoxylated mercaptan.

97. The composition as claimed in claim 67 wherein the at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan comprises mixtures of ethoxylated mercaptan and oxidized ethoxylated mercaptans.