Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...
Reexamination Certificate
2000-08-02
2002-02-19
Hardee, John (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
For cleaning a specific substrate or removing a specific...
Reexamination Certificate
active
06348440
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to cleaner compositions and processes useful for removing scale from metal surfaces. The present invention also relates to cleaner compositions and processes 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 and processes for removing magnetite containing scale from metal surfaces, especially in steam generating equipment, and especially high strength metals, such as high strength steels, steels used for pressure to vessel plating, welded metals including welded higher strength steels and welded steels used for pressure vessel plating, steels galvanically coupled to stainless steels, and steels containing heat affected zones resulting from a welding process.
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 (Fe
3
O
4
) 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® Alloy 600 and 690 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.
In U.S. application Ser. No. 09/407,173, filed Sep. 28, 1999, and application Ser. No. 09/245,440, filed Feb. 5, 1999, which are incorporated by reference herein in their entireties, cleaner compositions and methods are disclosed that avoid difficulties inherent in earlier processes. In these applications, compositions are disclosed that will remove iron-containing deposits at lower temperatures than EDTA-based cleaners. These cleaner compositions are disclosed to be less aggressive to the base metal being cleaned and will work at a neutral pH. Additionally, the cleaner compositions that are disclosed do not require halogen ions and have a lower sulfur content, as well as being of lower toxicity and easier to handle. In particular, these applications disclose methods 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.
There is still a need to provide further improvements in metal oxide dissolution while providing high corrosion inhibition in various environments.
SUMMARY OF THE INVENTION
The present invention is directed to a method for cleaning iron oxide containing scale from a surface of at least one of high strength steels, steels used for pressure vessel plating, welded metals, steels galvanically coupled to stainless steels, and steels containing heat affected zones (HAZ) resulting from a welding process, comprising contacting the surface with a composition comprising 1-hydroxy-ethylidene-1,1-diphosphonic acid; at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan; and at least one third component which in combination with the 1-hydroxy-ethylidene-1,1-diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan provides a percent corrosion inhibition of greater than about 75% as compared to a composition containing the 1-hydroxy-ethylidene-1,1-diphosphonic acid and the at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan in the absence of the at least one third component, and a percent oxide dissolution using 80 micron particle sized magnetite of at least about 30% when the solution is maintained at 110° F. at pH 6.5 with no agitation and measured at 72 hours.
Moreover, the present invention is directed to a method for cleaning iron oxide containing scale from a surface of at least one of high strength steels, steels used for pressure vessel plating, welded metals, steels galvanically coupled to stainless steels, and steels containing heat affected zones (HAZ) resulting from a welding process, comprising contacting the surface with a composition comprising 1-hydroxy-ethylidene-1,1-diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxytated mercaptan, and at least one of benzotriazole and benzimidazole compound having the following structure:
wherein X is C or N, each of R
1
, R
2
, R
3
and R
4
is hydrogen, halogen, or a hydrocarbyl group.
The surface can comprise a steel having a carbon content higher than 0.15 wt %, higher than 0.2 wt %, or higher than 0.3 wt %.
The surface comprise can comprise a steel having a Mn content of higher than 0.9 wt %.
The surface can comprise a steel containing up to 0.25 wt % C, 1.15-1.50 wt % Mn, 0.035 wt % P, 0.04 wt % S, 0.21 wt % Si, 0.45-0.60 wt % Mo, and balance Fe. The steel can further contain 0.40-0.60 wt % Ni.
The surface can comprise a steel containing 0.31-0.38 wt % C, 0.60-0.90 wt % Mn, up to 0.04 wt % P, up to 0.05 wt % S, balance Fe.
The surface can comprise a steel containing up to 0.35 wt % C, up to 0.90 wt % Mn, 0.35 wt % P, up to 0.04 wt % S, 0.15-0.30 wt % Si, balance Fe.
The surface can comprise a steel containing at least one of molybdenum, chromium and nickel.
The percent corrosion inhibition can comprise a percent corrosion inhibition of greater than about 80%, more preferably greater than about 85%, and even more preferably greater than about 90%.
The percent oxide dissolution using 80 micron particle sized magnetite, when the solution is maintained at 110° F. at pH 6.5 with no agitation and measured at 72 hours, can comprise a percent oxide dissolution of at least about 40%, more preferably at least about 45%, and even more preferably at least about 50%.
The percent corrosion inhibition can comprise a percent corrosion inhibition of greater than about 90%, and the percent oxide dissolution using 80 micron particle sized magnetite, when the solution is maintained at 110° F. at pH 6.5 with no agitation and measured at 72 hours, can comprise a percent oxide dissolution of at least about 35%.
Each of R
1
, R
2
, R
3
and R
4
can comprise hydrogen or an alkyl or substituted alkyl, the alkyl or substituted alkyl can contain C
1
to C
8
, more preferably the alkyl or substituted alkyl contains C
1
to C
6
, and even more preferably the alkyl or substituted alkyl contains C
1
to C
4
. The alkyl or substituted alkyl can be branched or straight chained. Three of the R
1
, R
2
, R
3
and R
4
groups can comprise hydrogen, with the fourth R
1
, R
Meskers, Jr. Donald A.
Tippett Roger John Arthur
BetzDearborn Inc.
Greenblum & Bernstein P.L.C.
Hardee John
LandOfFree
Method of cleaning a metal surface does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of cleaning a metal surface, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of cleaning a metal surface will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2973891