CN1262488C - Corrosion inhibition method for non-passive metal and boiler - Google Patents
Corrosion inhibition method for non-passive metal and boiler Download PDFInfo
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- CN1262488C CN1262488C CNB021499810A CN02149981A CN1262488C CN 1262488 C CN1262488 C CN 1262488C CN B021499810 A CNB021499810 A CN B021499810A CN 02149981 A CN02149981 A CN 02149981A CN 1262488 C CN1262488 C CN 1262488C
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- boiler
- water
- corrosion
- heat transfer
- citric acid
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
- C23F11/08—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids
- C23F11/10—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids using organic inhibitors
- C23F11/12—Oxygen-containing compounds
- C23F11/124—Carboxylic acids
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
- F22B37/00—Component parts or details of steam boilers
- F22B37/02—Component parts or details of steam boilers applicable to more than one kind or type of steam boiler
- F22B37/025—Devices and methods for diminishing corrosion, e.g. by preventing cooling beneath the dew point
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Preventing Corrosion Or Incrustation Of Metals (AREA)
Abstract
To suppress corrosion causing in a nonpassivated metallic body such as a heat transfer pipe of a boiler by the influence of water. The method of suppressing corrosion includes a stage where the concentration of citric acid contained in water influencing on a nonpassivated metallic body such as a heat transfer pipe of a boiler is set in at least 50 mg/l. Suppressible corrosion by this method is, e.g. local corrosion occurring in the thickness direction of a nonpassivated metallic body.
Description
[ technical field]
The present invention relates to a method for suppressing corrosion, and more particularly to a method for suppressing corrosion caused by moisture on a non-passivated metal body such as a heat transfer tube of a boiler.
[ background art]
A once-through boiler, which is a category of special cycle boilers specified in Japanese Industrial Standards (JIS), is provided with a heat transfer pipe that heats feed water to generate steam. Since such heat transfer tubes are made of a non-passivated metal such as carbon steel, the portions in contact with the boiler water are corroded and damaged by the boiler water, which may have a fatal influence on the life of the once-through boiler. For this reason, in order to stably operate the once-through boiler for a long period of time, it is necessary to effectively suppress corrosion of the heat transfer pipe.
Therefore, JIS B8223: 1999, from the viewpoint of suppressing the above corrosion occurring in the heat transfer tubes, various management items concerning the boiler water quality of the special cycle boiler are set and recommended standards thereof are defined.
Corrosion of heat transfer tubes is generally evaluated based on three criteria:
(1)mdd(mg/dm2day): is a unit surface area (1 dm) representing a contact surface with water2) Average daily mass loss (mg).
(2) ipy (inches/year): is an index showing the reduction (inches) in the thickness (wall thickness) of the heat transfer tube in one year.
(3) Number of etched holes/cm2: is a unit surface area (1 cm) representing a contact surface with water2) An indication of the number of pits produced. The term "etched hole" means a portion of the heat transfer pipe which faces the water from the side of the contact surface to the opposite side in the thickness direction (against the side of contact surface with the water)Side), i.e., pitting due to pitting corrosion (see, for example, journal industry news agency, corrosion protection association, "corrosion protection technical review", pages 31-33).
However, it is suitable for JIS B8223: 1999, and while evaluating the progress of corrosion of the heat transfer tubes based on the above-mentioned index, even if it can be judged that the corrosion of the heat transfer tubes at the portion in contact with the boiler water does not reach the damage, the portion of the heat transfer tubes may be unexpectedly damaged by corrosion. Accordingly, the boiler water control standard recommended by JIS is not necessarily effective for suppressing corrosion of the heat transfer tubes.
[ summary of the invention]
The purpose of the present invention is to suppress corrosion of a non-passivated metal body such as a heat transfer tube of a boiler due to the influence of moisture.
The corrosion inhibiting method for a non-passivated metal body according to the present invention is a method of inhibiting corrosion of a non-passivated metal body due to the influence of moisture. It comprises the following steps: the concentration of citric acid contained in the moisture affecting the non-passivated metal body is set to at least 50 mg/l. Corrosion that can be inhibited in this way is, for example, localized corrosion.
In addition, a corrosion inhibiting method according to another aspect of the present invention is a method for inhibiting corrosion generated in a heat transfer pipe of a boiler, including the steps of: the concentration of citric acid contained in the boiler water in the boiler is set to at least 50 mg/l. Corrosion that can be suppressed by this method is, for example, local corrosion of the heat transfer pipe from the side of the contact surface with water to the opposite side (opposite side) in the thickness direction.
[ brief description of the drawings]
FIG. 1 is a schematic view of a steam boiler plant including a once-through boiler to which the corrosion inhibition method of the present invention is applicable.
Fig. 2 is a partial sectional schematic view of the once-through boiler.
Fig. 3 is an enlarged view of a portion III of fig. 2.
Fig. 4 is a graph showing the results of examining the relationship between the citric acid concentration of the boiler water and the maximum erosion hole depth value generated in the heat transfer pipe.
[ description of symbols]
2-once-through boiler
5-Heat transfer tube
5 a-etching hole
W-boiler water
[ embodiments of the invention]
Referring to fig. 1, a schematic view of a steam boiler apparatus including a once-through boiler to which the corrosion inhibition method of the present invention is applicable will be described. In the figure, a steam boiler apparatus 1 is mainly provided with a once-through boiler 2 and a water supply apparatus 3.
As shown in fig. 2, the once-through boiler 2 mainly includes: the storage portion 4 for storing the feed water supplied from the water supply device 3, a plurality of heat transfer tubes 5 (an example of a non-passivated metal body) provided upright on the storage portion 4, a water tank (ヘフダ)6 having a supply line 6a for supplying steam to a load device (not shown) provided at an upper end portion of the heat transfer tubes 5, and a heating device 7 for heating the feed water and generating steam. The planar shapes of the reservoir 4 and the tank 6 are set in a ring shape. The reservoir 4 has a discharge port 4a having an unillustrated open/close valve for discharging the feed water (boiler water W) stored therein.
The heat transfer pipe 5 is a member made using a non-passivated metal, i.e., a non-passivated metal body. Here, the non-passivated metal body refers to a metal that is not naturally passivated in a neutral aqueous solution, and is usually a metal other than stainless steel, titanium, aluminum, chromium, nickel, zirconium, and the like. Specifically, carbon steel, cast iron, copper alloy, and the like. Further, carbon steel is sometimes passivated in the presence of a high concentration of chromate ions even in a neutral aqueous solution, but this passivation depends on the influence of chromate ions, and is hardly said to be a natural passivation in a neutral aqueous solution. Carbon steel is therefore within the scope of the non-passivated metals herein. Copper and copper alloys are expensive in the electrochemical series (emf series), and therefore are generally considered to be metals that are difficult to corrode due to the influence of moisture, but are not metals that are naturally passivated in a neutral aqueous solution, and therefore fall under the category of non-passivated metals.
The water supply device 3 is a device for supplying water to the once-through boiler 2, and mainly includes: a water injection line 8 for makeup water, a water supply tank 9 for storing makeup water from the water injection line 8, and a water supply line 10 (fig. 1) for supplying feed water to the storage section 4 of the once-through boiler 2.
Here, the water injection line 8 is provided with a soft hydration device 11 and a deoxidation device 12 in this order. The demineralizer 11 replaces various hardness components and the like contained in the makeup water with sodium ions, and converts the makeup water into demineralized water. On the other hand, the deoxidation apparatus 12 mechanically removes dissolved oxygen contained in the makeup water.
The water supply line 10 is provided with a chemical injection device 13 for injecting a chemical into the water supply. The agent injected into the water supply by the injection device 13 is an agent for adding citric acid to the water supply, and will be described in detail later.
When the steam boiler device 1 is operated, makeup water is supplied from the water injection line 8 to the water supply tank 9, and the makeup water is stored in the water supply tank 9. The stored feed water is treated by the water softening apparatus 11 and the deoxidation apparatus, that is, the soft water subjected to the deoxidation treatment. A pump, not shown, is operated to supply the feedwater stored in the feedwater tank 9 to the once-through boiler 2 through a feedwater line 10.
In the once-through boiler 2, the feed water supplied through the feed water line 10 is stored in the storage portion 4 as boiler water W. The boiler water W stored in the storage portion 4 rises in each heat transfer pipe 5 while being heated by the heating device 7, and gradually turns into steam. The steam generated in each heat transfer pipe 5 is collected in the water tank 6 and supplied to the load device through the supply pipe 6 a.
During the operation of the steam boiler device 1, the heat transfer tubes 5 used in the once-through boiler 2 are continuously in contact with the boiler water W at the lower end portion indicated by the chain line III in fig. 2, i.e., at the portion connected to the reservoir 4. Therefore, the heat transfer pipe 5 is susceptible to corrosion by the boiler water W. In particular, the lower end portion of the heat transfer pipe 5 is likely to be locally corroded in addition to corrosion in which the inner peripheral surface is thinned, and thus may be damaged by minute holes.
The local corrosion referred to herein is, as shown in fig. 3 (an enlarged view of a portion III in fig. 2), a hole-like corrosion of the heat transfer tube 5 from the side of the contact surface with water to the opposite side (opposite side) in the thickness direction, that is, a hole-like corrosion occurring in the thickness (wall thickness) direction of the heat transfer tube 5. Hereinafter, the occurrence of such local corrosion is referred to as "pitting corrosion", and pitting corrosion caused by the pitting corrosion is referred to as "etching hole" (indicated by reference numeral 5a in fig. 3).
In order to suppress damage to the heat transfer tubes 5 due to corrosion during operation of the steam boiler device 1, the concentration of citric acid contained in the boiler water W is continuously measured while injecting a chemical agent into the feed water from the chemical injection device 13 as appropriate. The concentration of citric acid contained in the boiler water W is set to be at least 50mg/l (i.e., 50mg/l or more), and preferably at least 100mg/l (i.e., 100mg/l or more). The upper limit of the citric acid concentration of the boiler water W is not particularly limited, but is usually preferably 800mg/l or less, and more preferably 500mg/l or less. When the citric acid concentration exceeds 800mg/l, the corrosion-inhibiting effect described later, particularly the effect of inhibiting the growth of corrosion pores, is hardly exhibited only by increasing the amount of the chemical to be injected into the water from the chemical injector 13, and there is a possibility of being uneconomical.
In the present invention, the "citric acid concentration" contained in the boiler water means that the concentrations of the isomers of citric acid and the salts of citric acid and its isomers are also included in addition to the citric acid contained in the boiler water. Here, the isomer of citric acid includes, for example, isocitric acid as a structural isomer, and other various isomers. In addition, citric acid and its isomer salts include (dissolved) normal salt (M) contained in boiler water3C6H5O7) Hydrogen salt (M)2HC6H5O7Or M1H2C6H5O7) Or as their hydrates. In the chemical formula of the salt, M represents a metal element such as an alkali metal or an alkaline earth metal. But the present inventionIn the specification, the "citric acid concentration" of such a salt is expressed as citric acid (C)6H8O7) The converted concentration. Hereinafter, the term "citric acid" may be used to encompass isomers thereof and the above salts.
Such a concentration of citric acid contained in the boiler water W can be generally determined by a method of developing the boiler water W with an enzyme and measuring the color based on the absorbance ofultraviolet rays. Specifically, citric acid contained in the boiler water W is decomposed into oxaloacetate and acetic acid in the presence of a citrate lyase, as shown in the following reaction formula (1). Oxaloacetate produced herein consumes NADH (nicotinamide nucleotide) in the presence of MDH (malate dehydrogenase) as shown in the following reaction scheme (2),decomposition into L-malic acid and NAD+. Oxaloacetate produced by the reaction of the reaction formula (1) is unstable and is decarboxylated to partially pyruvate. This pyruvate is decomposed into L-lactate and NAD in the presence of LDH (lactate dehydrogenase) as shown in the following reaction formula (3) by consuming NADH+). Therefore, the amount of NADH consumed by the reactions of the reaction formulae (2) and (3) is proportional to the amount of citric acid in the boiler water W, and therefore, if the amount of NADH consumed is measured based on the absorbance of ultraviolet light having a wavelength of 340nm, the citric acid concentration of the boiler water W can be determined.
[ solution 1]
The concentration of citric acid contained in the boiler water W is set in accordance with JIS B8223: 1999, the boiler water quality management standard which is not mentioned in the present invention for the first time.
When the concentration of citric acid contained in the boiler water W is adjusted as described above, the heat transfer tube 5 can suppress corrosion due to a reduction in the thickness of the portion in contact with the boiler water W, and also suppress the occurrence and growth of the erosionholes 5a, thereby making it difficult to cause damage due to corrosion (particularly, erosion holes 5 a). In other words, when the citric acid concentration of the boiler water W is less than 50mg/l, the ratio of JIS B8223: 1999, other control standards (for example, the PH value of the boiler water, the chloride ion concentration, etc.) are set in a required state, and corrosion of the heat transfer pipe 5, particularly the corrosion holes 5a by the pitting corrosion, is likely to occur.
When the citric acid concentration of the boiler water W is set as described above, it is considered that the corrosion of the heat transfer tubes 5 is suppressed because the components eluted from the heat transfer tubes 5 act on the citric acid due to the influence of dissolved oxygen, chlorine ions, or the like, which is a corrosion-promoting factor of the heat transfer tubes 5 contained in the boiler water W, and a corrosion-resistant coating (anti-corrosion coating) is formed on the inner surface of the heat transfer tubes 5. In particular, dissolved oxygen and chlorine ions may cause the heat transfer pipe 5 to locally exhibit an anode, thereby causing pitting corrosion. However, it is considered that citric acid contained in the boiler water W is generally present as an anion or a negatively charged colloidal ion (ミセル), and therefore, it is likely to be adsorbed on such an anode, and an anticorrosive film is likely to be selectively formed on the portion. Therefore, when the citric acid concentration of the boiler water W is adjusted as described above, progress of pitting corrosion in the heat transfer pipe 5 can be suppressed very effectively.
In the steam boiler device 1, the citric acid concentration of the boiler water W may be set, for example, as described above, such that an appropriate amount of chemical is injected into the feed water in the feed pipe 10 from the chemical injection device 13, and the concentration ratio of the feed water (i.e., the boiler water W) in the once-through boiler 2 due to heating is appropriately adjusted. When the amount of boiler water W discharged (so-called discharge) from the discharge port 4a is suppressed, the concentration ratio of the boiler water W can be increased. On the other hand, when the concentrated boiler water W is appropriately discharged from the discharge port 4a while diluting the boiler water W with the feed water from the feed water pipe 10, the concentration ratio of the boiler water W can be reduced.
The above-mentioned chemical to be injected into the water supply from the drug injection device 13 can increase the citric acid concentration in the water supply, and an aqueous solution of citric acid or a salt thereof can be usually used. The citrate to be used herein is not particularly limited as long as it is water-soluble, but it is usually a salt of an alkali metal such as sodium, potassium, or lithium, or a salt of an alkaline earth metal such as calcium or magnesium. However, the alkaline earth metal salt is preferably an alkali metal salt as the citrate because it imparts a hardness component such as calcium or magnesium to the feed water, which causes scale to be formed on the heat transfer tube 5.
The form of the citrate is not particularly limited, and is normal salt (M)3C6H5O7) Or hydrogen salt (M)2HC6H5O7Or M1H2C6H5O7) Or a hydrate thereof. In the chemical formula, M represents a metal element such as an alkali metal or an alkaline earth metal.
Preferred examples of the above-mentioned agent include aqueous solutions of citric acid, monopotassium citrate, tripotassium citrate monohydrate, sodium citrate dihydrate, disodium citrate n-hydrate, and trisodium citrate.
[ other embodiments]
(1) In the above embodiment, the concentration of citric acid contained in the boiler water W is set to the above range by appropriately adjusting the concentration ratio of the boiler water W while appropriately injecting the chemical into the feedwater. When citric acid is previously contained in the feed water, the concentration of citric acid in the boiler water W can be set in the above range by adjusting only the concentration ratio of the boiler water W.
(2) The corrosion inhibiting method of the present invention is described in the above embodiment by taking the case of inhibiting corrosion of the heat transfer pipe used in the once-through boiler as an example, but the corrosion inhibiting method of the present invention is not limited thereto. For example, the corrosion inhibiting method of the present invention can be similarly applied to a member which is likely to be corroded by the moisture such as water or steam (a non-passivated metal body) and which is particularly likely to cause the above-described localized corrosion (pitting corrosion), such as a heat transfer tube of a boiler other than a once-through boiler, a water storage tank, a water supply pipe, a condensate pipe, and a water supply pipe used in a steam boiler device using various boilers such as a once-through boiler, a heat transfer tube, a water storage tank, and various pipes used in various heat engine devices other than a boiler (for example, a water boiler, an absorption chiller, a cooling tower, and the like).
When the corrosion inhibiting method of the present invention is applied to a non-passivated metal body other than a heat transfer tube of a boiler, the concentration of citric acid contained in the water that affects the non-passivated metal body is set as described above (i.e., at least 50mg/l, preferably at least 100mg/l, preferably 800mg/l or less, and more preferably 500mg/l or less). For example, when the pitting corrosion is suppressed in the reservoir of the steam boiler device, the citric acid concentration of the water (feed water) stored in the reservoir is set as described above.
[ examples]
The feed water having different citric acid concentrations was supplied to a boiler manufactured by the applicant company while the operation was performed. At this time, the concentration ratio of the boiler water is adjusted so that: the M alkalinity (acid consumption (pH4.8)) of the boiler water was 300mg CaCO3The pH of the boiler water was adjusted to 11.5% by appropriately injecting an aqueous sodium hydroxide solution into the feed water, wherein the concentration of chloride ions was 200mg/l, the concentration of sulfate ions was 400mg/l, the concentration of dissolved oxygen was 4.0ppm, and the concentration of citric acid was 70mg/l. The boiler operating conditions were set to: the running time is 48 hours, the running pressure is 0.29MPa and the water supply temperature is 50 ℃.
The relationship between the citric acid concentration of the boiler water and the maximum value of the depth (μm) of the corrosion hole generated in the heat transfer tube was examined for the boiler operated under the above conditions. The citric acid concentration of the boiler water was confirmed by the method described in the instruction manual using a general food analysis enzyme reagent (trade name: F- キット citric acid) manufactured by Ross (ロシェ&ダィァグノスティックス). The results are shown in FIG. 4. As is clear from FIG. 4, when the concentration of citric acid is 50mg/l or more (particularly 100mg/l or more), the depth of the corroded hole formed in the heat exchanger tube tends to be small. It is understood that if the citric acid concentration of the boiler water is set to at least 50mg/l, the corrosion of the heat transfer tubes, particularly the boiler damage due tothe progress of pitting corrosion, can be effectively suppressed.
[ Effect of the invention]
The present invention relates to a method for suppressing corrosion of a non-passivated metal body, which can suppress corrosion, particularly localized corrosion, generated by the non-passivated metal body by setting the citric acid concentration in the water affecting the non-passivated metal body to at least 50 mg/l.
Further, the present invention relates to a method for suppressing corrosion of a boiler, which can suppress corrosion, particularly localized corrosion, generated on a heat transfer pipe by setting the citric acid concentration in boiler water in the boiler to at least 50 mg/l.
Claims (2)
1. A method for suppressing corrosion of a heat transfer pipe of a boiler, comprising the steps of: the concentration of citric acid contained in the boiler water in the boiler is set to 50mg/l to 800 mg/l.
2. The method of suppressing corrosion of a boiler according to claim 1, wherein the corrosion is localized corrosion of the heat transfer pipe from a side of a contact surface with water to an opposite side in a thickness direction.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001337727A JP2003147556A (en) | 2001-11-02 | 2001-11-02 | Method of suppressing corrosion in nonpassivated metallic body, and method of suppressing corrosion in boiler |
| JP337727/2001 | 2001-11-02 | ||
| JP337727/01 | 2001-11-02 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN1418829A CN1418829A (en) | 2003-05-21 |
| CN1262488C true CN1262488C (en) | 2006-07-05 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CNB021499810A Expired - Fee Related CN1262488C (en) | 2001-11-02 | 2002-11-01 | Corrosion inhibition method for non-passive metal and boiler |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JP2003147556A (en) |
| KR (1) | KR20030038373A (en) |
| CN (1) | CN1262488C (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100685289B1 (en) * | 2004-08-25 | 2007-02-22 | 이성호 | Apparatus removing harmonics of 3-phase multiple-line power line |
| JP5066972B2 (en) * | 2007-03-27 | 2012-11-07 | 栗田工業株式会社 | Boiler anticorrosion method |
| JP5145916B2 (en) * | 2007-12-18 | 2013-02-20 | 東亜ディーケーケー株式会社 | Electrolyte for polarographic diaphragm electrode and polarographic diaphragm electrode |
| JP6314560B2 (en) * | 2014-03-14 | 2018-04-25 | 栗田工業株式会社 | Water treatment method for steam generating equipment |
| JP6866695B2 (en) * | 2017-03-07 | 2021-04-28 | 三浦工業株式会社 | Water treatment agent, scale removal method, and scale suppression method |
-
2001
- 2001-11-02 JP JP2001337727A patent/JP2003147556A/en active Pending
-
2002
- 2002-10-24 KR KR1020020065271A patent/KR20030038373A/en not_active Application Discontinuation
- 2002-11-01 CN CNB021499810A patent/CN1262488C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CN1418829A (en) | 2003-05-21 |
| JP2003147556A (en) | 2003-05-21 |
| KR20030038373A (en) | 2003-05-16 |
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