JP2007131913A - Anticorrosive for reducing erosion or corrosion, and method for reducing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anticorrosive for reducing erosion or corrosion where, even if its amount to be added is controlled at the pH in 25°C, the pH in the range of 130 to 180°C can be highly held, thus the solubility of an iron oxide film is reduced, and the suppression of corrosion and thickness reduction can be attained, and to provide a method for reducing the same. <P>SOLUTION: The anticorrosive for reducing erosion or corrosion comprises 1 pts.wt. morpholine and 0.1 to 1 pts.wt. of at least one amine selected from the group consisting of alkanol amines and an aliphatic cyclic amines. In the corrosion prevention method for boiler equipment, the anticorrosive is added. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an anticorrosive agent and method for reducing erosion and corrosion (including FAC) in boiler equipment.

  The metal surface is covered with a protective film such as an oxide, and even when contacted with water, direct contact between the metal and water is prevented due to the film. However, when this film partially peels off due to the shearing force based on the flow rate of water or the collision effect of the water flow, the metal and water come into direct contact with each other at the peeled part and rapidly corrode.

  Such corrosion is called erosion / corrosion.

  In recent years, a problem of thinning of a large-diameter pipe for steam at a power plant has suddenly occurred, and investigation of the cause has revealed that there is a high possibility of occurrence of FAC (also called flow-induced corrosion or flow accelerated corrosion).

  FAC is strictly different from erosion and corrosion in that it occurs in the presence of a metal oxide film. That is, in the FAC, iron dissolved from the oxide film is carried away to the water side by the water flow or its disturbance. The higher the flow rate, the more iron in the film flows away, and the film dissolves faster to make up for it, making the film thinner and thinner. To compensate for this, the metal itself dissolves and reinforces the film thickness. However, as the flow rate increases, the supply of oxygen increases and the reaction between oxygen and the metal is promoted. Dissolution of metal is corrosion itself, and thus corrosion proceeds. Actually, not only the flow velocity, but also hydraulic factors (fluid properties, flow velocity, pipe shape, pipe inner surface roughness), material factors (steel material, Cr, Mo, Cu content), environmental factors (temperature, pH, Dissolved oxygen, ORP) also affects.

  The erosion / corrosion and the FAC both have a waveform pattern and a horseshoe shape in appearance, and are difficult to distinguish. In the present invention, FAC is a type of erosion / corrosion.

  Ammonia and amines are well known as anticorrosives for boiler steel materials. The use of amines was also examined for FAC ("Piping Technology" February 2005 issue, page 11, left column).

  The amine that has been used as a conventional anti-condensation agent for pure water supply is composed of neutralizing amines such as ammonia, morpholine, 2-ethanolamine, monoisopropanolamine (MIPA) and cyclohexylamine. In other words, cyclohexylamine and 2-ethanolamine are mixed and mixed as a mixture.

  In using these conventional feed and condensate anticorrosive agents, the amount of use is designed in consideration of the ability to raise pH at around room temperature. The pH management standard is also set at 25 ° C., and the temperature is measured and managed. The fact that there is a control standard for pH means that there is an upper limit of the amount added depending on the type of drug to be added.

  In general, the pH of boiler feedwater should be controlled as high as about 9.6 to 9.7 at 25 ° C. with ammonia or amine in order to suppress corrosion in steel pipes. When copper pipes or the like are used for the condenser or the condenser, an amine base agent having low corrosiveness to copper is selected to suppress the corrosion, and the upper limit of the pH when used is 25 ° C. It is necessary to suppress to about 9.3 to 9.4.

  Ammonia is easy to raise the pH at 25 ° C in a small amount, but it is easy to corrode copper parts, and it is easy to cause water leakage due to thinning and contamination problems due to intrusion into cooling water boiler water supply. In relatively few cases are used. In addition, there is a demand for amines that generate less ammonia due to thermal decomposition during operation.

When the boiler is operated under the condition that the pH at 25 ° C. is suppressed to about 9.3 to 9.4, the amount of the anticorrosive added is too low, so that the water contact surface of the pipe made of carbon steel in the temperature range of 130 to 180 ° C. In particular, thinning is likely to proceed in areas where the flow velocity changes rapidly, such as bent pipes, throttle parts, and pipe expansion parts (FAC).
"Piping Technology" February 2005 issue

  Many cases have been reported in which corrosion and thinning of carbon steel materials occurred in the low-pressure system of feed water heaters equipped with medium- and high-pressure pure water boilers and combined-pressure multi-pressure gas turbine exhaust heat recovery boilers. Is required.

  The portion where the corrosion thinning occurs is in a temperature range of about 130 to 180 ° C. during normal operation. The mechanism of corrosion thinning is related to the solubility of iron oxide formed on the surface of carbon steel in contact with water. In the temperature range of 130 to 180 ° C., it is estimated that when the pH is lowered, the solubility of iron oxide becomes higher than other temperature ranges, and the corrosion and thinning of the carbon steel are likely to proceed.

  The present invention can maintain a high pH in the temperature range of 130 to 180 ° C. by using specific amines in combination, thereby reducing the solubility of the iron oxide film, An object of the present invention is to provide an anticorrosive agent for reducing erosion / corrosion and a reduction method capable of suppressing the reduction in thickness.

  The anticorrosive agent for reducing erosion and corrosion according to claim 1 comprises 1 part by weight of morpholine and 0.1 to 1 part by weight of at least one amine selected from the group consisting of alkanolamines and aliphatic cyclic amines. Is.

  The anticorrosive agent for reducing erosion and corrosion according to claim 2 is characterized in that, in claim 1, the alkanolamine is monoisopropanolamine and / or 2-ethanolamine, and the aliphatic cyclic amine is cyclohexylamine. is there.

  The method for reducing erosion / corrosion in boiler equipment according to claim 3 comprises adding morpholine and at least one amine selected from the group consisting of alkanolamines and aliphatic cyclic amines to boiler feed water, The morpholine concentration is 1 to 15 mg / L, and the amine concentration is 0.1 to 1 times the morpholine concentration.

  The erosion / corrosion reduction method of claim 4 is characterized in that, in claim 3, the alkanolamine is monoisopropanolamine and / or 2-ethanolamine, and the aliphatic cyclic amine is cyclohexylamine.

  The erosion / corrosion reduction method according to claim 5 is characterized in that, in the claim 3 or 4, when steam is generated in the boiler equipment and a two-phase state of steam / water is generated, an alkanolamine is added as the amine. To do.

According to the present invention, the following effects are exhibited.
(1) When an anticorrosive agent comprising morpholine and at least one amine selected from the group consisting of alkanolamines and aliphatic cyclic amines is added to boiler feed water, compared to when morpholine is added as a single item With a small amount of addition, it is possible to raise the pH sufficiently in the temperature range of 130 to 180 ° C. In addition, the rate of thinning of the carbon steel can be greatly reduced as compared to the case of the same pH with the addition of other compounded amines. Further, even when steam of about 5 to 10% of the amount of water supplied is generated and a steam / water two-phase flow occurs, the rate of thinning of the carbon steel can be greatly reduced.
(2) The thickness reduction rate of carbon steel in a temperature range where erosion / corrosion is likely to occur can be significantly reduced.
(3) The pipe thinning rate in the low pressure system (0.3 to 1 MPa) of the high pressure feed water heater pipe of the pure water feed boiler or the multi-pressure gas turbine exhaust heat recovery boiler of the combined cycle can be reduced, and the equipment life is extended. Is done.
According to the present invention, a carbon steel water supply pipe / feed water heater pipe of a pure water feed boiler that is widely used in industrial private power generation equipment, and a multi-pressure gas of a combined cycle private power generation equipment that has recently been installed. It is possible to sufficiently suppress the thinning phenomenon that is likely to occur in the carbon steel piping and equipment of the low pressure system of the turbine exhaust heat recovery boiler.
(4) Pure water supply It is easy to reduce the iron concentration in the feed water of the boiler, the scale deposition rate and sludge accumulation amount of the evaporation pipe in the boiler can be reduced, and the efficiency of the boiler can be maintained.

  The anticorrosive agent for reducing erosion and corrosion of the present invention contains 1 part by weight of morpholine and 0.1 to 1 part by weight of at least one amine selected from the group consisting of alkanolamines and aliphatic cyclic amines.

  In the erosion / corrosion reduction method of the present invention, morpholine and at least one amine selected from the group consisting of alkanolamines and aliphatic cyclic amines are added to boiler feed water, and morpholine in boiler feed water is added. The concentration is 1 to 15 mg / L, and the amine concentration is 0.1 to 1 times the morpholine concentration.

  When morpholine and the above amine are added to boiler feed water, they may be mixed in advance and added as one agent, or may be added individually.

  By adding morpholine and the above amine, the pH can be made sufficiently high in the temperature range of 130 to 180 ° C. to prevent corrosion of the steel material.

  As the alkanolamine, monoisopropanolamine (hereinafter sometimes referred to as MIPA) and 2-ethanolamine are preferable.

  Cyclohexylamine is preferred as the aliphatic cyclic amine. In addition, cyclohexylamine has high volatility in the range of 100 to 200 ° C., and in a two-phase state of water / steam, it easily moves from the water side to the steam side, and the concentration on the water side decreases.

  In the present invention, 0.1 to 1 part by weight, preferably 0.4 to 0.7 part by weight, of at least one amine selected from the group consisting of alkanolamine and / or aliphatic cyclic amine with respect to 1 part by weight of morpholine. Use at the rate of. The amount of morpholine added to the aqueous system is 1 to 15 mg / L, preferably 3 to 10 mg / L, and the amount of amine added is 0.1 to 1 part by weight of this morpholine amount, preferably 0.4. -0.7 parts by weight.

  In a system in which steam is generated in the target system and water in a two-phase state of steam / water flows, an amine having a large distribution ratio (concentration ratio) between the vapor phase / water phase (the distribution ratio is greater than 1) There is a high possibility that the concentration in the aqueous phase is lowered by shifting to the phase side, and the initial compounding concentration of the amine is lowered. Therefore, in this case, it is appropriate to blend an alkanolamine having a distribution ratio smaller than 1.

  Hereinafter, examples and comparative examples will be described. In the following examples and comparative examples, the forced circulation test boiler shown in FIG. 1 was used.

  In FIG. 1, a gas purge line 2, a safety valve 3, a pressure regulating valve 4, a test liquid replenishment system 5, a temperature regulating heater 6, a water quality adjusting blow line 7, and the like are provided in the collective drum unit 1, and steam having a pressure reducing valve 8. An exhaust system 9 is connected.

  Water in the collecting drum 1 is introduced into a straight pipe 14 via a downpipe 10, a high-pressure circulation pump 11, a flow rate control valve 12, and a turbine flow meter 13. The inlet side of the pipe 14 is a running / rectifying section. A corrosion test piece mounting portion 15 is provided in the middle of the pipe 14, and a corrosion test piece is attached here. A temperature control thermometer 16 is provided on the outlet side of the pipe 14.

  A discharge line 19 having a cooling pipe / decompressor 17 and a pH meter 18 is connected to the end of the pipe 14. A gas purge line 20 and a bypass circulation line 21 are connected to the end of the pipe 14. The bypass circulation line 21 is connected to the collective drum unit 1.

  All the wetted parts of this test apparatus are made of SUS304.

Comparative evaluation was performed under the following test conditions.
Test piece: Carbon steel test piece (SPCC, 50 × 15 × 1.0 mm, # 400 emery polishing)
Temperature condition: 150 ° C
Test water: pure water + amine
The pH of the test water (25 ° C) assumes that there is a copper-based material in the feed water condensate system.
9.6, 9.6 assuming the case of only iron-based material was set.
Dissolved oxygen concentration in test water: 0.02 mg O / L or less (nitrogen purge of feed water + heating deaeration)
Flow velocity: 1.5m / sec
Test time: 240 hours Steam generation: Table 1: No steam generation (water single phase flow state)
Table 2: Steam generation (10% of water supply amount) [to create a two-phase flow state of steam / water]
The test results are shown in Tables 1 and 2.

  As shown in Tables 1 and 2, since the upper limit addition amount of each anticorrosive agent is determined based on the pH set at 25 ° C. with a single anticorrosive agent, the anticorrosive effect at the high temperature part is not satisfactory. On the other hand, according to the present invention, by combining a plurality of specific amines even within a pH range set at 25 ° C., the thinning rate can be sufficiently reduced even if a small amount of anticorrosive agent is used.

It is a systematic diagram of a test device.

Explanation of symbols

1 Collecting drum section 14 Pipe 15 Corrosion test piece mounting section

Claims (5)

  An anticorrosive agent for reducing erosion / corrosion, comprising 1 part by weight of morpholine and 0.1 to 1 part by weight of at least one amine selected from the group consisting of alkanolamines and aliphatic cyclic amines.   The anticorrosive agent for reducing erosion and corrosion according to claim 1, wherein the alkanolamine is monoisopropanolamine and / or 2-ethanolamine, and the aliphatic cyclic amine is cyclohexylamine.   To the boiler feed water, morpholine and at least one amine selected from the group consisting of alkanolamines and aliphatic cyclic amines are added, and the morpholine concentration in the boiler feed water is set to 1 to 15 mg / L. A method for reducing erosion and corrosion in boiler equipment, characterized in that the concentration is 0.1 to 1 times the morpholine concentration.   4. The erosion / corrosion reduction method according to claim 3, wherein the alkanolamine is monoisopropanolamine and / or 2-ethanolamine, and the aliphatic cyclic amine is cyclohexylamine.   5. The erosion / corrosion reduction method according to claim 3, wherein, when steam is generated in the boiler equipment and a two-phase state of steam / water occurs, alkanolamine is added as the amine.

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