JP5411461B2 - Corrosion preventive material for coating inner surface of corrosive fuel gas and anticorrosion method using the same - Google Patents

Description

  The present invention relates to an anticorrosion technique for corrosive fuel gas piping such as coke oven gas used mainly in ironworks and thermal power plants. In particular, on the inner surface of a coke oven gas pipe, a corrosion reaction that generates iron sulfide occurs at the same time as wet corrosion, so that the thickness of the pipe decreases and pitting corrosion progresses, and a gas leak accident due to a hole in the pipe is likely to occur. . The present invention relates to an anticorrosive material for coating the inner surface of a corrosive fuel gas and an anticorrosion method for solving such problems in equipment maintenance.

  Since the coke oven gas pipe is used for a long period of about 10 to several tens of years, corrosion of the inner surface of the pipe (usually a steel pipe) gradually proceeds, and the thickness of the pipe is reduced and pitting corrosion progresses. There is a problem in equipment maintenance that gas leaks occur due to holes.

The main components of the coke oven gas are hydrogen, methane, carbon monoxide, tar, and the like, and a trace amount ( ^{3 to 5} g / Nm ³ ) of hydrogen sulfide is also included (for example, Non-Patent Document 1 below). Therefore, coke oven gas is a flammable gas and is harmful to the human body. Therefore, if a gas leak occurs, there is a risk of a serious accident, which cannot be left unattended.

  In the conventional technology, as a post-maintenance measure when a gas leak from the coke oven gas pipe occurs, the FRP sheet is bonded as an emergency measure and wrapped with a band to stop the leak, and the pipe is renewed when the equipment is stopped as a permanent measure. ing. In addition, as a preventive maintenance measure to prevent the development of pitting corrosion from the inner surface of the coke oven gas piping, a flame lining as a corrosion prevention method (high corrosion resistance paint using vinyl ester resin in the vehicle and glass flakes mixed in as a scaly material) In order to lengthen the equipment life until drilling by increasing the corrosion allowance, the method of increasing the thickness of the steel pipe has been adopted.

However, the anticorrosion method by frame lining requires coating a single layer of primer and several layers of layer lining after adjusting the base material by blasting, and the construction cost is very expensive. Requires equipment outage.
On the other hand, the method of increasing the thickness of the steel pipe increases the weight of the pipe, leading to an increase in the strength of the pipe support and an increase in the construction cost of the pipe laying, and it is often difficult to employ. From such a state of the prior art, development of a more effective and inexpensive preventive maintenance technology for a coke oven gas pipe, that is, a corrosion prevention technology has been desired.

Edited by the Japan Iron and Steel Institute Iron and Steel Production Method (Volume 1) Maruzen Co., Ltd. (1982) Proceedings of the 28th Rust Prevention and Corrosion Technology Presentation Conference (2008) Edited by the Japan Road Association Steel Hand Bridge Painting and Anticorrosion Manual Maruzen Co., Ltd. (2005) JP 2005-255793 A

  In view of the state of the prior art, it is an object of the present invention to provide an anticorrosion technique for the inner surface of a coke oven gas pipe that is more effective and less expensive than conventional techniques such as frame lining and steel pipe thickness increase. In other words, it prevents the drilling due to the pitting corrosion of the coke oven piping over a long period of time, improves the reliability of the equipment while improving the safety of workers during inspection work, and the load of piping maintenance This makes it a challenge to realize inexpensive and safe equipment management of coke oven gas piping.

In order to solve the above-described problems, the present inventors have examined requirements necessary for an anticorrosive material for coating the inner surface of a coke oven gas pipe.
First, considering the internal environment of the coke oven gas piping, it is as follows. The main components of coke oven gas are hydrogen, methane, carbon monoxide, tar, etc. In addition to containing trace amounts of hydrogen sulfide (3-5g / Nm ³ ), drain, chloride ion, nitrate ion An aqueous solution containing sulfate ions, nitrite ions, thiosulfate ions, ammonium ions, benzene, toluene, and xylene collects in the lower part of the pipe. The pH of the drain is approximately 8-9 weak alkaline.

  The temperature of the coke oven gas is higher than the outside air temperature, and is usually about 30 to 60 ° C. The reason for the high temperature is as follows. Generally, high-temperature coke oven gas generated in a coke oven is temporarily stored in a coke oven gas holder. Since the holder is always supplied with hot gas and the heat conduction of the gas is poor, the heat radiation from the holder is relatively small. Therefore, the gas temperature in the holder is usually considerably higher than the outside air temperature, and is generally about 30 to 60 ° C. It is considered that the piping through which the gas at such a temperature flows is usually 30 to 60 ° C.

  In such an environment, when there is no anti-corrosion coating on the inner surface of the pipe, there is a trace amount of hydrogen sulfide, so the corrosion reaction that generates iron sulfide over the entire inner surface and the wet corrosion due to drain water and its water vapor are simultaneous. It is thought that progress will occur in parallel. In the coke oven gas piping, for example, Non-Patent Document 2 points out that there is a possibility that a reaction that generates iron sulfide occurs at the same time as wet corrosion, thereby accelerating the corrosion phenomenon.

On the other hand, when considering anticorrosion by coating, durability against gas temperature of 30 to 60 ° C., drain resistance not affected by each component of drain and pH of drain, durability against gas pressure of 0.1 to 0.5 MPa ( There must be an anticorrosive material having the property that coating film deterioration due to swelling is not accelerated under a pressure higher than atmospheric pressure.
Of particular note is that benzene, toluene, and xylene, which are usually used as solvents, are contained in the drain. These solvent components have an action of softening the coating film, losing the adhesive force, and peeling it off in the case of an anticorrosion coating film using an ordinary solvent type epoxy resin paint.

  In addition, it is necessary to pay attention to the fact that the temperature in the coke oven gas piping is 30 to 60 ° C. has an effect of softening the coating film itself and accelerating the swelling as compared with normal temperature. Therefore, the performance required for the anticorrosion material applied to the inner surface of the coke oven gas pipe is that it can form a coating film having no pores that has heat resistance, drain resistance, and pressure resistance and can block hydrogen sulfide.

When the anticorrosion material satisfying the above required performance is examined, the following is obtained.
(1) Being a solvent-free type paint: It is not desirable to use a paint containing a solvent from the viewpoint of drain resistance. As described above, the paint containing a solvent may have a residual solvent in the coating film after curing, and easily reacts with the solvent component in the coke oven gas drain to cause softening or peeling. .
In the case of a solvent-type paint, since the solvent volatilizes at the time of curing, voids are likely to be generated, which is not desirable from the viewpoint of blocking the corrosive components (particularly hydrogen sulfide) in the coke oven.

(2) It must be a room-temperature curable liquid paint: A thermosetting paint cannot be used to coat existing coke oven gas pipes on site.
(3) No special primer is required, and the painting work is simple: it is desirable that the minimum required coating thickness is obtained by coating with at most two layers. The flame lining, which is a prior art, is a resin with a high chemical resistance vinyl ester as a base resin, and glass flakes are dispersed in this. However, when applied to the steel surface, a minimum of two layers including a special primer, Usually, three to four layers of overcoating are necessary, and there is a problem that the construction cost is expensive and the construction period becomes long. Therefore, in order to reduce the construction cost, a dedicated primer is not required, and at least one film layer that can provide the required coating thickness with at most two layers is desirable.

(4) The glass transition temperature (Tg) is 70 to 150 ° C .: Since the temperature of the coke oven gas is 30 to 60 ° C., the heat resistance of the paint needs to be Tg of 70 to 150 ° C. It is.

  However, it is unfortunately difficult to obtain an anticorrosive material satisfying such conditions from the market. For example, a room-temperature curable liquid two-component solvent-free epoxy resin paint developed for the purpose of eliminating solvent odor and reducing environmental impact for water pipe inner surfaces (see Japan Water Works Association Standard JWWA K 157) However, since the glass transition temperature (Tg) is about 60 ° C. or less, the heat resistance is insufficient as an anticorrosive material for coke oven gas piping.

  In addition, the solventless one-component thermosetting epoxy resin composition disclosed in Patent Document 1 has a glass transition temperature (Tg) as high as 150 ° C. and is a liquid solventless type. It is a thermosetting material.

  Therefore, the present inventors improved the existing solvent-free epoxy resin paint for water pipes, and contained a suitable amount of aminoethylpiperazine as a curing agent, which is a liquid solvent-free type. It was found that an epoxy resin paint having a temperature of 70 to 150 ° C. can be realized.

Based on this finding, the first of the present invention is
Room temperature curing consisting of a liquid main component and a curing agent not containing a solvent component mainly composed of one or more epoxy resins selected from the group consisting of bisphenol A type epoxy resin, bisphenol F type and novolak type epoxy resin Type epoxy resin paint, containing 10 to 30 parts by weight of aminoethylpiperazine in 100 parts by weight of the curing agent, and the remainder of the curing agent is one or more of aliphatic polyamines, alicyclic polyamines and alcohols And a glass transition temperature (Tg) of the paint after curing is 70 to 150 ° C.

  When actually performing the inner surface corrosion prevention work of the existing coke oven gas pipe, the corrosion of the inner surface of the pipe has already progressed considerably. Work of unevenness to smooth the unevenness is necessary. It is difficult to deal with pitting corrosion and unevenness adjustment with coating anticorrosive materials, and putty-like anticorrosive materials are also required.

Therefore, the second of the present invention is
This is a putty material for covering the inner surface of a corrosive fuel gas by adding 10 to 30 parts by weight of talc to 100 parts by weight of the anticorrosive material of the first invention.

In the anticorrosive material of the first invention and the putty material of the second invention, the corrosive fuel gas is
2 g / Nm ³ or more of hydrogen sulfide, and the drain contains 0.01 to 10 g / mL each of chloride ion, nitrate ion, sulfate ion, nitrite ion, thiosulfate ion, ammonium ion, benzene, toluene and xylene. This is particularly effective when the aqueous solution contains L.
Both these materials are more effective when the corrosive fuel gas is coke oven gas.

The anticorrosion method of the present invention, when corroding the inner surface of a corrosive fuel gas pipe, is first a step of adjusting the base material of Sa2 or more by a blasting method, and then an organic zinc rich as a primary rust preventive primer if necessary. A step of coating the paint, a step of performing unevenness adjustment with the putty material of the second invention as necessary when there is a pitting corrosion progressing portion, and a step of coating the anticorrosion material of the first invention It is a corrosion prevention method characterized by doing.

In this anticorrosion method, the corrosive fuel gas contains 2 g / Nm ³ or more of hydrogen sulfide, and its drain is chloride ion, nitrate ion, sulfate ion, nitrite ion, thiosulfate ion, ammonium ion, benzene It is particularly effective when it is an aqueous solution containing 0.01 to 10 g / L each of toluene and xylene, and further effective when the corrosive fuel gas is coke oven gas.

  According to the present invention, inexpensive and high-performance anticorrosion construction has become possible as a countermeasure against drilling and gas leakage due to corrosion on the inner surface of a coke oven gas pipe. Thereby, from the viewpoint of equipment maintenance, a great economic effect of reducing repair costs can be obtained by reducing repair costs and reducing the frequency of inspections after repairs. Also, from the viewpoint of safety, the risk of gas leakage is reduced over a long period of time, so it is possible to avoid gas poisoning by the inspector, etc., and avoid the danger of ignition and explosion of the leaked gas. Can be improved.

  The anticorrosive material of the present invention is a two-pack type epoxy resin paint, the main agent is a liquid that does not contain a solvent component, contains 10 to 30% by weight of aminoethylpiperazine in the curing agent, and cures at room temperature. It is a type | mold and the glass transition temperature (Tg) of this coating film after hardening is 70-150 degreeC, It is characterized by the above-mentioned.

  First, the epoxy resin that is the main component of the main agent may be a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, or a novolac type epoxy resin. Further, it may be a mixture of bisphenol A type and bisphenol F type or novolac type. Since these resins are liquid at normal temperature and have an appropriate viscosity as a paint, they can be used as a main agent even without the addition of a solvent. The remaining component of the main agent may be a constitution in which an appropriate amount of thixotropic agent, modifier or adhesion-imparting agent is added to the extender pigment or colored pigment.

  Next, the reason why aminoethylpiperazine is added to the curing agent in the present invention will be described. In ordinary epoxy resin coatings, aliphatic polyamines and alicyclic polyamines are used as the main curing agents, but these polyamines have a single carbon bond (—C—) regardless of whether the molecular structure is linear or cyclic. C-). This bond has low bond strength, and it is difficult to obtain a sufficiently high glass transition temperature (Tg) even if a polyfunctional epoxy resin coating is brought as the main agent to increase the crosslinking density.

  On the other hand, when an aromatic amine is used as a curing agent, a high glass transition temperature (Tg) is obtained due to the strong bonding of the aromatic ring, but room temperature curing is difficult due to the steric hindrance of the aromatic ring, and it is difficult to cure as a thermosetting type. Heating is required. Therefore, an appropriate amount of aminoethylpiperazine is added to the curing agent in order to enable a room-temperature curing and a strong cyclic structure.

  The molecular structure of aminoethylpiperazine is shown in FIG. It has a primary amine, secondary amine, and tertiary amine in combination with an aromatic-like cyclic structure. While aromatic amines have poor reaction due to steric hindrance of the aromatic ring, they have primary amines away from the cyclic structure in the form of ethylamine, so they are highly reactive and allow room temperature curing. be able to. In addition, since the structure has a strong bonding force, which is a characteristic of the annular structure, and a structure having a low degree of freedom after crosslinking, a high glass transition temperature (Tg) may be realized. Moreover, it has a secondary amine in the cyclic portion, and here again, if the epoxy amine curing reaction proceeds, a stronger and more complex entangled cross-linked structure can be obtained.

  The present invention is characterized in that 10 to 30 parts by weight of such aminoethylpiperazine is added to 100 parts by weight of the curing agent. The remaining components of the curing agent may be composed of components that contribute to the reaction, such as alcohols and bisphenol A, in addition to various commonly used aliphatic or alicyclic polyamines.

  Next, the basis for determining the addition ratio of aminoethylpiperazine in the curing agent will be described. FIG. 2 shows a graph of the impact absorption energy according to ASTM D-256 and the water absorption rate of 3% ammonia water in a coating film of 1 mm after 24 hours when the weight% of aminoethylpiperazine is changed in the curing agent.

  As can be seen in the figure, the impact absorption energy is small when aminoethylpiperazine is less than 10% by weight because there is no coating strength, and when it exceeds 30% by weight, the coating becomes too hard and cracks occur. Because it occurs, it goes down. From this, it can be said that the addition of 10 to 30% by weight of aminoethylpiperazine is appropriate in order to obtain an appropriate strength necessary for a practical coating film.

  Further, it has been confirmed that the water absorption rate of 3% ammonia water used for examining chemical resistance is very easy to swell at 10% by weight or less. As the main agent at this time, as the epoxy resin, a novolac type epoxy resin having a weight of 60% by weight was used.

  Next, the putty material of the present invention will be described. The reason why this putty material is necessary is that the above-described anticorrosive material is prepared for coating and is not suitable for filling a pitting corrosion of an existing pipe where corrosion has progressed or for uneven adjustment of an uneven surface. That is, the viscosity at the time of painting is adjusted so that the coating anticorrosive material described above has a coating thickness of 300 μm per coat. Even if it is repeatedly applied before curing, sagging occurs when the coating thickness is 750 μm or more. Therefore, even if the pitting corrosion is filled on the inner surface of the upper part of the pipe, it drops before curing. Similarly, even if a thick coating is applied to adjust the unevenness, sagging occurs before curing, and a smooth surface cannot be obtained.

Therefore, a putty-like material was developed by adding 10 to 30% by weight of talc (Mg ₃ Si ₄ O ₁₀ (OH) ₂ ) to the above-mentioned anticorrosion material for coating. The reason for using talc as an additive is that the viscosity can be adjusted on-site by adjusting the addition amount without lowering the corrosion resistance, and is inexpensive.

  It was confirmed that this putty material can be worked sufficiently by hand-painting with a rubber spatula after filling the base material by blasting in the actual construction, and filling the uneven surface of the corrosive surface with a rubber spatula. . In addition, this putty material had a sag limit of 1.7 mm, and in the confirmation of the anticorrosion performance by the 80 ° C. cathode peeling test, it was almost equivalent to the anticorrosion material for coating as described below.

FIG. 3 is a diagram showing an example of the result of confirming the anticorrosion performance of the putty material of the present invention by an 80 ° C. cathode peeling test. In the 80 ° C. cathode peeling test, the coating surface is in contact with moisture at a temperature of 80 ° C. and a cathode voltage (−1, 50 ± 0.01 V) is applied to the coating ridge (population 疵 6 mmφ). It is a durability confirmation test (for example, a test specified in ASTM G 8-90) for measuring the peel distance.
As seen in the figure, the coating film of the putty material of the present invention was compared with the coating film of the anticorrosive material of the present invention (without talc) in both cases of talc addition of 10% and 20%. The peel width after the cathode peel test at 80 ° C. is almost the same. From this result, it is presumed that there is no decrease in the anticorrosion performance due to the addition of talc.

  Next, the anticorrosion method for the inner surface of the coke oven pipe using the above anticorrosive material and putty material will be described. The construction method can be roughly divided into two embodiments shown in Table 1. Embodiment 1 (hereinafter referred to as anticorrosion coating system 1) is a case where corrosion protection is performed on the existing pipe inner surface where corrosion has progressed to some extent, and Embodiment 2 (hereinafter referred to as anticorrosion coating system 2) is applied to the inner surface of the newly installed pipe. This is a case where anticorrosion is performed during construction.

In the anticorrosion coating system 1, when the inner surface anticorrosion of the existing coke oven gas pipe is actually performed using the above-described anticorrosion material and putty material of the present invention, one more device is required. For example, as shown in Non-Patent Document 3, for example, it is generally necessary to carry out the anticorrosion work after the substrate adjustment by blasting within 4 hours.
In the local anticorrosion work, a primer that enables the anticorrosion work to be performed in the range of 8 hours to 6 months from the preparation of the base by blasting is required for the construction efficiency.

  In the anticorrosion coating system 1, the anticorrosion coating is performed in a four-step process shown in Table 1. The first step is a process for adjusting the substrate, and the substrate is adjusted to a degree of rust removal Sa2 or higher by a blasting method. The reason why the degree of rust removal Sa2 or higher is necessary is that, if the degree of rust removal is less than Sa2, rust remains on 1/3 or more of the surface area, which hinders adhesion of the coating film.

Next, a primer is applied. As the primer, organic zinc-rich paint is preferable because it has excellent overall anticorrosion performance due to the combination of the base preparation surface of Sa2 or higher and the anticorrosive material and putty material of the present invention.
Thereafter, as a third step, filling of the pitting portion on the inner surface of the existing pipe and adjusting the unevenness of the surface unevenness are performed using the putty material of the present invention. The method for applying the putty material is not particularly limited, but can be sufficiently handled by hand coating.
Thereafter, as a fourth step, the anticorrosive material of the present invention is applied. This application can be performed in the same manner as a normal paint.

  On the other hand, when anticorrosion coating system 2 shown in Table 1, that is, when the inner surface of a new steel pipe is subjected to anticorrosion in a coating factory, a primer is unnecessary because there are many facilities that can be applied within 4 hours after blasting. The second step primer application step is unnecessary. In addition, in the manufacture of a new anticorrosion-coated steel pipe, there is no pitting or surface irregularity on the inner surface of the pipe, so that the third step of unevenness adjustment is not necessary. Therefore, the anticorrosive material in the fourth step may be applied immediately after the substrate adjustment in the first step.

  A test was conducted to compare the anticorrosion performance when the present invention was applied to the actual coke oven gas pipe inner surface with a conventional anticorrosion method. The present invention example 1 is the above-described anticorrosion coating system 1, that is, the case where the inner surface of the existing pipe which has been corroded is subjected to anticorrosion coating by the method of the present invention at the site construction. This is a case where the inner surface of the steel pipe is anticorrosive coated by the method of the present invention at factory construction.

  Comparative Example 1 is a case where a commonly used solvent type epoxy resin paint for the inner surface of a gas pipe is coated on the inner surface of the existing pipe with anticorrosion coating. It is a case where it is applied in the field construction. In order to confirm the anticorrosion performance in this test, test coating was actually performed on the coke oven gas piping, and the coating performance was investigated over 6 months. Specifically, test coating is applied to actual piping, and the adhesion strength of the coating film is measured after 1 month, 2 months, and 6 months (measurement method is by an adhesion tester (see ASTM D 4521-02)). Carried out. Table 2 shows the method of the anticorrosion construction of the present invention and the comparative example, and Table 3 shows the measured adhesion values of the test results.

In general, the adhesion required for anticorrosion coating is about 20 kg / cm ² or more, but in Examples 1 and 2 of the present invention, the adhesion of the coating film after 6 months is 100 kg / cm ² or more, which is a very high value. It was. In contrast, in Comparative Example 1 (solvent type epoxy resin for gas pipe inner surface), the adhesion after 6 months was 20 kg / cm ² or less, and it was known that sufficient anticorrosion performance could not be expected. In addition, it can be seen that in Comparative Example 2 (the frame lining used for the inner surface corrosion prevention of the coke oven gas pipes at present), the adhesion after 6 months is maintained at 20 kg / cm ² or more.

  However, as shown in Table 2, in the case of the frame lining, the number of times of coating is one more than the anticorrosion coating system 1 of the present invention, and the total coating thickness excluding the putty is thick, so the construction cost is also very expensive. . Further, regarding the anticorrosion performance, the adhesion between the anticorrosion coating systems 1 and 2 of the present invention is much greater than the adhesion of the frame lining and is stable over a long period of time.

  From the above, as the anticorrosive material of the present invention, the high Tg solventless type room temperature curing type epoxy resin paint of the present invention and the putty material of the present invention to which 10 to 30% by weight of talc is added (if necessary) The anticorrosion method of the present invention used was confirmed to have sufficient anticorrosion performance by an exposure test on the actual inner surface of the coke oven gas pipe.

It is explanatory drawing of the molecular structure of aminoethyl piperazine. It is a figure which shows the example of the result of investigating the weight% of aminoethyl piperazine in a hardening | curing agent, and the characteristic of anticorrosion material. It is a figure which shows the example of the result of having compared the anticorrosion performance in the case where talc is added to the anticorrosion material of this invention (putty material), and the case of no addition.

Claims (5)

Room temperature curing consisting of a liquid main component and a curing agent not containing a solvent component mainly composed of one or more epoxy resins selected from the group consisting of bisphenol A type epoxy resin, bisphenol F type and novolak type epoxy resin Type epoxy resin paint, containing 10 to 30 parts by weight of aminoethylpiperazine in 100 parts by weight of the curing agent, and the balance of the curing agent is one or two of aliphatic polyamine, alicyclic polyamine and alcohols from it, the glass transition temperature (Tg) of the pipe inner surface coating anticorrosive materials corrosive fuel gas is 70 to 150 ° C. of the paint after curing higher.   A putty material for covering the inner surface of a corrosive fuel gas by adding 10 to 30 parts by weight of talc to 100 parts by weight of the anticorrosive material according to claim 1.   When corroding the inner surface of the corrosive fuel gas pipe, first a step of adjusting the surface of Sa2 or more by blasting method, then a step of coating organic zinc rich paint as a primary rust-preventing primer if necessary, and pitting corrosion An anticorrosion method comprising a step of performing unevenness adjustment with the putty material according to claim 2 when necessary and a step of coating the anticorrosion material according to claim 1 as necessary. The corrosive fuel gas contains 2 g / Nm ³ or more of hydrogen sulfide, and its drain contains chloride ion, nitrate ion, sulfate ion, nitrite ion, thiosulfate ion, ammonium ion, benzene, toluene, xylene. The anticorrosion method according to claim 3, wherein each is an aqueous solution containing 0.01 to 10 g / L.   The anticorrosion method according to claim 4, wherein the corrosive fuel gas is coke oven gas.

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