JP2000192219A - Protective tube for measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film excellent in thermal conductivity, heat resistance and erosion resistance by plasma-spraying Cr3C2 cermet on the surface of a heat resistant metallic member in an inert gas atmosphere which does not contain oxygen and changing a part or the whole of metallic Cr in the sprayed coating into chromium carbide. SOLUTION: A Cr3C2 cermet material using Cr or a Cr alloy (such as Cr-Ni, Cr-Co or the like) as a binder metal is plasma-sprayed in an inert gas atmosphere of He or the like which does not contain oxygen, which is held at 500 to 900 deg.C for >=10 min to obtain cermet sprayed coating having 1100 to 1250 Hv hardness. The amt. of the binder metal to be added is desirably controlled to 5 to 60 wt.%. Prior to the thermal spraying working, the body to be thermal- sprayed is heated at 500 to 900 deg.C to improve the adhesion of the sprayed coating. The pressure in the thermal spraying atmosphere is 50 to 1100 hPa. For the purpose of improving its erosion resistance, the thickness of the Cr3C2 cermet sprayed coating is preferably controlled to 50 to 800 μm. It is suitable for surface treated coating for the protecting tube of a thermometer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a protective tube for a measuring instrument,
In particular, petroleum hydrocarbons are pyrolyzed in a cracking furnace, separated and refined, and rectified to produce ethylene or propylene (hereinafter referred to as "olefin").
Etc.) and a surface treatment technology for a thermometer protection tube disposed in a plant for producing a plastic raw material. The surface treatment technology adopted in the present invention is used as a surface treatment technology for a portion where erosion damage occurs due to fly ash generated in coal gasification, liquefaction plant, coal combustion boiler plant or the like, or an erosion damage portion generated by water slurry. Also available.

[0002]

2. Description of the Related Art Generally, in a process for producing olefins or the like, a cracking furnace for thermally cracking petroleum hydrocarbons is used. This decomposition furnace is provided with a thermometer with a protection tube in order to control the temperature of the reaction system. FIG.
It shows the outline of the above-mentioned cracking furnace, which mainly consists of a radiating section 1 for heating and decomposing the raw material and a convection section 2 for recovering heat from the combustion gas. In addition, a boiler system is attached as an auxiliary equipment. are doing. For example, the raw material 3 such as naphtha supplied to the cracking furnace is mixed with the diluted steam 4 in the convection section 2 and heated to about 600 ° C. by convective heat transfer with the combustion gas. Then, it is supplied to the reaction tube of the radiating section 1 and burned at about 800 ° C.
Heating to the above high temperature induces a thermal decomposition reaction to produce an olefin. On the other hand, the generated cracked gas is cooled by a cooler 6 installed at the outlet of the reaction tube in order to stop the reaction in order to prevent excessive cracking, and sent to a downstream separation tower 7. In the reaction of the cracking furnace, factors affecting the yield of olefins and the like include pressure, temperature, and reaction time. In order to control the temperature, which is one of the factors, a thermometer 8 is provided at the outlet coil of the reaction tube in the decomposition furnace via a protection tube.

By the way, the inside of the above-mentioned reaction tube means that a decomposition gas containing fine carbon particles having a flow velocity of about 150 to 200 m / sec flows, and the carbon particles attached to the inside of the reaction tube are periodically removed. It is characterized by remarkable wear reduction due to the decoking operation for removing. This phenomenon also acts on the thermometer protection tube 21 inserted in the reaction tube outlet coil as shown in FIG. 2, so that this protection tube also undergoes severe wear and thickness reduction. For this purpose, conventionally, the operation of the cracking furnace has been stopped and the thermometer protection tube 21 has been replaced, or a method has been devised in which the side of the fluid flow opposite to the non-thinned side is reset to face the flow. Was. This is because if the thinning of the thermometer protection tube 21 proceeds and breaks, the decomposition gas inside the reaction tube leaks, leading to an accident. In the drawing, reference numeral 22 denotes a reaction tube, 23 denotes a thermometer mounting hardware, and 24 denotes a flow of a hydrocarbon decomposition gas.

Conventionally, the following method has been adopted as a method for solving such a problem. (1) A surface thermometer is welded to the coil surface of the reaction tube outlet to control the temperature. (2) The length of the protection tube inserted into the reaction tube outlet coil is shortened, and the portion to be reduced in thickness is reduced. (3) Strengthen the material of the protection tube. However, in the above method (1), there is a difference between the temperature measured at the reaction tube outlet coil surface and the temperature of the fluid in the tube, and it is difficult to control the temperature. In addition, there has been a problem that the thermocouple is severely deteriorated, and it is difficult to replace the thermometer because the thermometer is fixed by welding. In addition, the method (2) has a problem that accurate temperature cannot be measured because the protective tube is not inserted up to the center of the axis of the reaction tube outlet coil, and the temperature varies greatly. On the other hand, in the above method (3), since the temperature conditions are severe, the effect of reducing the wall thickness was not sufficient only by changing the material of the protective tube.

[0005] Further, as a conventional technique other than the above (1) to (3), hard chromium plating, thermal spray coating of hard alloy or carbide cermet, TiN, CrN, TiCN by PVD method or CVD method are applied to the outer peripheral surface of the protective tube. There has been a method of applying a hard surface treatment film such as a film. However, the film formed by the application of these methods is easily destroyed at an early stage by erosion by carbon particles, and in fact, the expected results are not obtained.

[0006]

As described above,
Conventional thermometer protection tubes used in pyrolysis furnaces for the production of olefins are exposed to high-temperature hydrocarbon cracking gas, and are susceptible to erosion damage due to the impact of hard carbon particles flying at high speeds. Was short. In particular, the thermometer protection tube not only protects the thermometer from mechanical external pressure, but also plays a role in accurately and promptly transmitting the ambient temperature. for that reason,
The protection tube is usually made of a metal member having good thermal conductivity. However, metal (alloy) members are softened in a high-temperature environment, and are easily damaged by erosion when they come into contact with carbon particles flying at high temperatures and high speeds. On the other hand, a method of improving the erosion resistance by treating the surface of the metal protective tube is conceivable. However, there are many cases in which the thermal conductivity is impaired to deteriorate the measurement performance. The present invention seeks to overcome these problems.

Accordingly, a main object of the present invention is to provide a surface treatment film for a thermometer protection tube which is excellent in heat conductivity and heat resistance and erosion resistance.
Another object of the present invention is to improve the productivity of petrochemical raw materials such as olefins and reduce equipment maintenance by providing a long-life metal protective tube in addition to being able to accurately measure temperature. It is to propose a new component improvement technology.

[0008]

According to the present invention, in order to solve the above-mentioned problems of the prior art, the following means are used to provide excellent heat resistance and erosion resistance and to improve the heat resistance and erosion resistance. A thermometer protection tube showing thermal conductivity was developed. (1) The present invention provides a method for plasma-spraying a Cr ₃ C ₂ cermet on a surface of a heat-resistant metal member in an inert gas atmosphere substantially free of oxygen, whereby the metal in the sprayed coating is formed. A sprayed coating in which part or all of Cr is changed to chromium carbide. That is, it is a protective tube for a measuring instrument in which the surface of a metal member is hard and dense, and a chromium carbide cermet sprayed coating having excellent erosion resistance and thermal conductivity is formed. (2) Further, it is preferable that the chromium carbide cermet sprayed coating of the present invention is formed in a thickness of 50 to 800 μm, and the micro Vickers hardness of the coating is 1000 Hv or more on average.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the protective tube of the present invention is formed by spraying a thermal spray material having excellent thermal conductivity, heat resistance, abrasion resistance and erosion resistance on the surface of a metal substrate (pipe). And surface-treated. In particular, it has been found that, if the spraying material and the spraying environment are appropriately controlled, in addition to excellent blast erosion resistance and heat resistance, a dense sprayed coating showing good thermal conductivity can be obtained, and the present invention has been completed. .
Hereinafter, the protective tube for a measuring instrument according to the present invention will be described using an example of a thermometer protective tube.

(1) Thermal Spray Coating Coating on the Surface of Metal Protective Tube The environment in which the protective tube according to the present invention is used is, as described above, a high temperature and a condition where hard carbon particles collide at a high flow velocity. Below and hence the surface of the protective tube (sprayed coating)
Must be chemically stable and have excellent blast erosion resistance. In order to meet the demand for surface coating, that is, to form a thermal spray coating, the inventors have studied oxide ceramics, carbide cermets, and hard metals (alloy steels) as materials to be sprayed. As the thermal spraying method, an experimental study was conducted on a method using an electric arc as a heat source, a method using plasma or the like as a heat source, and a method using combustion energy of hydrogen or hydrocarbon and oxygen as a heat source.

In this experiment, first, on a substrate made of SS400 steel material, a hard spray material was coated on a substrate by an average of three times using various spraying methods.
A film having a thickness of 00 μm was formed, and then the Al ₂ O ₃ particles were sprayed on the film using a compressed air of 5 kgf / cm ² (spray distance 500 mm), and the erosion resistance of the sprayed film was qualitatively examined. Table 1 summarizes the results of this experiment. As shown in Table 1, the thermal spray coating of oxide ceramics such as Al ₂ O ₃ and TiO ₂ was hard but brittle, so local peeling occurred easily. However, the WC, Cr ₃ C ₂ cermet sprayed coating showed relatively good erosion resistance and was found to be the most suitable material for the purpose of the present invention. The self-fluxing alloy films did not show any peeling phenomena due to wear alone. However, these films were judged to be unsuitable because they had the characteristic that their hardness was significantly reduced in a high temperature environment around 800 ° C.

[0012]

[Table 1]

[0013] Based on the above results, the inventors focused on carbide cermet materials and further studied the high-temperature stability of these materials. As a result, it was found that the WC cermet film was poor in heat resistance such as being oxidized and decomposed in an environment of 550 ° C. or higher. Therefore, in the present invention, a Cr ₃ C ₂ cermet material having heat resistance, though inferior in hardness and erosion resistance as compared with WC cermet, is used.

(2) Cr ₃ C ₂ Cermet Sprayed Coating Due to the above progress, the present invention has decided to use Cr ₃ C ₂ as a surface coating sprayed material for a protective tube. Therefore, this Cr ₃ C ₂ cermet spray material is sprayed by various spray methods.
A sprayed coating having a thickness of about 150 μm was formed, and the porosity, adhesion, hardness, etc. of each coating were investigated.

Table 2 summarizes the above test results. As can be seen from the results shown in Table 2, in the atmospheric plasma spraying method tested as a comparative example, with or without preheating,
Both adhesion and hardness were poor. In contrast, the sprayed coating obtained by the high-speed flame spraying method has a small porosity even without preheating, and has a hardness of 750 to 850 Hv and an adhesion of 80.
Very high measured values of over MPa were obtained. However, the thermometer protection tube coated with the sprayed Cr ₃ C ₂ film formed by this method is connected to the olefin production apparatus shown in FIG. 1 (gas temperature 650 to 800 ° C.).
When the test was conducted on an actual machine, most of the film had disappeared due to erosion due to carbon particles in about 4 months of operation.

[0016]

[Table 2]

Therefore, the cause was investigated. As a result, the following was found. That is, although the Cr ₃ C ₂ particles themselves are hard and have erosion resistance, since the coexisting metal as a binder softens under a high temperature environment, only the metal component is selectively eroded, and as a result, the Cr ₃ It was found that the C ₂ particles lost their mutual binding force and were worn.

Next, the inventors continued to study whether there is a method of hardening a metal component added as a binder in an environment in which a sprayed coating is formed. as a result,
Cr ₃ C using Cr or Cr alloy as binder metal
₂ Plasma-spray the cermet material in a substantially oxygen-free, non-oxidizing atmosphere, and
(0 ° C) for more than 10 minutes. Then, Cr ₃ C ₂
Free carbon contained in itself or in Cr ₃ C ₂ reacts with some or all of Cr added as a binder to form Cr ₂₃ C ₆ , Cr ₇ C ₃ or Cr ₃ C ₂ or the like. It has been found that the reaction chromium carbide changed to hard carbide results in a Cr ₃ C ₂ cermet sprayed coating having higher hardness. Cr ₃ C thus formed
₍₂₎ The hardness of the sprayed cermet coating is hardened to 1100 to 1250 Hv, almost comparable to WC cermet. (For example, test piece 2 in Table 2)

As described above, if oxygen is contained in the sprayed atmosphere during the spraying, Cr in the formed sprayed coating is reduced.
The surfaces of the ₃ C ₂ particles and the binder metal component are oxidized, which hinders the carbonization reaction of Cr as the metal component, which is not preferable.

In the present invention, in order to further promote the carbonization reaction of Cr, the object to be sprayed (metal substrate) itself is also heated (500 to 900 ° C.) prior to the spraying.
By improving the adhesion of the thermal spray coating and reducing the residual stress of the thermal spray coating, a thick film can be formed. Also,
In order to further accelerate the carbonization reaction of Cr, it is preferable to post-heat to a high temperature of 500 to 900 ° C. even after thermal spraying. It was also found that the pre-treatment and post-treatment operations made the sprayed coating denser, significantly improved the thermal conductivity, and did not hinder the heat transfer to the thermometer.

In the present invention, the metal component added to Cr ₃ C ₂ (or Cr ₂₃ C ₆ ) may be Cr or an alloy containing Cr.
(Cr-Ni, Cr-Co, Cr-Fe, etc.) are suitable, and single metals, such as Ni, Co, Cu, which are difficult to form carbides, are unsuitable. The addition amount of this metal component is 5 to 60 wt%.
_{(Cr 3 C 2 95~40wt%)} , Cr content in the metal component 5
A range of 100100 wt% is suitable. 5wt metal component
%, The adhesion of the thermal sprayed coating and the bonding force between the particles are weak, and if it is more than 60 wt%, the ductility of the coating is improved, but the hardness is lowered, and the erosion resistance is poor.

The thermal spraying environment may be a non-oxidizing atmosphere containing substantially no oxygen, and is not limited to a reduced pressure plasma thermal spraying apparatus but may be an atmospheric thermal spraying method in which an inert gas is used to prevent air from being mixed. Application is possible. However,
A low-pressure plasma spraying apparatus is preferable because operations such as preheating of an object to be processed and maintaining a high temperature after spraying are easy. further,
The sprayed coating of the present invention can be obtained if the spraying atmosphere pressure is in the range of 50 to 1100 hPa of inert gas (for example, He, Ar, etc.) under the condition that there is no oxygen.

The Cr deposited under the above conditions and processes
The thickness of the ₃ C ₂ cermet coating may have a range of 50 to 800 [mu] m, it is particularly preferred 200 to 500 [mu] m. If the thickness is less than 50 μm, the erosion resistance is poor, and if the thickness is more than 800 μm, no particular effect is recognized, so that it is not economically advantageous.

The thus-obtained Cr ₃ C ₂ cermet sprayed coating is a hard and dense coating having excellent adhesion to the base material, as well as pores and pores which may hinder heat conduction. Since it did not contain an oxide, it was found that it exhibited extremely good thermal conductivity, and it was found to be excellent as a surface coating technology for thermometer protection tubes.

Although the chromium carbide used in the present invention is represented by the chemical formula Cr ₃ C ₂ , a survey of commercially available carbide cermet materials reveals that a small amount of Cr ₂₃ C ₆ , Cr ₇ C ₃
And the like, and the present invention can be applied to these carbides, and is not limited to only strict Cr ₃ C ₂ compounds.

[0026]

EXAMPLE 1 In this example, in addition to Cr ₃ C ₂ particles, Ni—Cu, Ni, Cr—N
Using a cermet material containing 25 wt% each of metal components such as i and Cr-Co, plasma spraying was performed to a thickness of 300 μm on an SUS410 substrate in an atmosphere of an Ar partial pressure of 100 hPa. afterwards,
The Vickers hardness of the obtained thermal spray coating was measured. In addition,
The thermal spraying conditions were performed for the presence or absence of preheating (550 ° C) of the SUS410 substrate and for the presence or absence of heat treatment after film formation (maintained at 700 ° C for 15 minutes). Table 3 shows the results at this time. The hardness of the thermal sprayed coatings (Nos. 1 to 8) to which Ni-Cu and Ni were added as metal components was all Vickers hardness even after preheating and post heat treatment. Less than 1000Hv. In contrast,
Thermal sprayed coating with added Cr-containing metal binder (No.
12, 14 to 16) showed that the film had a hardness of 1000 or more after undergoing any of the preheating and post-heat treatment steps, indicating that the film was hardened. Even when the same sprayed material was sprayed, unless the heat treatment was performed (No. 13), there was a tendency that the sprayed coating was not cured and the adhesion was low.

[0027]

[Table 3]

Example 2 A naphtha was used as a main raw material, the radiating section was set at 800 to 840 ° C., and the pressure was set at about 1 atm. Thermometer protection tube is made of stainless steel (Incoloy 8
00H), the following thermal spray coating was formed on the outer surface, and the surface was examined after being used for 6 consecutive months. 1. Test sprayed coating (1) Sprayed coating of the present invention Cr ₃ C ₂ -25 wt% Ni-Cr cermet is sprayed by reduced pressure plasma spraying and applied to a film thickness of 350 to 400 μm, Cr ₃ C ₂ -30 wt % Ni-Cr cermet is sprayed by vacuum plasma spraying to form a sprayed film with a thickness of 350-400 µm, and then heat-treated at 700 ° C for 10 hours in vacuum. (2) Thermal spraying of comparative example Coating JIS H8303 regulation SFNi ₄ Self-fluxing alloy is sprayed and the film thickness is 1200 ~
After forming a thermal spray coating of 1500 μm, this thermal spray coating is subjected to fusing treatment in the air, the above-mentioned self-fluxing alloy thermal spray coating is subjected to fusing treatment in vacuum, 25 wt% Cr-70 wt% Fe-2 wt% B -3wt% Si alloy
Thermal spray coating, Cr ₃ C ₂ -25 wt% Ni-Cr cermet applied to a thickness of 800 μm by arc spraying, thermal spray coating applied to a thickness of 350 to 400 μm by high-speed flame spraying, Cr ₃ Thermal spray coating of C ₂ -30wt% Ni-Cr cermet applied to a thickness of 350-400μm by atmospheric plasma spraying,

2. Test Results The test results for this example are summarized in Table 4. As can be seen from the results, all of the thermal sprayed coatings of Comparative Examples (Nos. 3 to 7) disappeared due to erosion by carbon particles after 6 months of operation of the plant. The base material is 30 ~ 70μ with the coating of
m. On the other hand, the thermal spray coatings (Nos. 1 and 2) conforming to the present invention showed no change in appearance at all, and showed only a decrease of about 3 to 15 μm by micrometer measurement.

[0030]

[Table 4]

Example 3 In this example, the thermal conductivity of a sprayed Cr ₃ C ₂ cermet coating conforming to the present invention was measured. The film for measurement is SS400
After forming a thermal sprayed coating having a thickness of 500 μm on the substrate, a disk-shaped sample having a diameter of 10 mm and a thickness of 1 mm was cut out together with the substrate and used for measurement. In addition, as a thermal spray coating for comparison, Cr ₃ C ₂ cermet coating in the air and Ar gas without preheating the substrate,
A plasma sprayed coating of a 50 wt% Cr-50 wt% Ni alloy was used.

Table 5 shows the test results of this example. Even if a metal having excellent thermal conductivity is subjected to plasma spraying in air (Nos. 5 and 6), the particles constituting the coating are oxidized. As a result, the thermal conductivity was extremely low due to the formation of materials and the presence of pores. It was also confirmed that this value hardly changed even at 500 ° C. These trends are observed for plasma sprayed Cr ₃ C ₂ cermet coatings in the atmosphere, but the inert gas (Ar gas)
Regarding the film sprayed in the inside (No. 4), it is recognized that the thermal conductivity is somewhat improved, probably because the formation of oxides is suppressed. On the other hand, the Cr ₃ C ₂ cermet film (Nos. 1 to 3) of the present invention, which was subjected to either preheating or post-heating in an inert gas, or both processes, exhibited the best thermal conductivity even at room temperature. At 500 ° C, the thermal conductivity tended to further increase, clearly showing no oxide in the film, and the film was densified by the sintering reaction due to preheating and post-heat treatment. It can be seen that the improvement in the adhesiveness with metal and the carbide conversion reaction of metal Cr contribute to the improvement in the thermal conductivity.

[0033]

[Table 5]

[0034]

As described above, according to the present invention, a thermometer protection tube attached to an apparatus for producing olefins such as ethylene and propylene by a thermal decomposition reaction of a hydrocarbon gas is provided with an average Vickers hardness. It has a high hardness of more than 1000Hv, is dense and has excellent erosion resistance, and if it is surface-treated to exhibit good thermal conductivity, it can measure accurate temperature over a long period of time and at the same time, for example, When the protective tube is applied to a device for producing olefins, the device can be operated continuously for a long time, and greatly contributes to improvement of productivity and reduction of maintenance and inspection costs.

[Brief description of the drawings]

FIG. 1 shows a process line of a cracking furnace for an olefin production apparatus.

FIG. 2 shows a mounting state of a thermometer provided at an outlet of a decomposition furnace radiant tube.

[Explanation of symbols]

 Reference Signs List 1 Radiant part for raw material decomposition 2 Convection part for heat recovery 3 Raw material naphtha line supplied to decomposition furnace 4 Steam line supplied to convection part 5 Burner for heating 6 Cooler for decomposition gas 7 Decomposition of decomposition gas component Separator 8 Thermometer 21 Thermometer protection tube 22 Reaction tube 23 Thermometer mounting bracket 24 Flow direction of decomposition gas

Continued on the front page (72) Inventor Tatsuo Mizuzu 2-3-2, Ouchi-dori, Nada-ku, Kobe-shi, Hyogo Prefecture 303 (72) Inventor Naoki Ento 2-12-16, Honcho, Funabashi-shi, Chiba Prefecture (72) Invention Osamu Takenaka 5-1, Anesaki Kaigan, Ichihara-shi, Chiba Sumitomo Chemical Engineering Co., Ltd. (72) Inventor Yoshihiko Nakata 5-1, Anesaki Kaigan, Ichihara-shi, Chiba F-term in Sumitomo Chemical Engineering Co., Ltd. 4K031 AA06 AB08 CB22 CB45 DA04 EA10 FA01

Claims (3)

[Claims] 1. A protective tube for a measuring instrument, wherein at least a part of the outer surface of a heat-resistant metal tube is covered with a chromium carbide cermet sprayed coating. 2. The chromium carbide cermet sprayed coating according to claim 1,
Cr added as a binder component in Cr ₃ C ₂ or
At least a part of the Cr alloy is Cr ₂₃ C ₆ , Cr ₇ C ₃ or Cr
Measuring equipment protection tube according to claim _{1, 3} reactions chromium carbides changed to hard carbides such as C ₂ is characterized in that it is a dispersed film. 3. The chromium carbide cermet sprayed coating according to claim 1,
2. The film according to claim 1, wherein the coating has a thickness of 50 to 800 [mu] m and a micro Vickers hardness Hv of 1000 or more on average.
Or the protective tube for a measuring instrument according to 2.