JP2015137398A - Boiler or water-cooling panel for converter og equipment and life extension method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boiler or water-cooling panel of converter OG equipment (non-combustion type exhaust gas treatment equipment) having durability in long period.SOLUTION: A boiler 1 or water-cooling panel of converter OG equipment, in which the boiler or water-cooling panel is formed by jointing mutually plural steel tubes 2 with a steel fin 3, and formed into a cylindrical shape. On a passage surface side of exhaust gas from a converter of the tubes and fin, a padding layer 5 formed of Inconel alloy whose thickness is 1.0 mm or more and 2.0 mm or less, is formed. The padding layer 5 has variation width of the thickness, preferably 0.5 mm or less in a range of 5 mm in an optional direction.

Description

  The present invention relates to a boiler or a water-cooled panel of an OG facility (non-combustion exhaust gas treatment facility) that recovers an exhaust gas mainly composed of carbon monoxide generated from a converter during decarburization and refining in the converter without burning. The present invention also relates to a method for extending the life of a boiler or a water-cooled panel.

  In the converter used for hot metal decarburization and refining, exhaust gas mainly composed of carbon monoxide discharged from the converter during decarburization and refining is recovered, dust in the recovered exhaust gas is removed, and dust is removed. OG equipment is installed as equipment for reusing the exhaust gas later as fuel gas. This OG equipment has a flue (duct) for collecting exhaust gas, and a cylindrical boiler or water cooling panel that opens toward the furnace port of the converter is installed at the lower end of this flue. Has been. A cylindrical skirt that can be moved up and down is installed on the outer periphery of the boiler or water-cooled panel, and by moving the skirt up and down, exhaust gas can flow out of the gap between the converter furnace opening during refining and the boiler or water-cooled panel. It is preventing.

  Since the temperature of exhaust gas from the converter during refining reaches a temperature exceeding 1600 ° C and is also affected by radiant heat from the converter furnace port, the boiler or water-cooled panel of the OG equipment is generally internal. A plurality of cooling-type steel tubes are joined to each other by heat-dissipating steel fins to form a cylindrical shape as a whole. Since the cooling water circulating inside the tube becomes high temperature, the equipment for recovering this heat is the boiler, and the equipment for simply cooling is the water cooling panel.

  The exhaust gas from the converter contains dust composed of scattered iron particles, slag particles, etc., and this dust collides with the tubes and fins forming the boiler or water-cooled panel. The tube and fin are gradually worn by the collision of the dust, and the tube and the fin are thinned over time. In particular, the internal water-cooled tube is susceptible to repeated thermal shocks caused by high-temperature exhaust gas and radiant heat from the converter, and this thermal shock may cause cracks and cracks in the tube, resulting in damage to the tube. There is also a risk of leakage of cooling water.

  To cope with this, the boiler or water-cooled panel is regularly maintained, and the repair worker confirms the state of damage to the tubes and fins. It was exchanged. This repair work was carried out between refining and within the repair period of the converter, which not only reduced the operating rate of the converter equipment, but also had problems in stable operation.

  Therefore, some proposals have been made for the purpose of extending the life of boilers or water-cooled panels of OG equipment. For example, in Patent Document 1, C: 0.03 to 0.3% by mass, Si: 0.2 to 1.2% by mass, Mn: 0.3 to 2.6% by mass on the surfaces of tubes and fins. Ni: 0.1-6.0% by mass, Cr: 8.0-15.0% by mass, Mo: 0.05-4.0% by mass, V: 0.1-3.0% by mass In addition, a technique has been proposed in which high alloy steel with the balance being Fe is welded so that the thickness thereof is 0.5 to 1.5 mm to protect the tube and the fin.

  Patent Document 2 proposes a method for repairing a tube in which the surface of the tube and fin is repaired by overlay welding an Inconel weld metal.

  According to Patent Literature 1 and Patent Literature 2, the tube can be extended in life by overlay welding a metal having superior heat resistance, wear resistance, and corrosion resistance than the steel constituting the tube on the surface of the tube. .

JP-A 64-55320 JP 2010-235982 A

  However, the above prior art has the following problems.

  That is, Patent Document 1 selects the above-mentioned high alloy steel as a metal for build-up welding, but this high alloy steel has a strength in a high temperature range as compared with an Inconel alloy (nickel base alloy). In addition, it is very difficult to use the tube without repairing over a long period of time due to its poor wear resistance.

  On the other hand, Patent Document 2 selects an Inconel-based alloy as a metal for build-up welding, but what is the optimum thickness of the build-up layer and what is the fluctuation range of the thickness of the build-up layer? It does not specifically describe whether it is acceptable. When the thickness of the build-up layer is not appropriate or when the fluctuation range of the thickness is large, the inventors will generate cracks in the build-up layer even if an Inconel alloy is used as the metal for build-up welding. It has been confirmed that the tube life cannot be extended.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a boiler or a water-cooled panel of a converter OG facility that can be used for a long period of time, and the converter OG facility. It is to provide a method for extending the service life of a boiler or water-cooled panel.

The gist of the present invention for solving the above problems is as follows.
[1] A boiler or a water-cooled panel of a converter OG facility in which a plurality of steel tubes are joined to each other by steel fins so as to have a cylindrical shape as a whole. A boiler or a water-cooled panel of a converter OG facility, characterized in that a build-up layer of an Inconel alloy having a thickness of 1.0 mm or more and 2.0 mm or less is formed on a passage surface side of exhaust gas from the converter. .
[2] The boiler of the converter OG facility according to the above [1], wherein the build-up layer has a thickness fluctuation range of 0.5 mm or less within a range of 5 mm in an arbitrary direction. Water cooling panel.
[3] A method for extending the life of a boiler or a water-cooled panel of a converter OG facility in which a plurality of steel tubes are joined to each other by steel fins and formed into a cylindrical shape as a whole. The inconel alloy is built up on the side of the tube and the fin passing through the exhaust gas from the converter, and then the built-up layer is surface polished so that the thickness of the built-up layer is 1.0 mm or more and 2.0 mm or less. A method for extending the life of a boiler or water-cooled panel of a converter OG facility, characterized in that:
[4] The converter OG equipment according to [3], wherein surface polishing is performed so that a fluctuation range of the thickness of the build-up layer is 0.5 mm or less within a range of 5 mm in an arbitrary direction. To extend the service life of boilers or water-cooled panels.

  According to the present invention, since the thickness of the built-up layer of the Inconel alloy on the inner surface of the boiler or water-cooled panel of the converter OG equipment is 1.0 mm or more and 2.0 mm or less, a load is applied to the built-up layer during use. Therefore, the occurrence of cracks and cracks in the build-up layer of the Inconel alloy can be suppressed, and the life of the tube can be greatly extended compared to the conventional case.

It is a figure which shows the calculation result which changed the thickness of the build-up layer and estimated the fatigue life by the thermal shock stress of the build-up layer at that time. It is a cross-sectional view of a part of the boiler of the converter OG facility.

  Hereinafter, the present invention will be described in detail.

  The inventors of the present invention intend to extend the life of a boiler or a water-cooled panel of a converter OG facility formed by joining a plurality of steel tubes to each other by steel fins and forming a cylindrical shape as a whole. As a purpose, a test was conducted in which an inconel alloy was built up on the inner surface side of a boiler or a water-cooled panel. The service life of the tube of the base material that does not build up is about 8 years empirically, and the test was conducted with the expectation that a service life of 12 years or more was obtained by building up the Inconel alloy.

  The Inconel alloy used as the build-up metal is Inconel 625 (Alloy625), and the steel pipe used as the tube is a carbon steel pipe for boiler / heat exchanger (STB410, outer diameter 38. The fin is a structural steel material (for example, SMn420H) having a thickness of 6.0 mm defined by JIS G 4052 (2003), a chemical component corresponding to STB410. The build-up of the Inconel alloy was performed by build-up welding, and the thickness of the build-up layer was 2.0 mm to 3.0 mm. The chemical components and mechanical properties of STB410 and Inconel 625 are shown in Table 1 below.

  However, even though Inconel 625 was built up, cracks occurred in the built-up layer when 6 months had passed since the installation in the actual machine. In some cases, the crack may reach the base material tube, and in this case, the service life of the tube base material alone cannot be achieved for about 8 years.

  In order to elucidate this cause, using the heat transfer calculation method and stress calculation method, it is loaded on the build-up layer in one cycle from heating (decomposing refining start) to cooling (after refining end) in decarburization refining. The thermal stress is calculated, the amplitude of the stress value (difference between the maximum value and the minimum value) is obtained, and the amplitude of the obtained stress value is compared with the fatigue curve used for the steel type by JIS, The fatigue life due to thermal shock stress of the layer was estimated. The calculation is an ideal form in which there is no melted layer of Inconel 625 and STB410, and the thickness of the build-up layer is 0 mm (case 1), 1.0 mm (case 2), 2.0 mm (case 3), 3 It was carried out at a total of five levels: 0.0 mm (case 4) and a case where the thickness fluctuated in the range of 2.0 mm to 3.0 mm (case 5). FIG. 1 and Table 2 show the calculation results.

As shown in Table 2, when the thickness of the built-up layer is 0 mm, that is, the calculated number of useful times of the tube of the base material alone is 5.7 × 10 ⁴ times, and this value is about 8 years (15 ch) / Day x 365 days / year x 8 years = 43800 ch), which is almost the same as the number of uses, confirming that the calculation results are sufficiently reliable.

  As shown in FIG. 1 and Table 2, when the thickness of the built-up layer of Inconel 625 is 1.0 mm, 2.0 mm, and 3.0 mm, the thickness of the built-up layer is 1.0 mm. It was found that the stress amplitude value was the smallest and the number of repetitions until fatigue failure due to thermal stress was the longest. On the other hand, when the thickness of the build-up layer is 3.0 mm, it has been found that the number of repetitions until fatigue failure is shorter than that of a single base material tube on which no build-up layer is formed. Moreover, when the thickness of the build-up layer was fluctuate | varied in the range of 2.0 mm to 3.0 mm, it turned out that the repetition number until fatigue failure becomes still shorter.

  The reason why the life is shortened when the thickness of the build-up layer is 3.0 mm is that the thermal conductivity of Inconel 625 is smaller than that of carbon steel such as STB410, and when the build-up layer is 3.0 mm, refining is performed. At the same time, the outer peripheral portion of the build-up layer becomes hot, while the joint surface of the build-up layer with the tube is cooled by cooling water, so that the temperature gradient in the build-up layer becomes large, which causes excessive heat. This is thought to be due to the generation of stress. In addition, after refining, the temperature of the atmosphere (atmosphere) around the built-up layer is low, and it may be cooled from the inside, so the temperature of the outer peripheral part of the built-up layer suddenly decreases and excessively increases. It is considered that the generation of a thermal stress is also a reason for shortening the life.

  The reason why the life is further shortened when the thickness of the build-up layer varies in the range of 2.0 mm to 3.0 mm is that the thermal stress is concentrated on the different parts of the build-up layer thickness. Conceivable. From this, it was confirmed that the life of the build-up layer was extended as the thickness of the build-up layer was uniform.

  The stress amplitude value is the smallest when the thickness of the build-up layer is zero, but the base material of the tube is carbon steel, and the tensile strength of the carbon steel is lower than the tensile strength of Inconel 625, This is the reason why the number of repetitions of only the base material is smaller than when the thickness of the build-up layer is 1.0 mm.

  The present invention has been made on the basis of the above examination results, and has a thickness of 1.0 mm or more on the passage side of the exhaust gas from the converter and the tube and fins forming the boiler or water-cooled panel of the converter OG equipment. It is an essential condition to form a build-up layer of Inconel alloy that is 0.0 mm or less.

  Hereinafter, a method for forming a built-up layer of an Inconel alloy on the inner surface of a boiler or water-cooled panel of a converter OG facility will be specifically described. Here, the case of a boiler will be described, but the case of a water-cooled panel may be the same as that of a boiler. FIG. 2 is a cross-sectional view of a part of the boiler of the converter OG facility.

  As shown in FIG. 2, the boiler 1 of the converter OG facility is formed such that a plurality of tubes 2 are joined to each other with steel fins 3 and is formed into a cylindrical shape as a whole. The tube 2 and the fin 3 are joined by a weld metal 4. A build-up layer 5 of an Inconel alloy is formed on the side of the exhaust gas passing surface from the converter of the boiler 1 configured as described above. Although the build-up layer 5 is formed by a welding method or a thermal spraying method, it is preferable to use a welding method because the amount of input heat is small and the amount of inconel alloy to be welded can be reduced in the tube 2.

  The Inconel alloy for forming the build-up layer 5 is not limited to Inconel 625, and various Inconel alloys such as Inconel 600, Inconel 718, and Inconel X750 can be used.

  In this invention, although the thickness of the build-up layer 5 is prescribed | regulated in the range of 1.0-2.0 mm, this is the thickness after grind | polishing the surface of the build-up layer 5. Therefore, the thickness of the build-up layer 5 immediately after the build-up operation is set to about 1.5 to 2.5 mm, and the surface is polished until the thickness of the build-up layer 5 is in the range of 1.0 to 2.0 mm. Surface polishing is performed with a grinder. By surface polishing, irregularities due to beads during the overlaying process are removed, and concentration of thermal stress in the concave portions is hindered. That is, surface polishing is performed at least until the irregularities due to the beads at the time of overlaying are removed.

  Further, as the thickness of the build-up layer 5 is uniform, the thermal stress concentration is reduced and the generated thermal stress is reduced. In other words, the number of times of service life is extended. Polish until uniform. Specifically, it is preferable to perform surface polishing so that the fluctuation range of the thickness of the build-up layer 5 is 0.5 mm or less within a range of 5 mm in an arbitrary direction.

  Steel pipes used as tube 2 include boiler and heat exchanger alloy steel pipes (JIS G 3462 (2004)), boilers and heat exchanger carbon steel pipes specified in JIS G 3461 (2005). Stainless steel pipes for heat exchangers (JIS G 3463 (2006)) can be used.

  As described above, according to the present invention, an inconel-based alloy having a thickness of 1.0 mm or more and 2.0 mm or less is formed on the exhaust gas passing surface side from the boiler 1 of the converter OG equipment or the converter of the water-cooled panel. Since the build-up layer 5 is formed, the repeated stress due to thermal shock when the build-up layer 5 of the Inconel alloy is formed on the tubes 2 having different thermal conductivities can be minimized. It is possible to prevent the generation of cracks and cracks over a long period of time. Thereby, the tube 2 inside the build-up layer 5 is protected by the build-up layer 5, and the tube 2 can be used for a long period of time.

  Inconel 625 was build-up welded so that the thickness would be about 2.2 mm on the exhaust gas passage surface side from the converter of the boiler of the converter OG facility. Thereafter, the surface of the build-up layer was polished with a grinder, and the thickness of the build-up layer was set to 1.7 mm. The tube is a carbon steel pipe (STB410) for boiler / heat exchanger having an outer diameter of 38.1 mm and a thickness of 5.0 mm. The thickness of the build-up layer was determined from the value obtained by calculating the thickness including the build-up layer from the reflection echo by ultrasonic flaw detection and subtracting the tube thickness from the obtained value. Moreover, the thickness fluctuation | variation width | variety was calculated | required from the thickness of the buildup layer calculated | required in this way. As a result, it was confirmed that the variation width of the thickness was 0.5 mm or less within a range of 5 mm in an arbitrary direction.

  The boiler of the converter OG equipment constructed as described above was installed in the actual converter. As a result of investigating the surface of the built-up layer when 25 months have passed since it was installed in the converter, no cracks and cracks occurred at all, although it had not been repaired at all before, and it was used for a long time It was confirmed that it was possible.

  As described above, in the test in which the thickness of the build-up layer of Inconel 625 is more than 2.0 mm and 3.0 mm or less, the build-up layer has cracked after 6 months, and the present invention is applied. Thus, it was confirmed that the life of the built-up layer made of Inconel 625 can be expected to be extended.

1 Boiler 2 Tube 3 Fin 4 Weld Metal 5 Overlay Layer

Claims (4)

  A boiler or water-cooled panel of a converter OG facility in which a plurality of steel tubes are joined to each other by steel fins and formed into a cylindrical shape as a whole, from the converter of the tubes and the fins A boiler or a water-cooled panel of a converter OG facility, wherein a build-up layer of an inconel alloy having a thickness of 1.0 mm to 2.0 mm is formed on the exhaust gas passage surface side.   The boiler or water-cooled panel of a converter OG facility according to claim 1, wherein the thickness of the build-up layer is 0.5 mm or less within a range of 5 mm in an arbitrary direction.   A method for extending the life of a boiler or a water-cooled panel of a converter OG facility in which a plurality of steel tubes are joined to each other by steel fins and formed into a cylindrical shape as a whole. Build up the Inconel alloy on the side of the passage of the exhaust gas from the fin converter, and then polish the surface of the built-up layer so that the thickness of the built-up layer is 1.0 mm or more and 2.0 mm or less. A feature is a method for extending the life of a boiler or water-cooled panel of a converter OG facility.   The boiler or water cooling of the converter OG equipment according to claim 3, wherein surface polishing is performed so that a fluctuation range of the thickness of the build-up layer is 0.5 mm or less within a range of 5 mm in an arbitrary direction. How to extend panel life.

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