JP2018013225A - Piping and compressor including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To apply an anticorrosive coating on a surface of a piping facility using general steel material on which rust easily developments, to thereby provide a piping facility with high a rust prevention function.SOLUTION: Piping comprises a pipe and a flange; any one of the pipe and flange is steel material; the steel material has a coating subjected to gas soft nitriding treatment and oxidation treatment; and the pipe and the flange are connected with welding using filler material. Consequently, piping with a high rust prevention function, and a compressor including the piping are provided at low cost.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pipe for pumping compressed gas in a compressor for pumping gas in a compression chamber, and relates to a pipe for performing surface treatment for improving corrosion resistance of a gas flow path and welding for forming the surface treatment.

  A compressor is a machine that pumps gas in a compression chamber composed of a casing. As the compressor system, a screw compressor that pumps gas by the rotational motion of a rotor, or a gas that is reciprocated by a piston. There are a reciprocating compressor for pumping, a scroll compressor for pumping gas by a swirling motion of a spiral tooth member, and the like. Hereinafter, a screw compressor will be described as an example.

  The screw compressor rotates in a compression chamber constituted by a suction-side casing and a discharge-side casing while a pair of male rotors and female rotors mesh with each other to form a space formed between both rotors and the casing and rotor. The fluid in the space is compressed by being reduced while being moved in the axial direction. Furthermore, in such screw compressors, there are an oil-cooled type that supplies oil as a fluid into the space and an oil-free type that does not supply oil.

  One factor that affects reliability in oil-free screw compressors is the generation of rust. Since a solid lubricating coating is applied to the surface of the rotor, rust is hardly generated, but rust is likely to be generated because the casing is made of cast iron.

  There are two types of screw compressors: a two-stage machine and a single-stage machine. The two-stage machine has two screw compressor bodies connected in series via a pipe and a cooler. The cooler uses the high-temperature compressed air discharged from the first-stage compressor body as outside air or water as a refrigerant. After cooling in step 2, it is compressed again by the second stage compressor body. Thereby, since the temperature of compressed air is once cooled, the compressed air temperature in the second stage can be kept low. However, condensed water is likely to be generated in the process of cooling the compressed air in the middle of the two-stage machine. The same applies to single-stage machines. Therefore, since the condensed water is generated in the compressor, rust is easily generated.

  The compressor is composed not only of the compressor main body that has the function of compressing gas, but also composed of components that suck in the gas, coolers, dryers, etc., and piping that connects them. It extends not only to the piping that connects them.

  As a method of improving the rust prevention property of the portion using the steel material that is easily rusted in the constituent elements of the compressor, there is a method of performing a surface treatment with high rust prevention property. However, the surface treatment to be selected varies depending on the material, size and shape of the component. Currently, cast iron casings are plated and coated to deal with rust.

  Moreover, the piping part etc. are comprised by welding each component. However, it has been difficult to surface-treat welded parts. This is because it causes welding defects. Welding defects include blowholes in which gas absorbed during welding becomes pores and weld cracks. Weld cracking may be caused by temperature control, or impurities (S, P, C, Si, Ni, etc.) may promote cracking. Therefore, it is said that if there is a surface-treated film, welding defects are more likely to occur.

  As a background art in this technical field, there is WO2012 / 026205 (Patent Document 1). Patent Document 1 states that “as a method of increasing the fatigue strength of steel products, heat treatment that causes martensitic transformation on the surface and generates compressive residual stress on the surface, such as carburizing quenching, induction quenching, soft nitriding method, etc. The method is well known, however, such a heat treatment cannot be used on welded parts, since it can contain weld defects, so it is not possible to harden the surface of the weld. This is because there is a risk of further reducing the reliability of the welded part, so when carburizing a part including the welded part, the carburizing process is performed after the carburizing process is performed so that the welded part is not carburized. It is common to do this. "

WO2012 / 026205

  Patent Document 1 simply describes, as a method for increasing the fatigue strength of steel products, performing a carbon-proofing treatment or a nitriding treatment on a welded portion, and masking the welded portion so that no weld defect occurs. There is no mention of rust prevention of piping parts.

  An object of the present invention relates to a pipe in a compressor, a pipe having a rust preventive function, which is formed by welding components that are less likely to generate rust and welding them, and a compressor including the pipe. It is to provide.

  In order to achieve the above-mentioned object, the present invention is, as an example, piping composed of a pipe and a flange, and either the pipe or the flange is a steel material, and the steel material is gas soft nitrided. It has a film formed by treatment and oxidation treatment, and the pipe and the flange are joined by welding using a filler metal.

  ADVANTAGE OF THE INVENTION According to this invention, a low cost and high antirust effect piping and a compressor provided with the same can be provided.

2 is a schematic diagram of a film formed by gas soft nitriding and oxidation treatment in Example 1. FIG. It is a graph which shows the relationship between the generation | occurrence | production area ratio of the rust which shows the corrosion resistance and the thinnest part film thickness of the film thickness which consists of a gas soft nitriding layer and an oxide layer in Example 2. It is the schematic diagram and cross-sectional photograph of the welding part of the pipe and flange which comprise piping in Example 3. FIG. FIG. 10 is a configuration diagram of a compressor system in Embodiment 4. It is explanatory drawing which shows the component of an oil free screw air compressor, and the flow of air. It is a side view inside the package of an oil free screw air compressor. It is a figure which shows piping of an oil free screw air compressor.

  First, a general screw compressor will be described. Screw compressors are classified into an oil-cooled type that supplies oil as a fluid into a compression chamber and an oil-free type that does not supply oil.

  In the oil-cooled type, the male rotor and the female rotor rotate while contacting with each other through an oil film. This oil-cooled type can prevent seizure between rotors by cooling the frictional heat generated by the rotation of the rotor with oil. Such an oil-cooled type is not suitable in fields that require clean air, such as the food industry and semiconductors, because oil mist is mixed in compressed air, for example.

  On the other hand, the oil-free type can provide clean air because it does not supply any oil into the compression chamber, but since there is no seal with oil, there is no seizure between the rotors and between the rotors and the casing. Is designed to rotate without contact. The rotor surface is coated with a solid lubricating film for the purpose of preventing galling at the time of contact and preventing rust. The oil-free type has a complicated structure compared to the oil-cooled type because a synchronous gear is attached to the shaft end portion of the rotor in order to give a rotational force to the rotor.

  Next, the flow of air in the oil-free screw air compressor will be described with reference to FIG. In FIG. 5, (A) shows the case of a two-stage machine, and (B) shows the case of a single-stage machine. In the air flow of the air compressor of the two-stage machine (A), first, outside air is taken in by the suction filter, and the air is compressed to a predetermined pressure by the first-stage compressor body. The compressed air discharged from the first-stage compressor body is cooled by an intercooler, and the drain water generated at this time is discharged to the outside by a drain separator. Thereafter, the cooled compressed air is further compressed by the second-stage compressor body to a predetermined pressure. The compressed air passes through a high precooler and a check valve, is cooled by an aftercooler, and is further discharged through a dryer. Note that the drain separator, high precooler, and dryer shown in FIG. 5 may not be connected depending on the model.

  In the case of the single stage machine of FIG. 5 (B), as shown in the figure, since there is only one compressor body, the configuration is simpler than that of the two stage machine. The temperature difference when stopping is increased.

  The compressor is configured as a compressor unit by connecting such components by piping and housed in a package.

  As described above, since the oil-free compressor has no medium for cooling the air that has been adiabatically compressed and increased in temperature as in the oil-cooled type, the temperature difference between the suction side and the discharge side of the rotor becomes large. The air sucked in at about room temperature is compressed to 800 kPa by the rotation of the screw and becomes hot when discharged by adiabatic compression, and may reach a high temperature of about 250 ° C. for a two-stage machine and about 400 ° C. for a single-stage machine. Therefore, a flow path (jacket) for cooling is provided in the casing portion of the compressor main body, and a fluid such as a coolant or oil is flowed depending on the model to cool the compressor main body from the outside. The water that existed in the gas in the high-temperature compressed air is cooled, so that the saturated water vapor pressure is lowered to become condensed water. This water is generally called drain water and is removed by a drain separator or the like, and the compressed air at that time is in a state where the humidity is 100%. The compressed air after passing through the drain separator is cooled little by little even when passing through the pipe, and air with high humidity always flows in the pipe.

  When the operation of the compressor is stopped, the high-temperature and high-humidity air cools and condensation occurs. Many of the rotors and casings that make up the compressor body, which is the heart of the compressor, have anti-corrosion treatments, but the metal base material is exposed in other components. There is a part. The rust generated in that part gradually spreads, and part of it is carried by the flow of compressed air. These cause further rusting in other places, and in the worst case, if they get mixed in the compressor body, galling will occur when starting up, and if it gets worse, the rotors will get stuck and cause compressor failure. Become.

  One of the parts where the base material is exposed is a pipe flange. The outer side is rust-preventive with anti-corrosion paint, but the inner part is exposed and the base material is exposed, and the part is rusted.

  In FIG. 6, the side view inside the package of a compressor is shown. FIG. 6 shows an example of a two-stage machine. In FIG. 6, both the first-stage compressor body 3 and the second-stage compressor body 6 are installed in the lower part of the package, and the intercooler 4 and the aftercooler 8 are both installed in the upper part. It connects with the piping 20 comprised by these. A suction filter (not shown) is located near the lower first-stage compressor body 3, and the compressed air is conveyed up and down through the pipe 20, and is finally installed behind the aftercooler 8. It is discharged through a dryer (not shown). In order to accommodate the entire compressor in a compact package, the pipes 20 that connect the components are arranged in a three-dimensionally complex manner in order to effectively use a narrow space in the package.

  FIG. 7 shows a configuration example of the pipe 20. (A) is a bottom view, and (B) is a side view. The pipe 20 is composed of a pipe 2 and a flange 1, and the bent portion of the pipe 2 uses an elbow. To create a pipe having a bent portion, first, the straight pipe portion and the elbow are joined by welding, and then the flange is welded. Usually, pipes and elbows are made of rust-proof materials such as SUS304. The custom-made square flange uses SS400, which is a general structural rolled steel. These are welded and joined to the filler using SUS for complex arrangements. Therefore, a special square flange with a small occupied volume is adopted as the flange. Since the square flange is custom-made, it uses a low-priced material because of the high processing cost. Since general steel materials are easily rusted as they are, after the piping is installed in the package, a rust preventive paint is applied to the outside. However, since the base material surface of the general steel material remains inside the pipe, and the high-temperature and high-humidity air described above flows therethrough, it is a place where rust is likely to occur.

  As a means corresponding to the rust of the flange portion, it is necessary to perform a surface treatment. However, there has been a problem that welding defects are likely to occur when a surface treatment such as normal plating or surface hardening treatment is welded. Therefore, when the surface treatment is performed on the parts first, protection such as masking is necessary so that the surface of the welded portion is not treated. Further, when a surface treatment is performed after welding, when a stainless steel material is used for the pipe, it is not necessary to perform the treatment up to the pipe portion. In addition, when the entire surface is treated, there is a problem that the area of the processing portion is increased and the cost is increased.

  Then, the Example of this invention is described below about the structure for solving this.

  In this example, a configuration in which a corrosion-resistant film is provided on the flange by gas soft nitriding will be described.

  First, gas soft nitriding treatment and oxidation treatment employed in this embodiment will be described. In general, the gas nitriding treatment is known as a surface hardening treatment for diffusing nitrogen into iron to form a nitrided layer. The gas nitriding treatment forms a compound of iron and nitrogen with Al, Cr, Mo, etc., and can be processed to high-grade steel containing Al, Cr, Mo.

  Unlike this, the gas soft nitriding treatment employed in the present example similarly diffuses nitrogen into iron to form a nitrided layer, but is a treatment that can be applied to low-grade steels such as general steel and carbon steel. It is distinguished from gas nitriding treatment.

  In the gas soft nitriding treatment method, an object is placed in a treatment furnace, ammonia gas and a carburizing gas are injected, heated, and held according to the reaction time. However, since the heating temperature can be processed at a temperature lower than the A1 transformation point of iron (726 ° C), the base iron is mixed with a mixture of iron, nitrogen and carbon compounds and iron nitride (Fe2-3 (N , C) + Fe4N). This is a gas soft nitriding layer.

  After this gas soft nitriding treatment, oxidation treatment is performed by holding in high-temperature air to form an iron oxide layer on the surface. The oxidation treatment is performed in a separate oxidation furnace after the gas soft nitriding treatment, but may be performed as long as it can be performed continuously in terms of equipment. By forming an oxide layer of triiron tetraoxide (Fe3O4) on the surface by oxidation treatment, the corrosion resistance can be further improved.

  FIG. 1 shows a schematic diagram of a film formed by gas soft nitriding and oxidation treatment. As shown in FIG. 1, gas soft nitriding forms a nitrided layer while nitrogen diffuses into the iron, so that a film is formed on both the upper surface side and the lower base metal side with respect to the dimensions before processing. grow up. Therefore, the film thickness of the gas soft nitride layer and the oxide layer (oxide layer) is generally thicker than the actual dimensional change that has changed with respect to the dimensions before processing. The film thickness can be controlled by processing conditions, that is, temperature and time, but basically the film thickness increases as the processing time increases.

  In this embodiment and the following embodiments, the oxide layer is small compared to the thickness of the gas soft nitride layer and can be ignored. Unless otherwise specified, the thickness of the gas soft nitride layer and the oxide layer is the gas thickness. It is described as the film thickness of the soft nitriding layer. However, when the thickness of the oxide layer is so large that it cannot be ignored, it can be replaced with a thickness composed of a gas soft nitride layer and an oxide layer.

  As described above, according to the present embodiment, the flange having a film formed by gas soft nitriding and oxidation treatment has improved corrosion resistance, and therefore it is possible to provide a pipe with reduced rust generation at low cost. it can. Further, since the gas soft nitriding treatment is performed on the entire surface of the flange, the coating on the outside of the flange, which has been conventionally required, is also unnecessary. Moreover, since the corrosion resistance of the piping in the compressor is improved, it is possible to provide a compressor in which the generation of rust is suppressed and the occurrence of galling and solid astringency due to rust is reduced.

  In the present embodiment, a corrosion resistant coating on the surface of a flange portion made of a general steel material in consideration of corrosion resistance will be described.

  FIG. 2 is a graph showing the relationship between the film thickness of a film composed of a gas soft nitriding layer and an oxide layer and the area ratio of rust that indicates corrosion resistance. This corrosion resistance is due to the occurrence of rust on the surface after holding a test piece of SS400 machined by gas soft nitriding and oxidation treatment for 500 hours in an environment of 60 ° C and 90% humidity. Is the situation.

  As shown in FIG. 2, in the case of a general steel base material that has not been subjected to gas soft nitriding (film thickness: 0 μm), rust was generated almost on the entire surface in one hour. However, it was found that if the film thickness is 1 μm, the incidence of rust is reduced by half even in high humidity for 500 hours, and if the film thickness is 2 μm, the incidence of rust is reduced to 10%. In addition, the occurrence of rust occurred in the first few hours, and thereafter, the amount of rust did not increase and was almost constant and never progressed.

  Even in an actual flange, rust is generated inside the pipe that is not surface-treated, but the effect of rust prevention is great even if it is reduced by half. If it is preferably 10% or less and does not proceed, the rust prevention effect is sufficient. Therefore, the thickness of the gas soft nitriding layer needs to be 2 μm or more.

  In this example, the results of welding a flange and a SUS pipe, which have been surface-treated with a gas soft nitriding layer and an oxide layer, to enhance the rust prevention function, using a SUS filler material will be described. A case will be described in which the pipe 2 is inserted into the hole of the flange 1 shown in FIG. 7 and the two outsides and the inside of the pipe are welded as shown in FIG.

  The welding of the pipe 2 and the flange 1 was the most commonly used arc welding method. This is a method in which a portion of a base material to be welded is heated, a base metal and a filler material (welding rod, etc.) are fused to form a molten metal, which is solidified and joined. Therefore, it is said that when other elements are present in a high concentration on the surface of the base material, the molten metal is not uniform and welding defects are likely to occur. However, as described in Example 2, in the case of gas soft nitriding treatment and oxidation treatment for the purpose of rust prevention, a film thickness of 2 μm has a sufficient rust prevention function. Therefore, there is no significant influence on the melting of the base material, and no welding defect occurs. FIG. 3B is a schematic diagram of the welded portion, and FIGS. 3C and 3D are cross-sectional photographs of the welded portion. It welds using the flange 1 which has a 20-micrometer-thick gas soft nitride layer. As shown in FIGS. 3C and 3D, since the pipe 2 and the filler metal are SUS of the same material, they are melted very well so that the weld seam cannot be confirmed. In addition, the base material is sufficiently melted and joined to the welded portion with the flange, and no welding defect occurs.

  Since this embodiment is intended for rust prevention, the gas soft nitriding layer needs to be at least 2 μm. The thicker the film, the better the rust prevention performance. However, if the thickness is too large, the risk of occurrence of welding defects increases and the processing cost also increases. Therefore, it is important to form a thin film of 2 μm or more. Desirably, the processing cost can be suppressed without welding defects by setting the thickness to 20 μm or less.

  As described above, from Examples 1, 2, and 3, it is possible to provide a film that has a rust preventive effect and does not inhibit welding by setting the film formed by gas soft nitriding to 2 μm or more, preferably 20 μm or less.

  In this embodiment, a general structural rolled steel material (SS material) is used as the general steel material. This is because the circulation is said to be the largest and the price is low. Of course, other steel materials may be used, for example, a rolled steel material for welded structure (SM material) or a carbon steel material for machine structure (S-C material).

  The present embodiment is an example in which the above-described piping is also used for the external piping of the air compressor.

  FIG. 4 is a configuration diagram of a compressor system in which the above-described air compressor is configured as a system. In FIG. 4, when the compressor is used effectively and systematically, a plurality of air compressors 10 are connected, the compressed air is pooled in an air tank 11, and then a dryer 12 or a filter is used depending on the purpose of use. 13, the compressor air is supplied to a necessary place. At this time, the pipes 20 are used to connect the air compressors 10, and the above-described pipes are also used for these. Thereby, since the corrosion resistance of piping outside a compressor improves, the compressor system which can suppress generation | occurrence | production of rust can be provided.

  In the above embodiment, the screw type compressor is used as the compressor method. However, the present invention is not limited to this, and it is an oil-free compressor that does not supply any oil into the compression chamber, and each component is connected by piping. A reciprocating compressor, a scroll compressor, or the like may be used as long as the compressor has a configuration in which high-temperature and high-humidity compressed air passes therethrough. Further, the present invention is not limited to an air compressor and may be a general gas compressor. In the above embodiment, air may be read as gas.

  Although the embodiments have been described above, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. For example, the pipe side may be a general steel material, gas soft nitriding treatment and oxidation treatment may be performed to prevent rust, and the flange may be welded as a SUS material. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

1: flange, 2: pipe, 3: first stage compressor body, 4: intercooler, 5: drain separator, 6: second stage compressor body, 7: check valve, 8: after cooler, 9: filler Material: 10: Air compressor, 11: Air tank, 12: Dryer, 13: Filter, 20: Piping

Claims (7)

A pipe composed of a pipe and a flange,
Either the pipe or the flange is a steel material, and the steel material has a film formed by gas soft nitriding treatment and oxidation treatment, and the pipe and the flange are joined by welding using a filler metal. Piping characterized by being. The piping according to claim 1,
The piping, wherein the flange is the steel material. The piping according to claim 1,
The pipe is a stainless steel material. The piping according to claim 1,
A pipe having a thickness of 2 μm or more formed by the gas soft nitriding treatment and the oxidation treatment. The piping according to claim 4,
A pipe having a thickness of 20 μm or less formed by the gas soft nitriding treatment and the oxidation treatment. A compressor having a suction filter that sucks air, a compressor body that compresses the gas sucked from the suction filter, and a cooler that cools the compressed gas,
A compressor comprising the pipe according to any one of claims 1 to 5, wherein the suction filter, the compressor body, and the cooler are respectively connected by the pipe. A compressor system comprising a plurality of the compressors according to claim 6 and connecting the plurality of compressors to pool the compressed gas in a gas tank,
A compressor system using the piping to connect the plurality of compressors.

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