A method for finishing stainless steel pipe

Abstract

The present invention relates to the technical field of stainless steel pipe processing, in particular to a stainless steel pipe finishing method, comprising the following steps: SA, bright annealing: SA1, putting the stainless steel pipe into an annealing furnace; SA2, introducing argon and hydrogen mixed gas into the annealing furnace and making the gas pressure in the annealing furnace reach a positive pressure of 5kPa; SA3, heating the temperature in the annealing furnace to a preset temperature; SA4, maintaining the temperature in the annealing furnace; SA5, reducing the temperature in the annealing furnace to 90 to 100°C and moving the stainless steel pipe out of the annealing furnace; SB, passivating the stainless steel pipe to the original color; in both the SA3 and SA4 steps, there is a pressure fluctuation control, which is to pump the argon and hydrogen mixed gas into or out of the annealing furnace so that the air pressure in the annealing furnace fluctuates back and forth between the positive pressure of 5kPa and the positive pressure of 100kPa. The implementation of the stainless steel pipe finishing method of the present invention can shorten the bright annealing time and the original color passivation time of the stainless steel pipe to shorten the total processing time, and improve the surface finish of the stainless steel pipe.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel pipe processing, in particular to a method for finishing a stainless steel pipe. Background Art

[0002] Stainless steel pipe is a hollow long round steel, which is widely used in industrial pipelines such as petroleum, chemical, medical, food, light industry, mechanical instrumentation, and mechanical structural parts. With the widespread use of stainless steel pipes, people have higher and higher requirements for application products, requiring stainless steel pipes to have a certain degree of finish. In fact, surface finish is another way of saying surface roughness. Surface finish is proposed from the perspective of human vision. For stainless steel pipes, bright and neat appearance is more in line with people's requirements.

[0003] The finishing methods for stainless steel pipes generally include bright annealing and primary color passivation. Bright annealing can eliminate the work hardening of the product, and primary color passivation can form a passivation protective film to improve the corrosion resistance of stainless steel pipes. However, bright annealing requires a long processing time, and during the heat preservation process of bright annealing, it is easy to make the grain refinement uneven, affecting the surface finish of the stainless steel pipe; in addition, the annealed stainless steel pipe must wait until the temperature drops to room temperature or is 20°C higher than the temperature of the primary color solution before it is placed in the primary color solution for passivation, which makes the total processing time longer. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for finishing a stainless steel pipe, which can shorten the bright annealing time and the primary color passivation time of the stainless steel pipe to shorten the total processing time and improve the surface finish of the stainless steel pipe.

[0005] In order to solve the above technical problems, a method for finishing a stainless steel pipe of the present invention comprises the following steps:

[0006] SA, bright annealing: SA1, put the stainless steel tube into the annealing furnace; SA2, introduce argon and hydrogen mixed gas into the annealing furnace and make the gas pressure in the annealing furnace reach a positive pressure of 5kPa; SA3, heat the temperature in the annealing furnace to a preset temperature; SA4, maintain the temperature in the annealing furnace; SA5, reduce the temperature in the annealing furnace to 90 to 100°C and remove the stainless steel tube from the annealing furnace;

[0007] SB, passivation of the original color of stainless steel pipe;

[0008] In both steps SA3 and SA4, pressure fluctuation control is provided. The pressure fluctuation control is to pump a mixed gas of argon and hydrogen into or out of the annealing furnace so that the pressure in the annealing furnace fluctuates back and forth between a positive pressure of 5 kPa and a positive pressure of 100 kPa.

[0009] Through the above technical solution, it is possible to shorten the bright annealing time and the primary color passivation time of the stainless steel pipe to shorten the total processing time, and improve the surface finish of the stainless steel pipe.

[0010] As an improvement of the above scheme, the air pressure fluctuation control time in step SA3 is equal to the total time of step SA3; the air pressure fluctuation control time in step SA4 is 1 / 3 to 1 / 2 of the total time of step SA4, and the air pressure fluctuation control in step SA4 starts at the same time as step SA4. The surface finish of the stainless steel pipe is improved to a greater extent and the annealing effect is ensured.

[0011] As an improvement of the above solution, the air pressure fluctuation control frequency in step SA3 is 2 to 4 times the air pressure fluctuation control frequency in step SA4, which reduces the impact on grain refinement.

[0012] As an improvement of the above solution, the frequency of air pressure fluctuation control in the SA4 step is 8 to 10 times per minute, which reduces the impact on grain refinement.

[0013] As an improvement of the above scheme, the inner and outer sides of the stainless steel tube are heated synchronously in step SA3; the inner and outer sides of the stainless steel tube are kept warm synchronously in step SA4 to reduce micro-deformation of the stainless steel tube with a larger inner diameter.

[0014] As an improvement of the above scheme, in the SB step, the stainless steel tube at a temperature of 90 to 100°C is completely immersed in a primary color passivation solution at a temperature of 20 to 40°C; ensuring that the temperature difference between the stainless steel tube and the primary color passivation solution is greater than or equal to 50°C.

[0015] As an improvement of the above scheme, pulse spraying is provided in the SB step, and pulse spraying is to periodically spray a mixture of nitrogen, oxygen mixed gas and primary color passivation liquid onto the surface of the stainless steel tube at a preset time interval to increase the passivation speed of the stainless steel tube surface and reduce the primary color passivation time of the stainless steel tube.

[0016] As an improvement of the above solution, the duration of each mixture injection in the pulse injection is 2 to 5 seconds, and the interval between two adjacent mixture injections is 8 to 10 seconds to prevent excessive oxidation of the stainless steel tube.

[0017] As an improvement of the above scheme, the primary color passivation liquid is placed in the passivation tank, and the passivation speed of the stainless steel pipe is further improved by extracting the primary color passivation liquid in the passivation tank and mixing it with nitrogen and oxygen mixed gas to form a mixture.

[0018] As an improvement of the above scheme, in the nitrogen and oxygen mixed gas, the volume of oxygen accounts for 10% to 15% of the volume of the nitrogen and oxygen mixed gas. Compared with direct exposure to air, the nitrogen and oxygen mixed gas contains less oxygen, which will not cause excessive oxidation of the surface of the stainless steel pipe. It is more suitable for accelerating the original color passivation of the stainless steel pipe and increasing the passivation speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The figure is a schematic diagram of the working process of a method for finishing a stainless steel pipe in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0021] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0022] like Figure 1 As shown, a method for finishing a stainless steel pipe in the present invention comprises the following steps:

[0023] SA, bright annealing: SA1, put the stainless steel tube into the annealing furnace; SA2, introduce argon and hydrogen mixed gas into the annealing furnace and make the gas pressure in the annealing furnace reach a positive pressure of 5kPa; SA3, heat the temperature in the annealing furnace to a preset temperature; SA4, maintain the temperature in the annealing furnace; SA5, reduce the temperature in the annealing furnace to 90 to 100°C and remove the stainless steel tube from the annealing furnace;

[0024] SB, passivation of the original color of stainless steel pipe;

[0025] In both steps SA3 and SA4, pressure fluctuation control is provided. The pressure fluctuation control is to pump a mixed gas of argon and hydrogen into or out of the annealing furnace so that the pressure in the annealing furnace fluctuates back and forth between a positive pressure of 5 kPa and a positive pressure of 100 kPa.

[0026] It should be noted that the bright annealing process parameters and the primary color passivation process parameters in the present invention are adjusted according to the type and wall thickness of the stainless steel pipe. The related bright annealing process parameters and the primary color passivation process parameters are already known in the prior art and will not be described one by one here.

[0027] In the SA2 step, before the argon-hydrogen mixed gas is introduced into the annealing furnace, the annealing furnace is first vacuumed, and then argon is introduced to reach a positive pressure of 200hPa, and then the vacuum is evacuated, and then argon is introduced to reach a positive pressure of 200hPa. This cycle is repeated many times until the residual oxygen and dew point in the annealing furnace reach the target values, and then the argon-hydrogen mixed gas is introduced according to the annealing process parameters.

[0028] In the present invention, the air pressure fluctuation control can be realized by a two-way pump in combination with a temporary storage tank. In the initial state, the air pressure in the annealing furnace is at a positive pressure of 5kPa. The two-way pump pumps the argon and hydrogen mixed gas from the temporary storage tank into the annealing furnace, so that the air pressure in the annealing furnace rises to a positive pressure of 100kPa. Then the two-way pump operates in the reverse direction, and the argon and hydrogen mixed gas is pumped from the annealing furnace into the temporary storage tank, and the air pressure in the annealing furnace drops to a positive pressure of 5kPa. This cycle is repeated to realize pumping the argon and hydrogen mixed gas into or out of the annealing furnace so that the air pressure in the annealing furnace fluctuates back and forth between a positive pressure of 5kPa and a positive pressure of 100kPa. In addition, the air pressure in the annealing furnace can be at a positive pressure of 5kPa during the cooling stage of bright annealing.

[0029] The working principle of a stainless steel pipe finishing method of the present invention is as follows:

[0030] In the SA3 step, which is the heating stage of bright annealing, the gas in the annealing furnace is controlled by air pressure fluctuation to make the gas flow, thereby increasing the heat transfer rate of the stainless steel pipe, making the inside and outside of the stainless steel pipe heated more evenly, and reducing the heating time of the stainless steel pipe. At the same time, under the control of air pressure fluctuation, the gas pressure in the annealing furnace fluctuates back and forth between 5kPa and the positive pressure of 100kPa, and the surface of the stainless steel pipe is hammered with obvious wave force under the action of the air pressure difference, flattening the protrusions and pits on the surface of the stainless steel pipe to a certain extent, thereby improving the surface finish of the stainless steel pipe.

[0031] In the SA4 step, which is the holding stage of bright annealing, the gas in the annealing furnace is made to flow through pressure fluctuation control to make the grain refinement more uniform and reduce the impact on the surface finish of the stainless steel pipe. At the same time, due to the increase in the heat transfer rate of the stainless steel pipe, the time of the holding stage of bright annealing can also be reduced.

[0032] In addition, when the temperature of the annealing furnace reaches 90 to 100°C, the temperature of the stainless steel pipe is also reduced accordingly, and then the primary color passivation is carried out directly. The temperature difference between the stainless steel pipe and the primary color passivation liquid is greater than or equal to 50°C. This temperature is used without the need for waste heat to harden the surface of the stainless steel pipe due to the rapid cooling of the stainless steel pipe, and the passivation speed is increased, thereby reducing the primary color passivation time.

[0033] The method for finishing a stainless steel pipe of the present invention can shorten the bright annealing time and the primary color passivation time of the stainless steel pipe to shorten the total processing time, and improve the surface finish of the stainless steel pipe.

[0034] In the present invention, the air pressure fluctuation control time in step SA3 is preferably equal to the total time of step SA3, that is, the air pressure fluctuation control time completely overlaps with the time of step SA3, thereby improving the surface finish of the stainless steel pipe to a greater extent; the air pressure fluctuation control time in step SA4 is preferably 1 / 3 to 1 / 2 of the total time of step SA4, and the air pressure fluctuation control in step SA4 starts at the same time as step SA4; that is, the stainless steel pipe enters the insulation stage from the heating stage of bright annealing, the air pressure fluctuation control continues, and within 1 / 3 to 1 / 2 of the total time from the start of step SA4, the grains of the stainless steel pipe are evenly heated, and then at least half of the total time of step SA4 is left for grain refinement of the stainless steel pipe to ensure the annealing effect.

[0035] As a preferred technical solution of the present invention, the air pressure fluctuation control frequency in step SA3 is 2 to 4 times that in step SA4. In step SA3, the air pressure fluctuation control frequency is higher, the air pressure changes faster, and the flattening effect on the bumps and pits on the surface of the stainless steel pipe is more obvious; in step SA3, the air pressure fluctuation control frequency is lower, the air pressure changes slower, and the effect on grain refinement is reduced. Furthermore, the air pressure fluctuation control frequency in step SA4 is 8 to 10 times per minute, so that the fluctuating force hammering effect on the surface of the stainless steel pipe is smaller, reducing the effect on grain refinement.

[0036] It should be noted that for stainless steel tubes with larger inner diameters and thickness angles, since the annealing furnace for stainless steel tubes generally adopts electromagnetic heating, the temperature of the stainless steel tube can be heated to the required temperature in a short time. Since the inside of the stainless steel tube is heated slowly, it is easy to cause micro deformation of the stainless steel tube. Therefore, in the present invention, it is preferred to heat the inside and outside of the stainless steel tube synchronously in the SA3 step; and it is preferred to keep the inside and outside of the stainless steel tube warm synchronously in the SA4 step. The insertion heating component can be inserted into the stainless steel tube, and the inside and outside of the stainless steel tube are heated synchronously, which can compensate for the heating heat provided by the inside of the stainless steel tube and reduce the micro deformation of the stainless steel tube.

[0037] In fact, in the SB step, it is preferred to completely immerse the stainless steel tube at a temperature of 90 to 100° C. in the primary color passivation solution at a temperature of 20 to 40° C.; ensuring that the temperature difference between the stainless steel tube and the primary color passivation solution is greater than or equal to 50° C.

[0038] Specifically, in the SB step, pulse spraying is preferably provided, and the pulse spraying is to periodically spray a mixture of nitrogen, oxygen mixed gas and primary color passivation liquid toward the surface of the stainless steel tube at a preset time interval. By spraying the nitrogen, oxygen mixed gas and primary color passivation liquid toward the surface, the relative flow velocity between the surface of the stainless steel tube and the primary color passivation liquid is increased and a certain amount of oxygen is provided for the passivation of the surface of the stainless steel tube, so as to increase the passivation velocity of the surface of the stainless steel tube and reduce the primary color passivation time of the stainless steel tube.

[0039] More specifically, the duration of each mixture injection in pulse injection is preferably 2 to 5 seconds, and the interval between two adjacent mixture injections is preferably 8 to 10 seconds, providing corresponding oxygen and nitrogen, and leaving sufficient interval time to prevent excessive oxidation of the stainless steel tube.

[0040] In the embodiment of the present invention, the primary color passivation liquid is placed in the passivation tank, and preferably the primary color passivation liquid in the passivation tank is extracted to form a mixture with nitrogen and oxygen mixed gas. The primary color passivation liquid in the passivation tank is extracted to make the primary color passivation liquid in the passivation tank flow, and the primary color passivation liquid is sprayed to form a mixture with nitrogen and oxygen mixed gas, so that the flow of the primary color passivation liquid in the passivation tank is more intense, and the passivation speed of the stainless steel pipe is further improved.

[0041] In the embodiment of the present invention, the volume of oxygen in the nitrogen and oxygen mixed gas preferably accounts for 10% to 15% of the volume of the nitrogen and oxygen mixed gas. Compared with direct exposure to air, the nitrogen and oxygen mixed gas contains less oxygen, which will not cause excessive oxidation of the surface of the stainless steel pipe, and is more suitable for accelerating the original color passivation of the stainless steel pipe and increasing the passivation speed.

[0042] The beneficial effects of a stainless steel pipe finishing method of the present invention are analyzed below through examples and comparative examples. It should be noted that the examples and comparative examples are all for stainless steel pipes with an outer diameter of 50 mm and a wall thickness of 3 mm.

[0043] Example 1

[0044] A method for finishing a stainless steel pipe in this embodiment includes the following steps:

[0045] SA1, put the stainless steel tube into the annealing furnace;

[0046] SA2, introduce argon and hydrogen mixed gas into the annealing furnace and make the gas pressure in the annealing furnace reach a positive pressure of 5kPa;

[0047] SA3, after 16 minutes, the temperature in the annealing furnace is heated to 1080°C;

[0048] SA4, maintain the temperature in the annealing furnace at 1080°C for 5 minutes;

[0049] SA5, lower the temperature in the annealing furnace to 95°C and remove the stainless steel tube from the annealing furnace;

[0050] SB, completely immerse the stainless steel tube at 95°C in the primary color passivation solution at 30°C for 3 minutes;

[0051] In both steps SA3 and SA4, there is a pressure fluctuation control, which is to pump the argon and hydrogen mixed gas into or out of the annealing furnace so that the pressure in the annealing furnace fluctuates back and forth between the positive pressure of 5 kPa and the positive pressure of 100 kPa; wherein, the pressure fluctuation control time in step SA3 is 16 minutes and the frequency is 30 times per minute, wherein, the pressure fluctuation control time in step SA4 is 2 minutes and the frequency is 8 times per minute, and the pressure fluctuation control in step SA4 starts simultaneously with step SA4.

[0052] Example 2

[0053] A method for finishing a stainless steel pipe in this embodiment includes the following steps:

[0054] SA1, put the stainless steel tube into the annealing furnace;

[0055] SA2, introduce argon and hydrogen mixed gas into the annealing furnace and make the gas pressure in the annealing furnace reach a positive pressure of 5kPa;

[0056] SA3, after 15 minutes, the temperature in the annealing furnace is heated to 1080°C;

[0057] SA4, maintain the temperature in the annealing furnace at 1080°C for 6 minutes;

[0058] SA5, lower the temperature in the annealing furnace to 98°C and remove the stainless steel tube from the annealing furnace;

[0059] SB, a stainless steel pipe at a temperature of 98°C is completely immersed in a primary color passivation liquid at a temperature of 30°C in a passivation tank for 2 minutes. In the SB step, a pulse jet is provided, and the pulse jet is to periodically spray a mixture of nitrogen, oxygen mixed gas and primary color passivation liquid onto the surface of the stainless steel pipe with each jet lasting 3 seconds and an interval of 10 seconds between two adjacent jets; the volume of oxygen accounts for 12% of the volume of the nitrogen and oxygen mixed gas.

[0060] In both steps SA3 and SA4, there is a pressure fluctuation control, which is to pump the argon and hydrogen mixed gas into or out of the annealing furnace so that the pressure in the annealing furnace fluctuates back and forth between the positive pressure of 5 kPa and the positive pressure of 100 kPa; wherein, the pressure fluctuation control time in step SA3 is 15 minutes and the frequency is 40 times per minute, wherein, the pressure fluctuation control time in step SA4 is 3 minutes and the frequency is 10 times per minute, and the pressure fluctuation control in step SA4 starts simultaneously with step SA4.

[0061] Comparative Example 1

[0062] A method for finishing a stainless steel pipe in this comparative example comprises the following steps:

[0063] Step 1, placing the stainless steel tube into an annealing furnace;

[0064] Step 2: introducing a mixed gas of argon and hydrogen into the annealing furnace and making the gas pressure in the annealing furnace reach a positive pressure of 5 kPa;

[0065] Step 3: After 25 minutes, the temperature in the annealing furnace is heated to 1080°C;

[0066] Step 4, maintaining the temperature in the annealing furnace at 1080° C. for 10 minutes;

[0067] Step 5, lowering the temperature in the annealing furnace to 50° C. and removing the stainless steel tube from the annealing furnace;

[0068] Step six, completely immerse the stainless steel pipe at a temperature of 50°C in the primary color passivation solution at a temperature of 30°C for 4 minutes.

[0069] Comparative Example 2

[0070] A method for finishing a stainless steel pipe in this comparative example comprises the following steps:

[0071] Step 1, placing the stainless steel tube into an annealing furnace;

[0072] Step 2: introducing a mixed gas of argon and hydrogen into the annealing furnace and making the gas pressure in the annealing furnace reach a positive pressure of 5 kPa;

[0073] Step 3: After 20 minutes, the temperature in the annealing furnace is heated to 1080°C;

[0074] Step 4, maintaining the temperature in the annealing furnace at 1080° C. for 7 minutes;

[0075] Step 5, lowering the temperature in the annealing furnace to 40° C. and removing the stainless steel tube from the annealing furnace;

[0076] Step six, completely immerse the stainless steel pipe at a temperature of 40°C in the primary color passivation solution at a temperature of 30°C for 5 minutes.

[0077] By using the surface finish control card, the finish before and after treatment of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were measured, and the surface finish level data were obtained as shown in the following table.

[0078] Before treatment After treatment Example 1 6 11 Example 2 6 11 Comparative Example 1 6 9 Comparative Example 2 6 8

[0079] Through the above data, it can be concluded that the method for polishing a stainless steel tube of the present invention can be a method for polishing a stainless steel tube, and through a time analysis of the processing process, it can be concluded that the method for polishing a stainless steel tube of the present invention can shorten the total processing time.

[0080] The above are only specific embodiments of the present invention, which show and describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. The above embodiments and descriptions only describe the principles of the present invention, and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for finishing a stainless steel pipe, characterized in that: The steps include: SA, bright annealing: SA1, put the stainless steel tube into the annealing furnace; SA2, introduce argon and hydrogen mixed gas into the annealing furnace and make the gas pressure in the annealing furnace reach a positive pressure of 5kPa; SA3, heat the temperature in the annealing furnace to a preset temperature; SA4, maintain the temperature in the annealing furnace; SA5, reduce the temperature in the annealing furnace to 90 to 100°C and remove the stainless steel tube from the annealing furnace; SB, passivation of the original color of stainless steel pipe; In both the SA3 and SA4 steps, a pressure fluctuation control is provided, and the pressure fluctuation control is to pump the argon and hydrogen mixed gas into or out of the annealing furnace so that the pressure in the annealing furnace fluctuates back and forth between a positive pressure of 5 kPa and a positive pressure of 100 kPa; The air pressure fluctuation control time in step SA3 is equal to the total time of step SA3; the air pressure fluctuation control time in step SA4 is 1 / 3 to 1 / 2 of the total time of step SA4, and the air pressure fluctuation control in step SA4 starts at the same time as step SA4.

2. A method for finishing a stainless steel pipe according to claim 1, characterized in that: The air pressure fluctuation control frequency in step SA3 is 2 to 4 times the air pressure fluctuation control frequency in step SA4.

3. A method for finishing a stainless steel pipe as claimed in claim 2, characterized in that: The frequency of air pressure fluctuation control in step SA4 is 8 to 10 times per minute.

4. A method for finishing a stainless steel pipe according to claim 1, characterized in that: In step SA3, both the inner and outer sides of the stainless steel tube are heated synchronously; in step SA4, both the inner and outer sides of the stainless steel tube are kept warm synchronously.

5. A method for finishing a stainless steel pipe according to claim 1, characterized in that: In the SB step, the stainless steel pipe at a temperature of 90 to 100° C. is completely immersed in the primary color passivation solution at a temperature of 20 to 40° C.

6. A method for finishing a stainless steel pipe as claimed in claim 5, characterized in that: In the SB step, pulse spraying is provided, and the pulse spraying is to periodically spray a mixture of nitrogen, oxygen mixed gas and primary color passivation liquid onto the surface of the stainless steel pipe according to a preset time interval.

7. A method for finishing a stainless steel pipe according to claim 6, characterized in that: The duration of each mixture injection in the pulse injection is 2 to 5 seconds, and the interval between two adjacent mixture injections is 8 to 10 seconds.

8. A method for finishing a stainless steel pipe as claimed in claim 6, characterized in that: The primary color passivation liquid is placed in the passivation tank, and a mixture is formed by extracting the primary color passivation liquid in the passivation tank and mixing it with nitrogen and oxygen gas.

9. A method for finishing a stainless steel pipe according to claim 6, characterized in that: In the nitrogen and oxygen mixed gas, the volume of oxygen accounts for 10% to 15% of the volume of the nitrogen and oxygen mixed gas.

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