A processing method for a stainless steel main pipeline with two branch nozzles

Abstract

The present invention discloses a processing method for a stainless steel main pipeline with two branch nozzles, belonging to the field of machining. Aiming at the problems of difficult processing and poor effect of existing pipelines with branch nozzles, the present invention provides a processing method for a stainless steel main pipeline with two branch nozzles, which includes confirming the blank allowance; milling the circle at the branch nozzle part according to the sampling requirements; removing the redundant part according to the delivery requirements; installing an eccentric counterweight tooling on the outer circle contact surface in the middle of the branch nozzle; machining the inner hole; machining the outer circle; machining the branch nozzle, and machining the transition areas of the two branch nozzles, the eccentric outer circle and the non-eccentric outer circle; finely milling the total length. The present invention completes the processing of the main pipeline through a reasonable process sequence arrangement, reduces the risk of internal defects of the workpiece while ensuring the quality of the workpiece, effectively improves the processing efficiency, overcomes the difficulties in the processing of nuclear power main pipelines, the production cycle is within the controllable range, and the dimensional accuracy meets the customer requirements, accumulating experience for the manufacture of subsequent similar products.

Description

Technical Field

[0001] The present invention belongs to the technical field of machining, and more specifically, relates to a machining method for a stainless steel main pipe with two branch nozzles. Background Art

[0002] With the country paying increasing attention to environmental protection, the gradual replacement of traditional fossil energy by clean energy is inevitable. As an efficient clean energy, nuclear power has broad development prospects. The technologies of AP1000, CAP1400, and the fully domestically produced Hualong One nuclear power units are becoming more and more mature step by step. The main pipe, as one of the main equipment of a nuclear power plant, is typically representative and has great machining difficulty and complex processes. Especially for the key part of some nuclear power project units - the hot section of the main pipe, its delivery size has an inner diameter of φ785mm, an outer diameter of φ963.5 / 981.5mm, and a total length of nearly 8000mm. There is eccentricity in the outer circle of the middle section of the pipe body. At the same time, there are two branch nozzles with an included angle of 43° distributed on the main pipe body. Analyzing from the machining processability, there are mainly two difficulties in machining this part: 1. Eccentric machining is prone to deformation: The two branch nozzles cause uneven overall mass distribution of the part. The machining is eccentric machining. When machining the inner hole, the machine tool rotates at a high speed, and eccentric machining is extremely prone to deformation, resulting in unqualified dimensions. 2. Deep hole machining is difficult: The inner hole diameter of the main pipe is large, and the rotary diameter reaches about φ2600mm. Conventional deep hole drilling and boring machine tools cannot machine it; the machinability of stainless steel materials is poor, and the machining is difficult; the machining volume is extremely large, and the machining cycle is long.

[0003] Corresponding modifications have also been made to the above problems. For example, Chinese Patent Application No. CN200910057934.8, with a publication date of April 20, 2011, discloses a forging method for a nuclear power main pipe blank with a branch nozzle. The first step is to roll and forge the ingot body of the forging and press the tongs; the second step is to upset; the third step is to draw out and determine the direction of the branch nozzle; the fourth step is to mark. Heat the forging temperature to 1180 - 1220°C and distribute the materials according to the weight of each section; the fifth step is to draw the straight pipe section to the set size of the forging; the sixth step is to draw two branch nozzles and make these two branch nozzles at an angle of 45 degrees to each other. The present invention can accurately forge two branch nozzles at an angle to each other on the main pipe wall, and the performance of the branch nozzles is stable, meeting the design requirements of the AP1000 nuclear power plant. The disadvantage of this patent is that it does not specifically involve the machining method of the branch nozzle, and its reference value is not great.

[0004] For another example, Chinese Patent Application No. CN201510597252.1, with a publication date of November 11, 2015, discloses a profiling forging method of a main pipeline hollow forging with an ultra-long asymmetric nozzle. An electroslag ingot is preferably selected as the ingot. First heating: After the ingot is peeled and inspected for defects, it is heated in the furnace to 1180 - 1220 °C and held for 6 - 10 h; after the billet is taken out of the furnace, it is upset, punched, and the outer circle is rolled in sequence. Second heating: The billet is heated in the furnace to 1180 - 1220 °C and held for 6 - 10 h; after using a mandrel to draw out the length, it becomes a hollow billet. Third to fifth heating: The billet is heated in the furnace to 1020 - 1060 °C and held for 4 - 6 h; after the billet is taken out of the furnace, a mandrel is inserted into the middle hole of the billet and drawn out in segments to obtain a hollow billet with two flanges. Sixth heating: The hollow billet is heated in the furnace to 1020 - 1060 °C and held for 4 - 6 h; after the billet is taken out of the furnace, the nozzle is pre-forged by differential temperature forging. Seventh heating: The billet is heated in the furnace to 1020 - 1060 °C and held for 4 - 6 h; after the billet is taken out of the furnace, the inner hole of the flange is extruded and finally forged by differential temperature process for cooling; the billet is corrected, and the corrected pipe blank is bent and formed by using a bending die. The disadvantages of this patent are: the product size accuracy is poor, and the cycle is long. Summary of the Invention

[0005] 1. Problems to be Solved

[0006] Aiming at the problems of difficult processing and poor effect of existing pipelines with branch nozzles, the present invention provides a processing method for a stainless steel main pipeline with two branch nozzles. The present invention completes the processing of the main pipeline through a reasonable process sequence arrangement, reduces the risk of internal defects of the workpiece while ensuring the quality of the workpiece, effectively improves the processing efficiency, overcomes the problems of processing nuclear power main pipelines, the production cycle is within a controllable range, and the dimensional accuracy meets the customer requirements, accumulating experience for the manufacture of subsequent similar products.

[0007] 2. Technical Solutions

[0008] To solve the above problems, the present invention adopts the following technical solutions.

[0009] A processing method for a stainless steel main pipeline with two branch nozzles includes the following steps:

[0010] S1: Confirm the allowance of the blank after forging.

[0011] S2: Wipe the side surface of the branch nozzle white, and perform ultrasonic non-destructive testing on the wiped white side surface of the branch nozzle.

[0012] S3: Preparation for outer circle processing: Mark the center cross lines at both ends of the total length of the main pipeline, the center punch hole lines, re-inspect the allowance of the branch nozzle, and process the center punch holes at both ends of the total length of the main pipeline.

[0013] S4: Polish the outer circle; reinspect the remaining amount of the outer circle. At a minimum, polish the outer circles of the three sections at both ends of the main pipe and the middle opening between the two branch nozzles, and at a minimum, polish the two side shoulders of the two branch nozzles.

[0014] S5: Conduct an overall ultrasonic non-destructive inspection on the workpiece.

[0015] S6: Redraw the center cross lines at both ends of the total length of the main pipe according to the flaw detection results, and draw the center line and end face line of the branch nozzle on the shoulder surface of the two branch nozzles.

[0016] S7: Milling the outer circle of the branch nozzle with a single-sided allowance according to the scribing and sampling requirements.

[0017] S8: Mark the sample position lines at both ends of the total length of the main pipe and at the end of the branch nozzle according to the sampling requirements, saw off the samples at both ends of the total length of the main pipe, mill the samples of the branch nozzles on the boring machine, and conduct mechanical property tests on the samples.

[0018] S9: Process the remaining amount of the branch nozzle: According to the delivery standard, mill off the outer circle remaining amount after leaving a single-sided allowance for the branch nozzle, mill off the remaining amount of the root and outer circle chamfer of the branch nozzle by profiling, mill off the remaining amount on the reverse side of the outer circle where the branch nozzle is located, and machine the center holes at both ends of the total length.

[0019] S10: Install an eccentric counterweight tooling on the middle outer circle contact surface of the branch nozzle.

[0020] S11: Preparation for deep hole machining: Turn the outer circle to make the outer circle diameters at both ends of the total length consistent.

[0021] S12: Finish machining the inner circle deep hole.

[0022] S13: Finish turning the outer shape: Remove the eccentric counterweight tooling, make a plug according to the measured inner hole diameter size at both ends of the total length, insert the plug into the inner hole and clamp it on the CNC horizontal lathe, and turn the three outer circles.

[0023] S14: Finish milling the branch nozzle.

[0024] S15: Finish milling the total length of the main pipe.

[0025] Furthermore, in steps S1 and S3, a laser tracker is used to perform three-dimensional scanning on the blank for allowance confirmation; and in step S2, the side surfaces of the branch nozzle are polished in the circumferential four side surfaces according to the blank surface of the branch nozzle, and ultrasonic non-destructive inspections are performed on all four side surfaces.

[0026] Furthermore, in step S11, the roundness of the outer circle is ensured with the outer circle runout value ≤ 0.15 mm; in step S12, when performing finish machining of the deep hole of the inner circle, it specifically includes: mounting the deep hole lathe and boring machine on the main pipe, calibrating the outer circle to a runout value ≤ 0.15 mm, nesting the material according to the guide groove of φ265 / φ355×100, gradually enlarging the hole to φ776 after nesting, and then rough turning, semi-finishing, and finish machining to φ783, φ784.2, φ784.75, and finally polishing the whole inner hole.

[0027] Furthermore, during the entire machining process of steps S12 and S13, an ultrasonic thickness gauge is used to monitor the wall thickness and control the coaxiality of the inner and outer circles.

[0028] Furthermore, in step S13, the machine tool speed is controlled at 15 - 20 r / min, and when finish turning the outer circle, an ultrasonic thickness gauge is used to monitor the wall thickness, calculate the coaxiality and the final wall thickness based on the measurement data, and ensure that the wall thickness dimension meets the drawing dimensional tolerance.

[0029] Furthermore, if the wall thickness dimension does not meet the requirements, the center hole is offset by using a gantry milling machine, and the offset distance is determined according to the measured wall thickness data.

[0030] Furthermore, in step S14, a numerically controlled floor - type boring and milling machine is used to machine two branch nozzles, and the workpiece is aligned according to the measured outer circle dimensions on both sides of the branch nozzles.

[0031] Furthermore, in step 10, the eccentric counterweight fixture includes an upper pressure plate and a cushion block. The upper pressure plate and the cushion block are respectively arranged on the upper and lower sides of the outer circle contact surface. The upper pressure plate and the cushion block are connected by stud bolts, and a counterweight block is arranged on the lower surface of the cushion block.

[0032] 3. Beneficial Effects

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] By confirming the stock removal of the blank to ensure the subsequent operation space, the present invention reduces errors at the source; and performs ultrasonic non - destructive testing on the branch nozzles with relatively high internal forging risks to ensure the internal quality of the product; then samples are taken for mechanical property tests to further ensure the product quality; an eccentric counterweight fixture is installed on the outer circle contact surface in the middle of the branch nozzle to eliminate the eccentric influence of the workpiece and ensure the dimensional accuracy of the product; then subsequent machining operations are carried out; the machining of the main pipe is completed through a reasonable process sequence arrangement, reducing the risk of internal defects of the workpiece while ensuring the quality of the workpiece, effectively improving the machining efficiency, overcoming the difficulties in the machining of nuclear power main pipes, keeping the production cycle within a controllable range, and the dimensional accuracy meeting the customer requirements, accumulating experience for the manufacture of subsequent similar products. Description of the Drawings

[0035] Figure 1Schematic diagram of the forging blank of the main pipeline;

[0036] Figure 2 Schematic diagram of a typical eccentric stainless steel main pipeline structure with branch nozzles;

[0037] Figure 3 Schematic diagram of the installation of the counterweight tooling for the main pipeline;

[0038] Figure 4 Schematic diagram of the internal hole machining of the main pipeline;

[0039] Figure 5 Schematic diagram of the outer circle of the main pipeline.

[0040] In the figure: 1. Main pipeline; 12. Eccentric counterweight tooling; 13. Support wheel; 14. Machine tool guide rail; 15. Lathe faceplate and chuck; 16. Removable tool holder; 17. Adjustable floating boring tool holder; 18. Guide block; 19. Drill rod; 2. Upper pressing plate; 3. Spacer block; 4. Counterweight block; 5. Stud; 6. Chuck on the headstock side; 7. Plug on the tailstock side of the lathe. Specific implementation method

[0041] The present invention will be further described below in conjunction with specific embodiments and the accompanying drawings.

[0042] Embodiment 1

[0043] A processing method for a stainless steel main pipeline with two branch nozzles includes the following steps:

[0044] S1: Confirm the remaining amount of the forging blank after forging; specifically, after the forging of the blank is completed, as shown, after the forging of the blank is completed, a laser tracker is used to perform three-dimensional scanning on the blank to confirm the remaining amount; Figure 1 S2: Wipe the side of the branch nozzle with the minimum amount according to the outer shape of the blank, and perform ultrasonic non-destructive testing on the wiped side of the branch nozzle; it should be noted here that since the risk of internal forging defects in the branch nozzle part is relatively large, therefore, prior to the wiping and flaw detection of the branch nozzle part is beneficial to ensure the internal quality of the product. At the same time, if the flaw detection result is unqualified, the forging process allowance can be used for repair; if the flaw detection result is qualified, the forging process allowance is sawn off; and the side of the branch nozzle is wiped white according to the four circumferential sides of the blank surface of the branch nozzle, and ultrasonic non-destructive testing is performed on all four sides. The circumferential direction is relative to the main pipeline 1;

[0045] S3: Preparation for outer circle machining: When the ultrasonic non-destructive testing in step S2 is qualified, saw off the forging process allowance, mark the center cross lines at both ends of the total length of the main pipeline, the center lines of the center holes, use a laser tracker to re-inspect the remaining amount of the branch nozzle, and machine the center holes at both ends of the total length of the main pipeline;

[0046] S4: Prepare for internal hole machining: After the outer circle machining is completed, machine the internal hole of the main pipeline;

[0047] S4: Polish the outer circle; use the machine tool to measure and re-inspect the outer circle allowance, minimally polish the outer circles at both ends of the main pipe, and the outer circles of the two open spaces between the two branch nozzles, a total of three outer circles, minimally polish the two side shoulders of the two branch nozzles. The minimum amount in this application refers to the minimum amount of the blank shape, and both ends of the total length refer to both ends of the total length of the main pipe;

[0048] S5: Conduct an overall ultrasonic non-destructive inspection on the workpiece;

[0049] S6: Re-draw the center cross lines at both ends of the total length of the main pipe according to the flaw detection results, and draw the center line and end face line of the branch nozzle on the shoulder surface of the two branch nozzles;

[0050] S7: According to the marking and sampling requirements, mill the outer circle of the branch nozzle with a single-sided allowance. Generally, the single-sided allowance is about 5 mm;

[0051] S8: Mark the sample position lines at both ends of the total length of the main pipe and the end of the branch nozzle according to the sampling requirements, saw off the samples at both ends of the total length of the main pipe, mill the samples of the branch nozzles on the boring machine, and conduct mechanical property tests on the samples;

[0052] S9: Process the allowance of the branch nozzle: Place the workpiece on the floor-type boring and milling machine. According to the delivery drawing standard, after leaving a single-sided allowance of about 20 mm for the branch nozzle, mill off the outer circle allowance, mill off the chamfer allowance at the root and outer circle of the branch nozzle by profiling, mill off the allowance on the reverse side of the outer circle where the branch nozzle is located, and process the center holes at both ends of the total length;

[0053] S10: Install the eccentric counterweight tooling 12 on the middle outer circle contact surface of the branch nozzle as Figure 3 shown, and pad a whole circle of copper sheet about 0.5 mm thick on the middle outer circle contact surface of the branch nozzle before installing the eccentric counterweight tooling 12 to increase the contact area and reduce the extrusion of the outer circle where the eccentric counterweight tooling 12 contacts the branch nozzle; at the same time, after the eccentric counterweight tooling 12 is installed, turn the workpiece forward and backward respectively on the horizontal lathe to confirm that the eccentric counterweight tooling 12 is fastened and does not slip or rotate; the eccentric counterweight tooling 12 includes an upper pressing plate 2 and a spacer block 3. The upper pressing plate 2 and the spacer block 3 are respectively arranged on the upper and lower sides of the outer circle contact surface. The upper pressing plate 2 and the spacer block 3 are connected by a stud 5, and a counterweight block 4 is arranged on the lower surface of the spacer block 3; both the upper pressing plate 2 and the spacer block 3 are welded by 30 mm thick steel plates to reduce the weight of the whole tooling and the manufacturing cost of the tooling;

[0054] S11: Preparation for deep hole machining: Minimally turn the outer circle of the round, and keep the outer circle diameters at both ends of the total length consistent; use the outer circle as the reference for subsequent deep hole machining to ensure that the outer circle runout value ≤ 0.15 mm; minimally mill the two end faces of the workpiece on the boring machine, and mill a φ265 / φ355×100 deep guide groove on one end face for subsequent deep hole trepanning reference;

[0055] S12: Finish machining the inner circle deep hole; as Figure 4As shown in the figure, specifically, take the deep-hole turning and boring lathe on the main pipeline 1 and the eccentric weight loading fixture 12 as a whole. Either side of either end of the total length of the main pipeline can be used as the chuck side. The lathe faceplate and chuck 15 of the turning and boring lathe clamp the outer circle of one side of the total length to provide rotational power. Two supporting wheels 13 below the main pipeline 1 are fixed on the machine tool guide rail 14 to provide support and auxiliary alignment. The two supporting wheels 13 and the lathe faceplate and chuck 15 of the turning and boring lathe together form a clamping system to ensure that no sliding or jumping that affects dimensional accuracy occurs when the main pipeline 1 rotates. The position of the supporting wheels 13 can be fine-tuned in real time according to the operating conditions. After the overall rotation of the workpiece is stable, the machining system composed of the detachable tool holder 16, the adjustable floating boring tool holder 17, the guide block 18, and the drill pipe 19 starts machining from one end face. Calibrate the outer circle to a runout value ≤ 0.15 mm, perform sleeve cutting according to the guide groove of φ265 / φ355×100, gradually expand the hole to φ776 after sleeve cutting, and then rough turn, semi-finish, and finish machine to φ783, φ784.2, φ784.75. Finally, perform overall internal hole polishing to improve the surface roughness. During the machining process, an ultrasonic thickness gauge is used to monitor the wall thickness throughout the process to ensure internal and external coaxiality;

[0056] S13: Fine turning of the outer shape: As Figure 5 shown in the figure, remove the eccentric weight loading fixture 12, make plugs according to the measured inner diameter dimensions of both ends of the total length, insert the plugs into the inner holes and clamp them on the CNC horizontal lathe, and turn the three-section outer circles round. Specifically, an ultrasonic thickness gauge is used to monitor the wall thickness throughout this step to ensure internal and external coaxiality. When using the ultrasonic thickness gauge to measure the wall thickness, find the positions with the maximum and minimum circumferential wall thicknesses, select measurement points with an axial interval of 500 and a circumferential interval of 90°. According to the measured data, reduce the axial spacing at the location with a large wall thickness deviation to 200 for detailed measurement. Calculate the overall wall thickness situation based on the final data, and ensure that the measured minimum and maximum wall thicknesses are within the theoretical wall thickness tolerance range according to the delivery size tolerance. If the wall thickness dimension does not meet the requirements, it is necessary to offset the center hole using a large gantry milling machine, and the offset distance is determined according to the measured wall thickness data; rough and fine turn the three-section outer circles according to the delivery drawing, and mark the lines on both end faces of the total length; place the workpiece on the large gantry milling machine, offset the center holes at both ends by 15 mm, place the workpiece on the CNC horizontal lathe, that is, place the main pipeline 1 on the CNC horizontal lathe, fix one end of the main pipeline 1 using the chuck 6 on the headstock side, use the plug 7 on the tailstock side of the lathe to turn out one section of the outer circle as the outer circle machining reference, machine the eccentric outer circle in the middle section, and at the same time measure the minimum wall thickness data. Control the machining dimensions based on both the machining diameter and the wall thickness. Use the CNC gantry milling machine to offset the center hole of the center drill, and complete the machining of the center holes at both ends under the same working station to ensure the offset accuracy; control the machine tool speed at 15 - 20 r / min. Through machining verification, when the machine tool speed is within this range, the centrifugal force generated during the eccentric machining of the workpiece has no impact on the dimensional accuracy of the workpiece;

[0057] S14: Fine milling of branch nozzles; specifically, the CNC floor-standing boring and milling machine processes two branch nozzles and eccentric transition areas on the workpiece, and the workpiece is leveled according to the actual diameter of the outer circle on both sides of the branch nozzle. One branch nozzle faces the machine tool spindle and is tightened. The CNC programming is milled to the front half range according to the delivery drawing, and the workpiece is re-clamped. The back of the branch nozzle faces the machine tool spindle, and the CNC programming is milled to the back area. The other branch nozzle is milled in the same way, and the bench grinds all surfaces of the branch nozzle, and the knife joint is polished and smoothed;

[0058] S15: Finish milling the total length of the main pipeline: The floor-type boring and milling machine mills the two end faces of the total length according to the total length marking line. At this point, all processing is completed. Figure 2 shown.

[0059] The present invention ensures the subsequent operation space by confirming the margin of the blank and reduces errors at the source; and performs ultrasonic non-destructive testing on the branch nozzles with relatively large internal forging risks to ensure the internal quality of the product; then samples are taken for mechanical property tests to further ensure product quality; an eccentric counterweight tool 12 is installed on the middle outer circle contact surface of the branch nozzle to eliminate the eccentricity of the workpiece and ensure the dimensional accuracy of the product; then subsequent processing operations are performed; the processing of the main pipeline is completed through a reasonable process sequence arrangement, the risk of internal defects in the workpiece is reduced while ensuring the quality of the workpiece, the processing efficiency is effectively improved, and the difficult problem of nuclear power main pipeline processing is overcome. The production cycle is within a controllable range, and the dimensional accuracy meets customer requirements, which accumulates experience for the subsequent manufacture of similar products.

[0060] The examples described in the present invention are merely descriptions of the preferred implementation modes of the present invention, and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made to the technical solutions of the present invention by engineers and technicians in this field should all fall within the protection scope of the present invention.

Claims

1. A processing method for a stainless steel main pipeline with two branch nozzles, characterized in that: It includes the following steps: S1: Confirm the surplus of the blank after forging; S2: Wipe the side surface of the branch nozzle, and perform ultrasonic non-destructive testing on the wiped side surface of the branch nozzle; S3: Preparation for outer circle machining: Mark lines, mark the center cross lines at both ends of the total length of the main pipe and the center punch hole lines, recheck the surplus of the branch nozzle, and machine the center punch holes at both ends of the total length of the main pipe; S4: Wipe the outer circle; Recheck the outer circle surplus, minimally wipe the outer circles at both ends of the main pipe and the three sections between the two branch nozzles, and minimally wipe the shoulder surfaces on both sides of the two branch nozzles; S5: Perform overall ultrasonic non-destructive testing on the workpiece; S6: Redraw the center cross lines at both ends of the total length of the main pipe according to the flaw detection results, and draw the center line and end face line of the branch nozzle on the shoulder surface of the two branch nozzles; S7: According to the marking and sampling requirements, mill the outer circle of the branch nozzle after leaving a single-sided allowance; S8: Mark the sample position lines at both ends of the total length of the main pipe and the end of the branch nozzle according to the sampling requirements, saw off the samples at both ends of the total length of the main pipe, mill the samples of the branch nozzle on the boring machine, and conduct mechanical property tests on the samples; S9: Machine the surplus of the branch nozzle: According to the delivery standard, mill off the outer circle surplus after leaving a single-sided allowance for the branch nozzle, mill off the chamfer surplus at the root and outer circle of the branch nozzle by profiling, mill off the surplus on the reverse side of the outer circle where the branch nozzle is located, and machine the center punch holes at both ends of the total length; S10: Install the eccentric counterweight fixture (12) on the middle outer circle contact surface of the branch nozzle; S11: Preparation for deep hole machining: Turn the outer circle to make the outer circle diameters at both ends of the total length consistent; S12: Finish machining of the inner circle deep hole; S13: Finish turning of the outer shape: Remove the eccentric counterweight fixture (12), make a plug according to the measured inner hole diameter size at both ends of the total length, insert the plug into the inner hole and clamp it on the CNC horizontal lathe, and turn the three outer circles; S14: Finish milling the branch nozzle; S15: Finish milling the total length of the main pipe.

2. The processing method of a stainless steel main pipeline with two branch nozzles according to claim 1, characterized in that: In step S1 and step S3, a laser tracker is used to perform three-dimensional scanning on the blank to confirm the surplus; and in step S2, the side surface of the branch nozzle is wiped by wiping the circumferential four side surfaces of the branch nozzle blank surface, and ultrasonic non-destructive testing is performed on all four side surfaces.

3. A processing method for a stainless steel main pipeline with two branch nozzles according to claim 1, characterized in that: In step S11, the outer circle is turned to ensure that the outer circle runout value ≤ 0.15 mm; in step S12, when performing finish machining of the inner circle deep hole, it specifically includes: Install the main pipe on the deep hole boring and turning machine, adjust the outer circle to a runout value ≤ 0.15 mm, perform trepanning according to the φ265 / φ355×100 guide groove, gradually expand the hole to φ776 after trepanning, and then rough turn, semi-finish and finish machine to φ783, φ784.2, φ784.75, and finally polish the overall inner hole.

4. A processing method for a stainless steel main pipe with two branch nozzles according to claim 3, characterized in that: During the machining processes of step S12 and step S13, an ultrasonic thickness gauge is used to monitor the wall thickness throughout the process to control the coaxiality of the inner and outer circles.

5. A processing method for a stainless steel main pipeline with two branch nozzles according to claim 1 or 4, characterized in that: In step S13, the machine tool speed is controlled at 15 - 20 r / min, and when finish turning the outer circle, an ultrasonic thickness gauge is used to monitor the wall thickness, calculate the coaxiality and the final wall thickness according to the measured data, and ensure that the wall thickness dimension meets the drawing dimensional tolerance.

6. The processing method of a stainless steel main pipe with two branch nozzles according to claim 5, characterized in that: If the wall thickness dimension does not meet the requirements, use a gantry milling machine to offset the center hole, and the offset distance is determined according to the measured wall thickness data.

7. A processing method for a stainless steel main pipeline with two branch nozzles according to claim 1, characterized in that: In step S14, a CNC floor boring and milling machine is used to machine the two branch nozzles, and the workpiece is aligned according to the measured outer circle dimensions on both sides of the branch nozzle.

8. A processing method for a stainless steel main pipeline with two branch nozzles according to claim 1, characterized in that: In the step 10, the eccentric weight tooling (12) includes an upper pressing plate (2) and a spacer block (3). The upper pressing plate (2) and the spacer block (3) are respectively arranged on the upper and lower sides of the outer circle contact surface. The upper pressing plate (2) and the spacer block (3) are connected by a stud (5), and a weight block (4) is arranged on the lower surface of the spacer block (3).

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