Austenitic stainless steel welded pipe for conveying high-temperature fused salt for photo-thermal power generation and manufacturing process

Abstract

The invention belongs to the field of stainless steel welded pipe production, and particularly discloses an austenitic stainless steel welded pipe for photo-thermal power generation high-temperature molten salt conveying and a manufacturing process, according to the requirement for the grain size of raw materials, the heat treatment temperature and the heat preservation time are controlled, and the grain size of a finished welded pipe base material meets the requirement of grade 4-7; according to the method, higher requirements are provided for control over the welding heat input quantity and the interlayer temperature, and the final normal-temperature tensile test (the tensile strength is larger than or equal to 515 MPa, the yield strength is larger than or equal to 205 MPa, and the percentage elongation after fracture is larger than or equal to 40%) and the bending test (no crack or other defects exist after bending) are achieved; the bending test is qualified), the hardness test is carried out (the hardness value is less than or equal to 92 HRB), the yield strength in the 575 DEG C high-temperature tensile test is more than or equal to 131 MPa, and the weld joint ferrite FN before postweld heat treatment is 3-10. The stainless steel welded pipe for conveying the photo-thermal power generation high-temperature fused salt meets the working condition requirement of high temperature of a fused salt pipeline in photo-thermal power generation, and is also suitable for stainless steel welded pipes of different specifications.

Description

Technical Field

[0001] The invention relates to the field of stainless steel welded pipes, and in particular to a manufacturing process of an austenitic stainless steel welded pipe for transporting high-temperature molten salt for photothermal power generation. Background Art

[0002] With the proposal of the "dual carbon" goals, my country's power installed capacity structure is facing tremendous changes, and it is urgent to build a new power system with new energy as the main body. In recent years, with the completion and grid-connected power generation of the first batch of solar thermal power generation demonstration projects, my country's solar thermal power generation technology has become increasingly mature. With the development of solar thermal technology in my country and the rapid growth of installed capacity, the market demand for welded pipes for high-temperature molten salt transportation will also grow rapidly, and the demand is huge. In addition to the conventional performance requirements such as room temperature tensile test, bending test, hardness test and radiographic inspection, austenitic stainless steel welded pipes for high-temperature molten salt transportation must also meet the requirements of 575°C high-temperature tensile test, parent material grain size, and weld ferrite (before post-weld heat treatment). Compared with the traditional austenitic stainless steel welded pipe production process, such as the manufacturing method of austenitic stainless steel pipes for transporting LNG in CN202110771391.7;

[0003] CN202110771392.1 A method for manufacturing a composite welded austenitic stainless steel pipe for fluid transportation;

[0004] CN202010919711.4 Preparation process of stainless steel welded pipe for offshore oil and gas transportation. These processes are suitable for the manufacture of products under different working conditions. The above three processes are respectively suitable for the transportation of liquefied natural gas under low-temperature conditions, the transportation of ordinary fluids and the transportation of offshore oil and gas. They cannot meet the transportation requirements of high-temperature molten salt under high-temperature conditions. Stainless steel welded pipes for high-temperature molten salt must meet the requirements of high-temperature tensile strength, grain size of base material, and ferrite of weld (before post-weld heat treatment). The welding process and solution heat treatment have a greater impact on the performance.

[0005] Under the uncertainty of the international environment, the problem of insufficient import quantity and long import cycle of welded pipes for high-temperature molten salt transportation has become one of the key factors restricting the development of solar thermal power generation technology. As a key component of solar thermal power generation units, "welded pipes for high-temperature molten salt transportation for solar thermal power generation" urgently need to be fully localized. Compared with the traditional process, the present invention has the following characteristics: ① The traditional process has no grain size requirements, and the present process puts forward grain size requirements for the raw materials, and controls the temperature and insulation time of the heat treatment process so that the grain size of the parent material of the finished welded pipe meets the requirements of 4 to 7 levels. ② In order to meet the test requirements of the pipeline molten salt working condition, the welding process of the pipeline weld: the control of welding heat input and interlayer temperature is different from the welding process of the traditional pipeline. ③ The heat treatment method different from the traditional pipeline is selected to reduce or avoid deformation such as pipe collapse due to its own gravity. It is preferred to use a rotary furnace heat treatment, that is, the pipe is rotated forward to keep its center in a state of change. ④ The pipe finally prepared by the present invention is used for the use of high-temperature molten salt, which cannot be met by the traditional process. 575℃ high-temperature tensile test requirements. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a manufacturing process of austenitic stainless steel welded pipes for transporting high-temperature molten salt for solar thermal power generation, which meets the use requirements of high-temperature molten salt working conditions.

[0007] The technical solution adopted by the present invention comprises the following steps:

[0008] a. Raw material requirements: Plate grain size is 6 to 8.5; austenitic stainless steel welded pipes for transporting molten salt for solar thermal power generation are made of TP347H.

[0009] b. Ultrasonic inspection of plates: After the plates pass the ultrasonic inspection, they are marked and stacked at the designated location;

[0010] c. Planing of plate edges: The cutting speed is 5-8m / min, and the cutting volume is controlled within 0.5mm per time. When the plate thickness is not more than 9mm, the plates can be stacked and pressed, but the total thickness after stacking shall not exceed 9mm. Different forms of bevels are processed according to the thickness of the plates: for plate thickness ≤9mm, I-type bevel is used; for plate thickness 9mm<plate thickness ≤28mm, Y-type bevel is used, with a blunt edge of 4-6mm and a bevel angle of 65-70°; for plate thickness>28mm, X-type bevel is used, with a blunt edge of 3-5mm and a bevel angle of 60-65°. The surface roughness of the planed edge is required to be no more than Ra6.3μm;

[0011] d. Sheet forming: The bending forming process is adopted. The folded tube is not allowed to have obvious creases through visual inspection, and the distance at the opening is controlled at 50-100mm;

[0012] e. Plastic spot welding: The formed open pipe is spot welded in a seaming machine. The spot welding adopts manual argon arc welding process, the welding current is 100-160A, the welding spot length is 5-10mm, and the distance between each welding spot is 195-205mm;

[0013] f. Pipe welding: 2mm<pipe thickness≤12mm, use plasma welding + argon arc welding process; 12mm<pipe thickness≤28mm, use plasma welding + submerged arc welding + argon arc welding process; pipe thickness>28mm, use plasma welding + submerged arc welding process.

[0014] The heat input of plasma welding shall not exceed 1.5KJ / mm, the heat input of argon arc welding shall not exceed 1.4KJ / mm, and the heat input of submerged arc welding shall not exceed 2.4KJ / mm. Heat input (KJ / mm) = welding current (A) * welding voltage (V) / welding speed (mm / min) * 0.06. Among them, the temperature between welding layers shall not exceed 120℃;

[0015] g. Solution heat treatment: heat treatment is carried out in a rotary solid solution furnace. The pipe moves forward in a rotary manner, which reduces or avoids deformation such as pipe collapse caused by the thin-walled pipe's own gravity. The heat treatment temperature is 1080℃~1130℃, and the holding time is min: pipe wall thickness*(1~2), and the unit of pipe wall thickness is mm; weld ferrite (before post-weld heat treatment) FN: 3~10.

[0016] Among them, the base plasma welding needs to set the back shielding gas, and ensure that the oxygen content on the back is not more than 500ppm. The plasma welding ion gas uses argon hydrogen mixed gas to increase the welding speed. In plasma welding, the ion gas uses 93% Ar + 7% H2, and the gas flow rate is 3-8L / min; the gun shielding gas uses 99.99% Ar, and the gas flow rate is 10-25L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 15-22L / min; the back shielding gas uses 99.99% Ar, and the gas flow rate is 20-30L / min. In argon arc welding, the gun shielding gas uses 93% Ar + 7% H2, and the gas flow rate is 10-25L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 15-22L / min.

[0017] h. Straightening: During the straightening process, pay attention to the surface quality of the pipe at any time. No pits should appear. After straightening, the straightness should not be greater than 1mm / m;

[0018] i. Hydrostatic and non-destructive testing: Hydrostatic tests are carried out on each pipe, and X-ray inspections are carried out on the pipe welds;

[0019] j. Pipe end beveling: Beveling both ends of the pipe on a beveling machine, with a beveling angle of 37.5°±2.5° and a blunt edge of 1.6mm±0.8mm;

[0020] k. Pickling and passivation: immerse the pipe in a mixed solution of nitric acid, hydrofluoric acid and water for pickling and passivation. The volume ratio of nitric acid and hydrofluoric acid is 10% to 13% and 5% to 7% respectively. Rinse it after leaving the tank; l. Finished product inspection: room temperature tensile test (tensile strength ≥515MPa, yield strength ≥205MPa, elongation after fracture ≥40%), bending test (after bending, if there are no cracks or other defects, the bending test is qualified), hardness test (hardness value ≤92HRB), parent material grain size 4 to 7, 575℃ high temperature tensile test yield strength is not less than 131Mpa.

[0021] Compared with the prior art, the present invention has the following beneficial effects: the present invention sets the welding process of the pipeline weld, especially controls the welding heat input and interlayer temperature, so that the product base material grain size is within the range of 4 to 7, the yield strength of the 575°C high temperature tensile test is not less than 131Mpa, and the room temperature tensile test and bending test meet the requirements. Therefore, the prepared stainless steel welded pipe for high temperature molten salt transportation in solar thermal power generation meets the high temperature working condition requirements of molten salt pipelines in solar thermal power generation. DETAILED DESCRIPTION

[0022] Example 1

[0023] Welded pipe material TP347H, product specifications The manufacturing method thereof comprises the following steps:

[0024] a. Raw material requirements: Plate grain size 6 to 7;

[0025] b. Ultrasonic inspection of plates: After the plates pass the ultrasonic inspection, they are marked and stacked at the designated location;

[0026] c. Plate planing: cutting speed is 7.5m / min, cutting volume is controlled at 0.5mm per time. Processing I-type groove; planing surface roughness Ra3.2μm;

[0027] d. Sheet forming: The bending forming process is adopted. The folded tube is not allowed to have obvious creases through visual inspection, and the distance at the opening is controlled at 60-100mm;

[0028] e. Plastic spot welding: The formed open pipe is spot welded in a seaming machine. The spot welding adopts manual argon arc welding process, the welding current is 100-120A, the welding spot length is 5-10mm, and the distance between each welding spot is 195-205mm;

[0029] f. Pipe welding: ① Plasma welding + argon arc welding process is adopted. ② Back-shielding plasma welding needs to set up back-shielding gas, and ensure that the oxygen content on the back is not more than 500ppm. ③ In plasma welding, the ion gas uses 93% Ar + 7% H2, and the gas flow rate is 5L / min; the gun shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min; the back shielding gas uses 99.99% Ar, and the gas flow rate is 25L / min. In argon arc welding, the gun shielding gas uses 93% Ar + 7% H2, and the gas flow rate is 16L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min. ④ The heat input of plasma welding is 1.2KJ / mm, and the heat input of argon arc welding is 1.1KJ / mm. Heat input (KJ / mm) = welding current (A) * welding voltage (V) / welding speed (mm / min) * 0.06. ⑤The temperature between welding layers shall not exceed 70℃;

[0030] g. Solution heat treatment: heat treatment is carried out in a rotary solid solution furnace. The tube moves forward in a rotary manner, which reduces or avoids deformation such as tube collapse caused by the thin-walled tube's own gravity. The heat treatment temperature is 1100°C and the holding time is 9 minutes. h. Straightening: pay attention to the surface quality of the tube at any time during the straightening process. No pits should appear. The straightness after straightening is 0.9mm / m.

[0031] i. Hydrostatic and non-destructive testing: Hydrostatic tests are carried out on each pipe, and X-ray inspections are carried out on the pipe welds;

[0032] j. Pipe end beveling: Beveling both ends of the pipe on a beveling machine, with a beveling angle of 37.5°±2.5° and a blunt edge of 1.6mm±0.8mm;

[0033] k. Pickling and passivation: Immerse the pipe in a mixed solution of nitric acid, hydrofluoric acid and water for pickling and passivation. The volume percentages of nitric acid and hydrofluoric acid are 10% to 13% and 5% to 7% respectively. Rinse it after leaving the tank;

[0034] l. Finished product inspection: qualified in room temperature tensile test (tensile strength 669MPa, yield strength 351MPa, elongation after fracture 51%), qualified in bending test (after bending, no cracks or other defects), qualified in hardness test (hardness value: base material 79HRB, heat affected zone 82HRB, weld 80HRB), base material grain size 4.5-6, 575℃ high temperature tensile test yield strength 149Mpa, weld ferrite (before post-weld heat treatment) FN: 5.3, performance meets the requirements. Among them, room temperature tensile test, bending test, hardness test are tested according to standard ASTMA370, base material grain size is tested according to ASTM E112, high temperature tensile test is tested according to standard ASTM E21, and weld ferrite is tested according to standard ISO8249.

[0035] Example 2

[0036] Welded pipe material TP347H, product specifications The manufacturing method thereof comprises the following steps:

[0037] a. Raw material requirements: Plate grain size 6 to 7.5;

[0038] b. Ultrasonic inspection of plates: After the plates pass the ultrasonic inspection, they are marked and stacked at the designated location;

[0039] c. Plate planing: cutting speed is 6.5m / min, cutting volume is controlled at 0.5mm per time. Processing I-type groove; planing surface roughness Ra3.2μm;

[0040] d. Sheet forming: The bending forming process is adopted. The folded tube is not allowed to have obvious creases through visual inspection, and the distance at the opening is controlled within 50-90mm;

[0041] e. Plastic spot welding: The formed open pipe is spot welded in a seaming machine. The spot welding adopts manual argon arc welding process, the welding current is 100-120A, the welding spot length is 5-10mm, and the distance between each welding spot is 195-205mm;

[0042] f. Pipe welding: ① Plasma welding + submerged arc welding + argon arc welding process is adopted. ② Back-shielding plasma welding requires the setting of back-shielding gas, and the oxygen content on the back side must be guaranteed to be no more than 500ppm. ③ In plasma welding, the ion gas uses 93% Ar + 7% H2, and the gas flow rate is 6.5L / min; the gun shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min; the back shielding gas uses 99.99% Ar, and the gas flow rate is 25L / min. In argon arc welding, the gun shielding gas uses 93% Ar + 7% H2, and the gas flow rate is 18L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min. ④ The heat input of plasma welding is 1.4KJ / mm, the heat input of submerged arc welding is 2.1KJ / mm, and the heat input of argon arc welding is 1.0KJ / mm. Heat input (KJ / mm) = welding current (A) * welding voltage (V) / welding speed (mm / min) * 0.06. ⑤ The temperature between welding layers is not more than 100℃;

[0043] g. Solution heat treatment: heat treatment is carried out in a rotary solid solution furnace. The tube moves forward in a rotary manner, which reduces or avoids deformation such as tube collapse caused by the thin-walled tube's own gravity. The heat treatment temperature is 1100°C and the holding time is 14 minutes. h. Straightening: pay attention to the surface quality of the tube at any time during the straightening process. No pits should appear. The straightness after straightening is 1.0 mm / m.

[0044] i. Hydrostatic and non-destructive testing: Hydrostatic tests are carried out on each pipe, and X-ray inspections are carried out on the pipe welds;

[0045] j. Pipe end beveling: Beveling both ends of the pipe on a beveling machine, with a beveling angle of 37.5°±2.5° and a blunt edge of 1.6mm±0.8mm;

[0046] k. Pickling and passivation: Immerse the pipe in a mixed solution of nitric acid, hydrofluoric acid and water for pickling and passivation. The volume ratio of nitric acid and hydrofluoric acid is 10% to 13% and 5% to 7% respectively. Rinse it after leaving the tank; l. Finished product inspection: The normal temperature tensile test is qualified (tensile strength 683MPa, yield strength 354MPa, elongation after fracture 48%), the bending test is qualified (after bending, there are no cracks or other defects), the hardness test is qualified (hardness value: parent material 77HRB, heat affected zone 80HRB, weld 78HRB), parent material grain size 5 to 6 levels, 575℃ high temperature tensile test yield strength 143Mpa, weld ferrite (before post-weld heat treatment) FN: 7.3, and the performance meets the requirements. Among them, the normal temperature tensile test, bending test, and hardness test are in accordance with the standard ASTMA370, the parent material grain size is in accordance with ASTM E112, the high temperature tensile test is in accordance with the standard ASTM E21, and the weld ferrite is in accordance with the standard ISO8249.

[0047] Comparative Example 1

[0048] Compared with Example 1, the main difference between Comparative Example 1 is that the heat treatment holding time is not within the range of "tube wall thickness mm*(1-2) min", and other operations are the same.

[0049] Welded pipe material TP347H, product specifications The manufacturing method thereof comprises the following steps:

[0050] a. Raw material requirements: Plate grain size 6 to 7;

[0051] b. Ultrasonic inspection of plates: After the plates pass the ultrasonic inspection, they are marked and stacked at the designated location;

[0052] c. Plate planing: cutting speed is 7.5m / min, cutting volume is controlled at 0.5mm per time. Processing I-type groove; planing surface roughness Ra3.2μm;

[0053] d. Sheet forming: The bending forming process is adopted. The folded tube is not allowed to have obvious creases through visual inspection, and the distance at the opening is controlled at 60-100mm;

[0054] e. Plastic spot welding: The formed open pipe is spot welded in a seaming machine. The spot welding adopts manual argon arc welding process, the welding current is 100-120A, the welding spot length is 5-10mm, and the distance between each welding spot is 195-205mm;

[0055] f. Pipe welding: ① Plasma welding + argon arc welding process is adopted. ② Back-shielding plasma welding needs to set up back-shielding gas, and ensure that the oxygen content on the back is not more than 500ppm. ③ In plasma welding, the ion gas uses 93% Ar + 7% H2, and the gas flow rate is 5L / min; the gun shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min; the back shielding gas uses 99.99% Ar, and the gas flow rate is 25L / min. In argon arc welding, the gun shielding gas uses 93% Ar + 7% H2, and the gas flow rate is 16L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min. ④ The heat input of plasma welding is 1.2KJ / mm, and the heat input of argon arc welding is 1.1KJ / mm. Heat input (KJ / mm) = welding current (A) * welding voltage (V) / welding speed (mm / min) * 0.06. ⑤The temperature between welding layers shall not exceed 70℃;

[0056] g. Solution heat treatment: heat treatment is carried out in a rotary solid solution furnace. The tube moves forward in a rotary manner to reduce deformation such as tube collapse caused by the thin-walled tube's own gravity. The heat treatment temperature is 1100°C and the holding time is 20 minutes.

[0057] h. Straightening: During the straightening process, pay attention to the surface quality of the pipe at any time. No pits should appear. The straightness after straightening is 1.0mm / m;

[0058] i. Hydrostatic and non-destructive testing: Hydrostatic tests are carried out on each pipe, and X-ray inspections are carried out on the pipe welds;

[0059] j. Pipe end beveling: Beveling both ends of the pipe on a beveling machine, with a beveling angle of 37.5°±2.5° and a blunt edge of 1.6mm±0.8mm;

[0060] k. Pickling and passivation: The pipe is immersed in a mixed solution of nitric acid, hydrofluoric acid and water for pickling and passivation, wherein the volume percentages of nitric acid and hydrofluoric acid are 10% to 13% and 5% to 7% respectively, and rinsed clean after leaving the cylinder; l. Finished product inspection: The normal temperature tensile test is qualified (tensile strength 563MPa, yield strength 244MPa, elongation after fracture 57%), the bending test is qualified (after bending, there are no cracks or other defects), the hardness test is qualified (hardness value: base material 73HRB, heat affected zone 74HRB, weld 74HRB), base material grain size 3.5 to 5.5 grade, 575℃ high temperature tensile test yield strength 127Mpa, weld ferrite (before post-weld heat treatment) FN: 5.7, the performance does not meet the high temperature working conditions of molten salt pipelines in solar thermal power generation. The room temperature tensile test, bending test and hardness test are in accordance with the standard ASTMA370, the base material grain size is in accordance with ASTM E112, the high temperature tensile test is in accordance with the standard ASTM E21, and the weld ferrite is in accordance with the standard ISO8249.

[0061] If the holding time of comparative example 1 is 5 minutes, which is lower than the lower limit, there is a risk of failure in the room temperature tensile test and hardness test of the pipe, and the process requirements of production cannot be met.

[0062] Comparative Example 2

[0063] The difference between Comparative Example 2 and Example 1 is that the grain size of the plate is not within the range of "6 to 8.5". The manufacturing method thereof comprises the following steps:

[0064] a. Raw material requirements: Plate grain size 5 to 6;

[0065] b. Ultrasonic inspection of plates: After the plates pass the ultrasonic inspection, they are marked and stacked at the designated location;

[0066] c. Plate planing: cutting speed is 7.5m / min, cutting volume is controlled at 0.5mm per time. Processing I-type groove; planing surface roughness Ra3.2μm;

[0067] d. Sheet forming: The bending forming process is adopted. The folded tube is not allowed to have obvious creases through visual inspection, and the distance at the opening is controlled at 60-100mm;

[0068] e. Plastic spot welding: The formed open pipe is spot welded in a seaming machine. The spot welding adopts manual argon arc welding process, the welding current is 100-120A, the welding spot length is 5-10mm, and the distance between each welding spot is 195-205mm;

[0069] f. Pipe welding: ① Plasma welding + argon arc welding process is adopted. ② Back-shielding plasma welding needs to set up back-shielding gas, and ensure that the oxygen content on the back is not more than 500ppm. ③ In plasma welding, the ion gas uses 93% Ar + 7% H2, and the gas flow rate is 5L / min; the gun shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min; the back shielding gas uses 99.99% Ar, and the gas flow rate is 25L / min. In argon arc welding, the gun shielding gas uses 93% Ar + 7% H2, and the gas flow rate is 16L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min. ④ The heat input of plasma welding is 1.2KJ / mm, and the heat input of argon arc welding is 1.1KJ / mm. Heat input (KJ / mm) = welding current (A) * welding voltage (V) / welding speed (mm / min) * 0.06. ⑤The temperature between welding layers shall not exceed 70℃;

[0070] g. Solution heat treatment: heat treatment is carried out in a rotary solid solution furnace. The tube moves forward in a rotary manner, which reduces or avoids deformation such as tube collapse caused by the thin-walled tube's own gravity. The heat treatment temperature is 1100°C and the holding time is 9 minutes. h. Straightening: pay attention to the surface quality of the tube at any time during the straightening process. No pits should appear. The straightness after straightening is 0.9mm / m.

[0071] i. Hydrostatic and non-destructive testing: Hydrostatic tests are carried out on each pipe, and X-ray inspections are carried out on the pipe welds;

[0072] j. Pipe end beveling: Beveling both ends of the pipe on a beveling machine, with a beveling angle of 37.5°±2.5° and a blunt edge of 1.6mm±0.8mm;

[0073] k. Pickling and passivation: Immerse the pipe in a mixed solution of nitric acid, hydrofluoric acid and water for pickling and passivation. The volume percentages of nitric acid and hydrofluoric acid are 10% to 13% and 5% to 7% respectively. Rinse it after leaving the tank;

[0074] l. Finished product inspection: room temperature tensile test qualified (tensile strength 661MPa, yield strength 343MPa, elongation after fracture 49%), bending test qualified (after bending, no cracks or other defects), hardness test qualified (hardness value: base material 81HRB, heat affected zone 84HRB, weld 83HRB), base material grain size 3.5-4.5, 575℃ high temperature tensile test yield strength 134Mpa, weld ferrite (before post-weld heat treatment) FN: 5.9. Among them, room temperature tensile test, bending test, hardness test are in accordance with ASTMA370, base material grain size is in accordance with ASTM E112, high temperature tensile test is in accordance with ASTM E21, and weld ferrite is in accordance with ISO8249.

[0075] The finished product of comparative example 2 showed that the base material grain size did not meet the requirements.

[0076] Comparative Example 3

[0077] Compared with Example 1, the difference between Comparative Example 3 is that the welding heat input is not within the range of "the heat input of plasma welding does not exceed 1.5KJ / mm, and the heat input of argon arc welding does not exceed 1.4KJ / mm".

[0078] Welded pipe material TP347H, product specifications The manufacturing method thereof comprises the following steps:

[0079] a. Raw material requirements: Plate grain size 6 to 7;

[0080] b. Ultrasonic inspection of plates: After the plates pass the ultrasonic inspection, they are marked and stacked at the designated location;

[0081] c. Plate planing: cutting speed is 7.5m / min, cutting volume is controlled at 0.5mm per time. Processing I-type groove; planing surface roughness Ra3.2μm;

[0082] d. Sheet forming: The bending forming process is adopted. The folded tube is not allowed to have obvious creases through visual inspection, and the distance at the opening is controlled at 60-100mm;

[0083] e. Plastic spot welding: The formed open pipe is spot welded in a seaming machine. The spot welding adopts manual argon arc welding process, the welding current is 100-120A, the welding spot length is 5-10mm, and the distance between each welding spot is 195-205mm;

[0084] f. Pipe welding: ① Plasma welding + argon arc welding process is adopted. ② Back-shielding plasma welding needs to set up back-shielding gas, and ensure that the oxygen content on the back is not more than 500ppm. ③ In plasma welding, the ion gas uses 93% Ar + 7% H2, and the gas flow rate is 5L / min; the gun shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min; the back shielding gas uses 99.99% Ar, and the gas flow rate is 25L / min. In argon arc welding, the gun shielding gas uses 93% Ar + 7% H2, and the gas flow rate is 16L / min; the tail shielding gas uses 99.99% Ar, and the gas flow rate is 20L / min. ④ The heat input of plasma welding is 1.7KJ / mm, and the heat input of argon arc welding is 1.6KJ / mm. Heat input (KJ / mm) = welding current (A) * welding voltage (V) / welding speed (mm / min) * 0.06. ⑤The temperature between welding layers shall not exceed 70℃;

[0085] g. Solution heat treatment: heat treatment is carried out in a rotary solid solution furnace. The tube moves forward in a rotary manner, which reduces or avoids deformation such as tube collapse caused by the thin-walled tube's own gravity. The heat treatment temperature is 1100°C and the holding time is 9 minutes. h. Straightening: pay attention to the surface quality of the tube at any time during the straightening process. No pits should appear. The straightness after straightening is 0.9mm / m.

[0086] i. Hydrostatic and non-destructive testing: Hydrostatic tests are carried out on each pipe, and X-ray inspections are carried out on the pipe welds;

[0087] j. Pipe end beveling: Beveling both ends of the pipe on a beveling machine, with a beveling angle of 37.5°±2.5° and a blunt edge of 1.6mm±0.8mm;

[0088] k. Pickling and passivation: Immerse the pipe in a mixed solution of nitric acid, hydrofluoric acid and water for pickling and passivation. The volume percentages of nitric acid and hydrofluoric acid are 10% to 13% and 5% to 7% respectively. Rinse it after leaving the tank;

[0089] l. Finished product inspection: room temperature tensile test qualified (tensile strength 607MPa, yield strength 319MPa, elongation after fracture 50%), bending test qualified (after bending, no cracks or other defects), hardness test qualified (hardness value: parent material 79HRB, heat affected zone 81HRB, weld 81HRB), parent material grain size 4.5-6, 575℃ high temperature tensile test yield strength 122Mpa, weld ferrite (before post-weld heat treatment) FN: 11.4, high temperature tensile test and weld ferrite do not meet the requirements. Among them, the room temperature tensile test, bending test, and hardness test are in accordance with the standard ASTMA370, the parent material grain size is in accordance with ASTM E112, the high temperature tensile test is in accordance with the standard ASTM E21, and the weld ferrite is in accordance with the standard ISO8249.

[0090] The yield strength and weld ferrite of the finished product of Comparative Example 3 in the 575°C high temperature tensile test did not meet the requirements, and the X-ray inspection of the pipe weld also showed more weld defects than in the embodiment.

[0091] Further research on the parameters in the pipe welding process shows that if the heat input of plasma welding alone does not meet the range requirements (such as the heat input of plasma welding is 1.7KJ / mm) or the heat input of argon arc welding alone does not meet the requirements (such as the heat input of argon arc welding is 1.6KJ / mm), the finished product cannot meet the high-temperature tensile test requirements. The test results are similar to those of Comparative Example 3.

Claims

1. A manufacturing process for austenitic stainless steel welded pipes for transporting high-temperature molten salt for solar thermal power generation, characterized in that: The following steps are involved: a. Raw material requirements: Stainless steel plate grain size 6 to 8.5; b. Ultrasonic inspection of plates: Plates are inspected by ultrasonic waves; c. Planing of plate: The cutting speed of planing is 5-8m / min, and the cutting volume is controlled within 0.5mm per time; the surface roughness of planing is required to be no more than Ra6.3μm; d. Sheet forming: using bending forming technology, the distance at the opening is controlled at 50-100mm; e. Plastic spot welding: The formed open pipe is spot welded in a seaming machine. The spot welding adopts manual argon arc welding process. The length of the welding spot is 5 to 10 mm, and the distance between each welding spot is 195 to 205 mm. f. Pipe welding: 2mm<pipe thickness≤12mm, plasma welding + argon arc welding process; 12mm<pipe thickness≤28mm, plasma welding + submerged arc welding + argon arc welding process; pipe thickness>28mm, plasma welding + submerged arc welding process; the heat input of plasma welding shall not exceed 1.5KJ / mm, the heat input of argon arc welding shall not exceed 1.4KJ / mm, and the heat input of submerged arc welding shall not exceed 2.4KJ / mm; the ferrite number FN of the weld after welding: 3~10; g. Solution heat treatment: heat treatment is carried out in a rotary solid solution furnace, the pipe moves forward in a rotary manner, the heat treatment temperature is 1080℃~1130℃, the holding time min=pipe wall thickness*(1~2), the pipe wall thickness unit is mm; h. Straightening: After straightening, the straightness is required to be no more than 1mm / m; i. Hydrostatic and non-destructive testing: Hydrostatic tests are carried out on each pipe, and X-ray inspections are carried out on the pipe welds; j. Pipe end beveling: Beveling both ends of the pipe on a beveling machine, with a beveling angle of 37.5°±2.5° and a blunt edge of 1.6mm±0.8mm; k. Pickling and passivation: Immerse the pipe in a mixed solution of nitric acid, hydrofluoric acid and water for pickling and passivation. The volume percentages of nitric acid and hydrofluoric acid are 10% to 13% and 5% to 7% respectively. Rinse it after leaving the tank; l. Finished product inspection.

2. The manufacturing process of austenitic stainless steel welded pipe for transporting high-temperature molten salt for solar thermal power generation according to claim 1 is characterized in that: The grade of the stainless steel plate in step a is TP347H.

3. The manufacturing process of austenitic stainless steel welded pipe for transporting high-temperature molten salt for solar thermal power generation according to claim 1 is characterized in that: In the plate planing process of step c, when the plate thickness is not more than 9 mm, the plates can be stacked and pressed, but the total thickness after stacking does not exceed 9 mm; different forms of bevels are processed according to different plate thicknesses: for plate thickness ≤9 mm, I-type bevel is adopted; for plate thickness 9mm<plate thickness ≤28mm, Y-type bevel is adopted, with a blunt edge of 4-6mm and a bevel angle of 65-70°; for plate thickness>28mm, X-type bevel is adopted, with a blunt edge of 3-5mm and a bevel angle of 60-65°.

4. The manufacturing process of austenitic stainless steel welded pipe for transporting high-temperature molten salt for solar thermal power generation according to claim 1 is characterized in that: In the pipe welding process of step f, all processes use plasma welding for base welding; the base welding plasma welding needs to set a back side protective gas and ensure that the back side oxygen content is not greater than 500ppm.

5. The manufacturing process of austenitic stainless steel welded pipe for transporting high-temperature molten salt for solar thermal power generation according to claim 1 is characterized in that: In the pipe welding process of step f, in plasma welding, the ion gas adopts 93% Ar+7% H2, and the gas flow rate is 3-8 L / min; the gun shielding gas adopts 99.99% Ar, and the gas flow rate is 10-25 L / min; the tail shielding gas adopts 99.99% Ar, and the gas flow rate is 15-22 L / min; the back shielding gas adopts 99.99% Ar, and the gas flow rate is 20-30 L / min; in argon arc welding, the gun shielding gas adopts 93% Ar+7% H2, and the gas flow rate is 10-25 L / min; the tail shielding gas adopts 99.99% Ar, and the gas flow rate is 15-22 L / min; the welding interlayer temperature is not more than 120°C.

6. Austenitic stainless steel welded pipe for transporting high-temperature molten salt for solar thermal power generation manufactured by the process according to any one of claims 1 to 5, characterized in that: The parent material grain size of the welded pipe for high-temperature molten salt transportation in solar thermal power generation is 4 to 7 grades, the yield strength of the 575℃ high-temperature tensile test is not less than 131Mpa, the tensile strength under room temperature tensile test is ≥515MPa, the yield strength is ≥205MPa, the elongation after fracture is ≥40%, the bending test is qualified, and the hardness value is ≤92HRB.