CN118256777A

CN118256777A - 625 Alloy pipe for tower type photo-thermal power station heat absorber

Info

Publication number: CN118256777A
Application number: CN202410417090.8A
Authority: CN
Inventors: 刘会群
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2024-04-08
Filing date: 2024-04-08
Publication date: 2024-06-28

Abstract

The invention discloses a 625 alloy pipe for a tower type photo-thermal power station heat absorber, which comprises the following elements ：Cr=21.0～23.0%,Mo=8.5～10.0%,Nb+Ta=3.50～4.15%,Fe=1～5%,C=0.01～0.03%,N≤0.015%,P≤0.01%,H≤0.008%,O≤0.003%,S≤0.003%, and the balance of Ni and unavoidable impurity elements in percentage by mass. The basic structure of the 625 alloy seamless precision welded pipe prepared by the invention is a single austenite structure, no continuous or semi-continuous netlike carbide is precipitated on the grain boundary, no strip-shaped structure is present in the crystal, and fine dispersion carbide and gamma' phase are precipitated in the crystal. The tissue state has stable performance under the working condition of 565-650 ℃, and can ensure excellent comprehensive mechanical properties.

Description

625 Alloy pipe for tower type photo-thermal power station heat absorber

Technical Field

The invention belongs to a manufacturing technology of high-performance special alloy materials, and particularly relates to a 625 alloy pipe for a tower type photo-thermal power station heat absorber.

Background

The photo-thermal power generation has the advantages of peak regulation, energy storage and power generation integration functions, and the photo-thermal power generation has the advantage that other clean energy sources cannot be replaced. By the end of 2023, the solar thermal power generation accumulated installed capacity 588MW of China accounts for 7.8% of the global solar thermal power generation accumulated installed capacity. 43 photo-thermal projects are under construction in China. In China running and building the photo-thermal power station, the tower type photo-thermal power station accounts for over 60 percent.

One of the core devices of the tower type photo-thermal power station is a heat absorber at the top of the tower, and the core component of the heat absorber is an N06625 nickel-based alloy welded pipe. The normal working temperature range of the welded pipe is 290-565 ℃, the highest working temperature is 650 ℃, the lowest non-working temperature is-20 ℃, the working medium is sodium nitrate and potassium nitrate binary molten salt with strong corrosiveness, and the working pressure is 2MPa. Under the working condition, once the pipe is broken, the high-temperature molten salt leaks, so that the whole power station is stopped, and dangerous accidents such as fire and explosion are easily caused. The 625 alloy welded pipe runs in the severe working condition environment of high temperature, high pressure and strong corrosion for a long time, and has high requirements on chemical components, purity, microstructure, mechanical property, surface quality and the like of the pipe. In addition, the 625 alloy welded pipe is welded with the upper header and the lower header in the installation process, and high requirements are set for the dimensional accuracy of the 625 alloy welded pipe.

Disclosure of Invention

The invention aims to overcome at least one defect of the prior art and provides a 625 alloy pipe for a tower type photo-thermal power station heat absorber.

The technical scheme adopted by the invention is as follows:

The invention provides a 625 alloy pipe for a tower type photo-thermal power station heat absorber, which comprises the following elements ：Cr＝21.0～23.0％,Mo＝8.5～10.0％,Nb+Ta＝3.50～4.15％,Fe＝1～5％,C＝0.01～0.03％,N≤0.015％,P≤0.01％,H≤0.008％,O≤0.003％,S≤0.003％, and the balance of Ni and unavoidable impurity elements in percentage by mass.

In some examples, the 625 alloy pipe composition further comprises the following element composition in mass percent: co is less than or equal to 1.0%, si is less than or equal to 0.50%, mn is less than or equal to 0.50%, al is less than or equal to 0.40%, and Ti is less than or equal to 0.40%.

In some examples, the 625 alloy tubing composition ：Cr＝21.0～23.0％,Mo＝8.5～10.0％,Nb+Ta＝3.50～4.15％,Fe＝1～5％,C＝0.01～0.03％,N≤0.015％,P≤0.01％,H≤0.008％,O≤0.003％,S≤0.003％,Co≤1.0％,Si≤0.50％,Mn≤0.50％,Al≤0.40％,Ti≤0.40％, is Ni and the balance unavoidable impurity elements.

In some examples, the method of preparing the 625 alloy welded pipe includes the steps of:

1) Carrying out hot rolling treatment and cold rolling treatment on the 625 alloy in sequence to obtain a 625 alloy strip;

2) Welding the 625 alloy strip in the step 1) into a tube, and then carrying out bright annealing treatment to obtain a 625 alloy tube blank;

3) Cold rolling the 625 alloy pipe blank subjected to the bright annealing treatment in the step 2);

4) Degreasing and cleaning the 625 alloy pipe subjected to the cold deformation treatment in the step 3);

5) Carrying out bright heat treatment on the 625 alloy finished tube subjected to degreasing and cleaning in the step 4);

6) Straightening and polishing the outer surface of the 625 alloy finished tube after the final bright heat treatment in the step 5);

7) And (3) carrying out surface treatment on the 625 alloy finished tube obtained in the step (6) to obtain the 625 alloy welded tube.

In some examples, the bright annealing treatment of step 2) is performed at a temperature of 1050-1100 ℃ for a holding time of 5-15 min.

In some examples, the deformation amount of the cold deformation process treatment of step 3) ranges from 30 to 60%.

In some examples, the temperature of the bright heat treatment of step 5) is 950-1100 ℃ and the holding time is 5-15 min.

In some examples, the surface roughness Ra of the 625 alloy welded pipe after the surface treatment of the step 7) is less than or equal to 1.60 mu m.

The rating of nonmetallic inclusion of the 625 alloy pipe provided by the invention meets the following requirements: A. the sum of the B, C, D coarse lines and the fine lines is not more than 1.0 level, and the sum of the A, B, C, D coarse lines and the fine lines is not more than 4.0 level; nitride inclusions are rated with reference to class B and class D, with both class B and class D coarse systems not exceeding class 1.0, class B fine systems not exceeding class 1.5, and class D fine systems not exceeding class 2.0.

The 625 alloy pipe provided by the invention has the room temperature yield strength of more than or equal to 414MPa, the room temperature tensile strength of more than or equal to 827MPa, the room temperature elongation of more than or equal to 35%, the 650 ℃ yield strength of more than or equal to 210MPa, the 650 ℃ tensile strength of more than or equal to 550MPa, and the 650 ℃ elongation of more than or equal to 40%.

According to the 625 alloy pipe provided by the invention, the grain size of the parent metal is larger than 5.0 level, the weld joint structure is an austenite structure, the grain size of the weld joint is not smaller than 6.0 level, and no continuous or semi-continuous carbide precipitation exists on the grain boundary.

The beneficial effects of the invention are as follows:

The invention controls the carbon content to be 0.01-0.03%, and the chromium content to be controlled according to the middle limit, and the target range to be 21.0-22.5%, so as to ensure that the alloy has better corrosion resistance and tissue stability, and also has certain mechanical properties.

The method can strictly control the content of N, H, O and other gas elements, greatly reduce the possibility of generating nonmetallic inclusions, and ensure good high-temperature performance and corrosion resistance while ensuring the high purity of the alloy.

The basic structure of the 625 alloy seamless precision welded pipe prepared by the invention is a single austenite structure, no continuous or semi-continuous netlike carbide is precipitated on the grain boundary, no strip-shaped structure is present in the crystal, and fine dispersion carbide and gamma' phase are precipitated in the crystal. The tissue state has stable performance under the working condition of 565-650 ℃, and can ensure excellent comprehensive mechanical properties.

Drawings

FIG. 1 is a microstructure of a welded pipe weld.

FIG. 2 is a microstructure and IPF map of a weld after annealing of a cold rolled welded tube.

Detailed Description

The present invention will be described in detail with reference to examples, comparative examples and experimental data.

The specific implementation process is as follows for the 625 alloy seamless precision welded pipe target product with the specification of phi 44.45 x 1.45 mm. Other specifications of 625 alloy seamless precision welded pipes can be implemented by referring to the method, and the specific deformation process and the heat treatment process can be adaptively adjusted.

Example 1

1) Smelting and hot working

The raw materials are smelted by adopting a vacuum induction and electroslag remelting method, the size of a vacuum induction electrode is 430mm, the weight of an electroslag ingot is 550, and the weight of the ingot is about 3 tons. Homogenizing heat treatment is carried out on the electroslag ingot, wherein the homogenizing heat treatment system is that the heat preservation time at 1200 ℃ is not less than 24 hours, and the electroslag ingot is discharged from a furnace for forging after heat preservation is finished. Hot forging to obtain plate blank with thickness of 150mm, initial temperature not lower than 1100 deg.c and final forging temperature not lower than 800 deg.c.

The hot forging slab was subjected to chemical component detection according to ASTM E2594 by taking one sample from each of the two ends corresponding to the head and tail of the steel ingot, and the detection results are shown in table 1 below, and the detection results can meet the requirements for chemical component control. The method is characterized in that a sample is taken from the head and the tail of an electroslag ingot on a hot forging plate blank to detect longitudinal nonmetallic inclusion, the nonmetallic inclusion grading is carried out according to an ASTM E45 standard A method, the nonmetallic inclusion grading results are shown in table 2, the thin-line A, B, C, D type inclusions of the forging bar are all less than or equal to 0.5 level, the class B thin-line nitride is less than or equal to 1.0 level, the class D thin-line nitride is less than or equal to 1.0 level, the inclusion content is low, and the design requirements are met.

Table 1 slab chemistry (wt.%)

Element(s)	C	S	Si	Mn	P	Cr	Ni	Fe
									Head part	0.015	0.001	0.09	0.02	0.006	21.7	60.5	1.40
Tail part	0.018	0.001	0.08	0.02	0.006	21.6	59.9	1.47
									Element(s)	Mo	Al	Co	Ti	Nb+Ta	N	H	O
Head part	8.86	0.10	0.04	0.10	3.72	0.005	0.0002	0.0025
									Tail part	8.91	0.10	0.04	0.07	3.69	0.006	0.0003	0.0024

TABLE 2 rating of nonmetallic inclusion in slabs

2) Cold-rolled strip

The thickness of the cold-rolled strip is 2.2mm, the thickness deviation is +/-0.05 mm, the width of the strip is 156.6mm, and the width deviation is +/-0.20 mm. The surface state is a 2B surface. The grain size of the strip is 6.0-7.0 grade, and the strip is a pure austenite structure, and no carbide strip structure appears.

3) Laser welding

Welding and forming by adopting a full-automatic numerical control laser welding machine, wherein the welding power is 2400W, the welding speed is 3.0m/min, the protective atmosphere is high-purity argon, the purity is not lower than 99.99%, the external protection gas flow is 10L/min, and the internal protection gas flow is 6L/min. The weld seam excess is 0.10mm. Welding the specification phi 50.8 x 2.2mm of the tube blank.

4) Annealing of tube blanks

And (3) annealing the tube blank by adopting a continuous bright annealing furnace, wherein the annealing temperature is 1100 ℃, and the heat preservation time is 8min.

5) Final cold rolling

Cold rolling is carried out by adopting an LG60 type two-weld rolling mill, and the cold working deformation process is shown in the following table 3.

Table 3 cold working deforming process

The lubrication of the inner surface and the outer surface in the rolling process is required to be sufficient, the quality inspection of the outer surface is carried out one by one in the rolling process, and the inner surface and the outer surface cannot have rolling defects such as cracks, folding, rolling damage, indentation and the like. The rolling process needs to check the size and the surface quality of the pipe frequently, and if the quality of the pipe is problematic, the abrasion condition of a tool and a die needs to be checked in time.

The finished pipe size control requirement: the outer diameter and the tolerance are 44.45 plus or minus 0.20mm, and the wall thickness and the tolerance are 1.45 plus or minus 0.12mm.

6) Degreasing and cleaning

And degreasing and cleaning the cold-rolled finished pipe by adopting an ultrasonic degreasing and cleaning device, wherein the degreasing liquid is alkaline cleaning liquid, and the concentration is not lower than 3%. And the cleaned pipe is subjected to cleanliness inspection, and the inner surface and the outer surface of the pipe are clean and dry, so that the pipe has no greasy dirt and residues.

7) Final heat treatment

The final heat treatment after the final cold rolling and degreasing cleaning adopts a protective atmosphere bright annealing process, the annealing temperature is 980 ℃, the heat preservation time is 10min, the protective atmosphere is hydrogen with the purity of more than 99.95%, the finished pipe is ensured to have higher mechanical property, the oxidation discoloration phenomenon does not occur on the inner surface and the outer surface of the pipe, and the pipe is ensured to have better surface quality.

8) Finishing of finished products

And straightening the final heat-treated finished pipe branch by branch, wherein the surface of the straightened finished pipe does not allow serious straightening defects such as shrinkage, scratch, pit pressing and the like, and the curvature is ensured to be not more than 1.0mm/m, and the total length curvature is ensured to be not more than 0.1% of the length.

9) Nondestructive testing

Ultrasonic detection

And carrying out ultrasonic detection on finished product pipes one by one. The pipe end detection blind area is not more than 100mm, and the pipe end blind area is completely cut off when the finished product is cut regularly.

The inner wall and the outer wall of the ultrasonic detection contrast sample tube are respectively provided with a longitudinal groove (rectangle), any two grooves are required to be separated to be distinguished, so that echoes can be clearly distinguished, and the size of the grooves is ensured: the depth is less than or equal to 0.10mm, the width is less than or equal to 0.20mm, and the length is less than or equal to 12.7mm.

Acceptance criteria: and if the echo signal of the defect of the detected pipe is equal to or exceeds the height of any defect echo signal of the contrast pipe, the pipe is unqualified.

Hydrostatic test

And carrying out hydrostatic test on the finished pipe qualified in ultrasonic detection one by one. The hydrostatic test pressure is 4MPa (gauge pressure), the dwell time is not less than 10 seconds, and no leakage is allowed. And after the hydrostatic test, the inner surface and the outer surface of the pipe are immediately dried by clean, oilless and dry compressed air, and the inner surface of the pipe is blown by dry and clean white cloth strips, so that the inner surface of the pipe is completely dried.

10 Fixed cutting of the finished product

And (3) carrying out fixed cutting, port flattening and deburring on the pipe qualified in the hydrostatic test according to the requirements, wherein the fixed cutting length is executed according to the requirements of a customer drawing, and the length deviation is 0- +5.0mm.

11 Size and surface inspection

And (5) carrying out size and surface inspection on the finished product pipe after the cleaning treatment one by one.

The outer diameter adopts an outer micrometer to respectively measure the outer diameters of the head, the middle and the tail, and records the maximum value and the minimum value; the wall thickness is measured by a wall thickness micrometer, and the maximum value and the minimum value of the wall thickness are recorded; the finished tube length was measured using a tape measure and recorded. The curvature of the finished product is measured by using a straightness flat ruler, and the maximum value is recorded. All of the gauges must go through the assay and be in the expiration date. The dimensions and deviations detected meet the following specifications:

Deviation of outer diameter: 44.5+ -0.20 mm

Wall thickness deviation: 1.45+ -0.12 mm

Length deviation: l (0-5.0) mm

Bending: the bending degree is not more than 1.0mm/m, the total bending degree is not more than 0.1% of the length, and the bending degree in the range of 200mm of the pipe end is not more than 0.25mm.

Ellipticity: not more than 0.32mm

Uneven wall thickness: not more than 0.20mm

And (5) checking the surface quality of the finished pipe by adopting a visual detection method. The inner and outer surfaces of the pipe should be smooth, and the pipe should not have the defects of cracks, folding, twisting, undercut, incomplete penetration, concave welding seams and other defects affecting the use. These defects should be completely removed, the actual wall thickness at the removal should be no less than the minimum allowed by the wall thickness, and the removal should be smoothly transitioned. The inner and outer surfaces of the pipe should be bright and clean, and the phenomena of greasy dirt, dust, water stain, fingerprint, oxidative discoloration and the like cannot be caused.

12 Cleaning treatment, identification and packaging

And cleaning the inner surface and the outer surface of the finished pipe which are qualified by inspection and checking the cleanliness, wherein the inner surface and the outer surface of the pipe are required to be cleaned and dried, and rust spots, dust and other pollutants are avoided. Each finished pipe is sprayed with a mark, and the mark information comprises a standard number, an alloy brand, a specification, a furnace number, a batch number, a pipe number and the like.

And finally, bagging the qualified pipes, putting the bagged pipes into a special wooden box for packaging, requiring the pipes to be tiled in a single layer in the wooden box, aligning one ends of the pipes, and isolating each layer by adopting pearl wool or foam to prevent bruise or scratch.

13 Tissue and performance detection

The finished product is sampled and detected according to the detection items in table 4 when being cut regularly, and all performance indexes meet the ASTM B704 standard and design requirements.

Table 4 tissue and Performance detection

Sequence number	Inspection item	Sampling frequency	Inspection standard
				1	Finished product component	1/Batch	ASTM E2594、ASTM E1019、ASTM B880
2	Nonmetallic inclusion	1/Batch	ASTM E45
				3	Stretching at room temperature	2/Batch	ASTM E8
4	High temperature stretching at 650 DEG C	2/Batch	ASTM E21
				5	Grain size of	1/Batch	ASTM E3ASTM E112
6	Flattening test	2/Batch	ASME SB751
				7	Hemming test	2/Batch	ASME SB751

The chemical composition detection results of the finished pipe are shown in table 5, and meet the design requirements.

Table 5 finished tube chemistry (wt.%)

The detection result of the nonmetallic inclusion of the finished pipe is shown in the table 6, meets the design requirement, has higher purity, and plays an important role in improving the high-temperature fatigue resistance and the corrosion resistance.

TABLE 6 rating of non-metallic inclusions in finished pipe

The room temperature tensile properties of the finished pipe are shown in Table 7, and the steel grade 1 standard is met and the design requirements are met.

Table 7 alloy 625 pipe tensile Properties at room temperature

The high-temperature tensile property of the finished pipe at 650 ℃ is shown in table 8, meets the design requirement, and the pipe has higher safety and better fatigue resistance under the condition of ensuring the use working condition.

Table 8 high temperature tensile properties of 625 alloy tubing

The finished product pipe parent metal grain size is 7.0 grade, the weld joint grain size is 9.0 grade, the finished product pipe parent metal grain size is an austenite structure, no continuous or semi-continuous carbide is precipitated at the grain boundary, and the finished product pipe meets the design requirement.

The flattened and curled samples have no cracks and meet the design requirements.

Example 2

1) Smelting and hot working

The raw materials are smelted by adopting a vacuum induction and electroslag remelting method, the size of a vacuum induction electrode is 510mm, the weight of an electroslag ingot is 660, and the weight of the ingot is about 5 tons. Homogenizing heat treatment of electroslag ingot, wherein the homogenizing heat treatment system is that the temperature is 1200 ℃ and the temperature is kept for 48 hours, and discharging and forging are carried out after the heat preservation is finished. Hot forging to obtain plate blank with thickness of 150mm, initial temperature not lower than 1100 deg.c and final forging temperature not lower than 800 deg.c.

The hot-forged slab was subjected to chemical composition measurement according to ASTM E2594 by taking one sample from each of the ends corresponding to the head and tail of the steel ingot, and the measurement results are shown in table 9 below.

TABLE 9 chemical composition of slabs (wt%)

Element(s)	C	S	Si	Mn	P	Cr	Ni	Fe
									Head part	0.023	0.001	0.10	0.05	0.007	21.8	60.3	3.50
Tail part	0.025	0.001	0.11	0.05	0.008	21.5	60.1	3.60
									Element(s)	Mo	Al	Co	Ti	Nb+Ta	N	H	O
Head part	8.90	0.12	0.04	0.13	3.65	0.007	0.0002	0.0022
									Tail part	9.10	0.12	0.04	0.11	3.73	0.008	0.0003	0.0025

TABLE 10 rating of nonmetallic inclusion in slabs

2) Cold-rolled strip

The thickness of the cold-rolled strip is 2.5mm, the thickness deviation is +/-0.10 mm, the width of the strip is 196.5mm, and the width deviation is +/-0.20 mm. The surface state is a 2B surface. The grain size of the strip is 6.0-7.0 grade, and the strip is a pure austenite structure, and no carbide strip structure appears.

3) Laser welding

Welding and forming by adopting a full-automatic numerical control laser welding machine, wherein the welding power is 2450W, the welding speed is 3.0m/min, the protective atmosphere is high-purity argon, the purity is not lower than 99.99%, the external protection air flow is 10L/min, and the internal protection air flow is 8L/min. The weld seam excess is 0.11mm. Welding tube blank specification phi 63.5 x 2.5mm.

4) Annealing of tube blanks

And (3) annealing the tube blank by adopting a continuous bright annealing furnace, wherein the annealing temperature is 1100 ℃, and the heat preservation time is 10min.

5) Final cold rolling

Cold rolling is carried out by adopting an LG60 type two-weld rolling mill, and the cold working deformation process is shown in the following table 11.

Surface 11 cold working deformation process

6) Degreasing and cleaning

7) Final heat treatment

The final heat treatment after the final cold rolling and degreasing cleaning adopts a protective atmosphere bright annealing process, the annealing temperature is 1100 ℃, the heat preservation time is 10min, the protective atmosphere is hydrogen with the purity of more than 99.95%, the high mechanical property of the finished pipe is ensured, the oxidation discoloration phenomenon of the inner surface and the outer surface of the pipe is avoided, and the good surface quality of the pipe is ensured.

8) Finishing of finished products

The same finished product finishing, nondestructive testing, finished product cutting, size and surface inspection, cleaning treatment, identification and packaging, and tissue property testing as in example 1 were performed on this example.

The chemical composition detection results of the finished pipe are shown in table 12, and meet the design requirements.

Table 12 finished tube chemistry (wt.%)

The detection result of the nonmetallic inclusion of the finished pipe is shown in table 13, meets the design requirement, has higher purity, and plays an important role in improving the high-temperature fatigue resistance and the corrosion resistance.

TABLE 13 rating of non-metallic inclusions in finished pipe

The room temperature tensile properties of the finished pipe are shown in Table 14, and meanwhile, the steel grade 2 is met, and the design requirement of the steel grade 2 is met.

Table 14, 625 alloy tubing room temperature tensile properties

The high-temperature tensile property of the finished pipe at 650 ℃ is shown in table 15, meets the design requirement, and the pipe has higher safety and better fatigue resistance under the condition of ensuring the use working condition due to higher high-temperature strength.

Table 15, 625 alloy tubing high temperature tensile properties

The finished product pipe base metal grain size is 6.0 grade, the weld joint grain size is 8.0 grade, the finished product pipe base metal grain size is an austenite structure, no continuous or semi-continuous carbide is precipitated at the grain boundary, and the finished product pipe meets the design requirement.

FIG. 1 is a microstructure of a welded pipe weld. As can be seen from the figure, the weld structure is characterized by a coarse columnar grain structure.

FIG. 2 is a microstructure and IPF map of a weld after annealing of a cold rolled welded tube. From the figure, the weld joint structure can be effectively refined after rolling processing and heat treatment.

The above description of the present invention is further illustrated in detail and should not be taken as limiting the practice of the present invention. It is within the scope of the present invention for those skilled in the art to make simple deductions or substitutions without departing from the concept of the present invention.

Claims

1. The 625 alloy pipe for the tower type photo-thermal power station heat absorber is characterized by comprising the following elements ：Cr= 21.0～23.0%,Mo= 8.5～10.0%,Nb+Ta=3.50～4.15%,Fe=1～5%,C=0.01～0.03%,N≤0.015%,P≤0.01%,H≤0.008%,O≤0.003%,S≤0.003%, in percentage by mass and the balance of Ni and unavoidable impurity elements.

2. The 625 alloy pipe according to claim 1, wherein the 625 alloy pipe further comprises the following elements in mass percent: co is less than or equal to 1.0%, si is less than or equal to 0.50%, mn is less than or equal to 0.50%, al is less than or equal to 0.40%, and Ti is less than or equal to 0.40%.

3. The 625 alloy pipe according to claim 1 or2, wherein the 625 alloy pipe comprises ：Cr= 21.0～23.0%,Mo= 8.5～10.0%,Nb+Ta =3.50～4.15%,Fe= 1～5%,C=0.01～0.03%,N≤0.015%,P≤0.01%,H≤0.008%,O≤0.003%,S≤0.003%,Co≤1.0%,Si≤0.50%,Mn≤0.50%,Al≤0.40%,Ti≤0.40%, by mass percent of Ni and unavoidable impurity elements as the rest.

4. The 625 alloy pipe according to claim 1, wherein the method for producing the 625 alloy welded pipe comprises the steps of:

3) Cold deformation treatment is carried out on the 625 alloy tube blank subjected to the bright annealing treatment in the step 2);

5. The 625 alloy pipe according to claim 4, wherein the bright annealing treatment in the step 2) is performed at 1050-1100 ℃ for 5-15 min.

6. The 625 alloy pipe according to claim 4, wherein the deformation amount of the cold deformation process treatment of the step 3) ranges from 30 to 60%.

7. The 625 alloy pipe according to claim 4, wherein the bright heat treatment in step 5) is performed at 950-1100 ℃ for a period of 5-15 min.

8. The 625 alloy pipe according to claim 4, wherein the surface roughness Ra of the 625 alloy welded pipe after the surface treatment in the step 7) is less than or equal to 1.60 μm.

9. The 625 alloy pipe according to claim 1, wherein the non-metallic inclusion rating of the 625 alloy pipe should meet the following requirements: A. the sum of the B, C, D coarse lines and the fine lines is not more than 1.0 level, and the sum of the A, B, C, D coarse lines and the fine lines is not more than 4.0 level; nitride inclusions are rated with reference to class B and class D, with both class B and class D coarse systems not exceeding class 1.0, class B fine systems not exceeding class 1.5, and class D fine systems not exceeding class 2.0.

10. The 625 alloy pipe according to claim 1, wherein the 625 alloy pipe has a room temperature yield strength of not less than 414MPa, a room temperature tensile strength of not less than 827MPa, a room temperature elongation of not less than 30%, a 650 ℃ yield strength of not less than 210MPa, a 650 ℃ tensile strength of not less than 550MPa, and a 650 ℃ elongation of not less than 40%.