Composite tube base tube and preparation method and application thereof

Abstract

The invention provides a composite pipe base pipe and a preparation method and application thereof. The wall thickness of the base pipe is 30 mm or above. The wall thickness deviation of the base tube is within 1mm; the deviation of the inner diameter of the base tube ranges from 0 mm to 1 mm. And the roughness of the inner surface of the base tube is below 8.4 microns. The wall thickness of the base pipe of the composite pipe is larger than or equal to 30 mm, the wall thickness deviation is within 1 mm, the inner diameter deviation ranges from 0 mm to 1 mm, the roughness of the inner surface is appropriate, no adverse application is brought to follow-up composite pipe machining, and the composite pipe can be directly used for bimetal composite pipe production.

Description

Technical Field

[0001] The present application relates to the technical field of steel pipes, and in particular to a composite pipe base pipe and a preparation method and application thereof. Background Art

[0002] Bimetallic composite pipe is a pipe that combines seamless steel pipe and stainless steel liner pipe, which retains the advantages of two different materials and is increasingly applicable in industries such as oil fields, chemicals and power. The base pipe is the outer layer of the composite pipe, which is mainly responsible for bearing pressure, rigid support of the pipe and resisting the influence of the external environment. The liner pipe is the inner layer of the composite pipe, which mainly plays a role in corrosion resistance and wear resistance.

[0003] There are two ways to assemble composite pipes in related technologies. One is to squeeze the base pipe and the liner together by mechanical pressure, and the other is to weld a layer of stainless steel on the inner wall of the base pipe to form an inner liner. Both methods have very high requirements on the inner surface of the base pipe, and there must not be any defects or oxide scale.

[0004] In order to reduce the defects on the inner surface of the base tube, the related technology performs internal grinding or shot blasting on the inner surface of the base tube after heat treatment. For thick-walled base tubes with a wall thickness of ≥30mm, due to the long heat treatment insulation time, it is easy to cause pitting and rough surface defects on the inner surface during heat treatment. Shot blasting is difficult to meet the inner surface requirements, and the production cycle of internal grinding is long and it is easy to cause thin wall thickness, resulting in the wall thickness failing to meet the requirements. In addition, for high-precision thick-walled composite tube base tubes, after the dimensional accuracy is achieved through the cold drawing process, if internal grinding and other treatments are performed later, the dimensional accuracy of the steel pipe will decrease, resulting in low dimensional accuracy.

[0005] The preparation method of the substrate tube in the related art has the following disadvantages:

[0006] (1) Thick-walled tubes are prone to quality problems such as pitting after heat treatment, which cannot be solved by shot blasting technology;

[0007] (2) The internal fine grinding process takes a long time and is costly;

[0008] (3) Internal fine grinding has a great influence on the dimensional accuracy of the steel pipe, and it is necessary to design it in advance and leave enough room for grinding.

[0009] Application Contents

[0010] The present application has been made in view of the above-mentioned problems, and an object of the present application is to provide a composite pipe base pipe having a high inner surface quality.

[0011] Specifically, in a first aspect, the present application provides a composite pipe base pipe, wherein the wall thickness of the base pipe is greater than 30 mm;

[0012] The wall thickness deviation of the base pipe is within 1 mm;

[0013] The inner diameter deviation of the base tube is 0 mm to 1 mm;

[0014] The inner surface roughness of the base tube is below 8.4 μm.

[0015] According to some embodiments of the present application, the inner wall of the base pipe is free of oxide scale.

[0016] According to some embodiments of the present application, the grain size of the substrate tube is above level 8.5.

[0017] According to some embodiments of the present application, the base tube is composed of the following elements in weight fractions:

[0018] C: 0.08% ~ 0.12%, Si: 0.25% ~ 0.35%, Mn: 1.35% ~ 1.50%, Cr: 0.20% ~ 0.30%, Ni: 0.10% ~ 0.30%, Mo: 0.15% ~ 0.30%, V: 0.02% ~ 0.06%, Nb: 0.020% ~ 0.050%, Al: 0.015% ~ 0.050%, Ti: 0.002% ~ 0.005%, the balance is Fe and inevitable impurities.

[0019] A second aspect of the present application provides a method for preparing a composite pipe base pipe, comprising the following steps:

[0020] The hot rolled rough tube is quenched, tempered, hot straightened, cold drawn and annealed;

[0021] The quenching temperature is 870°C to 940°C;

[0022] The tempering temperature is 600°C to 700°C;

[0023] The annealing temperature is 350°C to 550°C.

[0024] According to some embodiments of the present application, the wall thickness of the base pipe is above 30 mm.

[0025] According to some embodiments of the present application, the wall thickness deviation of the base tube is within 1 mm.

[0026] According to some embodiments of the present application, the inner diameter deviation of the base tube is 0 mm to 1 mm.

[0027] According to some embodiments of the present application, the inner wall of the base pipe is free of oxide scale.

[0028] According to some embodiments of the present application, the inner surface roughness of the substrate tube is below 8.4 μm.

[0029] According to some embodiments of the present application, the grain size of the substrate tube is above level 8.5.

[0030] According to some embodiments of the present application, the base tube is composed of the following elements in weight fractions:

[0031] C: 0.08% ~ 0.12%, Si: 0.25% ~ 0.35%, Mn: 1.35% ~ 1.50%, Cr: 0.20% ~ 0.30%, Ni: 0.10% ~ 0.30%, Mo: 0.15% ~ 0.30%, V: 0.02% ~ 0.06%, Nb: 0.020% ~ 0.050%, Al: 0.015% ~ 0.050%, Ti: 0.002% ~ 0.005%, the balance is Fe and inevitable impurities.

[0032] According to some embodiments of the present application, the quenching temperature is 900°C to 930°C.

[0033] According to some embodiments of the present application, the tempering temperature is 630°C to 670°C.

[0034] According to some embodiments of the present application, the temperature of the heat straightening is between 400°C and 550°C.

[0035] According to some embodiments of the present application, the annealing temperature is 350°C to 550°C.

[0036] According to some embodiments of the present application, the quenching time is 60 min to 80 min.

[0037] According to some embodiments of the present application, the tempering time is 90 min to 110 min.

[0038] According to some embodiments of the present application, the annealing time is 150 min to 180 min.

[0039] According to some embodiments of the present application, the method for preparing the hot-rolled mother tube comprises the following steps:

[0040] The molten steel is subjected to EAF, LF, VD argon blowing, vacuum degassing and continuous casting in sequence.

[0041] A third aspect of the present application provides a composite pipe, comprising the composite pipe base pipe as described in the first aspect of the present application and / or the composite pipe base pipe prepared by the preparation method according to the second aspect of the present application.

[0042] According to some embodiments of the present application, the composite pipe further includes a liner pipe;

[0043] The base pipe is arranged on the outer layer of the liner pipe.

[0044] According to at least one of the technical solutions of the present application, at least the following beneficial effects are achieved:

[0045] The wall thickness of the composite pipe base pipe is ≥30mm, the wall thickness deviation is within 1mm, the inner diameter deviation is 0mm~1mm, and the inner surface roughness is low, which will not bring adverse applications to the subsequent processing of the composite pipe and can be directly used in the production of bimetallic composite pipes.

[0046] The present application adopts a cold drawing process to improve the inner surface quality of the composite pipe base pipe, and improves the mechanical properties of the composite pipe base pipe through tempering treatment, which not only ensures the dimensional accuracy of the base pipe, but also saves the production cost of the surface treatment process; the present application also eliminates the cold drawing processing stress through annealing treatment.

[0047] The present application controls the preparation method of the composite pipe base pipe, thereby preparing a composite pipe base pipe with good inner surface quality (inner surface roughness ≤8.4μm), and the inner surface defects of the hot-rolled rough pipe are completely eliminated through the cold drawing process. There is no tempering heat treatment after cold drawing, and no oxide scale is generated on the inner surface, and there are no pitting defects.

[0048] The preparation method of the present application has good economy, and the composite pipe base pipe does not need to be internally ground separately, thereby reducing process costs and metal consumption.

[0049] The preparation method of the present application shortens the production cycle. The inner grinding of the substrate tube is an inefficient bottleneck process. Eliminating the inner grinding process can greatly shorten the product production cycle and reduce manufacturing costs.

[0050] The composite pipe base pipe prepared by the present application has high dimensional accuracy. No tempering heat treatment is performed after cold drawing, which can prevent the steel pipe from being deformed due to thermal stress after tempering heat treatment. At the same time, the internal grinding of the base pipe is eliminated, the cold drawing size is retained, and the dimensional accuracy is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present drawings or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present drawings. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0052] Figure 1 This is a metallographic image of the composite tube base tube prepared in Example 1.

[0053] Figure 2 1 is a metallographic image of the composite tube base tube prepared in Example 1 (different magnifications).

[0054] Figure 3 This is the appearance diagram of the composite pipe base pipe prepared in Example 1.

[0055] The purpose, features and advantages of this figure will be further described in conjunction with the embodiments with reference to the accompanying drawings. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0057] Obviously, the drawings described below are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios based on these drawings without creative work. In addition, it can also be understood that although the efforts made in this development process may be complicated and lengthy, for ordinary technicians in this field related to the content disclosed in this application, some changes in design, manufacturing or production based on the technical content disclosed in this application are just conventional technical means, and should not be understood as insufficient content disclosed in this application.

[0058] However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0059] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0060] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0061] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0062] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0063] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0064] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0065] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0066] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0067] The high-precision thick-walled composite pipe base pipe refers to the outer base pipe with a wall thickness of ≥30mm, a wall thickness deviation of ±1mm, and an inner diameter deviation of 0-1mm, which is used for the production of bimetallic composite pipes. The preparation process of the prior art is: steelmaking → hot-rolled rough pipe → finishing → cold drawing / cold rolling → quenching and tempering heat treatment (quenching + tempering) → hydraulic pressure test → flaw detection → manual inspection → internal fine grinding → length measurement and weighing → packaging and warehousing. There are two disadvantages of this process flow. First, the quenching and tempering heat treatment (quenching + tempering) after cold drawing will produce a large amount of iron oxide scale and even pits and pits, which requires further surface treatment steps; second, the internal grinding treatment after cold drawing will reduce the wall thickness and increase the inner diameter. If the grinding allowance is not designed in advance, it is very likely to cause unqualified dimensional accuracy. If the surface treatment allowance is designed in advance, metal consumption will increase, resulting in increased manufacturing costs.

[0068] Specifically, in a first aspect, the present application provides a composite pipe base pipe, wherein the wall thickness of the base pipe is greater than 30 mm;

[0069] The wall thickness deviation of the base pipe is within 1 mm;

[0070] The inner diameter deviation of the base tube is 0 mm to 1 mm;

[0071] The inner surface roughness of the base tube is below 8.4 μm.

[0072] According to some embodiments of the present application, the inner wall of the base pipe is free of oxide scale.

[0073] According to some embodiments of the present application, the grain size of the substrate tube is above level 8.5.

[0074] According to some embodiments of the present application, the base tube is composed of the following elements in weight fractions:

[0075] C: 0.08% ~ 0.12%, Si: 0.25% ~ 0.35%, Mn: 1.35% ~ 1.50%, Cr: 0.20% ~ 0.30%, Ni: 0.10% ~ 0.30%, Mo: 0.15% ~ 0.30%, V: 0.02% ~ 0.06%, Nb: 0.020% ~ 0.050%, Al: 0.015% ~ 0.050%, Ti: 0.002% ~ 0.005%, the balance is Fe and inevitable impurities.

[0076] A second aspect of the present application provides a method for preparing a composite pipe base pipe, comprising the following steps:

[0077] The hot rolled rough tube is quenched, tempered, hot straightened, cold drawn and annealed;

[0078] The quenching temperature is 870°C to 940°C;

[0079] The tempering temperature is 600°C to 700°C;

[0080] The annealing temperature is 300°C to 450°C.

[0081] According to some embodiments of the present application, the wall thickness of the base pipe is above 30 mm.

[0082] According to some embodiments of the present application, the wall thickness deviation of the base tube is within 1 mm.

[0083] According to some embodiments of the present application, the inner diameter deviation of the base tube is 0 mm to 1 mm.

[0084] According to some embodiments of the present application, the inner wall of the base pipe is free of oxide scale.

[0085] According to some embodiments of the present application, the inner surface roughness of the substrate tube is below 8.4 μm.

[0086] According to some embodiments of the present application, the grain size of the substrate tube is above level 8.5.

[0087] According to some embodiments of the present application, the base tube is composed of the following elements in weight fractions:

[0088] C: 0.08% ~ 0.12%, Si: 0.25% ~ 0.35%, Mn: 1.35% ~ 1.50%, Cr: 0.20% ~ 0.30%, Ni: 0.10% ~ 0.30%, Mo: 0.15% ~ 0.30%, V: 0.02% ~ 0.06%, Nb: 0.020% ~ 0.050%, Al: 0.015% ~ 0.050%, Ti: 0.002% ~ 0.005%, the balance is Fe and inevitable impurities.

[0089] According to some embodiments of the present application, the quenching temperature is 880°C to 930°C.

[0090] According to some embodiments of the present application, the tempering temperature is 620°C to 650°C.

[0091] According to some embodiments of the present application, the temperature of the heat straightening is between 400°C and 550°C.

[0092] According to some embodiments of the present application, the annealing temperature is 350°C to 550°C.

[0093] According to some embodiments of the present application, the annealing temperature is 350°C to 400°C.

[0094] According to some embodiments of the present application, the quenching time is 60 min to 80 min.

[0095] According to some embodiments of the present application, the tempering time is 90 min to 110 min.

[0096] According to some embodiments of the present application, the annealing time is 150 min to 180 min.

[0097] According to some embodiments of the present application, the method for preparing the hot-rolled mother tube comprises the following steps:

[0098] The molten steel is subjected to EAF, LF, VD argon blowing, vacuum degassing and continuous casting in sequence.

[0099] A third aspect of the present application provides a composite pipe, comprising the composite pipe base pipe as described in the first aspect of the present application and / or the composite pipe base pipe prepared by the preparation method according to the second aspect of the present application.

[0100] According to some embodiments of the present application, the composite pipe further includes a liner pipe;

[0101] The base pipe is arranged on the outer layer of the liner pipe.

[0102] According to at least one of the technical solutions of the present application, at least the following beneficial effects are achieved:

[0103] The wall thickness of the composite pipe base pipe is ≥30mm, the wall thickness deviation is within 1mm, the inner diameter deviation is 0mm~1mm, and the inner surface roughness is low, which will not bring adverse applications to the subsequent processing of the composite pipe and can be directly used in the production of bimetallic composite pipes.

[0104] The present application adopts a cold drawing process to achieve very good dimensional accuracy and improve the inner surface quality of the composite pipe base pipe, and improves the mechanical properties of the composite pipe base pipe through tempering treatment, which not only ensures the dimensional accuracy of the base pipe, but also saves the production cost of the surface treatment process; the present application also eliminates cold drawing processing stress through annealing treatment.

[0105] The present application controls the preparation method of the composite pipe base pipe, thereby preparing a composite pipe base pipe with good inner surface quality (inner surface roughness ≤8.4μm), and the inner surface defects of the hot-rolled rough pipe are completely eliminated through the cold drawing process. There is no tempering heat treatment after cold drawing, and no oxide scale is generated on the inner surface, and there are no pitting defects.

[0106] The preparation method of the present application has good economic efficiency, and the composite pipe base pipe does not need to be separately subjected to internal fine grinding, thereby reducing process costs and metal consumption.

[0107] The preparation method of the present application shortens the production cycle. The inner grinding of the substrate tube is a low-efficiency bottleneck process. Eliminating the inner grinding process can greatly shorten the product production cycle.

[0108] The composite tube base tube prepared by the present application has high dimensional accuracy. After cold drawing, no more quenching and tempering heat treatment (quenching + tempering) is performed, which can prevent the steel tube from being deformed due to thermal stress after quenching and tempering heat treatment (quenching + tempering). At the same time, the fine grinding inside the base tube is cancelled, and the cold drawing size is retained, which will also greatly improve the dimensional accuracy.

[0109] Example 1

[0110] This embodiment is a composite tube base tube and a preparation method thereof.

[0111] The chemical composition weight percentage (%) of the composite tube base tube in this embodiment is C=0.09, Si=0.28, Mn=1.39, Cr=0.21, Ni=0.12; Mo=0.17, V=0.06, Nb=0.022, Al=0.018, Ti=0.005, and the balance is Fe and unavoidable impurities.

[0112] The method for preparing the composite tube base tube in this embodiment comprises the following steps:

[0113] S1. Steelmaking is carried out according to the chemical composition weight percentage of the composite tube base tube, and round tube billets are made by electric furnace + refining + vacuum degassing + electromagnetic stirring + continuous casting.

[0114] LF refining time target: 70min±10min; VD holding time is 10min, and soft argon blowing time after air breaking and wire feeding is 15min;

[0115] S2, the ingot is pierced by a piercing machine and rolled by a continuous rolling mill to obtain a hot rolled rough tube;

[0116] The blank heating process is shown in Table 1 below:

[0117] Table 1 Billet heating temperature

[0118]

[0119] The piercing feed angle is 9.5°, using 325 ejector rod and 323 ejector head, and the piercing machine roll speed is controlled at 420rpm.

[0120] S3, hot rolled rough tube is quenched, tempered, hot straightened, pickled, phosphated, cold drawn and annealed;

[0121] The quenching temperature is 930℃ and the holding time is 70min±10min;

[0122] The tempering temperature is 670℃, and the holding time is: 100min±10min;

[0123] The temperature of heat straightening is 400℃;

[0124] The pickling parameters are as follows: pickling temperature 55℃±5℃, time 30min; water immersion after pickling, and phosphating after water immersion.

[0125] The parameters of phosphating are as follows: phosphating temperature 64℃±4℃, phosphating time 50min, water washing after phosphating. The parameters of cold drawing are as follows: outer die: φ273.8, inner die φ216.6 (216.4);

[0126] The annealing temperature is 550°C and the annealing time is 165min±10min.

[0127] Example 2

[0128] This embodiment is a composite tube base tube and a preparation method thereof, which is different from Embodiment 1 in that the tempering temperature is different.

[0129] The tempering temperature is 650℃.

[0130] Example 3

[0131] This embodiment is a composite tube base tube and a preparation method thereof, which is different from Embodiment 1 in that the tempering temperature is different.

[0132] The tempering temperature is 630℃ and the time is 90~110min;

[0133] Example 4

[0134] This embodiment is a composite tube base tube and a preparation method thereof, which is different from Embodiment 1 in that the annealing temperature is different.

[0135] The annealing temperature is 450°C.

[0136] Example 5

[0137] This embodiment is a composite tube base tube and a preparation method thereof, which is different from Embodiment 1 in that the annealing temperature is different.

[0138] The annealing temperature is 350°C.

[0139] Comparative Example 1

[0140] This comparative example is a composite pipe base pipe and a preparation method thereof, which differs from Example 1 in that:

[0141] The process of step S3 in this comparative example is as follows:

[0142] The hot rolled rough tube is pickled, phosphated, cold drawn, quenched, tempered, hot straightened and internally shot blasted;

[0143] The parameters of the same process in this comparative example are the same as those in Example 1;

[0144] The parameters of internal shot blasting are as follows: shot blasting pressure 8Kg, particles 0.6mm~0.8mm;

[0145] Comparative Example 2

[0146] This comparative example is a composite pipe base pipe and a preparation method thereof, which differs from Example 1 in that:

[0147] The process of step S3 in this comparative example is as follows:

[0148] The hot-rolled rough tube is pickled, phosphated, cold drawn, quenched, tempered, hot straightened, and internally finely ground; the parameters of the same process in this comparative example are the same as those in Example 1;

[0149] The parameters of internal fine grinding are as follows: 2 passes of internal grinding with grinding wheel + fine polishing with flap wheel.

[0150] The performance test methods of the composite pipe base pipes prepared in the examples and comparative examples of the present application are as follows:

[0151] Tensile yield strength at room temperature (25°C): 450MPa~570MPa;

[0152] Room temperature tensile strength: 535MPa~670MPa;

[0153] -50℃ low temperature impact energy: ≥80J;

[0154] Shear area: ≥85%;

[0155] Grain size: ≥8 levels;

[0156] Inner surface roughness: Inner surface roughness ≤8.3μm;

[0157] Internal surface cleanliness: cleanliness not less than ISO 8501Sa2.5;

[0158] Appearance: The inner surface of the steel pipe shall not have folds, scars, cracks, burrs, delamination, etc. that may affect the integrity of the inner surface, and the inner surface shall not have protrusions exceeding 1mm in height.

[0159] Dimension accuracy: wall thickness deviation 0mm~1mm, inner diameter deviation 0mm~1mm.

[0160] The test results are shown in Table 2

[0161] Table 2 Implementation and comparison case results

[0162]

[0163]

[0164] The high-precision thick-walled base pipe produced by the method of the embodiment of the present application has an average low-temperature impact of -50°C ≥150J, an average shear area ≥85%, a grain size ≥8.5, a yield strength of 500-550MPa, and a tensile strength of 610-660MPa. The inner wall of the steel pipe has no pitting, no obvious oxide scale, and an inner surface roughness of ≤8.4μm. It can fully meet the requirements of the composite pipe base pipe.

[0165] Figures 1-2 The microstructure diagram of the composite tube base tube (at different magnifications) shows that the metallographic structure of the base tube is B+F, the grain size is level 9, the structure is uniform, and the grains are fine. This kind of microstructure can obtain uniform mechanical properties and low-temperature toughness of the tube. Figure 3 This is a macroscopic picture of the inner surface of the composite tube base tube of Example 1, from Figure 2 There may be no mechanical scratches or oxide scale on the inner surface of the base tube, and the inner surface finish reaches SA3.0 level. This kind of inner surface quality can effectively prevent the delamination problem after mechanical compounding and can fully meet the PAUT inspection requirements after compounding.

[0166] The advantages of the preparation method of the present application are: the tempering heat treatment (quenching + tempering) process of the composite tube base tube is adjusted to before the cold drawing / cold rolling process, and the surface quality problems caused by the heat treatment process are completely eliminated through the cold drawing / process; the current mechanical properties are achieved while the stress is relieved by low-temperature tempering after cold drawing; the internal grinding process is cancelled, the production efficiency is improved, and the dimensional accuracy is effectively guaranteed.

[0167] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and the same effect as the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A composite pipe base pipe, characterized in that: The wall thickness of the base pipe is above 30 mm; The wall thickness deviation of the base pipe is within 1 mm; The inner diameter deviation of the base tube is 0 mm to 1 mm; The inner surface roughness of the base tube is below 8.4 μm.

2. The composite pipe base pipe according to claim 1, characterized in that: The inner wall of the base tube has no oxide scale; And / or, the grain size of the substrate tube is above grade 8.

5.

3. The composite pipe base pipe according to claim 1 or 2, characterized in that: The base tube is composed of the following elements in weight fractions: C: 0.08% ~ 0.12%, Si: 0.25% ~ 0.35%, Mn: 1.35% ~ 1.50%, Cr: 0.20% ~ 0.30%, Ni: 0.10% ~ 0.30%, Mo: 0.15% ~ 0.30%, V: 0.02% ~ 0.06%, Nb: 0.020% ~ 0.050%, Al: 0.015% ~ 0.050%, Ti: 0.002% ~ 0.005%, the balance is Fe and inevitable impurities.

4. A method for preparing a composite pipe base pipe, characterized in that: The following steps are involved: The hot rolled rough tube is quenched, tempered, hot straightened, cold drawn and annealed; The quenching temperature is 870°C to 940°C; The tempering temperature is 600°C to 700°C; The annealing temperature is 350°C to 550°C.

5. The preparation method according to claim 4, characterized in that: The wall thickness of the base pipe is above 30 mm; and / or, the wall thickness deviation of the base tube is within 1 mm; And / or, the inner diameter deviation of the base tube is 0 mm to 1 mm; and / or, the inner wall of the base tube is free of oxide scale; and / or, the inner surface roughness of the substrate tube is below 8.4 μm; And / or, the grain size of the substrate tube is above grade 8.

5. And / or, the base tube is composed of the following elements in weight fractions: C: 0.08% ~ 0.12%, Si: 0.25% ~ 0.35%, Mn: 1.35% ~ 1.50%, Cr: 0.20% ~ 0.30%, Ni: 0.10% ~ 0.30%, Mo: 0.15% ~ 0.30%, V: 0.02% ~ 0.06%, Nb: 0.020% ~ 0.050%, Al: 0.015% ~ 0.050%, Ti: 0.002% ~ 0.005%, the balance is Fe and inevitable impurities.

6. The preparation method according to claim 4 or 5, characterized in that: The quenching temperature is 870°C to 940°C; And / or, the tempering temperature is 630°C to 670°C; And / or, the temperature of the heat straightening is 400°C to 550°C; And / or, the annealing temperature is 350°C to 550°C.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The quenching time is 60min to 80min; And / or, the tempering time is 90min to 110min; And / or, the annealing time is 150 min to 180 min.

8. The preparation method according to any one of claims 4 to 6, characterized in that: The method for preparing the hot-rolled mother tube comprises the following steps: The molten steel is subjected to EAF, LF, VD argon blowing, vacuum degassing and continuous casting in sequence.

9. A composite pipe, characterized in that: It comprises the composite pipe base pipe as described in any one of claims 1 to 3 and / or the composite pipe base pipe prepared by the preparation method as described in any one of claims 4 to 8.

10. The composite pipe according to claim 9, characterized in that Also included is a liner pipe; The base pipe is arranged on the outer layer of the liner pipe.

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