Method for preparing oil and gas conveying steel pipe

Abstract

The invention relates to the technical field of oil and gas conveying steel pipes, and discloses a method for preparing an oil and gas conveying steel pipe. The method comprises the following steps: (1) determining a yield strength control target of a to-be-prepared steel pipe; (2) the value of x in the stress characterization parameter Rtx of the steel plate before forming is obtained, and the target Rtx of the steel plate before forming is obtained according to the yield strength control target of the steel pipe to be prepared; (3) the steel plate before forming is prepared according to the target Rtx, and the actual diameter expansion rate of the steel plate before forming in the pipe manufacturing process is obtained according to the quantitative relation between the actually measured Rtx of the steel plate before forming and the target Rtx; (4) according to the actual expanding rate, edge milling is carried out, and a steel plate needed for forming is obtained; and (5) the steel plate required for forming is formed and welded, and all welded pipes obtained through welding are subjected to mechanical diameter expansion with the same diameter expansion parameters, so that the oil and gas conveying steel pipe is obtained. And the fluctuation range of the yield strength of the manufactured steel pipe can be narrow.

Description

Technical Field

[0001] The present invention relates to the technical field of steel pipes for oil and gas transportation, and particularly relates to a method for manufacturing steel pipes for oil and gas transportation. Background Art

[0002] Oil and gas pipelines are the most economical and efficient way for large-scale and long-distance transportation of oil and gas. With the rapid development of the economy, the construction of domestic oil and gas pipelines has developed rapidly. Up to now, 150,000 kilometers of long-distance oil and gas pipelines have been built in China, but it still cannot meet the needs. In the future for some time, China will still be in the peak period of pipeline construction.

[0003] Yield strength is one of the most important properties of steel pipes for oil and gas transportation. It not only determines the pressure-bearing capacity of the pipeline, but also has an important impact on the strain capacity of the pipeline, the strength matching of girth welds, etc. When the yield strength of the steel pipe fluctuates greatly, when the pipeline is stressed and deformed, the steel pipe with lower strength will have a larger strain, while the steel pipe with higher strength has not started to strain yet, resulting in a reduction in the overall coordinated strain capacity of the pipeline. In addition, when the yield strength of the steel pipe fluctuates greatly, it is necessary for the girth weld of the pipeline to reach above the upper limit of the yield strength to achieve over-strength matching, which increases the difficulty of the girth weld and the risk of girth weld failure caused by under-strength matching. These factors will have a serious adverse impact on pipeline safety. Therefore, oil and gas pipeline standards have put forward requirements for the upper and lower limits of the yield strength of steel pipes, and the more important the pipeline is, the stricter the requirements for the yield strength fluctuation range are. For example, for X80 steel pipes, the yield strength range specified in the API Spec 5L standard is 555 - 705 MPa, the yield strength range specified in the technical requirements of the second West-East Gas Pipeline is 555 - 690 MPa, and the yield strength range specified in the technical requirements of the China-Russia Eastern Route is 555 - 675 MPa. For submarine pipelines, large-strain pipelines, etc., the yield strength fluctuation range of the steel pipe is generally required to be within 100 MPa. Strictly controlling the yield strength fluctuation of the steel pipe and narrowing the yield strength interval is the development trend of steel pipe products for oil and gas pipelines. With the increasing requirements for the safety of oil and gas pipelines, higher requirements are put forward for the quality and performance consistency of steel pipe products, and higher requirements are put forward for the yield strength control level of steel pipe products.

[0004] The yield strength of steel pipes is affected by multiple complex factors such as the chemical composition of raw materials, manufacturing processes, and pipe-making processes. Traditionally, the control method for the yield strength of steel pipes is first to formulate requirements for the yield strength of steel plates. However, due to the complexity of the chemical composition, rolling process, and accelerated cooling process of the steel plates during the manufacturing process, it is difficult to control the yield strength of the steel plates, and the fluctuation range is large. In addition, due to the significant change in the yield strength of the material during the pipe-making process of longitudinally submerged arc welded pipes, this change is affected by internal factors of the material and has a weak correlation with the yield strength value of the material, which results in that only controlling the yield strength of the steel plate cannot fully achieve the effect of controlling the yield strength of the steel pipe, resulting in large fluctuations in the yield strength of the steel pipe.

[0005] At present, it is still difficult to stably control the yield strength of oil and gas transmission steel pipes within the range of 120 MPa, and it is difficult to meet the higher requirements of the pipeline for the uniformity of the yield strength of steel pipes. Therefore, providing a new method for preparing oil and gas transmission steel pipes to improve the uniformity of the yield strength of steel pipes is of great significance for realizing the high-quality development of oil and gas transmission pipelines. Summary of the Invention

[0006] Aiming at the problems of large yield strength fluctuation range and poor uniformity of existing oil and gas transmission steel pipes, which in turn affect the safety of oil and gas pipelines, the present invention provides a method for preparing oil and gas transmission steel pipes.

[0007] In order to achieve the above object, the present invention provides a method for preparing an oil and gas transmission steel pipe, including:

[0008] (1) Determine the yield strength control target of the steel pipe to be prepared, the target lower limit value of the yield strength is Rt 0.5min , and the target upper limit value of the yield strength is Rt 0.5max ;

[0009] (2) Obtain the numerical value of x in the stress characterization parameter Rtx of the steel plate before forming, and obtain the lower limit value and upper limit value of the target Rtx of the steel plate before forming according to the target lower limit value Rt 0.5min of the yield strength of the steel pipe to be prepared and the target upper limit value Rt 0.5max of the yield strength; the lower limit value is the target Rtxmin, and the upper limit value is the target Rtxmax; wherein, Rtx is the stress value corresponding to the total strain of x% on the stress-strain curve obtained by the tensile test of the steel plate before forming;

[0010] (3) Determine the steel plate manufacturing process according to the target Rtx, prepare and obtain the steel plate before forming, and conduct a tensile test on the steel plate before forming to obtain the stress-strain curve and the measured Rtx of the steel plate before forming; according to the quantitative relationship between the measured Rtx of the steel plate before forming and the target Rtx, obtain the actual expansion rate of the steel plate before forming during the pipe manufacturing process;

[0011] (4) Calculate the width of the steel plate required for forming according to the actual expansion rate, and mill the edges of the steel plate before forming according to the width of the steel plate required for forming to obtain the steel plate required for forming;

[0012] (5) Form and weld the steel plate required for forming, and perform mechanical expansion on all the welded pipes obtained by welding with the same expansion parameters to obtain an oil and gas transmission steel pipe.

[0013] Through the above technical solutions, the present invention can obtain the following beneficial effects:

[0014] (1) The method for preparing oil and gas transmission steel pipes provided by the present invention can effectively reduce the fluctuation range of the yield strength of the steel pipes, and can control the yield strength of the steel pipes within a narrower range. After welding multiple steel pipes prepared by the method provided by the present invention into a pipeline, when the pipeline is strained by an external force, different steel pipes can enter the strain state simultaneously, avoiding strain concentration on a certain steel pipe, greatly improving the coordinated deformation ability of the pipeline, and enhancing the safety of oil and gas pipelines;

[0015] (2) The method for preparing oil and gas transmission steel pipes provided by the present invention is conducive to further compressing the upper limit of the yield strength of the steel pipes, thereby reducing the difficulty of high-strength matching during girth weld welding, facilitating high-strength matching of pipeline girth welds, reducing the probability of girth weld failure, and enhancing the safety of oil and gas pipelines;

[0016] (3) The method for preparing oil and gas transmission steel pipes provided by the present invention uses the steel plate stress characterization parameter to replace the steel plate Rt 0.5 , and controls the change of the yield strength by adjusting the strain amount during the pipe manufacturing process. Compared with the traditional method of ensuring the yield strength range of steel pipes by proposing more stringent requirements for the yield strength range of steel plates, it has less difficulty, higher reliability, and better economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the first fitting straight line diagram of the steel plate stress value and the yield strength value of the steel pipe sample in Embodiment 1 of the present invention.

[0018] Figure 2 is the second fitting straight line diagram of the steel plate stress value and the yield strength value of the steel pipe sample in Embodiment 1 of the present invention.

[0019] Figure 3 is the third fitting straight line diagram of the steel plate stress value and the yield strength value of the steel pipe sample in Embodiment 1 of the present invention.

[0020] Figure 4 is the fourth fitting straight line diagram of the steel plate stress value and the yield strength value of the steel pipe sample in Embodiment 1 of the present invention.

[0021] Figure 5 is the fifth fitting straight line diagram of the steel plate stress value and the yield strength value of the steel pipe sample in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0023] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0024] The present invention provides a method for preparing an oil and gas transmission steel pipe, including:

[0025] (1) Determine the yield strength control target of the steel pipe to be prepared. The target lower limit value of the yield strength is Rt 0.5min , and the target upper limit value of the yield strength is Rt 0.5max ;

[0026] (2) Obtain the numerical value of x in the stress characterization parameter Rtx of the steel plate before forming, and obtain the lower limit value and upper limit value of the target Rtx of the steel plate before forming according to the target lower limit value Rt 0.5min and the target upper limit value Rt 0.5max of the yield strength of the steel pipe to be prepared. The lower limit value is the target Rtxmin, and the upper limit value is the target Rtxmax; wherein, Rtx is the stress value corresponding to the total strain of x% on the stress-strain curve obtained by the tensile test of the steel plate before forming;

[0027] (3) Determine the steel plate manufacturing process according to the target Rtx, prepare and obtain the steel plate before forming, and conduct a tensile test on the steel plate before forming to obtain the stress-strain curve and the measured Rtx of the steel plate before forming; according to the quantitative relationship between the measured Rtx and the target Rtx of the steel plate before forming, obtain the actual expansion rate of the steel plate before forming during the pipe manufacturing process;

[0028] (4) Calculate the width of the steel plate required for forming according to the actual expansion rate, and mill the edge of the steel plate before forming according to the width of the steel plate required for forming to obtain the steel plate required for forming;

[0029] (5) Form and weld the steel plate required for forming, and perform mechanical expansion on all the welded pipes obtained by welding using the same expansion parameters to obtain the oil and gas transmission steel pipe.

[0030] The method for preparing an oil and gas transportation steel pipe provided by the present invention uses the steel plate stress characterization parameter Rtx based on the pipe-making strain, which can better characterize the yield strength of the material after pipe-making. Since the Rtx of the steel plate is close to the yield strength Rt of the steel pipe after pipe-making, after adopting Rtx, the guidance and timeliness for the steel plate manufacturing process are stronger, which is beneficial to obtaining a narrower tensile property control range. According to the yield strength control target of the steel pipe to be prepared and the target plastic strain ε at the wall thickness center during the pipe-making process 0.5 %, the target Rtx of the steel plate is determined and used as the requirement for the tensile property of the steel plate to guide the production and optimization of the tensile property of the steel plate. However, since the factors affecting the yield strength of the steel plate include complex factors such as chemical composition, rolling, and heat treatment processes, the yield strength of the steel plate may not reach the ideal range. Therefore, it is difficult to achieve the purpose of controlling the yield strength range of the steel pipe only by controlling the yield strength of the steel plate. During the pipe-making process, the plastic strain of the material has a significant impact on the yield strength of the steel pipe. Increasing the plastic strain during the pipe-making process can increase the yield strength of the steel pipe, while decreasing the plastic strain during the pipe-making process can decrease the yield strength of the steel pipe. Thus, the yield strength of the steel pipe can be further adjusted and controlled by adjusting the plastic strain during the pipe-making process. Based on the principle that the steel plate Rtx≈the yield strength Rt of the steel pipe 1 When the steel plate Rtx falls within the yield strength control range of the steel pipe, the pipe is made according to the target plastic strain ε1%; when the steel plate Rtx is higher than the upper limit of the yield strength control of the steel pipe, the plastic strain during pipe-making is measured and reduced for pipe-making; when the steel plate Rtx is lower than the lower limit of the yield strength control of the steel pipe, the plastic strain during pipe-making is measured and increased for pipe-making. Through the above two measures, the present invention can achieve precise control of the yield strength of the steel pipe product, improve the uniformity of the yield strength of the steel pipe product, and reduce the yield strength fluctuation range. 0.5 The method for preparing an oil and gas transportation steel pipe provided by the present invention is improved from two aspects: controlling the yield strength of the steel plate before forming and optimizing the plastic strain during pipe-making (directly related to the expansion ratio). These improvement measures are based on the existing steel pipe preparation process. It should be understood that in addition to the above improvement measures, the method for preparing an oil and gas transportation steel pipe provided by the present invention also includes the conventional steps and corresponding process parameters in the existing steel pipe preparation process, such as ultrasonic plate detection of the steel plate, edge milling, pre-bending, forming, welding, weld inspection (ultrasonic continuous detection, X-ray television inspection), mechanical expansion, flat head, hydrostatic test, chamfering, pipe body inspection (ultrasonic continuous detection, X-ray television inspection), and finished product inspection, etc. The present invention will not elaborate on these here.

[0031] According to the present invention, in the method for preparing an oil and gas transportation steel pipe, in step (3), the method for obtaining the actual expansion ratio includes:

[0032]

[0033] ​When the target Rtxmin ≤ measured Rtx ≤ target Rtxmax, the steel plate before forming is expanded during the mechanical expansion of the pipe manufacturing process (the steel plate before forming is rolled into a barrel shape, then welded, and then the welded steel pipe is mechanically expanded) at an actual expansion rate of k%; where k% is the target expansion rate;

[0034] When the measured Rtx < target Rtxmin, find the point with a strain of x 1 % on the stress-strain curve of the steel plate before forming, satisfying the target Rtxmin ≤ Rtx 1 ≤ target Rtxmax. The steel plate before forming is expanded during the mechanical expansion of the pipe manufacturing process (the steel plate before forming is rolled into a barrel shape, then welded, and then the welded steel pipe is mechanically expanded) at an actual expansion rate of (k + x 1 - x)%;

[0035] When the measured Rtx > target Rtxmax, find the point with a strain of x 2 % on the stress-strain curve of the steel plate before forming, satisfying the target Rtxmin ≤ Rtx 2 ≤ target Rtxmax. The steel plate before forming is expanded during the mechanical expansion of the pipe manufacturing process (the steel plate before forming is rolled into a barrel shape, then welded, and then the welded steel pipe is mechanically expanded) at an actual expansion rate of (k + x 2 - x)%;

[0036] According to the present invention, in the above method for obtaining the actual expansion rate, the limitation on x 1 and x 2 is relatively wide. As long as in the stress-strain curve of the steel plate before forming, the point with a strain of x 1 % satisfies the target Rtxmin ≤ Rtx 1 ≤ target Rtxmax, and the point with a strain of x 2 % satisfies the target Rtxmin ≤ Rtx 2 ≤ target Rtxmax. Among them, the closer the stress Rtx 1 corresponding to x 1 and the stress Rtx 2 corresponding to x 2 is to (target Rtxmin + target Rtxmax) / 2, the more beneficial it is to control the yield strength of the steel pipe product within a narrower range.

[0037] According to the present invention, in the method for manufacturing an oil and gas transmission steel pipe, step (1) further includes: obtaining the target width W 1 of the steel plate required for forming and the plastic strain ε 1 % at the wall thickness center during the pipe manufacturing process; where

[0038] W 1 = (D - t) × π / (1 + k%) – δ;

[0039] ε 1 = k + 100δ / W 1 ;

[0040] D is the outer circumference of the steel pipe to be prepared (unit: mm), t is the wall thickness of the steel pipe to be prepared (unit: mm), k% is the target expansion rate, and δ is the forming extension (unit: mm).

[0041] According to the present invention, considering that the value of 100δ / W is very small, in some embodiments, it can also be roughly considered that ε 1 = k.

[0042] According to the present invention, the target width W 1 is the basis for determining the width and also the basic basis for determining the width of the steel plate before milling in the subsequent step (4). In order to enable the pipe-making strain to be adjusted within a certain range, the steel plate before milling must have a certain width margin.

[0043] According to the present invention, in the method for preparing an oil and gas transmission steel pipe, in step (2), the method-I for obtaining the value of x in the stress characterization parameter Rtx of the steel plate before forming and the lower limit and upper limit values of the target Rtx includes:

[0044] (2-1) Select N steel plate specimens corresponding to the set specifications of the steel pipe to be prepared, and respectively obtain N stress-strain curves corresponding to the steel plate specimens through tensile tests; in each corresponding stress-strain curve, respectively select M steel plate strain values based on a preset interval a% with (ε 1 + Δε)% as the standard to obtain M steel plate stress values corresponding to different strain values; based on the N stress-strain curves corresponding to the steel plate specimens and the M steel plate stress values corresponding to different strain values, with the steel plate stress values corresponding to the same strain value as a group, obtain M groups of different strain values and N steel plate stress values corresponding to each group of the same strain value; where N ≥ 5, M ≥ 3, and Δε is the parameter corresponding to the yield strength selection standard of the steel pipe to be prepared;

[0045] (2-2) Respectively make N steel pipe specimens from the N steel plate specimens corresponding to the set specifications of the steel pipe to be prepared according to the parameters of the steel pipe to be prepared, and obtain N stress-strain curves of the N steel pipe specimens and the yield strength values of the N steel pipe specimens corresponding to a strain value of Δε% through tensile tests;

[0046] (2-3) Based on the N steel plate stress values corresponding to the same strain values obtained and the yield strength values of the N steel pipe specimens corresponding to a strain value of Δε%, M fitting lines are obtained through linear fitting. The fitting line RtΔx = a + b×Steel pipe Rt corresponding to the maximum goodness of fit among the M fitting lines is taken 0.5 The value of Δx in

[0047] as the value of x in the stress characterization parameter Rtx; 0.5 Based on the fitting line RtΔx = a + b×Steel pipe Rt corresponding to the maximum goodness of fit

[0048] the lower limit value and the upper limit value of the target Rtx of the steel plate before forming are calculated; where 0.5min +c 1 ;

[0049] Target Rtxmin = a + b×Target Rt of the steel pipe to be prepared 0.5max +d 1 ;

[0050] where c 1 and d 1 are safety margins.

[0051] According to the present invention, in the method for preparing an oil and gas transmission steel pipe, in step (2), preferably, Δε is 0.5. In the art, since the stress corresponding to a total deformation of 0.5% on the tensile stress-strain curve is usually used as the yield strength, the present invention mainly uses this as the selection criterion for the yield strength of the steel pipe to be prepared.

[0052] According to the present invention, in the method for preparing an oil and gas transmission steel pipe, in step (2-1), preferably, the steel plate specimen is a transverse sampling specimen. In the present invention, the sampling position of the steel plate specimen is the position corresponding to the sampling position of the tensile specimen required by the steel pipe standard, that is, if it is required to sample at the center position of the base material in the circumferential direction of the steel pipe after pipe making, then the steel plate specimen should also be taken from the center of the width of the steel plate. In addition, for materials with good uniformity of the performance of the entire steel plate, sampling can also be performed at other positions, and the present invention does not make special limitations on this.

[0053] According to the present invention, in the method for preparing an oil and gas transmission steel pipe, in step (2-1), preferably, the method for obtaining the M steel plate stress values includes: among the N stress-strain curves corresponding to the steel plate specimens, based on the preset interval a, with ε 1 +Δε as the center, take strain values on both the left and right sides of the center to obtain the corresponding M steel plate stress values;

[0054] where a > 0; M is an odd number;

[0055] According to the present invention, by using the above method to obtain the M steel plate stress values, the relationship between the Rtx of the steel plate before forming and the yield strength of the steel pipe (such as Rt 0.5 ) can be established more efficiently, and a representative Rtx value can be obtained quickly. The above method provided by the present invention is the uniform value-taking method. In addition, the present invention also includes the non-uniform interval value-taking method, that is, asymmetric value-taking. One point can be taken on the left side of ε 1 +Δε, and two points can be taken on the right side. At this time, that is, the minimum value selected on the left side is the strain value corresponding to the yield strength of the steel pipe, and the maximum value selected on the right side does not exceed 5.

[0056] According to the present invention, in the method for preparing the oil and gas transmission steel pipe, in step (2-2), in the tensile test, the selection position of the steel pipe specimen is the same as the selection position of the steel plate specimen, and the selection position is the same end of the steel plate, so as to reduce other cumulative errors between the steel plate in the test and the steel pipe after pipe making. Specifically, the selection of the steel plate specimen and the selection of the steel pipe specimen in the present invention can be sequentially selected at the set end of N base metal steel plates to ensure that the selection positions of the two are at the same end.

[0057] According to the present invention, in the method for preparing the oil and gas transmission steel pipe, in step (2-3), preferably, the method for obtaining the goodness of fit is:

[0058] where x i is the steel plate stress value variable, y i is the steel pipe specimen yield strength value variable, is the average stress corresponding to the same strain value of N steel plates, is the average yield strength corresponding to N steel pipe specimens.

[0059] According to the present invention, in the method for preparing the oil and gas transmission steel pipe, in step (2-3), c 1 ≥0, d 1 ≤0. Preferably, 0 ≤ c 1 ≤20, -20 ≤ d 1 ≤0, which can greatly reduce the risk of deviating from the target value caused by individual data points deviating from the regression curve inevitably during the fitting process, further narrow the range of the target Rtx, and further narrow the fluctuation range of the steel pipe yield strength.

[0060] According to the present invention, in the method for preparing an oil and gas transportation steel pipe, in step (2), in addition to the method-I described in the above steps (2-1), (2-2) and (2-3), the following method-II can also be used to quickly obtain the value of x in the stress characterization parameter Rtx of the steel plate before forming, as well as the lower limit value and the upper limit value of the target Rtx. Specifically:

[0061] The value of x in the stress characterization parameter Rtx of the steel plate before forming = ε 1 + 0.5;

[0062] Target Rtxmin = the target Rt of the steel pipe to be prepared 0.5min + c 2 ;

[0063] Target Rtxmax = the target Rt of the steel pipe to be prepared 0.5max + d 2 ;

[0064] Wherein, c 2 , d 2 are safety margins.

[0065] According to the present invention, in the method-II, c 2 ≥ 0, d 2 ≤ 0. Preferably, 0 ≤ c 2 ≤ 20, -20 ≤ d 2 ≤ 0, which can significantly reduce the risk of deviating from the target value caused by individual data points inevitably deviating from the regression curve during the fitting process, further narrow the range of the target Rtx, and further narrow the fluctuation range of the yield strength of the steel pipe.

[0066] In the present invention, in the method for preparing an oil and gas transportation steel pipe, in step (2), for obtaining the value of x in the stress characterization parameter Rtx of the steel plate before forming, as well as the lower limit value and the upper limit value of the target Rtx, either the above method-I can be used, or method-II can be used. The former has an advantage in terms of accuracy and is more conducive to precisely controlling the yield strength of the steel pipe product. The latter can obtain results more quickly and can also meet the control requirements for the yield strength of the steel pipe product.

[0067] According to the present invention, in the method for preparing an oil and gas transportation steel pipe, in step (3), before preparing the steel plate before forming, obtain the lower limit value W of the preparation width of the steel plate before forming (unmilled) 2 ; Wherein,

[0068] W 2 = (D - t) × π / (1 + k'%) – δ; Wherein, k' = k% - 0.5%;

[0069] Let D be the outer circumference of the steel pipe to be prepared (unit: mm), t be the wall thickness of the steel pipe to be prepared (unit: mm), k% be the target expansion rate, and δ be the forming extension (unit: mm).

[0070] According to the present invention, the lower limit value W of the preparation width of the steel plate (unmilled edge) before forming 2 is to reserve a surplus amount of (k - 0.5)% for the plate width before milling to ensure that the width of the steel plate required for forming can be obtained after milling.

[0071] According to the present invention, in steps (4) and (5) of the method for preparing the oil and gas transmission steel pipe, the milling, forming, welding, and mechanical expansion can all be carried out by using conventional processes and parameters in the art, and the present invention does not make special limitations thereto.

[0072] In the present invention, the yield strength of the steel plate and the steel pipe is measured by the method specified in GB / T 228.1 - 2021 (Metallic materials - Tensile testing - Part 1: Method of test at room temperature).

[0073] The present invention will be described in detail below through examples. In the following examples and comparative examples, unless otherwise specified, the materials used are all ordinary commercially available products.

[0074] Example 1

[0075] Prepare an X80 (D1219×22 mm) steel pipe, and the control range of the yield strength: 555 - 675 MPa

[0076] (1 - 1) The control target of the yield strength of the steel pipe, the lower limit Rt 0.5min = 555 MPa, the upper limit Rt 0.5max = 675 MPa.

[0077] (1 - 2) According to the outer circumference D = 3830 mm, wall thickness t = 22 mm, target expansion rate k% = 0.8%, and forming extension δ = 6 mm of the steel pipe after expansion, it is calculated that:

[0078] The target plate width of the steel plate after milling

[0079] The plastic strain at the wall thickness center during the pipe manufacturing process

[0080] (2) Use Method - I to obtain the value of x in the stress characterization parameter Rtx of the steel plate and the lower limit value and upper limit value of the target Rtx of the steel plate:

[0081] (2-1) Select 30 steel plate specimens corresponding to the set specifications of the steel pipes to be prepared, and obtain 30 stress-strain curves of the corresponding steel plate specimens through tensile tests; in each corresponding stress-strain curve, respectively take 1.5% (ε 1 1.0, Δε 1 being 0.5) as the standard, and select 5 steel plate strain values (0.5%, 1.0%, 1.55%, 2.0%, 2.5%) based on the preset interval a% (a is 0.5) to obtain 5 steel plate stress values (Rt 0.5 、Rt 1.0 、Rt 1.5 、Rt 2.0 、Rt 2.5 ) corresponding to different strain values; based on the 30 stress-strain curves of the corresponding steel plate specimens and the 5 steel plate stress values corresponding to different strain values, take the steel plate stress values corresponding to the same strain value as a group to obtain 5 groups of different strain values and 30 steel plate stress values corresponding to the same strain value in each group (the results are shown in Table 1);

[0082] (2-2) Make the above 30 steel plate specimens corresponding to the set specifications of the steel pipes to be prepared into 30 steel pipe specimens respectively according to the parameters of the steel pipes to be prepared (D1219×22mm), and obtain the stress-strain curves of the 30 steel pipe specimens and the yield strength values Rt 0.5 of the 30 steel pipe specimens through tensile tests (the results are shown in Table 1);

[0083] Table 1

[0084]

[0085]

[0086] (2-3) Input the 30 steel plate stress values corresponding to the same strain value and the yield strength values Rt 0.5 of the 30 steel pipe specimens into the data table of the origin software. Each column of data corresponds to a column in the data table. Take the steel plate stress values (steel plate Rt 0.5 、steel plate Rt 1.0 、steel plate Rt 1.5 、steel plate Rt 2.0 、steel plate Rt 2.5 ) as the Y-axis and the yield strength value Rt 0.5 of the steel pipe specimens as the X-axis to plot a graph, and perform linear fitting through the built-in linear fitting function of the software to obtain the fitting lines (denoted as the first fitting line, the second fitting line, the third fitting line, the fourth fitting line, and the fifth fitting line respectively, as shown in Figure 1 ) and the goodness of fit:

[0087] The first fitting line: steel plate Rt 0.5= 604 - 0.0745 × Steel pipe Rt 0.5 , Goodness of fit R 2 = 0.0035;

[0088] Second fitting line: Steel plate Rt 1.0 = 295 + 0.471 × Steel pipe Rt 0.5 , Goodness of fit R 2 = 0.2938;

[0089] Third fitting line: Steel plate Rt 1.5 = 188 + 0.671 × Steel pipe Rt 0.5 , Goodness of fit R 2 = 0.6532;

[0090] Fourth fitting line: Steel plate Rt 2.0 = 144 + 0.766 × Steel pipe Rt 0.5 , Goodness of fit R 2 = 0.7955;

[0091] Fifth fitting line: Steel plate Rt 2.5 = 237 + 0.634 × Steel pipe Rt 0.5 , Goodness of fit R 2 = 0.6641;

[0092] Among them, the steel plate Rt 2.0 and the steel pipe Rt 0.5 have the best goodness of fit. Therefore, the stress value Rt of the steel plate with the largest goodness of fit 2.0 is used as the stress characterization parameter of the steel plate;

[0093] Based on the linear relationship obtained from the above fitting: Steel plate Rt 2.0 = 144 + 0.766 × Steel pipe Rt 0.5 , substitute the upper and lower limits of the steel pipe yield strength control Rt 0.5max (675 MPa) and Rt 0.5min (555 MPa), and get:

[0094] The target Rt of the steel plate 2.0min = 144 + 0.766 × 555 = 569 MPa;

[0095] The target Rt of the steel plate 2.0max = 144 + 0.766 × 675 = 661 MPa.

[0096] (3) According to the requirement that the expansion rate meets 0.3% - 1.3%, it is calculated that the width of the steel plate should not be less than 3741 mm;

[0097] According to the target Rt of the steel plate 2.0min(569 MPa), the target Rt 2.0max (661 MPa), that is, the target Rt of the steel plate 2.0 The range is 569 - 661 MPa to determine the manufacturing process of the steel plate, and during the production inspection process, optimize and adjust the manufacturing process according to the above target Rt 2.0 range, so that the measured Rt of the manufactured finished steel plate 2.0 falls within the target range of 569 - 661 MPa as much as possible;

[0098] Take a transverse tensile specimen from the above-mentioned manufactured finished steel plate and conduct a tensile test to obtain the stress-strain curve and the measured Rt of the finished steel plate respectively 2.0 (The results are shown in Table 2),

[0099] Table 2

[0100]

[0101]

[0102] Determine the expansion rate during the pipe manufacturing process based on the tensile test results of the finished steel plate in Table 2:

[0103] For the 1# steel plate, Rt 2.0 <569 MPa (i.e., the lower limit of the target Rt 2.0min ), find Rt on the stress-strain curve of the 1# steel plate 2.5 =575 Mpa, 569 MPa < Rt 2.5 <661 MPa, then the 1# steel plate will be expanded at an actual expansion rate of (k + x 1 -x)% = (0.8 + 2.5 - 2.0)% = 1.3% during the subsequent mechanical expansion;

[0104] For the 2#, 3#, 4#, and 5# steel plates, their measured Rt 2.0 all fall within the range of 569 - 661 MPa, then the 2#, 3#, 4#, and 5# steel plates will be expanded at a target expansion rate of 0.8% during the subsequent mechanical expansion;

[0105] For the 6# steel plate, Rt 2.0 >661 MPa (i.e., the upper limit of the target Rt 2.0max ), find Rt on the stress-strain curve of the 6# steel plate 1.7 =650 < 661 MPa, then the 6# steel plate will be expanded at an actual expansion rate of (k + x 2 -x)% = (0.8 + 1.7 - 2.0)% = 0.5% during the subsequent mechanical expansion;

[0106] (4) Based on the actual expansion rates of the 1#, 2#, 3#, 4#, 5#, and 6# steel plates obtained in step (3), calculate the widths of the steel plates after milling, which are respectively:

[0107] 1# steel plate: 3706 mm

[0108] 2#, 3#, 4#, 5# steel plates: 3725 mm

[0109] 6# steel plate: 3735 mm

[0110] According to the above calculations, obtain the actual widths of the steel plates before forming, and adjust the milling process accordingly to ensure that the widths of the steel plates before forming obtained after milling meet the above calculated values.

[0111] (5) Form the above-mentioned steel plates before forming and weld them according to the submerged arc welding process for straight seam pipes to obtain welded pipes; when performing mechanical expansion, use the same expansion parameters for all the above welded pipes to make the outer circumferences of all the expanded steel pipes 3830 mm, and perform post-treatment after expansion to obtain oil and gas transmission steel pipes.

[0112] Take tensile specimens from the above-prepared oil and gas transmission steel pipes for tensile property tests. The results are shown in Table 3, and the yield strengths of all the pipes fall within the target control range of 555 - 675 MPa.

[0113] Table 3

[0114] Steel pipe number <![CDATA[Rt 0.5 > 1# (made from 1# steel plate) 573 2# (made from 2# steel plate) 620 3# (made from 3# steel plate) 600 4# (made from 4# steel plate) 615 5# (made from 5# steel plate) 595 6# (made from 6# steel plate) 645

[0115] Example 2

[0116] Prepare X70 (D1016×17.5 mm) steel pipes, and the control range of yield strength: 485 - 585 MPa

[0117] (1-1) The lower limit Rt of the target control of the yield strength of the steel pipe 0.5min = 485 MPa, and the upper limit Rt 0.5max = 585 MPa.

[0118] (1-2) According to the outer circumference D = 3192 mm, wall thickness t = 17.5 mm, target expansion rate 0.9%, and forming extension 5 mm of the steel pipe after expansion, calculate to obtain:

[0119] The target plate width of the steel plate after milling

[0120] The plastic strain at the wall thickness center during the pipe manufacturing process

[0121] (2) Use Method-II to obtain the value of x in the stress characterization parameter Rtx of the steel plate and the lower limit and upper limit of the target Rtx of the steel plate:

[0122] The value of x in the stress characterization parameter Rtx of the steel plate = ε 1 +0.5=1.06+0.5=1.56, so choose Rt 1.56 As the stress characterization parameter of the steel plate; the calculation results are:

[0123] Target Rt of steel plate 1.56min =Rt 0.5min +10(safety margin)=485+10=495MPa;

[0124] Target Rt of steel plate 1.56max =Rt 0.5max -10(safety margin)=585-10=575MPa;

[0125] (3) According to the requirement that the expansion rate meets the requirement of 0.4%-1.4%, it is calculated that the steel plate width should be no less than 3118mm;

[0126] According to the target Rt of the steel plate 1.56min (495MPa), target Rt 1.56max (575MPa), which is the target Rt of the steel plate 1.56 The range is 495-575MPa to determine the steel plate manufacturing process, and according to the above target Rt during the production inspection process 1.56 The scope is used to optimize and adjust the manufacturing process so that the measured Rt of the finished steel plate is 1.56 As far as possible, it should be within the target range of 495-575MPa;

[0127] Take transverse tensile specimens from the finished steel plate obtained above and conduct tensile tests to obtain the stress-strain curve and measured Rt of the finished steel plate. 1.56 (The results are shown in Table 4),

[0128] Table 4

[0129] Finished steel plate number <![CDATA[Measured Rt 1.56 > 7# 486 8# 515 9# 520 10# 580

[0130] Based on the tensile test results of the finished steel plate in Table 4, determine the expansion rate of the pipe making process:

[0131] For 7# steel plate, Rt 1.56 <495MPa(i.e. target Rt 1.56min lower limit), find Rt on the stress-strain curve of 7# steel plate 1.9 =496Mpa,495MPa<Rt 1.9 <575MPa, then the actual expansion rate of 7# steel plate in subsequent mechanical expansion is (k+x 1 -x)%=(0.9+1.9-1.56)%=1.24% for diameter expansion; ​​​​​​

[0132] For steel plates No. 8 and No. 9, their measured Rt 1.56 all fall within the range of 495 - 575 MPa. Then, steel plates No. 8 and No. 9 are expanded according to the target expansion rate of 0.9% during subsequent mechanical expansion;

[0133] For steel plate No. 10, Rt 1.56 > 575 MPa (i.e., the upper limit value of the target Rt 1.56max ). Find Rt 1.2 = 570 < 575 MPa on the stress-strain curve of steel plate No. 10. Then, steel plate No. 10 is expanded according to the actual expansion rate of (k + x 2 - x)% = (0.9 + 1.2 - 1.56)% = 0.54% during subsequent mechanical expansion;

[0134] (4) According to the actual expansion rates of steel plates No. 7, No. 8, No. 9, and No. 10 obtained in step (3), calculate the widths of the plates after edge milling, which are respectively:

[0135] Steel plate No. 7: 3092 mm

[0136] Steel plates No. 8 and No. 9: 3102 mm

[0137] Steel plate No. 10: 3113 mm

[0138] According to the actual widths of the plates before forming calculated above, adjust the edge milling process so that the widths of the plates before forming obtained after edge milling meet the above calculated values.

[0139] (5) Form the above plates before forming and weld them according to the submerged arc welding process for straight seam pipes to obtain welded pipes; during mechanical expansion, use the same expansion parameters for all the above welded pipes so that the outer circumferences of all the expanded pipes are 3192 mm. After expansion, perform post-treatment to obtain oil and gas transmission pipes.

[0140] Take tensile specimens from the above-prepared oil and gas transmission pipes for tensile property tests. The results are shown in Table 5,

[0141] The yield strengths of all the pipes all fall within the target control range of 485 - 585 MPa.

[0142] Table 5

[0143] Steel pipe number <![CDATA[Rt 0.5 > 7# (made from 7# steel plate) 500 8# (made from 8# steel plate) 519 9# (made from 9# steel plate) 530 10# (made from 10# steel plate) 565

[0144] As can be seen from the above Examples 1 and 2, by using the method for preparing oil and gas transmission steel pipes provided by the present invention, the yield strength of the obtained steel pipes can fall within the target control range, effectively solving the problem of large fluctuation range of the yield strength of oil and gas transmission steel pipes, and further realizing the improvement of the pipeline coordination deformation ability, enhancing the safety of oil and gas pipelines, and meeting the requirements of high-quality development of oil and gas pipelines for high-performance uniform steel pipe products.

[0145] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a steel pipe for oil and gas transportation, characterized in that: include: (1) Determine the yield strength control target of the steel pipe to be prepared, and the target lower limit of the yield strength is Rt 0.5min , the target upper limit of yield strength is Rt 0.5max ; (2) Obtaining the value of x in the stress characterization parameter Rtx of the steel plate before forming, and calculating the target lower limit value Rt of the yield strength of the steel pipe to be prepared according to the target lower limit value Rt 0.5min and the target upper limit value of yield strength Rt 0.5max Obtaining a lower limit value and an upper limit value of the target Rtx of the steel plate before forming, wherein the lower limit value is the target Rtxmin, and the upper limit value is the target Rtxmax; wherein Rtx is the stress value corresponding to the total strain of x% on the stress-strain curve obtained by the tensile test of the steel plate before forming; (3) determining a steel plate manufacturing process according to the target Rtx, preparing and obtaining the pre-formed steel plate, and performing a tensile test on the pre-formed steel plate to obtain a stress-strain curve and an actually measured Rtx of the pre-formed steel plate; and obtaining an actual diameter expansion rate of the pre-formed steel plate during the pipe making process according to a quantitative relationship between the actually measured Rtx and the target Rtx of the pre-formed steel plate; (4) calculating the width of the steel plate required for forming according to the actual diameter expansion rate, and milling the pre-forming steel plate according to the width of the steel plate required for forming to obtain the steel plate required for forming; (5) forming and welding the steel plates required for the forming, and mechanically expanding the diameters of all welded pipes obtained by welding using the same expansion parameters to obtain oil and gas transportation steel pipes.

2. The method according to claim 1, wherein: In step (3), the method for obtaining the actual diameter expansion rate includes: When the target Rtxmin≤measured Rtx≤target Rtxmax, the steel plate before forming is expanded in the mechanical expansion process of the pipe making process according to the actual expansion rate k%, wherein k% is the target expansion rate; When the measured Rtx is less than the target Rtxmin, a point with a strain of x1% is found on the stress-strain curve of the steel plate before forming, satisfying the target Rtxmin≤Rtx1≤target Rtxmax, and the steel plate before forming is expanded in the mechanical expansion process of the pipe making process according to the actual expansion rate of (k+x1-x)%; When the measured Rtx>target Rtxmax, a point with a strain of x2% is found on the stress-strain curve of the steel plate before forming to satisfy the target Rtxmin≤Rtx2≤target Rtxmax. The steel plate before forming is expanded according to the actual expansion rate of (k+x2-x)% during the mechanical expansion in the pipe making process.

3. The method according to claim 1 or 2, wherein: Step (1) also includes: obtaining the target width W1 of the steel plate required for forming and the target plastic strain ε1% at the center of the wall thickness during the pipe making process; wherein, W1=(Dt)×π / (1+k%)–δ; ε1=k+100δ / W1; D is the outer circumference of the steel pipe to be prepared, t is the wall thickness of the steel pipe to be prepared, k% is the target diameter expansion rate, and δ is the forming extension.

4. The method according to claim 3, wherein: In step (2), the method for obtaining the value of x in the stress characterization parameter Rtx of the steel plate before forming and the lower limit value and the upper limit value of the target Rtx includes: (2-1) Selecting N steel plate specimens of set specifications corresponding to the steel pipe to be prepared, and obtaining N stress-strain curves of the corresponding steel plate specimens through tensile tests; selecting M steel plate strain values ​​based on a preset interval a% based on (ε1+Δε)% as the standard in each corresponding stress-strain curve to obtain M steel plate stress values ​​corresponding to different strain values; based on the stress-strain curves of the N corresponding steel plate specimens and the M steel plate stress values ​​corresponding to different strain values, taking the steel plate stress values ​​corresponding to the same strain value as a group, obtaining M groups of different strain values ​​and N steel plate stress values ​​corresponding to each group of the same strain value; wherein N≥5, M≥3, and Δε is a parameter corresponding to the yield strength selection standard of the steel pipe to be prepared; (2-2) The N steel plate samples of the set specifications corresponding to the steel pipe to be prepared are respectively made into N steel pipe samples according to the parameters of the steel pipe to be prepared, and the stress-strain curves of the N steel pipe samples and the yield strength values ​​of the N steel pipe samples corresponding to the strain value of Δε% are obtained through tensile tests; (2-3) Based on the obtained N stress values ​​of the steel plate corresponding to the same strain value and the yield strength values ​​of the N steel pipe samples corresponding to the strain value of Δε%, M fitting straight lines are obtained by straight line fitting, and the fitting straight line RtΔx=a+b×steel pipe Rt corresponding to the largest goodness of fit among the M fitting straight lines is 0.5 Δx in is used as the value of x in the stress characterization parameter Rtx; The fitting straight line RtΔx=a+b×steel pipe Rt corresponding to the maximum goodness of fit 0.5 , calculate the lower limit and upper limit of the target Rtx of the steel plate before forming; wherein, Target Rtxmin = a + b × target Rt of the steel pipe to be prepared 0.5min +c1; Target Rtxmax = a + b × target Rt of the steel pipe to be prepared 0.5max +d1; Among them, c1 and d1 are safety margins.

5. The method according to claim 4, wherein: Δε is 0.5; And / or, in step (2-1), the steel plate sample is a transverse sampling sample; And / or, in step (2-1), the method for obtaining the M steel plate stress values ​​comprises: in the stress-strain curves of the N corresponding steel plate specimens, based on the preset interval a, taking ε1+Δε as the center, taking strain values ​​to obtain the corresponding M steel plate stress values; Wherein, a>0; M is an odd number; 6. According to the method of claim 4 or 5, in step (2-3), the method for obtaining the goodness of fit is: in, x i is the stress value variable of the steel plate, y i is the yield strength value variable of the steel pipe specimen, is the average stress value corresponding to the same strain value of N steel plates, is the average yield strength corresponding to N steel pipe specimens.

7. The method according to claim 4 or 5, wherein in step (2-3), 0≤c1≤20; -20≤d1≤0.

8. The method according to claim 3, wherein: In step (2), the method for obtaining the value of x in the stress characterization parameter Rtx of the steel plate before forming and the lower limit value and the upper limit value of the target Rtx includes: The value of x in the stress characterization parameter Rtx of the steel plate before forming = ε1 + 0.5; Target Rtxmin = target Rt of the steel pipe to be prepared 0.5min +c2; Target Rtxmax = target Rt of the steel pipe to be produced 0.5max +d2; Among them, c2 and d2 are safety margins.

9. The method according to claim 8, wherein: 0≤c2≤20;-20≤d2≤0.

10. The method according to claim 1 or 2, wherein: In step (3), before preparing the pre-formed steel plate, a lower limit value W2 of the preparation width of the pre-formed steel plate is obtained; wherein, W2=(Dt)×π / (1+k'%)–δ;wherein, k'%=k%-0.5%; D is the outer circumference of the steel pipe to be prepared, t is the wall thickness of the steel pipe to be prepared, k% is the target diameter expansion rate, and δ is the forming extension.

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