Method for preparing oil and gas conveying steel pipes

Abstract

A method for preparing oil and gas conveying steel pipes. The method comprises: (1) determining a yield strength control target of a steel pipe to be prepared; (2) obtaining the numerical value of x in a stress characterization parameter R TX of a steel plate before forming and, according to the yield strength control target of the steel pipe to be prepared, obtaining a target R TX of the steel plate before forming; (3) according to the target R TX, preparing the steel plate before forming and, according to the numerical relationship between an actually measured R TX and the target R TX of the steel plate before forming, obtaining the actual diameter expansion rate of the steel plate before forming during pipe manufacturing; (4) according to the actual diameter expansion rate, performing edge milling to obtain a steel plate required for forming; and (5) performing forming and welding on the steel plate required for forming, and using the same diameter expansion parameters to perform mechanical diameter expansion on all the welded pipes obtained by welding so as to obtain the oil and gas conveying steel pipes. The steel pipes prepared from said method have a narrow yield strength fluctuation range.

Description

Method for preparing oil and gas transportation steel pipe

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Chinese patent application No. 202311552753.9, filed on November 20, 2023, entitled “Method for Preparing Oil and Gas Transportation Steel Pipes,” the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of oil and gas transportation steel pipes, and in particular to a method for preparing oil and gas transportation steel pipes. Background Art

[0004] Oil and gas pipelines are the most economical and efficient means of transporting oil and natural gas over large, long distances. With rapid economic development, China's oil and gas pipeline construction has surged. To date, my country has built 150,000 kilometers of long-distance oil and gas pipelines, but this still falls short of demand. For some time to come, my country will continue to experience a peak in pipeline construction.

[0005] Yield strength is one of the most important properties of steel pipes for oil and gas transportation. It not only determines the pipeline's pressure-bearing capacity but also has a significant impact on the pipeline's strain capacity and girth weld strength matching. When the yield strength of a steel pipe fluctuates significantly, the lower-strength steel pipe will experience greater strain when the pipe is subjected to stress and deformation, while the higher-strength steel pipe has not yet begun to strain, resulting in a reduction in the pipeline's overall coordinated strain capacity. Furthermore, when the yield strength of a steel pipe fluctuates significantly, the girth weld must exceed the upper yield strength limit to achieve overstrength matching, increasing the difficulty of girth weld preparation and the risk of girth weld failure due to understrength matching. These factors can have a serious adverse impact on pipeline safety. Therefore, oil and gas pipeline standards set upper and lower limits for the yield strength of steel pipes. The more important the pipeline, the stricter the yield strength fluctuation range. For example, for X80 steel pipe, the API Spec 5L standard specifies a yield strength range of 555-705 MPa, the technical requirements for the West-East Gas Pipeline II specify a yield strength range of 555-690 MPa, and the technical requirements for the China-Russia East Line specify a yield strength range of 555-675 MPa. For submarine pipelines and high-strain pipelines, the yield strength fluctuation range of steel pipes is generally required to be within 100 MPa. Strictly controlling yield strength fluctuations and narrowing the yield strength range are the development trends of oil and gas pipeline steel pipe products. With the increasing safety requirements for oil and gas pipelines, higher requirements are being placed on the quality and performance consistency of steel pipe products, and higher requirements are being placed on the yield strength control level of steel pipe products.

[0006] The yield strength of steel pipes is influenced by multiple complex factors, including the chemical composition of the raw materials, the manufacturing process, and the pipe-making process. Traditionally, the yield strength of steel pipes has been controlled by first establishing yield strength requirements for the steel plate. However, due to the complexity of the chemical composition, rolling process, and accelerated cooling process involved in the steel plate manufacturing process, controlling the yield strength of the steel plate is difficult and subject to wide fluctuations. Furthermore, the yield strength of the material undergoes significant changes during the LSAW pipe-making process, a change that is influenced by inherent material factors and has little correlation with the material's yield strength value. Consequently, controlling the yield strength of the steel plate alone cannot fully achieve the desired effect, resulting in significant fluctuations in the yield strength of the steel pipe.

[0007] Currently, achieving a stable yield strength of 120 MPa for oil and gas pipelines remains challenging, making it difficult to meet the higher requirements for uniform yield strength. Therefore, providing a new method for preparing oil and gas pipelines to improve yield strength uniformity is crucial for achieving high-quality development of oil and gas pipelines. Summary of the Invention

[0008] The present invention aims to solve the problem that existing oil and gas transmission steel pipes have a large fluctuation range of yield strength and poor uniformity, which in turn affects the safety of oil and gas pipelines, and provides a method for preparing oil and gas transmission steel pipes.

[0009] In order to achieve the above object, the present invention provides a method for preparing an oil and gas transportation steel pipe, comprising:

[0010] (1) Determine the yield strength control target of the steel pipe to be prepared. The target lower limit of the yield strength is Rt 0.5min , the target upper limit of yield strength is Rt 0.5max ;

[0011] (2) Obtain the value of x in the stress characterization parameter Rtx of the steel plate before forming, and calculate 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 of yield strength Rt 0.5max Obtaining a lower limit value and an upper limit value of a target Rtx of the steel plate before forming, wherein the lower limit value is a target Rtxmin and the upper limit value is a target Rtxmax; wherein Rtx is a stress value corresponding to a total strain of x% on a stress-strain curve obtained by a tensile test of the steel plate before forming;

[0012] (3) determining a steel plate manufacturing process based on 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 a 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 based on a quantitative relationship between the measured Rtx and the target Rtx of the pre-formed steel plate;

[0013] (4) Calculating the width of the steel plate required for forming based on 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;

[0014] (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 transmission steel pipes.

[0015] Through the above technical solution, the present invention can achieve the following beneficial effects:

[0016] (1) The method for preparing an oil and gas transmission steel pipe provided by the present invention can effectively reduce the fluctuation range of the yield strength of the steel pipe and control the yield strength of the steel pipe within a narrower range. After welding and connecting multiple steel pipes prepared by the method provided by the present invention into a pipeline, when the pipeline is strained by external force, different steel pipes can enter the strain state at the same time, avoiding the strain concentration on a certain steel pipe, greatly improving the coordinated deformation ability of the pipeline and enhancing the safety of the oil and gas pipeline;

[0017] (2) The method for preparing an oil and gas transmission steel pipe provided by the present invention is conducive to further compressing the upper limit of the yield strength of the steel pipe, thereby reducing the difficulty of high-strength matching during girth weld welding, which is conducive to achieving high-strength matching of the pipeline girth weld, reducing the probability of girth weld failure, and improving the safety of the oil and gas pipeline;

[0018] (3) The method for preparing oil and gas transportation steel pipe provided by the present invention adopts the steel plate stress characterization parameter instead of the steel plate Rt 0.5 , and controlling the change of yield strength by adjusting the strain in the pipe making process is less difficult, more reliable and more economical than the traditional method of ensuring the yield strength range of steel pipes by proposing stricter requirements on the yield strength range of steel plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0020] FIG1 is a first fitted straight line graph of the stress value of the steel plate and the yield strength value of the steel pipe sample in Example 1 of the present invention.

[0021] FIG2 is a second fitted straight line graph of the steel plate stress value and the steel pipe sample yield strength value in Example 1 of the present invention.

[0022] FIG3 is a third fitted straight line graph of the stress value of the steel plate and the yield strength value of the steel pipe sample in Example 1 of the present invention.

[0023] FIG4 is a fourth fitted straight line graph of the stress value of the steel plate and the yield strength value of the steel pipe sample in Example 1 of the present invention.

[0024] FIG5 is a fifth fitted straight line graph of the stress value of the steel plate and the yield strength value of the steel pipe sample in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0026] 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 used to illustrate and explain the present invention and are not intended to limit the present invention.

[0027] The present invention provides a method for preparing a steel pipe for oil and gas transportation, comprising:

[0028] (1) Determine the yield strength control target of the steel pipe to be prepared. The target lower limit of the yield strength is Rt 0.5min , the target upper limit of yield strength is Rt 0.5max ;

[0029] (2) Obtain the value of x in the stress characterization parameter Rtx of the steel plate before forming, and calculate 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 of yield strength Rt 0.5max Obtaining a lower limit value and an upper limit value of a target Rtx of the steel plate before forming, wherein the lower limit value is a target Rtxmin and the upper limit value is a target Rtxmax; wherein Rtx is a stress value corresponding to a total strain of x% on a stress-strain curve obtained by a tensile test of the steel plate before forming;

[0030] (3) determining a steel plate manufacturing process based on 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 a 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 based on a quantitative relationship between the measured Rtx and the target Rtx of the pre-formed steel plate;

[0031] (4) Calculating the width of the steel plate required for forming based on 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;

[0032] (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 transmission steel pipes.

[0033] The method for preparing oil and gas transmission steel pipe provided by the present invention adopts 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. 0.5 Therefore, after adopting Rtx, the guidance and timeliness of the steel plate manufacturing process are stronger, which is conducive to obtaining a narrower tensile performance control range. According to the yield strength control target of the steel pipe to be prepared and the target plastic strain ε1% at the center of the wall thickness during the pipe making process, the target Rtx of the steel plate is determined and used as the tensile performance requirement of the steel plate to guide the production of the steel plate and the optimization of tensile properties. However, since the factors affecting the yield strength of the steel plate include complex factors such as chemical composition, rolling, and heat treatment process, 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 by controlling the yield strength of the steel plate alone. In the pipe making process, the plastic strain of the material has a significant effect on the yield strength of the steel pipe. Increasing the plastic strain of the pipe making process can increase the yield strength of the steel pipe, while reducing the plastic strain of the pipe making process can reduce the yield strength of the steel pipe. Therefore, the yield strength of the steel pipe can be further adjusted and controlled by adjusting the plastic strain of the pipe making process. According to steel plate Rtx≈steel pipe yield strength Rt 0.5 Based on this principle, when the steel plate Rtx falls within the steel pipe's yield strength control range, pipe production is carried out according to the target plastic strain ε1%. When the steel plate Rtx exceeds the upper control limit for the steel pipe's yield strength, the plastic strain is calculated and reduced before pipe production begins. When the steel plate Rtx falls below the lower control limit for the steel pipe's yield strength, the plastic strain is calculated and increased before pipe production begins. Through these two measures, the present invention achieves precise control of the steel pipe's yield strength, improves its yield strength uniformity, and reduces yield strength fluctuations.

[0034] The method for preparing oil and gas transportation steel pipes provided by the present invention is improved from two perspectives: controlling the yield strength of the steel plate before forming and optimizing the plastic strain of the pipe (directly related to the diameter expansion rate). These improvement measures are based on the existing steel pipe preparation process. It should be understood that in addition to the above-mentioned improvement measures, the method for preparing oil and gas transportation steel pipes provided by the present invention also includes conventional steps and corresponding process parameters in the existing steel pipe preparation process, such as ultrasonic plate probing, milling, pre-bending, forming, welding, weld inspection (ultrasonic continuous probing, X-ray television inspection), mechanical diameter expansion, flat head, water pressure test, chamfering, pipe body inspection (ultrasonic continuous probing, X-ray television inspection) and finished product inspection, etc. The present invention will not go into details here.

[0035] According to the present invention, in the method for preparing the oil and gas transportation steel pipe, in step (3), the method for obtaining the actual diameter expansion rate includes:

[0036] When the target Rtxmin≤measured Rtx≤target Rtxmax, the pre-formed steel plate is expanded according to the actual expansion rate k% during the mechanical expansion process of the pipe making process (the pre-formed steel plate is rolled into a barrel shape, then welded, and the welded steel pipe is mechanically expanded); where k% is the target expansion rate;

[0037] 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 pre-formed steel plate, satisfying the target Rtxmin≤Rtx1≤target Rtxmax. The pre-formed steel plate is expanded according to the actual expansion rate of (k+x1-x)% during the mechanical expansion process of the pipe making process (the pre-formed steel plate is rolled into a barrel shape, then welded, and the welded steel pipe is mechanically expanded);

[0038] When the measured Rtx>target Rtxmax, a point with a strain of x2% is found on the stress-strain curve of the pre-formed steel plate to satisfy the target Rtxmin≤Rtx2≤target Rtxmax. The pre-formed steel plate is expanded according to the actual expansion rate of (k+x2-x)% during the mechanical expansion in the pipe making process (the pre-formed steel plate is rolled into a barrel shape, then welded, and the welded steel pipe is mechanically expanded).

[0039] According to the present invention, in the above-mentioned method for obtaining the actual diameter expansion rate, the limits for x1 and x2 are relatively loose. As long as, in the stress-strain curve of the steel plate before forming, the point with a strain of x1% satisfies the target Rtxmin≤Rtx1≤target Rtxmax, and the point with a strain of x2% satisfies the target Rtxmin≤Rtx2≤target Rtxmax. The closer the stress Rtx1 corresponding to x1 and the stress Rtx2 corresponding to x2 are to (target Rtxmin+target Rtxmax) / 2, the more conducive it is to controlling the yield strength of the steel pipe product within a narrower range.

[0040] According to the present invention, in the method for preparing an oil and gas transmission steel pipe, step (1) further includes: obtaining a target width W1 of the steel plate required for forming and a 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;

[0041] 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 elongation.

[0042] According to the present invention, since the value of 100δ / W is very small, in some embodiments, it can be roughly considered that ε1=k.

[0043] According to the present invention, the target width W1 is used as a reference for determining the width and is 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.

[0044] According to the present invention, in the method for preparing an oil and gas transportation 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 value and upper limit value of the target Rtx includes:

[0045] (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% with (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, grouping the steel plate stress values ​​corresponding to the same strain value to obtain 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;

[0046] (2-2) N steel plate specimens of set specifications corresponding to the steel pipe to be prepared are respectively made into N steel pipe specimens according to the parameters of the steel pipe to be prepared, and stress-strain curves of the N steel pipe specimens and yield strength values ​​of the N steel pipe specimens corresponding to the strain value of Δε% are obtained through tensile testing;

[0047] (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 specimens corresponding to the strain value Δε%, M fitting straight lines are obtained by linear fitting, and the fitting straight line corresponding to the largest goodness of fit among the M fitting straight lines is RtΔx=a+b×steel pipe Rt 0.5 The Δx in is used as the value of x in the stress characterization parameter Rtx;

[0048] 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,

[0049] Target Rtxmin = a + b × target Rt of the steel pipe to be produced 0.5min +c1;

[0050] Target Rtxmax = a + b × target Rt of the steel pipe to be produced 0.5max +d1;

[0051] Among them, c1 and d1 are safety margins.

[0052] According to the present invention, in the method for preparing a steel pipe for oil and gas transportation, in step (2), preferably, Δε is 0.5. In the art, the stress corresponding to a total deformation of 0.5% on a tensile stress-strain curve is generally used as the yield strength, so the present invention primarily uses this as the criterion for selecting the yield strength of the steel pipe to be prepared.

[0053] According to the present invention, in the method for preparing a steel pipe for oil and gas transportation, in step (2-1), the steel plate sample is preferably a transverse sampling sample. In the present invention, the sampling position of the steel plate sample corresponds to the sampling position of the tensile test specimen required by the steel pipe standard. That is, if sampling is required at the center of the parent material in the circumferential direction of the steel pipe after pipe production, the steel plate sample should also be taken from the center of the steel plate width. In addition, for materials with relatively good performance uniformity throughout the entire steel plate, sampling can also be performed at other locations, and the present invention does not specifically limit this.

[0054] According to the present invention, in the method for preparing the oil and gas transmission steel pipe, in step (2-1), preferably, the method for obtaining the stress values ​​of the M steel plates includes: 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 the stress values ​​of the M steel plates on the left and right sides of the center respectively. strain values ​​to obtain the corresponding M steel plate stress values;

[0055] Wherein, a>0; M is an odd number;

[0056] According to the present invention, the above method is used to obtain the M steel plate stress values, which can more efficiently establish the steel plate Rtx before forming and the steel pipe yield strength (such as Rt 0.5 ) to quickly obtain a representative Rtx value. The present invention provides the above method as a uniform value method. In addition, the present invention also includes an unequal interval value method, that is, an asymmetric value method, which can take one point on the left side of ε1+Δε and two points on its right side. In this case, 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.

[0057] According to the present invention, in the method for manufacturing a steel pipe for oil and gas transportation, in step (2-2), during the tensile test, the steel pipe sample is selected at the same location as the steel plate sample, and both locations are selected from the same end of the steel plate, thereby reducing other cumulative errors between the steel plate under test and the steel pipe after pipe production. Specifically, the steel plate sample and the steel pipe sample in the present invention can be selected sequentially from the set ends of N parent steel plates to ensure that the two locations are selected from the same end.

[0058] According to the present invention, in the method for preparing an oil and gas transportation steel pipe, in step (2-3), preferably, the method for obtaining the goodness of fit is:

[0059] Among them, 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.

[0060] According to the present invention, in the method for preparing a steel pipe for oil and gas transportation, in step (2-3), c1 ≥ 0, d1 ≤ 0. Preferably, 0 ≤ c1 ≤ 20, -20 ≤ d1 ≤ 0. This can significantly reduce the risk of deviation 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.

[0061] According to the present invention, in the method for preparing the 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 and the lower limit and upper limit of the target Rtx, specifically:

[0062] The value of x in the stress characterization parameter Rtx of the steel plate before forming is equal to ε1+0.5;

[0063] Target Rtxmin = target Rt of the steel pipe to be produced 0.5min +c2;

[0064] Target Rtxmax = target Rt of the steel pipe to be produced 0.5max +d2;

[0065] Among them, c2 and d2 are safety margins.

[0066] According to the present invention, in Method-II, c2 ≥ 0, d2 ≤ 0. Preferably, 0 ≤ c2 ≤ 20, -20 ≤ d2 ≤ 0. This can significantly reduce the risk of deviation from the target value caused by the inevitable deviation of individual data points 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.

[0067] In the present invention, in the method for preparing the 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 and the lower limit and upper limit of the target Rtx, either the above-mentioned method-I or method-II can be used. The former has an advantage in accuracy and is more conducive to precise control of the yield strength of the steel pipe product, while the latter can obtain results more quickly and can also meet the control requirements for the yield strength of the steel pipe product.

[0068] According to the present invention, in the method for preparing an oil and gas transmission steel pipe, in step (3), before preparing the pre-formed steel plate, the lower limit value W2 of the preparation width of the pre-formed steel plate (without milling edge) is obtained; wherein,

[0069] W2 = (Dt) × π / (1 + k'%) - δ; where k'% = k% - 0.5%;

[0070] 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 elongation.

[0071] According to the present invention, the lower limit value W2 of the preparation width of the steel plate (without milling) before forming is to reserve a surplus of (k-0.5)% of the plate width before milling to ensure that the width of the steel plate required for forming can be obtained after milling.

[0072] According to the present invention, in the method for preparing the oil and gas transmission steel pipe, in step (4) and step (5), the milling, forming, welding and mechanical expansion can be implemented using conventional processes and parameters in the field, and the present invention does not impose any special restrictions on this.

[0073] 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 (Tensile testing of metallic materials - Part 1: Room temperature test method).

[0074] The present invention will be described in detail below through examples. In the following examples and comparative examples, unless otherwise specified, all methods are conventional; and all reagents and materials used, unless otherwise specified, can be obtained from commercial sources.

[0075] Example 1

[0076] Preparation of X80 (D1219×22mm) steel pipe, the yield strength control range is: 555-675MPa.

[0077] (1-1) Steel pipe yield strength control target, lower limit Rt 0.5min =555MPa, upper limit Rt 0.5max =675MPa.

[0078] (1-2) Based on the outer circumference of the expanded steel pipe D = 3830 mm, wall thickness t = 22 mm, target expansion rate k% = 0.8%, and forming extension δ = 6 mm, the following is calculated:

[0079] Target plate width after milling

[0080] Plastic strain at the center of wall thickness during pipe making

[0081] (2) Method-1 is used to obtain the value of x in the stress characterization parameter Rtx of the steel plate and the lower and upper limits of the target Rtx of the steel plate:

[0082] (2-1) 30 steel plate specimens of set specifications corresponding to the steel pipes to be prepared are selected, and 30 stress-strain curves of the corresponding steel plate specimens are obtained by tensile tests; in each corresponding stress-strain curve, 5 steel plate strain values ​​(0.5%, 1.0%, 1.55%, 2.0%, and 2.5%) are selected based on a preset interval a% (a is 0.5) with 1.5% (ε1 is 1.0, Δε1 is 0.5) as the standard to obtain 5 steel plate stress values ​​(Rt 0.5 , Rt 1.0 , Rt 1.5 , Rt 2.0 , Rt 2.5 ); Based on the stress-strain curves of 30 corresponding steel plate specimens and the 5 steel plate stress values ​​corresponding to different strain values, the steel plate stress values ​​corresponding to the same strain value were grouped together to obtain 5 groups of different strain values ​​and 30 steel plate stress values ​​corresponding to each group of the same strain value (results are shown in Table 1);

[0083] (2-2) The 30 steel plate specimens corresponding to the set specifications of the steel pipe to be prepared are respectively made into 30 steel pipe specimens according to the parameters of the steel pipe to be prepared (D1219×22mm). The stress-strain curves and yield strength values ​​Rt of the 30 steel pipe specimens are obtained through tensile tests. 0.5 (The results are shown in Table 1);

[0084] Table 1

[0085] (2-3) The obtained 30 steel plate stress values ​​corresponding to the same strain value and the yield strength values ​​Rt of 30 steel pipe samples 0.5 Input the data table of origin software, each column of data corresponds to a column in the data table, respectively with the stress value of steel plate (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 ) is the Y axis, the yield strength value Rt of the steel pipe sample 0.5 Draw a graph for the X-axis and perform linear fitting using the software's built-in linear fitting function to obtain the fitting straight lines (respectively recorded as the first fitting straight line, the second fitting straight line, the third fitting straight line, the fourth fitting straight line, and the fifth fitting straight line, as shown in Figure 1) and the goodness of fit:

[0086] The first fitting line: steel plate Rt 0.5 =604-0.0745×steel pipe Rt 0.5 , goodness of fit R 2 =0.0035;

[0087] Second fitting straight line: steel plate Rt 1.0 =295+0.471×steel pipe Rt 0.5 , goodness of fit R 2 =0.2938;

[0088] The third fitting line: steel plate Rt 1.5 =188+0.671×steel pipe Rt 0.5 , goodness of fit R 2 =0.6532;

[0089] Fourth fitting line: steel plate Rt 2.0 =144+0.766×steel pipe Rt 0.5 , goodness of fit R 2 =0.7955;

[0090] Fifth fitting straight line: steel plate Rt 2.5 =237+0.634×steel pipe Rt 0.5 , goodness of fit R 2 =0.6641;

[0091] Among them, steel plate Rt 2.0 With steel pipe Rt 0.5 With the best goodness of fit, the stress value of the steel plate with the largest goodness of fit Rt is used. 2.0 As a stress characterization parameter of the steel plate;

[0092] Based on the linear relationship obtained by the above fitting: Steel plate Rt 2.0=144+0.766×steel pipe Rt 0.5 , substitute the upper and lower limits Rt of the steel pipe yield strength control 0.5max (675MPa) and Rt 0.5min (555MPa), we get:

[0093] Target Rt of steel plate 2.0min =144+0.766×555=569MPa;

[0094] Target Rt of steel plate 2.0max =144+0.766×675=661MPa.

[0095] (3) According to the requirement that the diameter expansion rate meets 0.3%-1.3%, it is calculated that the steel plate width should be no less than 3741mm;

[0096] According to the target Rt of the steel plate 2.0min (569MPa), target Rt 2.0max (661MPa), which is the target Rt of the steel plate 2.0 The range is 569-661MPa to determine the steel plate manufacturing process, and in the production inspection process according to the above target Rt 2.0 The manufacturing process is optimized and adjusted within a certain range so that the measured Rt of the finished steel plate is within the range of 2.0 As far as possible, it should fall within the target range of 569-661 MPa;

[0097] Take the transverse tensile test specimens of the finished steel plate and conduct tensile test to obtain the stress-strain curve and measured Rt of the finished steel plate. 2.0 (See Table 2 for the results);

[0098] Table 2

[0099] Based on the tensile test results of the finished steel plates in Table 2, the diameter expansion rate of the pipe making process is determined:

[0100] For 1# steel plate, Rt 2.0 <569MPa(ie target Rt 2.0min Lower limit), find Rt on the stress-strain curve of 1# steel plate 2.5 =575Mpa, 569MPa<Rt 2.5 <661MPa, then the 1# steel plate is expanded in the subsequent mechanical expansion according to the actual expansion rate of (k+x1-x)%=(0.8+2.5-2.0)%=1.3%;

[0101] For 2#, 3#, 4#, and 5# steel plates, their measured Rt 2.0If all fall within the range of 569-661 MPa, the 2#, 3#, 4#, and 5# steel plates are expanded according to the target expansion rate of 0.8% in the subsequent mechanical expansion;

[0102] For 6# steel plate, Rt 2.0 >661MPa (i.e. target Rt 2.0max Upper limit), find Rt on the stress-strain curve of 6# steel plate 1.7 =650<661MPa, then the 6# steel plate is expanded in the subsequent mechanical expansion according to the actual expansion rate of (k+x2-x)%=(0.8+1.7-2.0)%=0.5%;

[0103] (4) Based on the actual diameter expansion rate of the 1#, 2#, 3#, 4#, 5#, and 6# steel plates obtained in step (3), the width of each steel plate after milling is calculated, which are:

[0104] 1# steel plate: 3706mm;

[0105] 2#, 3#, 4#, 5# steel plates: 3725mm;

[0106] 6# steel plate: 3735mm;

[0107] The actual width of the steel plate before forming is obtained according to the above calculation, and the milling process is adjusted accordingly so that the width of the steel plate before forming obtained after milling meets the above calculated value.

[0108] (5) The above-mentioned pre-formed steel plates are formed and welded according to the straight seam submerged arc welding process to obtain welded pipes; when mechanically expanding the diameter, the same expansion parameters are used for all the above-mentioned welded pipes so that the outer circumference of all the steel pipes after expansion is 3830 mm. After the diameter expansion, post-processing is performed to obtain oil and gas transmission steel pipes.

[0109] Tensile test specimens were taken from the oil and gas transmission steel pipes prepared above and subjected to tensile property tests. The results are shown in Table 3. The yield strengths of all pipes fell within the target control range of 555-675 MPa.

[0110] Table 3

[0111] Example 2

[0112] Preparation of X70 (D1016×17.5mm) steel pipe, the yield strength control range is: 485-585MPa.

[0113] (1-1) Steel pipe yield strength control target, lower limit Rt 0.5min =485MPa, upper limit Rt 0.5max =585MPa.

[0114] (1-2) Based on the outer circumference of the expanded steel pipe D = 3192 mm, wall thickness t = 17.5 mm, target expansion rate 0.9% and forming extension 5 mm, the following is calculated:

[0115] Target plate width after milling

[0116] Plastic strain at the center of wall thickness during pipe making

[0117] (2) Use Method-II to obtain the value of x in the stress characterization parameter Rtx of the steel plate and the lower and upper limits of the target Rtx of the steel plate:

[0118] The value of x in the stress characterization parameter Rtx of the steel plate = ε1+0.5=1.06+0.5=1.56, so Rt is selected 1.56 As the stress characterization parameter of the steel plate, it is calculated as follows:

[0119] Target Rt of steel plate 1.56min =Rt 0.5min +10 (safety margin) = 485 + 10 = 495 MPa;

[0120] Target Rt of steel plate 1.56max =Rt 0.5max -10 (safety margin) = 585-10 = 575 MPa;

[0121] (3) According to the requirement that the diameter expansion rate meets 0.4%-1.4%, it is calculated that the steel plate width should be no less than 3118mm;

[0122] 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 in the production inspection process according to the above target Rt 1.56 The manufacturing process is optimized and adjusted within a certain range so that the measured Rt of the finished steel plate is within the range of 1.56 As far as possible, it should fall within the target range of 495-575 MPa;

[0123] Take the transverse tensile test specimens of the finished steel plate and conduct tensile test to obtain the stress-strain curve and measured Rt of the finished steel plate. 1.56 (The results are shown in Table 4);

[0124] Table 4

[0125] Based on the tensile test results of the finished steel plates in Table 4, the diameter expansion rate of the pipe making process is determined:

[0126] For 7# steel plate, Rt 1.56 <495MPa(ie 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 7# steel plate is expanded in the subsequent mechanical expansion according to the actual expansion rate of (k+x1-x)%=(0.9+1.9-1.56)%=1.24%;

[0127] For 8# and 9# steel plates, their measured Rt 1.56 If both fall within the range of 495-575 MPa, the 8# and 9# steel plates will be expanded according to the target expansion rate of 0.9% in the subsequent mechanical expansion;

[0128] For 10# steel plate, Rt 1.56 >575MPa (i.e. target Rt 1.56max Upper limit), find Rt on the stress-strain curve of 10# steel plate 1.2 =570<575MPa, then the 10# steel plate is expanded in the subsequent mechanical expansion according to the actual expansion rate of (k+x2-x)%=(0.9+1.2-1.56)%=0.54%;

[0129] (4) According to the actual diameter expansion rate of the 7#, 8#, 9#, and 10# steel plates obtained in step (3), the width of each steel plate after milling is calculated, which are:

[0130] 7# steel plate: 3092mm;

[0131] 8#, 9# steel plate: 3102mm;

[0132] 10# steel plate: 3113mm;

[0133] The actual width of the steel plate before forming is obtained according to the above calculation, and the milling process is adjusted accordingly so that the width of the steel plate before forming obtained after milling meets the above calculated value;

[0134] (5) The above-mentioned pre-formed steel plates are formed and welded according to the straight seam submerged arc welding process to obtain welded pipes; when mechanically expanding the diameter, the same expansion parameters are used for all the above-mentioned welded pipes so that the outer circumference of all the steel pipes after expansion is 3192 mm. After the diameter expansion, post-processing is performed to obtain oil and gas transmission steel pipes.

[0135] Tensile test specimens were taken from the oil and gas transmission steel pipes prepared above and subjected to tensile property tests. The results are shown in Table 5. The yield strengths of all pipes fell within the target control range of 485-585 MPa.

[0136] Table 5

[0137] It can be seen from the above Examples 1 and 2 that the method for preparing oil and gas transportation steel pipes provided by the present invention can make the yield strength of the prepared steel pipe fall within the target control range, effectively solving the problem of large fluctuation range of the yield strength of oil and gas transportation steel pipes, thereby improving the coordinated deformation capacity of the pipeline, improving 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.

[0138] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection 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 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) further includes: obtaining the target width W1 of the steel plate required for forming and the target plastic strain ε1% of 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, obtain the lower limit value W2 of the preparation width of the pre-formed steel plate; 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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