Method of manufacturing oil and gas transport steel pipes

Abstract

The present application relates to the technical field of oil and gas conveying steel pipe, 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 steel pipe to be prepared; (2) obtaining a value of a stress characterization parameter Rtx of a steel plate before forming, and obtaining a target Rtx of the steel plate before forming according to the yield strength control target of the steel pipe to be prepared; (3) preparing the steel plate before forming according to the target Rtx, and obtaining an actual diameter expansion rate of the steel plate before forming in a pipe preparation process according to a quantitative relationship between a measured Rtx and the target Rtx of the steel plate before forming; (4) milling edges to obtain a steel plate required for forming according to the actual diameter expansion rate; and (5) forming and welding the steel plate required for forming, and mechanically expanding the diameter of all welded pipes obtained by welding by using the same diameter expansion parameters to obtain the oil and gas conveying steel pipe. The prepared steel pipe has a narrow yield strength fluctuation range.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas conveying steel pipes, and particularly relates to a method for preparing an oil and gas conveying steel pipe. BACKGROUND

[0002] Oil and gas pipelines are the most economical and efficient way for large-scale and long-distance transportation of oil and natural gas. With the rapid development of economy, the domestic oil and gas pipeline construction develops 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, China will still be in the peak period of pipeline construction.

[0003] The yield strength is one of the most important properties of oil and gas conveying steel pipes, which not only determines the pressure-bearing capacity of the pipeline, but also has an important influence on the strain capacity of the pipeline and the strength matching of the girth weld. When the yield strength of the steel pipe fluctuates greatly, the steel pipe with lower strength will have a larger strain when the pipeline is deformed, while the steel pipe with higher strength has not yet started to strain, resulting in a decrease in the overall coordinated strain capacity of the pipeline. In addition, when the yield strength of the steel pipe fluctuates greatly, the girth weld of the pipeline needs to reach above the upper limit of the yield strength to achieve over-matching, which increases the difficulty of the girth weld and the risk of girth weld failure caused by low strength matching. These factors will have a serious adverse effect on the safety of the pipeline. Therefore, the standards for oil and gas pipelines have requirements for the upper and lower limits of the yield strength of the steel pipe, and the more important the pipeline is, the more stringent the requirements for the fluctuation range of the yield strength 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-to-East Gas Pipeline is 555-690 MPa, and the yield strength range specified in the technical requirements of the East Line of China and Russia is 555-675 MPa. For submarine pipelines and large-strain pipelines, 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 range are the trends of the development of oil and gas pipeline steel pipe products. 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 control level of the yield strength of steel pipe products.

[0004] The yield strength of the steel pipe is affected by multiple complex factors such as the chemical composition of the raw material, the manufacturing process, and the pipe-making process. Traditionally, the control method for the yield strength of the steel pipe is to first develop the yield strength requirements of the steel plate. However, due to the complexity of the chemical composition, rolling process, and accelerated cooling process in the manufacturing process of the steel plate, it is difficult to control the yield strength of the steel plate, and the fluctuation range is large. In addition, the yield strength of the material will change significantly during the straight seam submerged arc welding pipe manufacturing process, which is affected by the internal factors of the material, and has a weak correlation with the yield strength value of the material. This results in that only controlling the yield strength of the steel plate cannot completely achieve the effect of controlling the yield strength of the steel pipe, causing the yield strength of the steel pipe to fluctuate greatly.

[0005] At present, it is difficult to reach the control range of 120MPa of the yield strength stability of the oil and gas conveying steel pipe, and it is difficult to meet the higher requirements of the pipeline on the uniformity of the yield strength of the steel pipe. Therefore, it is of great significance to provide a new method for preparing the oil and gas conveying steel pipe and improve the yield strength uniformity of the steel pipe for realizing the high-quality development of the oil and gas conveying pipeline. SUMMARY

[0006] The present application provides a method for preparing an oil and gas conveying steel pipe to solve the problem of large yield strength fluctuation range and poor uniformity of the existing oil and gas conveying steel pipe, thereby affecting the safety of the oil and gas pipeline.

[0007] In order to achieve the above-mentioned purpose, the present application provides a method for preparing an oil and gas conveying steel pipe, comprising:

[0008] (1) determining 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) obtaining the value of the stress characterization parameter Rtx of the steel plate before forming, and obtaining the lower limit value and the 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 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) determining the steel plate manufacturing process according to the target Rtx, preparing and obtaining the steel plate before forming, and performing 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 quantity relationship between the measured Rtx and the target Rtx of the steel plate before forming, obtaining the actual expansion rate of the steel plate during pipe manufacturing;

[0011] (4) calculating the width of the steel plate required for forming according to the actual expansion rate, and milling 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) forming and welding the steel plate required for forming, and mechanically expanding the entire welded pipe obtained by welding using the same expansion parameters to obtain the oil and gas conveying steel pipe.

[0013] Through the above technical scheme, the present application can obtain the following beneficial effects:

[0014] (1) The method for preparing oil and gas conveying steel pipes provided by the present application can effectively reduce the yield strength fluctuation range of the steel pipes, can control the yield strength of the steel pipes in a narrower range, and after a plurality of steel pipes prepared by the method provided by the present application are welded and connected into a pipeline, different steel pipes can enter the strain state at the same time when the pipeline is strained by external force, so that the strain is avoided to be concentrated on a certain steel pipe, the coordinated deformation ability of the pipeline is greatly improved, and the safety of the oil and gas pipeline is improved.

[0015] (2) The method for preparing oil and gas conveying steel pipes provided by the present application is beneficial to further compress the upper limit of the yield strength of the steel pipes, thereby reducing the difficulty of high-strength matching during welding of the girth weld, is beneficial to high-strength matching of the girth weld of the pipeline, reduces the failure probability of the girth weld, and improves the safety of the oil and gas pipeline.

[0016] (3) The method for preparing oil and gas conveying steel pipes provided by the present application uses the stress characterization parameter of the steel plate to replace the Rt 0.5 of the steel plate, and controls the change of the yield strength through the adjustment of the strain amount during the pipe preparation process, so that the method is less difficult than the traditional method of putting forward more stringent requirements for the yield strength range of the steel plate to ensure the yield strength range of the steel pipe, has higher reliability, and has better economy. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a first fitting 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 application.

[0018] Figure 2 is a second fitting 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 application.

[0019] Figure 3 is a third fitting 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 application.

[0020] Figure 4 is a fourth fitting 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 application.

[0021] Figure 5 is a fifth fitting 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 application. DETAILED DESCRIPTION

[0022] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the invention. Any numeric range recited is intended to include all values between the recited upper and lower values. In this sense, the phrased "ranging / ranges between" is used herein. For values which are less than one, one unit is considered to be 0.000... with the number of zeros being equal to the least significant place of the quantity that is being considered. For values which are greater than one, one unit is considered to be 1.0. These precise numerologies are not to be construed as critical or limiting in a way that is inconsistent with the purpose and spirit of the invention.

[0023] The specific embodiments of the present application are described herein. It is to be understood that the embodiments described herein are merely illustrative of the principles of the present application and are not intended to limit the present application.

[0024] The present application provides a method for preparing oil and gas transmission steel pipe, comprising:

[0025] (1) determining 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) obtaining the value of stress characterization parameter Rtx of the steel plate before forming, and obtaining the lower limit value and the 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) determining the steel plate manufacturing process according to the target Rtx, preparing and obtaining the steel plate before forming, and performing the tensile test on the steel plate before forming to obtain the stress-strain curve and the measured Rtx of the steel plate before forming; and obtaining the actual expansion rate of the steel pipe during the pipe manufacturing process according to the quantity relationship between the measured Rtx and the target Rtx of the steel plate before forming;

[0028] (4) calculating the width of the steel plate required for forming according to the actual expansion rate, and milling 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;

[0029] (5) forming and welding the steel plate required for forming, and mechanically expanding the entire welded pipe obtained by welding using the same expansion parameters to obtain the oil and gas transmission steel pipe.

[0030] The method for manufacturing the oil and gas conveying steel pipe provided by the application can better characterize the yield strength of the material after pipe manufacturing by using the steel plate stress characterization parameter Rtx based on pipe manufacturing strain. 0.5 Therefore, the Rtx is more instructive and timely for the steel plate manufacturing process, and is beneficial to obtaining a narrower tensile property control range. According to the yield strength control target of the steel pipe to be manufactured and the target plastic strain ε1% of the wall thickness center in the pipe manufacturing process, the target Rtx of the steel plate is determined and used as the tensile property requirement of the steel plate to guide the production of the steel plate and the optimization of the tensile property. However, due to the complex factors such as chemical composition, rolling and heat treatment process that affect the yield strength of the steel plate, the yield strength of the steel plate may not reach the ideal range, so it is difficult to control the yield strength range of the steel pipe only by controlling the yield strength of the steel plate. In the pipe manufacturing process, the plastic strain of the material has a significant effect on the yield strength of the steel pipe, and increasing the plastic strain in the pipe manufacturing process can increase the yield strength of the steel pipe, and reducing the plastic strain in the pipe manufacturing 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 in the pipe manufacturing process. According to the principle of Rtx of the steel plate ≈ yield strength Rt of the steel pipe 0.5 , when the Rtx of the steel plate falls within the yield strength control range of the steel pipe, the pipe is manufactured according to the target plastic strain ε1%; when the Rtx of the steel plate is higher than the upper limit of the yield strength control range of the steel pipe, the pipe is manufactured by measuring and reducing the plastic strain; and when the Rtx of the steel plate is lower than the lower limit of the yield strength control range of the steel pipe, the pipe is manufactured by measuring and increasing the plastic strain. Through the above two measures, the present application can realize precise control of the yield strength of the steel pipe product, improve the yield strength uniformity of the steel pipe product, and reduce the yield strength fluctuation range.

[0031] The method for manufacturing the oil and gas conveying steel pipe provided by the application is improved from two aspects of yield strength control of the steel plate before forming and optimization of the pipe manufacturing plastic strain (directly related to the expansion rate). These improvement measures are based on the existing steel pipe manufacturing process, and it should be understood that, in addition to the above improvement measures, the method for manufacturing the oil and gas conveying steel pipe provided by the application also includes the conventional steps and corresponding process parameters in the existing steel pipe manufacturing process, such as steel plate ultrasonic plate detection, edge milling, pre-bending, forming, welding, weld inspection (ultrasonic continuous detection, X-ray television inspection), mechanical expansion, flat head, water pressure test, chamfering, pipe body inspection (ultrasonic continuous detection, X-ray television inspection) and finished product inspection, and the like, which will not be described herein again.

[0032] According to the application, in the method for manufacturing the oil and gas conveying steel pipe, the method for obtaining the actual expansion rate in step (3) comprises:

[0033] When the target Rtxmin≤ measured Rtx≤ target Rtxmax, the preforming steel plate is expanded by k% in the mechanical expansion of the pipe making process (the preforming steel plate is rolled into a barrel shape, then welded, and then the welded steel pipe is mechanically expanded) according to the actual expansion rate.

[0034] When the measured Rtx< target Rtxmin, a point with a strain of x1% on the stress-strain curve of the preforming steel plate is found, which satisfies target Rtxmin≤ Rtx1≤ target Rtxmax, and the preforming steel plate is expanded by (k+x1-x)% in the mechanical expansion of the pipe making process (the preforming steel plate is rolled into a barrel shape, then welded, and then the welded steel pipe is mechanically expanded) according to the actual expansion rate.

[0035] When the measured Rtx> target Rtxmax, a point with a strain of x2% on the stress-strain curve of the preforming steel plate is found, which satisfies target Rtxmin≤ Rtx2≤ target Rtxmax, and the preforming steel plate is expanded by (k+x2-x)% in the mechanical expansion of the pipe making process (the preforming steel plate is rolled into a barrel shape, then welded, and then the welded steel pipe is mechanically expanded) according to the actual expansion rate.

[0036] According to the present application, in the above method for obtaining the actual expansion rate, the limits of x1 and x2 are relatively wide, as long as the point with a strain of x1% on the stress-strain curve of the preforming steel plate satisfies target Rtxmin≤ Rtx1≤ target Rtxmax, and the point with a strain of x2% on the stress-strain curve of the preforming steel plate satisfies 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 control the yield strength of the steel pipe product within a narrower range.

[0037] According to the present application, in the method for preparing an oil and gas conveying steel pipe, step (1) further comprises: obtaining a target width W1 of the steel plate required for forming and a plastic strain ε1% at the wall thickness center in the pipe making process; wherein,

[0038] W1=(D-t)×π / (1+k%)–δ;

[0039] ε1=k+100δ / W1;

[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 application, in view of the small value of 100δ / W, in some embodiments, ε1=k can also be roughly considered.

[0042] According to the present application, the target width W1 is the reference for determining the width, and is also the basis for determining the width of the steel plate before milling in subsequent step (4). In order to enable the pipe strain to be adjusted within a certain range, the steel plate before milling must have a certain width allowance.

[0043] According to the present application, in the method for preparing the oil and gas conveying 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 the upper limit value of the target Rtx includes:

[0044] (2-1) Select N pieces of steel plate samples corresponding to the set specifications of the steel pipe to be prepared, respectively obtain N stress-strain curves of the corresponding steel plate samples through tensile test; in each corresponding stress-strain curve, select M steel plate strain values based on a preset interval a% with (ε1+Δε)% as the standard, to obtain M steel plate stress values corresponding to different strain values; based on the stress-strain curves of the N corresponding steel plate samples and the M steel plate stress values corresponding to different strain values, the steel plate stress values corresponding to the same strain value are taken as a group, to obtain M groups of different strain values and N steel plate stress values corresponding to the same strain value in each group; wherein N≥5, M≥3, and Δε is a parameter corresponding to the yield strength selection standard of the steel pipe to be prepared;

[0045] (2-2) Respectively make N steel pipe samples according to the parameters of the steel pipe to be prepared, based on the N pieces of steel plate samples corresponding to the set specifications of the steel pipe to be prepared, obtain N stress-strain curves of the steel pipe samples and the yield strength values of the N steel pipe samples corresponding to the strain value of Δε%;

[0046] (2-3) Based on the N steel plate stress values corresponding to the same strain value, the yield strength values of the N steel pipe samples corresponding to the strain value of Δε% obtained, obtain M fitting straight lines through linear fitting, and take the fitting straight line RtΔx=a+b×steel pipe Rt 0.5 corresponding to the maximum fitting goodness of value in the M fitting straight lines as the value of x in the stress characterization parameter Rtx;

[0047] Based on the fitting straight line RtΔx=a+b×steel pipe Rt 0.5 corresponding to the maximum fitting goodness of value, calculate the lower limit value and the upper limit value of the target Rtx of the steel plate before forming; wherein,

[0048] The target Rtxmin=a+b×target Rt 0.5min of the steel pipe to be prepared+c1;

[0049] Target Rtxmax = a + b x Target Rt of steel pipe to be prepared 0.5max + d1;

[0050] Wherein, c1, d1 are safety margins.

[0051] According to the present application, in the method for preparing oil and gas conveying steel pipes, in step (2), preferably, Δε is 0.5. In the field, since the stress corresponding to the total deformation of 0.5% on the tensile stress-strain curve is usually taken as the yield strength, the present application mainly takes this as the selection standard of the yield strength of the steel pipe to be prepared.

[0052] According to the present application, in the method for preparing oil and gas conveying steel pipes, in step (2-1), preferably, the steel plate sample is a transverse sampling sample. In the present application, the sampling position of the steel plate sample is the position corresponding to the sampling position of the tensile sample required by the steel pipe standard, that is, if the center position of the base material in the circumferential direction of the steel pipe is required after pipe making, the steel plate sample should also be taken from the center of the width of the steel plate. In addition, for materials with good performance uniformity of the whole steel plate, sampling can also be taken at other positions, which is not particularly limited in the present application.

[0053] According to the present application, in the method for preparing oil and gas conveying steel pipes, in step (2-1), preferably, the method for obtaining the M steel plate stress values comprises: in the stress-strain curves of the N corresponding steel plate samples, based on the preset interval a, taking M strain values on the left and right sides of the center with ε1+Δε as the center to obtain the corresponding M steel plate stress values;

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

[0055] According to the present application, 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 (such as Rt 0.5 ) of the steel pipe can be more efficiently established, and a representative Rtx value can be quickly obtained. The present application provides the above method as a uniform value method, in addition, the present application also includes a non-uniform interval value method, that is, an asymmetric value, one point can be taken on the left side of ε1+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 application, in the method for preparing the oil and gas conveying steel pipe, in step (2-2), in the tensile test, the selection position of the steel pipe sample is consistent with the selection position of the steel plate sample, and the selection positions are both the same end of the steel plate, so as to reduce other cumulative errors of the steel plate in the test and the steel pipe after pipe making. Specifically, the selection of the steel plate sample and the selection of the steel pipe sample in the application can be sequentially selected at the set end of the N pieces of base steel plates, so as to ensure that the selection positions of the two are at the same end.

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

[0058] Wherein, x i is a steel plate stress variable, y i is a steel pipe sample yield strength variable, is an average stress value corresponding to the same strain value of the N pieces of steel plates, is an average yield strength value corresponding to the N steel pipe samples.

[0059] According to the application, in the method for preparing the oil and gas conveying steel pipe, in step (2-3), c1≥0 and d1≤0. Preferably, 0≤c1≤20 and -20≤d1≤0, which can greatly reduce the risk of deviating from the target value caused by the inevitable deviation of individual data points from the regression curve in 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.

[0060] According to the application, in the method for preparing the oil and gas conveying 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 pre-formed steel plate and 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 pre-formed steel plate = ε1+0.5;

[0062] The target Rtxmin = the target Rt 0.5min + c2;

[0063] The target Rtxmax = the target Rt 0.5max + d2;

[0064] Wherein, c2 and d2 are safety margins.

[0065] According to the present application, in the method-II, c2≥0, d2≤0. Preferably, 0≤c2≤20, -20≤d2≤0, which can greatly reduce the risk of deviating from the target value caused by the inevitable deviation of individual data points from the regression curve in the fitting process, further narrow the range of target Rtx, and further narrow the fluctuation range of the yield strength of the steel pipe.

[0066] In the present application, in the method for preparing the oil and gas conveying steel pipe, in step (2), for obtaining the numerical value of x in the stress characterization parameter Rtx of the pre-forming steel plate and the lower limit value and the upper limit value of the target Rtx, both the above-mentioned method-I and 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, and the latter can obtain results more quickly and can also meet the control requirements of the yield strength of the steel pipe product.

[0067] According to the present application, in the method for preparing the oil and gas conveying steel pipe, in step (3), before preparing the pre-forming steel plate, a lower limit value W2 of the preparation width of the pre-forming steel plate (not milled) is obtained; wherein,

[0068] W2=(D-t)×π / (1+k’%)-δ; wherein, k’%=k%-0.5%;

[0069] 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).

[0070] According to the present application, the lower limit value W2 of the preparation width of the pre-forming steel plate (not milled) is to reserve a surplus 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 application, in the method for preparing the oil and gas conveying steel pipe, in steps (4) and (5), the milling, forming, welding and mechanical expansion can be carried out using conventional processes and parameters in the art, and the present application does not make special limitations thereon.

[0072] In the present application, the yield strength of the steel plate and the steel pipe is determined by the method specified in GB / T 228.1-2021 (Metallic Materials Tensile Testing Part 1: Room Temperature Test Method).

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

[0074] Example 1

[0075] X80 (D1219x22mm) steel pipe was prepared, and the control range of yield strength was 555-675 MPa

[0076] (1-1) Steel pipe yield strength control target, lower limit Rt 0.5min = 555 MPa, 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, the following was calculated:

[0078] Target plate width of the steel plate after edge milling

[0079] Plastic strain of the wall thickness center during pipe making

[0080] (2) Method-I was used 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) 30 steel plate samples corresponding to the set specifications of the steel pipe to be prepared were selected, and 30 stress-strain curves of the corresponding steel plate samples were obtained by tensile test; in each corresponding stress-strain curve, 5 steel plate strain values (0.5%, 1.0%, 1.55%, 2.0%, 2.5%) were selected based on the preset interval a% (a is 0.5) at 1.5% (ε1 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 ) corresponding to different strain values; based on the stress-strain curves of the 30 corresponding steel plate samples and the 5 steel plate stress values corresponding to different strain values, the steel plate stress values corresponding to the same strain value were taken as a group, 5 groups of different strain values and 30 steel plate stress values corresponding to the same strain value in each group were obtained (see Table 1);

[0082] (2-2) The above 30 steel plate samples corresponding to the set specifications of the steel pipe to be prepared were respectively made into 30 steel pipe samples according to the parameters (D1219x22mm) of the steel pipe to be prepared, and the stress-strain curves of the 30 steel pipe samples and the yield strength values Rt 0.5 of the 30 steel pipe samples were obtained by tensile test (see Table 1);

[0083] Table 1

[0084]

[0085]

[0086] (2-3) The 30 steel plate stress values corresponding to the same strain values obtained, the yield strength values Rt 0.5 of the 30 steel tube samples are input into the data table of the origin software, and each column of data corresponds to a column in the data table. The steel plate stress value (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 taken as the Y axis, and the yield strength value Rt 0.5 of the steel tube sample is taken as the X axis. Linear fitting is performed by the linear fitting function provided by the software, and the fitting straight line (first fitting straight line, second fitting straight line, third fitting straight line, fourth fitting straight line, fifth fitting straight line, as shown in Figure 1 ) and the goodness of fit are obtained.

[0087] The first fitting straight line: steel plate Rt 0.5 = 604-0.0745x steel tube Rt 0.5 , the goodness of fit R 2 = 0.0035;

[0088] The second fitting straight line: steel plate Rt 1.0 = 295+0.471x steel tube Rt 0.5 , the goodness of fit R 2 = 0.2938;

[0089] The third fitting straight line: steel plate Rt 1.5 = 188+0.671x steel tube Rt 0.5 , the goodness of fit R 2 = 0.6532;

[0090] The fourth fitting straight line: steel plate Rt 2.0 = 144+0.766x steel tube Rt 0.5 , the goodness of fit R 2 = 0.7955;

[0091] The fifth fitting straight line: steel plate Rt 2.5 = 237+0.634x steel tube Rt 0.5 , the goodness of fit R 2 = 0.6641;

[0092] Among them, the steel plate Rt 2.0 and the steel tube Rt 0.5 have the best goodness of fit, so the steel plate stress value Rt 2.0 with the largest goodness of fit is taken 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 x Steel pipe Rt 0.5 , the upper and lower limits of Rt 0.5max (675 MPa) and Rt 0.5min (555 MPa) controlled by the yield strength of the steel pipe are substituted to obtain:

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

[0095] The target Rt 2.0max of the steel plate = 144 + 0.766 x 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 be not less than 3741 mm;

[0097] According to the target Rt 2.0min (569 MPa) and the target Rt 2.0max (661 MPa) of the steel plate, i.e. the target Rt 2.0 range of the steel plate is 569-661 MPa, the manufacturing process of the steel plate is determined, and the manufacturing process is optimized and adjusted during the production inspection according to the above target Rt 2.0 range, so that the measured Rt 2.0 of the finished steel plate falls in the target range 569-661 MPa as much as possible;

[0098] The transverse tensile sample of the above finished steel plate is taken to perform tensile test, and the stress-strain curve and the measured Rt 2.0 of the finished steel plate are obtained (the results are shown in Table 2),

[0099] Table 2

[0100]

[0101]

[0102] According to the tensile test results of the finished steel plate in Table 2, the expansion rate during pipe manufacturing process is determined:

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

[0104] For the 2#, 3#, 4# and 5# steel plates, the measured Rt 2.0 all fall within the range of 569-661 MPa, so the 2#, 3#, 4# and 5# steel plates are 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 target Rt 2.0max upper limit value), Rt 1.7 = 650 < 661 MPa is found on the stress-strain curve of the 6# steel plate, the 6# steel plate is expanded at an actual expansion rate of (k + x2 - x) % = (0.8 + 1.7 - 2.0) % = 0.5 % during the subsequent mechanical expansion;

[0106] (4) According to the actual expansion rates of the 1#, 2#, 3#, 4#, 5# and 6# steel plates obtained in step (3), the widths of the steel plates after milling are calculated as follows:

[0107] 1# steel plate: 3706 mm

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

[0109] 6# steel plate: 3735 mm

[0110] The actual widths of the steel plates before forming are obtained according to the above calculation, and the milling process is adjusted accordingly so that the widths of the steel plates before forming after milling meet the calculated values.

[0111] (5) The above steel plates before forming are formed, and welded according to the straight seam submerged arc welding process to obtain welded pipes; during the mechanical expansion, the same expansion parameters are used for all the welded pipes, so that the outer circumferences of all the expanded steel pipes are 3830 mm. After expansion, post-treatment is performed to obtain oil and gas transmission steel pipes.

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

[0113] Table 3

[0114] Steel pipe No. [Rt 0.5 ]]> 1# (made of 1# steel plate) 573 2# (made of 2# steel plate) 620 3# (made of 3# steel plate) 600 4# (made of 4# steel plate) 615 5# (made of 5# steel plate) 595 6# (made of 6# steel plate) 645

[0115] Example 2

[0116] A X70 (D1016 x 17.5 mm) pipe was manufactured, with a controlled range of yield strength: 485-585 MPa

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

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

[0119] Target plate width of the steel plate after milling

[0120] Plastic strain at the center of the wall thickness during pipe manufacturing

[0121] (2) Method-II was used to obtain the value of the stress characterization parameter Rtx of the steel plate and the lower limit and upper limit of the target Rt

[0122] The value of the stress characterization parameter Rtx of the steel plate = ε1+0.5 = 1.06+0.5 = 1.56, so Rt 1.56 was selected as the stress characterization parameter of the steel plate; the following was calculated:

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

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

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

[0126] According to the target Rt 1.56min (495 MPa) and target Rt 1.56max (575 MPa) of the steel plate, i.e., the target Rt 1.56 range of the steel plate is 495-575 MPa, the steel plate manufacturing process was determined, and the manufacturing process was optimized and adjusted during production inspection according to the above target Rt 1.56 range, so that the measured Rt 1.56 of the finished steel plate falls within the target range 495-575 MPa as much as possible;

[0127] The finished steel plate prepared above is taken for transverse tensile test, and tensile test is carried out to obtain stress-strain curve and measured Rt of the finished steel plate respectively 1.56 (see Table 4),

[0128] Table 4

[0129] Finished steel plate No. Measured Rt 1.56 ]]> 7# 486 8# 515 9# 520 10# 580

[0130] According to the tensile test results of the finished steel plate in Table 4, the pipe-making process expansion ratio is determined:

[0131] For the 7# steel plate, Rt 1.56 < 495 MPa (i.e. the target Rt 1.56min lower limit value), Rt 1.9 = 496 MPa is found on the stress-strain curve of the 7# steel plate, and 495 MPa < Rt 1.9 < 575 MPa, then the 7# steel plate is expanded in the subsequent mechanical expansion according to the actual expansion ratio (k + x1 - x) % = (0.9 + 1.9 - 1.56) % = 1.24 %;

[0132] For the 8# and 9# steel plates, their measured Rt 1.56 all fall within the range of 495-575 MPa, so the 8# and 9# steel plates are expanded in the subsequent mechanical expansion according to the target expansion ratio 0.9 %;

[0133] For the 10# steel plate, Rt 1.56 > 575 MPa (i.e. the target Rt 1.56max upper limit value), Rt 1.2 = 570 < 575 MPa is found on the stress-strain curve of the 10# steel plate, and then the 10# steel plate is expanded in the subsequent mechanical expansion according to the actual expansion ratio (k + x2 - x) % = (0.9 + 1.2 - 1.56) % = 0.54 %;

[0134] (4) According to the actual expansion ratios of the 7#, 8#, 9# and 10# steel plates obtained in step (3), the widths of the steel plates after milling are calculated as follows:

[0135] 7# steel plate: 3092 mm

[0136] 8# and 9# steel plates: 3102 mm

[0137] 10# steel plate: 3113 mm

[0138] The actual width of the steel plate before forming is obtained according to the above calculation, and the milling process is adjusted accordingly to make the width of the steel plate after milling meet the calculated value.

[0139] (5) plus the above-mentioned each forming steel plate is subjected to forming, and is subjected to welding according to a straight seam submerged arc welding pipe process, to obtain a welded pipe; when mechanical expanding is carried out, the same expanding parameter is used for all the welded pipes, so that the outer circumferential length of all the expanded steel pipes is 3192mm, post-treatment is carried out after expanding, to obtain the oil and gas conveying steel pipe.

[0140] Tensile property tests are carried out on the tensile samples of the oil and gas conveying steel pipe prepared above, and the results are shown in Table 5,

[0141] The yield strength of each pipe falls within the target control range of 485-585MPa.

[0142] Table 5

[0143] Steel pipe No. [Rt 0.5 ]]> 7# (made of 7# steel plate) 500 8# (made of 8# steel plate) 519 9# (made of 9# steel plate) 530 10# (made of 10# steel plate) 565

[0144] As can be seen from the above embodiment 1 and embodiment 2, the method for preparing the oil and gas conveying steel pipe provided by the present application can make the yield strength of the prepared steel pipe fall within the target control range, effectively solve the problem of large fluctuation range of the yield strength of the oil and gas conveying steel pipe, and further realize the improvement of the pipeline coordinated deformation ability, the improvement of the oil and gas pipeline safety, and the meeting of the requirements of the high-quality development of the oil and gas pipeline for the high-performance uniformity steel pipe product.

[0145] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as the disclosed content of the present application, and all belong to the protection scope of the present application.

Claims

1. A method for manufacturing oil and gas transmission steel pipes, characterized in that, include: (1) Determine the target yield strength 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 ; (2) Obtain the value of x in the stress characterization parameter Rtx of the steel plate before forming, and determine the value of x according to the target lower limit value Rt of the yield strength of the steel pipe to be prepared. 0.5min And the target upper limit value of yield strength Rt 0.5max Obtain the lower limit and upper limit of the target Rtx of the steel plate before forming. The lower limit is the target Rtxmin and the upper limit is the target Rtxmax. Wherein, Rtx is the stress value corresponding to x% of the total strain on the stress-strain curve obtained by the tensile test of the steel plate before forming. (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 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 diameter expansion rate of the steel plate before forming during the pipe making process; (4) Calculate the width of the steel plate required for forming based on the actual expansion ratio, 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; (5) The steel plate required for forming is formed and welded, and all the welded pipes are mechanically expanded using the same expansion parameters to obtain oil and gas transmission steel pipes; In step (3), the method for obtaining the actual diameter expansion ratio includes: When the target Rtxmin ≤ the measured Rtx ≤ the target Rtxmax, the steel plate before forming is expanded in the tube manufacturing process according to the actual expansion rate of k% during mechanical expansion; where k% is the target expansion rate. When the measured Rtx < the target Rtxmin, find the point with strain x1% on the stress-strain curve of the steel plate before forming, satisfying target Rtxmin≤Rtx1≤target Rtxmax. The steel plate before forming is expanded in the mechanical expansion process of the tube making process according to the actual expansion rate of (k+x1-x)%. When the measured Rtx > the target Rtxmax, find the point with strain of x2% on the stress-strain curve of the steel plate before forming, satisfying the target Rtxmin≤Rtx2≤target Rtxmax. The steel plate before forming is expanded in the mechanical expansion process of the tube making process according to the actual expansion rate of (k+x2-x)%.

2. The method according to claim 1, wherein, Step (1) further 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 tube manufacturing 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 elongation.

3. The method according to claim 2, wherein, In step (2), the method for obtaining the value of x in the stress characterization parameter Rtx of the steel plate before forming, as well as the lower limit and upper limit of the target Rtx, includes: (2-1) Select N steel plate samples of the specified specifications corresponding to the steel pipe to be prepared, and obtain N stress-strain curves of the corresponding steel plate samples through tensile tests; in each corresponding stress-strain curve, use ( M strain values ​​of steel plates are selected based on a preset interval a% as the standard to obtain M stress values ​​of steel plates corresponding to different strain values; based on the stress-strain curves of the N corresponding steel plate samples and the M stress values ​​of steel plates corresponding to different strain values, the stress values ​​of steel plates corresponding to the same strain value are grouped together to obtain M groups of different strain values ​​and N stress values ​​of steel plates corresponding to each group of the same strain value; where N≥5, M≥3, The parameter corresponding to the standard for selecting the yield strength of the steel pipe to be prepared; (2-2) Take the N steel plate samples corresponding to the specified specifications of the steel pipe to be prepared, and make N steel pipe samples according to the parameters of the steel pipe to be prepared. Obtain the stress-strain curves and strain values ​​of the N steel pipe samples by tensile testing. The yield strength values ​​of the N steel pipe specimens corresponding to the specified percentage; (2-3) Based on the N stress values ​​and strain values ​​of the steel plate corresponding to the same strain value obtained, The yield strength values ​​of the N steel pipe samples corresponding to the specified value at a given value are used to obtain M fitted lines through linear fitting. The fitted line RtΔx = a + b × steel pipe Rt is selected from the M fitted lines with the highest goodness of fit. 0.5 Δx is used as the value of x in the stress characterization parameter Rtx; Based on the fitting straight line RtΔx = a + b × steel pipe Rt corresponding to the maximum goodness of fit value. 0.5 The lower and upper limits of the target Rtx of the steel plate before forming are calculated; where, 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; Where c1 and d1 are safety margins.

4. The method according to claim 3, wherein, It 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 stress values ​​of the 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, and taking values ​​on the left and right sides of the center respectively. One strain value is used to obtain the corresponding M stress values ​​of the steel plate; Where a > 0; M is an odd number; .

5. The method according to claim 3 or 4, wherein in step (2-3), the method for obtaining the goodness of fit is as follows: ;in, x i y represents the stress value variable of the steel plate. i The variable is the yield strength value of the steel pipe specimen. Let N be the average stress corresponding to the same strain value of N steel plates. This represents the average yield strength of N steel pipe specimens.

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

7. The method according to claim 2, wherein, In step (2), the method for obtaining the value of x in the stress characterization parameter Rtx of the steel plate before forming, as well as the lower limit and upper limit of the target Rtx, includes: The value of x in the stress characterization parameter Rtx of the steel plate before forming is 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 prepared 0.5max +d2; Where c2 and d2 are safety margins.

8. The method according to claim 7, wherein, 0≤c²≤20; -20≤d²≤0.

9. The method according to claim 1, wherein, In step (3), before preparing the pre-forming steel plate, the lower limit value W2 of the pre-forming width of the pre-forming steel plate is obtained; wherein, W2 = (Dt) × π / (1 + k'%) – δ; where 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 elongation.

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