Method for improving flattening performance of medium-small-caliber high-carbon-equivalent thick-wall HFW welding pipe blank

Abstract

The invention provides a method for improving the flattening performance of a medium-small-caliber high-carbon-equivalent thick-wall HFW (High Frequency Welding) pipe blank, which is characterized in that a low-carbon microalloy rolled plate is prepared into the medium-small-caliber high-carbon-equivalent thick-wall HFW pipe blank by adopting the processes of FFX (Fin Fin X) forming, HFW welding, hot tension reducing, graded cooling and the like. By means of the method, the welding extrusion amount can be remarkably increased, welding seam inclusion and bad structures are reduced, the pipe blank welding seam structure performance is similar to or consistent with the base metal structure performance, and the forming and welding seam quality problems caused by small pipe diameter, wall thickness increasing and carbon equivalent increasing of the pipe blank are prevented.

Description

Technical field

[0001] The present invention relates to a method for improving the flattening performance of a tube blank, and in particular to a method for improving the flattening performance of a tube blank of a medium- and small-caliber high-carbon equivalent thick-wall HFW welded tube. [Background Technology]

[0002] Casing, tubing, and drill string components (drill pipe, drill collars, kelly, etc.) are collectively referred to as oil country tubing (OCTG). Oil and gas exploration and development consume a significant amount of OCTG. Statistics show that for every meter of drilling, approximately 62 kg of OCTG is required, including 48 kg of casing, 10 kg of tubing, 3 kg of drill pipe, and 0.5 kg of drill collars. Tubing accounts for approximately 60% of the value of oilfield equipment assets, making OCTG a crucial component of the oil industry.

[0003] In recent years, with the global oil market rebounding, domestic oil and gas production has been increasing year by year. With the depletion of conventional oil and gas resources and the implementation of oil and gas field exploration and development measures to increase reserves and production, the extraction of unconventional oil and gas, such as shale gas, has also been increasing year by year, leading to significant changes in the demand structure for oil casing. Due to the complex storage conditions and composition of unconventional oil and gas fields, the performance and requirements for oil casing have gradually increased. Demand for low-grade oil casing has been declining year by year, while demand for high-grade, thicker-walled oil casing, P110 and above, has been increasing year by year.

[0004] High-frequency resistance welding (HFW) is a cost-effective pipe manufacturing method. It uses low-carbon, microalloyed hot-rolled coils, which are then cold-bent and extruded. The skin and proximity effects of high-frequency resistance welding are then used to heat the coil edges to a molten state and weld them into a tube blank. After subsequent heat treatment, high-grade oil casing and tubing are formed. Compared to seamless pipe, HFW pipe boasts better wall thickness uniformity, high dimensional accuracy, and excellent collapse resistance, making it suitable for use in unconventional oil and gas well casing and tubing.

[0005] Because unconventional oil and gas resources are mostly deep wells with complex geological conditions, the wall thickness and alloy content of hot-rolled coil used in welded pipe will be significantly increased to meet the service conditions of casing. This makes welding and forming increasingly difficult. For welded pipe, the weld is the most vulnerable part of the pipe, and weld performance issues are also the main obstacle to its application. This is especially difficult for small and medium diameter pipe blanks with large wall thickness. This leads to poor weld quality and ultimately affects the weld strength and toughness of the welded casing. [Summary of the invention]

[0006] In order to solve the above problems, the present invention provides a method for improving the flattening performance of small and medium-caliber high-carbon equivalent thick-walled HFW welded pipe blanks. This method can significantly increase the welding extrusion amount and reduce weld inclusions and undesirable structures when processing small and medium-caliber welded pipe blanks, thereby making the weld microstructure properties similar to or consistent with those of the parent material, and preventing the forming and weld quality problems caused by smaller pipe diameter, increased wall thickness and increased carbon equivalent.

[0007] The present invention is achieved through the following technical solutions, providing a method for improving the flattening performance of small and medium-caliber high-carbon equivalent thick-walled HFW welded pipe blanks, comprising the following steps:

[0008] S1 uses FFX to form low-carbon microalloy coils;

[0009] S2 is formed and then HFW welded;

[0010] After S3 welding is completed, hot tension reduction and graded cooling are used to obtain HFW welded pipe blanks.

[0011] In particular, the low carbon microalloy coil comprises the following components calculated by mass percentage:

[0012] C 0.18~0.25%, Si 0.15~0.30%, Mn 0.5~1.5%, Cr 0.30~0.70%, Mo0.05~0.25%, Nb 0.01~0.03%, V 0.05~0.15%, Ni 0.01~0.2%, B 0.006~0.018%, S≤0.005%, P≤0.010%, the balance is Fe and unavoidable impurities, and the carbon equivalent Ceq is 5.0~6.0.

[0013] In particular, after the S1 is formed by FFX, the circumference of the tube blank is 615.5-616 mm.

[0014] In particular, the distance Vee between the welding electrode and the center of the welding extrusion roller in S2 is 200-250 mm, the welding power is 270-320 kW, the welding speed is 12-14 m / min, the welding line energy is controlled to be 1300-1500 J / mm, the circumference after welding extrusion is controlled to be less than 610.5 mm, and the extrusion amount (circumference before pressurization - circumference after extrusion) is ≥5 mm; argon protection is introduced during welding, and the gas flow rate is 3-10 L / min.

[0015] In particular, after completing HFW welding, an R25mm small arc weld bead burr scraping tool is used to remove the burrs inside the weld bead.

[0016] In particular, in S3, the welded mother pipe is heated to 920-980°C by medium frequency induction, the inlet speed of the tension-reducing machine is controlled to be ≥15m / min, and the tension coefficient is -1.5--2.2%; after the hot tension-reducing, it is water-mist cooled to below 600°C, and the water-mist cooling is controlled and then air-cooled.

[0017] The present invention also provides a small-to-medium-caliber, high-carbon equivalent, thick-walled HFW welded pipe blank prepared by the method.

[0018] Compared with the prior art, the present invention provides a method for improving the flattening performance of small and medium-caliber, high-carbon equivalent, thick-walled HFW welded pipe billets. This method can effectively solve the weld quality problems of small and medium-caliber, high-grade HFW welded pipe billets caused by small outer diameter, high carbon equivalent, and large wall thickness. At the same time, it can significantly reduce undesirable weld structures, making the overall weld performance basically consistent with that of the parent material, and avoiding problems such as unsatisfactory flattening performance caused by insufficient extrusion, insufficient extrusion of weld oxide inclusions, coarse weld structure, and weld widmanstatten structure, which lead to the scrapping of the billet.

Brief Description of the Drawings

[0019] Figure 1 This is the flattened fracture morphology of an embodiment of the present invention;

[0020] Figure 2 This is a metallographic diagram of the weld according to an embodiment of the present invention.

[0021] Figure 3 A pair of proportional flattened fractures and energy spectrum analysis;

[0022] Figure 4 A pair of proportional weld metallographic diagrams. [Specific implementation method]

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0024] Example

[0025] This embodiment is used to prepare a φ139.7×10.54mm 125ksi steel-grade welded pipe blank. The blank is made from a low-carbon microalloyed coil. The chemical composition of the low-carbon microalloyed coil, calculated by weight, includes the following components: C 0.23%, Si 0.22%, Mn 1.18%, Cr 0.42%, Mo 0.22%, Nb 0.03%, V 0.12%, Ni 0.08%, B 0.009%, S ≤ 0.005%, P ≤ 0.010%, with the balance being Fe and unavoidable impurities. The carbon equivalent (CE) is 0.58.

[0026] The specific preparation method is:

[0027] After rough forming the low-carbon microalloy coil through FFX, a tube blank with a front circumference of 616mm was obtained. The distance Vee between the welding electrode and the center of the welding extrusion roller was adjusted to 250mm. The welding power was 315kW, the welding speed was 13.2m / min, the welding line energy was 1413J / mm, and argon shielding was introduced with an argon flow rate of 5L / min and an extrusion volume of 5.5mm. After HFW welding, the tube blank had a rear circumference of 610.2mm. Burrs within the weld were removed using an R25mm small arc weld bead burr cutter. The welded mother pipe was heated to 950°C, the inlet speed of the tension-reducing machine was controlled at 18m / min, the tension coefficient was kept at -2.0%, and after hot tension-reducing, it was water-mist cooled to below 600°C and then air-cooled to obtain the welded tube blank.

[0028] Comparative Example

[0029] This comparative example is used to prepare a φ139.7×10.54mm 125ksi steel-grade welded pipe blank, which is made from a coil. The chemical composition of the coil, calculated by weight percentage, includes the following components: C 0.23%, Si 0.22%, Mn 1.18%, Cr 0.42%, Mo 0.22%, Nb 0.03%, V 0.12%, Ni 0.08%, B 0.009%, S ≤ 0.005%, P ≤ 0.010%, and the balance is Fe and unavoidable impurities. The carbon equivalent CE is 0.58.

[0030] The specific preparation method is:

[0031] After rough forming of the coiled sheet through FFX, the pre-weld circumference of the tube billet is 615.8mm, the Vee distance is 100mm, the welding power is 285kW, the welding speed is 12.8m / min, and the welding energy input is 1258J / mm. The post-extrusion circumference is 611mm, the extrusion volume is 4.8mm, and burrs within the weld bead are removed using an R25mm small arc weld bead burr cutter. The welded tube billet is heated to 950°C, the inlet speed of the tension-reducing mill is controlled at 18m / min, and the tension coefficient is -2.0%. After hot tension-reducing, it is air-cooled to obtain the welded tube billet.

[0032] In order to better understand the performance of the tube blank prepared by the present invention, the following is an explanation through experiments.

[0033] Please refer to Table 1 below, which shows the flattening performance results of the embodiment and the comparative example. As can be seen from Table 1, according to the requirements of the API Spec 5CT:2018 standard for flattening tests, the welded pipe blanks produced according to the process of the embodiment have a flattening pass rate of 100%, while the welded pipe blanks produced by the comparative example process have a flattening pass rate of only 18%, and the flattening pass rate is mainly concentrated at the 0° position of the weld.

[0034] Table 1 Flattening performance results

[0035]

[0036] It can be seen that the tube blank prepared by the method of the present invention has better flattening performance, so the tube blank prepared by this method has higher weld quality and can be applied to unconventional oil and gas wells.

[0037] See also Figure 1 , Figure 1 The flattened fracture morphology of the embodiment is shown by Figure 1 It can be seen that the fracture morphology of the tube prepared in the embodiment is mainly a quasi-cleavage fracture morphology of small dimples + tearing edges, the fracture surface is clean and tidy, and no second phase inclusions are precipitated. Figure 3 The flattened fracture morphology of the comparative example is shown in Figure 2. Figure 3 It can be seen that the fracture of the tube prepared in the comparative example is mainly composed of two forms: cold welding area, dimple + tearing edge and second phase inclusions. The inclusions are mainly blocky oxides. After analysis, it is found that the main reasons are: first, the welding heat input does not match the extrusion amount, resulting in too small welding heat input; second, due to the small extrusion amount and no atmosphere protection, the molten metal of the weld is oxidized in the air during welding and cannot be completely squeezed out of the weld.

[0038] See also Figure 2 , Figure 2 The metallographic structure of the weld is shown in FIG. Figure 2 It can be seen that the metallographic structure of the tube blank prepared in this embodiment is mainly ferrite + pearlite structure, the structure is uniform and fine, and the weld structure is consistent with the base material structure. Figure 4 , Figure 4 The metallographic structure of the comparative weld is Figure 4 It can be seen that the metallographic structure of the tube blank prepared in the comparative example is ferrite + pearlite + widmanstatten structure, the weld structure is coarse and has poor consistency with the parent material structure. The appearance of the widmanstatten structure is mainly due to the overheating of the structure caused by the high temperature during hot tension reducing and the slow cooling rate in the high temperature section.

[0039] In summary, the method described in the present invention can reduce weld inclusions and undesirable structures, so that the weld structure properties are close to or consistent with the parent material structure properties, and prevent forming and weld quality problems caused by smaller pipe diameter, increased wall thickness and increased carbon equivalent.

Claims

1. A method for improving the flattening performance of small and medium diameter high carbon equivalent thick wall HFW welded pipe blanks, characterized in that: The following steps are involved: S1 uses FFX to form low-carbon microalloy coils; S2 is formed and then HFW welded; After S3 welding is completed, hot tension reduction and graded cooling are used to obtain HFW welded pipe blanks.

2. The method for improving the flattening performance of small and medium diameter high carbon equivalent thick wall HFW welded pipe blanks according to claim 1, characterized in that: The low carbon microalloy coil comprises the following components calculated by mass percentage: C 0.18~0.25%, Si 0.15~0.30%, Mn 0.5~1.5%, Cr 0.30~0.70%, Mo0.05~0.25%, Nb 0.01~0.03%, V 0.05~0.15%, Ni 0.01~0.2%, B 0.006~0.018%, S≤0.005%, P≤0.010%, the balance is Fe, and the carbon equivalent Ceq is 5.0~6.

0.

3. The method for improving the flattening performance of small and medium diameter high carbon equivalent thick wall HFW welded pipe blanks according to claim 1, characterized in that: After the S1 is formed by FFX, the circumference of the tube blank is 615.5-616 mm.

4. The method for improving the flattening performance of small and medium diameter high carbon equivalent thick wall HFW welded pipe blanks according to claim 1, characterized in that: In S2, the distance Vee between the welding electrode and the center of the welding extrusion roller is 200-250 mm, the welding power is 270-320 kW, the welding speed is 12-14 m / min, the welding line energy is controlled to be 1300-1500 J / mm, the circumference after welding extrusion is controlled to be <610.5 mm, and the extrusion amount is ≥5 mm; argon gas protection is introduced during welding, and the gas flow rate is 3-10 L / min.

5. The method for improving the flattening performance of small and medium diameter high carbon equivalent thick wall HFW welded pipe blanks according to claim 1, characterized in that: After completing HFW welding, use an R25mm small arc weld bead burr scraping tool to remove the burrs inside the weld bead.

6. The method for improving the flattening performance of small and medium diameter high carbon equivalent thick wall HFW welded pipe blanks according to claim 1, characterized in that: In S3, the welded mother pipe is heated to 920-980° C. by medium frequency induction heating, the inlet speed of the tension-reducing machine is controlled to be ≥15 m / min, and the tension coefficient is -1.5--2.2%. After the hot tension-reducing, the pipe is water-mist cooled to below 600° C., and the water-mist cooling is controlled and then air-cooled.

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