Sulfur-resistant and corrosion-resistant low-carbon alloy coiled tubing and preparation method therefor

Abstract

A sulfur-resistant and corrosion-resistant low-carbon alloy coiled tubing and a preparation method therefor. The sulfur-resistant and corrosion-resistant low-carbon alloy coiled tubing has a metallographic structure of ferrite and pearlite, and is prepared by means of the butt joint of steel strip plates, coiling molding, tube blank welding, extrusion molding, a welding seam heat treatment and cooling. In the preparation method, welding seam grains of the steel strips are refined by means of a plasma welding method, such that the structure is uniform, and the strength is stable; and the heat treatment process refines the welding seam grains, makes the structure more uniform, and improves the strength and corrosion resistance of a coiled tubing.

Description

A sulfur-resistant and corrosion-resistant low-carbon alloy coiled tubing and its preparation method Technical Field

[0001] This invention relates to the field of coiled tubing technology, and in particular to a sulfur-resistant and corrosion-resistant low-carbon alloy coiled tubing and its preparation method. Background Technology

[0002] Currently, CT80 coiled tubing is commonly used in oil and gas drilling and extraction. CT80 coiled tubing is typically made from low-carbon, low-manganese steel strip, manufactured using high-frequency welding or laser welding, achieving a steel strength of only 80 grade steel. Therefore, while CT80 coiled tubing can meet the operating environment of hydrogen sulfide wellfields, its low strength, short lifespan, insufficient pressure and load-bearing capacity, and inadequate sulfur and corrosion resistance negatively impact resource recovery rates in the oil and gas sector. Furthermore, as well conditions in oil and gas resource extraction become increasingly complex, CT80 coiled tubing is insufficient to meet the demands of resource extraction. Summary of the Invention

[0003] In view of this, the present invention provides a sulfur-resistant and corrosion-resistant low-carbon alloy coiled tubing and its preparation method. The present invention improves the grain refinement and microstructure uniformity of the steel strip weld seam through plasma welding and optimized heat treatment process, which significantly improves the tensile strength, yield strength and corrosion resistance of the coiled tubing, which is superior to the traditional CT90 coiled tubing. The comprehensive performance can reach the 90 steel grade.

[0004] The sulfur-resistant and corrosion-resistant low-carbon alloy continuous tubing provided by this invention is manufactured through butt jointing of steel strips, coiling, tube blank welding, extrusion molding, weld heat treatment, and cooling. The sulfur-resistant and corrosion-resistant low-carbon alloy continuous tubing comprises, by weight percentage:

[0005] C 0.04%–0.08%, Mn 1.5%–2.0%, Si 0.1%–0.3%, Cr 0.1%–0.3%, Mo 0.05%–0.3%, Nb 0.04%–0.07%, Ti 0.005%–0.025%, Al 0.01%–0.05%, Ni≤0.3%, Cu≤0.3%, P≤0.02%, S≤0.02%, with the balance being Fe and unavoidable impurities.

[0006] This application also provides a method for preparing the sulfur-resistant and corrosion-resistant low-carbon alloy coiled tubing, comprising the following steps:

[0007] S1. The steel strip is extended by butt welding, and the weld area is subjected to rolling deformation heat treatment.

[0008] S2. The steel strip obtained in S1 is rolled into a circular tube blank with a weld.

[0009] S3, welding the round pipe blank obtained in S2, and extruding the weld by adding an extruding roller to the rear of the molten pool which has not solidified;

[0010] S4, heat treating the weld extruded in S3, and obtaining the sulfur-resistant and corrosion-resistant low-carbon alloy continuous oil pipe by air cooling to room temperature.

[0011] Preferably, the butt welding in S1 is performed by plasma welding, and a manganese-molybdenum steel high-strength copper-plated welding wire is used.

[0012] Preferably, the roll-shaping heat treatment in S1 refers to roll-shaping the weld area while heat treating, the roll-shaping pressure is 4-8T, one reciprocation, the roll-shaping heat treatment temperature is 600-750 DEG C, and the single roll-shaping heat treatment holding time is 10s.

[0013] Preferably, the welding in S3 is laser welding or high-frequency welding.

[0014] Preferably, the heat treatment in S4 is simulated normalizing and tempering, the simulated normalizing treatment temperature is 900-940 DEG C, the furnace is heated by induction heating, the heating coil length is 1.5m, the running speed is 2.8m / min, the heating is followed by air cooling, the air cooling section length is 50m, and then the pipe is cooled to room temperature in a water cooling section, the tempering treatment temperature is 500-600 DEG C, the tempering furnace holding section length is 4m, and the holding time is 79.8s.

[0015] Compared with the prior art, the steel strip weld grain is refined by plasma welding, the structure is uniform, the strength is stable, and the reduction of the plate interface strength and corrosion resistance is avoided. Meanwhile, the heat treatment process of the present application refines the weld grain, makes the structure more uniform, removes the stress, makes the whole pipe strength stable, and the structure uniform, and finally achieves the purpose of high strength and strong corrosion resistance.

[0016] The pipe body of the sulfur-resistant and corrosion-resistant low-carbon alloy continuous oil pipe of the present application has the same anti-HIC cracking, anti-SSC cracking and corrosion resistance in 95% N2+5% O2 environment as the pipe body of the CT90 continuous oil pipe. The tensile strength of the pipe body of the sulfur-resistant and corrosion-resistant low-carbon alloy continuous oil pipe of the present application is greater than 669MPa, the yield strength is greater than 620MPa, the average hardness is 95HRB, the metallographic structure is ferrite+pearlite, the average grain size of the metal in the weld, heat affected zone and base material is greater than 10.0, and the pipe can reach the 90 steel grade. BRIEF DESCRIPTION OF DRAWINGS

[0017] The present application will be further described below in combination with the drawings.

[0018] Fig. 1 is a weld equisection of the embodiment 1 of the present application.

[0019] Figure 2 is a weld bisecting section of Inventive Comparative Example 1;

[0020] Figure 3 is the surface of the Example 1 sample from Test Example 2 before cleaning of corrosion products;

[0021] Figure 4 is the surface of the Example 1 sample from Test Example 2 after cleaning of corrosion products;

[0022] Figure 5 is the surface of the CT90 sample from Test Example 2 before cleaning of corrosion products;

[0023] Figure 6 is the surface of the CT90 sample from Test Example 2 after cleaning of corrosion products;

[0024] Figure 7 is the surface of the sample at the weld from Test Example 3;

[0025] Figure 8 is the metallograph of the bisecting section at the weld from Test Example 3;

[0026] Figure 9 is the surface of the sample 90° from the weld from Test Example 3;

[0027] Figure 10 is the metallograph of the bisecting section 90° from the weld from Test Example 3;

[0028] Figure 11 is the surface of the sample 180° from the weld from Test Example 3;

[0029] Figure 12 is the metallograph of the bisecting section 180° from the weld from Test Example 3;

[0030] Figure 13 is the surface (front side) of the CT80-2 sample after 96h corrosion testing;

[0031] Figure 14 is the surface (back side) of the CT80-2 sample after 96h corrosion testing;

[0032] Figure 15 is the surface (front side) of the Example 1 sample after 96h corrosion testing;

[0033] Figure 16 is the surface (back side) of the Example 1 sample after 96h corrosion testing;

[0034] Figure 17 is the surface (front side) of the CT80-1 sample after 96h corrosion testing;

[0035] Figure 18 is the surface (back side) of the CT80-1 sample after 96h corrosion testing;

[0036] Figure 19 is the surface (front side) of the CT90 sample after 96h corrosion testing;

[0037] Figure 20 is the surface (back side) of the CT90 sample after 96h corrosion testing;

[0038] Figure 21 is a typical metallographic crack in the cross section of the CT80-1 sample;

[0039] Figure 22 is a typical metallographic crack in the cross section of the CT90 sample;

[0040] Figure 23 is a CT80-2 sample surface after 720h corrosion test;

[0041] Figure 24 is a sample surface after 720h corrosion test of Example 1;

[0042] Figure 25 is a CT80-1 sample surface after 720h corrosion test;

[0043] Figure 26 is a CT90 sample surface after 720h corrosion test. DETAILED DESCRIPTION

[0044] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0045] The present application provides a kind of anti-sulfur corrosion-resistant low-carbon alloy coiled tubing, it is made after butt joint by steel strip plate, curling forming, pipe blank welding, extrusion forming, weld heat treatment, cooling, the anti-sulfur corrosion-resistant low-carbon alloy coiled tubing of the present application includes, by mass percent:

[0046] C 0.04%~0.08%, Mn 1.5%~2.0%, Si 0.1%~0.3%, Cr 0.1%~0.3%, Mo 0.05%~0.3%, Nb 0.04%~0.07%, Ti 0.005%~0.025%, Al 0.01%~0.05%, Ni≤0.3%, Cu≤0.3%, P≤0.02%, S≤0.02%, the balance is Fe and inevitable impurities.

[0047] In the coiled tubing of the present application, the content of C affects the corrosion rate and hardness of the coiled tubing, the higher the carbon content, the more micro-batteries formed, the faster the corrosion rate of carbon steel, the lower the carbon content, the lower the basic strength (hardness) of carbon steel, therefore, the present application controls the carbon content to be 0.04%~0.08% to seek a balance between corrosion resistance and strength of the coiled tubing; the role of Mn is to increase the strength of carbon steel; the role of Si is to avoid the decrease of toughness; the role of Ti and Al is to refine the grain. Compared with conventional CT90 raw materials, the present application adjusts the elements to make the coiled tubing have strong corrosion resistance.

[0048] The present application also provides a preparation method of the anti-sulfur corrosion-resistant low-carbon alloy coiled tubing, comprising the following steps:

[0049] S1, the steel strip is connected by butt welding, and the weld area is subjected to rolling deformation heat treatment;

[0050] S2, the steel strip obtained in S1 is coiled to form a round pipe blank with a weld seam;

[0051] S3, the round pipe blank obtained in S2 is welded, and the rear of the molten pool which has not solidified is added with an extrusion roller to extrude and form the weld seam;

[0052] S4, the extrusion-formed weld seam in S3 is heat treated, and after air cooling to room temperature, an anti-sulfur and corrosion-resistant low-carbon alloy continuous oil pipe is obtained.

[0053] The butt welding method in S1 of the present application is preferably plasma welding, and the welding wire used is preferably a manganese-molybdenum steel high-strength copper-plated welding wire. The present application uses plasma welding to achieve the purpose of single-sided welding and double-sided forming, avoids oxidation of alloy steel, and has high penetration for welding various wall thickness plates.

[0054] The rolling deformation heat treatment in S1 of the present application refers to rolling the weld seam area while heat treating, the rolling pressure is 4-8T, one reciprocation, the rolling deformation heat treatment temperature is 600-750℃, and the single rolling heat treatment holding time is 10s. The rolling deformation heat treatment of the present application refines the weld seam grains, makes the structure uniform, stabilizes the strength, and avoids reducing the plate joint strength and corrosion resistance.

[0055] In some specific embodiments of the present application, the weld seam gap in S2 is 1-2mm.

[0056] The welding in S3 of the present application is preferably laser welding or high-frequency welding.

[0057] The heat treatment obtained in S4 of the present application is simulated normalizing and tempering treatment, wherein the heat treatment in S4 is simulated normalizing and tempering treatment, wherein the simulated normalizing treatment temperature is 900-940℃, the furnace is heated by induction heating, the heating coil length is 1.5m, the running speed is 2.8m / min, after heating, air cooling, the air cooling section length is 50m, and then enters the water cooling section to cool to room temperature, the tempering treatment temperature is 500-600℃, the tempering furnace holding section length is 4m, and the holding time is 79.8s. In some specific embodiments of the present application, the simulated normalizing treatment temperature is 910℃, and the tempering treatment temperature is 550℃. In another preferred embodiment of the present application, the simulated normalizing treatment temperature is 940℃, and the tempering treatment temperature is 550℃.

[0058] The present application adopts the mode of extrusion + laser welding or high frequency welding, when the plate is formed, the strip steel is gradually rolled up by the rolling roller to form a circular pipe blank with an opening gap, the reduction of the extrusion roller is adjusted to control the welding gap at 1-2mm, welding is carried out, after welding, the extrusion roller is added behind the molten pool which has not solidified, the rolling amount is increased to 0 between the edges of the two ends of the steel strip, and then the welding and extrusion forming are carried out, and then the welding heat treatment is carried out, so that the deformation strengthening and phase change strengthening are combined, and the welding strength is greatly improved.

[0059] In order to further illustrate the present application, the following examples are used for detailed description. The raw materials used in the following examples of the present application are all commercially available.

[0060] The CT80-1 involved in the specific embodiment of the present application includes, in mass percentage:

[0061] C 0.046%, Si 0.162%, Mn 0.745%, P 0.011%, S 0.001%, Cr 0.558%, Ni 0.040%, Mo 0.184%, Cu 0.206%, W 0.004%, Ca 0.001%, V 0.006%, Ti 0.020%, Nb 0.017%, Al 0.041%, Zr 0.011%, Co 0.007%, B 0.00001%, As 0.008%, Pb 0.001%, Bi 0.023%, Sn 0.001%, Sb 0.074%, Bi 0.023%, and the balance is iron and inevitable impurities.

[0062] The CT80-2 involved in the specific embodiment of the present application includes, in mass percentage:

[0063] C 0.062%, Si 0.253%, Mn 0.763%, P 0.008%, S 0.001%, Cr 0.679%, Ni 0.144%, Mo 0.160%, Cu 0.262%, W 0.010%, Ca 0.001%, V 0.005%, Ti 0.017%, Nb 0.017%, Al 0.043%, Zr 0.008%, Co 0.009%, B 0.00001%, As 0.004%, Pb 0.001%, Bi 0.015%, Sn 0.001%, Sb 0.050%, Bi 0.015%, and the balance is iron and inevitable impurities.

[0064] The CT90 involved in the specific embodiment of the present application includes, in mass percentage:

[0065] C 0.123%, Si 0.405%, Mn 0.898%, P 0.006%, S 0.0001%, Cr 0.546%, Ni 0.056%, Mo 0.159%, Cu 0.243%, W 0.004%, Ca 0.001%, V 0.005%, Ti 0.035%, Nb 0.018%, Al 0.061%, Zr 0.011%, Co 0.006%, B 0.00001%, As 0.008%, Pb 0.002%, Bi 0.022%, Sn 0.002%, Sb 0.070%, Bi 0.022%, balance of Fe and inevitable impurities.

[0066] Example 1 A sulfur-resistant corrosion-resistant low-carbon alloy coiled tubing, comprising, in mass percent:

[0067] C 0.0605%, Mn 1.7890%, Si 0.1675%, Cr 0.2080%, Mo 0.1375%, Nb 0.0620%, Ti 0.0100%, Al 0.0180%, Ni 0.0001%, Cu 0.0275%, P 0.0110%, S 0.0020%, balance of Fe and inevitable impurities.

[0068] The method for preparing the sulfur-resistant corrosion-resistant low-carbon alloy coiled tubing comprises the following steps:

[0069] S1, the steel strip is lengthened by plasma welding, the welding wire is a high-strength copper-plated manganese-molybdenum steel wire, the weld area is subjected to rolling deformation heat treatment, the rolling pressure is 6T, one reciprocation, the rolling deformation heat treatment temperature is 735°C, the single rolling heat treatment holding time is 10 seconds, and the treatment is completed by air cooling to room temperature;

[0070] S2, the steel strip obtained in S1 is coiled and formed to form a round pipe blank with a (1.5±0.5) mm weld;

[0071] S3, the round pipe blank obtained in S2 is subjected to laser welding, and an extrusion roller is added behind the molten pool that has not solidified to extrude and form the weld;

[0072] S4, the extrusion-formed weld in S3 is subjected to simulated normalizing heat treatment at 910°C and 940°C respectively, the simulated normalizing furnace adopts an induction heating mode for heating, the heating coil length is 1.5 m, the running speed is 2.8 m / min, after heating, air cooling is performed, the air cooling section length is 50 m, then the coiled tubing is cooled to room temperature in a water cooling zone, and then is subjected to tempering treatment at 550°C, the tempering furnace holding section length is 4 m, the holding time is 79.8 s, and after air cooling to room temperature, the sulfur-resistant corrosion-resistant low-carbon alloy coiled tubing is obtained.

[0073] Comparative Example 1

[0074] The same as Example 1, except that the simulated normalizing temperature is 910℃, and only laser welding is performed in the S3, without extrusion, specifically: laser welding is performed on the round pipe blank obtained in the S2.

[0075] Comparative Example 2

[0076] The same as Example 1, except that the simulated normalizing temperature is 890℃.

[0077] Comparative Example 3

[0078] The same as Example 1, except that the simulated normalizing temperature is 950℃.

[0079] Example 4

[0080] The same as Example 1, except that the simulated normalizing temperature is 980℃.

[0081] Test Example 1

[0082] The continuous oil pipe and weld performance of the size of 38.1mm x 3.7mm obtained in Example 1 and Comparative Examples 1-3 are detected, and the results are shown in Table 1.

[0083] Table 1: Continuous oil pipe and weld performance detection results

[0084] Test Example 2

[0085] The nitrogen and oxygen environment corrosion test is performed on the anti-sulfur and corrosion-resistant low-carbon alloy continuous oil pipe raw material of Example 1 and the traditional CT90 steel plate, and the test conditions are: N2 content is 95%, O2 content is 5%, total pressure is 10MPa, temperature is 150℃, solution is 5% NaCl, and cycle is 168h. The detection results are shown in Table 2.

[0086] Table 2: Steel plate nitrogen and oxygen environment corrosion test results

[0087] As shown in Table 2, the corrosion resistance of the continuous oil pipe is improved by adjusting the elements of the raw material.

[0088] Test Example 3

[0089] The hydrogen induced cracking (HIC) performance of the weld of the continuous oil pipe of Example 1 is evaluated, and the method is: samples are taken at the weld position, 90° and 180° positions from the weld on the pipe, the sample surface is polished, the test is performed according to the NACE TM0284 standard under A solution conditions, the sample is taken out after soaking for 96h, and the internal cracking of the sample is observed according to the equal section method, and the detection results are shown in Figures 7-12.

[0090] Test conditions: P H2S = 0.1 MPa, solution is NACE-A, temperature is (25±3) °C for 96h.

[0091] Test process parameters:

[0092] The prepared solution pH = 2.75, the initial solution pH = 3.03, the initial hydrogen sulfide concentration is 2409 mg / L, the end solution pH = 3.65, and the end hydrogen sulfide concentration is 2512 mg / L.

[0093] As shown in FIGS. 7-12, there are a small amount of cracks in the core of the weld position sample, but the crack rate meets the requirements of API5L, and no cracking is found in the samples at 90° and 180° positions from the weld.

[0094] Test Example 4

[0095] HIC tests were performed on the coiled tubing of Example 1 (1#) and CT80-1 (2#), CT80-2 (3#), and CT90 (4#).

[0096] (1) The HIC test is based on the standard NACE TM0284-2016, and the specific conditions are as follows:

[0097] Temperature 23-26 °C, deoxidizing gas: 99.999% N2, test gas: 99.9% H2S, test solution A, test period 96h, hydrogen sulfide concentration in solution 2460 mg / L, hydrogen sulfide concentration in solution after saturation 1h 2396 mg / L, initial pH = 2.7, test start pH = 2.9, test end pH = 3.7, sample nominal size L x W x t (mm) = 100 x 20 x 4, sampling direction: longitudinal direction of the pipe body. The HIC test results are shown in Table 3.

[0098] Table 3 HIC test results of coiled tubing

[0099] Test Example 5

[0100] Sulfide stress cracking (SSC) tests were performed on the coiled tubing of Example 1 (1#) and CT80-1 (2#), CT80-2 (3#), and CT90 (4#).

[0101] The standard is NACE TM0177-2016 and ISO 7539-2:1989 (four-point bending loading method), and the specific conditions are as follows:

[0102] Temperature 23°C to 26°C, pressure 1 atm, deoxidizing gas: 99.999% N2, test gas: 99.9% H2S, test solution A, test period 720 h, initial pH value = 2.7, test start pH value = 2.9, test end pH value = 3.7, sample nominal size L x W x t (mm) = 67.5 x 4.5 x 1.6, sampling direction: pipe body longitudinal direction. The HIC test results are shown in Table 4.

[0103] Table 4 Sulphide Stress Cracking (SSC) Test Results

[0104] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of the patent protection of the present application should be subject to the appended claims.

Claims

1. A sulfur-resistant, corrosion-resistant, low-alloy, coiled tubing, characterized in that, The anti-sulfur corrosion-resistant low-carbon alloy continuous oil pipe is made by butt jointing steel strips, curling forming, pipe blank welding, extruding forming, weld heat treatment and cooling, and comprises, in mass percent: C 0.04%~0.08%, Mn 1.5%~2.0%, Si 0.1%~0.3%, Cr 0.1%~0.3%, Mo 0.05%~0.3%, Nb 0.04%~0.07%, Ti 0.005%~0.025%, Al 0.01%~0.05%, Ni≤0.3%, Cu≤0.3%, P≤0.02%, S≤0.02%, and the balance of Fe and inevitable impurities.

2. A method of making the sulfur-resistant, corrosion-resistant, low-carbon alloy coiled tubing of claim 1, characterized by, The method comprises the following steps: S1, the steel strip is lengthened by butt welding, and the welding seam area is sequentially rolled and subjected to deformation heat treatment; S2, the steel strip obtained in S1 is curling formed to form a round pipe blank with a welding seam; S3, the round pipe blank obtained in S2 is welded, and the un-solidified rear of the molten pool is added with an extrusion roller to extrude and form the welding; S4, the welding subjected to the extruding forming in S3 is subjected to heat treatment, and the anti-sulfur corrosion-resistant low-carbon alloy continuous oil pipe is obtained after air cooling to room temperature.

3. The preparation method according to claim 2, characterized in that, The butt welding in S1 adopts plasma welding, and a manganese-molybdenum steel high-strength copper-plated welding wire is used.

4. The production method according to claim 2, characterized by, The rolling pressure in S1 is 4~8T, and one reciprocation is performed.

5. The preparation method according to claim 2, characterized in that, The rolling deformation heat treatment in S1 refers to rolling the welding seam area while heat treatment, the rolling pressure is 4~8T, one reciprocation is performed, the rolling deformation heat treatment temperature is 600~750℃, and the single rolling heat treatment holding time is 10s.

6. The method of claim 2, wherein, The welding seam gap in S2 is 1~2mm.

7. The preparation method according to claim 2, characterized in that, The welding in S3 is laser welding or high-frequency welding.

8. The preparation method according to claim 2, characterized in that, The heat treatment in S4 is simulated normalizing and tempering treatment, wherein the simulated normalizing treatment temperature is 900~940℃, and the tempering treatment temperature is 500~600℃.

9. The preparation method according to claim 8, characterized in that, The simulated normalizing treatment temperature is 910℃, and the tempering treatment temperature is 550℃.

10. The preparation method according to claim 8, characterized in that, The simulated normalizing treatment temperature is 940℃, and the tempering treatment temperature is 550℃.

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