US20240247350A1 - Seamless steel tube resistant to carbon dioxide corrosion and manufacturing method therefor

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Abstract

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US20240247350A1

Publication number: US20240247350A1
Application number: US18/290,401
Authority: US
Inventors: Suzhen LUO; Yameng Qi; Zhonghua Zhang
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2021-05-21
Filing date: 2022-05-20
Publication date: 2024-07-25
Also published as: CN115369316A; WO2022242742A1

Disclosed in the present application is a high-strength seamless steel tube resistant to carbon dioxide corrosion. In addition to containing Fe and inevitable impurities, the seamless steel tube comprises the following chemical elements in mass percentage: C: 0.05-0.18%, Si: 0.15-0.40%, Mn: 0.25-0.50%, Cr: 4.0-6.0%, Mo: 0.08-0.35%, Al: 0.020-0.055%, Ca: 0.001-0.004%; and one or more elements selected from Ti, Nb, V, Ce, and La, wherein 0.003%≤Ti+Nb+V+Ce+La≤0.20%. Also disclosed in the present application is a manufacturing method for the seamless steel tube. The method comprises the following steps: (1) manufacturing a tube billet; (2) subjecting the tube billet to heating, perforating, hot rolling, and sizing to obtain a hot-rolled tube; and (3) subjecting the hot-rolled tube to a quenching and tempering heat treatment: quenching within a temperature range of 860-940° C. for 15-120 min, and then tempering within a temperature range of 520-620° C. for 30-150 min.

TECHNICAL FIELD

The present disclosure relates to a metal material and a manufacturing method therefor, particularly to a seamless steel tube and a manufacturing method therefor.

BACKGROUND

In recent years, there have been frequent incidents failures induced by corrosion in oil well pipes and line pipes for transportation of gas and petroleum in major oil fields. Among these incidents, failures induced by CO₂corrosion account for a considerable proportion, resulting in substantial economic losses when they occur.
Research related to CO₂corrosion has a history of nearly a century, and some progress has been made in CO₂corrosion protection technology. Both domestic and foreign steel pipe manufacturers have successively developed a series of seamless steel pipes resistant to CO₂corrosion. At present, commercially available CO₂corrosion-resistant steel grades include corrosion-resistant alloy series, martensitic stainless steel series, and low-alloy series, such as the 1Cr series developed by Tenaris, 3Cr series such as TN80Cr3, TN95Cr3 and TN110Cr3, 13Cr series and 2205 duplex stainless steel series. V&M and JFE, as well as domestic Baosteel Group and Tianjin Iron and Steel Group, have also successfully developed the above-mentioned corrosion-resistant petroleum pipe series products.
With the change of oil and gas exploitation environment and the development of new exploitation technology, the problem of CO₂corrosion has become more prominent. In addition, given the continued downturn in the petroleum industry market, economically efficient exploitation is particularly important. Therefore, it is necessary to develop CO₂corrosion-resistant steel pipes that are more corrosion resistant than 3Cr and have superior cost-effectiveness.
From the number of papers published on CO₂corrosion in recent years, it can be seen that there are still a lot of scientific problems surrounding CO₂corrosion that have not been clarified, and the corrosion problem of oil fields has not been completely solved. With changes of oil and gas environment and the application of new exploitation technologies, the CO₂corrosion issues continue to be quite severe, presenting new demands and challenges for the development of new corrosion-resistant materials.
Both domestic and foreign scholars have conducted extensive research on the effect of Cr content on CO₂corrosion resistance. The research shows that as Cr content increases, CO₂corrosion resistance improves, but the degree of improvement varies in different content ranges. Additionally, studies have found that the influence of Mo, Cu, Ni, V, C, and other elements on CO₂corrosion may be completely opposite under different composition systems and different environmental conditions, which is the reason why the CO₂corrosion resistance among 5Cr products is quite different, and which is also the reason why both domestic and foreign steel pipe enterprises have not yet developed mature 5Cr series products.
Unlike the conventional CO₂corrosion-resistant petroleum pipe series products in the prior art, in order to avoid failures induced by CO₂corrosion in oil and gas development, the present disclosure aims to provide a seamless steel tube excellent in strength and resistance to CO₂corrosion as well as good processability. It is particularly suitable for casings, tubings and line pipes for transportation in the oil and gas environment with temperatures ranging from 60 to 90° C. and CO₂content of 0.5 MPa. Its applicability is extensive, and it holds prospects for promotion and application.

SUMMARY

One of the objectives of the present disclosure to provide a seamless steel tube resistant to carbon dioxide corrosion, which has high strength, good processability and CO₂corrosion resistance. It is particularly suitable for casings, tubings and transmission pipelines in the oil and gas environment with temperatures ranging from 60 to 90° C. and CO₂content of 0.5 MPa. Its applicability is extensive, and it holds prospects for promotion and application.
In order to achieve the above objectives, the present disclosure provides a seamless steel tube resistant to carbon dioxide corrosion. In addition to containing Fe and inevitable impurities, the seamless steel tube further contains the following chemical elements by mass percentage:

- C: 0.05-0.18%, Si: 0.15-0.40%, Mn: 0.25-0.50%, Cr: 4.0-6.0%, Mo: 0.08-0.35%, Al: 0.020-0.055%, Ca: 0.001-0.004%; and one or more selected from Ti, Nb, V, Ce, and La, wherein 0.003%≤Ti+Nb+V+Ce+La≤0.20%.

Preferably, the seamless steel tube of the present invention consists of the following chemical elements by mass percentage:

- C: 0.05-0.18%, Si: 0.15-0.40%, Mn: 0.25-0.50%, Cr: 4.0-6.0%, Mo: 0.08-0.35%, Al: 0.020-0.055%, Ca: 0.001-0.004%; and one or more selected from Ti, Nb, V, Ce, and La, wherein 0.003%≤Ti+Nb+V+Ce+La≤0.20%, with the balance being Fe and other inevitable impurity elements.

In the seamless steel tube according to the present disclosure, the design principles of chemical elements are as follows:

- C: In the seamless steel tube of the present disclosure, increasing the content of C in the steel is beneficial to enhancing the strength of the material. However, the C content should not be too high, as excessive C content can lead to a decrease in material toughness and plasticity and difficulties in decarburization control during high-temperature processing. The influence of the C content on the CO₂corrosion resistance of materials is very complicated. In different Cr content ranges, its effect may be precisely the opposite.

For example, in the 3Cr series of steels, increasing C content benefits the CO₂resistance of the material. However, it is found by the inventors that in 5Cr series steels, the influence of C content on the CO₂resistance of materials is exactly the opposite. Therefore, the C content in the present disclosure needs to be added in synergy with elements such as Cr and Mo to find the optimal balance between material strength and resistance to CO₂corrosion. Hence, in the seamless steel tube of the present disclosure, the mass percentage of C is controlled between 0.05% and 0.18%.
In some preferred embodiments, for better results, the mass percentage of C can be controlled between 0.09% and 0.15%.

- Si: In the seamless steel tube of the present disclosure, Si is a residual element in the steel after smelting deoxidation. Within the Si content range that meets the deoxidation requirements during steelmaking, Si content has no significant impact on the resistance to CO₂corrosion and material strength. Therefore, in the seamless steel tube of the present disclosure, the range is conventionally controlled, and the mass percentage of Si is controlled to 0.15-0.40%.

In some preferred embodiments, for better results, the mass percentage of Si can be controlled between 0.2% and 0.35%.

- Mn: In the seamless steel tube of the present disclosure, the strength of the material can be improved by adding an appropriate amount of Mn into the steel, Mn can also stabilize P and S elements, thereby avoiding the formation of low-melting-point sulfides and improving the hot workability of the material. Therefore, in order to achieve the above-mentioned desired effects, the content of Mn in the steel should not be too low, as low Mn content cannot effectively stabilize P and S elements. At the same time, the content of Mn in the steel should not be too high, as excessive Mn content can lead to solidification segregation during continuous casting. Micro-segregation or semi-macro-segregation can deteriorate deterioration the corrosion resistance of material. In addition, high Mn content can lead to serious deformation hardening during cold working, potentially exacerbating threading processing difficulties and other issues. Therefore, in the seamless steel tube of the present disclosure, the mass percentage of Mn is controlled to 0.25-0.50%.

In some preferred embodiments, for better results, the mass percentage of Mn can be controlled between 0.3% and 0.45%.

- Cr: In the seamless steel tube of the present disclosure, increasing the content of Cr can improve the harden-ability and resistance to CO₂corrosion. The addition of Cr affects the composition of the CO₂corrosion product film on the steel surface during service. The composition and structure of the corrosion product film determines the corrosion rate and service life of the material in the service environment. The inventors have found that when the content of Cr in steel reaches 4.0-6.0%, a relatively complete Cl⁻ selective corrosion product film is formed in CO₂corrosion environment. This film can completely isolate the diffusion of Cl⁻, preventing its corrosion product film and effectively inhibiting the initiation and propagation of pitting corrosion. Therefore, in the seamless steel tube of the present disclosure, the mass percentage of Cr is controlled between 4.0% and 6.0%.

In some preferred embodiments, for better results, the mass percentage of Cr can be controlled between 4.5% and 5.5%.

- Mo: In the seamless steel tube of the present disclosure, adding an appropriate amount of Mo into the steel can improve the solid solution strengthening capability and tempering stability of the material. In certain composition systems, it can improve the resistance to localized corrosion of the material. However, it should be noted that the ability of Mo to improve resistance to localized corrosion in low alloy systems is not as effective as its role in stainless steel. Therefore, in the seamless steel tube of the present disclosure, the mass percentage of Mo is controlled between 0.08% and 0.35%.

In some preferred embodiments, for better results, the mass percentage of Mo can be controlled between 0.1% and 0.25%.

- Al: In the seamless steel tube of the present disclosure, Al is added for deoxidation and is introduced into the molten steel to ensure the oxygen (O) content in the steel and to minimize adverse effects of the number and size of corresponding nonmetallic inclusions on mechanical properties and resistance to CO₂corrosion. Therefore, in the seamless steel tube of the present disclosure, the mass percentage of Al is controlled between 0.020% and 0.055%.

In some preferred embodiments, for better results, the mass percentage of Al can be controlled between 0.025% and 0.045%.

- Ca: In the seamless steel tube of the present disclosure, the addition of Ca is to further control the properties of Al/Si nonmetallic inclusions in steel, ensuring that the composition and size of nonmetallic inclusions have no impact on mechanical properties and resistance to CO₂corrosion. Therefore, in the seamless steel tube of the present disclosure, the mass percentage of Ca is controlled between 0.001% and 0.004%.

In some preferred embodiments, for better results, the mass percentage of Ca may be controlled between 0.0015% and 0.003%.
Additionally, it should be noted that in the present disclosure, elements such as Ti, Nb, V, Ce, and La can also be further added. These elements can further improve the performance of the seamless steel tube of the present disclosure.
In the seamless steel tube of the present disclosure, the content of Ti, Nb, V, Ce, and La can be controlled to satisfy the following: 0.003%≤Ti+Nb+V+Ce+La≤0.20%. In this equation, each chemical element of the above formula is substituted with the mass percentage of the corresponding chemical element when doing the calculation. Microalloying with Ti, Nb, V, Ce, and La can to some extent improve the strength, impact toughness, and corrosion resistance of the material.
In certain preferred embodiments, for better results, the content of Ti, Nb, V, Ce, and La can be optimally controlled to satisfy the following:
$0.005 % \leq Ti + Nb + V + Ce + La \leq 0.15 %$
However, it should be noted that the addition of the above elements will increase the cost of materials. Considering the balance between performance and cost control, it is preferable to selectively add at least one of the above elements in the technical solution of the present disclosure.
Preferably, in the seamless steel tube of the present disclosure, the content of each chemical element further satisfies at least one of the following:

- C: 0.09-0.15%,
- Si: 0.2-0.35%,
- Mn: 0.3-0.45%,
- Cr: 4.5-5.5%,
- Mo: 0.1-0.25%,
- Al: 0.025-0.045%,
- Ca: 0.0015-0.003%, and
- 0.005%≤Ti+Nb+V+Ce+La≤0.15%.

In the seamless steel tube of the present disclosure, among the inevitable impurities, the following maximum mass percentages are preferred: P≤0.015%, S≤0.008%, N≤0.006%, and O≤0.0035%.
In the seamless steel tube of the present disclosure, among the inevitable impurities, the following maximum mass percentages are more preferred: P≤0.012%, S≤0.005%, N≤0.0045%, and O≤0.002%.
In the above technical solution of the present disclosure, P, S, N, and O are all inevitable impurity elements in steel. Under the conditions allowed by the technology, it is necessary to control the content of impurity elements in the steel as low as possible.
In the seamless steel tube of the present disclosure, P and S are impurity elements introduced from raw materials or the production process of steel. P can cause grain boundary embrittlement leading to a degradation of the toughness and processability of the material. S forms low-melting-point sulfides, which decrease the processability and mechanical properties of the material.
Similarly, in the seamless steel tube of the present disclosure, N and O are impurity elements introduced during smelting and casting processes. N and O are prone to form inclusions in the steel, resulting in a degradation of the material properties. Therefore, in the present disclosure, it is necessary to strictly control the content of N and O in the seamless steel tube.
Preferably, in the seamless steel tube of the present disclosure, the microstructure is tempered sorbite.
Preferably, the properties of the seamless steel tube of the present disclosure satisfy at least one of the following:
$yield strength Rp 0.2 \geq 550 Mpa, tensile strength Rm \geq 670 MPa, elongation A 50 \geq 15 %, and impact property KV8 \geq 60 J;$

- under the dynamic corrosion environment conditions of 60-90° C., 0.5 MPa CO₂, 50,000 ppm Cl⁻, and 1 m/s, the weight loss corrosion rate is less than 0.08 mm/d, and the pitting corrosion rate is less than 0.2 mm/d.

Correspondingly, another objective of the present disclosure is to provide a manufacturing method for the seamless steel tube resistant to carbon dioxide corrosion. The seamless steel tube manufactured using the manufacturing method has excellent mechanical properties and resistance to CO₂corrosion, making it particularly suitable for casings, tubings, and transmission pipelines in oil and gas environments with a CO₂content of 0.5 MPa at 60-90° C. It has excellent prospects for promotion and application.
In order to achieve the above objectives, the present disclosure provides a manufacturing method for the above seamless steel tube, and the manufacturing method includes the following steps:

- (1) Manufacturing a tube billet;
- (2) Heating, perforating, hot rolling, and sizing the tube billet to obtain a hot-rolled tube; and
- (3) Subjecting the hot-rolled tube to quenching and tempering heat treatment.

In the manufacturing method of the seamless steel tube of the present disclosure, according to the chemical composition design requirements of the present disclosure, an electric furnace or converter is used for smelting+refining, casting the metal into tube billet. Then the tube billet is subjected to heating, perforating, hot rolling, and sizing to obtain a hot-rolled tube. In order to meet the requirements for tube strength and CO₂corrosion resistance in oil and gas exploitation, further quenching and tempering heat treatment is required for the hot-rolled tube obtained in step (2).
In the quenching and tempering heat treatment step of step (3) of the present disclosure, the hot-rolled tube needs to be quenched in a temperature range of 860-940° C. and held at this temperature for 15-120 min, followed by further tempering in a temperature range of 520-620° C. for 30-150 min to obtain a tempered sorbite structure. This process results in a seamless steel tube product satisfying the requirements of service conditions for strength, toughness, and CO₂corrosion resistance.
Preferably, in the manufacturing method of the present disclosure, in the heating step of step (2), the tube billet is heated at 1180-1280° C. for 120-350 min.
Preferably, in the manufacturing method of the present disclosure, in step (2), perforating, hot rolling, and sizing are performed in the range of 1160-1260° C.
In the technical solution of the present disclosure, in the heating step of step (2), the tube billet can be first heated at 1180-1280° C. for 120-350 min, and then high-temperature deformation such as high-temperature perforating, hot rolling, and sizing can be performed at 1160-1260° C. to obtain a hot-rolled tube with required gauges. In the present disclosure, the above-mentioned composition system designed in the present disclosure, when heated at 1180-1280° C. for 120-350 min, allows the tube billet to have good high-temperature plasticity. High-temperature deformation such as high-temperature perforating, hot rolling, and sizing at 1160-1260° C. is advantageous in preventing and controlling the generation of hot-rolling deformation defects.
The seamless steel tube prepared by this method exhibits almost no segregation of alloy elements and has a uniform distribution of alloy elements. Therefore, it is possible to eliminate the long-time annealing treatment step, such as spheroidizing annealing step, for the tube billet described in the prior art for alloy homogenization.
The seamless steel tube resistant to carbon dioxide corrosion and the manufacturing method therefor according to the present disclosure have the following advantages and beneficial effects:
As can be seen from the above, the present invention, through rational chemical composition design and optimized manufacturing processes, can obtain a seamless steel tube resistant to carbon dioxide corrosion. This seamless steel tube has high strength, good processability, and resistance to carbon dioxide corrosion, making it effective for use in oil and gas development to avoid perforation failure accidents.
The seamless steel tube of the present disclosure has good mechanical properties and resistance to CO₂corrosion. It has high-strength mechanical properties after quenching and tempering heat treatment and satisfies: yield strength Rp0.2≥550 MPa, tensile strength Rm≥670 MPa, elongation A50≥15%, and impact property KV8≥60 J. The prepared seamless steel tube has a weight loss corrosion rate of less than 0.08 mm/d and a pitting corrosion rate of less than 0.2 mm/d under the dynamic corrosion environment conditions of 60-90° C., 0.5 MPa CO₂, 50,000 ppm Cl⁻, and 1 m/s, making it highly promising and valuable for widespread use and application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of the microstructure of the seamless steel tube in Example 1 under an optical microscope.

DETAILED DESCRIPTION

Hereinafter, the seamless steel tube and the manufacturing method therefor according to the present disclosure will be further explained and described with reference to the specific embodiments and the accompanying drawings. However, this explanation and description are not intended to unduly limit the technical solution of the present disclosure.

Examples 1-15 and Comparative Examples 1-5

Seamless steel tubes in Examples 1-15 and Comparative Examples 1-2 and Comparative Examples 4-5 are all produced using the following steps:

- (1) Performing smelting and refining using electric furnace or converter smelting according to the chemical composition shown in Table 1, and then casting metal into tube billet.
- (2) Subjecting the tube billet to heating, perforating, hot rolling, and sizing to obtain a hot-rolled tube: heating the tube billet at 1180-1280° C. and holding for 120-350 min, and then performing high-temperature deformation such as high-temperature perforating, hot rolling, and sizing in the range of 1160-1260° C. to produce a hot-rolled tube with required sizes.
- (3) Subjecting the hot-rolled tube to quenching and tempering heat treatment: the hot-rolled tube is cut to the required dimensions. Then, it undergoes quenching within the temperature range of 860-940° C. with a holding time of 15-120 min (Comparative Example 3), followed by tempering within the temperature range of 520-620° C. with a holding time of 30-150 min.
- (4) The seamless steel tube in Comparative Example 3 is prepared using the same method as described above, with the only difference being quenching and holding at 946° C.

It should be noted that in the present disclosure, the chemical composition design and relevant manufacturing processes for the seamless steel tubes in Examples 1-15 meet the design specification requirements of the present disclosure. However, for the seamless steel tubes in Comparative Examples 1-5, there are parameters that do not meet the design requirements of the present disclosure in the chemical composition design and related manufacturing processes.
Table 1 lists the mass percentages of chemical elements in the seamless steel tubes in Examples 1-15 and the seamless steel tubes in Comparative Examples 1-5.

TABLE 1

(wt %, the balance being Fe and other inevitable impurities other than P, S, N, and O)

Serial

Ti + Nb +

Number

C

Si

Mn

P

S

Cr

Mo

N

O

Al

Ca

V + Ce + La

Remark

Example 1	0.065	0.34	0.27	0.012	0.0037	4.26	0.32	0.002	0.0011	0.030	0.0020	0.139	Ti + V
Example 2	0.104	0.21	0.38	0.012	0.0065	5.08	0.12	0.005	0.0019	0.041	0.0013	0.121	V + Ce
Example 3	0.091	0.19	0.42	0.009	0.0036	5.12	0.20	0.006	0.0009	0.033	0.0034	0.094	Ti + Ce + La
Example 4	0.072	0.29	0.45	0.002	0.0047	4.14	0.23	0.004	0.0023	0.031	0.0018	0.178	Ti + V + Ce
Example 5	0.093	0.16	0.30	0.006	0.0052	4.86	0.32	0.001	0.0022	0.030	0.0028	0.092	Nb + V
Example 6	0.092	0.38	0.26	0.006	0.0046	5.33	0.19	0.002	0.0011	0.035	0.0019	0.143	Ti + Nb + V
Example 7	0.050	0.29	0.42	0.008	0.0052	4.73	0.12	0.001	0.0018	0.040	0.0014	0.199	V
Example 8	0.180	0.27	0.49	0.007	0.0003	4.28	0.34	0.003	0.0026	0.051	0.0029	0.175	Nb + Ce
Example 9	0.150	0.38	0.39	0.013	0.0058	5.68	0.23	0.005	0.0021	0.022	0.0029	0.095	Nb + La + Ce
Example 10	0.127	0.17	0.37	0.009	0.0043	5.35	0.34	0.002	0.0016	0.035	0.0036	0.041	Ti + La
Example 11	0.081	0.15	0.50	0.001	0.0040	5.89	0.25	0.004	0.0026	0.043	0.0036	0.035	Ti
Example 12	0.152	0.33	0.46	0.007	0.0018	4.35	0.22	0.005	0.0031	0.039	0.0040	0.103	Ti + La
Example 13	0.180	0.30	0.33	0.009	0.0079	5.43	0.13	0.002	0.0030	0.021	0.0025	0.078	Na + La
Example 14	0.174	0.31	0.30	0.015	0.0019	5.14	0.33	0.003	0.0034	0.030	0.0037	0.153	V + La
Example 15	0.103	0.17	0.40	0.010	0.0029	4.51	0.13	0.001	0.0025	0.051	0.0015	0.134	Ti + Nb
Comparative	0.277	0.22	0.32	0.005	0.0011	2.58	0.35	0.005	0.0015	0.039	0.0022	—	—
Example 1
Comparative	0.267	0.17	0.40	0.004	0.0065	2.05	0.20	0.005	0.0036	0.042	0.0020	—	—
Example 2
Comparative	0.207	0.36	0.37	0.014	0.0019	2.00	0.37	0.003	0.0032	0.034	0.0038	—	—
Example 3
Comparative	0.321	0.26	0.38	0.003	0.0011	3.18	0.39	0.002	0.0019	0.023	0.0030	—	—
Example 4
Comparative	0.222	0.27	0.34	0.005	0.0030	3.05	0.32	0.005	0.0025	0.025	0.0032	—	—
Example 5

Table 2 lists specific process parameters of the seamless steel tubes in Examples 1-15 and Comparative Examples 1-5.

	TABLE 2

	Step (2)

Perforating,

Tube billet

hot rolling,

Step (3)

	heating	Tube billet	and sizing	Quenching	Quenching	Tempering	Tempering
Serial	temperature	holding	temperature	temperature	holding time	temperature	holding time
Number	(° C.)	time (min)	(° C.)	(° C.)	(min)	(° C.)	(min)

Example 1	1249	143	1222	863	79	605	69
Example 2	1280	228	1260	936	77	618	131
Example 3	1215	347	1202	939	62	558	70
Example 4	1244	308	1234	898	67	541	57
Example 5	1250	245	1205	927	67	590	63
Example 6	1280	346	1237	940	95	526	59
Example 7	1279	287	1237	907	16	604	100
Example 8	1206	152	1197	904	95	530	41
Example 9	1234	138	1220	919	93	579	146
Example 10	1214	217	1184	894	98	559	102
Example 11	1278	155	1175	864	100	537	143
Example 12	1235	165	1173	932	114	619	94
Example 13	1233	221	1217	870	16	596	118
Example 14	1245	279	1215	923	87	608	36
Example 15	1267	148	1233	863	62	585	70
Comparative	1227	161	1189	893	45	611	87
Example 1
Comparative	1275	299	1215	910	45	614	107
Example 2
Comparative	1201	347	1188	946	67	597	133
Example 3
Comparative	1185	213	1165	906	108	601	139
Example 4
Comparative	1242	147	1198	870	85	584	112
Example 5

The seamless steel tubes in Examples 1-15 and Comparative Examples 1-5 produced after quenching and tempering heat treatment were separately sampled and subjected to various property tests to measure the mechanical properties of the seamless steel tubes in Examples 1-15 and Comparative Examples 1-5. The test results obtained are listed in Table 3.
The relevant methods for testing mechanical properties are as follows:

- Tensile test: The test steel pipes were subjected to a tensile test according to GB/T 228.1-2010 “Metallic Materials-Tensile Testing-Part 1: Method of tensile test at room temperature” to evaluate the tensile properties of the steel tubes in each example and comparative example.

Charpy V-notch impact test: the test steel tubes were subjected to an impact test according to GB/T229-2020 “Metallic Materials-Charpy pendulum impact test method” to evaluate the impact properties of the steel tubes in each example and comparative example.
Table 3 lists the mechanical property test results of the seamless steel tubes in Examples 1-15 and Comparative Examples 1-5.

Example 1	656	733	21	198
Example 2	585	679	24	214
Example 3	851	931	18	115
Example 4	856	974	15	124
Example 5	792	975	20	189
Example 6	936	1068	15	61
Example 7	756	841	17	195
Example 8	878	1132	15	97
Example 9	806	1072	15	74
Example 10	850	971	17	158
Example 11	870	943	18	177
Example 12	936	1132	16	62
Example 13	793	978	19	121
Example 14	622	724	20	184
Example 15	793	902	18	163
Comparative	622	731	21	120
Example 1
Comparative	756	841	20	115
Example 2
Comparative	936	1128	15	58
Example 3
Comparative	832	896	15	97
Example 4
Comparative	1020	1159	14	35
Example 5

Accordingly, after the mechanical properties of the above-described seamless steel tubes in Examples 1-15 and Comparative Examples 1-5 were tested, the corrosion resistance, particularly resistance to CO₂corrosion, of the seamless steel tubes in each example and comparative example was further tested. This involves sampling from the seamless steel tubes in Examples 1-15 and Comparative Examples 1-5 and conducting corrosion tests. The samples from Examples 1-15 and Comparative Examples 1-5 were subjected to corrosion tests in an autoclave system under the dynamic corrosion environment conditions of 60-90° C., 0.5 MPa CO₂, 50,000 ppm Cl⁻, and 1 m/s to obtain the weight loss corrosion rate and the pitting corrosion rate of Examples 1-15 and Comparative Examples 1-5. The test results of the relevant corrosion tests are listed in Table 4 below.
Table 4 lists the results of the CO₂corrosion resistance test of the seamless steel tubes in Examples 1-15 and the seamless steel tubes in Comparative Examples 1-5.

TABLE 4

	Weight loss	Pitting
	corrosion rate	corrosion rate
Serial Number	(mm/d)	(mm/d)

Example 1	0.072	0.142
Example 2	0.052	0
Example 3	0.042	0
Example 4	0.079	0.133
Example 5	0.039	0
Example 6	0.038	0
Example 7	0.041	0
Example 8	0.062	0.131
Example 9	0.034	0
Example 10	0.043	0
Example 11	0.023	0
Example 12	0.061	0.121
Example 13	0.032	0
Example 14	0.059	0.117
Example 15	0.066	0.152
Comparative Example 1	0.165	0.266
Comparative Example 2	0.234	0.298
Comparative Example 3	0.261	0.377
Comparative Example 4	0.136	0.272
Comparative Example 5	0.169	0.293

It can be seen from Table 3 and Table 4 that the seamless steel tubes in Examples 1-15 of the present disclosure have not only excellent mechanical properties but also good resistance to CO₂corrosion. The yield strength of the seamless steel tubes in Examples 1-15 is between 585 MPa and 936 MPa, the tensile strength is between 679 MPa and 1132 MPa, the elongation A50 is greater than or equal to 15%, and the impact property KV8 is between 61 J and 214 J. Accordingly, the seamless steel tubes in each example has a weight loss corrosion rate of less than 0.079 mm/d and a pitting corrosion rate of less than 0.152 mm/d, under the dynamic corrosion environment conditions of 60-90° C., 0.5 MPa CO₂, 50,000 ppm Cl⁻, and 1 m/s.
In contrast to the seamless steel tubes in Examples 1-15, the seamless steel tubes in Comparative Examples 1-5 show significant fluctuations in mechanical properties, and their the weight loss corrosion rate (at least 0.136 mm/d) and the pitting corrosion rate (at least 0.266 mm/d) are higher than those of Examples 1-15, indicating poorer resistance to CO₂corrosion for the seamless steel tubes in Comparative Examples 1-5.
FIG. 1 is a photograph of the microstructure of the high-strength seamless steel tube in Example 1 under an optical microscope.
As shown in FIG. 1 , the microstructure of the high-strength seamless steel tube in Example 1 is a tempered sorbite structure.
In conclusion, it can be seen that the seamless steel tube resistant to carbon dioxide corrosion can be obtained by reasonable chemical composition design preferably combined with optimized manufacturing processes. The seamless steel tube has high strength, good processability, and resistance to carbon dioxide corrosion, making it suitable for applications in oil and gas development and helping prevent perforation failures. It holds significant promise and practical value.
Furthermore, the combinations of technical features described herein are not limited to the combinations specified in the claims or the specific embodiments herein. All technical features described herein may be freely combined or combined in any way unless contradicted by each other.
It should also be noted that only specific embodiments of the present disclosure have been illustrated above. It is obvious that the present disclosure is not limited to the above embodiments, and there may be various similar variations. All variations that may be derived directly or conceived by those skilled in the art from the present disclosure of the present disclosure are intended to fall within the scope of the present disclosure.

(0° C.), J

1. A seamless steel tube resistant to corrosion by carbon dioxide, comprising the following chemical elements in mass percentage, in addition to containing Fe and inevitable impurities:

C: 0.05-0.18%, Si: 0.15-0.40%, Mn: 0.25-0.50%, Cr: 4.0-6.0%, Mo: 0.08-0.35%, Al: 0.020-0.055%, Ca: 0.001-0.004%; and one or more selected from Ti, Nb, V, Ce, and La, wherein 0.003%≤Ti+Nb+V+Ce+La≤0.20%.

2. The seamless steel tube according to claim 1, wherein the seamless steel tube consists of the following chemical elements in mass percentage:

C: 0.05-0.18%, Si: 0.15-0.40%, Mn: 0.25-0.50%, Cr: 4.0-6.0%, Mo: 0.08-0.35%, Al: 0.020-0.055%, Ca: 0.001-0.004%; and one or more selected from Ti, Nb, V, Ce, and La, wherein 0.003%≤Ti+Nb+V+Ce+La≤0.20%, and the balance of Fe and inevitable impurities.

3. The seamless steel tube according to claim 1, wherein the content of the chemical elements in the seamless steel tube further satisfy at least one of the following:

C: 0.09-0.15%,

Si: 0.2-0.35%,

Mn: 0.3-0.45%,

Cr: 4.5-5.5%,

Mo: 0.1-0.25%,

Al: 0.025-0.045%,

Ca: 0.0015-0.003%, and

0.005%≤Ti+Nb+V+Ce+La≤0.15%.

4. The seamless steel tube according to claim 1, wherein among the inevitable impurities, P≤0.015%, S≤0.008%, N≤0.006%, and O≤0.0035%.

5. The seamless steel tube according to claim 4, wherein among the inevitable impurities, P≤0.012%, S≤0.005%, N≤0.0045%, and O≤0.002%.

6. The seamless steel tube according to claim 1, having a tempered sorbite structure.

7. The seamless steel tube according to claim 1, wherein the properties of the seamless steel tube satisfy at least one of the following:

yield strength Rp0.2≥550 MPa, tensile strength Rm≥670 MPa, elongation A50≥15%, and impact property KV8≥60 J;

under the dynamic corrosion environment conditions of 60-90° C., 0.5 MPa CO₂, 50,000 ppm Cl⁻, and 1 m/s, a weight loss corrosion rate is less than 0.08 mm/d, and a pitting corrosion rate is less than 0.2 mm/d.

8. A manufacturing method for the seamless steel tube resistant to carbon dioxide corrosion according to claim 1, wherein the manufacturing method excludes a spheroidizing annealing step and comprises the following steps:

(1) manufacturing a tube billet;

(2) subjecting the tube billet to heating, perforating, hot rolling, and sizing to obtain a hot-rolled tube; and

(3) subjecting the hot-rolled tube to quenching and tempering heat treatment: quenching the hot-rolled tube in a temperature range of 860-940° C. and holding for 15-120 min, followed by tempering the quenching tube in a temperature range of 520-620° C. and holding for 30-150 min.

9. The manufacturing method according to claim 8, wherein in the heating step of step (2), the tube billet is heated at 1180-1280° C. and held for 120-350 min.

10. The manufacturing method according to claim 8 or 9, wherein in step (2), perforating, hot rolling, and sizing are performed in a temperature range of 1160-1260° C.

11. The seamless steel tube according to claim 2, wherein the content of the chemical elements in the seamless steel tube further satisfy at least one of the following:

C: 0.09-0.15%,

Si: 0.2-0.35%,

Mn: 0.3-0.45%,

Cr: 4.5-5.5%,

Mo: 0.1-0.25%,

Al: 0.025-0.045%,

Ca: 0.0015-0.003%, and

0.005%≤Ti+Nb+V+Ce+La≤0.15%.

12. The seamless steel tube according to claim 2, wherein among the inevitable impurities, P≤0.015%, S≤0.008%, N≤0.006%, and O≤0.0035%.

13. The seamless steel tube according to claim 2, having a tempered sorbite structure.

14. The seamless steel tube according to claim 2, wherein the properties of the seamless steel tube satisfy at least one of the following:

15. The manufacturing method according to claim 9, wherein in step (2), perforating, hot rolling, and sizing are performed in a temperature range of 1160-1260° C.