Carbon dioxide corrosion resistant pipeline steel and preparation method thereof

Abstract

According to the X65 pipeline steel for conveying supercritical carbon dioxide and the manufacturing method of the X65 pipeline steel, the production process is simple, existing metallurgical equipment, steel rolling equipment and cooling equipment do not need to be updated, additional equipment does not need to be added, and industrial production can be directly conducted. The low-temperature crack initiation and crack arrest toughness of the steel plate can be greatly improved, the carbon dioxide corrosion resistance can be greatly improved, and large economic benefits are produced.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline steel, and particularly relates to a pipeline steel resistant to carbon dioxide corrosion and a preparation method thereof. Background Art

[0002] In recent years, the change in the energy structure and the growth in energy demand have greatly promoted the development of long-distance transmission pipelines. With the proposal of the "carbon peak and carbon neutrality" strategy and the wide application of carbon dioxide flooding technology, the large-scale and long-distance transportation of supercritical carbon dioxide through pipelines has become a current research hotspot.

[0003] After retrieval, it is found that the patents of steels for resisting carbon dioxide corrosion currently are basically used for manufacturing oil well pipes and casings, etc., which have great differences from the service conditions of pipeline steels for long-distance transportation pipelines suitable for carbon dioxide. The main manifestations are as follows: 1) The pipeline steel for long-distance transportation bears a relatively high internal pressure (generally above 8 MPa). In the case of carbon dioxide leakage, an extremely low temperature field will be generated. Therefore, it is required that the pipeline steel has good low-temperature toughness at -40°C to -80°C to prevent brittle fracture. 2) The supercritical carbon dioxide undergoes dehydration treatment, and the water vapor content is relatively low. Therefore, the corrosion rate of the pipeline steel for long-distance transportation is relatively low. Therefore, considering the operational stability, safety, and economy of the transportation pipeline, a special pipeline steel for transporting supercritical carbon dioxide should be developed to have good carbon dioxide corrosion resistance and excellent low-temperature toughness. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-efficiency pressurization system and method for a pneumatic launcher, which has sufficient strength and excellent low-temperature impact toughness and carbon dioxide corrosion resistance.

[0005] To achieve the above purpose, the present invention provides a pipeline steel resistant to carbon dioxide corrosion. The chemical composition of the pipeline steel by weight percentage includes: C is 0.025% - 0.035%, Mn is 1.10% - 1.40%, S ≤ 0.0012%, P ≤ 0.007%, Si is 0.1% - 0.3%, Cr is 6.0% - 8.0%, Nb is 0.01% - 0.02%, Ti is 0.01% - 0.03%, Ni is 0.30% - 0.50%, and the rest is iron and impurities.

[0006] The present invention also provides a preparation method of the pipeline steel, and the method includes:

[0007] Heating, rough rolling, and finish rolling the obtained pipeline steel billet to obtain a hot-rolled plate;

[0008] Cooling the hot-rolled plate to obtain a cooled steel plate;

[0009] The tempered steel plate is subjected to tempering treatment to obtain pipeline steel.

[0010] The technical effects and advantages of the present invention:

[0011] The present invention provides a pipeline steel resistant to carbon dioxide corrosion. The chemical composition of the pipeline steel by weight percentage includes: C is 0.025%-0.035%, Mn is 1.10%-1.40%, S≤0.0012%, P≤0.007%, Si is 0.1%-0.3%, Cr is 6.0%-8.0%, Nb is 0.01%-0.02%, Ti is 0.01%-0.03%, Ni is 0.30%-0.50%, and the rest is iron and impurities.

[0012] The X65 pipeline steel for transporting supercritical carbon dioxide and its manufacturing method of the present invention have a simple production process, without the need to update existing metallurgical equipment, rolling equipment, and cooling equipment, nor to newly add additional equipment, and can be directly industrially produced. The present invention can greatly improve the low-temperature crack initiation and arrest toughness of the steel plate, and can greatly improve the carbon dioxide corrosion resistance, resulting in greater economic benefits.

[0013] Other features and advantages of the present invention will be described in the subsequent specification, and, in part, will become apparent from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures pointed out in the specification and the drawings. Brief Description of the Drawings

[0014] Figure 1 It is a schematic diagram of the metallographic structure of hot-rolled steel. Detailed Description of the Invention

[0015] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the drawings provided by the present invention. Moreover, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0016] It should be noted that the structures, proportions, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention. Therefore, they do not have substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" cited in this specification are only for the convenience of clear description and are not used to limit the scope for the implementation of the present invention. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope for the implementation of the present invention.

[0017] To solve the deficiencies of the prior art, the present invention discloses a pipeline steel resistant to carbon dioxide corrosion. The chemical composition of the pipeline steel by weight percentage includes: C is 0.025% - 0.035%, Mn is 1.10% - 1.40%, S ≤ 0.0012%, P ≤ 0.007%, Si is 0.1% - 0.3%, Cr is 6.0% - 8.0%, Nb is 0.01% - 0.02%, Ti is 0.01% - 0.03%, Ni is 0.30% - 0.50%, and the rest is iron and impurities.

[0018] Among them, the mechanical properties of the pipeline steel include: the tensile strength is 600 - 700 MPa, the yield strength is 500 - 600 MPa, the shear area of DWTT (Drop Weight Tear Test) at - 30 °C is not less than 85%, and in a supercritical carbon dioxide environment with a water content of 200 - 800 ppmv, the corrosion rate is not greater than 0.04 mm / a.

[0019] Among them, the mechanical properties of the pipeline steel further include: the low-temperature crack initiation toughness at -70°C is not less than 80 J, and the crack arrest toughness at -30°C is not less than 300 J. The specific principle is as follows: when a supercritical carbon dioxide pipeline leaks and fails, an extremely low temperature field generally ranging from -40 to -70°C will be generated around the leakage point. At this temperature, the pipeline is required to have high low-temperature crack initiation toughness. The pipeline steel of the present invention can reach a toughness value of 80 J at -70°C, which is greater than the theoretically calculated minimum crack initiation toughness requirement, thereby reducing the probability of low-temperature fracture initiation of the pipeline. In addition, when the pipeline fracture propagates due to other factors (such as the initiation of a circumferential weld fracture, resulting in the crack propagating into the pipeline base metal), at the normal service temperature (generally greater than 0°C for buried pipelines and generally greater than -30°C for non-buried pipelines), the pipeline is required to have good crack arrest toughness. The pipeline steel of the present invention can reach a toughness value of 300 J at -30°C, which is greater than the theoretically calculated minimum crack arrest toughness requirement, and can achieve self-arrest of the pipeline under crack propagation conditions. Therefore, the pipeline steel of the present invention has excellent crack initiation toughness and crack arrest toughness, enabling the pipeline to avoid long-range fracture failure accidents.

[0020] The present invention also provides a preparation method of pipeline steel, and the method includes:

[0021] 1. Heat, rough roll, and finish roll the obtained pipeline steel billet to obtain a hot-rolled sheet.

[0022] Specifically, the heating temperature of the pipeline steel billet is controlled at 1150 - 1170°C, and the holding time is 2.5 - 3.0 h.

[0023] Specifically, the starting temperature of rough rolling is 1080°C - 1100°C, and the ending temperature is 985°C - 1010°C. And in the rough rolling stage, increase the pass reduction rate to ensure that the pass reduction rate is between 15% - 35%, and the total reduction rate is not less than 60%, so that the austenite grains can better undergo dynamic recrystallization and refine the austenite grains.

[0024] Specifically, the starting temperature of finish rolling is 920°C - 940°C, and the ending temperature is 790°C - 830°C, and the total reduction rate of finish rolling is not less than 65%.

[0025] 2. Cool the hot-rolled sheet to obtain a cooled steel sheet.

[0026] Specifically, use a rapid cooling method to cool the hot-rolled sheet to 300 - 550°C, and the cooling rate is 10 - 20°C / s, giving full play to the water cooling effect, refining the phase transformation structure, and improving the drop weight performance and Charpy impact performance of the steel sheet.

[0027] 3. Temper the cooled steel sheet to obtain pipeline steel.

[0028] Specifically, the cooled steel plate is tempered at 500 - 650 °C for 40 - 100 minutes, and then cooled in air to room temperature to further optimize the toughness of the steel and reduce the yield ratio.

[0029] Finally, the metallographic structure of the prepared pipeline steel is tempered martensite, as Figure 1 shown. Among them, the mechanical properties of the pipeline steel are: tensile strength of 600 - 700 MPa, yield strength of 500 - 600 MPa, low-temperature crack initiation toughness at -70 °C not less than 80 J, crack arrest toughness at -30 °C not less than 300 J, DWTT shear area at -30 °C not less than 85%, and corrosion rate not greater than 0.04 mm / a in a supercritical carbon dioxide environment with a water content of 200 - 800 ppmv.

[0030] It should also be noted that the pipeline steel in the present invention is X65 pipeline steel.

[0031] In the present invention, by adding an appropriate amount of Cr element to the steel and combining controlled cooling and tempering processes, the proportion of high-energy large-angle grain boundaries is reduced, and the corrosion rate is reduced. At the same time, Cr compounds Cr(OH) 3 are enriched in the corrosion product film, changing the compactness of the corrosion product and hindering the ion diffusion between the matrix surface and the liquid, further reducing the corrosion rate, thereby improving the carbon dioxide corrosion resistance of the pipeline steel. In addition, the present invention also reduces the content of S, P, and Mn, reducing the aggregation of P and S elements at the grain boundaries, thereby further improving the corrosion resistance and toughness. By precisely controlling the controlled cooling process and heat treatment process, the size of the original austenite grains is controlled to prevent coarsening. By strengthening the deformation in the high-temperature austenite recrystallization zone, the austenite grains are fully refined, obtaining excellent low-temperature crack initiation and crack arrest toughness.

[0032] To better illustrate the present invention, the following examples are also provided.

[0033] The present invention provides an X65 pipeline steel for transporting supercritical carbon dioxide, and the chemical composition and mass percentage are shown in Table 1.

[0034] Table 1 Chemical composition and content table of X65 pipeline steel

[0035] C Mn Si S P Nb Ti Ni Cr 0.035 1.20 0.22 0.0010 0.006 0.02 0.015 0.35 7.1

[0036] The following is the preparation method of X65 pipeline steel for transporting supercritical carbon dioxide, which specifically includes:

[0037] Obtain an X65 pipeline steel billet, and perform heating, rough rolling, and finish rolling on the X65 pipeline steel billet to obtain a hot-rolled plate;

[0038] Perform cooling treatment on the hot-rolled plate to obtain a cooled steel plate;

[0039] The tempered treatment is carried out on the cooled steel plate to obtain X65 pipeline steel.

[0040] Among them, the process parameters in the above preparation method are shown in Table 2.

[0041] Table 2 Process parameter table for the preparation of X65 pipeline steel

[0042]

[0043] The mechanical property test results of the finally obtained X65 pipeline steel for transporting supercritical carbon dioxide are shown in Table 3.

[0044] Table 3 Mechanical property data table of X65 pipeline steel

[0045]

[0046] Among them, R t0.5 represents the yield strength, R m represents the tensile strength, R t0.5 / R m represents the yield ratio, CVN -30℃ represents the crack arrest toughness at -30°C; CVN -70℃ represents the low-temperature crack initiation toughness at -70°C, and DWTT -30℃ represents the DWTT shear area at -30°C.

[0047] The present invention also provides a preparation device for pipeline steel resistant to carbon dioxide corrosion. The device includes: an obtaining unit for heating, rough rolling and finish rolling the obtained pipeline steel billet to obtain a hot-rolled plate; a cooling unit for cooling the hot-rolled plate to obtain a cooled steel plate; a tempering unit for tempering the cooled steel plate to obtain pipeline steel.

[0048] Since the content protected by this device is similar to the content protected by the above method, no more introduction will be made here. For details, please refer to the discussion part of the above method.

[0049] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A carbon dioxide corrosion resistant pipeline steel, characterized in that: The chemical composition of the pipeline steel includes, by weight percentage, 0.025%-0.035% C, 1.10%-1.40% Mn, S≤0.0012%, P≤0.007%, 0.1%-0.3% Si, 6.0%-8.0% Cr, 0.01%-0.02% Nb, 0.01%-0.03% Ti, 0.30%-0.50% Ni, and the rest is iron and impurities.

2. The pipeline steel according to claim 1, characterized in that: The mechanical properties of the pipeline steel include: tensile strength of 600-700MPa, yield strength of 500-600MPa, low-temperature cracking toughness of not less than 80J at -70°C, DWTT shear area of ​​not less than 85% at -30°C, and corrosion rate of not more than 0.04mm / a in a supercritical carbon dioxide environment with a water content of 200-800ppmv.

3. The method for preparing pipeline steel according to any one of claims 1-2, characterized in that: The method comprises: The obtained pipeline steel billet is subjected to heating, rough rolling and finish rolling to obtain a hot-rolled plate; Cooling the hot-rolled plate to obtain a cooled steel plate; The cooled steel plate is tempered to obtain pipeline steel.

4. The method according to claim 3, characterized in that The heating conditions include: a heating temperature of 1150-1170° C. and a heat preservation time of 2.5-3.0 h.

5. The method according to claim 3, characterized in that: The rough rolling conditions include: the starting temperature of the rough rolling is 1080°C-1100°C, the ending temperature of the rough rolling is 985°C-1010°C, the pass deformation rate of the rough rolling is 15%-35%, and the total reduction rate of the rough rolling is not less than 60%.

6. The method according to claim 3, characterized in that The conditions of the finishing rolling include: the starting temperature of the finishing rolling is 920° C.-940° C., the ending temperature of the finishing rolling is 790° C.-830° C., and the total reduction rate of the finishing rolling is not less than 65%.

7. The method according to claim 3, characterized in that The cooling conditions include: a cooling temperature of 300-550° C. and a cooling speed of 10-20° C. / s.

8. The method according to claim 3, characterized in that The tempering conditions include: a tempering temperature of 500-650° C. and a tempering time of 40-100 min.

9. The method according to claim 3, characterized in that: The mechanical properties of the pipeline steel include: tensile strength of 600-700MPa, yield strength of 500-600MPa, low-temperature cracking toughness of not less than 80J at -70°C, DWTT shear area of ​​not less than 85% at -30°C, and corrosion rate of not more than 0.04mm / a in a supercritical carbon dioxide environment with a water content of 200-800ppmv.

10. The method according to claim 3, characterized in that The pipeline steel is X65 pipeline steel.

Images