Anti-Collapse Oil Casing with High Strength and Manufacturing Method Therefor

Abstract

An anti-collapse oil casing with high strength and a manufacturing method therefor, comprising the following chemical elements in percentage by mass: C:0.08%-0.18%; Si:0.1%-0.4%; Mn:0.1%-0.28%; Cr:0.2%-0.8%; Mo:0.2%-0.6%; Nb:0.02%-0.08% b; V:0.01%-0.15%; Ti:0.02%-0.05%; B:0.0015%-0.005%; and Al:0.01%-0.05%. The manufacturing method for the anti-collapse oil casing with high strength comprises the steps of: (1) smelting and continuous casting; (2) perforating, rolling, and sizing; (3) controlled cooling: the initial cooling temperature being Ar3+50° C. and the final cooling temperature being ≤80° C.; the cooling step being performed only to the outer surface of the casing without performing to the inner wall of the casing; and the rate of the controlled cooling being 30-70° C./s; (4) tempering; and (5) thermal straightening. The anti-collapse oil casing with high strength according to the present invention has reasonable chemical composition and process design, which not only has excellent economic efficiency, but also has high strength, high toughness and high anti-collapse performance.

Claims

1. An anti-collapse oil casing with high strength, comprising the following chemical elements in percentage by mass: C: 0.08-0.18%; Si: 0.1-0.4%; Mn: 0.1-0.28%; Cr: 0.2-0.8%; Mo: 0.2-0.6%; Nb: 0.02-0.08%; V: 0.01-0.15%; Ti: 0.02-0.05%; B: 0.0015-0.005%; and Al: 0.01-0.05%.

2. The anti-collapse oil casing with high strength according to claim 1, characterized in that the content of each chemical element in percentage by mass satisfies the following: C: 0.08-0.18%; Si: 0.1-0.4%; Mn: 0.1-0.28%; Cr: 0.2-0.8%; Mo: 0.2-0.6%; Nb: 0.02-0.08%; V: 0.01-0.15%; Ti: 0.02-0.05%; B: 0.0015-0.005%; Al: 0.01-0.05%; and the balance of Fe and other inevitable impurities.

3. The anti-collapse oil casing with high strength according to claim 2, characterized in that the inevitable impurities comprise S, P and N, wherein contents of S, P and N satisfy at least one of: P≤0.015%, 0<N≤0.008%, and S≤0.003%.

4. The anti-collapse oil casing with high strength according to claim 1, characterized in that the content of each chemical element in percentage by mass satisfies at least one of the following: C: 0.1-0.16%; Si: 0.15-0.35%; Mn: 0.15-0.25%; Cr: 0.4-0.7%; Mo: 0.25-0.5%; Nb: 0.02-0.06%; V: 0.05-0.12%; Ti: 0.02-0.04%; B: 0.0015-0.003%; and Al: 0.015-0.035%.

5. The anti-collapse oil casing with high strength according to claim 1, characterized in that a microstructure of the anti-collapse oil casing is tempered sorbite.

6. The anti-collapse oil casing with high-strength according to claim 1, characterized in that the anti-collapse oil casing has properties satisfying at least one of: a yield strength of 758-965 MPa, a tensile strength of ≥862 MPa, an elongation rate of ≥18%, a residual stress of ≤120 MPa, a 0° C. transverse charpy impact energy of ≥80 J, and an anti-collapse strength of 55 MPa or more at a specification of Φ244.48*11.99 mm, which exceeds the required value of the API standard by 40% or more.

7. A manufacturing method for the anti-collapse oil casing with high strength according to claim 1, comprising the steps of: (1) smelting and continuous casting; (2) perforating, rolling, and sizing; (3) controlled cooling: an initial cooling temperature being Ar3+30° C. to Ar3+70° C., and a final cooling temperature being ≤80° C.; the cooling step being performed only to an outer surface of the casing without performing to an inner wall of the casing; and controlling a cooling rate to be 30-70° C./s. (4) tempering; and (5) thermal straightening.

8. The manufacturing method according to claim 7, characterized in that in the continuous casting of the step (1), controlling a superheat degree of molten steel to be less than 30° C., and a pulling rate of the continuous casting to be 1.6-2.0 m/min.

9. The manufacturing method according to claim 7, characterized in that in the step (2), a round billet is subjected to soaking in a furnace at 1260-1290° C.; a perforating temperature is controlled to be 1180-1260° C.; a final rolling temperature is controlled to be 900-980° C.; and a sizing temperature after final rolling is 850-920° C.

10. The manufacturing method according to claim 7, characterized in that in the step (4), a tempering temperature is 500-600° C., and a holding time is 50-80 min.

11. The manufacturing method according to claim 7, characterized in that in the step (4), a thermal straightening temperature is 400-500° C.

12. The anti-collapse oil casing with high strength according to claim 2, characterized in that the content of each chemical element in percentage by mass satisfies at least one of the following: C: 0.1-0.16%; Si: 0.15-0.35%; Mn: 0.15-0.25%; Cr: 0.4-0.7%; Mo: 0.25-0.5%; Nb: 0.02-0.06%; V: 0.05-0.12%; Ti: 0.02-0.04%; B: 0.0015-0.003%; and Al: 0.015-0.035%.

13. The anti-collapse oil casing with high strength according to claim 2, characterized in that a microstructure of the anti-collapse oil casing is tempered sorbite.

14. The anti-collapse oil casing with high-strength according to claim 2, characterized in that the anti-collapse oil casing has properties satisfying at least one of: a yield strength of 758-965 MPa, a tensile strength of ≥862 MPa, an elongation rate of ≥18%, a residual stress of ≤120 MPa, a 0° C. transverse charpy impact energy of ≥80 J, and an anti-collapse strength of 55 MPa or more at a specification of Φ244.48*11.99 mm, which exceeds the required value of the API standard by 40% or more.

Description

DETAILED DESCRIPTION

[0078] The anti-collapse oil casing with high strength and the manufacturing method therefor of the present invention are further explained and illustrated below in combination with specific examples. However, the explanation and illustration do not improperly limit the technical solutions of the present invention.

Examples 1-6 and Comparative Examples 1-4

[0079] Table 1 lists the chemical elements of each anti-collapse oil casing with high strength of Examples 1-6 and Comparative examples 1-4 in percentage by mass.

TABLE-US-00001 TABLE 1 (wt %, the balance of Fe and inevitable impurities except P, S and N) Chemical elements No. C Si Mn Cr Mo Nb Ti B Al N V P S Example 1 0.08 0.15 0.1 0.2 0.2 0.02 0.02 0.0015 0.01 0.004 0.01 0.015 0.001 Example 2 0.10 0.1 0.15 0.4 0.25 0.04 0.025 0.002 0.04 0.005 0.03 0.008 0.0015 Example 3 0.12 0.35 0.25 0.6 0.4 0.06 0.04 0.003 0.05 0.006 0.05 0.007 0.002 Example 4 0.16 0.4 0.2 0.8 0.6 0.08 0.04 0.004 0.035 0.007 0.12 0.011 0.0025 Example 5 0.18 0.25 0.25 0.7 0.5 0.05 0.05 0.005 0.015 0.008 0.15 0.005 0.003 Example 6 0.14 0.25 0.2 0.6 0.4 0.04 0.05 0.003 0.02 0.008 0.11 0.005 0.003 Comparative 0.25 0.26 1.2 0.4 0.4 0.04 0.02 0.0015 0.023 0.008 0.05 0.008 0.0015 example 1 Comparative 0.15 0.33 1.2 1.5 0.3 0.03 — — 0.04 0.005 0.03 0.007 0.002 example 2 Comparative 0.12 0.3 0.3 0.4 0.4 — 0.04 0.003 0.05 0.006 — 0.011 0.0025 example 3 Comparative 0.18 0.3 0.8 0.3 0.4 0.04 0.02 0.004 0.05 0.008 0.06 0.005 0.003 example 4

[0080] The anti-collapse oil casing with high strength of Examples 1-6 of the present invention and the Comparative examples 1-4 were all prepared by the following steps.

[0081] (1) Smelting and continuous casting: in the continuous casting step, controlling the superheat degree of molten steel to be less than 30° C., and the pulling rate of the continuous casting was controlled to be 1.6-2.0 m/min.

[0082] (2) Perforating, rolling and sizing: the round billet was subjected to soaking in a furnace at 1260-1290° C.; the perforating temperature was controlled to be 1180-1260° C.; the final rolling temperature was controlled to be 900-980° C.; and the sizing temperature after final rolling was 850-920° C.

[0083] (3) Controlled cooling: the initial cooling temperature was Ar3+30° C. to Ar3+70° C., and the final cooling temperature was ≤80° C.; the cooling step was performed only to the outer surface of the casing without performing to the inner wall of the casing; the cooling rate was controlled to be 30-70° C./s; specifically, the hot rolled casing undergoes the controlled cooling step while maintaining the high-temperature state after the sizing; cooling equipment was a cooling water ring with controllable water amount and pressure which sprays water to cool the outer surface of the casing body; the initial cooling temperature was Ar3+50° C., and the casing was subjected to water cooling at ≤80° C. Such process is online quenching.

[0084] (4) Tempering: the tempering temperature was 500-600° C., and the holding time was 50-80 min.

[0085] (5) Thermal straightening: the thermal straightening temperature was 400-500° C.

[0086] Table 2-1 and Table 2-2 list specific process parameters of the manufacturing methods for the anti-collapse oil casing with high strength of Examples 1-6 and Comparative examples 1-4.

TABLE-US-00002 TABLE 2-1 Step (1) Pulling speed Temperature Step (2) Superheat of continuous in Perforating Final rolling Sizing degree casting the furnace temperature temperature temperature No. (° C.) (m/min) (° C.) (° C.) (° C.) (° C.) Example 1 15 2.0 1260 1180 900 880 Example 2 20 1.8 1270 1200 910 850 Example 3 30 1.6 1280 1210 930 870 Example 4 25 1.8 1290 1190 960 920 Example 5 20 1.8 1260 1260 980 890 Example 6 20 1.7 1260 1260 970 900 Comparative 15 1.9 1260 1220 930 920 example 1 Comparative 20 1.8 1270 1210 920 860 example 2 Comparative 30 1.6 1280 1210 930 870 example 3 Comparative 25 1.9 1290 1240 980 890 example 4

TABLE-US-00003 TABLE 2-2 Step (3) Step (5) Final Step (4) Thermal Initial cooling Cooling cooling Tempering straightening temperature rate temperature temperature Holding time temperature No. (° C.) (° C./s) (° C.) (° C.) (min) (° C.) Ar3 (° C.) Example 1 910 30 20 540 50 400 858 Example 2 880 40 30 520 60 420 817 Example 3 870 50 40 590 60 440 812 Example 4 840 60 60 580 80 460 784 Example 5 840 70 80 550 70 480 784 Example 6 850 50 70 560 75 500 802 Comparative 780 40 40 520 70 420 699 example 1 Comparative 790 50 60 570 60 440 721 example 2 Comparative — — — 590 60 460 811 example 3 Comparative 820 60 150 600 60 480 754 example 4

[0087] The above anti-collapse oil casing with high strength of Examples 1-6 and Comparative examples 1-4 are made to form casings having a specification of Φ244.48*11.99 mm, which are then tested in various properties. The obtained results are listed in Table 3.

[0088] Table 3 lists the test results of the mechanical properties of the anti-collapse oil casing with high strength of Examples 1-6 and Comparative examples 1-4. The yield strength, the tensile strength, the elongation rate, and the transverse impact energy are measured in accordance with API SPEC 5CT, and the anti-collapse strength and the residual stress are measured in accordance with ISO/TR10400.

TABLE-US-00004 TABLE 3 Yield Tensile Elongation 0° C. transverse Anti-collapse Residual strength strength rate impact energy strength strength No. (MPa) (MPa) (%) (J) (MPa) (MPa) Example 1 810 870 26 115 59 80 Example 2 830 910 24 102 61 60 Example 3 790 970 23 98 58 90 Example 4 900 990 21 95 65 50 Example 5 960 1060 20 88 68 100 Example 6 910 1010 21 110 65 85 Comparative 920 990 18 30 56 70 example 1 Comparative 720 800 25 85 49 80 example 2 Comparative 730 790 24 90 52 170 example 3 Comparative 750 830 19 60 57 130 example 4

[0089] In combination with Table 1 and Table 3, the chemical components and related process parameters of the anti-collapse oil casing with high strength of Examples 1-6 all satisfy the design specifications required by the present invention. The components of Example 6 are within the preferred component range, and leads to better performance indexes. For Comparative example 1, the content of C in the chemical component design exceeds the scope defined by the technical solution of the present invention, and the initial cooling temperature also exceeds the scope defined by the technical solution of the present invention. For Comparative example 2, B and Ti are not added in the chemical component design. For Comparative example 3, V and Nb are not added, while offline quenching+tempering process were adopted instead of the controlled cooling process, wherein the quenching temperature was 900° C. and holding for 40 min, and the parameters of the tempering process are as shown in Table 2-2, and as a result, the obtained casing body had high residual stress. For Comparative example 4, the contents of Mn and Cr in the chemical component design exceeds the scope defined by the technical solution of the present invention, and the final cooling temperature exceeds the range defined by the technical solution of the present invention. At least one mechanical property of the casings in Comparative examples 1-4 failed to meet the standards of the oil casing with high strength, high toughness and high anti-collapse performance.

[0090] It can be seen from Table 3 that each Examples of the present invention has a yield strength of ≥758 Mpa, a tensile strength of ≥862 Mpa, a 0° C. transverse impact energy of ≥80 J, an elongation rate of ≥18%, a residual stress of ≤120 MPa, and an anti-collapse strength of ≥55 MPa, which exceeded the API standard by 50% or more (the API standard value is 36.5 MPa), that is, the anti-collapse oil casing with high strength in Examples 1-6 have high strength, high toughness and high anti-collapse performance, and suitable for making oil casings for deep well exploitation.

[0091] It should be noted that the above-listed examples are only specific examples of the present invention. Obviously, the present invention is not limited to the above examples, and similar changes or modifications made subsequently can be directly derived or be easily conceived by those skilled in the art based on the disclosure of the present invention, and should all fall within the protection scope of the present invention.