Ultra-high toughness and high strength drill pipe and manufacturing process thereof

Abstract

The invention discloses a drill pipe having ultra-high toughness and high strength and comprising the following chemical elements in mass percentage: C: 0.24-0.30%, Si: 0.1-0.5%, Mn: 0.7-1.5%, Cr: 0.7-1.5%, Mo: 0.5-0.75%, V: 0.01-0.10%, Nb: 0.01-0.05%, P0.015%, S0.005%, and the balance of Fe and unavoidable impurities; and a process of manufacturing the drill pipe having ultra-high toughness and high strength, comprising: heating the drill pipe as a whole to 900-950 C.; subjecting the inner surface of the drill pipe to axial-flow water-spray cooling and the outer surface of the drill pipe to laminar-flow water-spray cooling while controlling the amount of the water sprayed at thickened ends of the drill pipe and that along the pipe body to be different from each other; and controlling the tempering temperature to be 650-675 C. The inventive drill pipe having ultra-high toughness and high strength has a longitudinal full-size impact toughness at 20 C. of at least 100 J and has a strength of 135 ksi.

Claims

1. A drill pipe having ultra-high toughness and high strength, and consisting of the following chemical elements in mass percentage: C: 0.24-0.30%, Si: 0.1-0.5%, Mn: 0.92-1.5%, Cr: 0.7-1.5%, Mo: 0.5-0.75%, V: 0.01-0.10%, Nb: 0.01-0.05%, P0.015%, S0.005%, and the balance of Fe and unavoidable impurities; while the strength of the drill pipe having ultra-high toughness and high strength reaches 135 ksi, its longitudinal full-size impact toughness at 20 C. is 100 J or larger; wherein said drill pipe is manufactured by a process comprising the steps of: forming a drill pipe having an inner and outer surface, a pipe body between thickened ends and said chemical element composition in mass percentage; subjecting the drill pipe to a quenching step, wherein the drill pipe as a whole is heated to 900-950 C.; and then the inner surface of the drill pipe is subjected to axial-flow water-spray cooling and the outer surface of the drill pipe is subjected to laminar-flow water-spray cooling, with the amount of the water sprayed at thickened ends of the drill pipe and that along the pipe body being controlled to be different from each other, so that the pipe body and the thickened ends having different wall thicknesses have the same cooling rate; and subjecting the drill pipe to a tempering step, wherein the tempering temperature is controlled to be 650-675 C.

2. The drill pipe having ultra-high toughness and high strength according to claim 1, wherein the mass percentages of the chemical elements are: C: 0.25-0.29%, Si: 0.24-0.38%, Mn: 0.92-1.17%, Cr: 0.95-1.22%, Mo: 0.6-0.75%, V: 0.05-0.09%, Nb: 0.02-0.04%, P0.015%, S0.005%, and the balance of Fe and unavoidable impurities.

3. The drill pipe having ultra-high toughness and high strength according to claim 1, wherein the mass percentages of the chemical elements are: C: 0.26-0.28%, Si: 0.27-0.36%, Mn: 0.92-1.17%, Cr: 0.95-1.22%, Mo: 0.61-0.72%, V: 0.05-0.08%, Nb: 0.02-0.04%, P0.015%, S0.005%, and the balance of Fe and unavoidable impurities.

4. The drill pipe having ultra-high toughness and high strength according to claim 1, wherein the mass percentage of Mo is 0.66-0.70%.

5. A process of manufacturing the drill pipe having ultra-high toughness and high strength according to claim 1, comprising: forming a drill pipe having an inner and outer surface, a pipe body between thicked ends and the desired chemical element composition in mass percentage; subjecting the drill pipe to a quenching step, wherein the drill pipe as a whole is heated to 900-950 C.; and then the inner surface of the drill pipe is subjected to axial-flow water-spray cooling and the outer surface of the drill pipe is subjected to laminar-flow water-spray cooling, with the amount of the water sprayed at thickened ends of the drill pipe and that along the pipe body being controlled to be different from each other, so that the pipe body and the thickened ends having different wall thicknesses have the same cooling rate; and subjecting the drill pipe to a tempering step, wherein the tempering temperature is controlled to be 650-675 C.

6. The process according to claim 5, wherein the drill pipe as a whole is heated to 910-940 C., or 920-940 C., or 910-930 C. in the quenching step.

7. The process according to claim 5, wherein the tempering temperature is controlled to be 650-670 C. or 660-670 C. in the tempering step.

8. The process according to claim 5, wherein the amount of the water sprayed at the thickened ends of the drill pipe and that along the pipe body are controlled to be different from each other in the quenching step, so that the difference between the cooling rates of the pipe body and the thickened ends having different wall thicknesses is equal to or less than 10%, or equal to or less than 5%.

9. The process according to claim 5, wherein the drill pipe has the mass percentages of the chemical elements: C: 0.25-0.29%, Si: 0.24-0.38%, Mn: 0.92-1.17%, Cr: 0.95-1.22%, Mo: 0.6-0.75%, V: 0.05-0.09%, Nb: 0.02-0.04%, P0.015%, S0.005%, and the balance of Fe and unavoidable impurities.

10. The process according to claim 5, wherein the drill pipe has the mass percentages of the chemical elements: C: 0.26-0.28%, Si: 0.27-0.36%, Mn: 0.92-1.17%, Cr: 0.95-1.22%, Mo: 0.61-0.72%, V: 0.05-0.08%, Nb: 0.02-0.04%, P0.015%, S0.005%, and the balance of Fe and unavoidable impurities.

11. The process according to claim 5, wherein the drill pipe has a mass percentages of Mo of 0.66-0.70%.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The technical solution of the invention will be further illustrated with reference to the following specific examples and comparative examples.

EXAMPLES 1-6

(2) The chemical element compositions of Examples 1-6 according to the invention and CrMnMo steel commonly used in the prior art (Comparative Example) are listed in Table 1.

(3) TABLE-US-00001 TABLE 1 (wt %) Designation C Si Mn Cr Mo V Nb P S Example 1 0.27 0.24 1.17 1.01 0.68 0.05 0.02 0.010 0.002 Example 2 0.25 0.32 1.02 1.12 0.74 0.09 0.03 0.007 0.002 Example 3 0.29 0.36 1.10 1.17 0.61 0.07 0.04 0.008 0.001 Example 4 0.28 0.38 0.95 1.20 0.66 0.08 0.03 0.009 0.001 Example 5 0.26 0.30 1.15 0.95 0.72 0.06 0.04 0.006 0.002 Example 6 0.27 0.27 0.92 1.22 0.70 0.07 0.02 0.008 0.002 Comparative 0.26 0.27 1.02 1.00 0.34 0.07 / 0.007 0.002 Example

(4) The inventive drill pipes having ultra-high toughness and high strength were manufactured using the following steps (the detailed process parameters and mechanical properties of Examples 1-6 are listed in Table 2):

(5) First, the ends of the drill pipe were thickened to form a thickened drill pipe body. The drill pipe as a whole was heated to a temperature of 900-950 C. The drill pipe as a whole was placed on a rotating quenching table. While the steel pipe was rotating, the inner surface of the drill pipe was subjected to axial-flow water-spray cooling and the outer surface of the drill pipe was subjected to laminar-flow water-spray cooling. At the same time, the amount of the water sprayed at the thickened ends of the drill pipe and that along the pipe body were controlled to be different from each other, so that the pipe body and the thickened ends having different wall thicknesses had substantially the same cooling rate to ensure that the pipe body and the thickened ends of the drill pipe had identical quenched microstructure. Finally, the drill pipe was subjected to tempering treatment at 650-675 C., such that both the pipe body and the thickened ends had a desired mechanical strength of 135 ksi.

(6) TABLE-US-00002 TABLE 2 Impact Quenching Tempering Yield Tensile Toughness Temperature Temperature Strength Strength (J) L-10- Designation ( C.) ( C.) (MPa) (MPa) 20 C. Example 1 920 665 1010 1090 128 Example 2 920 675 975 1070 134 Example 3 920 655 1060 1130 121 Example 4 910 650 1070 1138 122 Example 5 940 660 1020 1100 127 Example 6 930 670 990 1090 130 Comparative 880 615 1010 1110 85 Example

(7) As known from Table 2, when the same strength of 135 ksi is achieved, the drill pipes having ultra-high toughness and high strength according to the technical solution of the invention have far higher tempering temperatures than that of the conventional 135 ksi drill pipe of the comparative example, such that the inventive drill pipes having ultra-high toughness and high strength have a longitudinal full-size impact toughness at 20 C. of at least 100 J, far higher than the impact toughness level of the conventional 135 ksi drill pipe. Hence, the inventive pipes are capable of long-term operation under harsh conditions where alternate stress, abrasion and collision occur frequently.

(8) It is to be noted that the above specific examples of the invention are only exemplary. Obviously, the invention is not limited to the above examples. Rather, many variations can be made. All variations derived directly or contemplated from the disclosure of the invention by one skilled in the art fall within the protection scope of the invention.