Stainless steel pipe and method for manufacturing same

Patent metadata

Field	Value
Publication number	US-12359752-B2
Application number	US-202117800294-A
Country	US
Kind code	B2
Filing date	Jan 20, 2021
Priority date	Feb 27, 2020
Publication date	Jul 15, 2025
Grant date	Jul 15, 2025

Abstract

A stainless steel pipe of a predetermined composition is provided that has an axial tensile yield strength of 689 MPa or more, an axial compressive yield strength/axial tensile yield strength ratio of 0.85 to 1.15, and a microstructure that is 20 to 80% ferrite phase by volume with the remainder containing an austenite phase, the stainless steel pipe having pipe end portions at least one of which has a fastening portion for an external thread or an internal thread, and having a curvature radius of 0.2 mm or more for a corner R formed by a bottom surface of a thread root and a pressure-side flank surface of the thread, measured in an axial plane section of the fastening portion.

First claim

The invention claimed is:

1. A stainless steel pipe of a composition that comprises, in mass %, C: 0.005 to 0.08%, Si: 0.01 to 1.0%, Mn: 0.01 to 10.0%, Cr: 20 to 35%, Ni: 1.0 to 15%, Mo: 0.5 to 6.0%, and N: 0.005% or more and 0.147% or less, and in which the balance is Fe and incidental impurities,
the stainless steel pipe having an axial tensile yield strength of 689 MPa or more, an axial compressive yield strength/axial tensile yield strength ratio of 0.85 to 1.15, and a microstructure that is 20 to 80% ferrite phase by volume with the remainder containing an austenite phase,
the stainless steel pipe having pipe end portions at least one of which has a fastening portion for an external thread or an internal thread, and having a curvature radius of 0.2 mm or more for a corner R formed by a bottom surface of a thread root and a pressure-side flank surface of the thread, measured in an axial plane section of the fastening portion.

2. The stainless steel pipe according to claim 1 , wherein the composition further comprises, in mass %, at least one of selected from Groups A, B, C and D:
Group A: one or two selected from
W: less than 6.0%, and Cu: less than 4.0%,
Group B: one or two or more selected from
Ti: 0.50% or less, Al: 0.30% or less, V: 0.55% or less, and Nb: 0.75% or less,
Group C: one or two or more selected from
B: 0.010% or less, Zr: 0.10% or less, Ca: 0.010% or less, Ta: 0.3% or less, REM: 0.10% or less, and Mg: 0.10% or less, and
Group D: one or two or more selected from
Sn: 0.30% or less, Sb: 0.30% or less, and Ag: 0.30% or less.

3. The stainless steel pipe according to claim 1 , wherein the stainless steel pipe is a seamless steel pipe.

4. The stainless steel pipe according to claim 2 , wherein the stainless steel pipe is a seamless steel pipe.

5. The stainless steel pipe according to claim 1 , wherein the corner R has a curvature radius of 0.3 mm or more.

6. The stainless steel pipe according to claim 2 , wherein the corner R has a curvature radius of 0.3 mm or more.

7. The stainless steel pipe according to claim 3 , wherein the corner R has a curvature radius of 0.3 mm or more.

8. The stainless steel pipe according to claim 4 , wherein the corner R has a curvature radius of 0.3 mm or more.

9. The stainless steel pipe according to claim 5 , wherein the fastening portion has a metal-to-metal seal portion and a torque shoulder portion.

10. The stainless steel pipe according to claim 6 , wherein the fastening portion has a metal-to-metal seal portion and a torque shoulder portion.

11. The stainless steel pipe according to claim 7 , wherein the fastening portion has a metal-to-metal seal portion and a torque shoulder portion.

12. The stainless steel pipe according to claim 8 , wherein the fastening portion has a metal-to-metal seal portion and a torque shoulder portion.

13. A method for manufacturing a stainless steel pipe of claim 1 ,
the method comprising circumferential bending and unbending.

14. A method for manufacturing a stainless steel pipe of claim 2 ,
the method comprising circumferential bending and unbending.

15. A method for manufacturing a stainless steel pipe of claim 2 ,
the method comprising circumferential bending and unbending.

16. A method for manufacturing a stainless steel pipe of claim 4 ,
the method comprising circumferential bending and unbending.

17. A method for manufacturing a stainless steel pipe of claim 5 ,
the method comprising circumferential bending and unbending.

18. A method for manufacturing a stainless steel pipe of claim 6 ,
the method comprising circumferential bending and unbending.

19. A method for manufacturing a stainless steel pipe of claim 7 ,
the method comprising circumferential bending and unbending.

20. A method for manufacturing a stainless steel pipe of claim 8 ,
the method comprising circumferential bending and unbending.

21. The stainless steel pipe according to claim 1 , wherein when the stainless steel pipe is immersed in a corrosive environment under an applied stress held constant at 90% of the axial tensile yield strength, the corrosive environment comprising an aqueous solution comprising a 20% NaCl+0.5% CH 3 COOH+CH 3 COONa combined with added H 2 S gas and adjusted to a pH of 3.0 at a test temperature of 25° C., corrosion of the stainless steel pipe does not occur.

Assignees

• Jfe Steel Corp

Inventors

• Sasaki Shunsuke
• Yuga Masao
• Katsumura Tatsuro
• Kijima Hideo

Classifications

• C21D8/10

  during manufacturing of tubular bodies · CPC title

• F16L15/06

  characterised by the shape of the screw-thread · CPC title

• C22C38/60

  containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur · CPC title

• C22C38/58 Primary

  with more than 1.5% by weight of manganese · CPC title

• C22C38/54

  with boron · CPC title