Martensitic stainless steel welded pipe

• US 20010030004A1
• Filed: 04/02/2001
• Published: 10/18/2001
• Est. Priority Date: 08/06/1999
• Status: Active Grant

• Current Assignee: Nippon Steel Corporation
• Original Assignee: Sumitomo Metal Industries Limited (Nippon Steel Corporation)
• Inventors: Omura, Tomohiko, Kondo, Kunio, Hamada, Masahiko, Ogawa, Kazuhiro, Kushida, Takahiro
• Granted Patent: US 6,379,821 B2
• Time in Patent Office: Days
• US Class Current: 148/325
• CPC Class Codes: B23K 2101/06 Tubes
• CPC Class Codes: B23K 35/308 with Cr as next major constituent
• CPC Class Codes: B23K 35/3086 containing Ni or Mn
• CPC Class Codes: B23K 9/0253 for the longitudinal seam of tubes
• CPC Class Codes: B23K 9/23 taking account of the properties of the materials to be welded
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/004 Very low carbon steels, i.e. having a carbon content of less than 0,01%
• CPC Class Codes: C22C 38/42 with copper
• CPC Class Codes: C22C 38/44 with molybdenum or tungsten
• CPC Class Codes: C22C 38/46 with vanadium
• CPC Class Codes: C22C 38/50 with titanium or zirconium
• CPC Class Codes: Y10S 148/909 Tube
• CPC Class Codes: Y10T 428/12958 Next to Fe-base component
• CPC Class Codes: Y10T 428/12979 Containing more than 10% nonferrous elements [e.g., high alloy, stainless]
• CPC Class Codes: Y10T 428/12986 Adjacent functionally defined components

Abstract

This invention relates to a large-diameter, thick-wall martensitic stainless steel welded pipe. For this welded pipe, the size of the raised weld bead portion on the inside surface is restricted to be small based on a conditional formula derived by considering the bead width and height and the yield strength of the base metal and of the weld metal. As a result, the base metal portion and pipe inside surface seam portion of this welded pipe are superior in corrosion resistance, in particular stress corrosion cracking resistance (SCC resistance). The sulfide stress corrosion resistance (sour gas resistance) and carbon dioxide corrosion resistance can be further improved by selecting the chemical compositions. This welded pipe is very well suited for use as a pipe for a pipeline for conveying a crude oil and a natural gas with no dehydration treatment, which is highly corrosive to metals.

Claims

1. A martensitic stainless steel welded pipe which comprises a base metal which is a stainless steel containing, on the mass % basis, not more than 0.05% of C and 9-20% of Cr and having a metallurgical microstructure comprising a full martensite phase or a martensite phase as the main constituent with a ferrite phase contained therein, and a seam weld metal which is a stainless steel containing, on the mass % basis, not more than 0.1% of C and 7-20% of Cr and having a metallurgical microstructure comprising a martensite phase as the main constituent with an austenite phase contained therein, a seam weld bead on the inside surface satisfying the following relation (1):

L≦

0.2×

W 

 

(1)

where

L;

the length of the portions of the seam weld bead which show a value of h exceeding 1.25 as calculated by the expression (2) shown below;

h={1+(2×

H/W)}×

(YS_B100/YS_w100) 

 

(2)

where

H;

the height of the bead from the pipe inside surface (mm),

W;

the width of the bead (mm),

YS_B100;

the yield strength of the base metal at 100°

C. (MPa),

YS_w100;

the yield strength of the weld metal at 100°

C. (MPa).

2. A welded pipe as claimed in

claim 1

, wherein the metallurgical microstructure of the base metal is constituted of, on the volume % basis, 55-90% martensite phase and 10-45% ferrite phase and that of the weld metal is constituted of, on the volume % basis, 70-95% martensite phase and 5-30% austenite phase, and wherein the chemical compositions of the base metal and weld metal are, on the mass % basis, as follows:

3. A welded pipe as claimed in

claim 1

or 2, wherein the contents of Cr, Ni and Ti in the base metal are, on the mass % basis, Cr:

11-20%, Ni;

3-7% and Ti;

not more than 0.05%, with the following relations (3) and (4) being satisfied;

Cr+1.5Mo−

Ni−

0.4Cu−

14≧

0 

 

(3) Cr+1.5Mo−

2Ni−

0.8Cu−

12.5≦

0 

 

(4)

4. A welded pipe as claimed in

claim 1

or 2, wherein the contents of Cr, Ni, Mo and Ti in the base metal are, on the mass % basis, Cr:

15-20%, Ni;

4-7%, Mo;

1.5-4% and Ti;

not more than 0.015%, and the contents of Cr, Ni, Mo, W and Ti in the weld metal are, on the mass % basis, Cr;

11-18%, Ni;

5-10%, Mo;

1.5-4%, W;

0-4% and Ti;

not more than 0.03%, with the chemical composition of the weld metal satisfying the following relations (5) and (6);

−

1≦

Cr+Mo−

1.7Ni≦

13−

220×

O (oxygen) 

 

(5) 25≦

Cr+Mo+1.8Ni≦

30 

 

(6).

5. A welded pipe as claimed in

claim 1

or 2, wherein the contents of Cr, Ni, Mo and Ti in the base metal are, on the mass % basis, Cr:

15-20%, Ni;

4-7%, Mo;

1.5-4% and Ti;

not more than 0.015%, and the contents of Cr, Ni, Mo, W and Ti in the weld metal are, on the mass % basis, Cr;

11-18%, Ni;

5-10%, Mo;

1.5-4%, W;

0-4% and Ti;

not more than 0.03%, with the chemical composition of the base metal satisfying the following relations (3) and (4); and

Cr+1.5Mo−

Ni−

0.4Cu−

14≧

0 

 

(3) Cr+1.5Mo−

2Ni−

0.8Cu−

12.5≦

0 

 

(4)

the chemical composition of the weld metal satisfying the following relations (5) and (6);

−

1≦

Cr+Mo−

1.7Ni≦

13−

220×

O (oxygen) 

 

(5) 25≦

Cr+Mo+1.8Ni≦

30 

 

(6).

6. A welded pipe as claimed in

claim 1

or

2

, wherein the base metal and the weld metal in the seam portion respectively have the following chemical compositions on the mass % basis:

7. Use of a welded pipe as described in

claim 1

or

2

, in a line pipe for conveying a crude oil or natural gas with no dehydration treatment.

8. Use of a welded pipe as described in

claim 3

, in a line pipe for conveying a crude oil or natural gas with no dehydration treatment.

9. Use of a welded pipe as described in

claim 5

, in a line pipe for conveying a crude oil or natural gas with no dehydration treatment.