JPH1180881A - High chromium welded steel pipe excellent in weld zone toughness and sulfide corrosion cracking resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high chromium welded steel pipe excellent in corrosion resistance and stress corrosion cracking resistance as wall as weld zone toughness. SOLUTION: Weld metal in the seam weld zone is composed of, by weight, <=0.03% C, <=1.0$ Si, <=5.0% Mn, <=0.03% P, <=0.008% S, <=400 ppm N, 10 to 20% Cr, 3.5 to 12% Ni and <=500 ppm oxygen, in which the value of P in the formula I is regulated to 15 to 25, and the value of Q in the formula II is regulated to >=-5.8, and base metal is composed of <=0.03% C, <=1.0% Si, <=5.0% Mn, <=0.03% P, <=0.008% S, <=300 ppm N, 10 to 14% Cr and 0.5 to 6.0% Ni, and in which the value of M in the formula III is regulated to <=14.0: the formula I: P=%Ni+30x%C+0.5x%Mn+0.8x(%Cr+%Mo+1.5x%Si+-0.5x% Nb), the formula II: Q=%Ni+30x%C+0.5x%Mn-0.72x(%Cr+Mo+-1.5x%Si+0.5x%Nb) and the formula III: M=%Cr+1.3x%Mo-%Ni.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high chromium welded steel pipe excellent in weld toughness and sulfide corrosion cracking resistance.

[0002]

2. Description of the Related Art In pipelines used for transporting gas or oil containing carbon dioxide or hydrogen sulfide,
It is necessary to take measures against stress corrosion cracking due to sulfide. Therefore, when a normal carbon steel pipe is used, a corrosion inhibitor (inhibitor) is used in combination, or a duplex stainless steel pipe or a clad steel pipe having high corrosion resistance is used. However, the use of a corrosion inhibitor has problems of environmental pollution as well as cost. Further, there is a problem that the material cost of the duplex stainless steel pipe and the clad steel pipe is high.

Against this background, AISI (American Iron and Steel Institute) 410 steel and the like are relatively inexpensive materials. However, this steel has a problem in weldability and the like, and also has a problem of stress corrosion cracking in a hydrogen sulfide environment.

[0004] Therefore, there have been proposed some materials having weldability and also having excellent resistance to stress corrosion cracking in a hydrogen sulfide environment and a method for producing the same. For example, JP-A-55-2
No. 1566 discloses a steel containing 1.0 to 3.5% of Mn and 10 to 13.5% of Cr.
(Martensitic stainless steel, the same applies hereinafter). Similarly, Japanese Unexamined Patent Publication No. 4-99128 discloses Cu of 1.2 to 4.
5%, steel containing 11 to 14% of Cr, Co.
Has been proposed containing 1.1 to 4.0% and 11 to 14% Cr.

Japanese Patent Laid-Open Publication No. 5-156408 discloses that
A steel with an increased steel content of 17% was proposed.
Steels with increased r to 13-17% have been proposed. On the other hand,
No. 6,306,549 proposes a steel having a low Cr of 10 to 13%. Further, JP-A-8-3642 discloses Cu and Ni.
A method for producing an electric resistance welded steel pipe in which the content of these elements is regulated by a certain relational expression while the content of these elements is regulated to 4.0% or less, Co to 2.0% or less, and Mo and W to 3.0% or less has been proposed.

[0006]

The above-mentioned prior art is a technique for improving the weldability, weld toughness, and sulfide corrosion cracking resistance of a martensitic stainless steel pipe. Limited and no consideration is given to weld metal. Also, regarding the weld toughness, only the influence of the chemical composition of the base material has been studied.

[0007] For example, the technique described in Japanese Patent Application Laid-Open No. 55-21566 is a technique mainly related to a steel plate, and does not specifically describe a seam welded portion of a welded steel pipe. JP 4-99
No. 128 and Japanese Patent Application Laid-Open No. 4-268019,
Although this is a technology related to line pipes, only the toughness of the heat affected zone is described for the toughness of the weld, and the toughness of the weld metal is not examined. In these techniques, it is necessary to add Cu and Co. These elements have a problem that weldability and weld toughness are low.

In the technique described in Japanese Patent Application Laid-Open No. 5-156408, only the presence or absence of crack occurrence is described as weldability. Also, there is no description about the production of a welded steel pipe. Japanese Patent Application Laid-Open No. 6-264192 describes the toughness of the heat affected zone, but does not describe the production of a welded steel pipe. The technique described in Japanese Patent Application Laid-Open No. 6-306549 is a technique relating to a thick steel plate, and does not describe production of a welded steel pipe.

The technique described in Japanese Patent Application Laid-Open No. 8-3642 is a method for manufacturing an electric resistance welded steel pipe, and the material is a hot rolled sheet (thin sheet). Accordingly, there is a limit in terms of the thickness and the material, and it is not possible to obtain a product equivalent to a thick material or a controlled rolled material (material) of a thick steel plate.

As described above, in the prior art, a method for manufacturing a high chromium welded steel pipe having a seam welded portion is as follows.
It has not been studied and can be manufactured with the same chemical composition as the seamless steel pipe. Therefore, the chemical composition and material of the seam weld, particularly the weld metal, have not been elucidated.

The present invention solves these problems of the prior art, and provides high chromium welding with excellent weld toughness of seam welds and excellent corrosion resistance and stress corrosion cracking resistance in carbon dioxide and hydrogen sulfide environments. The purpose is to provide steel pipes.

[0012]

According to a first aspect of the present invention, a chemical composition of a weld metal in a seam weld portion is as follows: C: 0.03% or less, Si: 1.0% or less, Mn: 5.0% or less, P: 0.03% or less, S: 0.008
% Or less, N: 400 ppm or less, Cr: 10 to 20%, Ni: 3.5 to 12%, oxygen: 500 ppm or less, and the value of P represented by the following formula (1) is 15 to 25, The value of Q represented by (2) is -5.8 or more, and the chemical composition of the base material is% by weight, C: 0.03% or less, S
i: 1.0% or less, Mn: 5.0% or less, P: 0.03% or less, S: 0.008% or less, N: 300ppm or less, Cr: 10 to 14%, Ni: 0.5 to 6.0%, and the following formula This is a high chromium welded steel pipe having excellent weld toughness and sulfide corrosion cracking resistance, where the value of M represented by (3) is 14.0 or less. P =% Ni + 30x% C + 0.5x% Mn + 0.8x (% Cr +% Mo + 1.5x% Si + 0.5x% Nb) (1) Q =% Ni + 30x% C + 0.5x% Mn-0.72 x (% Cr +% Mo + 1.5x% Si + 0.5x% Nb) (2) M =% Cr + 1.3x% Mo-% Ni (3)

The present invention has been made by focusing on not only the base material of the high chromium welded steel pipe but also the seam weld, and has studied the weld toughness and sulfide corrosion cracking resistance. In the process, the toughness, corrosion resistance under carbon dioxide gas environment, sulfide stress corrosion cracking resistance under hydrogen sulfide environment, and weldability were investigated by changing the chemical composition of the base metal and weld metal. As a result, a high chromium welded steel pipe excellent in weld toughness and sulfide corrosion cracking resistance could be obtained by using the chemical components of the present invention. Hereinafter, the reasons for limiting the chemical components will be described.

C: If the C of the base material exceeds 0.03%, the corrosion resistance, the sulfide stress corrosion cracking resistance, the toughness of the weld heat affected zone, and the weldability deteriorate. If the C of the weld metal exceeds 0.03%, the corrosion resistance, sulfide stress corrosion cracking resistance, and toughness will deteriorate. Therefore, the C content of both the base metal and the weld metal is specified to be 0.03% or less.

Si: More than 1.0% Si in both base metal and weld metal
, The weldability deteriorates. Therefore, the amount of Si is set to 1.0% or less for both the base metal and the weld metal.

Mn: More than 5.0% for both base metal and weld metal
When added, the toughness and sulfide stress corrosion cracking resistance of the weld metal and the weld heat affected zone deteriorate. Therefore, the Mn content of both the base metal and the weld metal is specified to be 5.0% or less.

P: If P exceeds 0.03% in both the base metal and the weld metal, the toughness, sulfide stress corrosion cracking resistance, and weldability of the heat affected zone are deteriorated. Therefore, P and P
The amount is specified as 0.03% or less.

S: If S exceeds 0.008% in both the base metal and the weld metal, the corrosion resistance, weldability and sulfide stress corrosion cracking resistance deteriorate. Therefore, the S content of both the base metal and the weld metal is specified to be 0.008% or less.

Cr: In order to obtain good corrosion resistance of the base material,
It is necessary to add 10% or more of Cr. However, if added in excess of 14%, the toughness and weldability of the heat affected zone deteriorate.
Therefore, the Cr content of the base material is specified in the range of 10 to 14%. In order to obtain good corrosion resistance of the weld metal, it is necessary to add 10% or more of Cr, and it is preferable to add more than the base metal. However, addition exceeding 20% leads to deterioration of weld toughness and weldability. Therefore, the Cr content of the weld metal is 10 ~
Specify within the range of 20%.

N: If the N of the base material exceeds 300 ppm, the toughness of the heat affected zone and the resistance to sulfide stress corrosion cracking deteriorate. Therefore, the N content of the base material is specified to be 300 ppm or less. N of weld metal
If it exceeds 400 ppm, toughness and sulfide stress corrosion cracking resistance deteriorate. Therefore, the N content of the weld metal is specified to be 400 ppm or less.

Ni: In the base metal, it is necessary to add 0.5% or more of Ni in order to obtain good toughness of the heat affected zone. However, if added in excess of 6.0%, the toughness and weldability of the heat affected zone deteriorate. Therefore, the amount of Ni in the base metal is 0.5 to
Specify within the range of 6.0%. In the weld metal, it is necessary to add 3.5% or more Ni to obtain good toughness and sulfide stress corrosion cracking resistance. However, if added in excess of 12%, the weldability deteriorates. Therefore, the Ni content of the weld metal is specified in the range of 3.5 to 12%.

P value: With respect to the weld metal, if the value of P (P value) represented by the formula (1) is less than 15, the structure contains a large amount of martensite, and the weld metal has toughness and resistance. Sulfide stress corrosion cracking and weldability deteriorate. If the P value exceeds 25, the structure will contain a lot of austenite,
The strength of the weld metal decreases. Therefore, the P value of the weld metal is set to 1
Specify in the range of 5 to 25.

Q value: With respect to the weld metal, when the value of Q (Q value) represented by the formula (2) is less than -5.8, the structure contains a large amount of δ ferrite, and the toughness and the toughness of the weld metal are reduced. The sulfide stress corrosion cracking resistance deteriorates. Therefore, Q of the weld metal
Specify a value of -5.8 or more (positive direction).

M value: For the base material, M represented by formula (3)
If the value (M value) exceeds 14.0, the corrosion resistance, sulfide stress corrosion cracking resistance, and toughness of the weld heat affected zone of the weld heat affected zone deteriorate. Therefore, in order to obtain good corrosion resistance and sulfide stress corrosion cracking resistance of the base material, the M value is specified to be 14.0 or less.

Oxygen: When the oxygen in the weld metal exceeds 500 ppm, the toughness of the weld metal deteriorates. Therefore, the amount of oxygen in the weld metal is specified to be 500 ppm or less.

The balance is Fe and impurities, but any element other than those described above may be included as impurities unless the object of the invention is impaired. The impurities include those mixed in from scrap and those mixed in steelmaking work, but may be included as impurities as long as they are mixed in normal work.

According to a second aspect of the present invention, the chemical component of the weld metal in the seam portion is M% by weight in addition to the chemical component of the first aspect.
o: 4.0% or less, Cu: 2.0% or less, Co: 1.0% or less, W: 1.0% or less,
Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10% or less, Zr: 0.10%
Hereinafter, one or more of B: 50 ppm or less and Ca: 50 ppm or less are contained, and the chemical component of the base material is, in addition to the chemical component of claim 1, Mo: 4.0% or less by weight, Cu: 2.0% or less, Co: 1.0% or less, W: 1.0% or less, Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10
% Or less, Zr: 0.10% or less, B: 50 ppm or less, Ca: 50 ppm or less, while containing one or more, P, Q according to claim 1,
A high chromium welded steel pipe having excellent weld toughness and sulfide corrosion cracking resistance in which the values of and M are within the ranges of the first invention, respectively.

The present invention is intended to improve the strength and toughness by adding the following chemical components to the chemical components of the first invention. Hereinafter, the reasons for limiting the chemical components will be described.

Mo, Cu, Co, W: These elements may be added to the base metal and the weld metal according to the target strength. However, if Mo is added in excess of 4.0%, Cu is 2.0%, Co is 1.0%, and W is added in excess of 1.0%, the toughness and weldability of the weld metal or weld heat affected zone deteriorate. Therefore, for both the base metal and the weld metal, the amount of addition of these elements, Mo is 4.0% or less, Cu is
2.0% or less, Co is 1.0% or less, and W is 1.0% or less.

Nb, V, Ti, Zr: The toughness and sulfide stress corrosion cracking resistance of the weld metal or the weld heat affected zone are improved by adding trace amounts of these elements to both the base metal and the weld metal. However, if any of them is added in excess of 0.10%, the toughness of the weld heat-affected zone is rather reduced, and the sulfide stress corrosion cracking resistance is deteriorated. Therefore, the addition amounts of Nb, V, Ti, and Zr are set to 0.10% or less for both the base metal and the weld metal.

Ca: Ca controls the form of sulfide in both the base metal and the weld metal, and improves the sulfide stress corrosion cracking resistance.
However, if added in excess of 50 ppm, the sulfide stress corrosion cracking resistance and weldability are rather deteriorated. Therefore, the Ca content of both the base metal and the weld metal is specified to be 50 ppm or less.

B: B improves the toughness of both the base metal and the weld metal. However, if it is added in excess of 50 ppm, the toughness of the weld metal or weld heat affected zone is reduced and the weldability is rather deteriorated. Therefore, both base metal and weld metal
The B content is specified to be 50 ppm or less.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION The steel of the present invention can be smelted by a converter, an electric furnace, or any other method capable of controlling chemical components within the scope of the present invention. The melted steel is cast into a shape such as a slab in order to be used as line pipe steel. Then, if a steel plate is manufactured by hot rolling, a steel plate for a line pipe is obtained. The hot rolling may be performed by a thick plate mill, but may be performed by a hot strip mill when the width may be narrow (for small diameter pipes).

[0034] The seam welding method for steel pipes is preferably submerged welding in terms of high efficiency and high workability. However, even with other welding methods, if the chemical composition of the weld metal satisfies the scope of the invention, good welding is performed. The toughness, sulfide stress corrosion cracking resistance and weldability of the metal can be obtained.

[0035]

EXAMPLES Steels having various chemical components were melted, and steel plates were manufactured by hot rolling. Table 1 shows the chemical composition of the steel sheet (base material).
Shown with M value. In Table 1, steels A to J indicate invention steels, and steels K to S indicate comparative steels.

[0036]

[Table 1]

Next, these steel sheets were formed into steel pipes, and seam welding was performed to produce welded steel pipes. Table 2 shows the chemical composition of the weld metal in the seam welded portion of the steel pipe together with the P value and the Q value.

[0038]

[Table 2]

The steel pipes A1 to H1 (the last one) and I1 and I2 in Table 2 are invention steel pipes, and the chemical composition is within the scope of the invention for both base metals and weld metals. Steel pipes A2 to H2 (end 2) and I3 are comparative steel pipes, and the base metal is within the scope of the invention, but the weld metal is outside the scope of the invention. K1 to P1 are comparative steel pipes, and the weld metal was prepared within the scope of the invention, but the base metal was outside the scope of the invention (comparative steel) as shown in Table 1 above. Furthermore, Q1 to S1 are comparative steel pipes, and both the base metal and the weld metal are outside the scope of the invention.

With respect to these steel pipes, corrosion resistance, sulfide stress corrosion cracking resistance, weldability, and toughness of the heat affected zone were examined. The corrosion resistance was examined by a corrosion test in artificial seawater saturated with carbon dioxide. The investigation of sulfide stress corrosion cracking resistance was performed by stress corrosion cracking test in artificial seawater saturated with a mixed gas of carbon dioxide and hydrogen sulfide.

In the weldability test, seam welding was performed, and evaluation was made based on the presence or absence of weld defects and weld cracks. Regarding the toughness of the heat-affected zone of the weld, a V-notch Charpy test piece was cut out from the heat-affected zone of the weld and an impact test was performed. A similar test was conducted for the toughness of the weld metal. The weld strength was evaluated by performing a tensile test on a welded joint and determining the fracture position (base metal, weld metal).

Table 3 shows the test results together with the chemical components. Here, the chemical components of the base metal and the weld metal (and
Regarding the M value, the P value, and the Q value), only the elements outside the scope of the present invention are indicated by crosses. As for the test results,
That is, those that have achieved the target characteristics are indicated by a mark. Weldability, when seam welding of steel pipe is performed, welding defects,
Those in which no weld cracking occurred were rated as good (marked with ○).
Regarding the toughness (HAZ toughness in the table) of the heat affected zone and the toughness of the weld metal, those having an absorbed energy at -20 ° C of 50 J or more were evaluated as good (marked with ○).

The corrosion rate was 0.1 mm / year or less, and the sulfide stress corrosion cracking resistance (SSC resistance in the table) was good if no cracking occurred in the 720-hour immersion test (marked with a circle). ). Regarding the strength of the welded portion, the fracture position of the base metal having a fracture position in the weld joint tensile test was good (○), and that of the weld metal was poor (x).

[0044]

[Table 3]

As shown in Table 3, the invention steel pipes A1 to H1 (suffix 1) and I1 and I2 satisfying the invention range in both the base metal and the weld metal have sufficient corrosion resistance, sulfide stress corrosion cracking resistance, weldability, and weldability. It shows the toughness and weld strength of the heat-affected zone.

Comparative steel pipes A2 to H2 (end 2) and I3 in which the base metal is within the scope of the invention but the weld metal is outside the scope of the invention
Have not reached the target characteristics. Weld metal
Steel pipe A2 having a high C and W content, a low Ni content and a low Q value has insufficient weldability, corrosion resistance, sulfide stress corrosion cracking resistance, and weld metal toughness. The steel pipe B2 having a high Mn and Co content and a low Cr content of the weld metal has insufficient weldability, toughness of the weld heat affected zone, corrosion resistance, sulfide stress corrosion cracking resistance, and toughness of the weld metal.

Steel pipe with high contents of Ni, Cu, Ti and oxygen in weld metal
C2 has insufficient weldability, corrosion resistance, sulfide stress corrosion cracking resistance, and weld metal toughness. Steel pipe D2 having a high S, Cr, Zr content and a low P value of the weld metal has insufficient weldability, corrosion resistance, sulfide stress corrosion cracking resistance, toughness of the weld metal, and weld strength. The steel pipe E2 having a high P, Mo, and V content of the weld metal has insufficient weldability, corrosion resistance, sulfide stress corrosion cracking resistance, and weld metal toughness.

The steel pipe F2 having a high Si, N, P value of the weld metal is
Insufficient weldability, corrosion resistance, sulfide stress corrosion cracking resistance, toughness and strength of weld metal. The steel pipe G2 having a high Nb and B content of the weld metal and a low Q value does not have sufficient weldability, sulfide stress corrosion cracking resistance, and toughness of the weld metal. Steel pipe H2 having a high Ca content in the weld metal, a high P value and a low Q value has insufficient weldability, sulfide stress corrosion cracking resistance, and toughness and strength of the weld metal. The steel pipe I3 having a high P value and a low Q value of the weld metal has insufficient weldability, sulfide stress corrosion cracking resistance, toughness and strength of the weld metal.

Also, even if the weld metal is within the scope of the invention,
None of the comparative steel pipes K1 to S1 whose base material is out of the range of the invention reach the target characteristics. Steel pipe K1 with high C, Ni, W content of base material, steel tube L1 with high Mn and Co content of base material and low Cr content
Has insufficient weldability, toughness, corrosion resistance, and sulfide stress corrosion cracking resistance of the heat affected zone. Steel pipe M1 having a high content of Cu, Nb, and Zr in the base metal does not have sufficient weldability, toughness of the heat affected zone, and resistance to sulfide stress corrosion cracking. The steel pipe N1 having a high content of S, Cr and Mo in the base metal does not have sufficient weldability, toughness of the heat affected zone, corrosion resistance, and sulfide stress corrosion cracking resistance. The steel pipe O1 having a high P and V content of the base material and the steel pipe P1 having a high Si and N content of the base material have insufficient weldability, toughness of the weld heat affected zone, and resistance to sulfide stress corrosion cracking.

Steel pipe whose base metal and weld metal are outside the scope of the invention
None of Q1 to S1 has reached the target characteristics. High Ti content and M value of base metal, low Ni content of weld metal and Q
Steel pipe Q1 with low value, Ca content and M value of base metal is high, Ni content of weld metal is high, and steel tube R1 with high M value and low Q value have weldability, toughness of weld heat affected zone, corrosion resistance , Sulfide stress corrosion cracking resistance, toughness of weld metal, and welding strength are not sufficient. Steel pipe S with high B and M values of base metal and low Q value of weld metal
1) The weldability, toughness of the heat affected zone, corrosion resistance, sulfide stress corrosion cracking resistance, and toughness of the weld metal are not sufficient.

[0051]

According to the present invention, by defining the chemical components of the base metal and the seam weld and the relationship between these constituent elements, the material characteristics of the base metal and the weld metal can be improved. . As a result, we provide a low-cost steel pipe for high Cr line pipes that excels in the toughness of the base material and seam welds, and has excellent corrosion resistance in carbon dioxide gas environments and sulfide stress corrosion cracking resistance in hydrogen sulfide environments. be able to.

Claims (2)

[Claims] The chemical composition of a weld metal of a seam weld is as follows:
By weight%, C: 0.03% or less, Si: 1.0% or less, Mn: 5.0% or less,
P: 0.03% or less, S: 0.008% or less, N: 400ppm or less, Cr: 10-20
%, Ni: 3.5 to 12%, oxygen: 500 ppm or less, the value of P represented by the following formula (1) is 15 to 25, and the value of Q represented by the formula (2) is -5.8. The chemical composition of the base material is as follows: C: 0.03% or less, Si: 1.0% or less, Mn: 5.0% or less, P:
0.03% or less, S: 0.008% or less, N: 300ppm or less, Cr: 10-14
%, Ni: 0.5 to 6.0%, and a high chromium welded steel pipe excellent in weld toughness and sulfide corrosion cracking resistance in which the value of M represented by the following formula (3) is 14.0 or less. P =% Ni + 30x% C + 0.5x% Mn + 0.8x (% Cr +% Mo + 1.5x% Si + 0.5x% Nb) (1) Q =% Ni + 30x% C + 0.5x% Mn-0.72 x (% Cr +% Mo + 1.5x% Si + 0.5x% Nb) (2) M =% Cr + 1.3x% Mo-% Ni (3) 2. The chemical composition of the weld metal in the seam portion is, in addition to the chemical composition according to claim 1, Mo: 4.0% or less, Cu: 2.0% or less, Co: 1.0% or less, W: 1.0% or less, Nb: 0.10%
Below, V: 0.10% or less, Ti: 0.10% or less, Zr: 0.10% or less, B: 5
0 ppm or less, Ca: 50 ppm or less containing one or more, the chemical component of the base material, in addition to the chemical components according to claim 1, Mo: 4.0% or less, Cu: 2.0% or less, by weight%, Co: 1.0% or less, W: 1.0
% Or less, Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10% or less, Z
r: 0.10% or less, B: 50 ppm or less, Ca: 50 ppm or less, and at least one of P, Q and M according to claim 1
2. A high chromium welded steel pipe having excellent weld toughness and sulfide corrosion cracking resistance, each having a value within the range of claim 1.