JP2000303148A - Stainless steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stainless steel tube having seam weld metal in which the toughness of the seam weld zone, corrosion resistance in a carbon dioxide environment and sulfide stress corrosion cracking resistance in a hydrogen sulfide environment are good even as-welded. SOLUTION: This stainless steel tube is the one having a seam weld zone, the seam weld metal contains, by weight, 10 to 25% Cr, also, the metallic structure thereof is formed of 2 to 30% ferrite, 10 to 55% austenite, and the balance martensite, and the base metal of the steel tube contains, by weight, >=0.03% C, <=1% Si, <=5% Mn, <=0.015% P, <=0.002% S, <=200 ppm N, 10 to 14% Cr, <=6% Ni, and the balance Fe with inevitable impurities, and in which M value defined by the formula of M=Cr%+1.3×Mo%-Ni% is <=14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel pipe for high Cr line pipe having excellent weldability and weld toughness, and is used for transporting gas or oil containing carbon dioxide or hydrogen sulfide.
The present invention relates to a stainless steel pipe having excellent corrosion resistance, weldability, and weld toughness.

[0002]

2. Description of the Related Art Pipelines used for transporting gas or oil containing carbon dioxide gas or hydrogen sulfide use ordinary carbon steel pipes and corrosion inhibitors (inhibitors) in combination.
A highly corrosive duplex stainless steel pipe or clad steel pipe is used. However, the use of the corrosion inhibitor has a problem of cost or environmental pollution, and there is a problem that the material cost of the duplex stainless steel pipe and the clad steel pipe is high. Against this background, as a relatively inexpensive material, there is AISI (American Iron and Steel Institute) 410 steel or the like, but this steel has difficulty in weldability and the like. There is also a problem of stress corrosion cracking in a hydrogen sulfide environment.

A high Cr steel having weldability and excellent resistance to sulfide stress corrosion cracking in a hydrogen sulfide environment and a method for producing the same are disclosed in
JP-A-99128, JP-A-4-26819, JP-A-5-156408, JP-A-6-306549
JP, JP-A-6-264192, JP-A-8-3
No. 642 has been proposed.

[0004]

However, in the techniques disclosed in the above-mentioned patent publications, there is no study on the weldability, sulfide stress corrosion cracking resistance, and the like of the seam weld metal as welded. An object of the present invention is to clarify the effect of component elements on seam weld toughness, corrosion resistance in a carbon dioxide gas environment, and sulfide stress corrosion cracking resistance in a hydrogen sulfide environment of a high Cr steel pipe having a seam weld, It is an object of the present invention to provide a stainless steel pipe having a seam weld metal having the above-mentioned properties even when welding is performed.

[0005]

In order to solve the above problems and achieve the object, the present invention uses the following means.

(1) The steel pipe of the present invention is a stainless steel pipe having a seam weld, wherein the seam weld metal contains 10 to 25% by weight of Cr and has a metal structure of ferrite. Rate: 2 to 30%, austenite rate: 10 to 55%, and the balance of martensite structure. The steel pipe base material is, by weight%, C: 0.03% or less;
Si: 1% or less, Mn: 5% or less, P: 0.015
%, S: 0.002% or less, N: 200 ppm
And Cr: 10 to 14% and Ni: 6% or less, the balance being Fe and unavoidable impurities, and the M value defined by the following formula (1) is 14 or less. It is a stainless steel pipe.

M = Cr% + 1.3 × Mo% −Ni% (1) (2) The steel pipe of the present invention further contains, by weight%, Mo: 4% or less and Cu: 2% as a steel pipe base material component. Below, Co: 1%
Below, W: 1% or less, Nb: 0.1% or less, V: 0.1
%, Ti: 0.1% or less, Zr: 0.1% or less,
The stainless steel pipe according to the above (1), characterized by containing one or more kinds selected from the group consisting of B: 50 ppm or less and Ca: 50 ppm or less.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solve the above-mentioned problems, the present inventors changed the base metal and the weld metal component of a line pipe steel pipe containing high Cr to improve toughness, corrosion resistance in a carbon dioxide gas environment, and hydrogen sulfide. The sulfide stress corrosion cracking and weldability in the environment were investigated.

As a result, to improve the toughness of the seam weld metal, it is necessary to control the amount of the weld metal, the amount of austenite and the amount of ferrite, and to improve the toughness of the heat affected zone of the base metal and the resistance to stress corrosion cracking. It has been found that it is effective to set the M value of the following equation (1) to 14 or less.

M = Cr% + 1.3 × Mo% −Ni% (1) Based on the above findings, the present inventors have determined the chemical composition of the weld metal, the amount of austenite and the amount of ferrite, and the chemical properties of the base metal. By adjusting the components within a certain range, a stainless steel pipe having excellent weld toughness and sulfide stress corrosion cracking resistance was found, and the present invention was completed. That is, the present invention, by limiting the composition of the seam weld metal, the metal structure, and the composition of the base metal to the following range, seam weld toughness, corrosion resistance in a carbon dioxide gas environment, and sulfide resistance in a hydrogen sulfide environment It is possible to provide a stainless steel pipe having a seam weld metal having good stress corrosion cracking properties even as welded.

The reasons for adding the components of the present invention, the reasons for limiting the components, and the reasons for limiting the metal structure of the weld metal will be described below.

(1) Component composition range and metal structure of weld metal Cr: 10 to 25% for weld metal, 10 to 14% for base metal
% In order to obtain good corrosion resistance of the weld metal, 10% or more of C
It is necessary to add r, and it is preferable to add r more than the base material. However, the addition exceeding 25% leads to deterioration in weld toughness and weldability. Therefore, the Cr content of the weld metal is 10 to 25%.

On the other hand, in order to obtain good corrosion resistance of the base material, it is necessary to add 10% or more of Cr. However, if it exceeds 14%, the toughness and weldability of the weld heat affected zone deteriorate. Therefore, the Cr content of the base material is 10 to 14%.

C: 0.03% or less If more than 0.03% of C is added to the base material, corrosion resistance, sulfide stress corrosion cracking resistance, toughness of the weld heat affected zone, and weldability are deteriorated. Therefore, the C content of the base material is 0.03% or less.

Si: 1% or less If more than 1% of Si is added, the weldability deteriorates. Therefore, the Si content of the base metal is 1% or less, and the Si content of the weld metal is also preferably 1% or less.

Mn: 5% or less When Mn is added in excess of 5%, the toughness and sulfide stress corrosion cracking resistance of the weld metal and the weld heat affected zone deteriorate. Therefore,
The Mn content of the base metal is 5% or less, and the Mn content of the weld metal is also 5%.
% Or less is preferable.

P: 0.015% or less If P is added in excess of 0.015%, the toughness, sulfide stress corrosion cracking resistance, and weldability of the weld heat-affected zone of the weld metal and base metal are deteriorated. Therefore, the P content of the base metal is preferably 0.015% or less, and the P content of the weld metal is also preferably 0.015% or less. S: 0.002% or less When S is added in excess of 0.002%, corrosion resistance, weldability, and sulfide stress corrosion cracking resistance are deteriorated. Therefore, the S content of the base metal is 0.002% or less, and the S content of the weld metal is preferably 0.002% or less.

N: 200 ppm or less If N is added to the base material in an amount exceeding 200 ppm, the toughness of the weld heat affected zone and the resistance to sulfide stress corrosion cracking are deteriorated. Therefore, the N content of the base material is 200 ppm or less.

Ni: 6% or less If Ni is added in excess of 6%, the toughness and weldability of the weld heat affected zone deteriorate. Therefore, the amount of Ni in the base material is 6% or less.

M value: 14 or less, where M = Cr% + 1.
3 × Mo% −Ni% When the M value exceeds 14, the toughness of the heat affected zone deteriorates.
Therefore, the M value of the base material is 14 or less.

In the present invention, as a component of the base material, if necessary, one or more selected from the following selected component group may be further contained.

(Selective component group) Mo: 4% or less When Mo is added, good sulfide stress corrosion cracking resistance can be obtained. If added in excess of 4%, the toughness and weldability of the heat affected zone deteriorate. Therefore, the amount of Mo in the base material is 4%
It is as follows.

Cu: 2% or less, Co: 1% or less, W: 1
% Or less Depending on the strength target, Cu, Co, or Mo may be added to the base material. Each upper limit is an upper limit that does not deteriorate the toughness and weldability of the heat affected zone. Therefore, Cu: 2% or less, Co: 1% or less, W: 1% or less.

Nb: 0.1% or less, V: 0.1% or less,
Ti: 0.1% or less, Zr: 0.1% or less Addition of Nb, V, Ti, and Zr improves the toughness and sulfide stress corrosion cracking resistance of the weld heat affected zone.
If added in excess of 1%, the toughness and sulfide stress corrosion cracking resistance of the heat affected zone deteriorate. Therefore, Nb, V, Ti,
The Zr contents are each 0.1% or less. Ca: 50 ppm or less Ca is an element that controls the form of sulfide and improves sulfide stress corrosion cracking resistance, but when added in excess of 50 ppm, conversely deteriorates sulfide stress corrosion cracking resistance and weldability. I will. Therefore, the amount of Ca is 50 ppm or less. B: 50 ppm or less If B is added in excess of 50 ppm, the toughness of the heat affected zone and the weldability are deteriorated. Therefore, the base material B
The amount is 50 ppm or less, and the B amount of the weld metal is 50 pp.
m or less is preferable.

(Metal structure of weld metal) Ferrite ratio: 2 to 30% If the ferrite ratio of the weld metal is less than 2%, high-temperature cracking tends to occur at the time of welding. It is necessary. On the other hand, if it exceeds 30% in the weld metal, the weld toughness deteriorates. Therefore, the ferrite ratio in the weld metal is 2 to 30%.

Austenite ratio: 10 to 55% If the austenite ratio of the weld metal is less than 10%, it is difficult to ensure the toughness of the weld. On the other hand, if it exceeds 55%, the strength of the welded portion is insufficient. Therefore, the austenite ratio in the weld metal is 10 to 55%.

The remaining structure is a martensite structure.

By adjusting the composition range and the metal structure of the weld metal to the composition range of the base metal, the toughness of the seam weld, the corrosion resistance in a carbon dioxide gas environment, and the sulfide stress in a hydrogen sulfide environment are adjusted. It is possible to obtain a stainless steel pipe having a good seam weld metal even when the corrosion cracking property is as-welded.

In the seam welding method for steel pipes, submerged welding is preferable because of high efficiency and high workability. However, even with other welding methods, satisfactory performance can be obtained as long as the above-described range of the present invention is satisfied.

Hereinafter, the effects of the present invention will be proved by giving examples of the present invention.

[0031]

EXAMPLE A test steel slab (base material) was heated to 1100 ° C. and hot-rolled to a thickness of 12.5 mm. Thereafter, heat treatment of quenching at 900 ° C. for 30 minutes and tempering at 650 ° C. were performed to form a tube by cold bending, and a welded steel pipe was manufactured by vertical seam welding. Here, the seam welding of the steel pipe was performed by submerged arc welding.

Table 1 shows the chemical composition of the base metal of the test steel pipe and the Cr content, the ferrite rate and the austenite rate of the weld metal (A to L: steel pipe of the present invention, MU: comparative steel pipe).

Table 2 shows the results of a corrosion test of carbon steel saturated in artificial seawater (90 ° C.) of carbon steel (99% by volume) and hydrogen sulfide (1% by volume). The results of a stress corrosion cracking test in artificial seawater (normal temperature, 20 ° C.) saturated with a mixed gas of, and the results of a Charpy impact test on a weld heat affected zone and a weld metal and a tensile test result on a weld are shown.

The corrosion resistance was as follows: corrosion rate: 0.1 mm / year or less; sulfide stress corrosion cracking resistance (SSC): cracks did not occur in a 720-hour immersion test; welding heat affected zone (HAZ); As for the metal toughness, the absorption energy at −20 ° C. was 50 J or more, respectively. The strength of the weld metal was determined to be equal to or higher than that of the base metal and good. The weldability was determined to be good if no weld defects or weld cracks were observed when seam welding was performed on the steel pipe.

The base material has a tensile strength of 600 to 850M.
Pa, and the absorbed energy was as good as 50 J or more at -20 ° C.

As shown in Tables 1 and 2, the steel pipe A of the present invention has the chemical composition and M value of the base metal within the range of the present invention, and the austenite ratio and the ferrite ratio of the seam weld metal structure within the range of the present invention. To L have sufficient corrosion resistance, sulfide stress corrosion cracking resistance, weld heat affected zone toughness, and weldability.

On the other hand, the comparative steel pipe M having a high base metal content of C, Ni and W, a low ferrite ratio of the weld metal and a high austenite ratio has corrosion resistance, sulfide stress corrosion cracking resistance, weld heat affected zone toughness, Insufficient weld strength and weldability. The comparative steel pipe N having a high Mn and Co content of the base material, a low Cr content, and a low Cr content of the weld metal has insufficient corrosion resistance, sulfide stress corrosion cracking resistance, toughness of the weld heat affected zone, and weldability. Base material C
The comparative steel pipe O having high amounts of u, Nb and Zr and having a high austenite ratio of the weld metal has insufficient sulfide stress corrosion cracking resistance, toughness of the weld heat affected zone, strength of the weld zone, and weldability. The comparative steel pipe P having a high base metal S, Cr, and Mo content and a high Cr content of the weld metal has insufficient corrosion resistance, sulfide stress corrosion cracking resistance, weld heat affected zone toughness, weld toughness, and weldability. The comparative steel pipe Q having a high P and V content of the base material and a low austenite ratio of the weld metal has insufficient sulfide stress corrosion cracking resistance, weld heat affected zone toughness, weld toughness, and weldability. Base material Si, N
Comparative steel pipe R with high amount and high ferrite ratio of weld metal
Has insufficient sulfide stress corrosion cracking resistance, weld heat affected zone toughness, weld zone toughness, and weldability. The comparative steel pipe S having a high Ti content and M value of the base metal and a high ferrite ratio of the weld metal has insufficient corrosion resistance, sulfide stress corrosion cracking resistance, weld heat affected zone toughness, and weld zone toughness. The comparative steel pipe T having a high Ca content and M value of the base metal, a high ferrite ratio of the weld metal, and a low austenite ratio has corrosion resistance, sulfide stress corrosion cracking resistance, weld heat affected zone toughness, weld zone toughness, weldability. Is not enough. The comparative steel pipe U has a high B content and M value of the base metal, a low ferrite ratio of the weld metal, and a high austenite ratio. not enough.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

As described above, according to the present invention,
By specifying the steel composition of the base metal, the Cr content of the weld metal, and the metal structure, it is possible to improve the toughness of the base metal and the welded parts and to improve the corrosion resistance and sulfide stress corrosion cracking resistance in carbon dioxide and hydrogen sulfide environments. An excellent high Cr content line pipe can be manufactured at low cost.

Claims (2)

[Claims] 1. A stainless steel pipe having a seam weld, wherein said seam weld metal contains 10 to 25% by weight of Cr and has a metal structure having a ferrite ratio of 2 to 30%.
%, An austenite ratio: 10 to 55%, and a balance of martensite structure. The steel pipe base material is, by weight%, C: 0.03% or less;
i: 1% or less, Mn: 5% or less, P: 0.015%
And S: 0.002% or less, N: 200ppm or less, Cr: 10 to 14%, Ni: 6% or less, the balance being Fe and unavoidable impurities, and the following (1) A stainless steel pipe, wherein the M value defined by the formula is 14 or less. M = Cr% + 1.3 × Mo% −Ni% (1) 2. The steel tube base material component further includes:
Mo: 4% or less, Cu: 2% or less, Co: 1% or less,
W: 1% or less, Nb: 0.1% or less, V: 0.1% or less, Ti: 0.1% or less, Zr: 0.1% or less, B: 5
The composition according to claim 1, further comprising at least one selected from the group consisting of 0 ppm or less and Ca: 50 ppm or less.
A stainless steel pipe as described in 1.