JPS62227067A - High toughness resistance welded tube having superior sour resistance - Google Patents

Abstract

PURPOSE:To obtain a high toughness resistance welded tube having superior sour resistance by vanishing platy crushed Ca oxide type inclusions present in the butted part of a resistance welded tube and in the heat-affected zones on both sides of the butted part. CONSTITUTION:The composition of a resistance welded tube is composed of, by weight, 0.01-0.35% C, 0.02-0.5% Si, 0.1-1.8% Mn, 0.001-0.1% Al, <=0.001% Ca, <=0.02% P, <=0.0012% S [P(%)+25XS(%)<=0.04], one or more among 0.2-0.6% Cu, 0.1-1% Ni and 0.2-3% Cr, one or more among 0.1-1% Mo, 0.01-0.15% Nb, 0.01-0.15% V and 0.01-0.1% Ti and the balance Fe with inevitable impurities.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a high toughness electric resistance welded steel pipe with excellent sour resistance.
In more detail, we will discuss electric resistance welded steel pipes that have high cracking resistance even in environments containing wet hydrogen sulfide (and have excellent low-temperature toughness, especially suitable for use in extremely cold regions, for example, in oil and natural gas drilling or transportation). .

(Conventional technology).

In recent years, the petroleum and natural gas produced often contain hydrogen sulfide, and when water such as seawater and fresh water coexists, it not only causes thinning due to corrosion that occurs on the steel surface, but also corrosion. This poses a problem as hydrogen generated on the steel surface can penetrate into the steel and cause destruction.

This fracture is different from sulfide stress cracking, which has long been recognized in high-strength steel, and can occur even without any externally applied stress. This fracture occurs when hydrogen that has entered from the environment accumulates at the boundary between the steel base and A-based sulfide inclusions such as MnS that are present in the base metal and extend in the rolling direction, and is gasified by the gas pressure. A of the above-mentioned MnS etc.
The sulfide-based inclusions form sharp notches, which serve as crack nuclei to grow into parallel cracks on the plate surface, and these parallel cracks are connected in the thickness direction of the plate. This type of cracking is hereinafter referred to as ``hydrogen bulging cracking.'' Various studies have been conducted on steels that have high resistance to hydrogen bulging cracking, and various steels have been proposed.

These include, for example, the prevention of cracking by adding Cu or Co, the reduction of MnS by extremely low S content, and the reduction of MnS by adding Ca or rare earth elements, as seen in, for example, Japanese Patent Publication No. 57-17065 or Japanese Patent Publication No. 57-16184. These techniques utilize methods such as fixing S by adding elements, etc., and steels that can withstand even harsh environments have been developed using these techniques.

On the other hand, in recent years, areas where oil and natural gas are produced have expanded to include extremely cold regions such as Alaska, the Soviet Union, and the Arctic Ocean, and the line pipes used in these areas are
Excellent low-temperature toughness is required for both the base metal and the electric resistance welded part. In such a case, it goes without saying that if the produced fluid contains hydrogen sulfide, not only low-temperature toughness but also sour resistance is required.

In ERW steel pipes, the toughness of the welded part is generally lower than that of the base metal, so various studies have been conducted on ERW steel pipes with excellent toughness, including the ERW welded parts, and various methods and is proposed. For example, JP-A-54-136512, JP-A-5'7-14082,
Typical examples include Japanese Patent Publication No. 3, Japanese Patent Publication No. 58-53707, and Japanese Patent Publication No. 5B-53708. This technology utilizes techniques such as controlling the crystal grain size by limiting the subsequent cooling rate, reducing solid solution N, and refining the crystal grains using Nb or V. To date, these technologies have produced electrical resistance welds with considerably superior toughness. Steel pipes have been developed.

However, these electric resistance welded steel pipes are used in normal environments, and are not intended to be used in so-called sour environments containing hydrogen sulfide and water.

(Problems to be Solved by the Invention) As a result of detailed study on the toughness of the electric lamination welded part of the electric resistance welded steel pipe, the present inventors found that the electric resistance welded abutment of the sour resistance welded steel pipe when Ca is added It has been found that in some cases, the toughness is significantly lower than that of the base material, and in this case, it was found that the various conventional techniques described above do not improve the toughness.

As a result of continuing research to develop a steel pipe with excellent sour resistance and toughness, the present inventors found that the cause of the decrease in toughness of the ERW welded part was as shown in Figure 2. ERW abutment part 2 of steel pipe 1 and its both sides Z.

and Z2 were found to be Ca oxide-based inclusions pulverized into plate shapes existing in the heat-affected zone 3 within 100 μm.

Furthermore, according to the research conducted by the present inventors, these plate-like oxide inclusions are caused by the near-spherical Ca oxide inclusions that already existed in the base metal due to the thermal influence during electric resistance welding. It has been revealed that the material is heated to near its melting point and then pressurized from both sides by squeeze rolls, resulting in the product deforming into a plate shape.

FIG. 3 shows a microscopic photograph of Ca oxide spheroidized, and FIG. 4 shows a microscopic photograph of Ca oxide deformed into a plate shape. Further, FIG. 5 shows the results of a laboratory test on the deformation behavior of Ca oxide-based inclusions during hot rolling. It can be seen that as the rolling temperature increases, the spherical inclusions change into plate shapes.

The present inventors have discovered for the first time the mechanism by which such Ca oxide-based inclusions deteriorate the toughness of the electric resistance stitched abutment.

An object of the present invention is to provide an electric resistance welded steel pipe that has excellent sour resistance and low-temperature toughness.

(Means and effects for solving the problem) The high toughness electric resistance welded steel pipe with excellent sour resistance according to the present invention has a weight% Tc of 0.01
~0.35%, Si:0.02~0.5%, Mn:o,
x ~1.8%, AI: 0.001~0.10%, Ca≦o, ooi%, P≦0.020%, S≦0.
0012% Big P (%) + 25xS (%) 50.04
%, further Cu: 0.2 to 0.6%, Ni: 0
．． 1 to 1.0%, Cr: 0.2 to 3.0%, one or more types, Mo: 0.1 to 1.0%, Nb: 0.0
1-0.15%, V: 0.01-0.15%, Ti: 0
．． 01 to 0.10% of one or more types, with the remainder consisting of Fe and unavoidable impurities.

The reasons for limiting each component will be explained below.

C is a basic element that most stably improves the strength of steel, so it must be contained at 0.01% or more to ensure strength, but if it exceeds 0.35%, it will affect the toughness of steel. 0.01 to 0.0.
It was set at 35%.

Si is set to 0.02% or more to improve strength, and the upper limit is set to 0.5% to ensure toughness.

Mn is an element necessary for strength, so it is set at 0.1% or more, and the upper limit is set at 1.8% to ensure weldability and toughness.

AI is an effective element for deoxidizing steel, and it is set at o, oot% or more in order to improve the strength and toughness of steel through grain refining action. However, if the AI content in the steel exceeds 0.10%, it will not only reduce the toughness but also the weldability, so the upper limit should be set at 0.1%.
It was set to 0%.

Limiting the contents of Ca, P and S is the most important thing in the present invention.

Ca is an effective element that improves the sour resistance of the base metal by fixing S in steel as CaS and preventing the formation of MnS, but Ca-based inclusions can reduce the toughness of electric resistance welds. deteriorate. These Ca-based inclusions have a nearly spherical shape in the base metal, but in the electric resistance welding part, they are heated to near the melting point of the steel and are squeezed into both [1, As explained above, since the weld is pressurized from scratch, it deforms into a plate shape, which deteriorates the toughness of the welded part.

First, regarding the deterioration of toughness due to increase in Ca content,
The relationship between the V notch Charpy transition temperature and the absorbed energy l is shown in Figures 6 and 7, respectively.

The minimum operating temperature for pipelines in Alaska and Canada is -4.
It is said to be around 6℃, and is often used in this Notch Charpy specification, but in order to have sufficient toughness at -46℃, the Ca content must be 0.001 as shown in Figures 6 and 7.
% or less. Therefore, in the present invention, Ca is limited to 0.001% or less.

However, if no Ca is added or if Ca is limited to 0.001% or less, the morphology of MnS cannot be controlled or is extremely insufficient, so other measures are required to prevent sourness. As a measure to improve sour resistance under the condition that the Ca content is limited to 0.001% or less, the present inventors
We investigated two points: extremely low sulfidation and extremely low phosphorus.

P115 for sour environments used in Alaska, Canada, etc.
．． There are many so-called BP environments of 1 to 5.4, but Ca≦0.
The conditions for extremely low sulfidation and extremely low phosphorous content were determined to satisfy this condition specification at 0.001%. Under conditions where the addition of Ca, which is effective as a measure against sourness, is restricted, it is sufficient to remove and purify these elements that are harmful to sourness resistance and replace them. According to research conducted by the present inventor, in order to obtain sufficient sour resistance in a BP (PH5, 1 to 5.4) environment, P
It was found that the S content should be within the range surrounded by ABCDO in FIG. Furthermore, Figure 1 shows the BP environmental test (PII4.
This figure shows the occurrence of cracks on the surface of the test piece after the test piece was immersed in a normal temperature solution of 8 to 5.4 for 96 hours with no stress applied, and CLI? is the crack length ratio. That is,
Hydrogen-induced cracking does not occur within the range surrounded by ABCDO in Figure 1 (although cracking may occur outside the range. Therefore, the P and S contents are set to P≦0.02.
0%, S≦0.0012% Big P (%) + 25 × S (
%) 50.04%.

Furthermore, in the present invention, one or more types of Cu, Ni, and Cr and one or more types of Mo, Nb, V, and Ti are included depending on the respective uses.

First, Cu, Ni, and Cr all have the effect of improving the corrosion resistance of the base metal and reducing hydrogen penetration into the steel.

If Cu is less than 0.20%, it has no effect, and if it exceeds 0.60%, it has a negative effect on hot workability.
It was limited to a range of 0.60%.

If Ni is less than 0.1%, it is ineffective, and if it exceeds 1.0%, it may induce sulfide stress cracking.
It was limited to a range of 1.0%. Note that Ni can be added simultaneously with Cu within the above range for the purpose of preventing hot embrittlement caused by Cu, but even if Ni is added for this purpose, this does not deviate from the scope of the present invention. .

Cr has no effect if it is less than 0.2%, and reduces the toughness of the steel if it exceeds 3.0%, so it is limited to a range of 0.2 to 0.3%.

Note that Cr can also be used as an element to improve strength and toughness by adding it to steel with a Mn content of less than 0.6%, and it can also be used to improve strength and toughness in other steels as well. Even if Cr is added to the steel for the purpose of achieving this, it does not deviate from the scope of the present invention.

Next, Mo, Nb, V, and Ti are all elements that improve the strength of steel, and by containing 0.10% or more of Mo and 0.01% or more of Nb, V, and Ti, the same level can be achieved. shows a strength improvement effect, but Mo is 1
．． 0%.

If Nb and V are added in an amount exceeding 0.15%, and Ti in an amount exceeding 0.1%, the toughness may decrease, so MO is added in an amount exceeding 0.15%.
10-1.0%, Nb and V 0.01-0.15%
, Ti was limited to a range of 0.01 to 0.10%. In particular, Ti also has the effect of improving toughness.

The manufacturing process for the ERW steel pipe of the present invention may include ERW welding the as-hot rolled material, or a controlled cooling process immediately after hot rolling, or further normalization of the rolled material.

It is also possible to apply a material that has gone through manufacturing processes used for ordinary steel materials, such as tempering or quenching and tempering. Furthermore, a process of normalizing, tempering, or quenching and tempering may be applied to a part or the whole of the manufactured electric resistance welded steel pipe of the present invention, without departing from the scope of the present invention. Which process to apply may be determined depending on the need to ensure properties such as strength and toughness.

〔Example〕

Azurol hot-rolled steel strips having the components shown in Table 1 were electrical resistance welded and normalized at Ac3 or higher to produce electrical resistance welded steel pipes of the sizes shown in Table 1.

Evaluations of sour resistance and low temperature toughness are shown in Table 2. For sour resistance, hydrogen-induced cracking resistance was evaluated using the same BP environmental test as shown in Figure 1, and both CLR (crack length ratio)
, C5R (cracking susceptibility rate) are both 0, and the sour resistance is excellent. In addition, low-temperature toughness is 14% in the Charpy test.
As evaluated by absorbed energy at 6°C, the material of the present invention is significantly superior to the comparative material.

〔Effect of the invention〕

The ERW steel pipe of the present invention is an ERW steel pipe with excellent sour resistance and low-temperature toughness, and is suitable for use in oil and natural gas drilling, transportation, etc., even in environments containing wet hydrogen sulfide, especially in extremely cold regions. It can be used for various purposes.

Table 2

[Brief explanation of drawings]

Figure 1 is a diagram showing the range of P and S contents in the present invention, Figure 2 is a diagram showing an electric resistance welded part, and Figure 3 is a diagram showing a spherical Ca
Figure 4 is a metallurgical microscope photograph showing oxide inclusions. Figure 4 is a metallurgical microscope photograph showing Ca oxide inclusions deformed into a plate shape by electric resistance welding. Figure 5 is a metallurgical microscope photograph showing the deformation behavior of Ca oxide inclusions. The schematic diagrams shown in Figures 6 and 7 show the effect of C on toughness.
It is a figure showing the description of a content. Patent applicant: Nippon Steel Corporation (Taisha) Figure 1 (〉, I/+1)
(<〆I77 Guran Figure 5 vTrs ('c)

Claims (1)

[Claims] C: 0.01-0.35%, Si: 0.02-0.02% by weight
0.5%, Mn: 0.1-1.8%, Al: 0.001
~0.10%, Ca≦0.001%, P≦0.
020%, S≦0.0012% and P (%) + 25×
Limit S (%)≦0.04%, and further Cu: 0.2~
0.6%, Ni: 0.1-1.0%, Cr: 0.2-3
．． 0% of one or more kinds and Mo: 0.1-1.
0%, Nb: 0.01-0.15%, V: 0.01-0
．． 15%, Ti: 0.01-0.10%, one or two
1. A high-toughness electric resistance welded steel pipe with excellent sour resistance, characterized in that the remainder consists of Fe and unavoidable impurities.