JPH0941082A - Resistance welded tube excellent in hic resistance and sscc resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resistance welded tube excellent in HIC resistance and SSCC resistance. SOLUTION: This resistance welded tube has a composition containing, as principal components, <=0.2%, by weight, C, <=0.5% Si, <=2% Mn, <=0.02% P, <=0.003% S, <=0.07% Al, and 0.001-0.006% Ca and having the balance essentially Fe. Moreover, the weld zone of this resistance welded tube has a melted and solidified structure. Further, as special components, Nb, Cu, Ni, Mo, Cr, V, and Ti can be incorporated. Its manufacturing method is characterized by using a laser beam.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electric resistance welded pipe having excellent hydrogen-induced cracking resistance and sulfide stress corrosion cracking resistance in a wet hydrogen sulfide environment, and a method for producing the same.

[0002]

2. Description of the Related Art Cracks called hydrogen induced cracking (hereinafter referred to as HIC) and sulfide stress corrosion cracking (hereinafter referred to as SSCC) occur in a steel pipe for transporting petroleum containing hydrogen sulfide, natural gas and the like. The generation mechanism of this HIC is considered as follows.

That is, in an environment in which hydrogen sulfide is present, hydrogen produced by corrosion of the steel surface becomes atomic and easily penetrates into the steel, but this atomic hydrogen is present around the non-metallic inclusions in the steel. It becomes a bubble and the pressure causes a crack.

Further, this crack is caused by segregation, ferrite,
Propagates to non-uniform parts of the material such as the pearlite interface and develops into large cracks. Therefore, as a countermeasure,
Japanese Patent No. 6184 describes that a method of making inclusions less likely to be a starting point of cracks by controlling the shape of inclusions by adding Ca is effective.

On the other hand, SSCC is a crack that occurs when a stress is applied, and although it depends on a mechanism different from that of HIC, it is the same as that caused by hydrogen in the steel starting from non-metallic inclusions. Reduction of metal inclusions is resistant to SSCC
Improve the characteristics. It is necessary to improve the HIC resistance and SSCC resistance characteristics of the steel strip as a raw material for ERW pipe, for example, hot rolled steel sheet, by the above measures.

However, the characteristics of the electric resistance welded pipe cannot be improved only by improving the base material. Generally, a method for manufacturing an electric resistance welded pipe is a method of performing high frequency resistance welding or high frequency induction welding on opposing edge portions of an open pipe formed by continuously forming a steel strip.

In this case, the welded portion is in an intermediate state between melt welding and pressure welding, and a clear molten pool is not formed, and inclusions generated by oxidation during welding are sufficiently discharged from the inside of the steel during upsetting. Therefore, inclusions mainly containing fine oxides are present on the joint surface of the weld.

Therefore, it is considered that hydrogen is concentrated in the welded portion during the use of the electric resistance welded pipe, and this becomes the starting point of crack generation. In order to improve the HIC resistance and SSCC resistance of the electric resistance welded pipe, in JP-A-63-241116, a method of shielding the welded portion with a non-oxidizing gas and performing electric resistance welding to reduce defects in the welded portion. However, in reality, no shield device has been developed that has excellent shielding properties and can withstand continuous operation.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electric resistance welded pipe having excellent HIC resistance and SSCC resistance in a wet hydrogen sulfide environment and a method for manufacturing the same.

[0010]

The inventors of the present invention have improved the composition of the composition of steel, and by irradiating a high energy beam, for example, a laser beam during electric resistance welding,
By sufficiently raising the temperature of the molten pool and melting and dispersing inclusions, the knowledge that the above problems can be solved by producing an electric resistance welded tube in which a melt-solidified structure is produced in the welded portion is obtained, The following invention has been reached.

(1) The invention of claim 1 is an electric resistance welded pipe having the following characteristics and excellent in HIC resistance and SSCC resistance. (A) As the main component (the component composition is wt%), C:
0.2% or less, Si: 0.5% or less, Mn: 2% or less, P: 0.02% or less, S: 0.003% or less, Al: 0.07% or less, Ca: 0.001 to 1 0.0
An electric resistance welded pipe containing 06% and the balance being substantially Fe, wherein (b) the welded portion of the electric resistance welded pipe has a melt-solidified structure.

(2) The invention of claim 2 is an electric resistance welded steel pipe having the following characteristics, which is excellent in HIC resistance and SSCC resistance. (A) As the main component (the component composition is wt%), C:
0.2% or less, Si: 0.5% or less, Mn: 2% or less, P: 0.02% or less, S: 0.003% or less, Al: 0.07% or less, Ca: 0.001 to 1 0.0
06%, Nb: 0.1% or less, Cu:
0.5% or less, Ni: 0.5% or less, Mo: 0.5% or less,
An electric resistance welded pipe containing one or more components of Cr: 1% or less, V: 0.1% or less, Ti: 0.1% or less, and the balance being substantially Fe, b) The welded portion of the electric resistance welded pipe has a melt-solidified structure.

(3) The invention according to claim 3 is characterized in that the rising angle of the metal flow in the vicinity of the welded portion of the welded portion is 45 ° or less, and the HI resistance according to claim 1 or 2.
It is an electric resistance welded tube with excellent C and SSCC resistance.

(4) The invention of claim 4 is a method for producing an electric resistance welded pipe having excellent HIC resistance and SSCC resistance, which is characterized by comprising the following steps. (A) As the main component (the component composition is wt%), C:
0.2% or less, Si: 0.5% or less, Mn: 2% or less, P: 0.02% or less, S: 0.003% or less, Al: 0.07% or less, Ca: 0.001 to 1 0.0
A step of preparing a steel strip containing 06% and the remainder being substantially Fe; (b) a step of continuously forming the steel strip into an open pipe by a multi-stage forming roll; and (c) the open. A step of heating both opposite edge portions of the pipe to a temperature range equal to or lower than the melting temperature of the steel; and (d) irradiating the heated both edge portions with a laser beam to a molten state, and an upset amount with a squeeze roll. Process of controlling and welding.

(5) The invention of claim 5 is a method for producing an electric resistance welded pipe having excellent HIC resistance and SSCC resistance, which is characterized by comprising the following steps. (A) As the main component (the component composition is wt%), C:
0.2% or less, Si: 0.5% or less, Mn: 2% or less, P: 0.02% or less, S: 0.003% or less, Al: 0.07% or less, Ca: 0.001 to 1 0.0
06%, Nb: 0.1% or less, Cu:
0.5% or less, Ni: 0.5% or less, Mo: 0.5% or less,
A step of preparing a steel strip containing one or more components of Cr: 1% or less, V: 0.1% or less, Ti: 0.1% or less, and the balance substantially consisting of Fe; (B) a step of continuously forming the steel strip into an open pipe with a multi-stage forming roll, and (c) a step of heating both opposing edge portions of the open pipe to a temperature range equal to or lower than the melting temperature of the steel strip. And (d) a step of irradiating the heated both edge portions with a laser beam to bring them into a molten state and controlling the amount of upset with a squeeze roll to perform welding.

(6) In the invention of claim 6, the upset amount by the squeeze roll is controlled so that the metal flow rising angle in the vicinity of the welded portion of the electric resistance welded pipe is 45 ° or less. And a method for manufacturing an electric resistance welded pipe having excellent SSCC resistance.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An electric resistance welded tube having excellent HIC resistance and SSCC resistance characteristics is required to have the following composition and a molten solidification structure in the welded portion of the electric resistance welded tube. First,
The compositional composition (wt%) of steel will be described.

The composition of the steel is such that P is 0.0
It has been found that it is necessary to limit S to 2% or less, S to 0.003% or less, and to add Ca in the range of 0.001 to 0.006%. Regarding other components, If necessary, the addition is carried out within the range shown above.

The upper limit of P is 0.01% because it deteriorates the HIC resistance of steel.

The upper limit of S is 0.003% because it deteriorates the HIC resistance of steel.

When Ca is added in an amount of 0.001% or more, the shape of inclusions is granulated, and it is desirable to add Ca as necessary in order to improve the HIC resistance through morphology control. However, excessive addition causes toughness of steel. The upper limit of 0.006
%.

C may be added as necessary to secure the strength of the steel, but the upper limit is 0.2% from the viewpoint of weldability and toughness.

Si is preferably added as a deoxidizing agent for steel in an amount of 0.1% or more, but an excessive addition makes the steel brittle, so the upper limit is made 0.5%.

It is desirable to add 0.5% or more of Mn in order to secure the strength of the steel, but an excessive addition causes the toughness to deteriorate, so the upper limit is made 2%.

Al is added to deoxidize the steel during melting, but if it exceeds 0.07%, the cleanliness of the steel generally deteriorates, so it is made 0.07% or less.

Further, the strength of steel is increased, and HIC resistance and S resistance are increased.
The elements described below are added to improve the SCC characteristics.

Nb is 0.001 to secure the strength of steel.
% Or more is desirable, but excessive addition exceeding 0.1% deteriorates toughness, so the upper limit is made 0.1%.

Cu may be added as necessary in order to prevent the diffusion of hydrogen into the steel and improve the HIC resistance, but excessive addition deteriorates the hot workability of the steel. The upper limit is 0.5%.

Ni and Mo may be added if necessary in order to further improve the HIC resistance of the steel, but excessive addition deteriorates the SSCC resistance, so the upper limit is made 0.5%.

Although Cr enhances the carbon dioxide corrosion resistance of steel, addition of more than 1% deteriorates the weldability of steel, so the upper limit is made 1%.

V and Ti improve the strength of the steel, but excessive addition deteriorates the toughness.
1%. The above is the reason for limiting the component composition.

In order to obtain an electric resistance welded tube having excellent HIC resistance and SSCC resistance, a melt-solidified structure is generated at the joint surface of the welded portion. Therefore, a unique texture existing in the conventional electric resistance welded pipe is generated. It is necessary to have a tissue that is significantly reduced in incidence. As a result, the HIC resistance and SSCC resistance characteristics are improved.

HIC resistance and SS resistance of the welded part of the conventional electric resistance welded pipe
The CC characteristics are inferior to the base material because of the conventional heating method,
This is because, for example, it is manufactured by a high frequency resistance heating method or a high frequency induction heating method. That is, in such a manufacturing method, since the edge portion of the open pipe is not heated to the melting temperature, a strong upset is unavoidably applied in order to discharge the oxide generated on the joint surface, resulting in a strong texture. Because it was.

Here, the upset amount is defined as follows. Upset amount (mm) = coil width before pipe making (mm) -pipe circumference length (mm)

Further, inclusions mainly composed of oxides which are generated at the time of electric resistance welding and remain on the joint surface are exposed on the outer surface of the bead by cutting of the welding bead, and hydrogen penetrates from this portion to start the hydrogen cracking. It is because FIG. 1 (a) shows a macro-etch photograph of a welded portion of a conventional electric resistance welded pipe. The texture generated as a result of adding upset can be observed as a rise of metal flow by a micrograph of a bead section. This structure is one of the causes of deterioration of the mechanical properties of the electric resistance welded pipe, and is not desirable from the viewpoint of SSCC resistance.

Therefore, in the present invention, at the time of electric resistance welding, first, the edge portion of the open pipe is heated to a temperature range below the melting temperature by a conventional heating method such as high frequency resistance heating or high frequency induction heating, and then high energy is applied. By irradiating a beam, for example, an electron beam, a plasma beam, or a laser beam, a completely melted state is generated on the bonding surface, and the generated oxide is melted and finely dispersed.

In this way, a melt-solidified structure as shown in FIG. 1 (b) is generated at the joint surface, and the generation of a peculiar texture existing in the conventional electric resistance welded pipe can be considerably reduced. As a result, the HIC resistance and SSCC resistance are improved.

The temperature range below the melting temperature differs depending on the energy intensity of the laser beam and cannot be determined unconditionally, but is, for example, the range from (melting temperature −800) ° C. to less than the melting temperature.

As the type of laser, there are a carbon dioxide gas laser, a YAG laser, and an excimer laser. When irradiated with a laser beam, a strong upset is no longer necessary because the joint becomes in a molten state, and the amount of upset is weakened to partially generate the melt-solidified structure, so that the texture unique to the welded part is not generated, It is possible to improve the mechanical properties of the welded part and the HIC resistance and SSCC resistance.

Further, the metal flow rising angle is an index of the texture of the welded portion, but if this angle exceeds 45 °, the SSCC resistance of the welded portion is significantly deteriorated.
It is desirable that the temperature be below °.

Therefore, in the present invention, a steel strip having the above-described composition, such as a hot-rolled steel sheet, is first subjected to high-frequency resistance heating or high-frequency induction to obtain a predetermined temperature below the melting temperature in conventional electric resistance welded pipe manufacturing equipment. A pipe forming method is adopted in which the laser beam is irradiated immediately before squeezing with a squeeze roll after heating to a temperature range, and the squeeze roll is used to slightly upset and weld.

[0042]

The equipment for carrying out the pipe making method of the present invention is shown in FIG. A steel strip is formed into an open pipe 1 with a multi-stage roll forming roll (not shown), and the contact tip 2 is energized to the edge portion of the open pipe 1 to preheat it in advance. After that, the laser beam 3 heats the edge to the melting temperature,
Lightly upset with squeeze roll 5 and weld.

If necessary, post-annealing is performed by the high frequency heating device (1) 6 in order to reduce the hardness of the welded portion. When quenching and tempering, the tube is quenched in a water cooling zone and tempered by the high frequency heating device (2) 6.

[0045]

[Example] A steel pipe was manufactured in a factory. Steel having the composition shown in Table 1 is melted in a converter, degassed, continuously cast,
A hot-rolled steel strip was obtained through processes such as hot-rolling. This steel strip is continuously formed into an open pipe with multi-stage forming rolls, the opposite edges of the open pipe are electrically heated, and the steel is melted by laser irradiation, and upset is performed to perform electric welding. And The outline of the manufacturing apparatus is as shown in FIG.

The welding conditions were such that the welding speed was 10 m / min, the high frequency power from the contact tip was 800 kw, and the upset amount was changed in the range of 0 to 5 mm. The output of the carbon dioxide gas laser was 10 kW, the beam diameter at the focal position was 0.5 mm, and the beam was irradiated from vertically above the steel sheet while focusing on the abutting point of the edge.

The outer diameter of each of the steel pipes is 609.6.
mmφ and wall thickness 11.1 mm. Steel Nos. 11 to 17 are all steels having compositions within the scope of the present invention, have low P and S, contain Ca, and contain other components within the scope of the present invention. The test results of these ERW pipes are shown in Tables 2-3.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

[Table 3]

A HIC test was conducted on the welded portion and the base material. The tests were basically based on NACETM 0284-87, but only the test solution was changed. Specimen size is 10 × 20 × 100mm, sampled in the welding length direction,
The entire surface was wet-polished to # 320.

The test solution is 5% NaCl + 0.5% CH ₃ C
A solution of saturated hydrogen sulfide at 1 atm in OOH aqueous solution,
The test piece was immersed for 96 hours while maintaining the temperature at 25 ° C. After that, the test piece was divided into four equal parts in the lengthwise direction, the cracks in the three cross sections were observed, and the crack susceptibility (CSR) was evaluated.

The SSCC test is performed by NACE TM01.
A 77-90 Method A tensile type test was employed. The test piece was a round bar tensile test piece taken at a right angle to the welding direction. The parallel part diameter was 3.81 mm and the parallel part length was 25 mm.
The parallel part was wet-polished to # 600.

A constant stress is applied to this test piece in the same test solution as in the HIC test, and the level of the stress is changed to the minimum stress (σth) at which cracking does not occur during the test time of 720 hours.
I asked. The SSCC resistance was evaluated by the ratio (σth / σys) of this stress to the yield stress (σys) obtained by a tensile test in the atmosphere.

The test piece is sampled in the direction perpendicular to the rolling direction and the welding direction. The sampling position is the center of the wall thickness. In the table, an example of pipe making without laser irradiation is also shown as a comparative example.

As is clear from the table, when welding is performed by laser irradiation, excellent HIC resistance and S resistance are obtained.
It has SCC property. Further, when the rising angle is 45 ° C. or less, the CSR value is 1.0% or less, which shows excellent characteristics.

The steels shown in Table 4 are examples whose compositions are outside the scope of the present invention. These steels were also pipe-formed similarly to the steels in Table 1 and their characteristics were investigated. However, the manufacturing conditions are
Laser irradiation is applied to both, and the upset amount is 2.0 m.
m, the rising angle of the metal flow is about 45 ° C.

The results are shown in Table 5. Steel 21 with high P and S
High steel 22 and steel 23 not containing Ca are HI resistant.
C property and SSCC resistance are inferior. Steel with high Ca 2
4, steel 25 with high C and steel 26 with high Si are HIC resistant,
And, although the SSCC resistance is sufficient, minute cracks occurred during electric resistance welding. Further, the absorbed energy in the impact test at 0 ° C. in which the notch is formed in the welded portion (depot portion) is steel 32,
The steels other than the steel 33 were all 100 J or more, whereas the steels 32 and 33 were less than 100 J.

Although the steel 28 having a high Cu content has a sufficient HIC resistance and SSCC resistance of the product, a large amount of ear cracking occurred during the production of the steel strip by hot rolling, and it took time to remove it. Steel 29 containing a large amount of Ni has poor SSCC resistance. C
Steel 30 having a high r has low weldability, and microrack occurred in the electric resistance welded portion. Steel 31 having a high Mo content is steel 29 having a high Mo content.
Similarly, the SSCC resistance was poor.

The steel 32 having a high Al and Ti and the steel 33 having a high Nb and V all have poor toughness, and like the steel 26, the absorbed energy in the impact test at 0 ° C. with a notch in the weld is less than 100 J. Met.

[0061]

[Table 4]

[0062]

[Table 5]

[0063]

The electric resistance welded pipe according to the present invention is resistant to HIC and SSC in a wet hydrogen sulfide environment in both the base material and the weld.
It is an electric resistance welded tube with excellent C characteristics. Further, the electric resistance welded tube manufactured by the method according to the present invention is particularly excellent in HIC resistance and SSCC resistance.

[Brief description of drawings]

FIG. 1 is a photograph replacing a figure showing a macroscopic metallographic structure of a welded portion of a conventional electric resistance welded pipe and a welded portion of the electric resistance welded pipe according to the method of the present invention.

FIG. 2 is a schematic diagram of equipment for carrying out the method of the present invention.

[Explanation of symbols]

 1 Open Pipe 2 Contact Tip 3 Laser Beam 4 Top Roll 5 Squeeze Roll 6 High Frequency Heating Device (1) 7 Water Cooling Zone 8 High Frequency Heating Device (2)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication C22C 38/50 C22C 38/50 38/58 38/58 (72) Inventor Kenichi Iwasaki Chiyoda-ku, Tokyo Marunouchi 1-2, Nihon Steel Pipe Co., Ltd. (72) Inventor Masaki Omura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd. (72) Moriaki Ono, Marunouchi, Chiyoda-ku, Tokyo 1st and 2nd Nihon Steel Pipe Co., Ltd.

Claims (6)

[Claims] 1. A HIC-resistant and SS-resistant having the following characteristics:
ERW pipe with excellent CC characteristics. (A) As a main component (component composition is wt%), C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, P: 0.02% or less, S: 0. An electric resistance welded tube containing 003% or less, Al: 0.07% or less, Ca: 0.001 to 0.006%, and the balance being substantially Fe, (b) welding of the electric resistance welded tube The part has a melt-solidified structure. 2. A HIC resistant and SS resistant having the following features:
ERW pipe with excellent CC characteristics. (A) As a main component (component composition is wt%), C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, P: 0.02% or less, S: 0. 003% or less, Al: 0.07% or less, Ca: 0.001 to 0.006% contained, and further Nb: 0.1% or less, Cu: 0.5% or less, Ni: 0.5% or less, E-sewn containing one or more components of Mo: 0.5% or less, Cr: 1% or less, V: 0.1% or less, Ti: 0.1% or less, and the balance being substantially Fe. (B) The welded portion of the electric resistance welded pipe has a melt-solidified structure. 3. The electric resistance welded pipe excellent in HIC resistance and SSCC resistance according to claim 1 or 2, wherein the rising angle of the metal flow in the vicinity of the welded portion of the electric resistance welded pipe is 45 ° or less. 4. A method for manufacturing an electric resistance welded pipe having excellent HIC resistance and SSCC resistance, which comprises the following steps. (A) As a main component (component composition is wt%), C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, P: 0.02% or less, S: 0. A step of preparing a steel strip containing 003% or less, Al: 0.07% or less, Ca: 0.001 to 0.006%, and the balance being substantially Fe.
(B) a step of continuously forming the steel strip into an open pipe with a multi-stage forming roll, and (c) a step of heating both opposing edge portions of the open pipe to a temperature range equal to or lower than the melting temperature of the steel strip. And (d) a step of irradiating the heated both edge portions with a laser beam to bring them into a molten state and controlling the amount of upset with a squeeze roll to perform welding. 5. A method of manufacturing an electric resistance welded pipe having excellent HIC resistance and SSCC resistance, which comprises the following steps. (A) As a main component (component composition is wt%), C: 0.2% or less, Si: 0.5% or less, Mn: 2% or less, P: 0.02% or less, S: 0. 003% or less, Al: 0.07% or less, Ca: 0.001 to 0.006% contained, and further Nb: 0.1% or less, Cu: 0.5% or less, Ni: 0.5% or less, Steel strip containing one or more components of Mo: 0.5% or less, Cr: 1% or less, V: 0.1% or less, Ti: 0.1% or less, and the balance being substantially Fe. And the step of preparing
(B) a step of continuously forming the steel strip into an open pipe with a multi-stage forming roll, and (c) a step of heating both opposing edge portions of the open pipe to a temperature range equal to or lower than the melting temperature of the steel strip. And (d) a step of irradiating the heated both edge portions with a laser beam to bring them into a molten state and controlling the amount of upset with a squeeze roll to perform welding. 6. The amount of upset by the squeeze roll is controlled so that the metal flow rising angle near the welded portion of the electric resistance welded pipe is 45 ° or less.
Alternatively, the method for producing an electric resistance welded pipe having excellent HIC resistance and SSCC resistance as described in 5 above.