JPH04268019A - Production of martensitic stainless steel line pipe - Google Patents

Abstract

PURPOSE:To produce a line pipe having high corrosion resistance to wet CO2 and wet H2S and superior impact toughness of the weld heat-affected zone. CONSTITUTION:A steel pipe is made of steel consisting of reduced amts. of C and N, <=1% Si, <=2% Mn, 11-14% Cr, 1.1-4.0% Co, 0.005-0.2% Al and the balance Fe with inevitable impurities or further contg. reduced amts. of P and S or Ni, Cu, Mo, W, V, Ti, Nb, Ta, Zr, Hf, Ca and REM added as required. The structure of the steel is then austenitized at 920-1,100 deg.C and the pipe is cooled at the water cooling rate or above, tempered at a temp. between 580 deg.C and the Ac1 point and cooled at the air cooling rate or above.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing a martensitic stainless steel line pipe with excellent weldability.
In more detail, for example, it has high corrosion resistance in environments containing wet carbon dioxide gas and wet hydrogen sulfide during the transportation of oil and natural gas, and has excellent impact toughness of the weld heat affected zone and reduces the hardness of the weld heat affected zone. This invention relates to a method for manufacturing line pipes with high productivity.

0002

[Prior Art] Oil and natural gas produced in recent years include
Cases containing a large amount of wet carbon dioxide gas are increasing. It is well known that carbon steel and low alloy steel corrode significantly in such environments. For this reason, corrosion inhibitors have traditionally been added as a corrosion prevention measure for line pipes used for transportation. However, corrosion inhibitors often lose their effectiveness at high temperatures, and in addition to the fact that the cost of adding and recovering corrosion inhibitors is enormous, they are often not applicable to submarine pipelines. Therefore, the need for corrosion-resistant materials that do not require the addition of corrosion inhibitors has recently increased. In addition to corrosion resistance, materials used for line pipes are required to have high strength to withstand the pressure of the transport fluid flowing inside them, and to have excellent weldability. As a typical characteristic of weldability, it is necessary that the welded part has excellent impact toughness. Furthermore, when transporting a fluid containing hydrogen sulfide, it is also required that the hardness of the welded part be low. Of course, it is also necessary that the base material has excellent impact toughness.

[0003] As a corrosion-resistant material for petroleum and natural gas containing a large amount of carbon dioxide, the use of stainless steel, which has good corrosion resistance, was first considered. For example, L. J. Klein, Corrosion '84, Paper No. 2
11, oil country tubular goods without a welded structure contain 0.1 or 0.2% C, such as AISI (American Iron and Steel Institute) 410 steel or 420 steel, which are high-strength and relatively low-cost steels. , martensitic stainless steels containing 12-13% Cr are beginning to be widely used. However, since these steels have a high C content,
It is difficult to use it as a line pipe because the welded part becomes very hard and the impact toughness of the welded part is poor. Line pipes using AISI410 steel have recently received an A.
Although it has been standardized by PI (American Petroleum Institute), for example, Masataka Suga et al., NKK Technical Report, published in 1989, Vol.
As stated in No. 29, pages 15 to 22, the problem is that the impact toughness of the on-site welded part is poor. This is because, as reported by them, the weld heat affected zone becomes a coarse ferrite-based structure.

[0004] When conventional martensitic stainless steel pipes are heat treated after pipe making, cooling during quenching is usually done by air cooling. This is because cooling at a faster cooling rate than air cooling, for example water cooling, will cause quenching cracks, so cooling must be done slowly at a cooling rate that does not cause quenching cracks. If air cooling is used for cooling during quenching, it takes a long time to cool down to room temperature, so it also has the disadvantage that productivity is significantly lower than, for example, water cooling. Therefore, it would be of great significance in terms of productivity if it could be produced by water cooling during quenching.

[0005] As a steel for line pipes, JP-A-61-
In Japanese Patent No. 119654, C and N are reduced, and A
1 or Ca and V, and Ni and M
Steel containing o has been proposed. However, since this steel contains a large amount of Ni, which is an expensive alloying element, it is expensive and its properties are not satisfactory.

[0006]

[Problems to be Solved by the Invention] In view of the current situation, the present invention provides a martensitic stainless steel that has sufficient corrosion resistance even in a carbon dioxide environment, has excellent impact toughness and weldability of the base material, and has excellent productivity. The purpose is to provide a method for manufacturing line pipes.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present inventor has conducted various studies on the components and heat treatment conditions of martensitic stainless steel line pipes, and has finally found the following knowledge. . First, Cr is 11 to 1
After reducing the C content of steel containing 4% to less than 0.02% and reducing N to 0.015% or less, a cooling rate faster than water cooling during quenching after forming the steel into a steel pipe. If the quenching and tempering conditions are appropriately selected, the strength and toughness required for line pipes can be obtained, and if C and N are reduced as described above, cooling can be achieved at a faster cooling rate than water cooling. We found that reducing C and N significantly reduces the hardness of the weld heat-affected zone and significantly improves corrosion resistance in carbon dioxide-containing brine. I found it. And 1.1 to 4.0% Co is added to such steel.
It has been found that by adding it, the microstructure of the base metal and the weld zone can be substantially made into a single martensite phase without significantly increasing the hardness of the weld zone, and the impact toughness of the base metal and the weld zone can be improved.

Further, the inventor of the present invention further investigated the composition of a line pipe made of martensitic stainless steel to be heat treated as described above, containing 11 to 14% Cr, reducing C and N, and reducing Co to 1. . Adding either Ni or Cu or both to steel containing 1 to 4.0% is effective in further improving the impact toughness of the weld heat affected zone, and adding Mo or W or both. The addition of one or more of V, Ti, Nb, Ta, Zr, and Hf is effective in further improving corrosion resistance. Ca and rare earth elements Adding one or more of the elements is effective in improving hot workability and corrosion resistance;
It has been found that even when these elements are added, if C and N are controlled within the above ranges, quench cracking will not occur even if rapid cooling such as water cooling is applied during quenching.

The present invention has been made based on the above findings, and the gist of the first invention is that in weight %,
Reduce C to less than 0.02%, Cr11-14%, Co
1.1 to 4.0%, Si 1% or less, Mn 2% or less, Al
After producing a steel pipe from a martensitic stainless steel containing 0.005 to 0.2%, reducing N to 0.015% or less, and the remainder consisting of Fe and unavoidable impurities, 9
A martensitic system characterized by austenitizing at 20 to 1100°C, then cooling at a cooling rate higher than water cooling, then tempering at a temperature of 580°C or higher and lower than AC1 temperature, and then cooling at a cooling rate higher than air cooling. The gist of the second invention lies in a method for manufacturing a stainless steel line pipe, in which one or two of Ni 4% or less and Cu 3% or less are further added to the steel covered by the first invention.
The gist of the third invention lies in a method for manufacturing a martensitic stainless steel line pipe using steel containing seeds, and the gist of the third invention is that the steel covered by the first and second inventions is further supplemented with A method for manufacturing a martensitic stainless steel line pipe using steel containing one or two of Mo2% or less and W4% or less,
The gist of the invention is that V0.
5% or less, Ti 0.2% or less, Nb 0.5% or less, Ta
A method for manufacturing a martensitic stainless steel line pipe using steel containing one or more of 0.2% or less, Zr 0.2% or less, and Hf 0.2% or less, The gist is that each steel targeted by the first, second, third, and fourth inventions further contains Ca0.008% or less and rare earth elements 0.0% by weight.
The present invention provides a method for manufacturing a martensitic stainless steel line pipe using steel containing one or two of the above 2% or less.

[0010] The gist of each of the sixth to tenth inventions is that in each of the first to fifth inventions, the method for manufacturing a steel pipe is a press pipe manufacturing method,
The present invention relates to a method of manufacturing a martensitic stainless steel line pipe, which is a hot rolling method, a method of manufacturing a UOE steel pipe, an electric resistance welded steel pipe, and a spiral steel pipe.

[0011]

[Operation] The reason why the ingredients and heat treatment conditions are limited in the present invention will be described below. C: When present in a large amount, C reduces corrosion resistance in a wet carbon dioxide environment and increases the hardness of the weld heat affected zone. If the amount of C is less than 0.02%, the effect of improving corrosion resistance and the effect of reducing the hardness of the weld heat affected zone is particularly significant, so the amount of C is limited to less than 0.02%.

Si: Si is an element necessary for deoxidation, but if added in an amount exceeding 1%, the toughness will be significantly reduced, so the upper limit content is set at 1%. Mn: Mn is an effective element for deoxidizing and ensuring strength, but its effect is saturated when added in excess of 2%, so the upper limit content is set to 2%. Cr: Cr is the most basic and essential element constituting martensitic stainless steel and is necessary to impart corrosion resistance, but the content is 11%.
If it is less than 14%, the corrosion resistance will not be sufficient, and on the other hand, if it is added in excess of 14%, no matter how you adjust the other alloying elements, it will be difficult to form a single austenite phase when heated to high temperatures, making it difficult to maintain strength. It should be 14%.

Co: Co improves the impact toughness of not only the base metal of steel with reduced C and N content but also the microstructure of the weld heat-affected zone by forming a martensitic structure, and also improves the corrosion resistance in a humid carbon dioxide environment. Although it is an extremely useful element for improving health, if the content is less than 1.1%, these effects are insufficient, and if it is added in excess of 4.0%, the effect will not only be saturated, but also be harmful. Since this only increases the cost, it is limited to a range of 1.1 to 4.0%.

Al: Al is a necessary element for deoxidation, and if the content is less than 0.005%, the effect is not sufficient, and if it is added in excess of 0.2%, coarse oxide inclusions are formed. Since C remains in the steel and reduces cracking resistance in hydrogen sulfide, the content range is set to 0.005 to 0.2%. N
: If N exceeds 0.015%, it increases the hardness of the weld heat affected zone and reduces the impact toughness of the base metal and the weld heat affected zone, so the upper limit content should be 0.015%. be.

[0015] The above are the basic components of martensitic stainless steel, which is the material for the line pipe targeted by the present invention, but in the present invention, the following elements are further added as necessary to further improve the characteristics. It also targets steel that has been Ni: Ni coexists with 1.1 to 4.0% Co and is effective in further improving the impact toughness of the weld heat affected zone, but the effect is saturated when added in excess of 4%. Moreover, the upper limit content is 4% because it only unnecessarily increases costs and increases the hardness of the weld heat affected zone.
shall be.

Cu: Cu also coexists with 1.1 to 4.0% Co and is effective in further improving the impact toughness of the weld heat affected zone, but even if it is added in excess of 3%, the effect is not only saturates, but also reduces hot workability.
The upper limit content is 3%. Mo: Mo is 1.1 to 4.0
% of Co, it is effective in improving corrosion resistance in a humid carbon dioxide environment, but if it is added in excess of 2%, the effect not only becomes saturated, but also decreases other properties such as toughness. Therefore, the upper limit content is set to 2%.

W: W also coexists with 1.1 to 4.0% Co and is effective in improving corrosion resistance in a wet carbon dioxide environment, but the effect is saturated even when added in excess of 4%. In addition, the upper limit of the content is set at 4%, as it also reduces other properties such as toughness. V, Ti, Nb, Ta, Zr,
Hf: V, Ti, Nb, Ta, Zr, and Hf are effective elements for further improving corrosion resistance, but Ti, Zr,
If Ta and Hf are added in excess of 0.2%, and V and Nb are added in excess of 0.5%, coarse precipitates and inclusions will be generated and the SSC resistance will decrease in an environment containing hydrogen sulfide, so the upper limit must be set. The content was 0.2% for Ti, Zr, Ta, and Hf, and 0.5% for V and Nb.

Ca and rare earth elements: Ca and rare earth elements (REM) are elements that are effective in improving hot workability and corrosion resistance. If more than 0.02% of Ca is added, coarse nonmetallic inclusions will be generated and the hot workability and corrosion resistance will be deteriorated, so the upper limit content is 0.00% for Ca.
8%, and 0.02% for rare earth elements. In the present invention, the rare earth elements refer to elements having atomic numbers of 57 to 71 and 89 to 103, and Y.

[0019] The austenitization temperature was set at 920 to 1100°C when the stainless steel having the above components was made into a steel pipe and then heat treated to give it a predetermined strength. This is because it is difficult to obtain the necessary strength, and if the austenitizing temperature exceeds 1100°C, the crystal grains will become coarse and the impact toughness of the base material will decrease, so the austenitizing temperature is 920°C. ~1100℃
And so.

[0020] The reason why the cooling rate for cooling after austenitization was set to be faster than water cooling is because if the cooling rate is slower than water cooling, it becomes difficult to secure the specified strength and toughness, and the corrosion resistance decreases. . The reason why the tempering temperature is set to 580°C or higher and lower than AC1 temperature is because if the tempering temperature is lower than 580°C, sufficient tempering will not occur, and if the tempering temperature exceeds AC1 temperature, part of the tempering temperature will become austenite and fresh martensite will be formed during subsequent cooling. This is because martensite that is generated and not sufficiently tempered remains, resulting in a decrease in impact toughness and an increase in SSC susceptibility in an environment containing hydrogen sulfide.

The reason why the cooling rate in cooling after tempering is set to be higher than air cooling is because toughness decreases if the cooling rate is slower than air cooling. In the steel of the present invention, a martensitic stainless steel having a predetermined composition is made into a steel pipe, and the pipe making method is to use a press pipe manufacturing method or a hot rolling method to make a seamless steel pipe. , welded steel pipes such as UOE steel pipes, electric resistance welded steel pipes, or spiral steel pipes are all subject to the present invention. Here, the press tube manufacturing method refers to a normal press tube manufacturing method such as a hot extrusion method or a push bench method. The hot rolling method refers to a normal hot rolling method such as a plug mill method or a mandrel mill method. UOE steel pipe, ERW steel pipe or spiral steel pipe refer to ordinary UOE steel pipe, ERW steel pipe or spiral steel pipe, respectively.

[0022]

[Examples] Examples of the present invention will be described below. Stainless steel with the components shown in Tables 1 and 3 was melted and made into steel pipes with a wall thickness of 12.7 mm through the steps shown in Tables 2 and 4, respectively, and then quenched and tempered under the conditions shown in the same table. Both have a 0.2% offset yield strength of 42kg/mm2.
The above high strength martensitic stainless steel pipes were used. All cooling during quenching was water cooling, and cooling during tempering was all air cooling. Next, these steel pipes were circumferentially welded by manual welding to produce a joint. Welding heat input is 17kJ/
It was cm. JIS No. 4 impact test pieces (full size) were taken from the base metal and the weld heat affected zone of the circumferential weld and an impact test was conducted. In addition, the maximum hardness of the weld heat affected zone is determined by a load of 1
It was determined by micro-Vickers measurement of 00 g. In addition, test pieces were taken from the base metal and subjected to corrosion tests in a humid carbon dioxide environment. For the corrosion test in a humid carbon dioxide environment, a test piece with a thickness of 3 mm, a width of 13 mm, and a length of 50 mm was used, and the specimen was placed in a 5% NaCl aqueous solution at a carbon dioxide partial pressure of 40 atm for 30 days in an autoclave at a test temperature of 150°C. The corrosion rate was calculated from the weight change before and after the test. The unit of corrosion rate is mm/y, but it is generally considered that if the corrosion rate of a material in a certain environment is less than 0.1 mm/y, the material is sufficiently corrosion resistant and can be used. .

The test results are also shown in Tables 2 and 4. In the impact test results in both tables, ○ indicates that the fracture surface transition temperature is -30℃
Hereinafter, × means that the fracture surface transition temperature exceeds -30°C and falls below 0°C, ×
× indicates that the fracture surface transition temperature was over 0°C, ○ indicates that the maximum hardness of the weld heat affected zone is less than 300, × indicates that the maximum hardness is 300 or more and less than 450,
XX indicates that the maximum hardness was 450 or higher, and in the corrosion test results, ◎ indicates that the corrosion rate was 0.
Less than 0.05 mm/y, ○ indicates corrosion rate of 0.05 mm/y or more and less than 0.10 mm/y, × indicates corrosion rate of 0.1 mm/y.
y or more and less than 0.5mm/y, XX indicates corrosion rate of 0.5m
Each represents that it was equal to or higher than m/y. In addition, in Tables 1 to 4, comparative steel No. 25 is AISI420
Steel, No. No. 26 is a 9Cr-1Mo steel, and all of them are conventional steels that have been conventionally used in a humid carbon dioxide environment.

As is clear from Tables 1 to 4, line pipe No. 1 manufactured according to the method of the present invention. Nos. 1 to 24 have significantly superior impact toughness of the base metal and weld heat affected zone, and the hardness of the weld heat affected zone is sufficiently low, even at extremely high temperatures of 150°C for a line pipe in a humid carbon dioxide environment. , 0.1 mm, which is a practically usable corrosion rate.
It can be seen that the corrosion rate is lower than that of /y, and that it has excellent corrosion resistance and weldability. Furthermore, all line pipes manufactured according to the method of the present invention can be water-cooled during quenching, and have excellent productivity. On the other hand, the comparative example No. 25-27 and No. In No. 29, quench cracking occurred during quenching by water cooling. Furthermore, Comparative Example No. 1 did not cause any quench cracking during quenching. 28 and no. Among 30, comparative example No. 28 has a corrosion rate of 0.1 mm in a wet carbon dioxide environment even at a temperature of 150°C.
/y, and Comparative Example No. 28 and no.
．． Both 30 and 30 had poor impact toughness of the base metal and weld heat affected zone.
Also, the hardness of the weld heat affected zone is high.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

[Table 4]

[0029]

[Effects of the Invention] As described above, the present invention provides a method for manufacturing a martensitic stainless steel line pipe that has excellent corrosion resistance and weldability in a humid carbon dioxide environment, and also has excellent productivity. This has made it possible to do so, and it has made an extremely large contribution to the development of industry.

Claims (10)

[Claims] Claim 1: In weight percent, C is reduced to less than 0.02%, Si is 1% or less, Mn is 2% or less, Cr is 11-14%, Co is 1.1-4.0%, Al is 0.005-0.2%. , N is reduced to 0.015% or less, the balance is Fe and unavoidable impurities, and the martensitic stainless steel is made into a steel pipe, and then it is austenitized at 920 to 1100°C, and then the cooling rate is faster than water cooling. Cool with
A method for producing a martensitic stainless steel line pipe, the method comprising: then performing a tempering treatment at a temperature of 580°C or higher and lower than AC1 temperature, and then cooling at a cooling rate higher than or equal to air cooling. 2. The martensitic stainless steel according to claim 1, wherein the martensitic stainless steel further contains one or two of Ni 4% or less and Cu 3% or less as additional components. Method of manufacturing stainless steel line pipe. 3. The martensitic stainless steel according to claim 1 or 2, wherein the martensitic stainless steel further contains one or two of Mo2% or less and W4% or less as additional components. Method for manufacturing site-based stainless steel line pipe. 4. The martensitic stainless steel further contains, in weight percent, the following additional components: V 0.5% or less, Ti 0.2% or less, Nb 0.5% or less, Zr 0.2% or less, Ta 0.2% or less, Hf0 4. The method for manufacturing a martensitic stainless steel line pipe according to claim 1, 2 or 3, wherein the martensitic stainless steel line pipe contains one or more of .2% or less. 5. Claim 1, wherein the martensitic stainless steel further contains one or two of Ca 0.008% or less and rare earth elements 0.02% or less as additional components. The method for manufacturing a martensitic stainless steel line pipe according to , 2, 3 or 4. 6. The method for manufacturing a martensitic stainless steel line pipe according to claim 1, wherein the method for manufacturing the steel pipe is a press pipe manufacturing method. 7. The method for manufacturing a martensitic stainless steel line pipe according to claim 1, wherein the method for forming the steel pipe is a hot rolling method. 8. The martensitic stainless steel according to claim 1, 2, 3, 4, or 5, wherein the method for producing a steel pipe is to produce a martensitic stainless steel plate and then produce a UOE steel pipe. Method of manufacturing stainless steel line pipe. 9. The martensitic method according to claim 1, 2, 3, 4, or 5, wherein the method for producing a steel pipe comprises producing a martensitic stainless steel plate and then producing an electric resistance welded steel pipe. A method for manufacturing stainless steel line pipes. 10. The method of forming a steel pipe is characterized in that a martensitic stainless steel plate is manufactured and then a spiral steel pipe is formed.
5. The method for manufacturing a martensitic stainless steel line pipe according to 4 or 5.