JPS58133350A - Steel for oil well excellent in sulfide stress corrosion crack resistance - Google Patents

Abstract

PURPOSE:To provide steel for an oil well having high yield strength and excellent SSCC resistance, containing C, Si, Mn, Cr, Co, sol. Al as main components respectively in a predetermined ratio and having an annealed martensite structure mainly. CONSTITUTION:Steel for an oil well excellent in sulfide stress corrosion resistance contains, on the basis of wt%, 0.15-0.50%C, 0.1-1.0% Si, 0.3-1.5% Mn, 0.6-2.0% Cr, 0.3- 5.0% Co and 0.001-0.10% sol. Al and comprises the remainder Fe and inevitable impurities. In the contents of each components as the aforementioned ineveitable impurities, P is limitted to 0.025% or less, S to 0.010% or less, Mo to 0.05% or less and W to 0.05% or less. In addition, this steel has an annealed martensite structure mainly. This steel has high yield strength of 70kg/mm.<2> or more and excellent sulfide stress corrosion crack resistance and especially suitable for steel used in an oil well or a gas well and a mateial used in preparing various valves.

Description

Detailed Description of the Invention This invention combines high strength with a yield strength of 9/- or more in '70 and excellent sulfide stress corrosion cracking resistance (hereinafter referred to as 5SCC resistance), and is particularly suitable for use in oil wells and gas wells. Steel pipes used in oil wells, such as drill pipes for drilling, tubing and cages for production, as well as sucker rods and pulp products used in oil and gas wells. It is related to.

In recent years, oil and gas fields have been actively developed in order to cope with the deteriorating energy situation. There is a strong need to develop oil and gas fields in the region. However, as the depth of the well increases, the pressure from the crude oil and gas produced, the earth pressure from the geological formations, and the tensile load due to the weight of the steel used also increase, so these sour environments The development of deep oil and gas fields requires steel that has both high strength to withstand these forces and excellent 5SCC resistance.
It is said that it is necessary to use steel that has a yield strength of 1 kg/- or more and a "cracking limit ratio" of 70 to 75% or more for 5SCC resistance.

The "cracking limit ratio" referred to here means that sulfide stress corrosion cracking (hereinafter referred to as 5scc) occurs when stress exceeding a certain value acts on steel materials used in a humid sour environment containing hydrogen sulfide, etc. Since this is a type of environmental embrittlement phenomenon that occurs in
Since the critical stress for SCC generation on this day depends on the strength of the steel material, the ratio of the yield strength to the critical stress for 5scc generation, that is, (ss
cc generation limit stress)/(yield strength) X 100(1)
This is the one obtained by using this "cracking limit ratio".
This is to evaluate scc property. 5 - The higher the cracking limit ratio, the better the 5SCC resistance of the steel material. For example, if the cracking limit ratio is close to 10096, that is, if the 5SCG generation limit stress is close to the yield strength of the steel material, 5 seconds when using the steel material
There is no need to consider cc, but if the cracking limit ratio is small, high stress cannot be applied to the steel material due to the 5scc problem, and even if the steel material has high strength, the 5scc
This means that it can only be used below the scc critical stress. What value is required as the cracking limit ratio that shows satisfactory 5scc resistance depends on how the safety factor is taken in steel material design, but it cannot be said unconditionally, but it is generally 70 to 75.
It is said that a cracking limit ratio of % or more is required.

On the other hand, various types of oil well steels have been proposed that have a yield strength of 'i'okg/- or more, but as the strength of the steel increases, 5scc is more likely to occur. Coupled with this fact, the current situation is that all of these conventional high-strength oil well steels have a cracking limit ratio of less than 70 inches.

-6-. From the above-mentioned viewpoints, the present inventors aimed to obtain oil well steel having high strength and excellent 5scc resistance required for the development of deep oil and gas fields in sour environments. As a result of research, it was found that C:O, 15 to 0.50% by weight,
Si: Q, 1~1.0t Blood: 0, "~""t
sr Cr: 0.6-2.0% HCo: 0.
3-5.0%, BOI, AI: 0.001-0
．． 1096, and further contains Cu: 0.
1-1.0%, Ni: 0.1-1.0qb, Nt
): 0.01-0.15 L V : α01-0.
50%, Zr: 0.01-0.50%, Ti: 0.
001-0.10chi, and B: 0.0003-0.0
The content of P, 'S, Mo, and W as inevitable impurities is P:
0.025% or less, 8:0,010% or less2MO20.
Steel having a composition of 0.05% or less, W: 0.05% or less, and a structure mainly composed of tempered martensite has a yield strength of 70 kg / d or more and a W: 0.05% or less.
This invention, which has the above cracking limit ratio and is therefore extremely excellent when used for oil wells, was made based on the above knowledge, and the reason for limiting the composition range as above is as follows. Explain.

(a) C The C component has the effect of increasing the strength of steel and improving hardenability and tempering resistance, but when its content is 0.1
If it is less than 5%, the desired effect for forest use cannot be obtained;
．． If the content exceeds 50%, quench cracking will increase and toughness will deteriorate, so the content should be reduced to 0.
．． It was set at 15% to 0.50%.

(b) 5i Sl component has a deoxidizing effect and also has the effect of improving the strength and hardenability of steel, but its content is 0.1%.
If it is less than 1.0, the desired effect cannot be obtained;
If the content exceeds 0.1 to 1.5 mm, the crystal grains will become coarse and the toughness will deteriorate.
It was set as 0%.

(c) Mn The Mn component has a deoxidation and oxidation effect similar to Sl, and also has the effect of improving the strength and toughness of steel, but if its content is less than 0.3%, the desired effect is not achieved. On the other hand, if the content exceeds 1.5%, 5scc resistance,
In other words, since the cracking limit ratio and toughness may deteriorate, the content was determined to be 0.3 to 1.5 yen.

(d) Cr The Cr component has the effect of improving the strength and tempering resistance of steel, but if its content is less than 0.6%, the desired effect cannot be obtained; If the content exceeds 0.6% to 2.0%, the toughness deteriorates, so the content was set at 0.6% to 2.0%.

(e) C.

5SCC is a type of hydrogen embrittlement that occurs when hydrogen generated by a corrosion reaction on the steel surface penetrates into the steel. Therefore, 5SCC
Suppression of hydrogen intrusion is considered to be an effective means of preventing c. The GoC component has the effect of suppressing hydrogen intrusion in a sour environment 9-, so the inclusion of Co is essential to ensure excellent 5scc resistance (cracking limit ratio). However, if the CO content is less than 0.3%, the desired 5scc resistance cannot be obtained, so it is necessary to contain 0.3% or more.
Even if the content exceeds 5.0%, no further improvement effect will be obtained, and in consideration of economic efficiency, the content was set at 0.3 to 5.0%.

(f) Sot, 1 dl eot, AL acid component has a deoxidizing effect and a grain refining effect, but if its content is less than O,0014, the desired effect cannot be obtained; on the other hand, at 0.10% If the content exceeds 0.001 to 0.10, the amount of nonmetallic inclusions increases and the steel becomes brittle, so the content was set at 0.001 to 0.10.

(r) Cu The Cu component has 5SC resistance provided by the CO acid component.
Since it has the effect of enhancing the effect of improving C properties (cracking limit ratio), it is included as necessary when even higher 5scc resistance is required, but if the content is less than 0.1%, the desired The effect of improving B'B CC resistance cannot be obtained, and on the other hand, even if it is contained in an amount exceeding 1.0%, no further improvement effect will be obtained, but rather it may cause deterioration of workability. , its content was determined to be 0.1 to 1.0.

(h) Ni, Nb, V, Zr, Ti, and B These components have a uniform effect of improving the strength of steel, so they can be added as necessary when even higher strength is required. However, the content is different from Ni
:Q, less than 1%, Nb: less than 0.01 m, V:
o, o less than 1%, Zr: less than 0,01%, T1: α
If Ni: less than 0.001% and B:O,0O003%, the desired strength improvement effect cannot be obtained, while Ni: 1.0%.
%t Nb'0.15+%, V: 0.50%, Zr
: 0.50%r 71:0.10chi, and B
If the S content exceeds 0.0050%, the toughness will deteriorate, so the content is changed to Ni:Q, 1 to 1.0%, tNb: 0.01 to 0.0%, respectively.
15qb, ■20, 01~0.50ts.

Zr: 0.01-0.50%, Ti:, 0.0
01~0.10chi.

B: It was determined to be 0.0003 to 0.0050.

(1) Unavoidable impurities P, S, Mo, and W as unavoidable impurities are P: 0.025, S: O, OIO, Mo: 0.0, respectively.
5%, W: If the content exceeds 0.05%, the 5SCC resistance of the steel will deteriorate significantly, so the content should be reduced to P: 0.025% or less, S2O, 0L, respectively.
O1 or less + MO: 0.05 inches or less, W: 0.
Must be 0.05 inches or less. In particular, P not only segregates at grain boundaries and promotes grain boundary cracking (but also segregates when coexisting with Mn, etc., and has the effect of deteriorating the 5SCC resistance of the segregated portion, so In order to ensure 5SCC resistance, the content is preferably 0.005% or less.

Furthermore, since S also has the effect of increasing sulfide-based inclusions and deteriorating 5SCC resistance, the S content is preferably 0.002% or less in order to ensure better 5SCC resistance.

Next, the steel for oil wells of the present invention will be explained using examples and comparing with comparative examples.

Inventive Steels 1 to 36 and Comparative Steels 1 to 10, each having the composition shown in Table 1, were melted by a normal melting method, cast under normal conditions, and then hot rolled. Thickness: 12. , and then heated to 920℃ for 30 minutes.
After holding for a minute, quenching with water cooling and 400~? A tempering treatment was performed at a predetermined temperature within the temperature range of 0°C.

In addition, Comparative Steels 1 to 10 all have compositions in which the content of any one of the constituent components (including unavoidable impurities) (marked with a square mark in Table 1) is outside the scope of the present invention. It is something that we have.

Next, the yield strengths and cracking limit ratios of the resulting steels of the present invention 1 to 36 and comparative steels 1 to 10 were measured.

The cracking limit ratio for evaluating the 5scc resistance was determined by using a 5scc testing device using the constant load method shown schematically in Fig. 1, and using a round bar tensile test piece with an outer diameter of 6.4 mm in the parallel part. 0.5% CH,C0OH-5 saturated with hydrogen sulfide
11% NaCt aqueous solution (pH: 2.8-3.6)
A constant tensile load 3 is applied to the container 2 filled with water, and the stress value that does not cause cracking within 720 hours is determined as the BBCC generation limit stress. It was determined by calculating the ratio of the stress to the previously measured yield strength, that is, (sscc generation limit stress)/(yield strength) x 100 (%). These results are shown in Table 1.

In addition, in FIG. 1, 4 is a flow meter, and 5 is a cock.

6 is a pump, and 7 is a constant temperature bath.

From the results shown in Table 1, the present invention steels 1 to 36 all exhibit a yield strength of 70 kg/- or more and a cracking limit ratio of 75 inches or more, and have high strength and excellent 5 SCC resistance. is clear. In contrast, comparative steels 1 to 10
As can be seen, it is clear that if the content of any one of the constituent components falls outside the range of the present invention, at least one of the properties of strength and cracking limit ratio becomes inferior.

As mentioned above, the steel of this invention has a yield strength near 0k19
It has high strength of /- or more and excellent 5 SCC resistance of cracking limit ratio of 75 inches or more, so it is suitable for the development of oil fields and gas fields in deep and sour environments where these characteristics are required. It exhibits extremely excellent performance when used as drill pipes for excavation, steel pipes such as tubing and casings for production, sucker rods, and various valves.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a 5scc test apparatus using the constant load method. In the drawings, l...test piece, 2...container, 3...
load. Applicant Sumitomo Metal Industries Co., Ltd. Agent Tomi 1) Kazuo 18-

Claims (1)

[Claims] ←) C: 0.15 to 0.50 yen, Si: Q, 1 to LO y. Mn: 0.3-1.5%l Cr: 0.6-2.
0%, Co: 0.3-5. O%teOl,
M: Contains 0.901 to 0.10' fly, the remainder consists of Fe and unavoidable impurities, and the content of P, S, MO, and W as unavoidable impurities is P: 0.025, respectively. % or less t”20, OIO% or less, MO
: 0.05% or less, W: 0.05% or less (weight es), and further has a structure mainly composed of tempered martensite, and has a yield strength near 0 to 9/- Steel for oil wells with high strength and excellent sulfide stress corrosion cracking resistance. (2) C: 0.15-yo, 50%, Si
: 0.1-1.0%. Mn: 0.3-1.5% + cr: 0.6
~2.0% s CO: 0.3~5.0%,
BOl, A1: Contains 0.001 to 0.10%,
Furthermore, it contains Cu: 0.1 to 1.0%, the remainder consists of Fe and unavoidable impurities, and P as unavoidable impurities,
8. The contents of Mo and W are respectively P:
0.025% or less + S: 0.010% or less, Mo: 0.
The yield strength near 0 kl?
Oil well steel with high strength of /- or more and excellent resistance to sulfide stress corrosion cracking. (3) C: 0.15-0.50%, Si:
0.1 to 1.0 chi. Mn: 0.3-1.5%, Cr: 0.6-2.0
%, Co: 0.3~5.0%+80t,
Contains A1: 0.001-0.10%, and further contains Ni: 0.1-1.01 Nb: 0.01-0.1
5%+V: 0.0-1~0.50%'*zr
: 0.01~0.50% +Ti: 0.001~
0.10chi, and B: 0.0003 to 0.00,
Contains one or more of 50% of the ingredients, and the rest is F.
e and unavoidable impurities, and the contents of P, S, Mo, and W as unavoidable impurities are set as P:0.
025chi or less +8': 0.010% or less e Mo; o
, o 5% or less, w: o, o 5% or less (weight%) 1, and further characterized by having a structure mainly composed of tempered martensite, with a yield strength near okg/- or more Oil well steel with high strength and excellent resistance to sulfide stress corrosion cracking. (4) C: 0.15-0.50q6. inhibition = 0.1
~1. O%. Mn: 0.3-1.5%l Cr: 0.6-2.0%
+ Co: 0.3-5.0 chips p 80t, Nl:
Contains 0.001 to 0.10%, and further Cu: 0
．． 1 to 1.0%, and Ni: 0.1 to 1.0 To
+Nt): 0.01-0.15%, V: 0.01-0
．． 50 chi. Zr, '0.01-0.50% ITi:
0.001-0.10%. and B: containing one or more of α0003 to 0.0050, with the remainder consisting of Fe and unavoidable impurities, and p and s as unavoidable impurities. The contents of Mo and W are P: 0.025% or less + S: 0.0, 10% or less MO: 0.
05% or less. W: Has a structure with 0.05% or less (more than 1%),
Further, an oil well steel having a yield strength of tokgAII or higher and excellent sulfide stress corrosion cracking resistance, characterized by having a structure mainly composed of tempered martensite.