JPS59123716A - Production of steel pipe for oil well having excellent resistance to sulfide cracking - Google Patents

Abstract

PURPOSE:To obtain a high strength steel pipe for oil well having improved hardness in a surface layer part and excellent resistance to sulfide cracking by subjecting a low alloy steel having a specific compsn. added with a small amt. of V, Ti, Nb and Zr to pipe making and rolling and performing a heat treatment in a reducing atmosphere. CONSTITUTION:A steel contg. 0.15-0.80wt% C, 0.1-1.0% Si, 0.3-2.0% Mn, 0.1- 3.0% Cr, 0.1-1.0% Mo, 0.001-0.100% Al, contg. 0.003-0.00050% B according to need, contg. further >=1 kind among 0.01-0.15% V, 0.01-0.15% Ti, 0.01-0.15% Nb and 0.01-0.15% Zr, and consisting of the balance Fe and inevitable impurities is subjected to pipe making and rolling to a prescribed shape. At least one stage in the heat treatment succeeding to said rolling is performed in a reducing atmosphere. A steel pipe for oil well of which the hardness in the surface layer part from the surface down to >=0.2mm. depth is made <=250 in Vickers hardness by such treatment and which has high resistance to sulfide stress corrosion cracking is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has a high yield strength of 70 kgf/w2 or more, and is capable of resisting sulfide stress corrosion cracking (hereinafter referred to as 5scc) in a humid hydrogen sulfide environment such as so-called sour oil wells or sour gas wells. The present invention relates to a method for manufacturing high-strength oil well steel pipes that have high resistance to

In recent years, due to the global energy situation, the development of oil and gas wells deep beneath the earth's surface has become more active.As a result, the depth of oil wells has increased, and the steel pipes used in them have High-strength steel has come to be used frequently in order to withstand the pressure of producing crude oil and the increased tensile load due to its own weight. However, when high-strength steel is used as oil country tubular goods, it is known that 5SCCk tends to occur in sour environments, and its application is severely restricted.

As mentioned above, sscc is a phenomenon that occurs when stress is applied to steel materials used in humid environments containing hydrogen sulfide. In recent years, attention has been focused on the development of oil and sour gas wells, and one issue that has been attracting particular attention is this:
It is one.

Based on past accidents at oil wells that can be used in sour environments and various research results, it has been revealed that as the strength of steel increases, its 5scc resistance decreases. It has also come to be known that in order to prevent 9.5 SCC, it is effective to limit the strength of steel materials to HRC 22 or less (hardness is proportional to tensile strength).

Therefore, in consideration of these matters, by subjecting the steel pipe to a treatment such as sieve temperature tempering, the hardness of the entire steel pipe is increased to HRC2.
It has been proposed to prevent the occurrence of sscc by reducing the tensile strength of the steel pipe to a hardness of HRC22 or less, but generally the yield ratio (yield strength/tensile strength) also decreases. The design stress (
Naturally, it was not possible to avoid the problem of either having to accept that the yield strength would be lower (which is proportional to the yield strength), or having to reduce the wall thickness for use. Especially when it comes to oil country tubular goods such as casings, even if you try to limit the increase in wall thickness only to the lower part, which is susceptible to corrosion in a corrosive environment, the increase in your own troops will end up being due to the increase in wall thickness in the upper part. Since it is necessary to supplement the amount, it is not desirable in practical terms.

Since then, research has been conducted from various fields,
Currently, a steel material with a yield strength of 70 kgf/- or more and a good 5 SCC resistance, which is required by the development of oil and gas wells, has not yet been realized.

From the above-mentioned viewpoint, the present inventors have determined that the yield strength is 70.
We conducted research in order to provide high-strength steel pipes that have a high strength of kgf/TRA or higher and also have excellent sscc resistance that is fully satisfactory as oil country tubular goods used in harsh sour environments. ) SSCC is likely to occur due to stress concentration, such as binding on the steel surface formed by corrosion or inclusions near the surface. (b) At least 0.2 tons from the surface can be prevented from occurring in the surface layer of the steel material, and therefore the propagation of 5scc from the surface layer to the inner layer cannot occur. The hardness is Hv250 over the range of 0.2 run or more from the surface.
If it is below, 5scc will not occur regardless of the hardness and strength of the inner layer of Steel I, (c) 0.2 from the surface
Low steel surface layer that exceeds fi? 1i12 degrees (Hv
250 or less) can be achieved by either quenching and/or tempering during the quenching/tempering process, or by IM welding and tempering during the rolling cooling process, if the chemical composition of the steel material is appropriately selected. This can be easily achieved by simply performing azuror tempering) in a reducing atmosphere. Sweet,
When the heat treatment is carried out in the above-mentioned atmosphere, the surface layer of the steel material is decarburized and the hardness of that part decreases.
(d) In this way, the good 5SCC resistance of the copper phase can be sufficiently ensured by the surface hardening layer (decarburized layer) that is generated during heat treatment in a reducing atmosphere. The knowledge shown in (a) to (d) above is that it is possible to manufacture steel pipes that are industrially inexpensive and have good 5scc resistance characteristics without the need for the addition of alloying elements or complicated processes. I was able to obtain this.

This invention (was made based on the above findings, C: 0.15 to 1,80% (hereinafter referred to as weight %),
Si: 0.1~], 0%, Mn:
0.3-2.0%.

Cr: 0.1-3.0%, Mo: 0
．． 1~], , 0%.

Az: o, oo 1~0.100% total content, or B: 0.0003~iJ, 0050 so, v: 0.01~0°15%, Ti: 0 .01～
0.15%.

Nb: o, o 1~0.15%, Zr: 0.01~
0.15% of Fe and unavoidable impurities: residual υ, after rolling for pipe production, at least one of the subsequent heat treatments is performed in a totally reducing atmosphere. By controlling the hardness of the surface layer of the steel pipe from the surface to a depth of 0.2 mm or more to a Vickers hardness of 250 or less, it is possible to obtain a steel pipe for oil wells with excellent resistance to sulfide stress corrosion cracking. It has the following characteristics.

In addition, in the method of this invention, ?
! ! 7! The reason for setting the hardness to Hv 250 or less is that if the hardness exceeds Hv 250, the sensitivity of the steel pipe to 5scc generation becomes too sensitive for practical use. If the depth does not exceed 0.2 rtvn, good machining SCC performance cannot be obtained due to pitting due to corrosion and inclusions near the surface. .2++
It is set as i or more. The deeper the surface softening layer is, the more effective it is in preventing 5SCC, but its upper limit is:
It goes without saying that it may be determined within a range that does not impair required properties such as strength, while taking into account the ratio of 1j with the steel pipe wall thickness.

Normally, steel pipes for oil wells are quenched and tempered after being rolled to make them.
Although the product is made after being subjected to treatments such as normalizing or annealing, heat treatment in a reducing atmosphere to form a softened layer on the surface of the steel pipe may be performed at any stage after rolling. It goes without saying that the atmosphere for the heat treatment is not particularly limited as long as the surface is effectively decarburized.

Next, the reason why the chemical composition of the target steel in the method of the present invention is limited as described above will be explained.

■ C The C component has the effect of ensuring the strength of steel, and in order to ensure the strength of the core as a steel pipe for oil wells, 0.15 is essential.
% or more content is required. On the other hand, if the content exceeds 0.80%, it will be difficult to reduce the hardness of the surface layer of the steel pipe to Hv 250 or less even after decarburization treatment, or a long decarburization treatment will be required. The C content was set to (1,
It was set at 15% to 0.80%.

(5i) The Si component has the effect of deoxidizing the steel and improving the strength of the steel material, but if its content is less than 0.1%, the desired effect cannot be obtained; on the other hand, 1. If the content exceeds 0%, the toughness of the steel will deteriorate, so the content was set at 0.1 to 1.0%.

■ Mn The Mn component has the effect of improving the strength and toughness of steel, but if its content is less than 0.3%, the desired effect cannot be obtained, and in particular the form of L This change causes extreme deterioration of toughness. -force, 2
．． If the hin content exceeds 0%, the toughness will deteriorate again, so the hin content should be set at 0.3 to 2. Oc! l
).

■ Cr The Cr component (V) has the effect of improving the hardenability of steel, improving the strength, especially the yield strength, and achieving thinner steel pipes, but if the content is less than 0.1%, the above effects will be reduced. On the other hand, even if the content exceeds 3.0%, no further quenching hardness improvement effect is observed, and the hardness of the surface layer of the steel material cannot be lowered to the desired value by adjusting the atmosphere during heat treatment. Since it is no longer possible to reduce the content to 0.
It was set as 1 to 3.0 progress.

■　M.

Like Cr, the Mo component also has the effect of improving the hardenability of steel, increasing the strength of steel, and achieving thinner steel pipes, but if its content is less than 1%, the desired effect cannot be achieved. On the other hand, even if the content exceeds 0%, no further strength improvement effect can be obtained. The content was determined to be 0.1 to 1.0% because the hardness of C could not be lowered to the desired value.

■ At The At component not only has a deoxidizing effect on steel, but also has the effect of refining the steel structure and improving toughness, but if its content is as low as 0.001%, the above effect will not be achieved. The desired effect cannot be obtained, and if the content exceeds 0.100%, the toughness of the weld heat affected zone deteriorates, so the content was set at 0.001 to 0.100%.

@B Component B, like Cr or Mo, has the effect of improving the hardening conditions of steel and increasing its strength, so it is added when it is desired to make the steel pipe even thinner. If the content is less than 0.0003, the desired effect on improving hardening properties cannot be obtained;
Even if the content exceeds ρ, no further quenching property improvement effect is observed, and the hardness of the steel surface layer cannot be reduced to the desired value by adjusting the atmosphere during heat treatment.
, KfX may cause cracking and deterioration of toughness; CI 05
It was set as 0%.

(h) v, T], Nb+ and Zr These components P improve the strength of steel through precipitation hardening, and improve the toughness of copper through grain refinement. Since it has the characteristics to achieve, it is a component that can be selected and included in one or two small V,
If each content is less than 0.01%, the desired effect cannot be obtained in the above-mentioned action, and on the other hand, if the content exceeds 0.15%, the effect of improving stiffness cannot be obtained. Therefore, the content of each is 0.101% to 0.15%.
It was determined that

Next, this emission #J will be specifically explained using an experimental example while comparing it with comparison ψ11.

Example: A steel ingot (50 kp) having the composition shown in Table 1 was melted using the vacuum method and hot rolled to produce a temporary phase with a thickness of 15 mm and a width of 120 m. did.

Next, a small round bar test piece (parallel part: 6.
4φx20z) was cut out and 10% H29
After heating at 910° C. for 10 minutes in a 0% N2 mixed gas, it was rapidly cooled in water, and further tempered at 630° C. for 30 minutes in an Ar atmosphere. Regarding the obtained treated steel material, Hz
In a Sk-saturated 0.5% acetic acid-5% NaCl solution, a stress of 75% of the yield strength was applied and held for 720 hours;
5SCC property was evaluated.

The results are shown in Table 2 along with the tensile strength and hardness of the steel materials.

From the results shown in Table 2, according to the method of the present invention,
It is clear that a steel material having sufficient 5scc resistance can be obtained.On the other hand, the 'fc steel material obtained by the comparative example in which the steel composition is outside the range of the present invention has a sufficient 5scc resistance.
It can be seen that the cc properties are poor or the desired strength cannot be achieved.

Next, a plurality of round bar test pieces cut out from the pre-warmed hot-rolled material having the composition of steel A in Table 1 were subjected to various heat treatments under the conditions shown in Table 3, and then treated in the same manner as above. A test on the S SCCCC side was conducted. The results are shown in Table 3 along with the tensile strength and hardness.

The results shown in Table 3 also show that the copper phase produced by the method of the present invention has high strength and has sufficient resistance to 5sc.
However, it is clear that all steel materials that have undergone treatment such that their surface hardness and softened layer depth are within the scope of the present invention are inferior in 5SCC resistance. be.

In the above experimental example, IJj was cut from a hot rolled steel plate.
Although the characteristics of the test specimens subjected to various treatments are shown, it is natural that similar results can be obtained with steel pipes actually obtained by pipe-making and rolling. The present inventors have clearly confirmed that the same results can be obtained in tests using actual steel pipes.

As mentioned above, according to the invention, yield strength = 70 k
High strength of gf/- or less than 2, and excellent 5scc resistance that can be used as oil country tubular goods in sauer environments.
Industrially useful effects are brought about, such as the ability to extremely efficiently manufacture high-strength steel pipes that have both strength and strength.

Applicant Sumitomo Kinshu Industries Co., Ltd. Agent Tomi 1) Kazuo 1 person, 1 person 93
−

Claims (1)

[Claims] ill C: 0.15 to O, SO%. Sl:O11-1.0%. IVIn: 0.3-2.0%. Cr: 0.1-3.0%. Mo: O1] to 1.0%. ht: o, o Contains 1 to 0.100% of O, and V: 0.01 to 0.15%. Ti: 0.01-0.15%. Nb: 0.01-0.15%. Zr: 0.01 to 0.15% of steel (at least 9% by weight), containing at least 1@ of Fe and unavoidable impurities: After rolling a metal tube, at least one of the following heat treatments is performed. The hardness of the surface layer of the steel pipe at a depth of 0.28 or more from the surface is reduced to 250 or less on the Vickers hardness scale by performing the two steps in a reducing atmosphere. A method for manufacturing superior high-strength steel pipes for oil wells. [21C: 0.15-0080%. Si: 0.1-1.0%. Mn: 0.3-2.0%. Cr: 0.1-3.0%. Mo: 0.1-1.0%. At: o, o O1-0.100%. B: Contains 0.0003 to 0.0050%, and V: 0.01 to 0.15%. Ti: 0.01-0.15%. Nb: o, o 1-0.15%. Zr: 0.01 to 0.15% of the steel (at least 1%) containing one or more of the following, and the remainder: Fe and non-EJ avoidance impurities: After rolling a metal tube, the following heat treatment is performed. Resistance to sulfide stress, characterized in that the hardness of the surface layer of the steel pipe from the surface to a depth of 0.2 (conversion) or more is 250 or less in terms of total Vickers hardness by performing at least one in a totally reducing atmosphere. A method for manufacturing high-strength oil well steel pipes with excellent resistance to corrosion cracking.