JPS59182918A - Production of two-phase stainless steel oil well pipe having high strength - Google Patents

Abstract

PURPOSE:To obtain a two-phase stainless steel oil well pipe having excellent corrosion resistance, etc. and high strength by heating a low-carbon two-phase stainless steel pipe having a specific component compsn. to a prescribed temp. range then subjecting the pipe to reduction rolling at a finishing temp. in the temp. range lower than said range and cooling quickly the pipe. CONSTITUTION:A two-phase stainless steel pipe contg., by weight, <=0.04% C, 0.1-3.0% Si, 0.5-3.0% Mn, 20-30% Cr, 4-9% Ni, 1-5% Mo, <=0.10% Al, 0.05-0.20% N, <=0.025% P, and <=0.010% S is subjected to reduction rolling with a stretch reducer The pipe is heated to 900-1,150 deg.C to prevent the precipitation of an alpha-phase prior to said reduction rolling and further the pipe is subjected to the reduction rolling at the finishing temp. in the reduction rolling stage limited to 750-1,000 deg.C. The steel pipe after the reduction rolling is quickly cooled by water or mist, by which the precipitation of the alpha-phase and carbide is prevented and the two-phase stainless steel oil well pipe having the high resistance to corrosion, SCC and SSC and >=63kg/mm.<2> yield pressure is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a duplex stainless steel oil country tubular goods having high strength, particularly corrosion resistance and stress corrosion cracking resistance (hereinafter referred to as S resistance).
The present invention relates to a method for producing seamless steel pipes with excellent CC properties (hereinafter referred to as CC properties) and sulfide cracking resistance (hereinafter referred to as SSC properties).

In recent years, the development of oil and gas wells has been progressing in a harsher drilling environment than before due to tight supply and demand for oil. These oil and gas wells are mostly deep, high temperature, and high pressure, producing H2S,
This is an environment containing Co, CL, etc. Therefore, there is a demand for the development of oil well materials with high strength and excellent corrosion resistance, SCC resistance, and SSC resistance.
0 series and 410 series martensitic stainless steel oil country tubular goods are used. One of the reasons for this is that OCTG for deep water use requires a yield stress of 80KSI (56Kf/d) or more, and carbon steel has a yield stress of 80KSI (56Kf/d) or more for deep water use.
Although the standard L80 has been determined, there is no standard for stainless steel yet, so the 5US420 series, which is manufactured as equivalent to L80,
This is because the 410 series can obtain high strength υ through heat treatment.

However, even in an environment containing only CO2, the 5US420 series and 410 series suffer from severe pitting corrosion when the temperature exceeds 120℃, and have poor SSC resistance.
It cannot be used in this environment. Actually, there is a trace amount of H2 in CO2.
Accidents thought to be caused by hydrogen cracking of steel materials due to H2S have occurred in oil wells containing S.

5US420 series and 410 series have the above-mentioned drawbacks, so they cannot be used under CO2G conditions of 120℃ or higher and CO2+H2S.
Duplex stainless steel oil country tubular goods are used under the EL environment. Duplex stainless steel is CO2゜CO2+H2Sf
Excellent corrosion resistance, SCC resistance, and SS resistance under f1 conditions
Although it exhibits C properties, it only shows a yield stress of 80 to 90 KSI (56 to 63 h/wj) in the annealed state and the same bath heat treatment state. If a yield stress of 80 to 90 KS I is sufficient, it can be supplied as is, but if higher strength is required, it is difficult to manufacture it to the point of heat treatment, and cold treatment is required. Processing is performed. Duplex stainless steel is often used in deep oil wells compared to 808420 thread and 410 series, but 5US420 thread and 41
0 series is 110-120KSL (77-54
It is possible to obtain a yield stress of Kf/-). However, due to cold working, the inherent characteristics of duplex stainless steel are significantly impaired, and the SCC resistance is greatly deteriorated.

An object of the present invention is to solve the problems of the prior art described above and to provide a method for manufacturing a duplex stainless steel oil country tubular goods having excellent corrosion resistance and high strength.

As a result of various studies, the present inventors have found that under CO2 and CO2+H2SjJ conditions, corrosion resistance, SCC resistance, and SSC resistance are not impaired, and the yield stress is 90 KSI (
We have developed a method for manufacturing duplex stainless steel oil country tubular goods that satisfies API standards of 63 odor/-) or higher.

The gist of the present invention is as follows.

That is, the weight ratio (-te, C: 0.04% or less, Si:
0, 1-3.0%, Mn:Q, 5-3.0%, Cr:2
0-30 饅, Ni: 4-9%, MO: 1-5%, At
: 0.10 inch or less, N: 0.05 to 0.20 inch, P
: 0.025% or less, S: 0.010% or less in a method for producing a two-phase stainless steel oil country tubular goods comprising the step of stretch reducer (two-way diameter reduction rolling), heating the two-phase stainless steel pipe to 900 to 1150°C before the diameter reduction rolling;
The finishing at 750 to 1000°C after the heating process is characterized by a process of diameter reduction rolling at a temperature, and a process of quenching with water or mist immediately after the completion of the diameter reduction rolling, so that the strength is increased. This is a method for producing steel oil country tubular goods.

The present invention will be explained in detail below. First, the present invention +7
) The reason for limiting the composition of 2m stainless steel will be explained.

C: C has the effect of increasing strength, but if it exceeds 0.04 inch, the pitting corrosion resistance and crevice corrosion resistance will deteriorate significantly, so it was limited to 0.04% or less.

Si: Sl is effective in improving strength, but if it is less than 0.1%, it is less effective and if it exceeds 3.0%, it becomes a stretch reducer.
During rolling, the σ phase precipitates and significantly impairs hot workability, so it is limited to a range of 0.5 to 3.0 inches.

Mn:・: Mn is effective in improving strength, but if it is less than 0.5%, the effect is small, and if it exceeds 3.0%, not only the effect in terms of strength is saturated, but also deterioration of corrosion resistance. 0.
It was limited to a range of 5 to 3.0%.

Cr; C'r has a strong effect of improving corrosion resistance under conditions of Co2 and CO2 + H2S, but if it is less than 20%, it is not sufficient in severe environments, and if it exceeds 30%, it will cause deterioration of toughness. limited to the range of

NI: In the method of the present invention, the higher the Ni content, the higher the strength.
If the modulus is less than 9, the effect is insufficient, and if it exceeds 9, the toughness will deteriorate significantly, so the range is limited to 4 to 9.

Mo: MO requires at least 1 modulus to maintain corrosion resistance in a CO2A-HtS environment, and if it exceeds 5 modulus, the toughness deteriorates significantly, so it was set in the range of 1 to 5 modulus.

Al: Ae is a strong deoxidizer and has the effect of improving the cleanliness of steel, but if it exceeds 0.10%, the effect is saturated, so it was limited to 0.10% or less.

N: N has the effect of improving corrosion resistance and increasing strength in CO2 and CO, +I (, S environments, but 0.
If it is less than 0.05%, the effect will be small, and if it exceeds 0.020, crevice corrosion resistance in CO, Co, -1-H,S environments will deteriorate, so 0.05 to 0.20%.
limited to the range of

P: It is desirable that P be small as an impurity, and since it deteriorates corrosion resistance, the northern limit was set to Q, 025%.

S: Since S tends to cause sulfide cracking, it was limited to 0.010 inch or less.

Next, the reasons for limitations in the method for manufacturing a duplex stainless steel pipe having the above-mentioned limiting components will be explained.

First, the heating temperature in the diameter reduction step was set to 900 to 1150°C, because in the temperature range below 900°C, the σ phase precipitates in the component system of the present invention, making rolling difficult and significantly deteriorating the toughness.
Furthermore, if the temperature exceeds 1150°C, the crystal grains will become coarser and the amount of austenite will decrease significantly, resulting in deterioration of toughness, and there is a risk of accidents due to embrittlement of the pipe material during construction or use of the oil country tubular goods. .

Next, the finishing temperature in the diameter reduction rolling process is set to 750~] 0
The reason for limiting the temperature to 00°C is that below 750°C, carbides will precipitate at the grain boundaries and the SCC resistance and SSC resistance will be significantly deteriorated, and above 1000°C, the specified strength cannot be ensured with the limited ingredients of the present invention. This is because it is difficult.

Further, the reason why the material is rapidly cooled with water or mist immediately after the diameter reduction rolling is completed is that cooling in the air causes carbides to precipitate at the grain boundaries and deteriorate the SCC resistance, and rapid cooling can prevent grain boundary precipitation.

The present invention prevents the precipitation of slag, σ phase, and carbide through such treatment, has excellent corrosion resistance, SCC resistance, and SSC resistance, and has a yield stress of 90 KSI (63 kg/s+tl) or more.
It was possible to manufacture phase stainless V steel oil country tubular goods.

Example Duplex stainless steel having the chemical composition shown in Table 1 was heated, rolled to reduce its diameter, and cooled under the manufacturing conditions shown in Table 2. However, comparison row Nn13 was manufactured in a separate process, subjected to solution treatment to adjust the phase ratio at the annealing temperature shown in Table 2, and then cold worked (11) to increase strength.

The strength, toughness, and corrosion resistance of steel pipes manufactured by these methods were investigated, and the results are also shown in Table 2.

The strength is the yield stress with a 0.2 modulus offset, and the toughness is the absorbed energy at 0°C in a 2 mm V-notch 2/3 size Charpy impact test.

Corrosion rate and SCC resistance were both tested in the following atmosphere, and in particular SCC resistance was tested in the U-bending state. Example solution composition: 3.5% NaCA' Gas partial pressure: PC□, 30 atm, PH2S
: 10 atm temperature = 150°C In addition, in Tables 1 and 2, items that do not satisfy the limiting conditions of the present invention and items with poor measurement results are underlined.

The following can be seen from the measurement results in Table 2. Comparative example N[1
1 has poor corrosion resistance because C exceeds the upper limit of 0.04% according to the present invention, Comparative Example N [12 has inferior strength because Ni is lower than the lower limit according to the present invention, and Comparative Example N [13 has MO according to the present invention] Since S is lower than the lower limit of the present invention, the corrosion resistance is poor 9. Comparison (12) Example Nn4 has S that exceeds the upper limit of the present invention, so the SCC resistance is poor.
In Comparative Example No. 5, Mn exceeds the upper limit of the present invention, resulting in poor corrosion resistance. In Comparative Example No. 6, Cr is lower than the lower limit of the present invention, resulting in poor corrosion resistance. In Comparative Example NC17, Cr exceeds the lower limit of the present invention. Since the upper limit of Nu is exceeded, the toughness is low, and Comparative Example Nu
No. 8 has poor toughness because Nj exceeds the upper limit of the present invention. Next, Comparative Example Nn9 has inferior toughness because the heating temperature before diameter reduction rolling is lower than the lower limit of the present invention, and Comparative Example Nn10
has poor toughness because the heating temperature exceeds the upper limit of the present invention, comparative example Nn1l has low strength because the finishing temperature of rolling exceeds the upper limit of the present invention, and comparative example Nn12 has poor corrosion resistance because it was air cooled after rolling. Comparative Example Nn13 was subjected to cold working after annealing in a separate step, and had poor SCC resistance.

On the other hand, Examples Nn14 to Nn20 exhibit excellent strength and toughness, corrosion resistance, and SCC resistance.

As is clear from the above examples, the present invention limits the components of the duplex stainless steel and heats the stainless steel to a temperature of 900 to 1150°C before diameter reduction rolling.
After heating, diameter reduction rolling is carried out to a finishing temperature of 750 to 1000°C, and immediately after rolling, quenching with water or mist improves strength, toughness, corrosion resistance, SCC resistance, and SSC resistance. It is possible to manufacture two-phase stainless steel oil country tubular goods with excellent properties.

Agent: Patent Attorney Takeo Nakaji

Claims (1)

[Claims] (1) Weight ratio C: 0.04- or less Si: 0.1-
3.0% Mn: 0.5-3.0% Cr: 20-30% Ni: 4-9 inches Mo: 1-5% At: 0.10 or less N: 0.05-0.20 points : 0.025% or less S: 0.010% or less A method for producing a two-phase stainless steel oil country tubular goods comprising the step of diameter-reducing a two-phase stainless steel pipe containing S: 0.010% or less using a stretch reducer. 2 above before diameter rolling
a step of heating a phase stainless steel pipe to 900 to 1150 ° C., a step of diameter reduction rolling at a finishing temperature of 750 to 1000 ° C. after the heating step, and a step of rapidly cooling with water or mist immediately after the end of the diameter reduction rolling, 1. A method for manufacturing a duplex stainless steel oil country tubular goods having high strength.