JPS62177124A - Manufacture of steel pipe for thermal well having low rate of creep deformation - Google Patents

Abstract

PURPOSE:To manufacture a steel pipe causing little creep deformation by hot rolling a steel contg. small amounts of carbonitride forming elements to make a pipe and by hardening and tempering the pipe under specified temp. conditions. CONSTITUTION:A steel consisting of, by weight, 0.15-0.6C, 0.1-0.5% Si, 0.5-2.0% Mn, 0.01-0.1% Al, one or more among 0.05-0.2% Mo, 0.01-0.1% Nb and 0.01-0.1% V and the balance Fe with inevitable impurities is hot rolled to make a pipe. This steel pipe is hardened by heating to the Ac3 point or above and rapid cooling and then it is tempered by heating to 550 deg.C- the Ac1 point. Proper amounts of Cr or Ti and B may be added to the composition as required. By this method, a steel pipe for a thermal well having a low rate of creep deformation in the temp. range of about 200-700 deg.F and a long service life is obtd.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a steel pipe for oil wells used in thermal wells for injecting steam in the secondary recovery of oil and gas.
The present invention relates to a method of manufacturing steel pipes for thermal wells, which lengthens the service life of the steel pipes by slowing down (reducing) the creep deformation speed in the region below 700°C using inexpensive means.

[Conventional technology]

The standard commonly used for oil country tubular goods is API 5AX, but this standard only stipulates the upper limits for the P and S components, so unless it is for a special purpose, it is difficult to keep costs low for oil country tubing. Due to necessity, Cr, M
Almost no alloying elements such as o, Nb etc.
Yield strength of C, Si, and Mn components is 55 ks
High strength steel of i=110 ksi class is used.

On the other hand, in the secondary recovery of oil and natural gas, steam injection is often performed in order to increase recovery efficiency, but naturally this well is heated to temperatures of 100°C (
The material is heated to a temperature range from about 200° F.) to the critical temperature (about 700° F.).

This well is generally called a thermal well (this term will be used hereafter).

According to conventional knowledge, for example, as shown in Figures 1 and 2 (Revised Metal Handbook, 3rd Edition, Japan Institute of Metals, June 25, 1971, (published by Maruzen), the temperature ranges from 200 to 700"F. In the temperature range, the high-temperature strength of steel, including creep strength, hardly changes compared to room temperature.

[Problem that the invention seeks to solve]

However, these refer to short-term high-temperature strength and creep rupture strength, and although it is true that most general-purpose oil country tubular goods do not experience creep rupture when used for a long time under conditions of external force in actual thermal wells, It is observed that creep deformation occurs.

When creep deformation occurs, not only the entire OCTG deforms, but also the threads of the threaded parts that make up the joints of the steel pipes become particularly deformed, loosening the threaded fittings, and eventually causing steam to leak from that part. This problem arises. Once a steam leak occurs, the well cannot function as a thermal well, so it must be discarded or the oil country tubular goods replaced. This situation has become a major problem because it ultimately leads to an increase in the cost of extracting oil and gas, resulting in large industrial losses.

On the other hand, steel to which appropriate amounts of heat-resistant alloys such as Cr, Mo, and W are added, such as steel for boilers, naturally has a low creep deformation rate in the low temperature range, making it suitable for use in steel pipes for thermal wells. If this is done, it will be easy to extend the service life and obtain the desired high strength by adjusting the heat treatment conditions. However, such measures cause an increase in material costs and do not meet the original purpose of reducing oil extraction costs.

Therefore, the present invention provides a means for suppressing the creep deformation rate in the temperature range without increasing the manufacturing cost too much.

[Means to solve the problem]

The present inventors conducted a detailed study on the causes of creep deformation that gradually develops over a long period of time in a low temperature range where creep is not a problem. Based on the results, new findings were discovered that could provide a solution to reduce creep deformation at low cost.

In other words, (1) Creep deformation at 200"F to 700"F is caused by dislocations that were stable at room temperature under constant stress, becoming activated as the temperature rises and gradually moving over time, resulting in the formation of grain boundaries. Caused by berry.

(2) Therefore, as a preventive measure, it is sufficient to inhibit the movement of dislocations and suppress the peripheries within the grains.

(3) As an inexpensive and specific means of suppressing the movement of dislocations in the relevant temperature range, the use of carbonitrides that are finely precipitated within the grains is very effective, and the use of solid solution C and N is also useful. It is. These phenomena are generally called age hardening, but unlike phenomena that correspond to short-term strength as is generally said, stability in which hardening is maintained over a long period of time is important. It is necessary to strictly control the steel composition and at the same time limit the manufacturing conditions.6 The feature of the present invention is that the above effects can be achieved by adding a small amount of carbonitride-forming elements, instead of using the simple conventional method of adding expensive alloying elements. is added to ensure low cost and high strength materials.

That is, the present invention provides: (1) In terms of weight ratio, C: 0.15 to 0.6%, Si: 0
．． 1-0.5%, Mn: 0.5-2.0%, Aj
! :0.01-0.1%, Mo: 0.05-0.2
%, Nb:Q, Ql~0.1%, V:0.01~0.1
% or more, with the remainder consisting of Fe and unavoidable impurities. (2) weight ratio C: 0.15 to 0.6; %, Si: 0
．． 1-0.5%, Mn: 0.5-2.0%, Aj
! : 0.01-0.1%, Mo: 0.05-0.
2%, Nb: 0.01~0.1%, V: 0.01~
Contains 0.1% of one or more kinds, and further contains Cr:0
．． 1 to 0%, and further contains either or both of Cr: 0.005 to 0.07% and B: 0.0007 to 0.003%, with the balance consisting of Fe and inevitable impurities. , Ac3 as hot pipe rolling or after hot pipe rolling
550°C after being quenched by heating above the point
This is a method for manufacturing a steel pipe for thermal wells with a low creep deformation rate, characterized by tempering at a temperature of = Ac.

Next, the reason for limiting the range of ingredients and manufacturing process in the present invention will be described.

CTC is an important component in terms of ensuring strength, and its lower limit is set at 0.15% because it is necessary to maintain the target lower limit strength in combination with other components and processing conditions within the scope of the present invention, and the upper limit is set at 0.15%. When approaching the composition, the toughness of the steel becomes extremely poor and restrictions on the handling and deformation of the steel pipe become large, so 0.6
%.

Si:Si is a residual substance used as a deoxidizing agent in the steelmaking process along with Al, and is not a component with a positive meaning, but it is an effective component although the extent to which it increases hardenability and temper softening resistance is small. Inclusion of 0.1% or excessive content exceeding 0.5% reduces toughness.

Therefore, the Si content was limited to 0.1 to 0.5%.

Mn: Mn fixes the unavoidably present S as MnS, and at the same time contributes to preventing cracking during hot manufacturing of steel pipes.
In order to increase the strength of steel through solid solution strengthening and hardenability improvement, it is added in an amount of 0.5% or more. Moreover, a Mn content of more than 2% is undesirable, especially since it causes melting damage to the refractory bricks in the melting furnace during steel production and increases the risk of cracking during hot pipe production.

Nb and ■: These components are strong carbonitride-forming elements, and when contained in small amounts, reduce the creep deformation rate in the relevant temperature range, and are essential in the present invention. The lower limit is 0.0, which is the lowest amount at which such an effect is clearly observed.
The upper limit is 0.1%, which is the limit amount at which the effect is saturated and the toughness of the steel is not impaired.

Mo: Mo is an effective component for increasing the room temperature and high temperature strength of steel, and is also a nitrogen carbide forming element, so it is an effective element in the structure of the present invention, but on the other hand, it is a very expensive alloying element. Therefore, in order to keep the range of addition to the necessary minimum, the lower limit was set at 0.05%, where it starts to have an effect in reducing the creep deformation rate, and the upper limit was set at 0.2%, which is an amount that does not impair toughness.

P, S, etc., which are contained as unavoidable impurities in addition to the above-mentioned components, are residual components that increase the strength, toughness, and creep deformation rate of the steel, so it is preferable to reduce them as much as possible.

Further, steel having the above-mentioned composition has high strength and produces a steel pipe with a low creep deformation rate.

Furthermore, in the present invention, Cr or Ti and B can be selectively added and contained in order to further improve strength and creep properties.

Cr: Cr is a selectively contained component, and is included for the purpose of increasing the strength of steel and increasing its corrosion resistance to some extent. At the same time, it forms carbonitrides and has the secondary effect of suppressing creep deformation, although the effect is smaller than that of Mo, Nb, and V. On the other hand, C
Addition of a large amount of r increases costs and should be avoided for the purposes of the present invention. Due to these needs, under the Cr component,
The upper limits were set to 0.1% and :0%, respectively.

Ti and B: Ti and B are used in combination to improve hardenability and improve the strength and toughness of quenched and tempered steel.

It is effective for blocking. In other words, Ti is added to prevent B from combining with N to form BN, which is a state of existence that is ineffective for hardenability. (T i addition amount = 3.4xN).

Normally N varies between 0.0002 and 0.02%, so T
The addition range of i is o, o o s to 0.07%.

For B, the upper and lower limits are the effective range for improving hardenability under the assumption that N is fixed with Ti, and is 0.0007 to O,OO3%.
is the addition range.

Af: /l! is the residual material used as a deoxidizing agent in the steelmaking process along with Si, and is used to obtain completely killed steel.
Moreover, as an effective component that increases the abnormal growth temperature of crystal grains when steel is heated to high temperatures, the lower limit is the minimum necessary amount of 0.01%, and the upper limit is the content that does not increase alumina inclusions and embrittle the steel. 0.1%.

The present invention uses molten steel melted in a melting furnace such as a converter or an electric furnace using the ingot-blumping method, or steel with the above components as hot pipe-making rolling or after hot pipe-making rolling. After being quenched by heating above and rapidly cooling, the temperature is 550° C. to A (tempering treatment is performed by heating to a temperature of one point).

The effect of the present invention is slightly greater when the tube is quenched and unrolled than when it is hot-rolled, but which process is used depends on the combination of the component system and the required strength.
Select how much toughness you want. Generally, when the yield stress is less than 80 ksi, the tube is left as hot rolled, and when it is higher than that, it is quenched under normal conditions and then tempered. On the other hand, if the tempering temperature is less than 550°C, precipitation of carbonitrides is insufficient and dislocations are not fixed sufficiently, so it is necessary to select a tempering temperature between 550°C and the A c + point.

〔Example〕

The specific contents and effects of the present invention will be explained below.

Table 1 shows the chemical composition and heat treatment conditions of the steel tested, the measurement results of yield stress at room temperature and high temperature, and the creep test results, as well as the results of actual use as oil country tubular goods in an actual well (thermal well). shows. NQ1 to 14 are the steels of the present invention, and 1k15 to [Effects of the invention] From these evaluation results, although there is no large difference in yield stress between the comparison steel and the steel of the present invention at room temperature and 700″17, It can be seen that there is a difference of more than 10 times in the creep deformation rate at 700°F, and as a result, there is a large difference in the life of oil country tubular goods in actual wells.In other words, the life of oil wells, etc. is at most Although the lifespan is 20 days, the steel of the present invention has a lifespan of about 1 year (375 days) or more.

As described above, the effects of the present invention are remarkable in terms of extending the life of oil country tubular goods, and contribute to a significant reduction in the cost of extracting oil and gas.

[Brief explanation of drawings]

FIG. 1 is a graph mainly showing the influence of Cr and Mo on high temperature hardness. FIG. 2 is a graph showing the relationship between the creep strength of various steel materials and the Larson Miller parameter. Note that the symbols in FIG. 2 indicate typical components of each steel. 1・CO, 15, 2・CO, 13, MoO, 5, 3...
CO, 11, Cr: 0. Mo0.5.4-CO,
24, Cr: 0. Ni2.5, Mo0.5
, Vo, 22.5-CO, 10, Cr 5.0, Mo
0.5.6 ・19-9DL: CO, 3, Mn: 0
．． Cr 19, Ni 9, Mo: 25, Wl,
25, Nb or Ta0.4, Ti O12, Fe remainder (
unit%). Agent Patent Attorney Masaru Inoue 10th 0 1CX) 2002CO='KII) 5C06C
O ancient horse gold temperature [0C] Figure 2

Claims (2)

[Claims] (1) Contains C: 0.15 to 0.6%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.0%, and Al: 0.01 to 0.1% in weight proportions. , further Mo:0.
05 to 0.2% Nb: 0.01 to 0.1% V: 0.01 to 0.1% of one or more types, and the balance is Fe and unavoidable impurities. During pipe rolling, or after hot pipe rolling, Ac
_550 after being heated and hardened to 3 points or more
A method for producing a steel pipe for thermal wells with a low creep deformation rate, characterized by tempering at a temperature of ℃ or higher to Ac_1 point. (2) Contains C: 0.15 to 0.6%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.0%, and Al: 0.01 to 0.1% in weight proportions. , further Mo:0.
Contains one or more of the following: 05-0.2% Nb: 0.01-0.1% V: 0.01-0.1%, and further contains Cr: 0.1-1.0%, or Ti: 0.005~0.07% and B: 0.0007~0
．． Steel containing one or both of 003% and the remainder consisting of Fe and unavoidable impurities is subjected to hot pipe rolling, or is further heated and quenched to Ac_3 point or higher after hot pipe rolling. A method for manufacturing a steel pipe for thermal wells with a low creep deformation rate, characterized by tempering at a temperature of 550°C to Ac_1 point after treatment.