JPS60238418A - Manufacture of sucker rod for wet environment containing gaseous carbon dioxide - Google Patents

Abstract

PURPOSE:To obtain a sucker rod for an oil well having superior resistance to corrosion and corrosion fatigue by heat treating a steel contg. prescribed percentages of C, Si, Mn, P, S, Cr and Sol.Al at a prescribed temp. CONSTITUTION:A steel contg., by weight, 0.1-0.3% C, 0.1-0.8% Si, 0.3-1.2% Mn, <=0.025% P, <=0.01% S, 8-15% Cr and 0.001-0.05% Sol.Al is refined. The surface of the steel is subjected to shot blasting, and the steel is quenched after heating in a carburizing atmosphere at 900-1,000 deg.C. The steel is then tempered at 600-700 deg.C and subjected to shot peening.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a sucker rod that has excellent corrosion resistance in a humid carbon dioxide environment.

More specifically, the present invention relates to a method for producing a sucker rod for oil wells that has excellent corrosion resistance and corrosion fatigue resistance in a humid carbon dioxide environment.

Prior art and its problems Sucker rods for oil wells are subjected to repeated stress during use, so corrosion fatigue resistance is important for corrosion resistance during use. Particularly in a wet carbon dioxide atmosphere, general corrosion and local corrosion are severe, and conventional API standard products cannot be used satisfactorily.

It has been found from experience with steel pipes for oil wells, such as casings and tubing, that the use of high Cr steel is effective against corrosion in such a humid carbon dioxide environment. Since the oil well environment in which the sucker rod is used is relatively low temperature, steel containing 9 to 13% by weight of Cr is used as the material in consideration of economic efficiency. However, as mentioned above, corrosion fatigue resistance is an important property for sucker rods because they are subjected to repeated stress unlike oil country tubular goods, and they are simply made of 9 to 13 Cr.
Even if steel is used, sufficient performance cannot be obtained.

OBJECTS OF THE INVENTION The present invention aims to solve the problems of the prior art mentioned above.

That is, an object of the present invention is to provide a method for economically manufacturing a sucker rod having excellent corrosion resistance and corrosion fatigue resistance in a humid carbon dioxide environment by combining optimal steel composition and heat treatment and other processing conditions. do.

Structure of the Invention In order to achieve the above object, according to the present invention, C:0.
10-0.30% by weight, Si: 0.10-0.80% by weight, Mn: 0.30-1.20% by weight, P: 0.025
S: 0.010 wt% or less, Cr: 8.0 to 15.0 wt%, Sol, 81: 0.001 to O, Q 50 wt% or less, the remainder being substantially Fe and When carrying out the final heat treatment for steel containing unavoidable impurities, the surface is shot blasted, heated to a temperature range of 900 to 1000°C in a carburizing atmosphere, and then quenched.
Provided is a method for producing a sucker rod for oil wells containing wet carbon dioxide gas, which is characterized by tempering at 0 to 700°C and further subjecting the surface to shot peening treatment. That is,
The present inventors have discovered that in a humid carbon dioxide environment, C'
We obtained the knowledge that the concentrated coating plays an important role in corrosion resistance and corrosion resistance fatigue properties, and using the following three items as indicators, 9 to 13C
We have developed a method for manufacturing sucker rods for oil wells, which can be suitably used in humid carbon dioxide environments, from RI.

■Concentrating Cr on the steel surface through shot blasting and austenitization before quenching, ■Performing quenching heating in a carburizing atmosphere to prevent the formation of a decarburized layer on the surface during quenching, ■Surface shot after tempering The reasons for limiting the constituent elements of the method of the present invention, which involve controlling the surface properties by peening, will be individually explained below.

(1) Optimization of steel composition Cr: Cr is an extremely effective element for preventing corrosion in a humid carbon dioxide environment, and if it is less than 8% by weight, sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 15% by weight, toughness and hot workability deteriorate.

C: C is an effective element for ensuring strength, and 0.10% by weight or more is required to obtain the strength required for a sucker rod. Moreover, if it is less than 0.10% by weight, ferrite will precipitate during hot rolling and the surface quality will deteriorate. On the other hand, if it exceeds 0.30% by weight, toughness and hot workability will deteriorate significantly. Usually 0.15
~0.25% by weight is desirable.

Sl: Si is added as a deoxidizing agent, and must be added in an amount of 0.10% by weight or more to ensure the cleanliness of the steel.

However, if a large amount of Sl is contained, the toughness and workability will be deteriorated, so the content must be 0.80% by weight or less.

Mn: Mn needs to be added in an amount of 0.30% by weight or more to ensure hardenability, strength, and toughness. On the other hand, if it exceeds 1.20% by weight, toughness deteriorates, segregation increases, and hydrogen embrittlement is more likely to occur, so it is set at 1.20% by weight or less.

P: Since P also promotes segregation and tends to cause troubles such as hydrogen embrittlement, it is necessary to keep the content to 0.025% by weight or less.

S: S increases nonmetallic inclusions and prevents local corrosion, so it needs to be kept at 0.010% by weight or less.

A1°A1 is added in an amount of 0.001% by weight or more for deoxidation. However, if it is contained in a large amount, the toughness will deteriorate, so 0.0
The content shall be 50% by weight or less.

(2) Heat treatment and other manufacturing conditions (a) Hardening and shot blasting treatment before hardening 9~
The carbon dioxide corrosion resistance of 13Cr steel is due to the Cr produced by corrosion.
This is due to the formation of a coating on the a-oxidized surface, and the higher the degree of Cr in the steel, the more Cr is concentrated, and the corrosion resistance improves. However, since sucker rods are subjected to repeated stress,
There is a high possibility that the surface coating will be damaged, and in order to improve the repairability of the surface coating, a higher Cr content is required than in oil well steel pipes. However, considering economic efficiency and hot workability, the present inventors investigated a method of enriching Cr on the steel surface, and found that after cleaning the surface by shot blasting, the austenitizing temperature It was found that heating to 100% was effective. By adopting this method, corrosion resistance and corrosion fatigue resistance in a humid carbon dioxide environment were greatly improved.

Regarding the quenching temperature, heating to 900° C. or higher is required to obtain complete austenitization in consideration of segregation.

On the other hand, if the temperature exceeds 1000°C, the austenite grains become coarse and the toughness deteriorates.

Furthermore, it is important that the heating atmosphere be a carburizing atmosphere to prevent the formation of a decarburized layer. The atmosphere may be adjusted so that the carbon activity in the atmosphere is greater than the carbon activity in the steel, and may be carried out by any known method.

(b) Tempering Treatment Tempering is performed to adjust the strength required for a sucker rod. If the temperature is lower than 600°C, the strength will be high, but hydrogen embrittlement will easily occur. On the other hand, since there is a risk that the segregated portions may undergo transformation at temperatures above 700°C, tempering was carried out at 600 to 700°C.

(C) Jut peening treatment after tempering Shot peening treatment of the surface produces compressive residual stress on the surface, improves surface roughness, and improves corrosion fatigue properties, so shot peening treatment is performed.

Hereinafter, the steel of the present invention and the method thereof will be explained using Examples, but it goes without saying that these Examples do not limit the technical scope of the present invention.

Example A sucker rod was manufactured by treating the steel used according to the method of the present invention shown in Table 1 (hereinafter referred to as "invention steel") and API standard D grade steel according to the method of the present invention and the conventional method. did.

Here, the method of the present invention consists of steel melting, hot rolling, upsetting, shot blasting, quenching after heating in a carburizing atmosphere, tempering and shot peening, and the quenching and tempering temperatures are As shown in Table 2.

On the other hand, the conventional method consists of steel melting, hot rolling, upsetting, quenching, tempering, and shot peening, and the quenching and tempering temperatures are as shown in Table 2.

The manufactured sucker rod is A inch (12.7mm)
It was the size of Corrosion resistance was evaluated by corrosion weight loss and corrosion fatigue -1 property.

Furthermore, the corrosion fatigue life test was conducted in CO2 at 80°C and 30 atmospheres, with a maximum stress of 40 ksi and a minimum stress of 20 ksi.
This was carried out by repeatedly applying stress using a oscillator tester at a cycle number of 0 cpm to measure the life at break.

As shown in the test results in Table 2, the 9-13 [:r steel used according to the invention has a low corrosion rate, and when the steel according to the invention is treated according to the steps of the method of the invention, the corrosion fatigue life is also significantly improved. be done.

Therefore, the subcar rod manufactured according to the method of the present invention can be suitably used in a harsh humid carbon dioxide gas environment where conventional sucker rods made of D grade steel of API standard cannot withstand use.

Effects of the Invention The present invention has succeeded in providing a sucker rod for oil wells that has excellent corrosion resistance and corrosion fatigue resistance and can be suitably used in a humid carbon dioxide environment.

In the present invention, 9 to 13 Cr steel is shot blasted before quenching and heated in a carburizing atmosphere.
The gist is that a r-concentrated surface coating is formed to improve corrosion resistance and corrosion fatigue resistance.

Claims (1)

[Claims] C: 0.10-0.30% by weight, Si: 0.10-0.80% by weight, Mn: 0.30-1.20% by weight, P: 0.025
Weight % or less, S: 0.010 weight % or less, Cr: 8. O~15.0% by weight, Sol, Al
: 0.001 to 0.050% by weight or less, with the remainder substantially consisting of Fe and unavoidable impurities, and in the final heat treatment, the surface is shot blasted and then heated at 900 to 1000°C. A method for producing a sucker rod for oil wells containing wet carbon dioxide gas, which comprises heating and quenching in a carburizing atmosphere within a temperature range, then tempering at 600 to 700°C, and further subjecting the surface to shot peening treatment.