JPS5844726B2 - Method for manufacturing high-strength ERW steel pipes for oil wells with excellent hydrogen embrittlement resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-strength electric resistance welded steel pipes for oil wells, which are mainly used as steel pipes for sour oil wells and have excellent hydrogen embrittlement resistance and a strength level of API standard N-80 class or higher. It is.

Conventionally, oil or gas wells (i.e., sour oil wells, sour gas wells, hereinafter abbreviated as sour oil wells) are used to extract oil or natural gas containing a large amount of hydrogen sulfide.

) Seamless steel pipes made of low-alloy steel or special alloys and resistant to hydrogen embrittlement are used for the casings and tubing in the sour systems.

In the case of ERW steel pipe, it is thought that it is used in some areas (probably in less severe sour oil wells).

) The only known use is steel pipe for sour oil wells with stiffness regulations.

Hydrogen embrittlement in the present invention refers to sulfide stress corrosion cracking, which has been known as sulfide stress corrosion cracking of steel materials in environments containing H2S, unlike hydrogen-induced cracking, which has become a problem in oil and natural gas line pipes in recent years. It is something that is
This is referred to as hydrogen embrittlement resistance to clearly distinguish it from hydrogen-induced cracking resistance.

This distinction is also clearly stated in, for example, Japanese Patent Laid-Open No. 50-97517.

Here, conventional knowledge regarding sulfide stress corrosion cracking (hydrogen embrittlement in the present invention) will be summarized.

This is, for example, Tetsu to Hagane No. 54 (1968) No. 5 R6
10 contains an explanation regarding ``sulfide corrosion cracking in high-strength steel,'' and part of the gist is as follows.

"Cracking has been known since about 1940 as sulfide stress corrosion cracking or hydrogen embrittlement cracking.

This is a fracture that exhibits a brittle fracture surface in a corrosive environment containing H2S and under conditions where stress is present in the steel material.

It is known that as the strength level of steel increases, its susceptibility to cracking increases.

It is known that the influence of alloying elements on sulfide stress corrosion cracking of oil well steel pipes (we estimate that all of these relate to seamless steel pipes) having APIN-80 class strength is known. This means that ■ Mn content of 1.65% or more is harmful ■ Ni is harmful ■ Cr
It is known that the addition of +Tt +Vr B is effective in preventing cracking.

Although there are various theories regarding the influence of the metal structure in this case, it is generally said that the quenched and tempered structure is better than the sintered structure.

Furthermore, conventional knowledge suggests that the hydrogen embrittlement resistance of hardened and tempered steel is affected by hardness, and the lower the hardness, the more difficult it is to break.

(T., M. Swanson and J., P., Tr.
almer: MaterialsProtecti
on & Performance, Vol. 11
.

Jan, (1972) P, 36-38) The above findings were obtained regarding seamless steel pipes, and do not relate to electric resistance welded steel pipes having welded portions as in the present invention.

As a prior art related to the present invention, "Method for manufacturing high-tensile resistance-welded steel pipes" by the present inventors (Japanese Patent Application No. 50-783)
No. 77 and Japanese Patent Application No. 50-91232).

Their summary is as follows. First, the special request was made in 1977.
No. 8377 is C:O, 15-0.30%t Mn≦1
．． 5%, Si<0.5%, P≦0.03%, S≦0.0
3%+'l'i≦0.03%, B: 0.0003-0.
0025%, N≦o, ooso%, remaining sol by adjusting the degree of deoxidation, A7゜ balance Fe and unavoidable impurities are used to make an ERW steel pipe by ERW welding, and then the steel pipe is sintered. Tensile strength is 65kg/rm by applying heating and tempering treatment! This is a method of manufacturing the above-described high-tensile resistance welded steel pipe.

Furthermore, Japanese Patent Application No. 1983-91232 has C: 0.06 to 0.
25%+□Mn≦1.5%, Si<0.5%, P<0.
03%, S≦0.03%, Ti≦0.03%, B:00
OOO3~0.0025%, N<0.0080%, in addition to the components, Ni≦1.0%+Cr≦1. o%.

One or more of Mo≦0.8%, ■≦0.2%, Nb≦0.2% is used as a component, and by adjusting the degree of deoxidation, remaining sol, Al, remaining Fe and unavoidable A method for manufacturing a high-tensile resistance welded steel pipe with a tensile strength of 75 kg/ym1 or more by using a steel plate made of material containing impurities and making it into an resistance welded steel pipe by electric resistance welding, and then subjecting the steel pipe to quenching and tempering treatment. It is.

The above two inventions relate to a "method for manufacturing high-tensile resistance welded steel pipes" and do not take into account hydrogen embrittlement resistance.

The present invention is based on the results obtained through intensive research on improving the hydrogen embrittlement resistance of ERW steel pipes, and relates to a high-tensile ERW steel pipe with excellent hydrogen embrittlement resistance and a method for manufacturing the same. The main point is the weight concentration, C: 0
．． 06-0.35%.

Si<0.50%, Mn<1.6%, P≦0.0
40%.

S≦0.010%, Ti≦0.040%, B: 0.00
01-0.0025%, N≦o, ooso%, Cu:0
．． 25-0.40%, Al≦0.1%, and T
Regarding i and N, if the N concentration in the steel is 0.0055% or more and ooso% or less, 0.040%≧[%
Ti) ≧3,42
If it is less than %, 0.040%≧[%Ti]≧10
．． 5
[%Ti]≧o, ooo% is satisfied, and Ca:
0.001~0.1%+ REM (Rare Ear
thMetals): 0.005-0.1% 1
or two species, and the weight (concentration) ratio is Ca/
S≧0.5゜REM/S≧1.0, and the remaining part is substantially made of Fe to produce an ERW steel pipe, and the ERW steel pipe is heated to a temperature higher than the austenitizing temperature determined by its chemical composition. A high tensile resistance welded steel pipe for oil wells having excellent hydrogen embrittlement resistance and a tensile strength of 65 kg/m4 or more, which is quenched at a temperature of 1100°C or lower for 770 degrees and tempered at a temperature of 500°C or higher and Ac3 or lower. This is the manufacturing method.

The present invention will be explained in detail below.

First, as a result of various studies, the present inventors have found that the hardenability of the ERW welded bond part (hereinafter abbreviated as "bond part") of quenched and tempered ERW steel pipes containing B can be improved to achieve the same level as that of the base material. succeeded in doing so.

In other words, in order to ensure hardenability, it is necessary for solid solution B to exist in steel, and in the first place, in order to ensure sufficient hardenability for steel having the component threads related to the present invention, it is necessary to have solid solution B in steel. In order to secure the amount of solid solution B required for
All of the N in the steel is precipitated as TiN, thereby preventing a decrease in the amount of solid solution B due to BN precipitation.

However, in the bond part of conventional ERW steel pipes, the decarburization reaction and oxidation reaction during ERW welding cause a decrease in C concentration and Ti concentration in the steel, and the hardenability of the bond part is lower than that of the base metal. The actual situation was that it was significantly lower than that of .

As a result of conducting various studies to compensate for this drawback, the present inventors discovered that it is possible to ensure bond hardenability by regulating the Ti and N concentrations in the steel, and The following results were obtained as the appropriate steel composition range.

That is, ■ o, oo when the N concentration in steel is 0.0055% or more.
If it is less than so%, 0.040% [%Ti)≧
3,42X(%N)+0.0022% (where 0 indicates the weight concentration of the element within 0 in the steel).

(below), ■ 0.0 when the N concentration in steel is 0.0035% or more
If it is less than 0.055%, 0.040%≧[%Ti
)≧10.5X(%N)-0,0368%,
■0.0 if the N concentration in the steel is less than 0.0035%.
040%≧[%Ti]≧o, ooo%, and the range is shown in the diagram as shown in Figure 1.The chemical composition range of the added elements in the steel should be within the range shown in Figure 1. It has been found that the difference in quality between the bond part and the base metal part is greatly reduced, and as a result, it greatly contributes to suppressing corrosion of the bond part and significantly improves hydrogen embrittlement resistance.

Additionally, Ca: 0.001-11%, REM:
By containing one or two types of 0.005~Q, 1%, and setting the weight ratio of Ca/S2O,5, REM/S≧1.0, welding that occurs during welding that is unique to ERW steel pipes. The weld bond has excellent hydrogen embrittlement resistance, which is almost at the same level as that of the base metal, by preventing the sharpening of the tip of inclusions that follow the metal flow near the weld bond. We have succeeded in manufacturing high-tensile resistance welded steel pipes for oil wells with excellent hydrogen embrittlement.

Seamless steel pipes conventionally used in sour oil wells are generally more expensive than ERW steel pipes, and the ability to use inexpensive ERW steel pipes by the method of the present invention is a significant industrial contribution. It is.

Next, the reason for limiting the composition of each component and the heat treatment temperature in the present invention will be explained.

C is an element necessary to ensure the strength of the steel material together with other alloying elements, and if it is less than 0.06, the necessary strength cannot be obtained and weld defects will occur, so it is set to 0.06% or more.

Furthermore, if the C concentration exceeds 0.35%, weldability and workability deteriorate.

Therefore, the C concentration is set to 0.06 to 0.35%.

Mn and Si are important elements for maintaining the integrity of the welded joint, and are also important for ensuring strength.

The upper limit of Mn is 1.60% from the viewpoint of weldability.

Si is 0.50% because it deteriorates weldability and heat resistance.
is the upper limit.

Mn/Si is desirably about 3 to 10 from the viewpoint of preventing welding defects.

In addition, from the viewpoint of hydrogen embrittlement resistance, it is desirable that the Mn concentration is low, and exhibits excellent properties particularly when it is 0.5% or less.

In this case, the Si concentration must be particularly strictly controlled, and MrL
It is necessary to ensure that /si is 3 to 10 to prevent welding defects.

As is well known, P and S are elements that significantly impair toughness and ductility, and the smaller the amount, the better. However, from the perspective of hydrogen embrittlement resistance, S is particularly harmful, and the upper limit should be set at 0.
．． 010°C.

The upper limit of P is 0.040%.

B is an element added for the purpose of improving the hardenability of steel and is 0.0
If it is less than 0.001%, no improvement in hardenability can be expected;
,0025% or more causes surface flaws and toughness deterioration.

Therefore, the B concentration is set to 0.0001 to 0.0025%.

Since the hardenability improving effect of B is impaired by the presence of N, Ti is added for the purpose of fixing N as TiN.

If the Ti concentration as an additive exceeds 0.04%, quality defects such as occurrence of surface flaws on the steel material and reduction in machinability will occur.

Therefore, the Ti concentration is set to 0.04% or less.

N is usually 0.0010-0.00 even if you keep it at a minimum.
About 20% is unavoidably present, and even without special addition 770, it may be present up to about o, ooso%.

In particular, the upper limit of the N concentration is o, oo in the sense of not adding calories.
So%, but the lower the N concentration, the more desirable it is from the viewpoint of improving hardenability.

Therefore, although it is physically impossible, Oppm is the most desirable state.

As described in detail above, the Ti and N concentrations need to be within the composition range shown in FIG. 1 in order to ensure hardenability of the pound part.

Cu needs to be at least 0.25% to obtain the effect of inhibiting corrosion and improving hydrogen embrittlement resistance.

Moreover, in terms of electric resistance weldability, if it exceeds 0.40%, difficulties arise and welding becomes difficult.

Therefore, the Cu concentration is set to 0.25 to 0.40%.

If A7 exceeds 0.1%, the quality of the steel will deteriorate.

REM and Ca are intended to prevent inclusions along the metal flow near the bond part during electric resistance welding from becoming sharp.
The minimum concentrations required to achieve this objective are 0.005% for REM and 0.001% for Ca.

Further, even if REM is added in an amount exceeding 0.1% and Ca is added in an amount exceeding 0.1%, no increase in the effect is obtained, and on the contrary, difficulties in manufacturing such as addition techniques increase.

In addition, in order to meet the purpose of preventing sharpening, REM/S
≧1.0. It is necessary that Ca/S≧0.5.

It goes without saying that REM, Ca, and other elements may be added in appropriate combinations depending on the toughness, ductility, or strength required of the steel pipe.

The reason why the heating temperature during quenching of the electric resistance welded steel pipe is set to be higher than the austenitizing temperature determined by its chemical composition is as follows.
This is because rapid cooling from austenite is essential for quenching.

The reason why the isotropic solar temperature is set to 1100° C. or lower is to prevent coarsening of austenite crystal grains and prevent deterioration of hydrogen embrittlement resistance due to coarsening of crystal grains.

The reason why the tempering temperature of the ERW steel pipe is set to 500°C or higher is that below 500°C, the steel is insufficiently tempered and its hydrogen embrittlement resistance is low, and sufficient hydrogen embrittlement resistance is achieved only at temperatures above 500°C. It's for a reason.

The reason why the tempering temperature is set to Ac 3 or lower is that at AC 3 or higher, the structure of the steel changes and the hydrogen embrittlement resistance decreases.

Here, prior to a detailed explanation of the present invention based on examples, a hydrogen embrittlement test will be outlined.

The test method for evaluating the hydrogen embrittlement resistance of steel is, for example, DCB.
Various methods are known, such as testing, constant load tensile testing, 3-point bending tests, and 4-point bending tests, but when the purpose is to evaluate the welds of steel pipes, especially welded steel pipes, the CIJ song test is considered to be optimal.

The CIJ song test has the feature that a test piece can be cut out from a steel pipe in its original shape without applying any external force or deformation, and the test can be conducted under stress conditions close to the state in which the steel pipe is in use.

Regarding the CIJ song test, various test methods with different details are known, but the present inventors believe that the test method shown in Table 1 and Figure 2 is the most widely and commonly practiced. This test method was used to evaluate the hydrogen embrittlement resistance of the base metal and welded parts of steel pipes. , which measures the time until cracking occurs.

Next, a general explanation regarding the hydrogen embrittlement resistance of steel pipes will be given, followed by a detailed explanation of the present invention by showing examples of the present invention.

Various studies have been conducted on the hydrogen embrittlement resistance of seamless steel pipes, and as mentioned above, much knowledge has been obtained.

However, we believe that the level of hydrogen embrittlement resistance of high-strength ERW steel pipes has not yet been generally clarified.

In order to clarify the level of hydrogen embrittlement resistance of general high-tensile resistance welded steel pipes, the present inventors conducted the above-mentioned CIJ song test (hereinafter simply referred to as the C-ring test) on conventionally known high-tensile resistance welded steel pipes. ) was carried out.

The results are Comparative Examples 1 and 2.3 in Tables 2 to 4.

As is clear from the above, the hydrogen embrittlement resistance of high-strength electric resistance welded steel pipes is as follows: (1) The higher the yield point, the shorter the time until cracking occurs, and the rate of change is relatively large.

(2) The hydrogen embrittlement resistance of the welded part (ERW weld bond part) is significantly inferior to that of the base metal part, and the time until cracking occurs is 172 times shorter than that of the base metal part.

It has the following characteristics.

Note that Comparative Example 3 is a material with a low Mn concentration of about 0.5% in steel, and has relatively good hydrogen embrittlement resistance.

Next, Examples of the present invention are shown in Tables 2 to 4.

Example 1 is a steel pipe in which the C concentration in the steel is relatively low at 0.12%, and the yield point is 63.8 kg/mi after induction quenching and induction heat tempering.

■Ti and N concentrations, which are the basic constituents of the present invention, are the first
Included in the region shown in the figure; ■ Contain a predetermined amount of Ca or REM; ■ Contain a predetermined amount of Cu. Manufactured under almost the same conditions as Example 1 and with the same level of yield. Comparative material with points is Comparative Example 1
Comparing the CIJ song test results for both, it is clear that in Example 1, the hydrogen embrittlement resistance of both the base metal part and the welded part is greatly improved.

Example 2 has a steel C concentration of 0.25%, and Example 3 has a steel C concentration of 0.24% and a steel Mn concentration of 0.5.
3%.

It is clear from Example 3 that when the Mn concentration in the steel is low, a high-tensile resistance welded steel pipe having extremely excellent hydrogen embrittlement resistance can be obtained.

Comparative examples other than the present invention having similar chemical compositions and manufacturing methods to those of Examples 2 and 3 are Comparative Examples 2 and 3, respectively.

Example 4 is an example in which the C concentration in the steel is 0.33%.

Further, Comparative Examples 4 and 5 show examples in which one part of the three basic constituent requirements of the present invention was satisfied but one part was not satisfied.

The effects of the present invention are clear from the above Examples and Comparative Examples, and the industrial contribution of the present invention is very large.

[Brief Description of the Drawings] Figure 1 is an explanatory diagram showing the range of Ti and N concentrations in the steel necessary to ensure the hardenability of the bond part of the present invention and obtain good hydrogen embrittlement resistance. The figure is an explanatory diagram of a CIJ song specimen.

Claims (1)

[Claims] 1. C: 0.06 to 0.35%ysjt in terms of weight concentration
≦0.50%+Mn:≦1.6%, P≦0.040
%, S≦0.010%, Ti<:0.040%, B:
0.0001-0.0025%, N<0.0080%
, Cu: 0.25-0.40%, A7≦0.1%, and the N concentration in the steel is 0.00 for Ti and N.
o if 55% or more, 0.0 if ooso% or less
40%≧[%Ti)≧3.42X(%N)+0.00
22% and the N concentration in the steel is 0.0035% or more.
．． If it is less than 0.055%, 0.040%≧[%T
i]≧10.5X(%N)-0,0368%,
0.0 if the N concentration in steel is less than 0.0035%
40%≧[%Ti)≧o,ooo%, and further Ca20.001~0.1%, REM (Rare
Earth Met-als): 0.005~0
．． The remainder containing 1% of one or two types and having a weight (concentration) ratio of Ca/S≧0.5゜REM/S≧1.0 is electrolyzed using a steel material consisting essentially of Fe. Hydrogen embrittlement resistance obtained by manufacturing a welded steel pipe, heating the electric resistance welded steel pipe to a temperature above the austenitizing temperature determined by its chemical composition and below 1100°C, quenching, and tempering at a temperature above 500°C and below AC3. A method for manufacturing a high-tensile resistance-welded steel pipe for oil wells having an excellent tensile strength of 65 kg/mA or more.