JPS6160866A - Steel material for line pipe superior in sour resistance - Google Patents

Abstract

PURPOSE:To obtain the titled material superior in hydrogen induced cracking resistance and sulfide stress corrosion cracking resistance by specifying a compsn. and its relation consisting of C, Si, Mn, Al, P, S, Ca, Ni, Cr, Mo and Fe in said material. CONSTITUTION:The titled material is composed of 0.01-0.25wt% C, 0.010-0.50% Si, 0.70-2.00% Mn, 0.01-0.10% Al, <=0.030% P, <=0.0030% S, 0.0005-0.0050% Ca, further 0.20-3.0% Ni and one or 2 kinds of 5.0% Cr, <=2.0% Mo under >=0.5% Cr + Mo, further if necessary >=one kind among 0.10-0.60% Cu, <=rho@@@@@@@@@00X00'0000'00$rhoBETA@@@@@@@Fe with inevitable impurities and is suitable to submerged arc welded steel 0.10% Nb, <=0.15% V, <=0.10% Zr, <=0.10% Ti, <=0.005% B and the balance Fe with inevitable impurities and is suitable to submerged arc welded steel pipe or electric welded steel pipe, etc.

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to steel materials for line pipes used for transporting crude oil, natural gas, etc.), in which hydrogen-induced cracking and sulfide stress corrosion cracking are particularly problematic. This invention relates to steel materials suitable for submerged arc welded steel pipes or electric resistance welded steel pipes for two-in-vib applications that are used in humid hydrogen sulfide environments, that is, so-called sour environments.

Prior Art In recent years, hydrogen-induced cracking and sulfide stress corrosion cracking have become a problem in line pipes used to transport crude oil and natural gas containing hydrogen sulfide. Countermeasures are being taken.

However, recently, as high-quality oil resources have been depleted, there has been a rapid increase in the development of oil and gas fields with extremely high concentrations of hydrogen sulfide, which had previously been neglected. In order to improve line transportation efficiency, the operating pressure of lines is often increased, and as a result, compared to the conventional environment in which line pipes are used, it is necessary to use harsh environments with low noise values and high hydrogen sulfide pressure. The reality is that as environmental conditions have become more demanding, the requirements for steel materials for line pipes have become more stringent than ever.

By the way, as for the cause of hydrogen-induced cracking (hereinafter referred to as HIC), previous research has revealed that hydrogen generated by a corrosion reaction on the steel surface penetrates into the steel, causing non-metallic inclusions in the steel,
In particular, hydrogen accumulates at the interface between the so-called A-based inclusions such as MnS and the steel base, where stress concentration is likely to occur due to the notch effect at the tip of the inclusion, and gasifies, creating the starting point of cracks, which occur in the segregation area at the center of the plate thickness. It is known that cracks propagate and expand in low-temperature transformed abnormal structures (hereinafter simply referred to as abnormal structures) such as band-shaped martensite and bainite.

In addition, sulfide stress corrosion cracking (hereinafter referred to as SSC), which forms an interlayer at the same time as HIC, is a hydrogen embrittlement phenomenon that occurs when hydrogen generated by a corrosion reaction of steel in an environment containing hydrogen sulfide penetrates into the steel. It is known that metallurgical factors, such as the composition and structure of the steel, and various factors, such as the state of stress applied to the steel, are complexly related to each other.

Therefore, the conventional measures to improve HIC resistance are (1).

The methods shown in (2) and (3) have been adopted or proposed.

(1) Catalyze sulfide inclusions that are the starting point of cracks)
Or, by adding REM (rare earth element), the metal is dispersed and spheroidized, making it difficult to become a starting point for cracks (for example, Japanese Patent Publication No. 54-38568).

(2) A method of reducing the content of Mn, P, etc. and heat-treating rolled semi-finished products to reduce abnormal structures and prevent crack propagation and expansion (for example, JP-A-52-111815) .

(3) A method of reducing hydrogen intrusion into steel by adding elements such as Cu that form a stable film on the steel surface (for example, JP-A-52-111815).

Problems to be Solved by the Invention As mentioned above, in the recent harsh environment, rice fields are close, so even if the conventional method (3) is applied, it is difficult to form a film in which Cu is effective. Traditional method (
3), it was difficult to obtain a sufficient HIC resistance effect. In addition, in such an environment, a large amount of hydrogen enters the steel, so the conventional method (1) is used.

It was difficult to obtain a sufficient HIC resistance effect only with the measure (2). Therefore, in order to sufficiently improve the HIC resistance under the above-mentioned harsh environment, it is considered necessary to reduce the amount of hydrogen penetrating into the steel.

Therefore, this invention provides a steel material for line pipes that reduces hydrogen intrusion into the steel and improves HIC resistance while also having sufficient SSC resistance, that is, a steel material for line pipes with excellent sour resistance. The objective is to provide steel materials.

Means for Solving the Problems The present inventors reduced the penetration of hydrogen into the steel and increased the resistance to I (I).
As a result of various experiments and studies on measures to improve carbon properties, we found that adding Nt is effective in suppressing hydrogen penetration, and that adding 1ccr and/or M at the same time as Ni
It has been found that by adding o, the effect is dramatically increased and the HIC resistance is significantly improved. Also N
There is a concern that the SSC resistance will decrease if C is added, but C
SSC resistance by adding r and/or Mo
It has been found that a steel material with excellent both HIC resistance and SSC resistance can be obtained by preventing a decrease in properties. That is, in this invention, the composite addition of Ni, Cr and/or Mo
This is because it has become possible to obtain a steel material for line pipes that is extremely superior in both HIC resistance and SSC resistance.

Therefore, the steel material for line pipes of the first invention has a C0.0
1-0.25%, Si 0.010-0.50%, M
n0.70-2.00%, AI0. O1~0.10%,
P0.030- or less, 80.0030% or less, Ca 0
．． 0005-0.0050% and 0.20%
Contains more than 3.0% Ni, and further contains 0.5% or more of 5.0% or less Cr and 2.0% or less Mo, with the balance being re. and unavoidable impurities.

Further, the steel material for line pipes of the second invention contains Cu0. L O
~0.60'lr, Nb0.10% or less, V0.15
Ti or less, Zr0.10% or less, Ti0. 10%, B
0. ooss or more selected from the following.

Next, the reason for limiting the components in the steel material for line pipes of the present invention will be explained.

c0. oi ~ 0.25%: If C is less than 0.01%, the strength required for line pipe steel cannot be obtained, and if it exceeds -0.25%, it will not be possible to obtain the welded part of line pipe steel used as welded steel pipe. Since the toughness of t- is impaired, it is limited to a range of 0.01 to 0.25%.

Si0.010~0.50-Si is an element necessary for deoxidation in the normal steelmaking process, and if it is less than 0.010%, there is no deoxidation effect; s
If it exceeds 0%, it will deteriorate the toughness of the steel. oto
-0.50%.

Mn 0.70-2.00%: Calm is an effective element for improving strength, but if it is less than 0.70%, it is difficult to secure the required strength.
If it exceeds 0.0%, the toughness and weldability will deteriorate.
It was set within the range of 70 to 2.00%.

AA! 0. OL~0. -10%: AA' is an element necessary for deoxidation in the normal steelmaking process, and is effective in improving the addition yield of Ca, which is added to improve HIC resistance, but less than 0.01%. However, if it is added in excess of 0.01 to 0.1 O, the crystal grains will become coarser and the material will deteriorate. It was limited to a range of lO%.

P0.030 or less: P is a harmful impurity element, and it also segregates and increases the hardness of the central segregation area, promoting the propagation and expansion of cracks, so it is best to keep the amount as small as possible. Although desirable, it is set to 0.030 inch or less in view of manufacturing cost.

S 0.0030% or less: S is 1 (since it is an element that generates sulfide inclusions that become the starting point of IC, it is desirable to have as little as possible to improve HIC resistance, and it should not exceed 0.0030%. sufficient H resistance.
Since IC properties cannot be obtained, S is limited to 0.0030 or less.

Ca 0.0005-0. OO50%: Ca makes the shape of sulfide inclusions spheroidal, and the sulfide inclusions become f(IC
It is an element that is more effective in suppressing the formation of the starting point of HIC and ensuring HIC resistance than K, and 0.00% S is added to obtain the effect of securing HIC resistance by adding Ca. Even when the S content is extremely low, 0.0005% or less, at least 0.0005% or more is required. Addition of Ca in excess of 0.0005 to 0.000 is likely to increase large inclusions and reduce HIC resistance and hydrogen blistering resistance.
It was limited to a range of 0.050 cm.

Ni more than 0.20 and less than 3.0: Ni is effective not only for improving corrosion resistance and toughness, but also for reducing the amount of hydrogen penetrating into the steel and significantly improving HC resistance. element, and this invention basically! Depends on the required additive elements. I resistance (IC property improvement effect by adding Ni is 0.
If Ni is less than 20%, it cannot be obtained, and on the other hand, adding more than 3.0% of Ni will only increase the cost.
It exceeded 0% and was set in the range of 3.0-.

Cr≦5.0%, Mo≦2.0%, Cr+Mo≧0.5
%: Both Cr and Mo have the effect of improving the corrosion resistance of the steel, reducing hydrogen penetration into the steel, and preventing deterioration of the SSC resistance due to the addition of Ic and Ni. Cr.

Since these effects cannot be obtained if the total amount of Mo is less than 0.5, the total amount of Cr and Mo is set to 0.54 or more. On the other hand, if Cr exceeds 5.0 cm, Mo also increases to 2.0 cm.
If it exceeds 0%, the toughness deteriorates, so Cr is 5%.
．． 0% or less, and Mo was 2.0% or less. Furthermore, Cr.

Either one of Mo may be added alone, or both may be added simultaneously.

In addition to the above-mentioned component elements, in the case of the second invention, Cu,
One or more of Nb, V, Zr, Ti, and B are added. Therefore, the reason for limiting these component elements will be explained below.

Cu0. lO ~ 0.60%: Cu is added in an amount of 0.10% or more to form a stable film on the steel surface in a high-I content environment, improving corrosion resistance and also having the effect of improving HIC resistance. show.

However, if the amount of Cu added exceeds 0.60%, hot workability will be impaired, so it is limited to a range of 0.10 to 0.60.

Nb 0.10% or less: Addition of Nb is effective in improving hardenability and strength, but if added in excess of 0.10%, toughness will decrease, so it is limited to 0.10% or less. .

v0. Below ts, zr0. Below tochi: ■ and Zr
The addition of is also effective in improving hardenability and strength in the same way as adding Nb, but if the content exceeds 0.15% V or 0.10% Zr, the toughness deteriorates, so V should be 0.15% or less.
Zr was limited to 0.10% or less.

Ti: 0.10 mm or less: Ti is effective in improving strength and corrosion resistance, and when it coexists with B, it has the effect of promoting the effect of B. It is desirable to add more than 0.1%, but if it exceeds 0.10%, the toughness deteriorates, so it is limited to 0.10% or less.

80.005% or less: B is an element that improves hardenability, and its effect becomes noticeable at 0.0005% or more, but if it exceeds 0.005%, there is a risk of deteriorating toughness, so B is an element that improves hardenability. 005- or less.

Example In order to clarify that it is possible to produce steel materials with excellent HIC resistance and SSC resistance by adding Ni, Cr, and Mo, Ni and Cr were added to the base of conventional steel with different C levels.
and/or Mo, and some also include Ca, Nb, V, Zr, Ti
, B was added to create the steel of the present invention, and at the same time, a comparative steel outside the composition range of the present invention was created. The chemical composition and mechanical properties of each sample material are shown in Tables 1 and 2. Each sample material was melted according to a conventional method and hot-rolled as a cis slab by continuous casting.

Each of these sample materials was evaluated for HIC resistance and SSC resistance as follows.

In other words, the evaluation of HIC resistance is as follows (1):
The method described in (2) was applied.

(1) A method based on the so-called BP test method. That is, a method in which a sample is immersed in a NACE solution (0,5 thiacetic acid + 5-salt water, saturated at 1 atm of H2S) for 96 hours, and then a cross section of the sample is examined under a microscope to evaluate hydrogen-induced cracking resistance.

(2) A test piece is inserted between the environment side (autoclave side) and the measurement side (hydrogen permeation measurement chamber side), and the hydrogen that enters the test piece steel from the environment side and permeates to the measurement side is ionized. Hydrogen permeation test method using so-called electrochemical permeation method.

In carrying out method (1), three test pieces 1 of each steel type are placed as shown in Figure 2 from a position corresponding to the widthwise center of the continuously cast slab where segregation is considered to be the greatest. Collected. As shown in Figure 3, the HIC resistance was evaluated for each test piece by 3i11? ? 1ff2A,
2E and 2C were examined using a microscope at 10x magnification.

In addition, in the hydrogen permeation test (2), the environment was changed to a NACE l environment and a 5% NaCl aqueous solution/H2S I Oatm environment for 2 seconds, and the amount of hydrogen permeated per unit area during the test period of 100 hours was determined. I looked into it.

On the other hand, needle SSC properties were evaluated using a stress corrosion cracking test using four-point bending. That is, a test piece 4 having a notch 3 as shown in FIG. 4 is prepared, and a four-point bending stress is applied to the test piece 4 using a four-point bending test jig 5 as shown in FIG. After being immersed in NACE solution for 7.20 hours, the presence or absence of cracks was examined.

The above test results are shown in Table 3 (SS resistance according to BP test method)
C property test results), Table 4 (hydrogen permeation test results), and Table 5 (SSC resistance test results by 4-point bending stress corrosion cracking test). In Table 3, step-like cracks are cracks that are continuous in a step-like manner in the thickness direction of the test piece.
The distance from the tip of a crack to the tip of another crack is 0.515
Linear cracks mean those within 0.1 of each other, and linear cracks do not meet the stair-step cracks mentioned above. s means isolated linear cracks separated by more than m.

As is clear from the HIC resistance test results in Table 3, the invention steel (Al-11) has no cracks or only very small cracks, showing excellent HIC resistance. On the other hand, the occurrence of HIC was observed in the comparison steels Al 2 and A13, which have less Nti. Also, even if it contains Ni, the amount of S is 0. It is clear that the HIC resistance is also deteriorated in the case of the comparative steel of L7, which exceeds OO3'16, and the comparative steel of N18, which does not contain Ca.

Furthermore, as is clear from the hydrogen permeation test results in Table 4, N
In both the ACE liquid environment and the H2S 10 a Lm g environment, the steel of the present invention A L = A L l is
As shown in Comparative Copper Genus 12.13 (compared to the case where Ni is not added, the amount of hydrogen permeation is significantly lower. Bacteria 1
The figure shows the hydrogen permeation amount and N1 in steel in the NACEtL environment.
Shows the relationship with quantity. From Figure 1, Ni! It can be seen that when l exceeds 062 inches, the amount of hydrogen permeation decreases significantly.

Furthermore, from the SSC resistance test results in Table 5, it was found that the present invention
-11 all show excellent SSC resistance, but as in Comparative Copper Metals 14 and 15.16 (when the amount of Cr + Mo is less than 0.5%, it is clear that the SSC resistance deteriorates). In the case of comparative steel 417.18, the SSC resistance also deteriorated as the HIC resistance deteriorated.

As is clear from the above experimental results, adding more than 0.2% Ni suppresses hydrogen intrusion into the steel, and at the same time reduces the amount of S to 0.2%. By controlling OO to 30% or less and adding Ca, the HC resistance is significantly improved, and at the same time, C
Excellent SSC resistance can be obtained by adding R and/or Mo in a total amount of 0.5 mm or more.

@Table 2: Mechanical properties of test materials Table 3: HIC resistance test results ◎I am not there, ○I am small, ΔI am x I am large.

Table 4: Hydrogen permeation test results (standard condition) Table 5: Results of SSC resistance test Effects of the invention As is clear from the above explanation, the steel material for line pipes of the present invention has excellent HIC resistance. It was concerned about its sour resistance, which combines good SSC resistance, and therefore, it reliably prevents the occurrence of hydrogen-induced cracking and sulfide stress corrosion cracking even in harsh environments where hydrogen sulfide pressure is high and the field is low. This can improve the reliability of line pipes.

[Brief explanation of drawings]

Figure 1 is a correlation diagram showing the influence of the amount of Ni in steel on hydrogen permeation tK, Figure 2 is a perspective view showing the sampling position of the test piece used in the IC resistance test, and Figure 3 is the HIC resistance test. Fig. 4 is a schematic perspective view showing the shape and dimensions of the test piece used in the SSC resistance test, and Fig. 5 shows the stress application method in the SSC resistance test. It is a schematic front view shown.

Claims (2)

[Claims] (1) C0.01-0.25% (weight%, same below),
Si0.010~0.50%, Mn0.70~2.00
%, Al0.01-0.10%, P0.030% or less,
S0.0030% or less, Ca0.0005-0.005
Contains 0% of Ni, and furthermore contains more than 0.20% of Ni and 3.0% of Ni.
Contains within the following range and 5.0% or less of Cr and 2.0
% or less of Mo in a total amount of Cr + Mo in a range of 0.5% or more, with the remainder consisting of Fe and inevitable impurities.For line pipes with excellent sour resistance. Steel material. (2) C0.01~0.25%, Si0.010~0.
50%, Mn0.70-2.00%, Al0.01-0
．． 10%, P 0.030% or less, S 0.0030% or less, Ca 0.0005 to 0.0050%, and further contains Ni in the range of more than 0.20% and 3.0% or less, and 5 Contains one or both of .0% or less Cr and 2.0% or less Mo in a range where the total amount of Cr+Mo is 0.5% or more, and further includes Cu0.10 to 0.60% and Nb0.1
0% or less, V0.15% or less, Zr0.10% or less, T
For line pipes with excellent sour resistance, characterized by containing one or more selected from i0.10% or less and boron 0.005% or less, with the remainder consisting of Fe and unavoidable impurities. Steel material.