JPS6199656A - High strength welded steel pipe for line pipe - Google Patents

Abstract

PURPOSE:To obtain a high strength welded steel pipe for a line pipe having superior corrosion resistance as welded by adding specified percentages of C, Si, Mn, P, S, sol. Al, Ni, Cr, Cu, Mo and W to Fe. CONSTITUTION:A steel pipe having a composition consisting of, by weight, <=0.02% C, <=1% Si, <=2% Mn, <=0.03% P, <=0.01% S, <=0.3% sol. Al, 27-40% Ni, 18-25% Cr, 0.3-3% Cu, <=5% Mo and/or <=10% W, and the balance Fe with other inevitable impurities and satisfying equations Cr (%) + 10 Mo (%) + 5 W (%) >= 40% and 2% <= Mo (%) + 1/2 W (%) <= 40% is manufactured. The steel pipe is suitable for use as a pipeline for petroleum or natural oil.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to the transportation of petroleum or natural gas containing corrosive components such as hydrogen sulfide, carbon dioxide gas, and chlorine ions, as welded. etc. (below)

The present invention relates to a high-strength welded steel pipe that exhibits excellent corrosion resistance, particularly excellent stress corrosion cracking resistance, when used as a line pipe in an H2S-Co2-C) environment.

[Conventional technology]

Generally, line pipes exposed to the H2S-Co2-ci-3Jl environment are made of welded steel pipes made from, for example, austenitic stainless steel plates, which exhibit excellent corrosion resistance in the environment.

[Problem that the invention seeks to solve]

However, in the above-mentioned welded austenitic stainless steel pipes, carbides precipitate at grain boundaries during pipe manufacturing by welding, and these carbides significantly reduce corrosion resistance. For the purpose of achieving the above, it is necessary to perform solution treatment on the welded steel pipe, and this solution treatment is not only uneconomical, but also
Reduces the strength of welded steel pipes, whose tensile strength is 3
Therefore, it cannot be used for line pipes that require high strength.

[Means for solving problems]

Therefore, the inventors of the present invention, from the above-mentioned viewpoint.

We conducted research to obtain welded steel pipes that have high strength and excellent corrosion resistance in the as-welded state.
(indicates weight %), C: 0.02% or less, si: 1% or less.

Mn: 2% or less %So1. AI: 0.3% or less, Ni: 27-40%, Cr: 18-25%.

Cu: 0.3-3%.

One of MO: 5% or less and W: 10% or less. 2 m.

and, if necessary, 'N: 0.05 to 0.3%, rare earth elements: o, ooi to 0.
．． Section 1, Y: 0.001~o, i 迤, Mg: 0.0
01=0.1%.

Ca: 0.001-0.1%, Ti: 0.01
~0.5%.

The composition contains one or more of the following, and the remainder is Fe and other unavoidable impurities.

Cr (%) + 10 Mo (%) + 5 W (
+ )240%, 2%≦Mo (%) +172W (%)
65%.

In welded steel pipes manufactured from hot-rolled steel sheets that satisfy the assembly bottom conditions of In its as-is state, it exhibits excellent corrosion resistance because there is no grain boundary precipitation of carbides, especially stress corrosion cracking resistance in H2S-C02-Ct environments, and therefore is suitable for use in petroleum, natural gas, etc. that require these properties. They obtained the knowledge that when used as a line pipe, it exhibits excellent performance over a long period of time.

This invention was made based on the above knowledge'(a)
C If the content of the C component exceeds 0.02%, carbides will precipitate at the grain boundaries during 1m welding pipe manufacturing, making stress corrosion cracking more likely to occur. .02%
It was determined as follows.

(bl Si: 81 (it part is an essential component as a deoxidizing component,
If the content exceeds 1%, hot workability deteriorates, so the content t was set at 1% or less.

(c) Mn The Mn component has a deoxidizing effect like the Si component, and even if it is contained up to 2%, it will not have a negative effect on the properties.
% is allowed.

(dl P The P component has the effect of increasing susceptibility to stress corrosion cracking, and this effect appears rapidly when its content exceeds 0.03%, so it is necessary to reduce its content to 0.
．． It was set at 0.3% or less.

(el 5 Sfy has the effect of deteriorating hot workability.

This effect becomes noticeable when the content [1 exceeds 0.01% ft.
% or less.

(fl sol.Al Aj Acid component Like the Si and Mn components, it is a necessary component because it has a deoxidizing effect, but if its content exceeds 0.3% in sol.Al, it will adversely affect the characteristics. Therefore, the content was determined to be 0.3% or less for soJ and AJ.

(g) Ni Ni component has the effect of improving corrosion resistance, especially stress corrosion cracking resistance, but if its content is less than 27%, the desired excellent stress corrosion cracking resistance cannot be secured, and - 40,000
Even if the content exceeds 0%, no further improvement effect on stress corrosion cracking resistance appears, so the content was set at 27 to 40% in consideration of economic efficiency.

(hl Cr The Cr component has the effect of significantly improving corrosion resistance when coexisting with Ni and later Mo and W components, but if its content is less than 18%, the desired excellent corrosion resistance cannot be secured. Therefore, it is necessary to contain 18% or more, but even if the content exceeds 25%, no further improvement effect will be obtained. Therefore, considering economic efficiency, the content should be reduced to 18-25%. It was determined that

(i) Mo1d and W As mentioned above, these components have the effect of improving corrosion resistance when coexisting with Ni and Cr, but even if they are contained in excess of 5% Mo and 10% W, respectively. , H2S-CO2-Cl- with an environmental temperature of 150℃ or less
Since further improvement effects do not appear under the M condition, considering economic efficiency, the content of
O: 5% or less, W: 10% or less.

In addition, one conditional expression regarding the content of Mo and W: Mo (%)
The reason for specifying + L/2 W (%) is that the atomic weight of W is approximately twice that of Mo, and the effect is approximately 1/2, which is equivalent, and this value is less than 2%. In particular, H2S -Co2- (J-
It is not possible to secure the desired corrosion resistance under extreme conditions, and on the other hand, even if this value exceeds 5%, as mentioned above, it will contain substantially unnecessary amounts of Mo and W, which is not economical.
Therefore, the value of Mo (%) + 172 W (%) was determined to be 2 to 5%.

(jl Cu Although the Cu component has the effect of improving corrosion resistance, if its content is less than 0.3%, the desired corrosion resistance cannot be ensured. On the other hand, if it is contained in excess of 3%.

Since hot workability deteriorates, its content is set at 0.3 to 3%.

(The kl N N component has the effect of improving 1st set a and strengthening it by bathing with the base material, so it is included as necessary especially when even higher strength is required. However, if the content is less than 0.05%, the desired strength improvement effect cannot be obtained,
On the other hand, if the content exceeds 0.3%, hot workability will deteriorate, so the content should be adjusted to 0.05 to 0.3%.
%.

(ll Rare earth elements, Y 1Mg, Ca %, and Ti These components have the effect of improving hot workability, so they may be added as necessary when hot working is required under particularly severe conditions. However, the content of rare earth elements: less than 0.001%, Y:O,
less than 0.001%, Mg: less than 0.001%, Ca:
If the content is less than 0.0O1% and Ti: less than 0.01%, the desired effect on hot workability cannot be obtained; 1%1
Mg: 0.1%, Ca: 0.1%, and Ti: 0.5
%, the hot workability tends to deteriorate, so the content of rare earth elements: 0
．． 001-0.1%, Y: 0.001-0.1%,
Mg: 0.001-0.1%, Ca:O, OO1
~0.1%, and Ti: 0.01~0.5%.

@ Cr (%) + 10Mo (%) + 5 W (%
) Ni-Cr-Mo yarn, Ni-Cr-W yarn, and Ni-Or-Mo-W yarn with varying contents of Ni, Cr, Mo%, and W were made from steel and cast. , forged and hot-rolled to obtain a hot-rolled steel plate with a thickness of near m, and then this hot-rolled steel plate is subjected to cold processing 5 during the production of welded steel pipes.
For example, in consideration of U-07 ohming, cold rolling was performed at a working rate of 20%, and a test was performed using this cold rolled steel sheet with dimensions of thickness: 2 mm x width: 10 m x length near 5 u at right angles to the rolling direction. A piece was cut out, and this test piece was saturated with H2S and CO2 using 10 atm H2S and 10 atm CO2 while applying a tensile stress corresponding to 0.2% proof stress using a 4-point bending jig. 20% Na Cl solution (solution temperature 1
A stress corrosion cracking test was conducted by immersing the test piece in 50°C for 1000 hours, and after the test, the presence or absence of cracking in the test piece was observed.Based on this observation result, the inventors independently set a conditional formula: Cr. (%) + 10 Mo (%) + 5
Relationship between W (%) and Ni content 4. Cr (%) + 1
Taking 0 Mo(+) + 5 vv(To) on the horizontal axis,
On the other hand, when Ni (%) was plotted on the vertical axis, it was found that Ni
(%)≧27%, Cr(%)+10Mo(%)+5W(
+) showed the desired excellent stress corrosion cracking resistance in the range of 240%. Based on these results, the lower limit of Ni content was set to 27%, Cr (%) + 10Mo (%) + 5
The lower limit of the content of W (fluent) was set at 40 yen.

In addition, in the welded steel pipe of this invention, B, ISn, Pb1g and Zn are each 0.1g as unavoidable impurities.
% or less will not have an adverse effect on the properties, so the content up to the above upper limit is permissible.

〔Example〕

Next, the welded steel pipe of the present invention will be specifically explained using examples.

After preparing molten steel having the composition shown in Table 1 by a normal melting method, 70t) tax 250 am
It is cast into a flat ingot and then processed at a temperature of:
The plate was forged and forged at 1280°C to a thickness of ~20 mm, and then hot rolled at a hot rolling start temperature of 00°C to a plate thickness of 6.1 m*. A hot-rolled steel plate was used, and the hot-rolled steel plate was then made using the normal U-07 ohming pipe manufacturing method at °C, outer diameter: 406m1 x inner diameter: 394y+
F14 welded steel pipes 1 to 26 of the present invention and conventional welded steel pipes (made of austite stainless steel W4) having dimensions of xX length: 6000 mm were manufactured, respectively.

Next, test pieces for tensile tests and stress corrosion cracking tests were cut out from the resulting welded steels of the present invention [1 to 26] and conventionally welded steel pipes, and tests were conducted, respectively.
The stress corrosion cracking test was conducted under the same conditions as above.
The presence or absence of cracking was observed. These results are shown in Table 2.

Table 2 also shows the observation results regarding the presence or absence of grain boundary precipitation of carbides in the F4 pipes 1 to 26 welded according to the present invention and the conventionally welded steel pipes.

〔Effect of the invention〕

From the results shown in Table 2, the aA welded steel pipes 1 to 26 of the present invention all have a tensile strength of 70 to 9/- or more, and in the bath-contact state, the carbide grain boundaries Since there is no precipitation, it exhibits excellent resistance to stress corrosion and corrosion cracking without the need for bulk treatment.Contrary to this, conventional welded steel pipes have relatively high strength in the as-welded state, but carbide It is clear that this carbide is the cause of the grain boundary precipitation, resulting in poor stress corrosion cracking resistance.

As mentioned above, the welded steel pipe of the present invention has high strength while still in contact with the bath, and it also has high strength under particularly severe H2 conditions.
It shows excellent corrosion resistance in S-Co2-CJ- environment, so
When used as line pipes for oil, natural gas, etc., which require special orders, they exhibit excellent performance over a long period of time.

Claims (4)

[Claims] (1) C: 0.02% or less, Si: 1% or less, Mn: 2
% or less, P: 0.03% or less, S: 0.01% or less, sol. Al: 0.3% or less, N
i: 27-40%, Cr: 18-25%, Cu: 0.3
~3%, Mo: 5% or less and W: 10% or less, and the remainder is Fe and other unavoidable impurities (weight %), and Cr (%) + 10Mo (%) + 5W (%) ≧ 40%, 2
A high-strength welded steel pipe for a line pipe that exhibits excellent corrosion resistance as welded and is characterized by satisfying the following composition condition: %≦Mo(%)+1/2W(%)≦5%. (2) C: 0.02% or less, Si: 1% or less, Mn: 2
% or less, P: 0.03% or less, S: 0.01% or less, sol. Al: 0.3% or less, N
i: 27-40%, Cr: 18-25%, Cu: 0.3
-3%, one or two of Mo: 5% or less and W: 10% or less, and further contains N: 0.05-0.3%, the rest being Fe and others. Cr (%) + 10Mo (%) + 5W (%) ≧ 40%, 2
A high-strength welded steel pipe for a line pipe that exhibits excellent corrosion resistance as welded and is characterized by satisfying the following composition condition: %≦Mo(%)+1/2W(%)≦5%. (3) C: 0.02% or less, Si: 1% or less, Mn: 2
% or less, P: 0.03% or less, S: 0.01% or less, sol. Al: 0.3% or less, N
i: 27-40%, Cr: 18-25%, Cu: 0.3
-3%, one or two of Mo: 5% or less and W: 10% or less, and further contains rare earth elements: 0.001-0.1%, Y: 0.001-
0.1%, Mg: 0.001-0.1%, Ca: 0.0
01 to 0.1%, and one or more of Ti: 0.01 to 0.5%, with the remainder consisting of Fe and other unavoidable impurities (wt%). and Cr(%)+10Mo(%)+5W(%)≧40%, 2
A high-strength welded steel pipe for a line pipe that exhibits excellent corrosion resistance as welded and is characterized by satisfying the following composition condition: %≦Mo(%)+1/2W(%)≦5%. (4) C: 0.02% or less, Si: 1% or less, Mn: 2
% or less, P: 0.03% or less, S: 0.01% or less, sol. Al: 0.3% or less, N
i: 27-40%, Cr: 18-25%, Cu: 0.3
-3%, one or two of Mo: 5% or less and W: 10% or less, and further contains N: 0.05-0.3%, and rare earth element: 0.001-0. .1%, Y: 0.001~
0.1%, Mg: 0.001-0.1%, Ca: 0.0
01 to 0.1%, and one or more of Ti: 0.01 to 0.5%, with the remainder consisting of Fe and other unavoidable impurities (wt%). and Cr(%)+10Mo(%)+5W(%)≧40%, 2
A high-strength welded steel pipe for a line pipe that exhibits excellent corrosion resistance as welded and is characterized by satisfying the following compositional condition: %≦Mo(%)+1/2W(%)≦5%.