JPS6199660A - High strength welded steel pipe for line pipe - Google Patents

Abstract

PURPOSE:To obtain the titled steel pipe exhibiting superior corrosion resistance in as welded state, by incorporating specified ratios of C, Si, Mn, P, S, sol. Al, Ni, Cr, Cu, Mo, W, Ti, Nb to Fe. CONSTITUTION:Alloy contg. by weight, <=0.07% 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, one or 2 kinds among <=5% Mo and <=10% W, one or 2 kinds among <=1% Ti and <=1% Nb and the balance Fe with inevitable impurities, further satisfying Cr % + 10 Mo % + 5 W % >= 40%, 2% <= Mo % + 1/2 W % <= 5%, Ti % / C % >= 5, Nb % / C % >= 5, is prepared, to manufacture welded steel pipe.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is applicable to transportation of petroleum and natural gas containing corrosive components such as wet hydrogen sulfide, carbon dioxide gas, and chlorine ions, etc., while welding. (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 a H,3-c'o2-C1- environment.

[Conventional technology]

In general, line pipes exposed to the HaS-C02-CL environment described above use welded steel pipes made from, for example, austenitic stainless steel plates, which exhibit excellent corrosion resistance against the environment.

[Problem that the invention seeks to solve]

However, in the above welded austenitic stainless steel pipe, when manufacturing the pipe by welding.

Carbides precipitate at grain boundaries, and since these carbides significantly reduce corrosion resistance, it is necessary to perform solution treatment on the welded steel pipe in order to dissolve them into the base material and improve corrosion resistance. This solution treatment is not only uneconomical, but also reduces the strength of the welded steel pipe, whose tensile strength is reduced to less than 30 to 4t/-, thus making it possible to achieve high strength. It cannot be used for line pipes that require

[Failure to solve the problem]

Therefore, from the above-mentioned viewpoint, the present inventors conducted research to obtain a welded steel pipe that has high strength and excellent corrosion resistance in an as-welded state.
%).

C: 0.07 inches or less, Si: 1% or less.

Mn: 2% or less, sot, At: 0.3%
below.

Ni: 27-40%, Cr: 18-25%
.

Cu: 0.3-3chi.

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

One or two of T1: 1% or less and Nb: 1% or less.

Contains and further if necessary.

N: O05-03%, rare earth elements: O,001-01%
.

Y: 0.001-01%, Mg: 0.001-0.1
%.

Ca: 0.001 to 0.1%, contains one or more of the following, with the remainder consisting of Fe and other inevitable impurities, and.

cr(1+10Mo(%9+5W(%)≧40%,2
Chi≦Mo(proboscis+l/2 W (%)≦5chi.

Tl(@/C(%)≧5.Nb(%)/C(%:
In welded steel pipes manufactured from hot-rolled steel sheets that satisfy the composition condition of ≧5°, high strength of 60 Ksi (42.2 kg/ij) or more at the yield point is ensured by hot working during the production of hot-rolled steel sheets, and carbide grains in the as-welded state,
Excellent corrosion resistance, especially H2S-co, as there is no interfacial precipitation.
Shows excellent stress corrosion cracking resistance under w-Ct environment.

Therefore, we have found that when used as line pipes for oil and natural gas, which require these characteristics, they exhibit excellent performance over a long period of time.

This invention has been made based on the above findings, and the reason why the composition range and composition conditions of the welded steel pipe are limited as described above will be explained below.

(a) CC If the content of C component exceeds 0.07%, Ti
The content was determined to be 0.07% or less because the fixation by Nb becomes insufficient and carbides precipitate at grain boundaries during welding, making stress corrosion cracking more likely to occur at grain boundaries.

(b) 5i The Si component is an essential component as a deoxidizing component.

If the content exceeds 1%, hot workability deteriorates, so the content 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.
It is permissible to contain up to

(d) P The P component has the effect of increasing susceptibility to stress corrosion cracking, and this effect becomes apparent rapidly when its content exceeds 0.03 g.

Its content was set at 0.03% or less.

(e) S The S component has the effect of deteriorating hot workability (1), and this effect becomes noticeable when its content exceeds 1%, so its content is reduced to 0.01%. It was determined as follows.

(r) sot, At The M component is a necessary component because it has a deoxidizing effect like the Si and Mn components, but its content is sot, Al4
If it exceeds 0.03%, it will have a particularly negative effect, so the content was set at 0.3% or less in terms of sot and AE.

(g) Ni The N1 component has the effect of improving corrosion resistance, especially stress corrosion cracking resistance, but if its content is less than 27%, the desired stress corrosion cracking resistance cannot be secured, On the other hand 4
Even if the content exceeds 0%, no further improvement effect on stress corrosion cracking resistance appears, so the content was set at 27-40% in consideration of economic efficiency.

(b) Cr The Cr component contains N1. In addition, when coexisting with the Mo and W components described later, it has the effect of significantly improving corrosion resistance, but if the content of 3H is less than 18%, the desired excellent corrosion resistance cannot be ensured. Although it is necessary, even if it is contained in excess of 25%, no further improvement effect will appear, so considering economic efficiency,
Its content was determined to be 18 to 25 inches.

(i) Mo and W As mentioned above, these components have the effect of improving corrosion resistance when coexisting with Ni and Cr, but if Mo: 5%: l'-'' and W: exceed 10%, respectively. H2S-CO at an environmental temperature of 150°C or less
In a 2-ct environment, no further improvement effect appears, so in consideration of economic efficiency, the contents were determined to be Mo: 5% or less and W: 10% or less, respectively.

In addition, regarding the content of MO and W, the conditional expression: Mo (%)
The reason why W is specified as + 1/2 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 this case, it is not possible to secure the desired corrosion resistance especially in the H2S-Cow-CL- environment at 150°C or less, and on the other hand, even if this resistance exceeds 5%, it is practically unnecessary to Since it contains MO and W, it is not economical, and therefore the value of Mo (%) + 1/2 W (5) is set to 2~
It was set at 5%.

(j) 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 K deteriorates hot workability, its content was determined to be 0.3 to 3%.

(k) Ti and Nb These components have the effect of fixing the C component and preventing grain boundary precipitation of carbides that cause corrosion resistance deterioration in the welded part during welding during pipe manufacturing.

Even if the content exceeds Tl: 1% and Nb: 1%, a further improvement effect does not appear, so in consideration of economic efficiency, the content is set to TL: 1% or less and Nb: 1% or less, respectively. It was set at 1% or less.

In addition, as mentioned above, T1 and Nb components have the effect of fixing the C component and suppressing the grain boundary precipitation of carbides, but T1 (@ / C (%) and Nb (%) / C (%)
) is less than 5, the content of T1 and Nb components relative to the C component is too small to completely prevent carbide precipitation.
/C@) and Nb (%) /C (%) values were set to be 5 or more.

The N component has the effect of improving one structure and strengthening it by solid solution in the base material, so it is included as necessary especially when even higher strength is required. If the amount 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%.
It was set as 3chi.

(d) Rare earth elements, Y, Mg, and Ca These components have the effect of improving hot workability, so it is necessary to perform hot working under particularly severe conditions. Although it is included.

The contents are respectively rare earth elements: O, less than 1%, Y: O, less than 1%, and Mg: less than 0.001%.

If the content is less than 0.01% for rare earth elements, 0.1% for Y, 1% for Y, and 1% for Mg, the desired effect of improving hot workability cannot be obtained. :0.1%
, and Ca:O, since hot workability tends to deteriorate when the content exceeds 1%, the content is reduced to 0.001 to 0.1% for rare earth elements and 0.0% for Y, respectively.
01-0.1%, Mg: 0.001-0.1%.

and Ca:O, 001-01%.

(n) Cr (%) + l 0M0 (%) + 5 W
Ni-Cr-Mo, N1-Cr-W, and N1-Cr-Mo-W steels with varying contents of (%) Ni, Cr, Mo, and W are melted and cast. And forged and stretched.

The hot-rolled steel sheet is hot-rolled to a thickness of about
Cold rolling was performed at a processing rate of 20 inches in consideration of -0 forming, and a test piece with dimensions of thickness: 2 mm x width: 1 O 1 lll x length near 5 B was prepared from this cold rolled steel plate at right angles to the rolling direction. Cut out the test piece, use a four-point bending jig, and apply a tensile stress equivalent to 0.2% proof stress.
20% NaCL solution (W f7
A: A stress corrosion cracking test was performed by immersing the sample in 150°C for 1000 hours, and after the test, the presence or absence of cracking in the test piece was observed.Based on the observation results, the inventors independently set a conditional expression: Cr(%)-1-10M0(
%)-1-5W(%) and Ni content, cr
(%) + l oMo (%) + 5 W (%) is taken on the horizontal axis.

On the other hand, when Ni (%9) was plotted on the vertical axis, N
i(%)≧27%, cr(%D+l OMo(%
) + 5 W (%)≧40%, the desired excellent stress corrosion cracking resistance was exhibited. Based on these results, we set the lower limit of Ni content to 27% and Cr (%
)+10M0(%9+5) The lower limit of the content of W (%) was set at 40%.

In addition, in the welded steel pipe of the present invention, B, Sn, Pb, and Zn are each contained in amounts of 0.
Even if the content is less than 1 inch, the properties will not be adversely affected, 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 each steel having the composition shown in Table 1 was prepared by a normal melting method, it was cast into a flat ingot of 700111 x 250 mm, and then processing started at a temperature of 1280 mm.
Forged and forged at ℃ to obtain a plate with a thickness of 20 fLl, followed by hot rolling at a hot rolling start temperature of 00 ℃ to obtain a hot rolled steel plate with a thickness of 6.1 mm, moreover,
From this hot rolled steel plate, using the normal U-07 ohming pipe manufacturing method, outer diameter: 406 mm x inner diameter: 394 mm x length: 60 mm
A welded steel pipe 1-27 of the present invention and a conventional welded steel pipe (made of autenitic stainless steel) having dimensions of 0.00 mm were manufactured, respectively.

Next, test pieces for tensile tests and stress corrosion cracking tests were cut out from the welded steel pipes 1 to 27 of the present invention and the conventionally welded steel pipes obtained as a result, and tested respectively. In addition,
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 1 for welded steel pipes 1 to 27 of the present invention.
The composition condition values and observation results regarding the presence or absence of grain boundary precipitation of carbides are also shown.

C Effects of the invention] From the results shown in Table 2, welded steel pipes 1 to 27 of the present invention all have a high tensile strength of 75 Y/- or more, and in the as-welded state, the welded steel pipes 1 to 27 of the present invention are Since there is no grain boundary precipitation, there is no need for solution treatment and it exhibits excellent stress corrosion cracking resistance, whereas conventional welded steel pipes have relatively high strength in the as-welded state. It is clear that since carbides precipitate at grain boundaries, this carbide causes poor stress corrosion cracking resistance.

As mentioned above, the welded steel pipe of the present invention has high strength in the as-welded state, and also has high strength under particularly severe conditions, H2
Since it exhibits excellent corrosion resistance in the S-C02-CL- environment, it exhibits excellent performance over a long period of time when used as line pipes for oil, natural gas, etc., which require these characteristics.

Claims (4)

[Claims] (1) C: 0.07% 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, one or two of Ti: 1% or less and Nb: 1% or less, and the remainder is It has a composition (weight% or more) consisting of Fe and other unavoidable impurities, and Cr (%) + 10Mo (%) + 5W (%) ≧ 40%, 2
%≦Mo(%)+1/2W(%)≦5%, Ti(%)/
A high-strength welded steel pipe for a line pipe that exhibits excellent corrosion resistance as welded and is characterized by satisfying the composition conditions of C (%)≧5 and Nb (%)/C (%)≧5. (2) C: 0.07% or less, Si: 1% or less, Mn: 2
% or less, sol. Al: 0.3% or less, Ni: 27-4
0%, Cr: 18-25%, Cu: 0.3-3%, Mo: 5% or less and W: 10% or less, Ti: 1% or less and Nb: 1% or less Contains one or two of the following, and further contains N: 0.05 to 0.3%, and has a composition (the above weight %) consisting of Fe and other unavoidable impurities, And, Cr(%)+10Mo(%)+5W(%)≧40%, 2
%≦Mo(%)+1/2W(%)≦5%, Ti(%)/
A high-strength welded steel pipe for a line pipe that exhibits excellent corrosion resistance as welded and is characterized by satisfying the composition conditions of C (%)≧5 and Nb (%)/C (%)≧5. (3) C: 0.07% or less, Si: 1% or less, Mn: 2
% or less, sol. Al: 0.3% or less, Ni: 27-4
0%, Cr: 18-25%, Cu: 0.3-3%, Mo: 5% or less and W: 10% or less, Ti: 1% or less and Nb: 1% or less Contains one or two of the following: Rare earth element: 0.001-0.1%, Y: 0.001-0.001%
0.1%, Mg: 0.001-0.1%, and Ca:
Cr (%) + 10Mo %)+5W(%)≧40%, 2
%≦Mo(%)+1/2W(%)≦5%, Ti(%)/
A high-strength welded steel pipe for a line pipe that exhibits excellent corrosion resistance as welded and is characterized by satisfying the composition conditions of C (%)≧5 and Nb (%)/C (%)≧5. (4) C: 0.07% or less, Si: 1% or less, Mn: 2
% or less, sol. Al: 0.3% or less, Ni: 27-4
0%, Cr: 18-25%, Cu: 0.3-3%, Mo: 5% or less and W: 10% or less, Ti: 1% or less and Nb: 1% or less Contains one or two of the following, further comprising: N: 0.05-0.3%, Rare earth element: 0.001-0.1%, Y: 0.001-0.001%.
0.1%, Mg: 0.001-0.1%, and Ca:
Cr (%) + 10Mo %)+5W(%)≧40%, 2
%≦Mo(%)+1/2W(%)≦5%, Ti(%)/
A high-strength welded steel pipe for a line pipe that exhibits excellent corrosion resistance as welded and is characterized by satisfying the composition conditions of C (%)≧5 and Nb (%)/C%≧5.