JPS61201759A - High-strength, high-toughness welded clad steel pipes for line pipes - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is characterized in that the inner material is free from corrosive components such as wet hydrogen sulfide, carbon dioxide gas, and chloride ions in the as-welded state during pipe manufacturing. Environments exposed to oil, natural gas, etc. containing

In addition to exhibiting excellent stress corrosion cracking resistance in the -Ct'' environment), it also exhibits excellent pitting corrosion and crevice corrosion resistance in seawater, and furthermore, The present invention also relates to a welded clad steel pipe that has excellent resistance to hydrogen sulfide-induced cracking and is therefore suitable for use as a line pipe that requires these characteristics.

[Conventional technology]

Generally, welded clad steel pipes are used as line pipes, with the inner material made of austenitic stainless steel and the outer material made of low alloy steel.

[Problem that the invention seeks to solve]

In the above-mentioned conventional welded clad steel pipe, when the pipe is manufactured by welding from the clad steel plate, carbides are precipitated at the grain boundaries, especially in the stainless steel that is the inner material, and these carbides are particularly (:
This is because this is a problem that causes deterioration of stress corrosion cracking resistance (hereinafter referred to as SCC resistance) in the above-mentioned Has -CO, -Ct- environment.

For the purpose of improving corrosion resistance, it has been considered to perform solution treatment on welded clad steel pipes after pipe production to dissolve the carbides in the matrix. Although the corrosion resistance of the material improves, the structure of the outer material, low alloy steel, becomes a quenched structure and hardens, resulting in a deterioration in toughness. The above Has-C which requires corrosion resistance
o, -Ct-'' environment, there is a problem in terms of toughness, and when this line pipe is laid in seawater, the line pipe is There was a problem in that the seawater enclosed in the pipe was likely to cause pitting and crevice corrosion to the inner material.

In addition, in this case, it was considered to perform further tempering treatment after solution treatment, but if tempering treatment was performed, the stainless steel that was the inner material would also be tempered, and as a result, it would be necessary to re-temper it. A problem arises in that carbides begin to precipitate at grain boundaries and the corrosion resistance deteriorates. Currently, it is being put into practical use in the same welded state.

[Means for solving problems]

Therefore, from the above-mentioned viewpoints, the present inventors conducted research to obtain a welded clad steel pipe that has high strength and toughness as well as excellent corrosion resistance in the as-welded state during pipe manufacturing. , the inner material (inner member) of the welded clad steel pipe is
In a weight pot (the following indicates weight%), C: 0.02% or less, Si: 1% or less, Mn: 2%
Below, P: 0.034 or less, S: 0.005
0.3 or less, aol, Al: 0.3 or less, Ni: 2
7-45%, Cr: 18-25%, Cu: 0.
3-3%, N: 0.0 5-0.3%
, Mo: 2 to 5% and W: 2% or less.

CrN+3Mo('11+1.5W(@+16NetG
≧ 33 sections, 2 width ≦ Mo (a) + 1/2 W (a) ≦ 5 sections,
It is constructed of high-alloy steel that satisfies the compositional conditions of - Mansaku side material (outer member).

C: 0.05-0.2%, Si: 0.01-085%.

Mn: 0.8-2%, P: 0.0154
Below, S: 0.002% or less, Ca: 0.0005-0.02%, and further contains Cu: 0.05-0.51%, Ni: 0.05-0.
5%, Cr: 0.05-0.5%, Mo: 0
．． 05~O-5%, Nb: 0.01~0.1%, V
: 0.01-0.1%, Ti: 0.005-0.05
%.

B: Manufactured from a clad steel plate made of low alloy steel containing one or more of the following: In welded clad steel pipes, there is no grain boundary precipitation of carbides in the inner material in the welded state during pipe manufacturing, so H
,S-Co,-C1- exhibits excellent SCC resistance in the environment, and is resistant to seawater.

The above N content and C beak + 3 M0 (a) + 15 beak + 1
The specified amount of 6N porcelain shows excellent pitting corrosion and edge corrosion resistance, and the outer material has high strength and toughness, as well as excellent hydrogen sulfide-induced cracking resistance (hereinafter referred to as resistance). It has been found that when used as a line pipe for oil, natural gas, etc., which require these characteristics, it exhibits excellent performance over an extremely long period of time.

This invention was invented based on the above knowledge, and the reason why the composition ranges of the inner material and outer material of the welded two-piece steel pipe are limited as described above will be explained below.

Inner material (a) C Inner material with various C contents is heated at 1000°C for 30 minutes +
A Strauss test (JIS-G-0575) performed rolling finishing treatment under rolling + AC conditions (650°C to 850°C) to examine the effects of this C content and rolling finishing temperature of 650°C to 850°C on intergranular corrosion. ), it was investigated by
If the content of the C component is 0.024 or less, stress corrosion cracking is suppressed in the above temperature range, whereas if the content exceeds 0.02%, carbides may be formed at the grain boundaries during pipe manufacturing by welding. The content is limited to 0.024 or less because it tends to precipitate and cause stress corrosion cracking.

(b) 5I The Si component is an essential component as a deoxidizing component, but (c) Mn The Mn component has a deoxidizing effect like the Si component, and even if it is contained up to 2°, the characteristics will not change. Since it does not have any negative effects,
It is allowed to contain up to 2.

1d) P The P component has the effect of increasing the susceptibility to stress corrosion cracking, and this effect appears rapidly when the content exceeds 0.03 tsu. 034 or less.

(e) SS The S component has the effect of deteriorating hot workability, and this effect appears markedly when the content exceeds 0.0054 (for two reasons, the content is reduced to O, OO54).
It was determined as follows.

(f) sot, A/: The A4 component is the same as St and excitation component (it is a necessary component because it has a double deoxidizing effect, but if its content exceeds 0.3% for aot and At, it will have an adverse effect on the characteristics. 〇 (g) Ni Ni component has the effect of improving corrosion resistance, especially SCC resistance, but its content is set at 0.3% or less for 5 ot 4 t. If the content is less than 45%, the desired excellent SCC resistance cannot be ensured, and on the other hand, if the content exceeds 45%, no further improvement in SCC resistance will be achieved. The amount is 27-45t6
(iii) Cr The Cr component includes Ni and MO and/or W as described below.
Furthermore, when N coexists with each component, it has the effect of significantly improving corrosion resistance, but if the content is less than 184, the desired excellent corrosion resistance cannot be ensured.
However, even if the content exceeds 25t6, no further improvement in corrosion resistance will be obtained.Therefore, in consideration of economic efficiency, the content was set at 18 to 25t6.

(i) Cu Although the Cu component has the effect of improving corrosion resistance, if the content is less than 0.3%, the desired corrosion resistance cannot be ensured, while if the content exceeds 3%, hot workability is impaired. The content was determined to be 0.3 to 3.

(j) N The N component has the effect of significantly improving pitting corrosion resistance and crevice corrosion resistance against seawater in coexistence with the above-mentioned Ni and Cr and the MO and/or W components described below, and its content is 0. If it is less than 0.051, the desired excellent pitting corrosion and crevice corrosion resistance cannot be secured, so it is necessary to contain it at least 0.051. However, even if it is contained in excess of 0.3, the above effects cannot be achieved. Since no further improvement was observed, the content was determined to be 0.05 to 0.34.

■　M.

As mentioned above, the MO acid component has the effect of improving corrosion resistance when coexisting with each component of Nt, (::r and N, or even W), but if its content is less than 2 parts, the desired excellent corrosion resistance is not achieved. On the other hand, even if it contains more than 5 H,
In an S-Cot-Ct environment, the effect of further improving corrosion resistance cannot be obtained, so the content was determined to be between 2 and 5 in consideration of economic efficiency.

(6W What is the W component? Similar to Mo, Ni e Cr and N
, or further has the effect of improving corrosion resistance in coexistence with each component of MO, and also has the effect of improving hot workability compared to MOζ2. However, even if more than 2 H,S-Co is contained, the environmental temperature is 150°C or less.

-Ct- Since further improvement in corrosion resistance cannot be obtained in an environment, the content is reduced to 2 in consideration of economic efficiency.
It was set as 1 or less.

frd Mo%+1/2W- 1 conditional expression regarding the content of MO and W = MO (to) + 17
The reason why it is specified as 2W- is that the atomic weight of IW is about twice that of Mo, and in terms of effects, they are equal at about 172.
Even if the desired corrosion resistance cannot be ensured in the following H, S -co, -CL- environment, and this value exceeds 54, as described above.

In fact, it is not economical to include unnecessary amounts of Mo and W, and therefore the MO(1)+17
The value of 2W import was set as 2 to 54.

(id Cr(1+3MoeQ+1.5W(11+1
6Ne61Ni, and (Ni-Cr-Mo-N system with various contents of Cr + Mo, W and N,
N1-Cr-W-N system and Ni-Cr-Mo-W-N
The steel is melted, forged, forged, and hot-rolled to produce a hot-rolled steel plate with a near-thickness.Then, this hot-rolled steel plate is subjected to cold processing during the production of welded steel pipes, such as U- Cold rolling was carried out at a processing rate of 20 mm in consideration of zero forming, and a test piece with dimensions of thickness: 2 fi x width: 10 m x length near 54 was cut out from this cold rolled steel plate at right angles to the rolling direction. , This test piece was subjected to 10 atm H, S and 10 atm using a 4-point bending jig and applying a tensile stress equivalent to 0.2% proof stress.
20 saturated H, S and CO8 with CO2 at atmospheric pressure
4 A stress corrosion cracking test (SCC test) was conducted by immersing the specimen in a NaCt solution (liquid temperature: 150°C) for 360 hours, and after the test, the presence or absence of cracking in the test piece was observed, and based on this observation result, the inventor Conditional expressions set independently by etc.:
Cr(I)+3 M o(I)+i, sw(I)+16
The relationship between the value of N and the Ni content is expressed as Cr@+3M
Taking o (I) + 1.5W (I + 16N (to) on the horizontal axis,
On the other hand, when Ni (A) is plotted on the vertical axis, %N
Section 1(a)≧27.

Cr(@+3MoWa+1.5WC@+16Nf@≧3
It shows the desired excellent SCC resistance in the range of 3.
The above various test pieces have l content in the range of 27 to 45.

JIS-G-0578-198 with test temperature = 30°C
1, and after the test, the weight loss (mg/d) of the test piece based on the pitting and crevice corrosion that occurred in each test piece was investigated. While the desired pitting corrosion/crevice corrosion resistance was stably obtained within this range, when the value decreased from 33, the weight loss due to the pitting/crevice corrosion rapidly increased. Therefore, based on the SCC test and the pitting corrosion/crevice corrosion test, the lower limit of the Ni content was set to 27, C increase + 3M - 1,000 groups (to) + 1, respectively.
The lower limit for six schools was set at 33.

B Outer material (a) C The C component is a necessary component to ensure strength.

For this purpose, the content is preferably 0.051 or more, but 0.051 or more is desirable.
If the content exceeds 2%, segregation increases (=involves) and HIC resistance deteriorates, so the content was set at 0.05 to 0.2%.

佽) St Sl component (: has a deoxidizing effect, but its content is 0.0
If it is less than 1%, the desired deoxidizing effect cannot be achieved,
On the other hand, if the content exceeds 0.5%, the toughness will decrease (:), so the content should be adjusted to 0.01 to 0.5%.
(c) Mn In addition to improving the strength of steel, the Mn component also has a deoxidizing effect, but if its content is less than 0.81, the desired strength cannot be achieved; If the content exceeds 0.2, not only will segregation increase and HIC resistance deteriorate, but also toughness and weldability will deteriorate, so the content should be reduced to 0. It was set at 8 to 2 width.

(b) P The P component is an unavoidable impurity that forms Ill precipitates and deteriorates the HIC resistance of steel, so it is desirable that its content be as low as possible, but if the content exceeds 0.015%, segregation will occur. The content should not exceed 0.0154, since this will cause a rapid increase in HIC resistance and a significant deterioration of HIC resistance.

(e) SS The S component is an unavoidable impurity that forms nonmetallic inclusions and reduces the HIC resistance of steel like the P component, so it is desirable that its content be as low as possible;
．． If it exceeds 0.021, nonmetallic inclusions will increase significantly and HIC resistance will drop sharply.
The content must not exceed 0.0021.

(f) Ca The Ca component has the effect of spheroidizing inclusions and preventing them from becoming crack starting points, thereby improving the HIC resistance of steel, but if the content is o, o o o s
If it is less than 0.0%, the desired effect cannot be obtained;
Even if the content exceeds 0.0296, no further improvement effect is observed, so the content is set at 0.0005 to 0.0.
It was set as 2'1. In addition, for sulfide inclusions, C
d/Destruction: There is a particularly remarkable effect when conditions 2 to 6 are satisfied.

(m Cu5Ni+Cr+Mo+Nb+V+Ti, and B None of these components promotes segregation,
Since it has the effect of improving the strength of steel, C is included as required when particularly high strength is required, but the content is less than 0.05 for Cu and 0.05 for Ni.
054, Cr: less than 0.05%, M.

: less than 0.0596, Nb: less than 0.011, V: 0.
On the other hand, if the value is less than 0.01 tatami, 'I'i: O, OO less than 5 tatami, and B: less than 0.0005 tatami, the desired strength improvement effect cannot be obtained.

The content is Cu: 0.5 tly, respectively.
Ni: 0.54, Cr: 0.5e61Mo: 0
．． 5, Nb: 0.1%, V: 0.1 (i.

Even if Ti: 0.05 and B: o, 00B were exceeded, no further improvement effect was observed, and in consideration of economic efficiency, the content was changed to Cu: 0.05 to 0.5, respectively. %, Ni
: 0.05~0.54. Cr: 0.05~0.5
qblMo: 0.05~0.5%, Nb: 0.01~
0.1%, V: 0.01-0.14. Ti: 0
．． 005~0.05 section, and B: o, ooos~o,
It was determined as ooss.

〔Example〕

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

Molten steel having the compositions shown in Tables 1 and 2, respectively, was prepared by a normal melting method, and 750 wq x 250
m+ flat ingot was cast, and this ingot was subjected to hot forging and hot forging at a processing start temperature of 1280°C to obtain a plate material with a thickness of 60m+, and this plate material was further heated to a rolling start temperature of 1150°C. hot rolling to produce hot-rolled steel sheets that will serve as the inner and outer materials of the welded clad steel pipe to be manufactured, respectively, and then combine these inner and outer materials into the combinations shown in Table 3. Superimposed at.

Heating temperature = 900-1100°C.

Cladding rolling temperature: 2650-850°C.

A clad steel plate with a thickness of 13 m was obtained by cladding under the following conditions, and then the clad steel plate was made using the normal U-0 forming pipe manufacturing method: Outer diameter: 406 mm × Inner diameter: 394 mm × Length: It has the dimensions of 6000 cod, and the inner material thickness: 3
．． Welded clad steel pipes 1 to 12 of the present invention and conventional welded clad steel pipes having outer material thickness of 8.3 m were manufactured, respectively.

Next, the welded crat of the present invention obtained as a result.

Steel pipes 1 to 12 and conventional welded clad steel pipes were used for tensile testing, Charpy impact test (vE-20),
For SCC testing, pitting/crevice corrosion testing, and HIC
Test specimens were cut out and each test was conducted.

In addition, the SCC test is as follows: Specimen dimensions - Width: 10m x Thickness = 2 length x length near, 5
m.

Jig used: 4-point bending jig, additional pressure crab, tensile stress equivalent to 0.21 proof stress, solution used = 10 atm H, S and 10 atm CO, H, S
The pitting and crevice corrosion tests were conducted under the following conditions: 204 NaC6 solution saturated with and CO, solution temperature = 150°C, test time = 336 hours, and the test piece dimensions - Width: 20mm x Thickness: 2w *X length: 40 tone, solution used: 104 FeC1,6H,0 test source degree = 3
The HIC test was conducted under the conditions of 0°C and test time = 24 hours, and the HIC test was as follows: Test piece dimensions - Width: 25 mm x Thickness: 10 sm x Length: 10
0 tone, solution used: NACE bath (an aqueous solution of 0,5-linked acetic acid + 54 sodium chloride saturated with H and S), solution temperature: 25°C, test time: 96 hours, conducted under the following conditions, and in the above SCC test The presence or absence of cracks in the inner material was observed, and in the pitting and crevice corrosion test, the mass loss per unit area and unit time after the 24-hour immersion test was determined in g/d-hr. In the HIC test, the presence or absence of flaws on the outer material after the test was observed using ultrasonic flaw detection. These results are also shown in Table 3. In addition.

Since the mechanical properties of welded clad steel pipes are determined by the outer material, Table 3 (2) also lists the mechanical properties of the outer material.

〔Effect of the invention〕

From the results shown in Table 3, welded clad steel pipe 1 of the present invention
In 12 to 12, high strength and toughness are ensured especially by the outer material in the welded state during pipe manufacturing,
Moreover, the outer material shows excellent HIC resistance, and the inner material (
: Since no grain boundary precipitation of carbides is observed, it exhibits excellent SCC resistance (2) It also exhibits excellent pitting corrosion and crevice corrosion resistance, whereas conventional welded clad steel pipes have a high Although it exhibits high toughness, it cannot avoid grain boundary precipitation of inner material carbide during welding, so it is resistant to SC.
It is clear that the C properties are inferior.

As mentioned above, the welded clad steel pipe of the present invention not only has high strength and toughness, and is excellent in SCC resistance and HIC resistance, but also in pitting corrosion and crevice corrosion resistance. Therefore, various line pipes that require these characteristics, especially line pipes for oil and natural gas transportation that are exposed to H,S -COm -CL'' environments, and especially line pipes of this type installed in seawater. When used as a line pipe, it can exhibit excellent performance over a long period of time.

Claims (2)

[Claims] (1) The inner material is C: 0.02% or less, Si: 1% or less, Mn: 2% or less, P: 0.03% or less, S: 0.005% or less, sol. Al: 0.3% or less,
Ni: 27-45%, Cr: 18-25%, Cu: 0.
3 to 3%, N: 0.05 to 0.3%, Mo: 2 to 5%, and W: 2% or less, and the remainder is Fe and unavoidable impurities. and Cr(%)+3Mo(%)+1.5W(%)+16N(
%)≧33%, 2%≦Mo(%)+1/2W(%)≦5
%, while the outer material is C: 0.05-0.2%, Si: 0.01-0.5%,
Mn: 0.8-2%, P: 0.015% or less, S: 0.
0.002% or less, Ca: 0.0005 to 0.02%, and the remainder is Fe and unavoidable impurities (weight %). High strength, high toughness welded clad steel pipe with excellent corrosion resistance. (2) The inner material is C: 0.02% or less, Si: 1% or less, Mn: 2% or less, P: 0.03% or less, S: 0.005% or less, sol. Al: 0.3% or less,
Ni: 27-45%, Cr: 18-25%, Cu: 0.
3 to 3%, N: 0.05 to 0.3%, Mo: 2 to 5%, and W: 2% or less, and the remainder is Fe and unavoidable impurities. and Cr(%)+3Mo(%)+1.5W(%)+16N(
%)≧33%, 2%≦Mo(%)+1/2W(%)≦5
%, while the outer material is C: 0.05-0.2%, Si: 0.01-0.5%,
Mn: 0.8-2%, P: 0.015% or less, S: 0.
002% or less, Ca: 0.0005-0.02%, and further contains Cu: 0.05-0.5%, Ni: 0.05-0.5%
, Cr: 0.05-0.5%, Mo: 0.05-0.5
%, Nb: 0.01-0.1%, V: 0.01-0.1
%, Ti: 0.005 to 0.05%, B: 0.0005 to 0.008%, and the remainder is Fe and unavoidable impurities. %), a high-strength, high-toughness welded clad steel pipe having excellent corrosion resistance in an as-welded state, characterized in that it is constructed of low-alloy steel with a low alloy steel.