JPH09241797A - Steel plate for amine environment gas cleaning equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel plate for amine environment gas cleaning equipment, excellent in the prevention of the occurrence of amine cracking caused by intergranular cracking. SOLUTION: This steel plate has a composition containing, by weight, 0.01-0.35% C, 0.05-1.0% Si, 0.2-1.5% Mn, =<=0.035% P, <=0.04% S, 0.01-0.1% Al, 0.02-0.01% N, and 0.0005-0.006% Ca, also containing two components of 0.05-1.5% Cu and 0.05-0.2% Ni or containing one component of 0.1-1.5% Cr or containing all of these three components, and having the balance Fe with inevitable impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet for a gas cleaning device, which has good resistance to environmentally accelerated cracking in an amine aqueous solution environment.

[0002]

2. Description of the Related Art In a gas cleaning apparatus for removing an acidic impurity gas (hydrogen sulfide, carbon dioxide, etc.) in a hydrocarbon gas using an aqueous amine solution, it has been a problem that environmentally assisted cracking occurs in a steel sheet used. . The gas scrubber mainly consists of an absorption tower and a regeneration tower.The aqueous amine solution used is a rich liquid in which the concentration of the acidic impurity gases has increased due to absorption of acidic impurity gas in the lower portion of the absorption tower and a lower portion of the regeneration tower. The acidic impurity gas is released and is roughly divided into lean liquids in which their concentrations are low, and the impurity gas concentration changes between the rich liquid and the lean liquid are repeated while circulating in the apparatus. The cracks that occur in the steel plate used in the gas cleaning device occur in both the rich liquid environment and the lean liquid environment.

Of these, cracks in a rich liquid environment are cracks caused by invading hydrogen called sulfide stress cracking (SSC) and hydrogen induced cracking (HIC), and a method of manufacturing a steel sheet already excellent in cracking resistance. Have been proposed (for example, JP-A-3-236420). On the other hand, regarding cracking in a lean liquid environment (hereinafter referred to as amine cracking), cracking often occurs along the grain boundaries, carbon dioxide in the environment promotes cracking, and the electric potential of the steel material is in the active state. /
It is known that cracking susceptibility increases in the passive state transition potential region.
Seed to be a species (RN Parkins et al., M.
materials Performance Magazine, 27th
Vol., January issue, p. 19, 1988). As measures to prevent such amine cracking, it is considered effective to relax stress conditions (increase design stress, carry out post-weld heat treatment, etc.) and environmental conditions (replace amine solution, change amine concentration, etc.). However, there are very few proposals for steel components that improve crack susceptibility. The only applicant of the present invention is JP-A-6-306.
Japanese Patent No. 541 only proposes a technique for preventing intragranular cracking by limiting the Ni content to 0.2% or less.

[0004]

However, according to the subsequent studies by the present inventors, amine cracks include intragranular cracks with slow growth and intergranular cracks with fast growth and high possibility of penetrating the steel sheet. It turned out to be. That is, it has been found that the regulation of Ni is effective in preventing the former, but is hardly effective in the latter only with Ni.

It is an object of the present invention to provide a steel sheet for amine environmental gas cleaning equipment, which is excellent in the prevention of amine cracking, particularly in the prevention of amine cracking due to grain boundary cracking.

[0006]

Among the amine cracks, the present inventors have found that not only Ni, but also Cu, Cr, and Al can be used for intergranular cracks that grow rapidly and are likely to penetrate the steel sheet.
As a result of discovering that is important, the present invention has been completed.
C: 0.01% or more and 0.35% or less, Si: 0.05%
Or more and 1.0% or less, Mn: 0.2% or more and 1.5% or less,
P: 0.035% or less, S: 0.04% or less, Al:
0.01% to 0.1%, N: 0.002% to 0.01%, Ca: 0.0005% to 0.006
% Or less and Cu: 0.05% or more and 1.5% or less, Ni: 0.05% or more and 0.2% or less, or Cr: 0.1% or more and 1. A steel sheet for an amine environmental gas cleaning device, characterized by containing 5% or less of one kind, or containing all of these three kinds, and the balance Fe and unavoidable impurities.

In addition to the above, the present invention provides
And V: 0.01% or more and 0.3% or less, Ti: 0.01
% To 0.1%, Nb: 0.01% to 0.1%, B: 0.0003% to 0.005%, Rare Earth Element (REM): 0.0005% to 0.01% One or more of the above may be contained. Here, the amine environment is defined as an aqueous solution containing 10 to 70% by weight of amine, and the types of amine include monoethanolamine, diethanolamine, diglycolamine, diisopropanolamine, methyldiethanolamine, and triethanolamine. Etc. The gas to be cleaned means natural gas, process gas containing hydrocarbon as a main component due to fractionation / refining of petroleum, petroleum gas such as off gas, and combustion waste gas of various fuels, which are to be cleaned. Hydrogen sulfide and carbon dioxide are removed from the gas.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The mechanism of active path corrosion type stress corrosion cracking such as amine cracking is generally considered as follows from an electrochemical viewpoint. (1) A protective film is formed on the metal surface immersed in the solution.

(2) When a part of the film is broken by the tensile stress, the exposed part (new surface) is intensively dissolved in the anode. In this case, in a place where a lot of lattice defects or impurities / inclusions exist (for example, a crystal grain boundary), re-restoration of the film is delayed because it is chemically unstable, and selective dissolution is likely to occur. Further, inside the locally dissolved portion (pitting corrosion or cracking), the pH is lowered by the hydrolysis of the dissolved metal ion, so that the dissolution reaction occurs more and more selectively.

(3) Generation and propagation of stress corrosion cracking progresses based on the balance between local destruction and re-repair of the film. Therefore, the corrosion-resistant steel in which the corrosion (general corrosion) reaction of the entire material is suppressed does not take into consideration the resistance to the application of tensile stress, and therefore is not excellent in the stress corrosion cracking resistance.

The present inventors have obtained the following findings as a result of detailed examination of the amine cracking resistance improving factor. 1) Film formed in amine environment (mainly magnetite Fe
₃ O ₄ ) was observed and analyzed by a computer-controlled X-ray microanalyzer (CMA), and the time course of the dissolution current was also observed during the amine crack reproduction test. A trace amount of Cu-added steel film was found to be a Cu-free steel film. It was found that the Cu content in the film was higher than that in the film and the properties of the film were more stable. Therefore, in the case of a trace amount of Cu-added steel, "breakage of the coating film due to stress" is less likely to occur in the cracking process (2), and "re-restoration of the coating film" is more likely to occur.

2) The welding part of the amine environmental gas cleaning device is
Post-weld heat treatment (PWHT) is always performed as a measure to prevent cracking due to relaxation of welding residual stress. At that time, fine cementite Fe ₃ C is decomposed, reduced and disappeared, and specific cementite grows (Ostwald growth). However, when a small amount of Cr is added and a small amount of Cr is solid-dissolved in cementite, (Fe, Cr) ₃ C is more stable than Fe ₃ C, so the reaction rate of decomposition of cementite is small, and the growth of specific cementite Is less likely to occur. As a result, in a small amount of Cr-added steel, the cementite existing at the grain boundaries remains fine, so that “re-restoration of the grain boundary film” is likely to occur in the cracking process (2).

3) Addition of Al as a deoxidizing element is unavoidable, but a part of Al is combined with N in steel to form AlN.
And contributes to the refinement of crystal grains. These Al ₂ O ₃
It was found that aluminum inclusions such as AlN and AlN do not adversely affect amine crack resistance unless they are coarsened. Therefore, when the crystal grain becomes small and the total grain boundary area becomes large by the addition of a trace amount of Al, if the same amount of impurities that adversely affect amine cracking, such as cementite, exists in the grain boundary, The amount of grain boundary cementite existing in the steel becomes small, and the cracking susceptibility decreases.

Based on the above examination, various alloying elements of the steel of the present invention and their addition amounts were determined. The details are described below. C is an element necessary to secure strength, and 0.
If the content is less than 01%, the desired strength cannot be obtained, so
The lower limit value was 0.01%. Further, if over 0.35% is added, it is difficult to make the grain boundary cementite fine, and further the toughness and weldability deteriorate, so the upper limit of C was made 0.35%.

Si is an effective component for improving strength in addition to being necessary as a deoxidizing agent.
If it is less than 05%, no effect is obtained, and if it exceeds 1.0%, the toughness is significantly reduced.
0% or less. Mn is an element that increases the strength without significantly lowering the toughness, and it is necessary to add 0.2% or more to obtain sufficient strength. However, if added in a large amount, the hardenability will increase and the weldability and weld heat affected zone (HA
Z) Not only deteriorates toughness, but promotes formation of inclusions MnS. Since the rich liquid environment and the lean liquid environment are adjacent to each other in the amine environmental gas cleaning device, it is presumed that a part of the rich liquid is mixed in the lean liquid when trouble occurs.
In that case, not only amine cracking resistance but also HIC resistance is required. MnS extends in a plate shape during rolling and facilitates the accumulation of diffusible hydrogen, which is not preferable in consideration of HIC resistance. Therefore, the upper limit of Mn is set to 1.5%.

P is a harmful component that causes grain boundary segregation to easily cause cracks during processing. The smaller the amount, the more preferable.
The content was 0.035% or less. Since S forms MnS-based inclusions, it is preferable to reduce S as much as possible. Therefore, the upper limit is set to 0.04%. Al, which is one of the points of the present invention, is necessary as a deoxidizing agent and, in addition, contributes to the refinement of crystal grains by forming inclusions AlN, which is effective for improving amine crack resistance. And 0.01% or more is added. On the other hand, excessive addition of Al promotes the formation of coarse Al oxynitrides and becomes the starting point of amine cracking, which adversely affects amine cracking resistance and lowers HAZ toughness. The value was 0.1%.

Like the above, N is necessary for producing AlN, and its lower limit was made 0.002%. However, if added in a large amount, coarse nitrides are formed and the amine crack resistance is adversely affected, so the upper limit was made 0.01%. Ca is added in an amount of 0.0005% or more in order to control the morphology of MnS-based inclusions and improve the HIC resistance. However, 0.
If it exceeds 006%, the HAZ toughness and HIC resistance are deteriorated due to the formation of Ca-based large inclusions and clusters, so the upper limit was made 0.006%.

Cu, which is the key point of the present invention, has the effect of stabilizing the formed film in an amine environment and improving the amine cracking resistance. Addition of 0.05% or more provides the effect. On the other hand, a large amount of addition promotes hot cracking, which is not preferable, and in such a case, the slab heating temperature may be set to a low temperature (about 950 to 1050 ° C.). Even so, if it exceeds 1.5%, the hot workability is impaired, so C
The upper limit of u was set to 1.5%.

Ni improves the strength and toughness of the base metal without adversely affecting the weldability and HAZ toughness, and when hot cracking due to Cu addition poses a problem, C under scale.
An alloy of u + Ni is produced to prevent hot cracking. The lower limit for obtaining this effect was set to 0.05%. But,
If it exceeds 0.2%, intragranular cracking tends to occur in an amine environment, so the upper limit of Ni is made 0.2%.

Cr, which is one of the points of the present invention, is a carbide forming element, and not only improves the strength but also forms a solid solution in the grain boundary cementite, so that the growth of a specific grain boundary cementite occurs during PWHT. Is effective to suppress amine cracking resistance. The lower limit for obtaining this effect was 0.1%. On the other hand, a large amount of addition (C
Since it promotes the formation of coarse lump-shaped carbides such as r, Fe) ₇ C ₃ and (Cr, Fe) ₂₃ C ₈ and reduces amine cracking resistance, the upper limit of Cr is made 1.5%.

Further, in some cases, it is effective to add at least one of the following elements. V forms a carbide or the like, and if added in an amount of 0.01% or more, it has a remarkable effect on the strength improvement, but if it exceeds 0.3%, weldability and reheat cracking resistance are impaired. .3
% Or less.

Ti has the effect of improving the toughness by forming a nitride and refining the crystal grain size.
The effect is obtained by the above addition. However, if it exceeds 0.1%, not only the toughness is lowered, but also the strength is lowered, so 0.01% or more and 0.1% or less are set. N
b has the effect of forming a carbide or the like to improve the strength, and also has the effect of making the crystal grain size finer to improve the toughness, and when 0.01% or more is added, the effect is obtained. However, if it exceeds 0.1%, the toughness is rather decreased and the weldability is impaired.
It was as follows.

B is an element for improving the hardenability and is added for improving the strength of the quenched and tempered steel, or is an element for increasing the grain boundary strength and is added to the heat resistant steel for the purpose of enhancing the creep property. In the present invention, the above effect can be expected by adding 0.0003% or more even in the normalizing or normalizing and tempering state, but even if added in excess of 0.005%, the effect does not increase. In addition to 0.003% or more, 0.005% or more
% Or less.

Similar to Ca, the rare earth element (REM) is effective if added in an amount of 0.0005% or more for controlling the morphology of inclusions MnS, but if added in excess of 0.01%, cleanliness is impaired. Since the HIC resistance deteriorates, the upper limit value is set to 0.01%.

[0025]

[Examples] Among experimental examples in which the influence of each additive element was investigated, the present invention steel 23 steel type, comparative steel 21 steel type, total 44 steel types will be shown. Melt in a vacuum induction melting furnace, 90 × 1
A 10 x 300 mm slab was cast. Then, using a multi-functional rolling mill, hot rolling was performed to a plate thickness of 15 mm under the temperature conditions of a slab heating temperature of 1050 ° C. and a finishing temperature of 900 ° C. Further, normalization of heating at 920 ° C. for 1 hour → air cooling was performed, and then heat treatment equivalent to PWHT of heating at 625 ° C. for 1 hour was performed.

These chemical components are shown in Table 1, Table 2 (continued-1 of Table 1), Table 3 (continued-2 of Table 1) and Table 4 (continued-3 of Table 1). Here, the comparative steel A corresponds to the carbon steel plate A516-70 for pressure vessels. Compact type (CT) test pieces shown in FIG. 1 were produced using these test steels. Here, W = 50.8 mm, B = 12.7 m
m, φ = 16.2 mm, h = 61.0 mm, l = 63.
5 mm. Furthermore, a / W = 0.5 (a = 25.4 mm) with a hydraulic servo fatigue tester at room temperature and in the air.
Fatigue pre-crack was introduced up to. The load conditions at the time of introducing the fatigue pre-crack are such that the size of the plastic deformation region at the crack tip is sufficiently small, and the maximum load is 400 kgf and the minimum load is 4
The frequency was 0 kgf and the cycle was 10 Hz.

The above test piece was set in the amine crack reproduction test apparatus shown in FIG. Here, 1 is a CT test piece, 2 is a stainless steel test tank, 3 is a load cell, 4 is a constant temperature circulation tank, 5 is a constant potential applying device (potentiostat), and 6 is a load spring. A 20% monoethanolamine aqueous solution having a concentration by weight of about 20% was placed in a constant temperature circulating tank, heated to 80 ° C., and carbon dioxide was constantly bubbled into the test solution. The test solution was circulated to and from the test tank. Further, a constant potential applying device was used to apply −650 mV (SCE), which is the potential in the active / passive transition potential region, to the test piece.

A constant load was applied to the test piece by the load spring, and the stress intensity factor K was calculated from the load P and the size of the test piece. The formula for calculating K is ASTM E399 (ASTM S
standard E399, Standard tes
t method forplane-strain
fracture toughness of met
The following equation, which is a recommended equation of allic materials, 1983), was used.

K = P · f (α) / (B · √W) α = a / W f (α) = (2 + α) · (0.886 + 4.64α−1)
3.32α ² + 14.72α ³ -5.6α ⁴ ) / (1-
α) K _ISCC is the lower limit stress intensity factor at which ^3/2 cracking occurs
The amine cracking resistance property was evaluated. The test period was about 1000 hours per test.

The test results are shown in Tables 1 to 4 and FIGS. 3 to 5.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

[0034]

[Table 4]

From FIG. 3, it can be seen that K _ISCC is dramatically improved when the Cu content is 0.05% or more. However, Cu
In the vicinity of the content of 1.5%, the Ni content of steels P, Q and R exceeds 0.20%, so that the steel S has a C content of 0.3%.
Since it is more than 5%, steel T has an N content of less than 0.002%, and steel U has an N content of more than 0.010%, so that K _ISCC is lowered. FIG.
Then, if the Cr content is 0.1% or more and 1.5% or less, K _ISCC
Has improved dramatically. However, even if the Cr content is within the range, the Ni content exceeding 0.20% (steels P and Q) still has a lowered K _ISCC . Further, in FIG. 5, K _ISCC is dramatically improved when the Al content is 0.01% or more and 0.1% or less. However, steel S is C
Regarding the contents of steels T and U, the N content deviates from the range of the present invention, and K _ISCC is lowered.

As can be seen from Tables 1 to 4, the invention steels V to
K _{ISCC of} Z and a to r is 15.0 to 18 of conventional steel.
8 is improved to 37.0 to 38.8.

[0037]

As is clear from the above examples, when the steel sheet of the present invention is used as a gas cleaning device material using an amine aqueous solution, amine cracking is less likely to occur in the device, and industrial effects are obtained. Is quite noticeable.

[Brief description of drawings]

FIG. 1 is a view showing a CT test piece used for evaluation of amine crack resistance.

FIG. 2 is a diagram showing an amine crack reproduction test device.

[Explanation of symbols]

 1 CT test piece 2 Stainless steel test tank 3 Load cell 4 Constant temperature circulation tank 5 Constant potential application device (potentiostat) 6 Spring for load application

FIG. 3 is a diagram showing the relationship between the Cu content and the amine cracking resistance of the steel produced according to the present invention and the steel deviating from the components specified in the present invention for comparison.

FIG. 4 is a diagram showing the relationship between the Cr content and the amine cracking resistance of the steel produced according to the present invention and the steel deviating from the components specified in the present invention for comparison.

FIG. 5 is a diagram showing the relationship between the Al content and the amine cracking resistance characteristics of the steel produced according to the present invention and the steel deviating from the components specified in the present invention for comparison.

Claims (2)

[Claims] 1. As weight%, C: 0.01% or more and 0.35% or less, Si: 0.05% or more and 1.0% or less, Mn: 0.2% or more and 1.5% or less, P: 0.035% or less, S: 0.04% or less, Al: 0.01% or more and 0.1% or less, N: 0.002% or more and 0.01% or less, Ca: 0.0005% or more and 0.006 % Or less and Cu: 0.05% or more and 1.5% or less, Ni: 0.05% or more and 0.2% or less, or Cr: 0.1% or more and 1. A steel sheet for an amine environmental gas cleaning device, characterized by containing 5% or less of one kind, or containing all of these three kinds, and the balance Fe and unavoidable impurities. 2. As weight%, V: 0.01% or more and 0.3% or less, Ti: 0.01% or more and 0.1% or less, Nb: 0.01% or more and 0.1% or less, B: 0.0003% to 0.005%, rare earth element (REM): 0.0005% to 0.01%
The steel sheet for amine environmental gas cleaning device according to claim 1, containing one or more of the following.