JPS63216984A - Method for preventing intergranular damage of ni alloy member - Google Patents

Abstract

PURPOSE:To prevent the intergranular corrosion and intergranular stress corrosion cracking of an Ni alloy member brought into contact with a degassed aq. alkali soln. at a high temp. by adding a chain amine having a COOH or OH group to the alkali soln. and gaseous H2 to a vapor phase coming in contact with the alkali soln. CONSTITUTION:When an Ni alloy member is brought into contact with a degassed aq. alkali soln. such as an aq. NaOH soln. at >=300 deg.C, one or more kinds of chain amines each having a COOH or OH group are added to the alkali soln. by 0.1ppm-1% by weight. The chain amines may be sarcosine, alanine and 2-amino-2-methyl-1-propanol. Gaseous H2 is further added to a vapor phase coming in contact with the alkali soln. contg. the added chain amines by 3X10<-3>-1X10<-1>atm per 1atm vapor phase. By this simple means, the intergranular damage of the Ni alloy member brought into contact with the degassed aq. alkali soln. at a high temp. due to intergranular corrosion and intergranular stress corrosion cracking is effectively prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is directed to the use of Ni
This invention relates to a method for preventing intergranular corrosion and intergranular stress corrosion cracking (hereinafter α, collectively referred to as intergranular damage, abbreviated as IOA) in base alloy members.

[Conventional technology]

Conventionally, for example, in weight% (% below α indicates weight%), 16
Ni-based alloys such as Alloy 600, which has a composition of
Because of its excellent resistance to 8CCw (denoted by C), it is particularly suitable for use in materials that are exposed to environments that are susceptible to (=8CCw), especially heat exchanger tube materials (: For example, the inside is exposed to a high-temperature, high-pressure water stream of 3001S or higher, while the outside is exposed to a water flow of 250~
It is exposed to a high-temperature, high-pressure water stream (including steam) at 300°C, but if the high-temperature water on the outside is simply degassed, the heat exchanger tube material is made of a Ni-based alloy such as Alloy 600. However, since there is a tendency to cause IGAv, current
(A# Vocatiae Treatment)
Processing 1. Teiroko's AVT treatment involves adding ammonia to the water supplied to the outside of the heat exchanger tube material to obtain 1) HY8.5
~9.2, thereby suppressing the corrosion of external members, such as the carbon steel support members incorporated to secure the pipe, and the magnetite (Fe304) that melts into this. ) while minimizing the amount of dissolved oxygen fjr in the water (this water becomes an alkaline aqueous solution by adding ammonia and hydrazine) by adding hydrazine (N2H4): 10 ppb
IJ, evacuate the bottom and reduce the remaining amount of hydrazine to a maximum of s.
This is a treatment that prevents the occurrence of two-grain boundary stress corrosion cracking in alloy 600 pipe material by controlling the ppb to ppb.

[Problem that the invention seeks to solve]

However, even if the degassed alkaline aqueous solution prepared by the above-mentioned AVT treatment (-) is used, if it is concentrated at high temperatures and the alkaline concentration becomes high in the gap between the Ni alloy pipe material and the pipe material support member, this pipe material Particularly in the area near the outer surface gap.
The current situation is that OA begins to occur, and particularly when oxide slurry such as Fe3O4 adheres to the surface of the pipe material, IOA is significantly accelerated.

[Means for solving problems]

Therefore, as a result of repeated research to solve the above-mentioned problems, the present inventors found that according to the degassed alkaline aqueous solution C2 prepared by the above-mentioned AvT treatment, the alloy 600 in contact with it
The corrosion potential of Ni-based alloy members should fall and move out of the IOA generation potential region. : If present, for example in Figure 1, the temperature containing 40% NaOH = 325 °C
Fe3O4:
Alloy 600 with 467 f 'l addition L e HA
As shown by the curve (cr) showing the change in corrosion potential over time, the corrosion potential of alloy 600 is higher than that in the case without Fe3O4Y [shown by curve (a)], and
In the A generation potential region (:), IOA is generated in alloy 600.

(b) However, when a chain amine having a carboxyl group or an alcohol group is added to the above degassed alkaline aqueous solution, the corrosion potential of the Ni-based alloy member that comes into contact with the chain amine increases due to oxide sludge such as Fe3O4, etc. does not rise even if it exists, so the Ni-based alloy member CIGA does not occur.

fcl This effect of addition of a chain amine is accelerated by -1 when hydrogen gas is added to the gas phase in contact with the degassed alkaline aqueous solution.

The findings shown above have been obtained.

The present invention has been made based on the above findings, and the present invention has been made based on the above findings. At the same time, 0.1 pI) m to 1% by weight of the degassed alkaline aqueous solution is added to the degassed alkaline aqueous solution, and 3×10 -5
Adding hydrogen gas at a rate of ~1×10 atm (;
Therefore, the present invention is characterized by a method for preventing the formation of Ni-based alloy member i:IGA that comes into contact with a high-temperature degassed alkaline aqueous solution.

The high-temperature degassed alkaline aqueous solution in the method of the present invention is an AVT-treated aqueous solution that is used on the outside of the tube of the heat exchanger and is normally exposed to a temperature of 300°C or higher, that is, general ζ: p with ammonia. 1vs, s~9
．． 2 and degassed with hydrazine to remove dissolved oxygen
Lower ppbL2L and add hydrazine ft5ppl
Although the aqueous solution that remains under L and is in contact with a gas phase, generally consisting of water vapor, on the outside of the tube material, the degassed alkaline aqueous solution to which the method of the present invention is directed applies to such heat exchanger tube materials. It is not limited to aqueous solutions used outside of the tank, but covers all degassed alkaline aqueous solutions that are in contact with the gas phase and exposed to high temperatures.
This prevents IOA from being generated in Ni-based alloy members due to the high temperature degassed alkaline aqueous solution.

In addition, in the method of the present invention, examples of the chain amine having a carboxyl group include sarcosine, alanine, β-aminoisovaleric acid, α-aminoisovaleric acid, L-arginine,
Examples include α-aminobutyric acid and β-aminobutyric acid.
There are no restrictions on the type, and any type of amine is applicable, but preferably sarcosine, alanine, and L-arginine are used.As the chain amine having an alcohol group, for example, 2-amino-2-meth Leh 1
It is desirable to use probal (hereinafter referred to as AMP), 2-amino-ethanol (hereinafter referred to as α-AB), and the like.

As mentioned above, the power in this inventive method! A chain amine having a levoxyl group or an alcohol group is produced in a high-temperature degassed alkaline aqueous solution together with hydrogen gas added to the gas phase in contact with the aqueous solution (which in turn dissolves into the aqueous solution and creates sludge). Fe3 precipitates in a shape or a scale shape
It has the effect of suppressing the increase in the corrosion potential of Ni-based alloy members due to impurities such as O4 and preventing the corrosion potential from entering the IOA generation potential region, but its addition has the effect of reducing the weight ratio to the degassed alkaline aqueous solution. Therefore, if the amount is less than o,ippm, the desired effect cannot be obtained in the above action, and on the other hand, even if the addition amount exceeds 1% at the same ratio, the effect of further improvement in the above action will not appear. , its addition amount Y0
．． 1pI)m~1%.

Furthermore, the hydrogen gas in the method of the present invention may be caused by the adverse effects of impurities such as Fe3O4 in the degassed alkaline aqueous solution of the chain amine. In order to promote the counteracting effect, that is, the effect of suppressing the increase in the corrosion potential of the Ni-based alloy member that is in contact with the degassed alkaline aqueous solution (:, something added to the gas phase that joins with the degassed alkaline aqueous solution) As mentioned above, if the amount added is less than 3 x 10-5 atm relative to 1 atm in the gas phase, the desired effect will not be obtained and corrosion of the Ni-based alloy member will occur. The potential is (
On the other hand, if the amount added exceeds the GA generation potential range (I x 10-1 atm?), there is a risk of hydrogen embrittlement in Ni-based alloy members such as Alloy 600, and If this is applied, the amount of hydrogen gas consumed will be very large, leading to high costs, so the amount added should be 3 x 10-5 to 1
Must be at 10 atmospheres.

Note that the addition of hydrogen gas in the method of this invention is determined by the ratio to the gas phase = 1 atm as described above.
Even if the pressure of the gas phase fluctuates, the pressure of the hydrogen gas added will vary (in proportion) to the total pressure of the gas phase, so the amount of hydrogen gas added will depend on the pressure of the gas phase ( It remains constant regardless of fluctuations in the total pressure.

〔Example〕

Next, the method of the present invention will be specifically explained using examples.

First, as test piece 1 for corrosion potential measurement, a second
Figure (shape shown in one plan view, length: 200 w x width: 2 cm elongated arc-shaped part 1a, and a plate-like part 1b of 10 days x 10 m protruding from one end of this arc-shaped part, curving shape C=,
A C-ring test piece 2 cut out along the direction perpendicular to the axial direction of the pipe material and used as a test piece for the IOA test,
Similarly, from the above-mentioned 600 alloy pipe material, the shape shown in the front view in Fig. 3 (a) and in the side view in Fig. The C-ring test piece 2 has the through-holes 2a and 2a formed therein as shown in FIG.
A, 2aC bolt 3 was inserted and tightened with a nut 4°4 from the outside to set the Young's modulus of alloy 600 to 20,000, and a stress of zoK4f/- was applied to it.

On the other hand, as an alkaline aqueous solution, NaOH with a concentration of 40%
Fe3O4:467f as pure substance in 11 in aqueous solution
◎ Next, the above two types of test pieces were charged into an autoclave made of alloy 600 having an internal volume of 21 mm, together with the above aqueous alkali solution, and the above alkali solution was added to accelerate the IOA. Degassing with an aqueous Ar solution, followed by adding hydrogen gas (the rest is Ar gas) into the gas phase at a pressure (feed pressure) = 1 atm in the autoclave at the partial pressure shown in Table 1, Furthermore, the same <Mike A syringe with various chain amines in the proportions shown in Table 1? and added to the degassed alkaline aqueous solution, and then
Autoclave? The degassed alkaline aqueous solution therein was heated to 325°C, and the internal pressure of the autoclave was raised to ? 6
5~/d, each test piece was exposed to this temperature and pressure for 20 minutes.
Methods 1 to 19 of the present invention and comparative methods 1 to 6 are carried out for 0 hours, and the corrosion magnetic potential generated during this period is measured by connecting a potenduo stand (potential measurement instrument) to the corrosion potential measurement test piece. The standard electrode was Ag/
AgC/! electrode? The C-ring test piece was taken out from the autoclave, and the central part (the part facing the notch) was cut with a micro cutter in the width direction. What is the maximum crack depth of IGA that is formed on the cut surface by cutting, embedding the cut surface in epoxy resin, and polishing? Measured using an optical microscope. The results of these measurements are shown in Table 1.

In addition, Comparative Method 1-6 is a case where a chain amine and hydrogen gas are not added (Comparative Method 1), a case where a chain amine is added but no hydrogen gas is added (Comparative Method 2.3), and (Comparative Methods 4 to 6) where the addition of hydrogen gas is lower than the scope of the present invention even if a chain amine is added;

〔Effect of the invention〕

From the results shown in Table 1, in Comparative method 1 without adding chain amine and hydrogen gas, the corrosion potential was -1.30V.
The IOA resistance reached 41,270 pm, penetrated through the wall thickness, and had extremely poor IGA resistance. In Comparative Methods 2 and 3, in which lppm was added, the corrosion potential decreased slightly, but the IO
The maximum crack depth of IOA is in the A generation potential region, and the maximum crack depth of IOA is only slightly reduced (as seen in Comparative Methods 4 to 6, even if chain amine is added, the amount of hydrogen gas added is When C2 is outside the range of this invention, the maximum crack retention of IOA decreases as well, but it is still quite large at 300 to 400/7 m.
In No. 9, the corrosion potential is outside the IOA generation potential region and is low, and there is almost no IOA generation, and it is clear that even if IOA generation occurs, it is significantly suppressed.

In addition, in the above example, the explanation was given using an alloy 600 member as an example of a Ni-based alloy member that is currently widely used in an environment where it comes into contact with a high-temperature degassed alkaline aqueous solution. This (without limitation) any N that may cause IOA under the above environment.
Of course, it can be applied to i-based alloy members.

As described above (-1) According to the method of the present invention, IOA generated in a Ni-based alloy member that comes into contact with a high-temperature degassed alkaline aqueous solution that is in contact with a gas phase is removed by adding a small amount of hydrogen gas to the gas phase, Moreover, the problem can be effectively prevented by simply adding a small amount of chain amine to the aqueous solution, and the Ni-based alloy member can exhibit its performance for an extremely long period of time.

[Brief explanation of the drawing]

Figure 1 shows alloy 600 in two types of high-temperature degassed alkaline aqueous solutions.
FIG. 2 is a plan view of a test piece for corrosion potential measurement, and FIGS. 3(A) and 3(B) are a front view and a side view of a test piece for IOA testing. 1... Test piece for corrosion potential measurement, 2... CIJ song test piece as a test piece for IOA test, 3... Bolt, 4... Nut.

Claims (1)

[Scope of Claims] One or more types of chain amines having a carboxyl group or an alcohol group are added to a high-temperature degassed alkali aqueous solution that comes into contact with the Ni-based alloy member, based on the weight relative to the degassed alkali aqueous solution. 0.1 ppm to 1% in proportion, and 3 x 10^-^5 to 1 x 10 in proportion to 1 atmosphere of gas phase in the gas phase that contacts the high temperature degassed alkaline aqueous solution.
^-^ A method for preventing grain boundary damage in a Ni-based alloy member, characterized by adding hydrogen gas at a rate of 1 atm.