JPH063287B2 - Light water reactor steam generator tube - Google Patents

Description

The present invention relates to a tube for a light water reactor steam generator having excellent stress corrosion cracking resistance.

[Conventional technology]

In the steam generator tube of a light water reactor type reactor, the inner surface is the primary side environment in which pure water that has passed through the reactor circulates, and the outer surface is cooled by seawater and is circulated for use. It becomes the secondary environment.

Currently, such a steam generator tube has a secondary side (AV
T treatment) environment, that is, Cl ⁻ when seawater leaks
Alloy 600 (trade name), which has excellent corrosion resistance in the environment, is mainly used.

However, it has recently been reported that stress corrosion cracking, which is thought to be caused by alkali concentration, occurs in the Alloy 600 tube in the secondary environment. It is considered that the largest factor of this alkali concentration is that Na ⁺ ions flow out from the resin due to a defective ion exchange resin in the system and flow into the system.

In addition, the primary side environment (main component is, for example, several hundred ppm B ³⁺ + 1pp
It is said that stress corrosion cracking also occurs inside the U bend tip of the small diameter tube of Alloy 600 even under mLi ⁺ + H ₂ ).

The following countermeasures have been conventionally taken against these stress corrosion cracking, but in reality, they all have the problems as described.

Measures from environmental (i): Cl which is corrosion factor ^-, O _2, Na ^+, metal oxides
_{(Fe 3 O 4, Cu 20} ) reduction of such, (b) inhibitors There is corrosion due to the addition of (corrosion inhibitor), (b), the reaction system _{^{Cl -, O 2, Na +}} , metal oxides (Fe ₃ O ₄ , C
It is extremely difficult to reduce u ₂₀ ), etc., and in (b), the inhibitor is generally very expensive, and it is economically disadvantageous to add a large amount of it to the system.

Measures from the material side (a): As material improvement (a) Optimization of basic Ni-Cr-Fe components (b) Addition or reduction of minor components, but primary and secondary environment inside and outside the tube However, it is difficult to develop a Ni-Cr-Fe basic component alloy that is suitable for both. Further, even if the addition or reduction of the trace component is added, the influence of the trace element varies, and it is difficult to select an appropriate element and content for the stress corrosion resistance.

(B): As a special heat treatment application, there is a method of heating at 650 to 800 ℃ for a long time to sufficiently recover the Cr deficient layer and precipitate Cr carbide, but this is costly and depending on the case. Is preferable in one environment, but stress corrosion cracking resistance is extremely deteriorated in the other environment, which is not preferable.

(C): Even with the method combining the above (A) and (B), it is still difficult to obtain a proper material for both different environments inside and outside.

As described above, any of the conventional measures is insufficient as a measure for preventing stress corrosion cracking, and therefore a new measure has been desired.

[Object of the Invention]

The present invention meets the above-mentioned demand, and an object of the present invention is to provide a pipe for a light water reactor steam generator, which exhibits extremely good stress corrosion cracking resistance against different corrosive environments inside and outside the pipe.

[Structure of Invention]

The gist of the present invention is a pipe for a light water reactor steam generator, characterized in that a Ni plating layer is provided on the outer surface of a Ni-based alloy pipe containing Ni40 to 70 Wt% and Cr20 to 35 Wt%.

In other words, the steam generator tube of the present invention is an improvement in terms of material, and is made of pure Ni which exhibits excellent stress corrosion cracking resistance not only in Cl ⁻ but also in the secondary side environment consisting of an alkali-concentrated corrosive environment. It is placed on the outer surface and the main component is, for example, several hundreds.
Using a Ni-based alloy with a component composition that exhibits excellent stress corrosion cracking resistance in a primary environment consisting of ppmB ³ + 1ppmLi ⁺ + H ₂ corrosive environment as an inner substrate, to withstand both different corrosive environments flowing inside and outside It is the one.

Next, a method for manufacturing the steam generator tube of the present invention will be described.

) First of all, a pipe to be the inner basic (a coated original pipe) is manufactured.

A predetermined alloy material (for example, Alloy 600 or Alloy 690) is melted in a vacuum melting furnace, then forged, and peeled to form a billet having a predetermined size. This billet is then machined to form a raw tube by hot-tube extrusion, which is cold-worked and softened halfway,
It is subjected to cold drawing and then subjected to a final heat treatment to obtain a coated raw tube.

) Next, this original pipe is plated with Ni.

As a plating method, basically any method may be used as long as Ni plating is possible. Specifically, electroplating, thermal spraying,
Although electroless plating or the like can be adopted, the practical one is electroplating, and among these, the Japanese Patent Application No.
The plating method of -129321 (Japanese Patent Application No. 58-31097) is recommended.

In the case of electroplating, the following procedure is common.

First, the outer surface of the raw tube is velder-polished, degreased with an organic solvent (acetone, trichlene) and dried, then electrolytically polished with a 10% NaOH solution, and immediately after washing with water, electroplating is performed in a Ni plating bath.

By the way, plating of Ni or the like is generally difficult to obtain a sufficient coating film with a material containing a large amount of Cr such as the above-mentioned raw pipe, but in order to cope with such a tendency, it is necessary to perform prior electroplating. It is effective to perform the following pretreatment for surface activation (Japanese Patent Application No. 56-129321). That is, anodic electrolysis is once carried out in an acidic aqueous solution containing chloride, and then, cathodic electrolysis is carried out while keeping this aqueous solution.
The acidic aqueous solution containing chloride means a pH acidic aqueous solution containing Cl ⁻ and plating metal (here, Ni) ions. As an additive in this acidic aqueous solution
LiCl, NaCl, KCl, MgCl ₂ , CaCl ₂ may be contained.

Next, the reason why the contents of Ni and Cr of the inner base in the present invention are limited as described above will be explained.

If the Ni content is less than 40%, the Ni content will be insufficient and high temperature (400 to 50
This is because embrittlement is likely to occur in a hydrogen atmosphere (0 ° C), and if it exceeds 70%, the Ni content is too high for the primary side environment, and the passivation film becomes unstable at a high temperature of 360 ° C. This is because stress corrosion cracking easily occurs. Also, if the Cr content is less than 20%, a complete stable layer of Cr ₂ O ₃ cannot be obtained, and if it exceeds 35%, the hot forgeability is greatly deteriorated, which is not preferable.

On the other hand, the Ni plating layer on the outer surface layer shows excellent stress corrosion cracking resistance not only in Cl ⁻ but also in the secondary environment of alkali concentration.

The thickness of the Ni plating layer is not particularly limited, but as will be apparent from the examples described below, if it is less than 50 μm, the stress corrosion cracking resistance is not sufficient, so it is preferable to make it more than this, and from the viewpoint of cost, at most 200 μm. It is preferable to stop it to some extent.

〔Example〕

Alloys (A) to (E) having the composition shown in Table 1 to be the inner substrate of the steam generator tube are vacuum melted to 500 kg each, and after peeling, a billet with a predetermined size (180 mmφ to 100 mmφ) is made. After machining, it is extruded by heating at 1200 ℃ to form a blank tube, then cold working, after softening on the way, cold drawing is performed to obtain a tube of 19.05mmφ × 1.3mmt, which is heat-treated into a product (1050 ℃ × 2 minutes). AC) was applied to make a raw tube.

Next, using this raw pipe, outer surface velder polishing-degreasing with organic solvent, drying-10 electrolytic polishing using 10% NaOH solution (raw pipe: +
Electrode, iron removal: − electrode, 4 A / dm ² , 5 minutes, room temperature) − Immediately after washing with water, electroplating (plating bath: Ni sulfonate bath, anode: Ni, 2 A / dm ² , 50) Ni coating tube was manufactured through the above steps of conducting electricity up to 60 ° C) until the required coating thickness is reached.

The following corrosion test was performed on the Ni-coated tube thus obtained and the above-mentioned original tube without Ni plating.

(B) Test in secondary environment From each test tube, an arc type test piece as shown in Fig. 2 (2mm thickness x
(10 mm width × 75 mm length) was sampled, 5 mmφ drill holes were formed at both ends of the sample, then bent into a U shape with a radius of 5 mmR, and further restrained by a bolt / nut for 5 mm for the test. The test is 15% NaOH
After degassing the solution, it was heated and maintained at 330 ° C., and the test piece was immersed in this for 600 hours.

(B) Test in the primary side environment Each test tube was cut into a length of 500 mm, 15% tensile strain was applied to it, and then the same arc-shaped test piece (Fig. 2) was sampled. It was bent so that the basic side was the outside, and subjected to the same U-bend test as in (a). The test is 800ppmB ³⁺ ＋ 2p
A solution of pmLi ⁺ +30 CCH ₂ / H ₂ O · kg was degassed, heated at 360 ° C. and held, and immersed in this for 500 hours.

After each of the above tests was completed, the test piece was cut in half, a resin was embedded in the cut surface, and the crack depth was measured with an optical microscope to determine whether the stress corrosion cracking resistance was good or bad.

The results of each test are shown in Table 2.

In Table 2, all conventional examples (raw pipes) are alkali resistant
SCC property (under secondary environment) is inferior. In addition, in the comparative examples in which the basic materials are D and E (Ni ≧ 70 Wt%), the Ni plating layer is present, so the alkali SCC resistance is good, but the SCC resistance in the primary side environment is poor. On the other hand, all of the examples of the present invention having the Ni plating layer and the component range of the substrate within the range of the present invention showed excellent SCC resistance in any environment.

Although not shown here, the Ni plating layer is Cl ^−.
Excellent SCC resistance under the environment.

As is clear from the data shown in FIG. 3 (subject to No. 2 in Table 2), if the thickness of the Ni plating layer is less than 50 μm, the effect is small. Therefore, the thickness is preferably 50 μm or more.

〔The invention's effect〕

As is clear from the above description, the pipe for a light water reactor steam generator of the present invention uses a Ni-containing alloy containing Cr on the outside and a Ni content lower on the inside to make the primary side (usually several hundreds ppmB ³⁺ +1).
(ppmLi ⁺ + H ₂ ) and secondary side (Cl ⁻ or alkali-concentrated) different corrosion environments, it exhibits excellent stress corrosion cracking resistance, so it has a significant effect on extending the life of the pipe. Demonstrate.

[Brief description of drawings]

FIG. 1 is a process diagram showing the plating apparatus used in the examples, and FIG.
The figure is a perspective view showing the shape of the test piece, and FIG. 3 is experimental data showing the relationship between the thickness of the Ni plating layer and the stress corrosion cracking depth.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-55-125251 (JP, A) JP-A-56-25958 (JP, A) JP-A-61-122403 (JP, A)

Claims (1)

[Claims] 1. A pipe for a light water reactor steam generator, wherein a Ni plating layer is provided on the outer surface of a Ni-based alloy pipe containing Ni of 40 to 70 Wt% and Cr of 20 to 35 Wt%.