JPS62124274A - Member for heat exchanger - Google Patents

Abstract

PURPOSE:To extend the life of a heat exchanger and to improve the reliability thereof by coating AlN on the surface of a member for the heat exchanger to be used in hot water thereby improving the corrosion resistance and oxidation resistance thereof. CONSTITUTION:The surface of the member for the heat exchanger to be used in hot water such as light water reactor is coated with AlN to improve the corrosion resistance and oxidation resistance thereof. The above-mentioned AlN has relatively high heat conductivity and minimizes the decrease of the heat exchanging efficiency by the above-mentioned coating. the AlN has a large coefft. of thermal expansion, and is hardly exfoliatable during use; further, the resistance to exfoliation is additionally improved by interposing at least either of TiN or ZeN. The AlN coating is preferably formed by using Al(OC3H8)3 and C as starting soln. by an alkoxide method, coating the coln. on the member surface, then hydrolyzing the coating to form Al2O3 and further heating the coating in a nitrogen atmosphere kept at >=800 deg.C or growing the AlN on the member surface by a CVD method, then heating the same to 800 deg.C.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a heat exchanger used in hot water such as a nuclear reactor or high-temperature gas reactor.
This invention relates to a heat exchanger member that has improved corrosion resistance by coating with N.

[Technical background of the invention and its problems]

The heat exchanger has a relatively low temperature (25
0~320℃), medium temperature like fast reactor (400~600℃)
℃) Furthermore, 6 as considered in high temperature gas furnaces.
Some have high temperatures of 50 to 1000°C. Corrosion resistance is primarily important for the former two materials, but heat resistance is additionally required for the latter. However, even if they have the same corrosion resistance, the cooling water used is different from water, carbon dioxide, liquid metal, and helium, so the characteristics vary widely.For example, in the case of helium, the temperature is higher due to the slight impurities contained in it than the helium itself. Even more so when deterioration due to corrosion becomes a problem.

When hydrogen is used as a heat transfer material, there are also problems such as hydrogen permeation through the material and the formation of hydrides. Specifically, heat exchanger materials include low and medium carbon steels, various stainless steels, and nickel alloys for water-cooled nuclear reactors, and 2.25%Cr-1%Mail and its improved steels for sodium-cooled fast reactors. Nbe Tll Ni, add) is used. These materials were selected for their corrosion resistance and heat resistance, but the efficiency life of the heat exchanger,
In order to improve reliability etc.

Even more reliable materials are desired.

[Purpose of the invention]

The present invention aims to provide a component for a heat exchanger whose surface is coated with ARN to improve corrosion resistance and oxidation resistance, in order to improve the lifespan and reliability of the heat exchanger.

[Summary of the invention] TINT ZrN+^Q, 04. AQNHSxCw
S,tO,*Tl01w n,c.

Many ceramics, such as Tic, 5l) N41 Y2O11+ CaO, have better insulation and oxidation resistance than metals. By coating metals and surfaces with this material, it is expected that the life of the material will be improved. However, not all ceramics are stable in hot water; for example, y, o,
A part of the powder easily undergoes a YOO-old structure change and deterioration in pure water at 250°C.

Therefore, a large number of ceramic raw material powders and sintered bodies were produced.
0℃ internal pressure 100kg/ad (7), 1i1i water temperature, m
An 800-hour immersion test was conducted while changing the acidic sta in the range of 20 Pppb to 8 ppm, and the corrosivity was examined from the weight change. As a result, Ties tA(t, 0.
In addition to many oxides such as ARN, Si, and N4, it has been found that they have excellent corrosion resistance in hot water.

Considering the efficiency of the heat exchanger, coating with ceramics having low thermal conductivity should be avoided.

In the heat transfer characteristics of a heat exchanger, for example, the inner diameter d. , outer diameter d
Considering the amount of heat transfer q in a circular pipe of long length Q.

The ceramic to be coated, expressed as L (ih-ie) at q=, has a thermal conductivity d(
, ) is too small, it is found to be inconvenient.

Table 1 shows the thermal conductivity d of various ceramics.

Table 1 From Table 1^0. N, Ag, 0. , Bed, ? ;j
It has been found that C, TiN, ZrN, etc. have a relatively large d, and it seems that the heat exchange efficiency will not deteriorate so much when these are thinly coated.

In fact, when a coating was applied to a thickness of 50 wm, the difference in heat exchange efficiency was only 5% or less compared to when no coating was applied.

Next, we investigated the bondability between ceramics and metals, such as AgN and A et al. 03, which have good corrosion resistance and a relatively large coefficient of thermal expansion, and TiN and ZrN, which have large coefficients of thermal expansion. Based on the following considerations.

In order to suppress the peeling of ceramics, it is preferable to laminate the ceramics densely and thinly, and the closer the thermal expansion coefficient of the laminated ceramics is to that of the metal, the smaller the interfacial stress will be, and the more peeling can be prevented.

Metals often used in heat exchangers include Fe and Mo.

Table 2 shows the thermal expansion coefficients of selected Ni and Cr and those of ceramics.

Table 2 Thermal expansion coefficient Fo of metals and ceramics
12. I TiN 9,3Mo
5. I ZrN 6~7Ni
13.3 Si 3.5~4Cr
8.2 Afl, 0. 7.3 Inconel 11. OSiC3,l 5US 304 17~18 Sin,
0.5AαN 4~7 Si, N, 2.5~3 From Table 2, Ding LN, ZrN and Al! It is clear that N is a material with good metal bonding properties, and peeling can be avoided if these are laminated extremely thinly. Therefore, using CvD@, Ti
Grow N, ZrN, and A4N on the surface of N1,
Results of holding these in the atmosphere at 600℃ for 500 hours A
For QN, peeling of about 5% was observed on the surface at 90 nm or more, but no peeling occurred on other areas. Therefore, AgN
To completely prevent peeling of the metal, place TiN or Z between the ON and the metal.
It is thought that it is better to have a structure in which rN is sandwiched, and in fact, no peeling was observed in a stack of 50 nw of TiN and 1100 n of AgN.

Furthermore, in the case where only AgN is used as a coating material without setting an intermediate layer, a method of laminating AffN using an alkoxide method was tried in order to layer AffN densely and thinly.

As a result, the layers were very densely laminated, so there were no particular problems, but in order to withstand long-term operation, it is effective to heat and stabilize the laminated layers at a temperature of 800°C or higher. It turns out that there is something.

When the corrosion resistance and oxidation resistance heat conduction efficiency of members not coated with ON were compared using the above experimental method, it was found that the former was better.

(Example of the invention) Next, in order to confirm the effects of the present invention, a double-tube heat exchanger made of the same material layer as a light water reactor heat exchanger was prototyped, and a part of the tube was replaced with the AQN cladding of the present invention. Instead, we conducted a comparative test with conventional materials.

5US with an inner diameter of 15 mm, an outer diameter of 30 mm, and a length of 7.2 m.
31 (Part of the double-walled tube manufactured by I was replaced with an AQN clad tube. The AgN tube was made as follows.

Average particle size 0.15m (7) CVD of high purity Al2N particles
By law 5 US 316! A double layer of 0.1 tm thick was uniformly laminated on both sides of the inner and outer surfaces of a double tube (1) to a thickness of 0.1 tm, and this was maintained at 500° C. for 24 hours in an Ar gas atmosphere to obtain a substitute tube. This was welded to a part of the double pipe.

In the above piping system, a test was conducted for 500 hours by flowing pure water at 200°C into the inner pipe ■ and pure water at 25°C into the outer pipe ■ at a rate of io, sg per minute, and the corrosion status of the inner pipe was observed. .

As a result, no increase or decrease in corrosion was observed in the alternative pipe coated with Al2N.

In 5O8316 steel pipes without any surface treatment, an oxidation layer of o, slm was observed on the surface, and the corrosion products were (Fe, Cr, Nj,), 0. It turned out to be.

Furthermore, in order to investigate the change in heat exchange efficiency due to one alternative tube, we monitored the speed of temperature change of the water flowing through the outer tube, and found that when the alternative tube was used, the efficiency decreased by 2% in the first 10 hours. However, during the subsequent 5 hours, the efficiency was comparable to that of the conventional tube, and after 15 hours, it was found that the alternative tube was actually more efficient.

The reason for this is presumed to be that an oxidized layer is formed on the surface of conventional tubes, causing the thermal efficiency to drop at a very rapid rate.

〔Effect of the invention〕

As explained above, the heat exchanger according to the present invention has a low heat exchange efficiency even when used for a long time.

Claims (6)

[Claims] (1) A heat exchanger member whose surface is coated with AlN. (2) The heat exchanger member according to claim 1, wherein the heat exchanger member is used in hot water. (3) Claims characterized in that the surface of a heat exchanger member used in hot water is coated in advance with at least one of TiN and ZrN, and the coating layer is further coated with AlN. The heat exchanger member according to item 1. (4) The heat exchanger member according to claim 1, wherein the surface is coated with AlN by an alkoxide method. (5) In the alkoxide method, the starting solution is Al(OC_3H
_8) _3 and C, applied to the surface of the member, brought into contact with water to induce a hydrolysis reaction to make the surface layer Al_2O_3, and after drying, heated in a nitrogen atmosphere at a temperature of 800°C or higher. A heat exchanger member according to claim 4, characterized in that: (6) Growing AlN on the surface of the member by CVD method,
The member for a heat exchanger according to claim 1, wherein the member is heated to a temperature of 800° C. or higher to improve oxidation resistance.