JPH06170468A - Method for joining zirconium alloy tube and martensitic stainless steel tube - Google Patents

Abstract

PURPOSE:To suppress damages due to crevice corrosion by inserting the inner side of a zirconium tube after generating oxide film at the end of a stainless steel tube. CONSTITUTION:An end part of a tubular member 2 made of martensitic stainless steel is inserted into the tube end of a tube 1 made of zirconium or zirconium alloy, and joined from the inside through expansion. The inner and outer surface of the end part of the martensitic stainless steel tube 2 are heated to 250 deg.C or over to generate the oxide film. Then, the end part is inserted into the inner surface of the zirconium alloy tube 1. An outer ring 3 is fitted while the outer circumferential surface of the expanded part of the zirconium alloy tube 1 being pressed. Thus, when being exposed to the water of high temperature of 200-350 deg.C, absorption of hydrogen by zirconium and zirconium alloy due to dissimilar metal contact corrosion can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for mechanically connecting a pipe made of zirconium or a zirconium alloy and an extension pipe made of a martensitic stainless steel pipe to a high temperature water of a pipe made of zirconium or a zirconium alloy at a connecting portion. The present invention relates to a method for connecting a martensitic stainless steel pipe and a pressure pipe made of zirconium or a zirconium alloy suitable for suppressing hydrogen absorption.

[0002]

2. Description of the Related Art A connection between a tube made of zirconium or a zirconium alloy and a stainless steel tube, which is a dissimilar metal, is difficult to perform metallurgically by welding.
As described in the specifications of No. 59-6751 and Japanese Patent Application No. 63-279250, the pipe is expanded and mechanically joined.

However, crevice corrosion occurs at the connection surface between the conventional tube made of a zirconium alloy and a stainless steel tube which is a dissimilar metal, and the generated hydrogen is easily absorbed by the zirconium alloy tube. as a result,
It is feared that the zirconium alloy tube becomes brittle as the hydrogen concentration increases.

[0004]

SUMMARY OF THE INVENTION The above-mentioned prior art is a sacrifice of stainless steel because the dissimilar metal of zirconium alloy and stainless steel constitutes a gap, and electrochemically stainless steel has the most base potential. There is a problem that it becomes an anode and the anode dissolves to cause corrosion damage, and that the generated hydrogen is absorbed by zirconium.

An object of the present invention is to prevent martensitic stainless steel and zirconium alloy from being damaged by crevice corrosion.

[0006]

In order to achieve the above object, at the contact portion between martensitic stainless steel and zirconium and zirconium alloy, the martensitic stainless steel that comes into contact with zirconium and zirconium alloy before joining by expansion is performed. The surface portion on the stainless steel side is kept in a high temperature atmosphere to form a high temperature oxide film.

[0007]

[Function] The surface of the martensitic stainless steel is heated at a high temperature for surface modification. That is, a high temperature oxide film is formed on the surface of the martensitic stainless steel by the high temperature heat treatment. As a result, the surface of the martensitic stainless steel has remarkable corrosion resistance, which is effective in suppressing contact corrosion with zirconium and zirconium alloys. Therefore, from 200 ℃ to 3
When exposed to high temperature water of 50 ° C., it is possible to suppress zirconium and the zirconium alloy from absorbing hydrogen due to corrosion of dissimilar metals.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a zirconium-niobium alloy pipe according to the present invention and a martensitic stainless steel pipe before being connected.
An inner surface of the end surface of the martensitic stainless steel pipe is machined with an inner sleeve 2 having an outer diameter larger than the inner diameter of the zirconium-niobium alloy pipe 1. The surface of the taper portion of the sleeve 2 is preliminarily 1
A high temperature oxide film 4 formed by holding for 0 hour is added. The zirconium-niobium alloy tube 1 is preliminarily inserted with an outer ring 3 having a tapered portion opposite to the tapered portion of the inner sleeve 2. The inner diameter of the tapered portion of the outer ring 3 is the outer diameter of the inner sleeve 2 plus a value slightly smaller than twice the wall thickness of the zirconium-niobium alloy tube 1. The state in which the zirconium-niobium alloy tube 1 is inserted along the tapered portion of the inner sleeve 2 while applying a load and the zirconium-niobium alloy tube 1 is expanded is shown in FIG.
Is. After completing the insertion into the inner sleeve 2 while expanding the zirconium-niobium alloy tube 1, a non-destructive inspection such as visual inspection and ultrasonic flaw detection is performed from the outer surface of the expanded zirconium-niobium alloy tube 1. After confirming that the expanded part of the zirconium-niobium alloy tube 1 has no harmful defects, as shown in FIG.
The zirconium-niobium alloy tube 1 is fitted while pressing the outer peripheral surface of the expanded portion. The outer ring 3 is screwed to the inner sleeve 2.

After joining, 561K (288 ° C), 7.8M
FIG. 4 shows the relationship between the hydrogen concentration increase amount and time of the zirconium-niobium alloy tube immersed in high-temperature water of Pa 2. The hydrogen concentration increase amount of the zirconium-niobium alloy tube of this example is
It is clear that it is as low as about 1/5 as compared with the conventional technique.
The initial hydrogen content of the zirconium-niobium alloy tube of this example was about 10 ppm.

According to this embodiment, the surface of the inner sleeve which comes into contact with the zirconium-niobium alloy tube has remarkable corrosion resistance, which is effective in suppressing contact corrosion. Therefore, when exposed to high temperature water of 200 ° C. to 350 ° C., damage to zirconium and zirconium alloy due to corrosion of dissimilar metals can be suppressed. That is, there is an effect of reducing embrittlement of zirconium and a zirconium alloy tube due to hydrogen absorption.

[0012]

According to the present invention, when the gap between the dissimilar metal joint between the zirconium and zirconium alloy pipe and the martensitic stainless steel is exposed to high temperature water of 200 ° C to 350 ° C, the martensitic stainless steel is Damage to the zirconium and zirconium alloy pressure pipes due to crevice corrosion can be suppressed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a zirconium or zirconium alloy pipe and a martensitic stainless steel pipe before joining, showing an embodiment of the present invention.

FIG. 2 is a sectional view illustrating a joining method according to the present invention.

FIG. 3 is a cross-sectional view showing the joining of zirconium and a zirconium alloy tube and a martensitic stainless steel tube according to the present invention.

FIG. 4 is a characteristic diagram showing hydrogen absorption characteristics of a zirconium alloy tube according to the related art and the present invention.

[Explanation of symbols]

1 ... Zirconium alloy tube, 2 ... Martensitic stainless steel tube inner sleeve, 3 ... Outer ring, 4 ... High temperature oxide film of martensitic stainless steel tube.

Claims (1)

[Claims] 1. A method of inserting an end of a tubular member made of martensitic stainless steel into a pipe end of a pipe made of zirconium or a zirconium alloy and connecting from the inside by expanding the pipe, wherein the end of the martensitic stainless steel pipe is A method for joining a zirconium alloy tube and a martensitic stainless steel tube, which comprises heating the inner and outer surfaces of the part to 250 ° C. or higher to form an oxide film and then inserting the oxide film into the inner surface of the zirconium or zirconium alloy tube.