Sheathed thermocouple for high-temperature hydrogen atmosphere

Abstract

To provide a sheathed thermocouple for high-temperature hydrogen atmosphere, which is capable of preventing reduction in temperature measurement accuracy and in strength of a metal sheath.SOLUTION: Thermocouple wires 31, 32 are Nicrosil-Nisil thermocouple wires, and a metal sheath 2 has a multilayer structure comprising an inner layer 21 made of a nickel-based alloy and an outer layer 22 made of an austenitic stainless steel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sheathed thermocouple for use in a high-temperature hydrogen atmosphere, which is used for measuring temperatures in a high-temperature hydrogen-containing atmosphere such as a hydrogen reduction furnace. [Background technology]

[0002] Conventionally, sheathed thermocouples for temperature measurement have been provided in which two different types of thermocouple wires are connected to each other at their tips, and when a temperature difference occurs between this connection (hot junction), a thermoelectric power is generated in a closed circuit, causing a current to flow through the circuit, thereby measuring temperature using the Seebeck effect. A sheathed thermocouple is formed by encasing a thermocouple wire in a metal sheath, which is then filled and sealed with an inorganic insulator such as magnesium oxide (MgO) to form an integrated unit (see, for example, Patent Documents 1 and 2).

[0003] In recent years, the use of hydrogen has been promoted as a measure against global warming. For example, hydrogen reduction furnaces are being put into practical use in steelmaking furnaces, and temperature measurement in such hydrogen-containing atmospheres is required. In high-temperature environments above 800°C, especially in temperatures exceeding 1000°C like those in steelmaking furnaces, there have been problems such as a decrease in temperature measurement accuracy and a decrease in strength due to embrittlement of the metal sheath caused by the hydrogen contained in the atmosphere. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-82557 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-165780 Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above-mentioned circumstances, the present invention aims to solve the problems by providing a sheathed thermocouple for use in a high-temperature hydrogen atmosphere, which can prevent a decrease in the accuracy of temperature measurement and a decrease in the strength of the metal sheath. [Means for solving the problem]

[0006] In light of this current situation, the present inventors have focused on "stable austenitic stainless steels" with a nickel equivalent of around 40%, such as Type 310 stainless steel (SUS310S), which is resistant to hydrogen embrittlement, as the material for the metal sheath (Shigeo Nomura et al., "Hydrogen Damage in Austenitic Stainless Steels," Journal of the Japan Institute of Metals, 15-9, pp. 563-570 (1976)). They also focused on Nicrosil-Nisil thermocouple (N thermocouple) wires, which generally have stable thermoelectric properties in high-temperature environments, as the internal thermocouple wires. However, although embrittlement of the metal sheath can be prevented, a new problem has arisen: in high-temperature environments, mutual diffusion between the austenitic stainless steel and the Nicrosil-Nisil thermocouple wires causes a thermoelectric power change (drift), which reduces the accuracy of temperature measurement.

[0007] As a result of further intensive research, the inventors have found that by providing a layer of a nickel-based alloy, which is a material with the same or similar composition as the wire of the Nicrosil-Nisil thermocouple (N thermocouple), inside the "austenitic stainless steel," it is possible to prevent the thermoelectric power change and maintain both the temperature measurement accuracy and the strength of the metal sheath in a high-temperature, hydrogen-containing atmosphere. This finding led to the completion of the present invention.

[0008] That is, the present invention includes the following inventions. (1) A sheathed thermocouple for use in a high-temperature hydrogen atmosphere used for measuring temperature in a high-temperature hydrogen-containing atmosphere, which includes a metal sheath containing at least one pair of thermocouple wires and an inorganic insulator filling the gap between the thermocouple wires and the metal sheath, the thermocouple wires being Nicrosil-Nisil thermocouple wires, and the metal sheath having a multilayer structure with an inner layer made of a nickel-based alloy and an outer layer made of austenitic stainless steel.

[0009] (2) A sheathed thermocouple for use in a high-temperature hydrogen atmosphere according to (1), wherein the inner layer is made of Inconel (registered trademark) Alloy TD.

[0010] (3) The sheathed thermocouple for use in a high-temperature hydrogen atmosphere according to (1) or (2), wherein the outer layer is made of SUS310S. [Effects of the Invention]

[0011] According to the sheathed thermocouple for use in a high-temperature hydrogen atmosphere according to the present invention configured as described above, it is possible to prevent a decrease in the accuracy of temperature measurement and a decrease in the strength of the metal sheath. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a longitudinal cross-sectional view showing a sheathed thermocouple for use in a high-temperature hydrogen atmosphere according to a representative embodiment of the present invention. [Figure 2] FIG. 10 is a cross-sectional view of a sheathed thermocouple for use in a high-temperature hydrogen atmosphere. [Figure 3] FIG. 10 is an explanatory diagram showing a manufacturing procedure for a sheathed thermocouple for use in a high-temperature hydrogen atmosphere. [Figure 4] 10A to 10C are explanatory views showing another manufacturing procedure for the sheathed thermocouple for use in a high-temperature hydrogen atmosphere. DETAILED DESCRIPTION OF THE INVENTION

[0013] Next, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0014] As shown in FIGS. 1 and 2 , a sheathed thermocouple 1 for use in a high-temperature hydrogen atmosphere according to the present invention is a sheathed thermocouple for use in a high-temperature hydrogen atmosphere, in which at least a pair of Nicrosil-Nisil thermocouple wires 31, 32 and an inorganic insulator 4 that fills the gap between these thermocouple wires 31, 32 and the metal sheath 2 are housed inside a metal sheath 2.

[0015] In this example, the thermocouple contains only one pair of wires 31 and 32, but it may contain three or more wires. The inorganic insulator 4 can be any of the materials commonly used for sheathed thermocouples (e.g., magnesium oxide (MgO)).

[0016] The sheathed thermocouple 1 for use in high-temperature hydrogen atmospheres of the present invention is characterized in that, in addition to using the above-mentioned Nicrosil-Nisil thermocouple wire as the thermocouple wire, the metal sheath 2 has a multilayer structure having an inner layer 21 made of a nickel-based alloy and an outer layer 22 made of austenitic stainless steel. With such a multilayered metal sheath 2, the outer layer 22 is less susceptible to embrittlement due to high-temperature hydrogen, maintaining the strength of the entire metal sheath 2 and preventing thermoelectromotive force changes (drift) due to interdiffusion between the inner layer 21 and the thermocouple wires 31, 32, thereby maintaining good temperature measurement accuracy.

[0017] In the following embodiment, an example will be described in which the inner layer 21 and the outer layer 22 are formed by combining two sheath tubes that are each separately constructed, but the present invention is not limited to such a double-tube structure, and various configurations are possible, such as one in which one of the inner layer 21 and the outer layer 22 is constructed from a sheath tube and the other is formed on the inner or outer surface of the sheath tube by plating, thermal spraying, etc., or one in which the inner layer 21 and the outer layer 22 are attached to a base sheath tube by plating, thermal spraying, etc.

[0018] Furthermore, as long as the inner layer 21 and the outer layer 22 are positioned inside and outside each other, a third layer may of course be present in between or further outside. It is preferable that no other layer is present further inside the inner layer 21, that is, the inner layer 21 is the innermost layer of the metal sheath 2. This is because the presence of other layers may increase the effect of interdiffusion with the thermocouple wire.

[0019] Among nickel-based alloys, the inner layer 21 is preferably made of an alloy (Nicrosil material) mainly composed of nickel, chromium, and silicon, which is the same as or similar to the material of the positive wire of the thermocouple wires 31, 32, or an alloy (Nisil) mainly composed of nickel and silicon, which is the same as or similar to the material of the negative wire. Specifically, Inconel AlloyTD, which has a composition similar to that of the positive wire (Nicrosil) and does not contain aluminum or manganese, which are likely to cause drift, is preferred.

[0020] Furthermore, among austenitic stainless steels, SUS310S with a nickel equivalent of 39% is suitable for the outer layer 22. SUS310S is not susceptible to hydrogen embrittlement or hydrogen attack even in high-temperature and high-pressure environments, so the strength of the metal sheath is maintained.

[0021] The metal sheath 2, consisting of the inner layer 21 and the outer layer 22, is supported at its base end by a protective tube (not shown) and configured as a sheath-side thermocouple connected to a measuring instrument by a compensating conductor extending from a terminal box. It can also be configured as various types of sheathed thermocouples similar to conventional types, such as those in which the compensating conductor is directly connected without going through a terminal box or those provided with a detachable connector.

[0022] In this embodiment, as described above, the inner layer 21 and the outer layer 22 are formed by stacking the inner and outer sheath tubes 5 and 6, which are separately constructed, one on the other, and the tip portion 2a has two tip sealing portions 5a and 6a formed by welding and sealing the tip portions of the sheath tubes 5 and 6, respectively, and the gap s1 between the tip sealing portions 5a and 6a is filled with a powdered inorganic insulator 41 such as magnesium oxide (MgO).

[0023] By providing such a gap s1, it is possible to prevent the stable austenitic stainless steel (SUS310S in this example) at the tip of the molten outer sheath tube 6 from coming into contact with the inner tip sealing portion 5a and diffusing into the inner sheath tube 5 (inner layer 22), particularly when the outer tip sealing portion 6a is formed by welding, and this in turn causes the thermocouple wires 31, 32 inside the inner sheath tube 5, particularly the hot junction 33 (temperature measurement portion), which would result in temperature drift.

[0024] 3, in this example, thermocouple wires 31, 32 are first inserted into the inside of an inner sheath tube 5 in a single tube state together with an inorganic insulator 4, and a hot junction 33 is formed at the tip and sealed, thereby forming a thermocouple structure using a conventional method. Then, an outer sheath tube 6 is placed over the outer periphery of the inner sheath tube 5 and stretched (drawn) in the axial direction, so that the outer sheath tube 6 is in close contact with the outer surface of the inner sheath tube 5 in a state where it protrudes further toward the tip side than the tip sealing portion 5a of the inner sheath tube 5.

[0025] Next, powdered inorganic insulator 41 is compressed and filled into this protruding interior. Thereafter, the protruding interior is sealed by lap welding using a welding rod made of the same material as the outer layer (stable austenitic stainless steel (SUS310S in this example)), to form the tip sealing portion 6a. Here, as shown in Figure 4, it is also preferable to insert a plug material 61 made of the same material as the outer layer (stable austenitic stainless steel (SUS310S in this example)) to compress and fill the inorganic insulator 4, and then similarly lap welding to form the tip sealing portion 6a.

[0026] However, the manufacturing method is not limited to this, and for example, the inner sheath tube 5 may be covered with the outer sheath tube 6 and drawn to bring them into close contact with each other, and then the thermocouple wires 31, 32 may be inserted into the double tube together with the inorganic insulator 4 to form a hot junction 33 and the tip of the inner sheath tube 5 may be sealed by welding. Thereafter, as described above, the inside of the protruding outer sheath tube 6 may be filled with inorganic insulator 41 and sealed by welding with a material made of the same material as the outer layer 22, thereby forming the sealed tip portion 6a.

[0027] Although the embodiments of the present invention have been described above, the present invention is not limited to these examples, and it goes without saying that the present invention can be embodied in various forms without departing from the spirit of the present invention. [Explanation of symbols]

[0028] 1. Sheathed thermocouple for high-temperature hydrogen atmosphere 2. Double metal sheath 2a Tip 4. Inorganic insulators 5 Inner sheath tube 5a Tip sealing part 6. Outer sheath tube 6a Tip sealing part 21 Inner layer 22 Outer layer 31, 32 Thermocouple wire 33 Hot junction 41 Inorganic insulators 61 Plug material s1 gap

Claims

1. A sheathed thermocouple for use in a high-temperature hydrogen atmosphere used for measuring temperature in a high-temperature hydrogen-containing atmosphere, At least one pair of thermocouple wires and an inorganic insulator that fills the gap between the thermocouple wires and the metal sheath are housed inside the metal sheath, the thermocouple wire is a nicrosil-nicol thermocouple wire, The metal sheath has a multilayer structure having an inner layer made of a nickel-based alloy and an outer layer made of austenitic stainless steel. Sheathed thermocouple for use in high-temperature hydrogen atmospheres.

2. 2. The sheathed thermocouple for use in a high-temperature hydrogen atmosphere according to claim 1, wherein the outer layer is made of SUS310S.

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