JPH08159903A - Differential-pressure detector for conductive fluid - Google Patents

Abstract

PURPOSE: To obtain a differential-pressure detector in which a zero point is not drifted and which comprises a metal diaphragm used to detect the differential-pressure of a conductive fluid by forming an electrically insulating substance layer on the pressure-receiving face of the metal diaphragm for differential-pressure detection. CONSTITUTION: Electrically insulating substance layers 10, 10a are applied on sides of pressure-receiving faces of diaphragms 7, 7a. When the electrically insulating substance layers 10, 10a are formed on the pressure-receiving faces of the diaphragms 7, 7a, a galvanic cell is not constituted, a corrosive action is not generated on surfaces of the diaphragms 7, 7a, and hydrogen does not permeate. Then, a fluid pressure which is applied to the high-pressure side and to the low-pressure side is applied to both sides of the pressure-sensitive diaphragm of a pressure sensor 9. The pressure-sensitive diaphragm is displaced in proportion to the differential pressure, between the high-pressure side and the low-pressure side, which is applied to both sides, its displacement is output as a differential-pressure signal in such a way that a change in a capacitance generated across two fixed electrodes opposed on both sides is converted and amplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential pressure detector used when measuring the differential pressure / pressure of various process fluids. More specifically, the differential pressure / pressure of a conductive fluid is made of metal. The present invention relates to a differential pressure detector (transmitter) that uses a membrane such as a diaphragm for detection.

[0002]

FIG. 20 shows an example of a conventional differential pressure detector, which is a differential pressure detector (transmitter) for a process using a conductive fluid such as seawater. 1 is a conductive fluid line such as seawater, 2
Is a high pressure side detection end, 2a is a low pressure side detection end, 3 and 3a are pressure guiding pipes made of carbon steel material, 4 and 4a are joints, 5 are joints 4 and 4a, and are used as pressure guiding pipes 3 and 3a. This detector 5 is a detector connected to the cover flanges 6 and 6a. The diaphragms 7 and 7a made of a stainless steel material are incorporated in the cover flanges 6 and 6a, and a filling liquid (silicon oil) 8 is placed between the diaphragms 7 and 7a. , 8a, and the pressure of the conductive fluid is directly applied to the pressure receiving surfaces of the diaphragms 7 and 7a via the pressure guiding tubes 3 and 3a.

[0003]

In the differential pressure detector having the above construction, no problem occurs in the initial stage of operation, but there is a problem that the zero point drifts with time. This is because hydrogen is introduced into the diaphragms 7 and 7a via the diaphragms 7 and 7a by a galvanic cell corrosion action (electrochemical reaction) formed between different metals in a conductive fluid such as seawater (electrolyte). This is because the hydrogen permeates and mixes with the filled liquids 8 and 8a to cause a volume change, and the diaphragms 7 and 7a swell. The mechanism of this hydrogen permeation will be described below.

Hydrogen ions are produced by the water contained in seawater. The formula for generating this hydrogen ion is shown in Equation 1.

[Equation 1]

The diaphragm itself or the surrounding metal is corroded and melts into seawater as shown by the equation 2, and emits electrons. At the same time, the hydrogen ions receive the electrons according to Equation 3 and adsorb as atomic hydrogen on the surface of the metal material. Especially, the diaphragm is made of high-resistant materials such as stainless steel,
If a material with poor corrosion resistance such as mild steel is used for the cover flange and pressure guiding tube, the galvanic battery (Galvanic corrosio
n) occurs, the diaphragm side becomes the cathode, the cover flange and the pressure guiding tube side become the anode, and the reaction of several 3 occurs in an inclined manner on the surface of the diaphragm.

[Equation 2]

(Equation 3)

Most of the adsorbed hydrogen atoms become molecular hydrogen gas according to the equation (4) or (5).

[Equation 4]

(Equation 5)

Some of the adsorbed hydrogen atoms are adsorbed → dissolved → diffused → permeated through the diaphragm as atomic hydrogen, reach the inside of the diaphragm (filled liquid), and then become hydrogen gas and accumulate. The above phenomenon (generation of hydrogen gas) also occurs in the diaphragm that detects a conductive fluid other than seawater. Therefore, in order to prevent the zero point from drifting in the differential pressure detector, it is necessary to have a structure in which no galvanic battery is generated.

It is an object of the present invention to propose a differential pressure detector having a metal diaphragm for detecting the differential pressure of a conductive fluid in which the zero point does not drift.

[0009]

The structure of the differential pressure detector for the conductive fluid according to the present invention is as follows. 1. A differential pressure detector for a conductive fluid, in which an electrically insulating material layer is formed on the pressure receiving surface of a metal diaphragm for detecting a differential pressure. 2. The non-electrolyte sealing liquid is filled in the pressure receiving surface side cover casing of the metal diaphragm for detecting the differential pressure, and the differential pressure is transmitted to the diaphragm surface via this sealing liquid. Pressure detector. 3. A differential pressure detector for a conductive fluid, wherein a connecting mechanism such as a joint made of an electrically insulating material is interposed in a portion connecting the differential pressure detecting pressure guiding tube and the detector. 4. A differential pressure detector for a conductive fluid, which is formed by forming a metal layer, which is nobler than the diaphragm, on a pressure receiving surface of a metal diaphragm for detecting a differential pressure. 5. A differential pressure detector for conductive fluid, which is formed by forming a metal layer, which is more precious than the diaphragm, on the inner surface near the metal diaphragm for detecting the differential pressure such as a cover flange. 6. A differential pressure detector for a conductive fluid, in which the same metal material as the diaphragm is used for all or part of the differential pressure detecting pressure guiding tube. 7. In the above 1 or 2 or 3 or 4 or 5 or 6,
A differential pressure detector for conductive fluid where the differential pressure detector is a remote seal type. 8. In the above 1 or 2 or 3 or 4 or 5 or 6,
Differential pressure detector for conductive fluid, which is a direct flange type.

[0010]

The fluid pressure applied to the high pressure side and the low pressure side is applied to both sides of the pressure sensitive diaphragm (movable electrode) of the pressure sensor through the filled liquid. The pressure-sensitive diaphragm is displaced in proportion to the pressure difference between the high pressure side and the low pressure side applied to both sides, and this displacement is caused by, for example, the capacitance generated between the two fixed electrodes facing each other on both sides. The change is converted / amplified by an electric circuit to be converted into a current signal of 4 to 20 mA DC and output as a differential pressure signal. When detecting the differential pressure, the inventions described in 1, 2, and 3 above do not generate a hydrogen gas because a galvanic battery is not formed, and the invention described in 4 does not move electrons to the diaphragm.
Further, the invention described in 5 is by suppressing generation of adsorbed hydrogen atoms, and the invention described in 6 is by the action of not chemically adsorbing adsorbed hydrogen atoms on the surface of the diaphragm. Prevent.

[0011]

【Example】

Embodiment 1 (FIG. 1) This embodiment corresponds to the invention described in claim 1, 1 is a seawater line, 2 is a high-pressure side detection end, 2a is a low-pressure side detection end, and 3 and 3a are The pressure guiding tubes 4, 4a are joints, and 5 is a differential pressure detector connected to the pressure guiding tubes 3, 3a using the joints 4, 4a. 6, 6a are cover flanges that constitute the detector 5, 7 and 7a are SUS316 diaphragms, 8,
Reference numeral 8a is a fill liquid using silicone oil, and 9 is a pressure sensor. Reference numerals 10 and 10a denote electrically insulating material layers coated on the pressure receiving surfaces of the diaphragms 7 and 7a, which are ceramics in the embodiment. In addition to ceramics,
Materials having equivalent properties can be used. In the case of the embodiment, the electrically insulating material layers 10 and 1 are formed by coating.
Although 0a is formed, the electrically insulating material layers 10 and 10a may be formed by a spraying method, a vapor deposition method, a laminating method or the like, and the formation means of the layers 10 and 10a is not limited in the present invention. As described above, the diaphragm 7, 7a
When the electrically insulating substance layers 10 and 10a are formed on the pressure receiving surface, the galvanic battery is not formed, and therefore, the corrosive action, that is, the electrochemical reaction does not occur on the surfaces of the diaphragms 7 and 7a, and hydrogen is not permeated.

Embodiment 2 (FIG. 2) This embodiment corresponds to the invention described in claim 2, and the reference numerals 1 to 9 indicate the same structure as that of the embodiment 1, so that the description thereof will be omitted. Is omitted. 11 and 11a are detectors 5
It is a non-electrolyte sealing liquid which is an electrically insulating substance sealed inside, and the seawater which is a conductive fluid does not enter the inside of the detector 5 due to the action of these sealing liquids 11 and 11a. In this case, no electrons are emitted due to the corrosion of the metal, and therefore, hydrogen that permeates the diaphragms 7 and 7a is not generated.

Embodiment 3 (FIG. 3) This embodiment corresponds to the invention described in claim 3, and the reference numerals 1 to 9 indicate the same structure as that of the embodiment 1, so that the description thereof will be omitted. Is omitted. However, an electrically insulating material joint using Teflon or the like is used for the joints 4 and 4a.
The a side and the detector 5 side are insulated from each other to prevent generation of galvanic cells.

Embodiment 4 (FIG. 4) This embodiment corresponds to the invention described in claim 4, and the reference numerals 1 to 9 indicate the same structure as that of the embodiment 1, so that the description thereof will be omitted. Is omitted. Reference numerals 14 and 14a are diaphragms 7 and 7a formed on the pressure receiving surfaces of the diaphragms 7 and 7a.
Which is a noble metal layer than SUS316, which is a material of the above, does not adsorb hydrogen atoms to the diaphragms 7 and 7a by the metal layers 14 and 14a, and as a result, prevents permeation of hydrogen into the diaphragms 7 and 7a, respectively. It is a thing.

Embodiment 5 (FIG. 5) This embodiment corresponds to the invention described in claim 5, and the reference numerals 1 to 9 indicate the same structure as that of the embodiment 1, so that the description thereof will be omitted. Is omitted. 13, 13a are cover flanges 6, 6 facing the pressure receiving surface of the diaphragm 7, 7a.
Noble metal (SUS) than the diaphragms 7 and 7a on the a-side surface
A metal more precious than 316), for example, a metal layer formed by coating or laminating or applying or vapor depositing gold, and by the action of the noble metal layers 13 and 13a,
The generation of galvanic cells is prevented between the diaphragms 7 and 7a, respectively.

Embodiment 6 (FIG. 6) This embodiment corresponds to the invention described in claim 6, and the reference numerals 1 to 9 indicate the same structure as that of the embodiment 1, so that the description thereof will be omitted. Is omitted. However, the pressure guiding tubes 3 and 3a and the joints 4 and 4a use SUS316 which is the same material as the diaphragms 7 and 7a, thereby preventing generation of galvanic cells.

Embodiment 7 (FIGS. 7 and 8) This embodiment is an embodiment of a remote seal type differential pressure detector corresponding to the invention described in claim 7, and is a differential pressure conduit 1
Non-electrolyte sealing liquids 11 and 11a similar to those described in the second embodiment are sealed in the tanks 5 and 15a, and the tank 1
The diaphragms 7 and 7a are incorporated in the flange 18 attached to the pressure detecting port 17a of No. 7, and the pressure receiving surfaces of the diaphragms 7 and 7a are coated with the electrically insulating substances 10 and 10a as in the first embodiment. There is.

FIG. 9 shows the non-electrolyte sealing liquids 11 and 1 between the filled liquids 8 and 8a and the conductive fluid in the remote seal system.
1a and the diaphragm 7,7
FIG. 10 shows an embodiment in which an electric insulating flange 19 is used for the pressure detecting portion, and FIG. 11 shows an electric insulating packing 20 (or gasket, joint) and an electric insulating bolt 21.
12 is an example in which a packing 22 (or a gasket, a joint) made of a metal nobler than the diaphragm is used in the detection part, and FIG. 13 is an example in which a flange 23 made of a metal nobler than the diaphragm is used. 14 is an embodiment in which a diaphragm cover 24 made of an electrically insulating material is used, FIG. 15 is an embodiment in which the nozzle 25 is made of the same material as the diaphragm, and FIG. 16 is used in the flange 26 is made of the same material as the diaphragm. 17 shows an embodiment in which the surface of the diaphragm 7 is plated with a metal 27 which is more precious than the diaphragm. Although the above embodiment describes only the high voltage side, it goes without saying that the same structure can be taken on the low voltage side.

FIG. 18 shows a remote seal method.
This is an embodiment in which the pressure detection unit is changed to the flange direct mounting method, and this direct mounting method can also utilize the galvanic prevention means of the remote seal method shown in FIGS. 8 and 10 to 17. For example, FIG. 19 shows an example in which an electrically insulating flange 19 is used between the direct mounting flanges.

[0020]

As described above, according to the present invention, in the detector for detecting the differential pressure, pressure, etc. of the conductive fluid, hydrogen permeation in the diaphragm is prevented by preventing occurrence of galvanic cell corrosion action, or hydrogen. By preventing the occurrence itself of, the zero point was prevented from drifting. As a result, the differential pressure detector for the conductive fluid containing seawater can accurately detect the differential pressure and the pressure for a long period of time, and the complexity of zero point correction is eliminated. In addition to the differential pressure detector, the present invention can be applied to prevention of generation of hydrogen that permeates the diaphragm when the conductive fluid is sealed or partitioned by the diaphragm.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment in which the surface of a diaphragm is coated with an electrically insulating material.

FIG. 2 is an explanatory diagram of an example in which a non-electrolyte sealing liquid is filled.

FIG. 3 is an explanatory diagram of an embodiment in which a pressure guiding tube and a differential pressure detector are connected by using an electrically insulating material joint.

FIG. 4 is an explanatory view of an embodiment in which a pressure receiving surface of the diaphragm is provided with a metal layer which is more precious than the diaphragm.

FIG. 5 is an explanatory diagram of an embodiment in which a metal layer that is more precious than the diaphragm is formed on the surface of the cover casing that faces the diaphragm.

FIG. 6 is an explanatory view of an embodiment in which the pressure guiding tube and the joint are made of the same metal as the diaphragm.

FIG. 7 is an explanatory diagram of an embodiment in which the present invention is applied to a remote seal type detector.

FIG. 8 is an explanatory diagram of an embodiment in which the present invention is applied to a remote seal type detector.

FIG. 9 is an explanatory diagram of an embodiment in which the present invention is applied to a remote seal type detector.

FIG. 10 is an explanatory diagram of an embodiment in which the present invention is applied to a remote seal type detector.

FIG. 11 is an explanatory diagram of an embodiment in which the present invention is applied to a remote seal type detector.

FIG. 12 is an explanatory diagram of an embodiment in which the present invention is applied to a remote seal type detector.

FIG. 13 is an explanatory diagram of an embodiment in which the present invention is applied to a remote seal type detector.

FIG. 14 is an explanatory diagram of an embodiment in which the present invention is applied to a remote seal type detector.

FIG. 15 is an explanatory diagram of an embodiment in which the present invention is applied to a remote seal type detector.

FIG. 16 is an explanatory diagram of an embodiment in which the present invention is applied to a remote seal type detector.

FIG. 17 is an explanatory diagram of an embodiment in which the present invention is applied to a remote seal type detector.

FIG. 18 is an explanatory diagram of an embodiment in which the present invention is applied to a flange direct-attaching type detector.

FIG. 19 is an explanatory diagram of an embodiment in which the present invention is applied to a detector of a flange direct mounting type.

FIG. 20 is an explanatory diagram of a differential pressure detector used for detecting a differential pressure of a conventional seawater line.

[Explanation of symbols]

 1 Sea Water Line 2 High Pressure Side Detection End 2a Low Pressure Side Detection End 3, 3a Pressure Guide Tube 4, 4a Joint 5 Detector 6, 6a Cover Flange 7, 7a Diaphragm 8, 8a Enclosed Liquid 9 Pressure Sensor 10, 10a Electrical Insulation Material Layer 11, 11a Seal liquid 13, 13a Metal layer 14, 14a Metal layer 15, 15a Differential pressure conduit 17 Tank 17a Pressure detection port 18 Flange 19 Electrical insulating flange 20 Electrical insulating packing 21 Electrical insulating bolt 22 Packing 23 Flange 24 Diaphragm cover 25 Nozzle 26 Flange 27 Metal

Claims (8)

[Claims] 1. A differential pressure detector for a conductive fluid, which is formed by forming an electrically insulating material layer on the pressure receiving surface of a metal diaphragm for differential pressure detection. 2. A non-electrolyte sealing liquid is filled in the pressure-receiving-side cover casing of the metal diaphragm for differential pressure detection,
A differential pressure detector for a conductive fluid, which is configured to transmit the differential pressure to the diaphragm surface via the sealing liquid. 3. A differential pressure detector for a conductive fluid, wherein a connecting mechanism such as a joint made of an electrically insulating material is interposed in a portion connecting the differential pressure detecting pressure guiding tube and the detector. 4. A differential pressure detector for a conductive fluid, comprising a pressure-sensitive surface of a metal diaphragm for differential pressure detection, on which a metal layer nobler than the diaphragm is formed. 5. A differential pressure detector for a conductive fluid, which is formed by forming a metal layer, which is nobler than the diaphragm, on an inner surface near a metal diaphragm for detecting a differential pressure such as a cover flange. 6. A differential pressure detector for a conductive fluid, which is formed by using the same metal material as the diaphragm for all or part of the differential pressure detecting pressure guiding tube. 7. The differential pressure detector for a conductive fluid according to claim 1, 2 or 3 or 4 or 5 or 6, wherein the differential pressure detector is a remote seal type. 8. The differential pressure detector for a conductive fluid according to claim 1, 2 or 3 or 4 or 5 or 6, wherein the differential pressure detector is a flange direct mounting type.