JP2019039828A - Pump having crevice corrosion detector, and operation management method of the same - Google Patents

Abstract

To provide a device and method capable of directly monitoring the occurrence of a crevice corrosion of a pump operating under the water.SOLUTION: A pump includes a crevice corrosion detector 20 including an electrode 21 for crevice corrosion detection and a potentiometer 22. The electrode 21 for crevice corrosion detection is disposed at a position at which it does not come into contact with a pump body and it is immersed in a liquid having a conductivity in the operation of the pump, and detects a crevice corrosion on a mating surface or contact surface between the components of the pump. The potentiometer 22 is electrically connected to the electrode 21 for crevice corrosion detection and the pump body, and detects the potential difference between the pump body and the mating surface or contact surface between the components of the pump.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a technique for detecting crevice corrosion of members constituting a pump, and more particularly to a pump having a crevice corrosion detector, a method of monitoring crevice corrosion occurrence in the pump, and an operation control method of the pump.

  Since the pump is used by being immersed in water, it is subject to corrosive effects such as chloride ions in water. In particular, chloride ions are likely to be concentrated in the gaps between the flanges and bolt fastening parts that constitute the pump, and crevice corrosion and pitting corrosion occur. In a pump that pumps up seawater containing a large amount of chloride ions, stress is applied to the component members, and stress corrosion cracking may occur from crevice corrosion or pitting corrosion as a starting point. Although the corrosion resistance is improved by the improvement of the material of the component members, the occurrence of crevice corrosion and pitting corrosion can not be avoided. In particular, in pumps used in severe environments, such as environments containing high concentrations of chloride ions, high temperature environments, and environments with large temperature differences, crevice corrosion and pitting corrosion occur frequently.

  As a method of preventing metal corrosion, in a system in which water is fed into a copper tube, a method of adding a corrosion inhibitor so that the value thereof becomes less than the pitting potential while monitoring the natural potential of the metal (Patent Document 1) ) Has been proposed. In Patent Document 1, since the pitting potential is influenced by the type of metal, the geometrical shape of the metal surface, the nature and temperature of the water in contact, etc., the pitting potential in the system should be obtained in advance. Required to compare the natural potential of the monitored metal with the pitting potential to determine the possibility of the occurrence of corrosion, and to determine whether the corrosion actually occurs or not. is not.

  As a monitoring method under conditions simulating the environment in a real machine, overlap metal pieces of the same material as the metal in contact with the aqueous medium, weld some parts together, create gaps between the metal pieces in other parts, and weld There has been proposed a corrosion monitoring sensor having a part, a gap part and a heat transfer part (Patent Document 2). In Patent Document 2, the corrosion monitoring sensor is fixed so that the water of the monitoring water system passing water in the sensor installation device does not leak to the outside, and the water of the water system to be monitored is introduced into the sensor installation device. Simulating the water system environment inside the steel pipe is described, and it is possible to judge the possibility of the occurrence of corrosion under the simulation environment, but it is judged whether or not the corrosion actually occurs in the actual machine is not.

Japanese Patent Application Laid-Open No. 05-98476 JP 2000-304684 A

  The corrosion monitoring method proposed previously is a method to judge the possibility of the occurrence of corrosion of metal surface inside piping, especially pitting corrosion, and both the inside and the outside of the device are submerged in water like a submersible pump. It was not possible to monitor the occurrence of corrosion of the actual machine under the environment.

  An object of the present invention is to provide an apparatus and method capable of directly monitoring the occurrence of crevice corrosion of a pump operating in water.

According to the present invention, there is provided an apparatus and method capable of directly monitoring the occurrence of crevice corrosion of a pump operating in water. The specific aspect is as follows.
[1] A pump having a crevice corrosion detector including a crevice corrosion detection electrode and a potentiometer, wherein the crevice corrosion detection electrode is not in contact with the pump body, and the liquid having conductivity when the pump is operated It is provided at a position where it is immersed, and detects corrosion in the gap between mating surfaces or contact surfaces of components of the pump, and the potentiometer is electrically connected to the gap corrosion detection electrode and the pump body. A pump comprising a gap corrosion detector for detecting a potential difference between a pump body and a mating surface or a contact surface of component parts of the pump.
[2] A pump having a crevice corrosion detector including a crevice corrosion detection electrode and a potentiometer, wherein the crevice corrosion detection electrode has a diameter of 30 mm centered on the mating surface or contact surface of the constituent members of the pump At least the tip of the electrode is located in the virtual circular area, and the entire electrode is not in contact with the pump body, and is provided at a position where it is immersed in a conductive liquid when the pump is in operation. A pump comprising a gap corrosion detector electrically connected to a gap corrosion detection electrode and a pump body and detecting a potential difference between a pump body and a mating surface or a contact surface of constituent members of the pump.
[3] The mating surfaces or contact surfaces of the components of the pump are fastened between the rotating side and the stationary side of the rotating body, between the washer and the flange, between the bolt and the nut, between the washer and the nut, It is defined between one or more members selected from the surface of both flanges, the seal and the bolt, the seal and the washer, and the seal and the flange. 1] or the pump as described in [2].
[4] When the constituent members of the pump are different materials, the gap corrosion detection electrode is positioned in a region including a member having a material with a relatively small pitting resistance (PRE), [1] -The pump as described in any one of [3].
[5] The pump according to any one of [1] to [4], wherein the gap corrosion detection electrode is an insoluble electrode.
[6] The method according to any one of [1] to [5], wherein the gap corrosion detector monitors the presence or absence of gap corrosion during operation of the pump.
[7] The pump management method according to any one of the above [1] to [5], wherein the gap corrosion detector detects the occurrence of gap corrosion during operation of the pump.

  According to the present invention, it is possible to directly monitor the occurrence of crevice corrosion of a pump operating in water.

The schematic explanatory drawing which shows the example by which the crevice corrosion detector is attached to the flange part which connects between a pump casing and a suction cover. The enlarged view of the part to which the crevice corrosion detector of the pump of FIG. 1 is attached. The schematic explanatory drawing which shows the example by which the crevice corrosion detector is attached to the flange part which connects between a pump casing and a pumping pipe. The enlarged view of the part to which the crevice corrosion detector is attached to the pump casing in the pump of FIG. The enlarged view of the part to which the crevice corrosion detector is attached to the pumping pipe in the pump of FIG. The pump of FIG. 3 WHEREIN: The enlarged view of another aspect by which the crevice corrosion detector is attached to the pumping pipe. The enlarged view of the tip part of the electrode of the crevice corrosion detector of Drawing 6, and the portion of resin which has a penetration hole. The schematic explanatory drawing which shows the example which attached the crevice corrosion detector which detects the electrical potential difference of the contact surface of the main shaft or sleeve of a pump, and a bearing to a bearing support. The schematic diagram of the sample for gap electric potential detection used in the Example. Explanatory drawing of the apparatus structure of electric potential measurement experiment. Potential distribution in 0.35 wt% sodium chloride aqueous solution. Potential distribution in 3.5 wt% sodium chloride aqueous solution.

Hereinafter, the present invention will be specifically described with reference to the attached drawings, but the present invention is not limited thereto.
The present invention is a pump having a crevice corrosion detector including a crevice corrosion detection electrode and a potentiometer, wherein the crevice corrosion detection electrode is not in contact with the pump body, and the liquid has conductivity when the pump is in operation. And detects corrosion of the gap between the mating surfaces or contact surfaces of the pump components, and the potentiometer is electrically connected to the gap corrosion detection electrode and the pump body. A pump comprising a crevice corrosion detector for detecting the potential difference between the pump body and the mating or contact surface of the pump components.

  More specifically, it is a pump having a crevice corrosion detector including a crevice corrosion detection electrode and a potentiometer, wherein the crevice corrosion detection electrode is centered on the mating surface or contact surface of the constituent members of the pump. At least the tip of the electrode is located in a virtual circle area of 30 mm in diameter, preferably 20 mm in diameter, more preferably 10 mm in diameter, the entire electrode is not in contact with the pump body, and is immersed in a liquid having conductivity when the pump is operated. The potentiometer is electrically connected to the gap corrosion detection electrode and the pump body, and detects the potential difference between the pump body and the mating surface or contact surface of the components of the pump. Provide a pump having a crevice corrosion detector.

The example of the aspect which provides a crevice corrosion detector in case the structural members of a pump are the same material is shown for FIGS.
FIG. 1 is a schematic explanatory view for explaining an essential part of a pump equipped with the gap corrosion detector of the present invention, and FIG. 2 is an enlarged view of a portion of the pump of FIG. 1 to which the gap corrosion detector is attached. .

  The vertical axis mixed flow pump shown in FIG. 1 comprises a main shaft 1 having a rotational axis (vertical axis) P, an impeller 2 mounted integrally rotatably at the lower end of the main shaft 1, and a pump casing enclosing the impeller 2 3. A suction case 4 connected to the lower side of the pump casing 3, a pumping pipe 5 connected to the upper side of the pump casing 3, and a bearing case integrally formed inside the pump casing 3 via the flow straightening plate 7. 6, a flange portion 10 connecting the pump casing 3 and the suction cover 4, and a gap corrosion detector 20 attached to the suction cover 4 in proximity to the flange portion 10. Through holes and screw holes are provided at equal intervals in the flange surface circumferential direction for fastening by fastening members such as bolts to each flange of the pump casing 3, the suction cover 4 and the pumping pipe 5. The flanges of the pump casing 3 and the suction cover 4 or the pump casing 3 and the pumping pipe 5 are connected by bolts or bolts and nuts. A seal member (not shown) such as a packing is provided at the joint of each flange and sealed in a watertight state. In FIG. 1, the pump casing 3, the suction cover 4, and the pumping pipe 5 operate in a submerged state.

The portion of the flange portion 10 connecting the pump casing 3 and the suction cover 4 is, as shown in FIG. 2 in an enlarged manner, a bolt 11 and a nut for fastening the flange portion 10a of the pump casing 3 and the flange portion 10b of the suction cover 4 13, which is in the form of a stud bolt having a gap A of 0.1 mm or less between mating surfaces of the bolt 11 and the nut 13. The crevice corrosion detector 20 comprises an electrode 21, a potentiometer 22, a lead 23 between the electrode 21 and the potentiometer 22, and a lead 24 between the potentiometer 22 and a suction cover 4 which is part of the pump body. Do. The crevice corrosion detector 20 is attached such that at least the tip 21 a of the electrode 21 is positioned within a virtual circle of 30 mm in diameter centered on the crevice A. The gap corrosion detector 20 is submerged in water when the pump is in operation, so the potentiometer 22 and the leads 23 and 24 are sealed in the casing 25.

  FIG. 3 shows an example in which a gap corrosion detector 20 is provided at a position close to a flange 30 connecting the pump casing 3 and the pumping pipe 5. The configuration of the pump is as described in connection with FIG.

  As shown in an enlarged view in FIG. 4, the flanges 30 a and 30 b have a bolt 11 for fastening the flange portion 30 a of the pump casing 3 and the flange portion 30 b of the pumping pipe 5, a washer 12, 12 ′ and a nut 13. Gaps are respectively formed between the mating surfaces of the and the washers 12, 12 '. The crevice corrosion detector 20 comprises an electrode 21, a potentiometer 22, a lead 23 between the electrode 21 and the potentiometer 22, and a lead 24 between the potentiometer 22 and the pump casing 3 which is part of the pump body Do. In the illustrated embodiment, at least the tip 21a of the electrode 21 is positioned within an imaginary circular area of 30 mm in diameter centered on the mating surface (gap) A of the flange portion 30a of the pump casing 3 and the washer 12 in the illustrated embodiment. It is attached to be able to

  5 and 6 show an example in which a crevice corrosion detector 20 is mounted close to a crevice formed on the mating surface of the flanges 30a and 30b of the flange 30 connecting the pump casing 3 and the pumping pipe 5 Indicates The crevice corrosion detector 20 comprises an electrode 21, a potentiometer 22, a lead 23 between the electrode 21 and the potentiometer 22, and a lead 24 between the potentiometer 22 and the pumping pipe 5 which is part of the pump body. Do.

  In the embodiment shown in FIG. 5, in the gap corrosion detector 20, at least the tip 21a of the electrode 21 has a diameter of 30 mm centered on the mating surface (gap) A of the flange portion 30a of the pump casing 3 and the flange portion 30b of the pumping pipe 5. It is attached so as to be positioned within the virtual circle area of (the range shown by the dotted circle).

  In the embodiment shown in FIGS. 6 and 7, in the gap corrosion detector 20, at least the tip 21a of the electrode 21 is surrounded by the insulating resin 26, and the through hole 27 for fluid communication is formed in the insulating resin 26. Have a configuration. The through hole 27 allows fluid to communicate between the tip 21 a of the electrode 21 and the mating surface (gap) A between the flange portion 30 a of the pump casing 3 and the flange portion 30 b of the pumping pipe 5. The tip of the through hole 27 is positioned within a virtual circle area (a range indicated by a dotted line circle) having a diameter of 30 mm centering on the mating surface A of the flange portion 30a of the pump casing 3 and the flange portion 30b of the pumping pipe 5 As attached. The through hole 27 preferably has an inner diameter of 0.2 mm or more and 10 mm or less. In this aspect, the potential at the tip of the inner surface of the through hole 27 and the potential of the tip 21a of the electrode 21 are the same potential, so if the tip of the through hole 27 is within a virtual circle area of 30 mm in diameter from the flange surface, The detected potential difference can be regarded as the potential difference between the pump body and the gap between the mating surfaces of the flange portion 30 a of the pump casing 3 and the flange portion 30 b of the pumping pipe 5.

FIG. 8 shows an imaginary circle area of 30 mm in diameter (indicated by a dotted line circle) with a gap A formed on the contact surface between the rotation side (spindle 1 or sleeve 1a) of the rotary body and the fixed side (bearing 6a) 7 shows an example in which the crevice corrosion detector 20 shown in FIG. 7 is attached to the bearing support in FIG. In this example, a clearance is formed on the sliding surface between the rotating side (spindle 1 or sleeve 1a) and the fixed side (bearing 6a) of the rotating body during the operation of the pump. A contact is made between the rotating side (spindle 1 or sleeve 1a) and the fixed side (bearing 6a), and a gap of 0.1 mm or less is formed around the contact portion. The fixed side (bearing 6a) is fixed to the pump body by bolts or fitting, and the fixed side (bearing 6a) and the pump body are in electrical conduction. For this reason, the electric potential detected by the gap corrosion detector 20 can be regarded as the potential difference between the pump body and the contact surface between the rotation side (spindle 1 or sleeve 1a) and the fixed side (bearing 6a) of the rotating body. .

When the constituent members of the pump forming the mating surface are different materials, it is preferable to place the electrode at a position close to the constituent member of a material having a small pitting resistance index (PREN). The pitting resistance index (PREN) is an index of pitting resistance of corrosion resistant stainless steel, and is generally represented by the following formula.
[Equation 1] PREN = Cr% + 3.3 × Mo% + 16 × N%
It is known that the larger the PREN, the better the corrosion resistance, and for the detection of crevice corrosion, it is preferable to be provided close to a component of a material of low PREN with low corrosion resistance.

  As an electrode, an insoluble electrode can be used preferably. The insoluble electrode is an electrode which does not dissolve or is less dissolved chemically or electrochemically, and examples thereof include electrodes coated with platinum, carbon, graphite, iron oxide, chromium oxide, noble metal oxides, etc. Be

The potential measurement experiment shown in FIG. 10 was performed using the gap portion potential detection sample shown in FIG.
First, on a stainless steel (SUS 304) plate of 55 mm wide x 40 mm long x 5 mm thick, a stainless steel (SUS 304) plate of 15 mm wide x 40 mm long x 5 mm thick is overlapped, and a gap is formed between the two mating surfaces. , A gap potential detection sample was prepared.

  Next, the sample for gap potential detection was immersed in a test solution (0.35 wt% or 3.5 wt% sodium chloride aqueous solution), and the potential distribution of the metal around the mating surface was measured. The potential is measured by using a saturated silver-silver chloride electrode as a detection electrode (SSE) for a control electrode (RE) and a working electrode (WE), and immersing the control electrode (RE) in a test solution absorbed through a capillary The working electrode (WE) was connected to the end of the gap of the gap potential detection sample, and the counter electrode (CE) was connected to a predetermined position on the metal plate which is not the mating surface of the gap potential detection sample. First, while applying a constant potential of 0.3 V to the detection electrode (SSE) (the potential shown when the stainless is immersed in seawater is 0.3 V), the potential sensor is placed along the gap (X The axial direction was moved to measure the potential, the position of the lowest potential was determined, and the crevice corrosion occurrence location was identified. Next, measure the potential by moving the potential sensor away from the location where the gap corrosion occurred along the direction (Y-axis direction) orthogonal to the gap of the gap part potential detection sample, and for gap part potential detection The potential distribution with respect to the separation distance from the gap of the sample was created. A potential distribution diagram in the case of a 0.35 wt% sodium chloride aqueous solution is shown in FIG. 11, and a potential distribution diagram in the case of a 3.5 wt% sodium chloride aqueous solution is shown in FIG.

  From FIGS. 11 and 12, it can be confirmed that the potential fluctuates up to a position separated by 15 mm from the gap corrosion occurrence position regardless of the concentration of the sodium chloride aqueous solution, and no fluctuation of the potential is observed at a position separated by more than 15 mm , I understand. From this result, when crevice corrosion has occurred, it can be said that there is fluctuation in the potential within a virtual circle area of 30 mm (radius 15 mm) in diameter centering on the crevice corrosion occurrence location. Therefore, it is possible to confirm the presence or absence of the occurrence of crevice corrosion by detecting the potential fluctuation in the virtual circle region of 30 mm in diameter from the crevice.

A: Gap 20: Gap corrosion detector 21: Electrode 22: Potentiometer 23: Conductor 24 between the electrode and the potentiometer: Conductor between the potentiometer and the pump body

Claims (7)

A pump comprising a crevice corrosion detector comprising a crevice corrosion detection electrode and a potentiometer, comprising:
The gap corrosion detection electrode is not in contact with the pump body, and is provided at a position where it is immersed in a conductive liquid when the pump is in operation. Detect
The potentiometer includes a gap corrosion detector which is electrically connected to the gap corrosion detection electrode and the pump body, and detects a potential difference between the pump body and the mating surface or contact surface of the components of the pump. Pump to do. A pump comprising a crevice corrosion detector comprising a crevice corrosion detection electrode and a potentiometer, comprising:
At least the tip of the electrode is located in a virtual circular area of 30 mm in diameter centered on the mating surface or contact surface of the constituent members of the pump, and the entire electrode does not contact the pump body. At a position where it is immersed in a liquid having conductivity,
The potentiometer includes a gap corrosion detector which is electrically connected to the gap corrosion detection electrode and the pump body, and detects a potential difference between the pump body and the mating surface or contact surface of the components of the pump. Pump to do.   The mating or contact surfaces of the components of the pump are fastened between the rotary and stationary sides of the rotor, between the washer and the flange, between the bolt and the nut, and between the washer and the nut. The method according to claim 1 or 2, defined between one or more members selected from the surfaces of both flanges, between the seal and the bolt, between the seal and the washer, and between the seal and the flange. The pump according to 2.   The crevice corrosion detection electrode is positioned in a region including a member of a material having a relatively small pitting resistance index (PRE) when constituent members of the pump are different materials. The pump according to any one.   The pump according to any one of claims 1 to 4, wherein the gap corrosion detection electrode is an insoluble electrode.   The pump according to any one of claims 1 to 5, wherein the crevice corrosion detector monitors the presence or absence of crevice corrosion during operation of the pump.   The pump according to any one of claims 1 to 5, wherein the gap corrosion detector detects the occurrence of gap corrosion during pump operation.