JPWO2019208462A1 - Equipment equipped with a corrosive environment monitoring method and a corrosive environment monitoring system - Google Patents

Abstract

We provide equipment that incorporates a corrosive environment monitoring method and a corrosive environment monitoring system to obtain environmental information for each operating condition. Provided is an apparatus equipped with a monitoring method and a monitoring system that monitor the immersion potential of a metal member and the potential when a minute current is applied, and estimate the corrosiveness of the usage environment by Bayesian estimation using the monitored potential. ..

Description

The present invention relates to a device provided with a corrosive environment monitoring method and a corrosive environment monitoring system.

Passivation metals such as stainless steel are known to cause pitting corrosion and crevice corrosion in aqueous chloride solutions. It is known that these pitting corrosion and crevice corrosion proceed by forming macrocells in the pitting corrosion or in the corroded crevice and between the non-corroded passivation metal surface. However, since crevice corrosion occurs especially in structural crevices, it is difficult to determine whether or not corrosion is progressing during the operation of the equipment. Therefore, large-scale overhauls and inspections are carried out on a regular basis to investigate the presence or absence of corrosion, and repairs and parts replacement are carried out as appropriate. In addition to requiring a great deal of time and cost for this overhaul, if the inspection time is incorrect, corrosion may progress remarkably, leading to damage to the equipment or the inability to repair.

On the other hand, the corrosiveness of the usage environment has a great influence on the occurrence and progress of corrosion. For example, in the case of seawater, the salinity and water temperature have a great influence on the occurrence and progress of corrosion, but the salinity and water temperature differ depending on the water area, and there are also seasonal fluctuations. In addition, the usage environment of the device differs depending on the place of use. When multiple pumps are installed in the same water area, the corrosive environment of each pump will be different if the operating conditions of the pumps are different. Furthermore, the presence or absence of marine organisms adhering to the equipment and the difference in the pretreatment method of the liquid introduced into the equipment also affect the corrosiveness. Therefore, it is very important to obtain environmental information for each usage condition of equipment that may be corroded when selecting the constituent materials of the equipment.

In order to evaluate the corrosion rate of a metal material in a predetermined environment such as an atmospheric environment or an aqueous solution environment, monitoring by an ACM (Atmospheric Corrosion Monitor) sensor or a galvanic sensor has been proposed (Patent Documents 1 and 2). Corrosion can be estimated by applying a potential or current from the outside to a metal material installed in the usage environment using a potentiostat or the like and measuring the potential dependence of the corrosion reaction rate. Equipment is required, and basically an external power supply is required. Further, when the wetted area of the device becomes large, it is necessary to apply a current of several tens of A, which may affect the operation of the device.

Japanese Unexamined Patent Publication No. 2001-201451 Japanese Unexamined Patent Publication No. 2012-208088

An object of the present invention is to provide an apparatus incorporating a corrosive environment monitoring method and a corrosive environment monitoring system for obtaining environmental information for each usage condition.

The present invention provides a monitoring method and a monitoring system that monitor the immersion potential of a metal member and the potential when a minute current is applied, and estimate the corrosiveness of the usage environment by Bayesian estimation using the monitored potential. Provide equipment.

By attaching a sensor to a metal member for continuous monitoring and applying data assimilation to the acquired time-series observation data (immersion potential, applied potential, temperature, electrical conductivity, etc.), the corrosiveness of the environment that cannot be directly observed. And estimate the corrosion current. Environmental corrosiveness is estimated by setting several parameters contained in the anodic and cathode polarization curves as state variables in data assimilation. A sequential Bayesian filter is used as a data assimilation method.

The present invention
With a reference electrode
An application electrode that applies a minute current to the environment in which the metal member is positioned,
A current generator that applies a minute current to the application electrode,
A potentiometer that measures the immersion potential of a metal member and the potential when a small current is applied,
A storage device that stores the immersion potential and current-applied potential measured by the potentiometer, and
A control device that controls the potentiometer, current generator, and storage device and executes the above-mentioned corrosive environment monitoring method.
A housing that encloses a storage device, a control device, a potentiometer, and a current generator,
Equipped with
A reference electrode and a part of the current application electrode provide a corrosive environment monitoring system exposed to the outside of the housing.

In addition, it is equipped with at least one type of measuring device such as a thermometer, an electric conductivity meter, a turbidity meter, a dissolved oxygen concentration meter, and a pH meter that are electrically connected to the control device, and the detection part of the measuring device is a casing. The above-mentioned corrosive environment monitoring system exposed to the outside of the body is also provided.

Further, an apparatus equipped with the above-mentioned corrosive environment monitoring system is also provided.

According to the present invention, a corrosive environment monitoring method, a corrosive environment monitoring system, and a device incorporating a corrosive environment monitoring system for obtaining environmental information for each usage condition are provided.

It is a flowchart of a sequential Bayesian filter. It is a schematic diagram which showed the current flow by potential measurement and current application. It is a schematic diagram of the polarization curve in the system which applies an electric current. It is a graph which shows the simulated observation data (time series data of immersion potential). It is a graph which shows the simulated observation data (time series data of the potential at the time of application). It is a graph which shows the simulated observation data (time series data of temperature). It is a graph which shows the estimation result (estimation time series of log (α)) of the state variable of an Example. It is a graph which shows the estimation result (estimation time series of log (Cb)) of the state variable of an Example. It is a graph which shows the estimation result (estimation time series of water temperature T) of the state variable of an Example. It is a graph which shows the estimated current time series of an Example. It is a graph which shows the estimated current time series of the common logarithmic scale of an Example. It is a graph which shows the estimation result (estimation time series of log (α)) of the state variable of the comparative example. It is a graph which shows the estimation result (estimation time series of log (Cb)) of the state variable of the comparative example. It is a graph which shows the estimation result (estimation time series of water temperature T) of the state variable of the comparative example. It is a graph which shows the estimated current time series of the comparative example. It is a graph which shows the estimated current time series of the common logarithmic scale of the comparative example. It is a schematic diagram of a mode in which a monitoring sensor is connected in seawater to a vertical axis oblique flow pump installed in seawater. It is a schematic diagram of a mode in which a monitoring sensor is connected in the atmosphere to a vertical axis oblique flow pump installed in seawater. It is explanatory drawing which shows the structure of a monitoring system. It is explanatory drawing which shows the structure of the monitoring of another aspect.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a flow of corrosiveness estimation using a sequential Bayesian filter. Predict changes in the state variables of the system by repeating the operations of one-term advance prediction (time evolution of the system) and filtering (acquisition of observation data).

The initial distribution p (x ₀ | y _{1: 0} ) of the state variable is used as the input information. As state variables, we use several parameters included in the functions that represent the anodic and cathode polarization curves.

により表現され、一期先予測分布は

として合成積で計算される。The time evolution of state variables is the equation of state:

Expressed by, the one-term forecast distribution is

Is calculated as a convolution.

実際の観測量：

観測方程式：

および観測ノイズの確率分布モデルにより尤度を計算し、尤度と一期先予測分布からフィルタ分布を求める。In filtering, the calculated value of the observable calculated by the observation operator:

Actual observables:

Observation equation:

And the likelihood is calculated by the probability distribution model of the observed noise, and the filter distribution is obtained from the likelihood and the predicted distribution one period ahead.

In the present invention, a polarization curve model is used as an observation operator. FIG. 2 shows a schematic diagram showing the current flow between the electrodes. In the figure, "anode" indicates a part where corrosion occurs and a half-cell reaction of metal oxidation occurs, and "cathode" indicates a part where a half-cell reaction paired with "anode" occurs. Since it is not possible to separate the "anode" and the "cathode" when crevice corrosion is occurring, it is not possible to insert an ammeter between the "cathode" and the "anode" to measure the _{current I a.} The potential of the metal member is measured with the reference electrode "RE" as the reference potential. An ammeter and a power source are connected to an insoluble electrode for applying a current (for example, platinum, titanium, carbon, etc.), and the applied current is passed.

FIG. 3 shows a schematic diagram of the polarization curve in a system in which such a current is applied. In a state that does not perform current application, immersion potential phi ₀ is measured. When a current is applied, the potential changes up to the _{potential φ ip} at the time of application depending on the value of the _{applied current I ip and the shape of the polarization curve.}

カソード分極曲線は

で表される。ここで、ｇ_aはアノード電流Ｉ_aおよび状態変数ｘから電位を計算するアノード分極曲線を表すある関数であり、ｇ_cはアノード電流Ｉ_cおよび状態変数ｘから電位を計算するアノード分極曲線を表すある関数である。また、

が成り立つため、Ｉ_aおよびＩ_cを消去して、Ｉ_cpとφに関する方程式を作ることができる。その式において状態変数ｘから電位を計算する処理が観測演算子ｈとなる。

At this time, the anodic polarization curve is

Cathode polarization curve

It is represented by. Here, g _a is a function representing an anodic polarization curve for calculating the potential from the anodic current I _{a and the state variable x, and g c} represents the anodic polarization curve for calculating the potential from the anodic current I _{c and the state variable x.} It is a function. Also,

Therefore, I _a and I _c can be eliminated to create an equation for _{I cp and φ.} In that equation, the process of calculating the potential from the state variable x is the observation operator h.

で表現すると、フィルタ分布は

で表現される。このとき尤度

となる。ただし、nは状態変数の次元である。Normal distribution of observed noise

Expressed in, the filter distribution is

It is expressed by. Likelihood at this time

Will be. However, n is the dimension of the state variable.

Corrosion can be estimated from the obtained filter distribution by estimating the parameters of the cathode polarization curve by MAP (Maximum a posteriori) estimation (maximum posteriori estimation) or the like.
Table 1 shows a description of the symbols in the above formula.

Corrosion environment information was estimated by setting each item shown in Table 2 below.

この場合の一期先予測分布は、

で計算できる。・ One-term prediction The equation of state is a random walk model.

In this case, the forecast distribution for the first period is

Can be calculated with.

これらの式からＩ_aとＩ_cを消去すると、次の方程式が得られる。

この式はφ について明示的に書き表すことができないので、数値的に解く。
周辺尤度は以下のように全格子点に対する総和の式で計算できる。

-Filtering Assume the following polarization curve model.

_{Eliminating I a} and I _c from these equations gives the following equation.

This equation cannot be explicitly written for φ, so it is solved numerically.
Marginal likelihood can be calculated by the sum of all grid points as follows.

The simulated observation data shown in FIGS. 4 to 6 (time-series data of immersion potential, time-series data of applied potential, and time-series data of temperature) were used as inputs. In the figure, "true" is the true value, "observed" is the observed value, and "estimated" is the estimated value.

The estimation results of the state variables are shown in FIGS. 7 to 9 (estimated time series of log (α), estimated time series of Cb, and estimated time series of water temperature θ). After 200 steps, the estimated value matches the true value within 1σ, and it can be seen that the MAP solution can accurately reproduce the true state variable.

FIG. 10 shows the estimated current (MAP estimation) time series obtained by substituting the observation data of the state variable estimation time and the potential into the equation of the anodic polarization curve, and FIG. 11 shows the estimated current (MAP estimation) on the common logarithm scale. Shows the time series. The true current value (true) calculated from the true state variable by the same method is also shown. In FIG. 10, if there is a large change in α or Cb, the estimation accuracy drops at the initial stage of the change, but it can be estimated accurately after 200 steps, and it is confirmed that the estimation of the state variable considering the change with time is effective. it can.

For comparison, the results of estimating only the immersion potential using the simulated observation data of FIGS. 4 and 6 (time series data of immersion potential and time series data of temperature) are shown in FIGS. 12 to 14 (estimated time series of log (α)). , Cb estimated time series and water temperature θ estimated time series). It can be seen that the MAP solution is not within 1σ of the true state variable, and the state variable cannot be reproduced accurately.

FIG. 15 shows the estimated current (MAP estimation) time series obtained by substituting the state variable estimation time series and the potential observation data into the equation of the anodic polarization curve, and FIG. 16 shows the estimated current (MAP estimation) at the common logarithm scale. Shows the series. The true current value (true) calculated from the true state variable by the same method is also shown. It can be confirmed that the estimated value does not approach the true value even if the steps are repeated, and the true state variable cannot be estimated only by the immersion potential measurement.

In this example, the probability distribution was calculated by grid search. A Kalman filter or a particle filter may be used.

Next, a device equipped with a corrosive environment monitoring system that executes the corrosive environment monitoring method of the present invention will be described by taking a pump as an offshore structure as an example.

FIG. 17 shows a schematic view of a mode in which a corrosion environment monitoring system is connected to a vertical axis oblique flow pump installed in seawater in seawater.

The vertical oblique flow pump shown in FIG. 17 is a pump casing that encloses a spindle 1 having a rotary axis (vertical center) P, an impeller 2 rotatably attached to the lower end of the spindle 1, and an impeller 2. 3. A bearing case integrally formed inside the pump casing 3 via a suction cover 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 rectifying plate 7. 6. It has a flange portion 10 that connects the pump casing 3 and the suction cover 4, and a gap corrosion detector 20 that is attached to the suction cover 4 in close proximity to the flange portion 10. The flanges of the pump casing 3, the suction cover 4, and the pumping pipe 5 are provided with through holes and screw holes at equal intervals in the circumferential direction of the flange surface for fastening with fastening members such as bolts. 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 sealing member (not shown) such as packing is provided at the joint of each flange, and the flange is sealed in a watertight state. The vertical axis oblique flow pump shown in FIG. 17 operates with the pump casing 3, the suction cover 4, and a part of the pumping pipe 5 submerged in water.

In FIG. 17, the connection terminal 23 of the corrosive environment monitoring system 20 is electrically connected to the connection portion between the pump casing 3 submerged in water and the pumping pipe 5.

The vertical oblique flow pump shown in FIG. 18 is shown in FIG. 18 except that the connection terminal 23 of the corrosive environment monitoring system 20 is electrically connected to the wall surface of the pumping pipe 5 exposed to the atmosphere on the water surface. It has the same structure as the vertical axis mixed flow pump shown in 17.

The corrosive environment monitoring system of the present invention includes a reference electrode, an application electrode that applies a minute current to the environment in which the metal member is positioned, a current generator that applies a minute current to the application electrode, and immersion of the metal member. A potentiometer that measures the potential and the current-applied potential when a minute current is applied, a storage device that stores the immersion potential and the current-applied potential measured by the potentiometer, a potentiometer, a current generator, and a storage device. A control device for controlling the above-mentioned corrosive environment monitoring method of the present invention, and a housing for surrounding the storage device, the control device, the potentiometer, and the current generator are provided, and the reference electrode and the current application device are provided. A part of the electrode is exposed to the outside of the housing.

An example of the monitoring system 20 is shown in FIG.
The monitoring system 20 includes a connection terminal 21 connected to a monitoring object, a potential difference meter 22 electrically connected to the connection terminal 21, a reference electrode 23 electrically connected to the potential difference meter 22, and a potential difference meter. A DC current generator 24 that applies a current to the 22, an application electrode 25 that is electrically connected to the reference electrode 23 and the DC current generator 24, a control device 26 that controls the potential difference meter 22, and a control device 26. Encloses a storage device 27 electrically connected to, a power supply 28 for operating the control device 26 and the control device 27, a potential difference meter 22, a DC current generator 24, a control device 26, a storage device 27, and a power supply 28. The housing 29 is provided. A part of the reference electrode 23 and the application electrode 25 and the connection terminal 21 are positioned outside the housing 29.

As the reference electrode 23, a silver chloride electrode, a sweetened electrode, a copper sulfate electrode, a mercury sulfide electrode, a mercury oxide electrode, a lead peroxide electrode, an insoluble electrode and the like can be preferably used.

The application electrode 25 is preferably an insoluble electrode that is chemically or electrochemically insoluble or less soluble, and is, for example, platinum, carbon, graphite, iron oxide, chromium oxide, or a noble metal type. An electrode or the like in which a metal substrate such as titanium is coated with an oxide or the like can be preferably used.

The connection terminal 21 is preferably an insoluble electrode, and for example, an electrode in which a metal substrate such as titanium is coated with platinum, carbon, graphite, iron oxide, chromium oxide, or a noble metal oxide is preferably used. it can.

The connection terminal 21 is electrically connected to the object to be monitored. The electrical connection between the connection terminal 21 and the object to be monitored may be in liquid or in the atmosphere.

The corrosive environment monitoring system 20 is installed at a position where the corrosive potential generated in the monitoring object installed in the corrosive environment can be detected. The distance between the corrosive environment monitoring system 20 and the monitoring object depends on the electrical conductivity of the liquid such as seawater in which the monitoring object is located. When installed in a liquid with high electrical conductivity, the distance between the monitoring object and the monitoring system 20 may be large, but when installed in a liquid with low electrical conductivity, the distance may be short. It is necessary to. For example, when installing in seawater, the corrosive environment monitoring system 20 is preferably installed within about 1 m from the monitoring object. In the examples shown in FIGS. 17 and 18, the monitoring object is a vertical axis oblique flow pump installed in seawater. In the examples shown in FIGS. 17 and 18, it is possible to monitor the occurrence of gap corrosion at the connection portion between the pump casing 3 and the pumping pipe 5.

As shown in FIG. 20, the corrosion environment monitoring system 20 may further include one or more measuring instruments of a thermometer 30, an electric conductivity meter 31, a turbidity meter 32, a dissolved oxygen concentration meter 33, and a pH meter 34. it can. It can also include other measuring equipment needed depending on what is being monitored. These additional measuring instruments are connected to a conductor that electrically connects the potentiometer 22 and the control device 26. The detection sites of these additional measuring instruments are exposed to the outside of the housing 29.

The corrosive environment monitoring method of the present invention is executed by the control device 26 and the storage device 27. For example, the control device 26 controls the measurement timing of the potentiometer and various measuring devices, and measures the immersion potential of the monitoring object with respect to the reference electrode. After the immersion potential measurement is completed, a DC current is applied between the current application electrode 25 and the monitoring object, the potential of the monitoring object when the current is applied to the reference electrode 23 (current application potential) is measured, and the storage device. It is stored as data in 27. The immersion potential and the potential when a current is applied are measured in one measurement. The current application time is preferably 10 seconds or more and 5 minutes or less, and more preferably 1 minute or more and 2 minutes or less. The measurement cycle can be, for example, about 5 minutes to 1 month, and is preferably set according to the measurement period so that the number of measurement points is 200 or more.

Claims (5)

A corrosive environment monitoring method in which the immersion potential of a metal member and the potential when a minute current is applied are monitored, and the corrosiveness of the usage environment is estimated by Bayesian estimation using the monitored potential. The corrosion environment monitoring method according to claim 1, wherein the parameters included in the anodic polarization curve and the cathode polarization curve are set as state variables in data assimilation, and a sequential Bayesian filter is used as data assimilation. With a reference electrode
An application electrode that applies a minute current to the environment in which the metal member is positioned,
A current generator that applies a minute current to the application electrode,
A potentiometer that measures the immersion potential of a metal member and the potential when a small current is applied,
A storage device that stores the immersion potential and current-applied potential measured by the potentiometer, and
A control device that controls a potentiometer, a current generator, and a storage device to execute the corrosion environment monitoring method according to claim 1 or 2.
A housing that encloses a storage device, a control device, a potentiometer, and a current generator,
Equipped with
A corrosive environment monitoring system in which a reference electrode and a part of the current application electrode are exposed to the outside of the housing. Further, it is equipped with at least one kind of measuring device such as a thermometer, an electric conductivity meter, a turbidity meter, a dissolved oxygen concentration meter, and a pH meter which are electrically connected to the control device, and the detection part of the measuring device is a casing. The corrosive environment monitoring system according to claim 3, which is exposed to the outside of the body. An apparatus including the corrosive environment monitoring system according to claim 3 or 4.

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