JP7131622B2 - METHOD AND APPARATUS FOR CLEANING METAL PIPE - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to a cleaning method and cleaning apparatus for metal pipes.

Conventionally, in the manufacturing process of metal pipes, pickling treatment is performed in order to remove scales generated on the surface of metal pipes. After the pickling treatment, the metal pipe is washed with a cleaning liquid to remove scale remaining on the surface (for example, water washing treatment (rinse) is performed). After the pickling treatment, the metal pipe can be subjected to, for example, ultrasonic cleaning in which ultrasonic waves are applied to the cleaning liquid.

Patent Literature 1 discloses an ultrasonic cleaning apparatus configured to ultrasonically clean an object to be cleaned in the presence of microbubbles. The ultrasonic cleaning device includes an ultrasonic generator and a degassing device. The ultrasonic generator is provided in a cleaning tank in which cleaning liquid is stored. A degassing device is provided in a circulation path connected to the washing tank. The cleaning liquid in the cleaning tank is introduced into the degassing device through the circulation path. The deaerator separates dissolved air from the cleaning liquid to generate gas bubbles, preferably microbubbles. These air bubbles (microbubbles) are returned to the cleaning tank through the circulation path together with the cleaning liquid. As a result, the concentration of dissolved air in the cleaning liquid in the cleaning tank gradually decreases. When the dissolved air concentration becomes equal to or less than the predetermined value, the object to be cleaned is immersed in the cleaning liquid in the cleaning tank, and the ultrasonic generator irradiates the cleaning liquid with ultrasonic waves.

JP 2007-29944 A

Patent Literature 1 describes that by setting the dissolved air concentration of the cleaning liquid to a specified value or less, efficient and excellent ultrasonic cleaning can be performed without lowering the sound pressure of the ultrasonic waves. However, when the ultrasonic cleaning apparatus of Patent Document 1 is used for cleaning metal pipes after pickling, there is a concern that the cleanability may deteriorate. That is, in ultrasonic cleaning of metal pipes, the amount of scale in the cleaning liquid increases with time. These scales attenuate the ultrasonic waves irradiated to the cleaning liquid, thereby degrading the cleaning performance.

An object of the present disclosure is to provide a cleaning method and cleaning apparatus for metal pipes that can maintain high cleaning performance over a long period of time.

A method for cleaning a metal pipe according to the present disclosure includes a storage step of storing a cleaning liquid in a cleaning tank, generating fine bubbles by generating bubbles in gas dissolved in the cleaning liquid in the cleaning tank, and adding superfine bubbles to the cleaning liquid in the cleaning tank. An immersion step of immersing the metal pipe in the cleaning liquid in the cleaning tank while irradiating sound waves, a supply step of supplying new cleaning liquid to the cleaning tank, and a reference liquid level where the liquid level of the cleaning liquid in the cleaning tank is a predetermined level. and a discharging step of discharging an amount of the cleaning liquid corresponding to the height exceeding the reference liquid level from the cleaning tank when the height exceeds the reference liquid level.

According to the present disclosure, high detergency can be maintained for a long period of time in cleaning metal pipes.

1 is a plan view of a cleaning device according to an embodiment; FIG. FIG. 2 is a cross-sectional view of the cleaning apparatus shown in FIG. 1 taken along the line II-II. FIG. 3 is a diagram illustrating a discharge mechanism that can be employed in the cleaning device according to the embodiment; FIG. 4 is a diagram illustrating another discharge mechanism that can be employed in the cleaning device according to the embodiment; FIG. 5 is a graph showing the relationship between the dissolved oxygen concentration of the cleaning liquid, the sound pressure of the ultrasonic waves, and the detergency of the metal pipe. FIG. 6 is a graph showing the relationship between the overflow time of the cleaning liquid, the dissolved oxygen concentration of the cleaning liquid, and the amount of cleaning liquid supplied to the cleaning tank. FIG. 7 is a graph showing the relationship between the scale density of the cleaning liquid, the sound pressure attenuation rate of ultrasonic waves, and the cleanability of metal pipes. FIG. 8 is a graph showing the relationship between the surface area of the cleaned metal pipe, the scale density of the cleaning liquid, and the amount of cleaning liquid supplied to the cleaning tank.

A method for cleaning a metal pipe according to an embodiment includes a storage step of storing a cleaning liquid in a cleaning tank; An immersion step of immersing the metal pipe in the cleaning liquid in the cleaning tank while irradiating sound waves, a supply step of supplying new cleaning liquid to the cleaning tank, and a reference liquid level where the liquid level of the cleaning liquid in the cleaning tank is a predetermined level. and a discharging step of discharging from the cleaning tank an amount of cleaning liquid corresponding to the height exceeding the reference liquid level when the height exceeds the reference liquid level (first configuration).

In the cleaning method according to the first configuration, by generating fine bubbles in the cleaning liquid in which the metal pipe is immersed, the ultrasonic waves irradiated in the cleaning liquid are scattered to improve cleaning performance. In addition, the dissolved oxygen concentration in the cleaning liquid is reduced during the ultrasonic cleaning by generating fine bubbles by forming gas dissolved in the cleaning liquid into bubbles. This makes it possible to ensure good ultrasonic cleaning performance.

In the cleaning method according to the first configuration, for example, by supplying the cleaning liquid to the cleaning tank or by immersing the metal pipe in the cleaning liquid in the cleaning tank, the liquid level height of the cleaning liquid in the cleaning tank rises and exceeds the standard liquid level height, the cleaning liquid is discharged from the cleaning tank by the height exceeding the standard liquid level height. As a result, the scale that has been separated from the metal pipe and dispersed and suspended in the cleaning liquid is discharged from the cleaning tank together with the cleaning liquid. New cleaning liquid is also supplied to the cleaning tank. Therefore, it is possible to reduce the scale density in the cleaning liquid in the cleaning tank. Therefore, it is possible to reduce the attenuation of ultrasonic waves irradiated into the cleaning liquid, and to maintain high cleaning performance for a long period of time.

In the immersion step, the dissolved oxygen concentration of the cleaning liquid in the cleaning tank is preferably 5.2 mg/L or less (second configuration).

According to the second configuration, it is possible to more reliably ensure good ultrasonic cleaning performance.

The supply step can be performed simultaneously with the immersion step. In the supply step, the amount of cleaning liquid supplied to the cleaning tank per minute is preferably 0.17% or more and 1.25% or less of the amount of cleaning liquid stored in the cleaning tank (third configuration).

According to the third configuration, an increase in the amount of scale in the cleaning liquid can be suppressed more reliably, and the dissolved oxygen concentration in the cleaning liquid can be maintained within a preferred range.

More preferably, the supply amount is 0.17% or more and 0.83% or less of the storage amount (fourth configuration), and is 0.33% or more and 0.83% or less of the storage amount. More preferred (fifth configuration).

According to the fourth or fifth configuration, it is possible to more reliably suppress an increase in the amount of scale in the cleaning liquid, and to maintain the dissolved oxygen concentration in the cleaning liquid within a more preferable range.

The metal pipe may be a steel pipe with a specific chemical composition. The chemical composition is, in mass%, C: 0.01 to 0.13%, Si: 0.75% or less, Mn: 2% or less, P: 0.045% or less, S: 0.030% or less, It is preferable to contain Ni: 7 to 14% and Cr: 16 to 20%, with the balance being Fe and impurities (sixth configuration).

The above chemical composition is, in mass %, replacing part of the remaining Fe, Nb: 0.2 to 1.1%, Ti: 0.1 to 0.6%, Mo: 0.1 to 3%, Cu: Any one or more of 2.5 to 3.5% may be contained (seventh configuration).

The above chemical composition may contain B: 0.001 to 0.1% and N: 0.02 to 0.12% by mass in place of part of the remaining Fe (eighth Constitution).

A metal pipe cleaning apparatus according to an embodiment includes a cleaning tank, a supply mechanism, a discharge mechanism, a fine bubble generation mechanism, and an ultrasonic irradiation mechanism. The cleaning tank stores the cleaning liquid and accommodates the metal pipe. The supply mechanism supplies cleaning liquid to the cleaning tank. When the liquid level of the cleaning liquid in the cleaning tank exceeds a predetermined reference liquid level, the discharge mechanism discharges an amount of cleaning liquid corresponding to the height exceeding the reference liquid level from the cleaning tank. . The fine-bubble generating mechanism generates fine bubbles by forming gas bubbles dissolved in the cleaning liquid in the cleaning tank. The ultrasonic irradiation mechanism irradiates the cleaning liquid in the cleaning tank with ultrasonic waves (ninth configuration).

A cleaning device according to a ninth configuration includes a fine bubble generating mechanism. The fine bubble generating mechanism generates fine bubbles in the cleaning liquid by bubbling gas dissolved in the cleaning liquid. Therefore, in the ultrasonic cleaning of metal pipes, good cleaning performance can be ensured.

In the cleaning apparatus according to the ninth configuration, when the liquid level height of the cleaning liquid in the cleaning tank exceeds the reference liquid level height, the cleaning liquid is removed by the height exceeding the reference liquid level height. Drain the cleaning solution from the bath. As a result, the scale that has been separated from the metal pipe and dispersed and suspended in the cleaning liquid is discharged from the cleaning tank together with the cleaning liquid. On the other hand, the supply mechanism supplies new cleaning liquid to the cleaning tank. In the cleaning tank, the supply and discharge of the cleaning liquid can reduce the scale density in the cleaning liquid. Therefore, attenuation of ultrasonic waves can be reduced, and high cleaning performance can be ensured.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each figure, the same or corresponding configurations are denoted by the same reference numerals, and the same description will not be repeated.

[Washing equipment]
FIG. 1 is a plan view schematically showing a cleaning device 1 according to an embodiment. FIG. 2 is a II-II sectional view of the cleaning apparatus 1 shown in FIG.

Referring to FIG. 1, cleaning apparatus 1 performs ultrasonic cleaning on a metal pipe 2, which is an object to be cleaned. The cleaning device 1 can, for example, perform a water cleaning process on the metal pipe 2 that has been subjected to the pickling process.

The cleaning apparatus 1 includes a cleaning tank 10 , a supply mechanism 20 , a plurality of discharge mechanisms 30 , a plurality of ultrasonic irradiation mechanisms 40 , and a plurality of fine bubble generation mechanisms 50 . The cleaning device 1 further includes a plurality of cushioning members 60 .

(Washing tank)
The cleaning tank 10 is configured to accommodate the metal pipe 2 . During ultrasonic cleaning, a plurality of metal tubes 2 are normally housed in the cleaning tank 10 at the same time.

A cleaning liquid 3 for cleaning the metal pipe 2 is stored in the cleaning tank 10 . The type of cleaning liquid 3 is not particularly limited, and can be appropriately selected from known cleaning liquids. The cleaning liquid 3 is, for example, water (tap water or industrial water).

In this embodiment, the cleaning tank 10 has a rectangular shape in plan view. The cleaning tank 10 has an open upper surface. The bottom surface of the cleaning tank 10 is, for example, an inclined surface that inclines from one longitudinal end to the other longitudinal end. That is, in the cleaning tank 10, the depth of one end in the longitudinal direction (height of the inner wall surface) is different from the depth of the other end in the longitudinal direction (height of the inner wall surface). The cleaning tank 10 is, for example, a large cleaning tank having a length of about 10 to 25 m, a width of about 1 to 2 m, and a maximum depth of about 0.4 to 1 m.

The material of the cleaning tank 10 is not particularly limited. Examples of the material of the cleaning tank 10 include metal materials such as stainless steel, plastic resins such as fiber reinforced plastic (FRP) and polypropylene (PP), acid-resistant bricks, and the like.

(supply mechanism)
The supply mechanism 20 supplies the cleaning liquid 3 to the cleaning tank 10 . The supply mechanism 20 has at least one supply pipe 21 . In this embodiment, the supply mechanism 20 has multiple supply pipes 21 . The cleaning liquid 3 is supplied to the cleaning tank 10 through each supply pipe 21 . The plurality of supply pipes 21 are arranged at intervals. Therefore, the cleaning liquid 3 is dispersedly supplied to the cleaning tank 10 . When there are three or more supply pipes 21, it is preferable that the intervals between the supply pipes 21 are approximately even from the viewpoint of uniform supply of the new cleaning liquid 3.

In this embodiment, the plurality of supply pipes 21 are provided along one side wall of a pair of longitudinal side walls of the cleaning tank 10 . However, the position and number of supply pipes 21 are not particularly limited. One or more supply pipes 21 may be provided on both longitudinal side walls of the cleaning tank 10 . One or more supply pipes 21 can also be provided on the lateral side walls of the cleaning tank 10 in addition to or instead of the longitudinal side walls of the cleaning tank 10 .

(Ejection mechanism)
Each discharge mechanism 30 discharges the cleaning liquid 3 from the cleaning tank 10 when the amount of the cleaning liquid 3 in the cleaning tank 10 exceeds a predetermined amount. A plurality of ejection mechanisms 30 are arranged at intervals. Therefore, the cleaning liquid 3 is dispersed and discharged from the cleaning tank 10 . When three or more ejection mechanisms 30 are present, it is preferable that the intervals between the ejection mechanisms 30 are generally even. In addition, the number of ejection mechanisms 30 may be one.

In this embodiment, the plurality of discharge mechanisms 30 are provided along the side wall opposite to the supply pipe 21 among the pair of longitudinal side walls of the cleaning tank 10 . However, the position and number of the ejection mechanisms 30 are not particularly limited. A discharge mechanism 30 can also be provided on the side wall of the supply pipe 21 side of the pair of side walls in the longitudinal direction of the cleaning tank 10 . In addition to or instead of the longitudinal side walls of the cleaning tank 10 , one or more discharge mechanisms 30 may be provided on the lateral side walls of the cleaning tank 10 .

FIG. 3 illustrates a discharge mechanism 30A that can be employed in the cleaning device 1. As shown in FIG. The ejection mechanism 30A includes an ejection port 31 and an ejection pipe 32 .

The discharge port 31 is an opening formed in the side wall of the cleaning tank 10 . The discharge pipe 32 is provided outside the cleaning tank 10 and connected to the discharge port 31 . The cleaning liquid 3 is discharged from the cleaning bath 10 through the discharge port 31 and the discharge pipe 32 .

In the cleaning apparatus 1, a reference liquid level S of the cleaning liquid 3 in the cleaning tank 10 is set. When cleaning the metal tube 2 , the cleaning liquid 3 is supplied to the cleaning tank 10 until the liquid level reaches the reference liquid level S. The position of the lower end of the discharge port 31 substantially coincides with the position of the reference liquid surface S in the depth direction of the cleaning tank 10 .

As indicated by the two-dot chain line in FIG. 3, when the liquid level of the cleaning liquid 3 in the cleaning tank 10 exceeds the height of the reference liquid level S, the cleaning liquid 3 exceeding the reference liquid level S is discharged. Overflow from outlet 31 . For example, when the supply mechanism 20 supplies a new cleaning liquid 3 to the cleaning tank 10 in a state where the liquid level of the cleaning liquid 3 in the cleaning tank 10 is equal to the reference liquid level S, an amount substantially equal to the supply amount is supplied. The cleaning liquid 3 overflows from the outlet 31 .

Thus, the discharge mechanism 30A discharges the cleaning liquid 3 from the cleaning tank 10 when the amount of the cleaning liquid 3 in the cleaning tank 10 exceeds the liquid amount (predetermined amount) corresponding to the reference liquid surface S.

4 illustrates another discharge mechanism 30B that can be employed in the cleaning apparatus 1. As shown in FIG. The discharge mechanism 30B includes a discharge port 33, a discharge pipe 34, a discharge pump 35, and a liquid level detection means (not shown). A commercially available liquid level sensor or the like can be used as the liquid level detection means.

The discharge port 33 is an opening formed in the side wall of the cleaning tank 10 . The discharge port 33 is provided at an arbitrary height lower than the reference liquid level S on the side wall of the cleaning tank 10 . The discharge pipe 34 is provided outside the cleaning tank 10 and connected to the discharge port 33 . The cleaning liquid 3 is discharged from the cleaning bath 10 through the discharge port 33 and the discharge pipe 34 .

The discharge pump 35 is provided in the middle of the discharge pipe 34 . When the liquid level of the cleaning liquid 3 in the cleaning tank 10 exceeds the reference liquid level S, the discharge pump 35 sucks out the cleaning liquid 3 exceeding the reference liquid level S from the cleaning tank 10 . controlled. For example, when the liquid level of the cleaning liquid 3 exceeds the reference liquid level S in response to a signal from the liquid level detection means arranged in the cleaning tank 10, the discharge pump 35 is driven to increase the liquid level of the cleaning liquid 3. is controlled to stop driving the discharge pump 35 when the liquid level falls below the height of the reference liquid level S.

Thus, the discharge mechanism 30B also discharges the cleaning liquid 3 from the cleaning tank 10 when the amount of the cleaning liquid 3 in the cleaning tank 10 exceeds a predetermined amount, like the discharge mechanism 30A (FIG. 3).

(Ultrasonic irradiation mechanism)
Returning to FIG. 1, the ultrasonic irradiation mechanism 40 irradiates the cleaning liquid 3 in the cleaning tank 10 with ultrasonic waves. As the ultrasonic irradiation mechanism 40, a known ultrasonic oscillator generally used in ultrasonic cleaning can be used.

The frequency of the ultrasonic waves emitted by the ultrasonic emission mechanism 40 is preferably 20 kHz to 200 kHz. By setting the frequency of the ultrasonic wave to 20 kHz or more, it is possible to prevent large-sized bubbles generated from the surface of the metal tube 2 from impeding the propagation of the ultrasonic wave in the cleaning liquid 3 and deteriorating the cleaning performance. can. By setting the frequency of the ultrasonic wave to 200 kHz or less, it is possible to prevent deterioration of the cleaning uniformity due to the strong straightness of the ultrasonic wave. The frequency of ultrasonic waves is more preferably 20 kHz to 150 kHz, still more preferably 25 kHz to 100 kHz.

The ultrasonic irradiation mechanism 40 preferably has a frequency sweep function. The frequency sweep function is a function of irradiating the cleaning liquid 3 with ultrasonic waves while sweeping the frequency in a range of ±0.1 kHz to ±10 kHz centering on a specific selected frequency.

In this embodiment, at least one ultrasonic irradiation mechanism 40 is provided on the inner surface of each side wall of the cleaning tank 10 . However, the position and number of the ultrasonic irradiation mechanisms 40 are not particularly limited. One or a plurality of ultrasonic irradiation mechanisms 40 can also be installed on the bottom surface of the cleaning tank 10 . When installing a plurality of ultrasonic irradiation mechanisms 40 in the cleaning tank 10 , it is preferable to arrange the ultrasonic irradiation mechanisms 40 so that the ultrasonic waves are uniformly propagated throughout the cleaning tank 10 . As a result, the oscillation load of each ultrasonic irradiation mechanism 40 becomes uniform, so that interference between the generated ultrasonic waves can be prevented.

(Fine bubble generation mechanism)
The fine bubble generating mechanism 50 bubbles dissolved gas in the cleaning liquid 3 in the cleaning tank 10 to generate fine bubbles. The fine bubble generating mechanism 50 is arranged outside the cleaning tank 10 . A plurality of fine bubble generating mechanisms 50 are arranged along one side wall of the cleaning tank 10 in the longitudinal direction. However, the position and number of fine bubble generating mechanisms 50 are not particularly limited.

Each fine bubble generating mechanism 50 has pipes 51 and 52 and a fine bubble generating device 53 . Pipes 51 and 52 connect the cleaning tank 10 and the fine bubble generator 53 . The cleaning liquid from the cleaning tank 10 is introduced into the fine bubble generator 53 through the pipe 51 . The fine bubble generator 53 uses gas dissolved in the cleaning liquid 3 to generate fine bubbles. The fine bubbles are returned to the cleaning tank 10 through the pipe 52 together with the cleaning liquid 3 .

The fine bubble generator 53 can be appropriately selected from known fine bubble generators. As a known fine bubble generator, for example, fine bubbles are generated by shearing bubbles, passing bubbles through fine pores, decompressing liquid (pressure change), dissolving gas under pressure, ultrasonic waves, electrolysis, chemical reaction, etc. known to cause It is preferable that the fine bubble generator 53 can easily control the diameter and concentration of the fine bubbles. As the fine bubble generator 53, for example, a known fine bubble generator that generates fine bubbles by causing a pressure change in the liquid in the liquid circulation path can be employed.

Here, fine bubbles refer to fine bubbles having an average bubble diameter of 100 μm or less. In particular, fine bubbles having an average bubble diameter of μm are sometimes referred to as microbubbles, and fine bubbles having an average bubble diameter of nm are sometimes referred to as nanobubbles. The average bubble diameter is the diameter at which the number of samples is the maximum in the number distribution of the diameters of fine bubbles.

In ultrasonic cleaning, the fine bubbles improve the efficiency of ultrasonic wave propagation to the object to be cleaned, and improve cleaning performance as the nucleus of ultrasonic cavitation. Fine bubbles are often negatively charged in surface potential under the general liquid condition of the cleaning liquid 3 . On the other hand, objects to be cleaned (for example, scale, smut, oil, etc.) existing on the surface of the metal tube 2 are often positively charged. Therefore, when the fine bubbles reach the vicinity of the metal tube 2, the fine bubbles are adsorbed to the metal tube 2 due to the difference in electrification. Cavitation is generated on the surface of the metal pipe 2 by irradiating the cleaning liquid 3 to which fine bubbles are imparted with ultrasonic waves, so that the metal pipe 2 can be cleaned efficiently.

The average bubble diameter of the fine bubbles in the cleaning liquid 3 is preferably 0.01 μm or more from the viewpoint of preventing the fine bubble generating mechanism 50 from becoming large and facilitating control of the bubble diameter. Moreover, the average bubble diameter of the fine bubbles is preferably 100 μm or less from the viewpoint of increasing the floating speed of the fine bubbles and preventing the impediment of the propagation of ultrasonic waves to the metal tube 2 . More preferably, fine bubbles are microbubbles having an average bubble diameter of 1 μm to 50 μm.

At least part of the fine bubbles in the cleaning liquid 3 preferably have a bubble diameter equal to or smaller than the frequency resonance diameter. The frequency resonance diameter is the diameter that resonates with the frequency of the ultrasonic waves in the cleaning liquid 3 . The fine bubble generating mechanism 50 preferably generates fine bubbles in the cleaning liquid 3 so that the number of fine bubbles having a bubble diameter equal to or smaller than the frequency resonance diameter is 70% or more of the total number of fine bubbles. The reason for this will be explained below.

The natural frequency of various bubbles including fine bubbles is also called Minnaert resonance frequency, and is given by the following equation (1).

In the above formula (1),
f ₀ : Natural frequency of bubbles (Minnaert resonance frequency)
R ₀ : average radius of bubble p _∞ : average pressure of surrounding liquid γ: adiabatic ratio (γ of air = 1.4)
ρ is the liquid density.

Assuming that there is air inside the bubble of interest, the liquid around the bubble is water, and the pressure is atmospheric pressure, the product of the natural frequency _f0 of the bubble and the average radius _R0 of the bubble The value of ₀ R ₀ is approximately 3 kHz·mm according to the above equation (1). From this, if the frequency of the ultrasonic waves to be irradiated is 20 kHz, the radius of the resonating bubbles (resonance radius) _R0 is approximately 150 μm. Since the frequency resonance diameter _2R0 is the diameter of bubbles that resonate with ultrasonic waves, it is about 300 μm when the frequency of ultrasonic waves is 20 kHz. Similarly, when the frequency of ultrasonic waves is 100 kHz, the resonance radius _R0 is approximately 30 μm, and the frequency resonance radius _2R0 is approximately 60 μm.

Bubbles with radii larger than the resonance radius R ₀ are inhibitors. This is because when a bubble containing fine bubbles resonates, the bubble repeats expansion and contraction in a short period of time, and finally collapses. This is because if the diameter is larger than _2R0 , the ultrasonic waves will diffuse on the bubble surface. Conversely, if the size of the bubble is equal to or smaller than the frequency resonance diameter _2R0 when the first sound wave passes through the bubble, the ultrasonic wave can pass through the bubble without diffusing on the surface of the bubble.

Therefore, it is preferable that the ratio of the number of fine bubbles having a bubble diameter equal to or smaller than the frequency resonance diameter _2R0 to the total number of fine bubbles in the cleaning liquid 3 is 70% or more. Considering the presence of bubbles that expand immediately after the generation of fine bubbles, the ratio is more preferably 80% or more and 98% or less. Thereby, the propagation efficiency of ultrasonic waves in the cleaning liquid 3 can be improved. Further, by propagating the first sound waves to the wall and/or bottom of the cleaning tank 10, the ultrasonic waves are repeatedly diffused and reflected throughout the cleaning tank 10, making it possible to achieve uniform ultrasonic cleaning performance. Become. Bubbles having a frequency resonance diameter of _2R0 or less are crushed by repeated expansion and contraction after a predetermined ultrasonic wave irradiation time, and can contribute to cavitation cleaning.

The concentration (density) of the fine bubbles in the cleaning liquid 3 is preferably 10 ³ /mL or more from the viewpoint of improving the propagation of ultrasonic waves and securing the number of nuclei for ultrasonic cavitation. Further, the concentration of the fine bubbles generated in the cleaning liquid 3 is preferably 10 ⁶ /mL or less in order to prevent the size and number of the fine bubble generation mechanism 50 from increasing.

The average bubble diameter and concentration of fine bubbles can be measured with a known device such as a liquid particle counter or a bubble diameter distribution measuring device.

(buffer member)
The buffer member 60 is arranged inside the cleaning tank 10 . A plurality of cushioning members 60 are arranged in the longitudinal direction of the cleaning tank 10 .

As shown in FIG. 2, the cushioning member 60 is generally U-shaped. The metal pipe 2 in the cleaning tank 10 is placed on the cushioning member 60 . The inner surface of the buffer member 60 is located inside the ultrasonic irradiation mechanism 40 in the cleaning tank 10 . Therefore, the ultrasonic wave irradiation mechanism 40 is protected from the metal pipe 2 without the metal pipe 2 coming into contact with the ultrasonic wave irradiation mechanism 40 .

[Washing method]
A method for cleaning the metal pipe 2 using the cleaning apparatus 1 will be described below.

The metal pipe 2 is subjected to hot working, heat treatment, etc., and scales are generated on the surface thereof. In order to remove scale, the metal pipe 2 is subjected to a pickling treatment. The cleaning method according to the present embodiment is a method of cleaning the metal pipe 2 after a step of immersing the metal pipe 2 in an acid solution for a predetermined period of time for pickling (a known pickling step).

The metal pipe 2 as an object to be cleaned is, for example, a pipe made of stainless steel or a pipe made of Ni-based alloy. When the metal pipe 2 is a stainless steel pipe, the metal pipe 2 is a steel pipe containing 10.5% or more of Cr by mass %. For example, in mass %, C: 0.01 to 0.13%, Si: 0.75% or less, Mn: 2% or less, P: 0.045% or less, S: 0.030% or less, Ni: 7 14%, Cr: 16-20%, and the balance is Fe and impurities. The chemical composition is, in mass%, replacing part of the remaining Fe, Nb: 0.2 to 1.1%, Ti: 0.1 to 0.6%, Mo: 0.1 to 3%, Cu: Any one or more of 2.5 to 3.5% may be contained. Further, in place of part of the remaining Fe, 0.001 to 0.1% by mass of B and 0.02 to 0.12% of N may be contained.

The metal pipe 2 having the above chemical composition has an austenite steel structure, and thus has excellent heat resistance, corrosion resistance, and steam oxidation resistance. The metal tube 2 has an excellent strength, for example, a tensile strength of 550 MPa or more. Since such a metal pipe 2 is subjected to heat treatment at a high temperature exceeding 1000° C. in its manufacturing process, a large amount of scale is generated on its surface. Therefore, it is necessary to carry out a pickling treatment after the heat treatment and a washing treatment (rinse treatment) for washing away the scale remaining on the surface after the pickling treatment.

Moreover, when the metal tube 2 is a Ni-based alloy tube, for example, it has the chemical composition shown below. % by mass, C: 0.05% or less, Si: 0.5% or less, Mn: 1% or less, P: 0.030% or less, S: 0.030% or less, Cr: 19.5-24. 0%, Mo: 2.5 to 4.0%, Ti: 1.2% or less, and Fe: 22% or more, and the main balance is Ni (typically, the balance is Ni and impurities is). The chemical composition contains at least one of Cu: 0.5% or less, Nb: 4.5% or less, and Al: 2.0% or less, in mass%, in place of part of the remaining Ni. good too. Since such a metal pipe 2 is also subjected to heat treatment at a high temperature in its manufacturing process, a large amount of scale is generated on its surface. Therefore, it is necessary to carry out a pickling treatment after the heat treatment and a washing treatment (rinse treatment) for washing away the scale remaining on the surface after the pickling treatment.

The method for cleaning the metal pipe 2 according to the present embodiment includes the steps of storing the cleaning liquid 3 in the cleaning tank 10, immersing the metal tube 2 in the cleaning liquid 3 in the cleaning tank 10, and supplying the cleaning liquid 3 to the cleaning tank 10. and a step of discharging the cleaning liquid 3 from the cleaning tank 10 .

(Storage process)
Referring to FIG. 1 again, when cleaning the metal pipe 2 , first, the cleaning liquid 3 is stored in the cleaning tank 10 . A cleaning liquid 3 is supplied to the cleaning tank 10 by a supply mechanism 20 . However, at the stage of the storage step of supplying the cleaning liquid 3 to the empty cleaning tank 10 , the cleaning liquid 3 may be supplied to the cleaning tank 10 by means other than the supply mechanism 20 . The cleaning liquid 3 supplied to the cleaning tank 10 preferably has a dissolved oxygen concentration of about 7 mg/L to 11 mg/L, and preferably has a dissolved oxygen concentration of about 8 mg/L to 10 mg/L. is more preferred. The cleaning liquid 3 is typically water (tap water or industrial water). When the cleaning liquid 3 is water (tap water or industrial water) with a water temperature of 10 to 35° C., the dissolved oxygen concentration of the cleaning liquid 3 is 7 mg/L to 11 mg/L. When the cleaning liquid 3 is water (tap water or industrial water) with a water temperature of 15 to 25° C., the dissolved oxygen concentration of the cleaning liquid 3 is 8 mg/L to 10 mg/L. The dissolved oxygen concentration serves as an indicator of the dissolved gas amount in the cleaning liquid 3 .

When the liquid level of the cleaning liquid 3 in the cleaning tank 10 exceeds the reference liquid level S (FIG. 3 or FIG. 4), the discharging mechanism 30 starts discharging the cleaning liquid 3 . The supply mechanism 20 continues to supply the cleaning liquid 3 to the cleaning tank 10 even after the liquid level of the cleaning liquid 3 reaches the reference liquid level S. As a result, in the cleaning tank 10, the cleaning liquid 3 is discharged at the same time as the cleaning liquid 3 is supplied. The amount of cleaning liquid 3 discharged at this time is substantially equal to the amount of cleaning liquid 3 supplied. The cleaning liquid (water) 3 discharged by the discharge mechanism 30 is discarded after being subjected to predetermined waste water treatment.

(Immersion process, supply process, and discharge process)
Next, the metal pipe 2 is immersed in the cleaning liquid 3 stored in the cleaning tank 10 for a predetermined time. The metal pipe 2 can be immersed in the cleaning liquid 3 in the cleaning tank 10 using a crane or the like. Normally, a plurality of metal tubes 2 are immersed in the cleaning liquid 3 at the same time, but the metal tubes 2 may be immersed in the cleaning liquid 3 one by one.

In the immersion step, the immersion of the metal tube 2 in the cleaning liquid 3 in the cleaning tank 10, the holding of the metal tube 2 in the cleaning liquid 3, and the pulling up of the metal tube 2 from the cleaning tank 10 are defined as one cycle. A predetermined number of times. The retention time of the metal tube 2 in the cycle and the number of times the cycle is performed can be determined so that the total immersion time of the metal tube 2 in the cleaning liquid 3 is equal to or longer than a predetermined time. The total immersion time of the metal pipe 2 may be appropriately set according to the amount of scale adhering to the metal pipe 2 and the like. The total immersion time of the metal tube 2 is, for example, preferably 30 seconds or longer, more preferably 1 minute or longer.

When pulling up the metal pipe 2 from the cleaning tank 10, it is preferable to incline the metal pipe 2 with respect to the horizontal plane. As a result, the liquid inside the metal tube 2 can be drained. When performing the above cycle a plurality of times, it is preferable to change the tilting direction for each cycle.

During the immersion process, a new cleaning liquid 3 is continuously supplied to the cleaning tank 10 by the supply mechanism 20 . Then, the discharge mechanism 30 continuously discharges the cleaning liquid 3 in an amount corresponding to the height above the reference liquid surface S from the cleaning tank 10 . That is, in this embodiment, the immersion process, the supply process, and the discharge process are performed simultaneously. The supply mechanism 20 supplies the amount of the cleaning liquid 3 stored in the cleaning tank 10 per minute (the cleaning liquid 3 when the cleaning liquid 3 is stored in the cleaning tank 10 up to the reference liquid level S in the state where the metal pipe 2 is not immersed). is preferably 0.17% or more and 1.25% or less, more preferably 0.17% or more and 0.83% or less, and still more preferably 0.33% or more and 0.83% or less of the cleaning liquid 3 is supplied to the cleaning tank 10 .

During the immersion process, the cleaning liquid 3 in the cleaning tank 10 is irradiated with ultrasonic waves by the ultrasonic irradiation mechanism 40 and fine bubbles are supplied by the fine bubble generation mechanism 50 .

In the cleaning method according to the present embodiment, the dissolved oxygen concentration in the cleaning liquid 3 is lowered by the fine bubble generating mechanism 50 bubbling the dissolved gas in the cleaning liquid 3 . The fine bubble generating mechanism 50 reduces the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 to 5.2 mg/L or less. The fine bubble generating mechanism 50 reduces the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 to preferably 4.5 mg/L or less, more preferably 4.2 mg/L or less.

Specifically, the supply mechanism 20 supplies the cleaning liquid 3 having a dissolved oxygen concentration of approximately 7 mg/L to 11 mg/L, preferably approximately 8 mg/L to 10 mg/L, to the cleaning tank 10 . When this cleaning liquid 3 passes through the fine bubble generator 53 of the fine bubble generating mechanism 50, the dissolved gas in the cleaning liquid 3 is converted into fine bubbles, and the dissolved oxygen concentration of the cleaning liquid 3 decreases. By circulating the cleaning liquid 3 between the cleaning tank 10 and the fine bubble generating mechanism 50, the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 is 5.2 mg/L or less, more preferably 4.5 mg/L or less. , and more preferably 4.2 mg/L or less.

After the metal pipe 2 is immersed in the cleaning liquid 3 for a preset total immersion time or more, the metal pipe 2 is recovered from the cleaning bath 10 using a crane or the like. Also at this time, it is preferable to pull up the metal tube 2 while tilting it. Thereby, it is possible to prevent the cleaning liquid 3 from remaining inside the metal pipe 2 .

By recovering the metal pipe 2, the cleaning of the metal pipe 2 is completed. In the cleaning tank 10, ultrasonic waves and fine bubbles are continuously applied to the cleaning liquid 3, and the cleaning liquid 3 is supplied and discharged. Therefore, the step of immersing another metal tube 2 can be subsequently performed.

If the metal pipe 2 brings into the cleaning tank 10 an acid solution or water that does not contain fine bubbles, the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 may increase. When the dissolved oxygen concentration of the cleaning liquid 3 becomes high, it is preferable to stop the ultrasonic cleaning of the metal tube 2 until the fine bubble generating mechanism 50 sufficiently reduces the dissolved oxygen concentration. Immersion of the metal tube 2 may be restarted when the dissolved oxygen concentration of the cleaning liquid becomes 5.2 mg/L or less, 4.5 mg/L or less, or 4.2 mg/L or less.

In this embodiment, after the cleaning liquid 3 is stored in the cleaning tank 10 in the storing step, the metal pipe 2 is arranged in the cleaning tank 10 in the immersion step. However, in the storing step, the cleaning liquid 3 can be stored in the cleaning tank 10 after the metal pipe 2 is placed in the empty cleaning tank 10 .

[Numerical range]
Numerical ranges of the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 and the amount of the cleaning liquid 3 supplied to the cleaning tank 10 will be described below with reference to FIGS. 5 to 8. FIG. In the explanation and verification using FIGS. 5 to 8, the metal pipe 2 as the object to be cleaned was an austenitic stainless steel pipe (Ni: 9% by mass, Cr: 18.5% by mass, Cu: 3% by mass, Nb: 0.5% by mass), the cleaning liquid 3 supplied to the cleaning tank 10 is water (industrial water) with a water temperature of about 20° C., and the storage amount of the cleaning liquid 3 in the cleaning tank 10 (when it is stored up to the reference liquid level S volume) is about 12000L.

(Dissolved oxygen concentration)
FIG. 5 is a graph showing the relationship between the dissolved oxygen concentration in the cleaning liquid 3 , the sound pressure of the ultrasonic waves irradiated into the cleaning liquid 3 , and the detergency of the metal pipe 2 . 5, the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 and the sound pressure of the ultrasonic waves irradiated into the cleaning liquid 3 in the cleaning tank 10 were changed to change the cleaning performance of the metal tube 2. verified.

The dissolved oxygen concentration [mg/L] is a value measured with a commercially available dissolved oxygen concentration meter (LAQUA OM-71, manufactured by Horiba, Ltd.). This measured value is defined as the dissolved oxygen concentration in the present disclosure. The sound pressure [mV] was measured using a commercially available ultrasonic sound pressure meter (sound pressure level monitor 19001D manufactured by Kaijo Co., Ltd.) in a measurement mode in which the average measured value for 5 seconds was measured. 100 mm from the liquid surface of the cleaning liquid 3, and measured by immersing the vibration transmission rod in the water. This measured value is the sound pressure in the present disclosure. Note that the frequency of the ultrasonic waves is 38 kHz.

In the graph of FIG. 5, "◯", "Δ", and "X" represent the evaluation results of detergency. "O" means that the scale was completely removed from the surface of the metal tube 2 and the cleanability by ultrasonic waves was extremely good. “Δ” means that although scale remains on a part of the surface of the metal tube 2, it can be said that the cleanability by ultrasonic waves is good. "x" means that the cleanability by ultrasonic waves was poor.

As can be seen from FIG. 5, when the dissolved oxygen concentration of the cleaning liquid 3 is 5.2 mg/L or less, there are many evaluation results of ◯ or Δ, and the cleaning property is good in many sound pressure ranges. Therefore, in this embodiment, the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 is set to 5.2 mg/L or less.

As can be seen from FIG. 5, if the dissolved oxygen concentration of the cleaning liquid 3 is set to 4.5 mg/L or less, or 4.2 mg/L or less, the sound pressure range in which cleaning performance is good is further increased. Therefore, the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 is preferably 4.5 mg/L or less, more preferably 4.2 mg/L or less.

When the dissolved oxygen concentration of the cleaning liquid 3 is 5.2 mg/L or less and the sound pressure of the ultrasonic waves is 120 mV or more, the evaluation result in FIG. When the dissolved oxygen concentration of the cleaning liquid 3 is 4.5 mg/L or less, or 4.2 mg/L or less, and the ultrasonic sound pressure is 120 mV or more, the evaluation result in FIG. Therefore, the ultrasonic wave irradiation mechanism 40 preferably outputs ultrasonic waves so that the sound pressure of the ultrasonic waves in the cleaning liquid 3 is 120 mV or more.

The dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 is usually 2.0 mg/L or more. However, the lower limit of the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 may not be particularly managed or controlled.

(Relationship between cleaning liquid supply amount and dissolved oxygen concentration)
FIG. 6 is a graph showing the relationship between the overflow time of the cleaning liquid 3, the dissolved oxygen concentration of the cleaning liquid 3, and the amount of cleaning liquid 3 supplied to the cleaning tank 10. As shown in FIG. In preparing the graph of FIG. 6, the supply rate was changed to 40 L/min, 100 L/min, and 150 L/min, and the dissolved oxygen concentration in the cleaning liquid 3 was measured for each supply rate. The cleaning liquid 3 supplied by the supply mechanism 20 is water (industrial water) with a water temperature of about 20° C., and is considered to have a dissolved oxygen concentration of about 8 mg/L to 10 mg/L. The overflow time is the duration of the overflow of the cleaning liquid 3 in the cleaning tank 10 (drainage from the discharge mechanism 30), in other words, the time during which the supply mechanism 20 continuously supplies the cleaning liquid 3 to the cleaning tank 10. is.

6, the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 was 4.5 mg/ It can be seen that it can be maintained at L or less. When the supply rate is 40 L/min and 100 L/min, the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 is maintained at 4.2 mg/L or less. If the supply rate is less than 40 L/min, the dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 is expected to further decrease.

From FIG. 6, when the cleaning liquid 3 having a dissolved oxygen concentration of about 8 mg/L to 10 mg/L is supplied to the cleaning tank 10 having a storage volume of about 12000 L, the supply rate is preferably 150 L/min or less. , 100 L/min or less. Converting these supply amounts to the storage amount (about 12000 L), the supply amount of the cleaning liquid 3 to the cleaning tank 10 per minute is preferably 1.25 of the storage amount of the cleaning liquid 3 in the cleaning tank 10. % or less, more preferably 0.83% or less of the storage amount. As a result, the dissolved oxygen concentration described above can be ensured in the cleaning liquid 3 in the cleaning tank 10 .

(Relationship between cleaning liquid supply amount and scale density)
FIG. 7 is a graph showing the relationship between the scale density of the cleaning liquid 3, the sound pressure attenuation rate of ultrasonic waves (frequency of 38 kHz and sound pressure of 120 mV) irradiated into the cleaning liquid 3, and the cleanability of the metal pipe 2.

As can be seen from FIG. 7, the lower the scale density in the cleaning liquid 3, the lower the sound pressure attenuation rate, and the higher the scale density, the higher the sound pressure attenuation rate. When the scale density is 2.5 g/L or less, the scale adhering to the metal tube 2 is completely removed, and the ultrasonic cleanability is extremely good. When the scale density exceeds 2.5 g/L, part of the scale remains on the metal tube 2 (residue after washing). When the scale density exceeds 5.0 g/L, the cleanability by ultrasonic waves becomes poor. Therefore, the scale density in the cleaning liquid 3 is preferably 2.5 g/L or less.

FIG. 8 is a graph showing the relationship between the surface area of the cleaned metal pipe 2 , the scale density of the cleaning liquid 3 , and the amount of cleaning liquid 3 supplied to the cleaning tank 10 . The supply amount conditions in FIG. 8 are no supply, 20 L/min, and 40 L/min. The cleaning liquid 3 in the cleaning tank 10 was irradiated with ultrasonic waves having a frequency of 38 kHz and a sound pressure of 120 mV.

From FIG. 8, when the cleaning liquid 3 is not supplied to the cleaning tank 10, the processing surface area is about 4000 m ² and the scale density of the cleaning liquid 3 is slightly less than 2.0 g/L. Extending the approximate straight line shown in FIG. 8, it is considered that the scale density reaches 2.5 g/L when the treatment surface area is about 5000 m ² . As described above, when the scale density exceeds ^2.5 g/L, uncleaned residue begins to occur. , it is considered that the cleaning liquid 3 in the cleaning tank 10 needs to be replaced.

When the cleaning liquid 3 is supplied to the cleaning tank 10, almost the same amount of the cleaning liquid 3 as the supplied amount overflows from the cleaning tank 10, and the cleaning liquid 3 in the cleaning tank 10 is gradually replaced. From FIG. 8, when the cleaning liquid 3 is supplied to the cleaning tank 10, the scale density of the cleaning liquid 3 is 1.0 g/L or less even if the processing surface area reaches 6000 m ² . Therefore, when the cleaning liquid 3 is supplied to the cleaning tank 10, the intervals at which the cleaning liquid 3 in the cleaning tank 10 is replaced become longer than when the cleaning liquid 3 is not supplied to the cleaning tank 10. FIG. When the supply rate of the cleaning liquid 3 to the cleaning tank 10 is 40 L/min, compared with the case where the supply rate is 20 L/min, the rate of increase in scale density becomes smaller, and the cleaning liquid 3 in the cleaning tank 10 is replaced. longer intervals.

As can be seen from FIGS. 7 and 8, when the cleaning liquid 3 is supplied to the cleaning tank 10 having a storage volume of about 12000 L, the supply rate is preferably 20 L/min or more, and preferably 40 L/min or more. is more preferred. Converting these supply amounts to the storage amount (about 12000 L), the supply amount of the cleaning liquid 3 to the cleaning tank 10 per minute is preferably 0.17 of the storage amount of the cleaning liquid 3 in the cleaning tank 10. % or more, more preferably 0.33% or more of the storage amount. Thereby, the scale density of the cleaning liquid 3 can be maintained at 2.5 g/L or less for a long time. Therefore, the intervals at which the cleaning liquid 3 in the cleaning tank 10 is replaced become longer, and the number of times the cleaning liquid 3 is replaced can be reduced.

[Effects of Embodiment]
In this embodiment, by generating fine bubbles in the cleaning liquid 3 in which the metal pipe 2 is immersed, the ultrasonic waves in the cleaning liquid 3 can be scattered and propagated three-dimensionally. Thereby, the washability of the metal pipe 2 is improved. Further, in the present embodiment, the dissolved oxygen concentration in the cleaning liquid 3 is reduced to 5.2 mg/L or less by making the gas dissolved in the cleaning liquid 3 into fine bubbles. Therefore, as described with reference to FIG. 5, good ultrasonic cleaning performance can be ensured.

In this embodiment, in the immersion step of the metal tube 2, the cleaning liquid 3 is supplied to the cleaning tank 10 and the cleaning liquid 3 is discharged from the cleaning tank 10 continuously. As a result, the scale separated from the metal pipe 2 is discharged from the cleaning tank 10 together with the cleaning liquid 3 , while new cleaning liquid 3 is supplied to the cleaning tank 10 . Therefore, as described with reference to FIGS. 7 and 8, an increase in the scale density of the cleaning liquid 3 can be suppressed, and attenuation of ultrasonic waves can be reduced. Therefore, in the ultrasonic cleaning of the metal tube 2, high cleaning performance can be ensured.

In this embodiment, the dissolved oxygen concentration of the cleaning liquid 3 is preferably 4.5 mg/L or less, more preferably 4.2 mg/L or less. As a result, the ultrasonic cleaning property can be improved in a wide sound pressure range.

In the present embodiment, the amount of the cleaning liquid 3 supplied to the cleaning tank 10 per minute is preferably 0.17% or more and 1.25% or less, more preferably 0%, of the amount of the cleaning liquid 3 stored in the cleaning tank 10. 0.17% or more and 0.83% or less, more preferably 0.33% or more and 0.83% or less. As a result, the dissolved oxygen concentration of the cleaning liquid 3 can be maintained within a preferable range, and an increase in the scale density of the cleaning liquid 3 can be suppressed. Therefore, ultrasonic cleaning properties can be further improved.

In this embodiment, the bottom surface of the cleaning tank 10 is an inclined surface that inclines from one longitudinal end to the other longitudinal end. This makes it easier for the cleaning liquid 3 to enter the interior of the metal tube 2, and the inner peripheral surface of the metal tube 2 can be reliably cleaned.

In this embodiment, the ultrasonic irradiation mechanism 40 preferably has a frequency sweep function. Thereby, the cleaning efficiency of the metal pipe 2 can be improved.

More specifically, when ultrasonic waves are applied to microbubbles including fine bubbles, a force called Bjerknes force acts on the microbubbles, and the microbubbles act on the antinodes and nodes of the ultrasonic waves according to their diameters. Gravitate. Microbubbles having a bubble diameter equal to or smaller than the frequency resonance diameter _2R0 are attracted to the antinode of the ultrasonic wave and can contribute to cavitation cleaning. When the frequency of the ultrasonic wave is changed by the frequency sweeping function of the ultrasonic wave irradiation mechanism 40, the frequency resonance diameter _2R0 is changed according to the frequency change, and microbubbles contributing to cavitation cleaning increase. Therefore, many microbubbles can be used as cavitation nuclei. Thereby, the cleaning efficiency of the metal pipe 2 is improved.

When the wavelength of the ultrasonic wave becomes 1/4 of the wavelength corresponding to the thickness of the object to be irradiated, the ultrasonic wave passes through the object to be irradiated. Therefore, the ultrasonic waves that pass through the peripheral wall of the metal tube 2 can be increased by applying the ultrasonic waves while the ultrasonic wave irradiation mechanism 40 sweeps the frequency within an appropriate range. Therefore, the cleaning efficiency of the metal pipe 2 is improved.

By the way, ultrasonic waves are not only vertically incident on an object to be irradiated, but also propagate while repeating multiple reflections. Therefore, a constant sound field tends to be difficult to form. On the other hand, according to the frequency sweeping function of the ultrasonic irradiation mechanism 40, ultrasonic waves are irradiated into the cleaning liquid 3 while sweeping the frequency within a range of ±0.1 kHz to ±10 kHz centering on a specific frequency. This satisfies the condition that the wavelength of the ultrasonic wave is 1/4 of the wavelength corresponding to the wall thickness of the metal tube 2 at various positions of the metal tube 2 . Therefore, ultrasonic waves can be transmitted from the outside to the inside of the metal tube 2 at various positions of the metal tube 2 .

Although the embodiments according to the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present disclosure.

In the present embodiment, the step of immersing the metal pipe 2, the step of supplying the cleaning liquid 3 to the cleaning tank 10, and the step of discharging the cleaning liquid 3 from the cleaning tank 10 were performed simultaneously, but these steps are not necessarily performed simultaneously. does not need to be Further, the supply or discharge of the cleaning liquid 3 in the cleaning tank 10 may not be performed continuously. For example, when the metal tube 2 is immersed in the cleaning liquid 3 while the supply of the cleaning liquid 3 to the cleaning tank 10 is stopped, the liquid level of the cleaning liquid 3 in the cleaning tank 10 rises by the volume of the metal tube 2, and the reference liquid It may exceed the surface S. At this time, an amount of the cleaning liquid 3 corresponding to the height above the reference liquid surface S is discharged from the cleaning tank 10 . Here, the cleaning liquid 3 in the cleaning tank 10 is agitated as the metal pipe 2 is put in and taken out, and the cleaning liquid is mixed between the cleaning tank 10 and the fine bubble generator 53 via the pipes 51 and 52 . By circulating 3, the scale is evenly dispersed and floating. Therefore, the cleaning liquid 3 in which the scale is dispersed and suspended is discharged from the cleaning tank 10 . After pulling up the metal pipe 2, if a new cleaning liquid 3 is supplied into the cleaning tank 10 in which the amount of the cleaning liquid 3 has decreased, the scale density of the cleaning liquid 3 in the cleaning tank 10 decreases. Thus, it is possible to suppress the increase in scale density without simultaneously performing the immersion process, the supply process, and the discharge process.

The present disclosure will be described in more detail below by way of examples. However, the present disclosure is not limited to the following examples.

Using the cleaning apparatus 1 shown in FIGS. 1 to 3, the results of ultrasonic cleaning of a large number of metal pipes 2 were evaluated for four days. Each metal pipe 2 is subjected to heat treatment after cold drawing, and then to pickling treatment. Each metal tube 2 has an outer diameter of 38 mm to 95 mm. Each metal pipe 2 is an austenitic stainless steel pipe and has the following chemical composition.
[Chemical composition]
in % by mass,
C: 0.07 to 0.13%,
Si: 0.30% or less,
Mn: 1.0% or less,
P: 0.040% or less,
S: 0.010% or less,
Ni: 7.5 to 10.5%,
Cr: 17.0 to 19.0%,
Nb: 0.30 to 0.60%, and
Cu: 2.5-3.5%
contains
The remainder consists of Fe and impurities.

In the cleaning process of this embodiment, the cleaning liquid 3 in the cleaning tank 10 was irradiated with ultrasonic waves by the ultrasonic irradiation mechanism 40 and fine bubbles were supplied by the fine bubble generation mechanism 50 . The cleaning conditions in this example are shown below.
[Washing conditions]
・Washing liquid: normal temperature industrial water ・Storage volume of cleaning tank: 12000L
・Ultrasonic frequency: 38kHz
・Amount of cleaning liquid supplied to the cleaning tank: about 40 L/min

In the cleaning process of the metal pipe 2, the average ultrasonic sound pressure and the average dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 were measured for each treatment day. The average sound pressure was measured using a commercially available ultrasonic sound pressure meter (sound pressure level monitor 19001D manufactured by Kaijo Co., Ltd.) in a measurement mode in which the average measurement value was measured for 5 seconds, and the probe was placed 100 mm from the surface of the cleaning liquid 3. Measured in water. The average dissolved oxygen content was measured using a commercially available dissolved oxygen concentration meter (LAQUA OM-71, manufactured by Horiba, Ltd.). Table 1 shows the weight (treatment amount) of the cleaned metal pipe 2, the measurement results, and the cleaning performance evaluation.

As shown in Table 1, on the 4th day, the cumulative processing amount of the metal pipe 2 exceeds 200 tons. However, the average dissolved oxygen concentration of the cleaning liquid 3 in the cleaning tank 10 is 3.55 mg/L, which is maintained at 5.2 mg/L or less. Further, the scale density of the cleaning liquid 3 is 0.108 g/L, which does not exceed 2.5 g/L at which the detergency begins to deteriorate. Therefore, the cleanability was good for 4 days. Therefore, according to the cleaning method and cleaning apparatus according to the present disclosure, it was confirmed that high ultrasonic cleaning performance can be ensured.

1: Cleaning device 2: Metal pipe 3: Cleaning liquid 10: Cleaning tank 20: Supply mechanism 30: Drainage mechanism 40: Ultrasonic irradiation mechanism 50: Fine bubble generation mechanism

Claims (8)

A method for cleaning a metal pipe,
a storage step of storing the cleaning liquid in the cleaning tank;
The gas dissolved in the cleaning liquid in the cleaning tank is bubbled to generate fine bubbles, and the metal pipe is passed through the cleaning liquid in the cleaning tank while irradiating the cleaning liquid in the cleaning tank with ultrasonic waves. a dipping step of dipping;
a supply step of supplying a new cleaning liquid to the cleaning tank;
When the liquid level height of the cleaning liquid in the cleaning tank exceeds a predetermined reference liquid level height, the amount of cleaning liquid corresponding to the height exceeding the reference liquid level height is discharged from the cleaning tank. comprising a process and
The supplying step is performed simultaneously with the immersing step,
The cleaning method , wherein in the supplying step, the amount of the cleaning liquid supplied to the cleaning tank per minute is 0.17% or more and 1.25% or less of the amount of the cleaning liquid stored in the cleaning tank . The cleaning method according to claim 1,
The cleaning method, wherein in the immersion step, the dissolved oxygen concentration of the cleaning liquid in the cleaning tank is 5.2 mg/L or less. The cleaning method according to claim 1 or 2 ,
The cleaning method, wherein the supply amount is 0.17% or more and 0.83% or less of the storage amount. The cleaning method according to claim 3 ,
The cleaning method, wherein the supply amount is 0.33% or more and 0.83% or less of the storage amount. The cleaning method according to any one of claims 1 to 4 ,
The metal tube is
in % by mass,
C: 0.01 to 0.13%,
Si: 0.75% or less,
Mn: 2% or less,
P: 0.045% or less,
S: 0.030% or less,
Ni: 7 to 14%, and
Cr: 16-20%,
and the balance being Fe and impurities. The cleaning method according to claim 5 ,
The chemical composition is, in mass %, replacing part of the remaining Fe, Nb: 0.2 to 1.1%, Ti: 0.1 to 0.6%, Mo: 0.1 to 3%, Cu: A cleaning method containing any one or more of 2.5 to 3.5%. The cleaning method according to claim 5 or 6 ,
The cleaning method, wherein the chemical composition contains B: 0.001 to 0.1% and N: 0.02 to 0.12% by mass% in place of part of the remaining Fe. A cleaning device for metal pipes,
a cleaning tank in which a cleaning liquid is stored and the metal pipe is accommodated;
a supply mechanism that supplies cleaning liquid to the cleaning tank;
When the liquid level height of the cleaning liquid in the cleaning tank exceeds a predetermined reference liquid level height, the amount of cleaning liquid corresponding to the height exceeding the reference liquid level height is discharged from the cleaning tank. a mechanism;
a fine-bubble generating mechanism for generating fine bubbles by forming gas bubbles dissolved in the cleaning liquid in the cleaning tank;
an ultrasonic irradiation mechanism for irradiating ultrasonic waves into the cleaning liquid in the cleaning tank;
with
The cleaning device , wherein the supply mechanism supplies the cleaning liquid in an amount of 0.17% or more and 1.25% or less of the amount of the cleaning liquid stored in the cleaning tank per minute to the cleaning tank .

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