JP6871794B2 - Manufacturing method of anticorrosion coated metal tube - Google Patents

Description

The present invention relates to a method for producing an anticorrosion coated metal pipe that can be used as a line pipe or the like. Specifically, by changing the output of the heating device in the heating process before coating with the powder epoxy primer or organic resin, the metal tube is heated uniformly, and the deterioration of the quality and corrosion resistance of the metal tube is suppressed. The present invention relates to a method for manufacturing a coated metal tube.

Pipelines are used for transportation from natural gas producing areas to consuming areas or LNG terminals, and the development of long-distance pipelines is being actively promoted with the remoteization of gas producing areas. Since corrosion protection of these line pipes is an important issue for prolonging the life of the pipes, the outer surface of the line pipes is coated with a powder epoxy primer to provide long-term corrosion resistance. Since this powder epoxy primer can have a thicker film thickness than the conventional liquid epoxy primer, corrosion resistance can be improved. On the other hand, in order for the powder epoxy primer to be sufficiently melted and cured, it is generally necessary to heat the steel pipe to 180 ° C. to 240 ° C. The powder epoxy primer melts after coating the steel pipe, and the entire surface of the steel material gets wet in a low viscosity state, so that the contact area between the steel material surface and the powder epoxy primer increases, and the corrosion resistance of the steel pipe is improved. The viscosity of the powder epoxy primer immediately after being painted on the steel pipe decreases as the temperature of the steel pipe increases. Therefore, in order to wet the molten powder epoxy primer on the entire surface of the steel material, paint at a high temperature of 180 ° C or higher. Is desirable. On the other hand, the higher the coating temperature, the faster the powder epoxy primer cures. Therefore, the air contained in the powder epoxy primer cures before it escapes from the coating film during coating, so that bubbles exist in the coating film. , Poor corrosion resistance. Further, the higher the coating temperature, the faster the curing and the less the amount of functional groups that contribute to adhesion. Therefore, when the outer layer of the powder epoxy primer is coated with polyolefin, sufficient adhesive strength cannot be obtained. Therefore, it is necessary to heat the steel pipe in the range of 180 ° C. to 240 ° C.

In the production of resin-coated steel pipes coated with polyolefins, etc., in order to improve production efficiency and reduce loss of resins such as powdered epoxy primers and polyolefins, steel pipes of a certain length are connected to each other with connecting metal fittings, and this connection is made. The steel pipe is passed through the covering device, and the resin is coated on the outer surface of the metal pipe and the connecting metal fittings. After that, the resin coating portion is cut by running at the metal pipe connecting portion, the connection fitting is removed, and the end face of the resin coating portion is finished to obtain a product.

As a connecting metal fitting for manufacturing a coated metal tube by continuously coating the outer surface of the metal tube with a resin, for example, as shown in Patent Document 1, the cylindrical frame and the inner diameter of the connecting metal tube are slightly larger than the inner diameter. A cylindrical insertion portion having a small outer diameter is provided detachably from each other, a screw rod is provided at the center of the frame body, and a mechanism capable of expanding / contracting from the inside to the outside of the frame body by rotating the screw is provided. There is known a connection fitting that connects steel pipes by pressing a pusher radially against the inner surface of the fitting to be connected. In addition, as shown in Patent Document 2, a connection fitting having a diameter slightly smaller than the inner diameter of the steel pipe is known. When the outer surface of the metal pipe is continuously coated with resin, the above-mentioned connecting metal fittings are used, but since the ambient temperature including the connecting metal fittings is significantly lowered when the metal pipe is heated, it is applied to the metal pipe in the subsequent process. There are places where the powder epoxy primer does not cure sufficiently. On the other hand, as a method of uniform heating of a metal pipe, as shown in Patent Document 3, the electric power required for the induction heating device is calculated from the heating target temperature of the steel pipe and the measured moving speed of the steel pipe, and only the first heating means is used. , A method of accurately controlling the target temperature is known. However, when heating the connecting pipe including the connecting fitting, the part where the metal pipe and the connecting fitting are in contact and there is a difference in thickness, the part where the metal pipe and the connecting pipe and the metal pipe are not in contact, and the material of the metal pipe and the connecting fitting are Since they may differ and do not have a uniform steel pipe shape, the connecting pipe cannot be uniformly heated only by the first heating means. From the above, there is a need for a simple and uniform method for heating a connecting pipe that does not have a uniform steel pipe shape.

Tokukousho 60-29317 Gazette Japanese Unexamined Patent Publication No. 7-16926 Japanese Unexamined Patent Publication No. 2000-208241

To apply the powder epoxy primer to the metal tube, the metal tube is preheated using a heating device such as an induction heating device. In the vicinity of the end of the metal pipe into which the metal fitting is inserted, the connection metal fitting itself is heated and a part of the heat required for heating the metal pipe is consumed by the connection metal fitting, so that the temperature of the metal pipe is remarkably lowered. Therefore, the curing of the powder epoxy primer is insufficient, and the corrosion resistance of the anticorrosion coated metal tube is significantly inferior. From the above, uniform heating of the metal tube is required.

An object of the present invention is a method for producing an anticorrosion-coated metal tube that can be used as a line pipe, wherein the anticorrosion-coated metal tube having excellent corrosion resistance without curing failure of a powder epoxy primer by uniformly heating the metal tube. To provide a manufacturing method.

The present inventor has diligently studied and found a method for solving the above problems to complete the present invention.
In the present invention, a connecting pipe formed by connecting using a metal connecting metal fitting so that the axes of two or more metal pipes coincide with each other is moved in the direction of the shaft to pass the heating means and the coating means. it is, for heat-treatment and painting process, including operation of forming the d port carboxymethyl primer layer on the surface of the connection pipe, a manufacturing method of anticorrosive coated metal tube,
The heating means includes a first heating means and a second heating means.
_{A step of measuring the surface temperature (Ti1} ) of the connecting pipe before heating the connecting pipe by the first heating means, and a step of measuring the surface temperature (Ti1) of the connecting pipe.
After heating the connecting pipe with a _{constant output (W 1} ) by the first heating means, the temperature of one or more of the metal pipes (T ₀₁ ) and the temperature of one or more of the connecting fittings (T _{02) after heating.} ) And the process of measuring
The process of calculating the output coefficient K in the metal tube by the following formula (1) and
The process of calculating the output coefficient K'in the connection fitting by the following formula (2) and
A step of measuring the surface temperature (T _i2 ) of one or more of the metal pipes and the surface temperature (T _i3 ) of one or more of the connection fittings before heating the connecting pipe by the second heating means.
The step of calculating _{the output W 21} when the metal tube is heated by the second heating means by the following formula (3), and
The step of calculating _{the output W 22} when the connection fitting is heated by the second heating means by the following formula (4), and
By heating the surface of two or more of the metal pipes by the output W ₂₁ by the second heating means and heating the surface of one or more of the connection fittings by the output W ₂₂ by the second heating means, it is compared with that before heating. In the process of reducing the difference between the surface temperature of the metal tube and the surface temperature of the connecting fitting,
Wherein the heating by the second heating means connecting pipe after heating by the first heating means, get disappeared Po carboxymethyl primer layer prior to subsequent subjected to the coating treatment method of anticorrosive coated metal tube.
Equation (1): K = W ₁ / {(T ₀₁ −T _i1 ) × (D _p −D _t ) × D _t × v}
Equation (2): K'= W ₁ / {(T ₀₂ −T _i1 ) × (D _p −D _t ) × D _t × v}
Equation (3): W ₂₁ = (T ₀₃ −T _i2 ) × (D _p −D _t ) × D _t × v × K
Equation (4): W ₂₂ = (T ₀₃ −T _i3 ) × (D _p −D _t ) × D _t × v × K ´
In the formulas (1) to (4), D _p means the outer diameter of the metal pipe (mm), D _t means the wall thickness of the metal pipe (mm), and v means the speed of the metal pipe (m / min).
In the formulas (3) and (4), T ₀₃ means the target temperature (° C.) of the metal tube and the connecting fitting after heating by the second heating means.
The method for manufacturing such an anticorrosion-coated metal tube is also referred to as the "manufacturing method of the present invention" below.

According to the present invention, there is provided a method for producing an anticorrosion-coated metal tube, wherein the metal tube is uniformly heated to suppress deterioration of the coating quality of the powder epoxy primer. Can be done.

As anticorrosive coated metal tube which can be produced by the production method of the anti-corrosion coated metal tube of the present invention where the quality of the Rue Po carboxymethyl primer layer put on the entire steel pipe including a steel tube end is good, and a line pipe ..

It is the schematic sectional drawing for demonstrating one aspect of the manufacturing method of this invention. It is the schematic sectional drawing for demonstrating the preferable aspect of the manufacturing method of this invention. It is a flow chart until the output of the 2nd heating means of this invention is calculated. Example 1; It is a temperature history in the vicinity of the steel pipe connecting portion when heated by the first heating means. Example 1; It is a temperature history in the vicinity of the steel pipe connecting portion when heating is performed by increasing the output in the vicinity of the connecting fitting by using the second heating means. Comparative Example 1; It is a temperature history in the vicinity of the steel pipe connecting portion when heating is performed at a constant output by using the second heating means.

The production method of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a cross-sectional view (schematic view) of the connecting pipe, FIG. 2 is a cross-sectional view (schematic view) showing a state in which the connecting pipe is processed, and FIG. 3 is a calculation of the output of the second heating means. It is a flow chart up to.

In the manufacturing method of the present invention, the connecting pipe 1 as shown in FIG. 1 is prepared. The connecting pipe 1 is connected by using a metal connecting metal fitting 4 so that the axes 3 of the two or more metal pipes 2 and 2 coincide with each other. Although FIG. 1 shows an embodiment in which two metal pipes 2 are connected by one connecting metal fitting 4, a plurality of metal pipes 2 can be further connected by using the connecting metal fitting 4.
When the metal pipes are connected by using the conventionally known connecting metal fittings 4, the axes of the metal pipes usually match as shown in FIG.

Here, the metal pipe 2 is preferably a steel pipe. Further, in steel pipes made of ordinary steel, high alloy steel and the like, and high-strength line pipes, it is preferable that the grade of API (American Petroleum Institute) is API X50 or higher.
The size and cross-sectional diameter of the metal tube 2 are not particularly limited. For example, the axial length may be 6-18 m. The cross-sectional diameter may be, for example, 50 mm to 1600 mm.

The size and shape of the connection fitting 4 are not particularly limited. Examples of the material of the connection fitting include ordinary steel and aluminum.

In the manufacturing method of the present invention, the connecting pipe 1 is moved in the direction of its axis (the direction of the arrow in FIG. 2) and passed through the heating means and the painting means to perform heat treatment and painting treatment, and the connecting pipe including the operation of forming the d port carboxymethyl primer layer to one surface.

Here, the heating means includes a first heating means 5 and a second heating means 6. The temperature of the connecting tube 1 before being heated by the first heating means 5 such as an induction heating device is measured using a thermometer 7 such as a radiation thermometer to obtain T _i1 . Here, it is not always necessary to always measure the temperature (surface temperature) of the connecting pipe 1, and as will be described next, the temperature of the metal pipe 2 in the connecting pipe 1 and the temperature of the connecting metal fitting 4 can be compared. It should be measured in.

_{Next, the output W 1} in the first heating means 5 is determined.
It is preferable to calculate the approximate output by the method exemplified in Example 1 described later, and then determine the _{output W 1 with reference to the calculation result.}

Next, the connecting pipe 1 is heated by the first heating means 5 with a constant output W _1. Then, the surface temperature of the connecting pipe 1 after heating is measured using a radiation thermometer or the like. Then, the temperature (T ₀₂ ) of the connection fitting 4 becomes significantly lower than _{the temperature (T 01} ) of the surface of the metal tube 2.

Next, the output coefficient K in the metal tube 2 is calculated using the following equation (1).
K = W ₁ / {(T ₀₁ −T _i1 ) × (D _p −D _t ) × D _t × v} ・ ・ ・ Equation (1)

Further, the output coefficient K'in the connection fitting 4 is calculated by using the following equation (2).
K'= W ₁ / {(T ₀₂ −T _i1 ) × (D _p −D _t ) × D _t × v} ・ ・ ・ Equation (2)

In the formulas (1) and (2), T ₀₁ and T ₀₂ are the temperatures (° C.) of the metal tube 2 and the connecting metal fitting 4 after heating by the first heating means 5, and _{Ti 1} is the temperature (° C.) before heating by the first heating means 5. The metal tube temperature (° C.), D _p is the outer diameter of the metal tube (m), D _t is the wall thickness of the metal tube (m), and v is the velocity of the metal tube (m / min).

_{Next, the output W 21} in the second heating means 6 when heating the metal tube 2 is calculated using the following equation (3).
W ₂₁ = (T ₀₃ −T _i2 ) × (D _p −D _t ) × D _t × v × K ・ ・ ・ Equation (3)

Further, using the equation (4), the output W ₂₂ in the second heating means 6 when heating the connection fitting 4 is calculated.
W ₂₂ = (T ₀₃ −T _i3 ) × (D _p −D _t ) × D _t × v × K ´ ・ ・ ・ Equation (4)

In equations (3) and (4), T ₀₃ is the target temperature (° C.) of the metal pipe 2 and the connecting fitting 4 after heating by the second heating means 6, and Ti 2 and _{Ti 3} are immediately before heating by the second heating means 6. The temperature (° C.) of the metal pipe 2 and the connection fitting 4 measured in 1), D _p is the outer diameter of the metal pipe (m), D _t is the wall thickness of the metal pipe (m), and v is the speed of the metal pipe (m / min). ..
The target temperature (° C.) of T ₀₃ is determined in consideration of using a powder epoxy primer in the next step.

Next, the surface of the metal tube 2 is _{heated by the output of W 21 and} the surface of the connection fitting 4 is heated by the output _{of W 22 by the second heating means 6.}

By controlling the temperature of the second heating means 6 as described above, it is possible to flatten the entire temperature distribution of the connecting pipe after heating. As a result, it becomes possible to coat the powder primer in a temperature range that does not cause curing failure.
Then, when painting powder epoxy primer by coating means 11, the entire surface of the connecting pipe 1, to cure uniformly and sufficiently, it is possible to form a high-quality et Po carboxymethyl primer layer 12.
After forming the d port carboxymethyl primer layer 12 by the coating means 11, the adhesive layer 14 is formed by an adhesive layer forming means 13, further, it is possible to form the organic resin layer 16 by the organic resin layer forming means 15.

Although the adhesive layer forming means 13 and the organic resin layer forming means 15 are not essential constituent requirements in the manufacturing method of the present invention, it is preferable that the manufacturing method of the present invention includes them.

In the production method of the present invention, it is preferable to remove scales, contaminants, etc. on the surface of the connecting pipe 1 in advance before heating by the first heating means 5. As a means for removing, pretreatment such as alkaline degreasing, pickling, sandblasting, grid blasting, and shot blasting can be performed.

The first heating means 5 and the second heating means 6 may be gas furnaces, but are preferably induction heating devices.
It is preferable that the connecting pipe 1 is heated to a desired temperature (for example, about 100 to 180 ° C.) by the first heating means 5, and then heated to 180 to 240 ° C. by the second heating means 6.

When a high-strength line pipe is obtained by the production method of the present invention, heating at 250 ° C. or lower, preferably 200 ° C. or lower is preferable in order to suppress a decrease in deformability due to strain aging. On the other hand, the recommended coating temperature of the powder epoxy primer is generally 180 ° C. to 240 ° C. Therefore, in order to ensure the quality of the powder epoxy primer while maintaining high deformability, it is desirable to heat and paint in the range of 180 ° C. to 200 ° C. When the temperature of the outer surface of the connecting pipe 1 is continuously measured using a thermometer 8 installed immediately after heating by the first heating means 5, the temperature near the connecting fitting 4 is usually lower than that of other parts. You can check. In order to prevent non-uniformity of the temperature of the connecting pipe 1, in the second heating means 6 installed immediately after, the output coefficients calculated from the above equations (1) and (2) are used, and the equations (3) and By heating the connection fitting 4 with the output obtained from the formula (4), the steel pipe can be heated in the range of 180 ° C. to 200 ° C. Thereafter, a d port carboxymethyl primer layer 12, if necessary, may be further formed an adhesive layer 14 and the organic resin layer 16 by an adhesive layer forming means 13 and the organic resin layer forming means 15.

It explained et Po carboxymethyl primer layer 12. Generally bisphenol A type as the epoxy resin which is a main component of e Po carboxymethyl primer layer 12, using a bisphenol F type resin alone, or in combination. When higher temperature characteristics are required, a polyfunctional phenol novolac or halogenated resin is used in combination with the above-mentioned bisphenol A type or bisphenol F type resin. By providing the d port carboxymethyl primer layer 12 on the chemical conversion coating layer, to further improve the adhesion of the corrosion protection layer.

Further, by adding the inorganic pigment added to the primer in the range of 3 to 30 vol% with respect to the total volume, the shrinkage strain is reduced and the adhesion property is greatly improved. Inorganic pigments include pigments such as silica, titanium oxide, wollastonite, mica, talc, kaolin, chromium oxide, zinc borate, zinc borate, zinc phosphate, metal powders such as zinc and Al, and ceramic powders. In addition, a rust preventive pigment such as a vanadium phosphorus compound is appropriately used.

By using the above powder epoxy primer, the corrosion resistance of the anticorrosion layer is further improved against the formation of the organic resin layer 16. The powder epoxy primer can be formed by using a coating means 11 such as electrostatic powder coating. The film thickness is not particularly limited, but it is preferably applied in the range of 20 to 1000 μm. If the film thickness is thinner than 20 μm, pinholes may occur. On the other hand, the upper limit of the film thickness differs depending on the type of resin, but in thick film coating exceeding 1000 μm, characteristics such as impact resistance at low temperature tend to deteriorate.

As the organic resin used for forming the organic resin layer 16, a polyolefin resin can be mainly used. Examples of the polyolefin resin include conventionally known polyolefins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and polypropylene, and ethylene-propylene block or random copolymer, polyamide-propylene block or random. A resin containing a known polyolefin copolymer such as a copolymer.

As components other than the polyolefin resin, carbon black or other coloring pigments, filling enhancers, antioxidants, ultraviolet absorbers, hindered amine-based weathering agents, etc. may be added in any combination as measures against heat resistance and weather resistance. it can.

A polyolefin-modified adhesive can be used to form the adhesive layer 14. This polyolefin adhesive modifies known polyolefins such as polyethylene, polypropylene, and nylon, and known polyolefi copolymer resins with unsaturated carboxylic acids such as maleic acid, acrylic acid, and methacrylic acid, or acid anhydrides thereof. It is a conventionally known modified polyolefin, such as one obtained by diluting the modified product with a polyolefin resin as appropriate.

A method of using a thin modified polyolefin adhesive layer 14 having a thickness of 50 to 700 μm in combination with an organic resin layer 16 having a polyolefin having a thickness of 0.3 to 10 mm is preferable from the viewpoint of price and performance balance.

As the polyolefin coating method, for example, an extrusion coating method in which a steel material is directly coated with a polyolefin resin heated and melted using a die of an extruder can be used. Alternatively, there are a method of attaching a preformed polyolefin sheet to a heated steel material, a method of powder coating crushed polyolefin and melting it to form a film, and the like. By these methods, the organic resin layer 16 having a film thickness of 0.3 mm to 10 mm can be formed.

Hereinafter, the present invention will be specifically described with reference to Examples.

<Example 1>
An experiment was conducted to verify that uniform heating can be performed by the present invention.
First, a carbon steel pipe (outer diameter 609.6 mm, plate thickness 11.5 mm) was used and grid blasted in advance. Then, an iron connecting metal fitting was installed in the steel pipe, the connecting pipe was conveyed at a speed of 0.9 m / min, and heating was performed using two high-frequency induction heating devices. Here, the high frequency induction heating device on the upstream side corresponds to the first heating means, and the high frequency induction heating device on the downstream side corresponds to the second heating means. Hereinafter, the high frequency induction heating device which is the first heating means is also referred to as a first heating device, and the high frequency induction heating device which is a second heating means is also referred to as a second heating device.

Next, the output in the first heating device is calculated by the following formula (A) based on the general formula of Q (J) = m × c × ΔT (Q: heat quantity, m: mass, c: specific gravity, ΔT: temperature difference). Calculated from.

Output = ΔT x unit weight x transport speed x specific heat x 1000/60 ... Equation (A)

Here, the target steel pipe temperature after the first heating device was set to 150 ° C. Further, the temperature of the connecting pipe before heating by the first heating device was 20 ° C. Therefore, ΔT in the formula (A) is 130 ° C. (= 150 ° C.-20 ° C.).

The unit weight (kg / m) in the formula (A) is obtained from the following formula (B).
Unit weight (kg / m) = (D _p −D _t ) × D _t × 0.02466 ・ ・ ・ Equation (B)
In the formula (B), D _p is the outer diameter of the metal tube (mm) (= 609.6 mm), and D _t is the wall thickness of the metal tube (mm) (= 11.5 mm).

The transport speed in the formula (A) is 0.9 m / min as described above.

For the specific heat in the formula (A), 0.460 kJ / (kg · ° C.) is used in the case of carbon steel pipe.

From these, the output was calculated to be 152 kW from the formula (A). Therefore, it was decided to set the output of the first heating device to 160 kW. In calculation, if the surface temperature is set to 152 kW, the surface temperature of the carbon steel pipe should be 150 ° C, or the actual surface temperature may be lower than that, so the intention is to set it to a slightly higher output. Is.

In this way, the output of the first heating device was set to 160 kW, heating was performed by the first heating device, and the temperature of the steel pipe surface immediately after that was measured using a radiation thermometer. The result is shown in FIG.
As shown in FIG. 4, it was found that the temperature of the surface of the metal tube was about 150 ° C., whereas the temperature of the connecting metal fitting was about 130 ° C., which was extremely low.

Next, K in the metal tube and K'in the connection fitting were calculated using the above equations (1) and (2). Specifically, K was calculated as follows.
K = 160 × 1000 / {(150-20) × (609.6-11.5) × 11.5 × 0.9}
From this, K = 0.199 was calculated.

Specifically, K'was obtained as follows.
K'= 160 x 1000 / {(130-20) x (609.6-11.5) x 11.5 x 0.9}
From this, it was calculated that K'= 0.235.

Next, using the above equations (3) and (4), the output W _{21 in the second heating device when heating the metal tube and the output W 22} in the second heating device when heating the connection fittings. Was calculated. Here, the target value of the steel pipe surface temperature immediately after heating by the second heating device was set to 190 ° C. This is because the optimum steel pipe surface temperature when considering the use of the powder epoxy primer in the next step is 190 ° C.
Further, the surface temperature of the metal tube immediately before being heated by the second heating device was lowered from 150 ° C. to 145 ° C. Further, the surface temperature of the connecting fitting immediately before being heated by the second heating device was lowered from 130 ° C. to 125 ° C. _{Therefore, the output W 21} and the output W ₂₂ were obtained in consideration of the temperature after the decrease.

Specifically, W ₂₁ was calculated as follows.
W ₂₁ = (190-145) x (609.6-11.5) x 11.5 x 0.9 x 0.199
From this, W was calculated to be 55.4 kW.

Specifically, W ₂₂ was calculated as follows.
W ₂₂ = (190-125) × (609.6-11.5) × 11.5 × 0.9 × 0.235
From this, W ₂₂ was calculated to be 94.6 kW.

The surface of the metal tube was heated at 55.4 kW and the surface of the connecting metal fitting was heated at 94.6 kW by the second heating device.
As a result, as shown in FIG. 5, the surface temperature of the entire connecting pipe including the metal pipe and the connecting fitting could be adjusted within the temperature range of 185 to 195 ° C.

After heating, the connecting tube was subjected to electrostatic powder coating with a powder epoxy primer (BASEPOX PE50-1081, manufactured by Arsonsisi) by a powder primer coating machine 11 so that the film thickness was 250 μm. After that, NE080 manufactured by Mitsui Chemicals Co., Ltd. was coated with 0.2 mm as the adhesive, and NOVATEC ER002S manufactured by Japan Polyethylene Corporation was used as the polyethylene, and the coating was coated so that the total thickness of the coating was 3 mm.
Then, the coated connecting tube was cut into 100 mm × 150 mm, an artificial flaw having a diameter of 6 mm reaching the steel surface was provided, and this was contacted with 3% NaCl saline solution kept at 80 ° C., and 1 with respect to the saturated caromel electrode. It was held at a potential of .5 V for 30 days. The peeling distance from the artificial flaw was measured and the corrosion resistance was evaluated.
The results are shown in Table 1.

<Comparative example 1>
In Example 1, the surface of the connecting fitting was heated at 94.6 kW by the second heating device, but in Comparative Example 1, the surface of the connecting fitting was also heated at 55.4 kW in the same manner as the surface of the metal tube.
Then, all other operations were performed in the same manner as in Example 1, and the same evaluation was performed.
In Comparative Example 1, as shown in FIG. 6, the temperature of the connecting pipe around the metal fitting was 160 ° C., which was significantly lowered.
Table 1 shows the evaluation results of the cathode peeling test performed in the same manner as in Example 1.

As shown in Table 1, in the cathode peeling test, an artificial flaw with a diameter of 6 mm reaching the steel surface was provided on the coated steel pipe, and this was contacted with 3% NaCl saline solution maintained at 80 ° C. on the saturated caromel electrode. The potential was maintained at 1.5 V for 30 days. The peeling distance from the artificial flaw was measured and the corrosion resistance was evaluated. In Example 1, the distance was 13 mm, which satisfied ISO21809-1, but in Comparative Example 1, the peeling distance was 27 mm, which was a large peeling. This is because the powder epoxy primer is uncured and the corrosion resistance is significantly inferior. From the above, it is possible to manufacture a coated steel pipe having excellent corrosion resistance by uniformly heating the steel pipe.

1 Connecting pipe 2 Metal pipe 3 Shaft 4 Connecting bracket 5 1st heating means 6 2nd heating means 7 Thermometer for measuring connecting pipe temperature before heating by 1st heating means 8 Connecting pipe temperature after heating by 1st heating means thermometer 11 coating unit 12 et Po carboxymethyl primer layer 13 adhesive layer for connecting pipe temperature measured after the heating by the thermometer 10 second heating means for connecting pipe temperature measured prior to heating by the thermometer 9 second heating means for measuring Forming means 14 Adhesive layer 15 Organic resin layer Forming means 16 Organic resin layer

Claims (1)

A connecting pipe connected by using a metal connecting metal fitting so that the axes of two or more metal pipes are aligned is moved in the direction of the shaft and passed through a heating means and a painting means to heat the pipe. processing and subjected to coating treatment, including operation of forming the d port carboxymethyl primer layer on the surface of the connection pipe, a manufacturing method of anticorrosive coated metal tube,
The heating means includes a first heating means and a second heating means.
_{A step of measuring the surface temperature (Ti1} ) of the connecting pipe before heating the connecting pipe by the first heating means, and a step of measuring the surface temperature (Ti1) of the connecting pipe.
After heating the connecting pipe with a _{constant output (W 1} ) by the first heating means, the temperature of one or more of the metal pipes (T ₀₁ ) and the temperature of one or more of the connecting fittings (T _{02) after heating.} ) And the process of measuring
The process of calculating the output coefficient K in the metal tube by the following formula (1) and
The process of calculating the output coefficient K'in the connection fitting by the following formula (2) and
A step of measuring the surface temperature (T _i2 ) of one or more of the metal pipes and the surface temperature (T _i3 ) of one or more of the connection fittings before heating the connecting pipe by the second heating means.
The step of calculating _{the output W 21} when the metal tube is heated by the second heating means by the following formula (3), and
The step of calculating _{the output W 22} when the connection fitting is heated by the second heating means by the following formula (4), and
By heating the surface of two or more of the metal pipes by the output W ₂₁ by the second heating means and heating the surface of one or more of the connection fittings by the output W ₂₂ by the second heating means, it is compared with that before heating. In the process of reducing the difference between the surface temperature of the metal tube and the surface temperature of the connecting fitting,
Wherein the heating by the second heating means connecting pipe after heating by the first heating means, get disappeared Po carboxymethyl primer layer prior to subsequent subjected to the coating treatment method of anticorrosive coated metal tube.
Equation (1): K = W ₁ / {(T ₀₁ −T _i1 ) × (D _p −D _t ) × D _t × v}
Equation (2): K'= W ₁ / {(T ₀₂ −T _i1 ) × (D _p −D _t ) × D _t × v}
Equation (3): W ₂₁ = (T ₀₃ −T _i2 ) × (D _p −D _t ) × D _t × v × K
Equation (4): W ₂₂ = (T ₀₃ −T _i3 ) × (D _p −D _t ) × D _t × v × K ´
In the formulas (1) to (4), D _p means the outer diameter of the metal pipe (mm), D _t means the wall thickness of the metal pipe (mm), and v means the speed of the metal pipe (m / min).
In the formulas (3) and (4), T ₀₃ means the target temperature (° C.) of the metal tube and the connecting fitting after heating by the second heating means.

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