JPS60110368A - Method and apparatus for applying corrosion-proof coating to inner surface of pipe body - Google Patents

Abstract

PURPOSE:To uniformly apply corrosion-proof coating to the inner surface of a welded joint part, by heating the vicinity of the welded joint of a pipe body to which linking is applied and spraying a selected powder to the heated inner surface of said pipe body to melt the same. CONSTITUTION:A thermocoupler 16 is attached to the outer surface of pipes 1, 1 to which the inner surface lining of plastic films 2 is applied with a welded joint place 3 thereof, and a lining machine 20 and a powdery resin supply apparatus 21 are sent in the vicinity of the joint part in the pipes 1, 1. A current is supplied to an induction heating coil 12 to heat the pipes 1, 1 and the temps. of the existing lining films of the metal exposed part of the joint part 3 and in the vicinity thereof are raised to a temp. of the m.p. or more of a powder resin to be sprayed. In the next step, the powdery resin is sprayed to the inner surfaces of the high temp. pipe bodies 1, 1 to form a film with a desired thickness. As the poqdery resin, tone having good thermal fusion property to the existing lining film is selected. The heating of the pipe bodies 1), is successive even after the film is formed and the film is sufficiently melted and fusion bonded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for applying an anti-corrosion coating to the inner surface of the weld joint after welding pipe bodies such as steel pipes with plastic inner lining, and an apparatus used therefor.

In recent years, fluid transportation through pipelines, such as water supply and sewage systems, nuclear and thermal power plant seawater introduction pipes, and oil and chemical transport pipes, has made rapid progress, and pipe sizes are gradually becoming larger in diameter. Accordingly, there is an increasing demand for lined steel pipes whose inner surfaces are lined with plastic such as polyethylene in order to prevent corrosion of the inner surfaces of the pipe bodies by transport fluids.

Generally, when connecting steel pipes, it is desirable to use welded joints on-site to take advantage of the strength characteristics of the steel pipes and from a cost perspective. However, inner lining steel pipes cannot be easily welded. That is,
To use welded joints for lined steel pipes, first remove the lining film from the joint end that would deteriorate due to welding heat, and after the welding process is complete, apply anti-corrosion treatment by forming a plastic film on the exposed metal parts. However, at present, there are almost no anti-corrosion processing technologies developed for welded joints. Conventionally known anti-corrosion processing technology for welded joints involves laminating 71 coats of tar-epoxy paint on the above-mentioned welded joints of polyethylene-lined steel pipes to a predetermined film thickness (1 ttrm or more). This is the way to get it. However, the film thickness obtained with a single layer of 71 coats is approximately 150 to 200μ, and it takes more than 10 hours to dry before the next coat is applied. The curing period takes more than 10 days, and the workability is extremely poor (poor).In addition, the joint lining material (tar epoxy) and the main pipe lining material (polyethylene) are different materials, so the performance against fluids is also poor. There is also the disadvantage that the range of use is unreasonably limited by the performance of the joint coating.

As an alternative method, the present applicant first developed a method for forming an anticorrosive film using powdered resin and filed a patent application (Japanese Patent Application Laid-Open No. 56-115668). What is disclosed in this public bulletin is:
A method of filling a part of a tube body with powdered resin where a corrosion-resistant coating is to be formed, heating the tube body to melt and adhere the powdered resin to the inner surface to form a coating, and then removing excess powdered resin. This is a method in which powdered resin is sprayed onto the inner surface of a heated tube from a porous cylinder arranged concentrically within the tube, and is melted and adhered to the inner surface of the tube to form a coating. Although this method is superior in that it can form a film much more quickly than the conventional method of applying tar-epoxy paint, it requires an operation to collect excess powder resin, and The larger the diameter, the more difficult it is to use a large amount of powdered resin.

Due to this situation, welding is not often used to connect lining steel pipes at present, and mechanical joints such as flange joints and Victory joints are generally used. However, these joints are expensive, and in particular, the larger the diameter of the pipe, the more expensive they become, leading to an increase in the cost of piping.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, it is an object of the present invention to provide a method and apparatus that can easily and uniformly apply an anticorrosive coating to the inner surface of a welded joint.

The present invention, which was made to achieve the above object, selects a powder resin with good thermal fusibility for the existing lining film made of polyethylene, polypropylene, polyester, polyamide, fluororesin, vinyl chloride, etc., and The exposed metal part of the inner surface of the tube and its vicinity are heated from the outside of the tube to raise the temperature of the inner surface to a temperature higher than the melting temperature of the powder resin, using a powder spray nozzle that moves circumferentially along the inner surface of the tube, The method is characterized in that the powdered resin is sprayed onto the heated inner surface, adhered and melted to form an anticorrosion coating.

The powder resin C used to form the film is as described above↓ In addition to having good thermal fusion properties with the existing lining film, it is also easy to spray with a spray nozzle and easily melts and adheres when sprayed onto a heated surface. It is preferable that the surface of the ivy coating is easily smoothed after adhesion. Further, the powder resin is preferably the same type of resin as the material constituting the existing lining film, but it is not necessarily limited to the same type and may be of a different type.

In addition, when spraying powder resin onto the heated inner surface,
An appropriate primer may be used depending on the resin.

Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings.

FIG. 1 shows a welded joint of a tube 1.1 whose inner surface is lined with a plastic coating 2. FIG. In the figure, the coating near the welding point 3 at the end of the tubular body 1.1 where there is a risk of deterioration due to the influence of welding heat has been removed, and the metal surface 4 is exposed. The present invention aims to form an anti-corrosion coating 5 that covers this metal surface 4 and overlaps the existing lining coating 2 in the vicinity thereof.

FIG. 2 shows a coating device 10 for forming this anticorrosion coating 5. As shown in FIG. The coating device 10 has a heating device 11 arranged outside the tube body 1 . In this embodiment, the heating device 11 uses induction heating, including an induction heating coil 12, a power transformer 13, an input couple 14, an output cable 15, a temperature detection end, a (CA thermocouple) 16, a temperature controller 11, etc. has.

The induction heating filter 12 is of a split type (for example, a leek split type) so that it can be easily set on the outside diameter of the pipe, and the set is distributed around the welding location 3 with a constant clearance. The temperature detection end 16 is crimped to the outer surface of the tube near the welding point and detects the temperature of the tube body, while the temperature controller 17 controls the tube by turning on and off the input power to the power transformer 13 according to the set temperature. It acts to maintain a constant body temperature. Note that the heating device is not limited to induction heating, and other heating means such as a band heater, gas burner, infrared heater, etc. may be used.

The coating device 10 further includes a lining machine 20 and a powder resin supply device 21 arranged inside the pipe.

The lining machine 20 has a trolley 22 that can run inside the pipe and a motor 23 that drives the wheels of the trolley 22.The lining machine 20 has a trolley 22 that can run inside the pipe and a motor 23 that drives the wheels of the trolley 22. It is preferable to provide a detection sensor so that the trolley 22 traveling inside the pipe automatically stops at a predetermined position near the exposed metal portion.

A vertical shaft 24 is mounted on the cart 22, and a bearing 25 is mounted on the vertical shaft 24 so that its position in the vertical direction can be adjusted.
A hollow shaft 26 is rotatably held therein. hollow shaft 2
The mounting position of the tube 6 is determined so that its center axis substantially coincides with the center axis of the tube body 1. This hollow shaft 26 holds a powder spray nozzle 27 at its tip, and the spray nozzle 2
7 faces the inner surface of the tube so as to spray powder resin onto the inner surface of the tube. Several motors 28 are mounted on the bearing 25, and the motors 28 rotate the hollow shaft 26 through gears. A rotary joint 29 that receives powder resin from the powder resin supply device 21 is attached to the rear end of the hollow shaft. Thus, the powder spray nozzle 27 rotates approximately around the center of the tube 1,
Powdered resin is sprayed onto the inner surface of the tube while moving circumferentially along the inner surface of the tube. As the powder spray nozzle 27, in addition to a normal spray nozzle, an electrostatic (including frictional electrostatic) coating gun may be used. Although one powder spray nozzle 27 is shown in the illustrated embodiment, the number is not limited to this, and a plurality of spray nozzles may be used in the longitudinal direction or circumferential direction of the tube, thereby improving efficiency. can be raised. The rotational speed of the powder spray nozzle 27 is desirably changed depending on the inner diameter of the tube, the physical properties of the powder resin, the amount of powder discharged, etc. Therefore, the motor 28 is a variable speed motor or a variable speed motor.

On the other hand, the powder resin supply device 21 is connected to the lining machine 20.
A trolley 31 connected to the trolley 22 of the
, a fluidization tank 33 that maintains the powdered resin in a fluidized state with compressed air from the compressed air pipe 32, a pneumatic transport device (not shown) disposed within the fluidization tank 33 that sends out the fluidized powdered resin, and It has a hose 34 etc. that connects the air transport device to the rotary joint 29, and supplies powder resin to the rotary joint of the lining machine 20 via the hose 34. As will be described later, the powder resin in the fluidization tank 33 is sprayed onto the inner surface of the pipe body and melts and adheres to form an anti-corrosive coating, and a resin with good thermal fusion properties for the existing lining coating 2 is selected and placed. It is being

Next, a method of coating a welded joint using the above-mentioned apparatus will be explained with reference to the process diagram of FIG. 3.

(1) Grinding of the joint After welding the end of the pipe body 1.1 as shown in Figure 1,
Clean the joint. That is, welding spatter is removed using a power brush, sander, etc., the bead portion of the welding point 3 is smoothed, and then the dust is sucked out with a vacuum cleaner.

(2) Heating device set An induction heating coil is set on the outer diameter of the tube, and a CA thermocouple 16 is attached to the outer surface of the tube at approximately the center of the heating width.

(3) Carrying the lining device into the pipe The lining machine 20 and the powder resin supply device 21 are introduced into the pipe from the open end of the pipe body 1, and are fed into the vicinity of the welded joint by being driven by themselves or by hand.

(4) Start energizing the tubular body heating induction heating coil 12 to heat the tubular body 1,
The temperature of the exposed metal surface 4 of the joint portion and the existing lining film in the vicinity thereof is raised to at least the melting point of the powdered resin to be sprayed.

(5) Lining Next, while slowly rotating the powder spray nozzle 27, powder resin is sprayed onto the hot inner surface of the tube.

At this time, the discharge amount from the powder spray nozzle 27 and the rotation speed of the spray nozzle in the circumferential direction are set such that the powder resin sprayed onto the inner surface of the tube is immediately melted due to the heat capacity of the tube and adheres to the inner wall of the tube. Since the sprayed powder resin adheres to the inner surface of the tube and melts, it forms a thin film. The thickness of the coating formed by one spraying is, for example, about 70 to 100 microns in the case of polyethylene. Since the tubular body 1 is continuously heated, the surface of the formed coating also reaches a temperature higher than the melting point of the powdered resin, and the coating is laminated by softening the powdered resin again on the coating. In this way, a coating of desired thickness can be formed by repeating spraying.

By the way, normally the width of the anticorrosion coating 5 is equal to the width of the spray nozzle 2T.
wider than the width of A specific procedure for forming a film having a constant thickness over such a wide width will be explained. When the spray nozzle 27 is positioned at one end of the anticorrosive coating, the trolley 22 is stopped at that position and spraying is started. When the spray nozzle 2T rotates once, the cart 22 is advanced by one pitch, with a width narrower than the width of the spray being made one pitch, and spraying is continued until the spray nozzle 27 rotates once at that position. Thereafter, this operation is repeated one after another to move the lining machine 20. Once the spray nozzle reaches the other end of the anti-corrosion coating, it will be moved sequentially in the opposite direction.

This process is repeated until a predetermined film thickness is achieved.

In addition, as another method, both ends of the anti-corrosion coating are sprayed in the same manner as above, that is, by stopping the trolley 22 and rotating only the spray nozzle, but spraying is carried out on the middle part by the same method as above.
There is also a method in which the film is formed in a spiral manner by continuously moving the film. In either case, the motor 23 that moves the cart 22 and the motor 28 that rotates the spray nozzle 27 may be manually operated, or may be automatically controlled using a thorn board, limit switch, timer, or the like.

In addition, when the width of the spray nozzle 2T is sufficiently large or when a large number of spray nozzles are used in line in the width direction, when spraying can be performed simultaneously all over the anti-corrosion coating, the lining machine 20 is moved in the width direction (tube direction). There is no need to move it in the longitudinal direction.

Moreover, in order to move the spray nozzle 27 in the width direction,
Instead of moving the trolley 22 as in the illustrated embodiment, the rotating shaft 26 may be configured to be able to slide back and forth.

As mentioned above, the discharge amount from the powder spray nozzle 2T is determined so that the powder resin sprayed on the inner wall of the pipe immediately melts and adheres, but in reality, the adhesion efficiency of the powder spray varies. Since it is not 100%, the lower coating becomes thicker due to the falling of floating powder. As a countermeasure for this, the difference in film thickness can be reduced by interlocking a limit switch or timer with a valve when the spray nozzle passes under the spray nozzle to reduce or stop the powder discharge at an appropriate ratio.

(6) When coating formation by the post-heated powder spray nozzle 27 is completed,
The spraying is stopped and the lining machine 20 is moved back. Even after the spraying is completed, heating of the tube body 1 is continued to sufficiently melt and fuse the coating. Wait until the surface of the coating has sufficiently melted, become glossy and smooth, and then turn off the power to the heating device.

(7) Cooling Water cooling or air cooling is performed from the outer surface of the pipe.

(8) Inspection Performs various inspections such as pinhole inspection and film thickness inspection.

This completes the anticorrosive coating work.

Note that this anti-corrosion coating method and device can be used not only for welded joints, but also for repairing pinholes, repairing lining pipes that have rolled up part numbers, or corrosion-protecting short pipes for current use. It can also be used for coating.

As explained above, the present invention heats the tube from the outside, sprays powder resin on the inner surface with a powder spray nozzle,
Since the anticorrosive coating is formed by adhering and melting, the anticorrosive coating can be easily and quickly formed to a desired thickness. Moreover, almost all of the powder resin blown out from the powder spray nozzle adheres to the inner surface of the tube, so there is no need to collect excess powder resin, and the powder spray nozzle sprays a fixed amount of powder resin onto the inner surface of the tube. Since it moves while spraying, it is possible to form a coating with an extremely uniform thickness on the inner surface of the tube. In addition, since any powder resin may be used as long as it has good thermal fusibility with respect to the existing lining film, it is now possible to use the same resin as the existing lining film. As a result, it has become possible to use a screw joint for connecting plastic lined pipes, which has the excellent effect of reducing piping costs and greatly contributing to the spread of plastic lined pipes.

The device shown in Fig. 2 was used to weld the joint of a 1000A polyethylene lined steel pipe (lining thickness 1 m).
Anticorrosion coating was applied according to the procedure shown in the figure. The lining conditions are as follows.

Heating humidity of steel pipe 230℃ Type of powder resin Particle size of polyethylene 100 mesh under MI 4 (melt index flow) Spray nozzle rotation speed 2 rpm Width 120 mm Discharge amount 100 to 150 g Anin lining The machine sprays a coating with a thickness of 70 to 100 microns per layer, and in about 40 minutes, the formation of a corrosion-resistant coating of 500 yatt width (including the overlapping part to the existing lining coating) is completed, and it is well coated on the metal surface and the existing lining coating. A bonded film with an average thickness of 1.4 mm was obtained.

In addition, when lining conditions for polyethylene lined steel pipes were examined, the following conditions were found to be suitable.

Pipe heating temperature: 150-280°C Type of powder resin: Polyethylene Particle size: MI of 100-200 mesh 3-9 Example 2 A welded joint of a steel pipe coated with about 300 μm of powdered epoxy on the inner surface of the pipe was heated from the outside by approx. Heat to 220℃, and
Using the apparatus shown in the figure, the same resin was sprayed to obtain a 300 μm anticorrosion coating.

Example 3 Primer was applied to the welded joint of a steel pipe whose inner surface was rubbed with nylon 12 by about 0.15 mm, and about 25 mm was rubbed from the outside.
Heated to 0℃, sprayed with nylon 12 powder and
A corrosion protection coating of No. 511 was obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a welded joint part coated with anti-corrosion coating according to the method of the present invention, FIG. 2 is a cross-sectional view showing an embodiment of the present invention,
FIG. 3 is a process diagram showing the procedure for carrying out the method of the present invention. 1... Pipe body 2... Existing lining coating 3... Welding location 4... Metal surface 5... Anti-corrosion coating 1o... Coating device 11... Heating device 2o... Lining machine 26・・・Hollow shaft
2T...Powder spray nostle 28...Motor agent Patent attorney Kyo Matsu Sanga 1 figure Fang 3 figure

Claims (2)

[Claims] (1) In a method of applying an anticorrosive coating to the exposed metal part of the inner surface of a lining tube that has a plastic lining coating on the inner surface of the tube, a powder resin with good heat fusibility for the existing lining coating is selected, and the inner surface of the tube is The exposed metal part and the lining coating in the vicinity thereof are heated from the outside of the tube to a temperature higher than the melting point of the powder resin, and a powder spray nozzle that moves circumferentially along the inner surface of the tube is used to spray the powder resin onto the metal. A method for anti-corrosion coating on the inner surface of a tube, comprising spraying the lining coating on the exposed portion and the vicinity thereof and melting the lining coating to form an anti-corrosion coating on the inner surface of a pipe. (2) Equipped with a heating device placed outside the tube and a lining machine movable longitudinally within the tube, the lining machine being placed facing the inner surface of the tube and aligned with the central axis of the tube. 1. An anticorrosive coating device for an inner surface of a tube, comprising a powder spray nozzle that can rotate approximately around the center, and a drive device that rotationally drives the powder spray nozzle.