JPS61264166A - Covering method of inner surface of metal tube - Google Patents

Abstract

PURPOSE:To form a cover having resistances for corrosion, heat and wear, etc., at inner surface of large caliber metal tube at a good operability, by plasma spraying metal or ceramic to inner surface of metal tube whose inner part is maintained to nonoxidizing atmosphere. CONSTITUTION:Covers 4, 5 are provided at both ends of a steel tube 1 mounted on a roller 20 of a bearing base 19 on a truck 18 to intercept the inner part from air. Next, a conduit 9 supported to a frame base 7 is inserted inside the tube 1 while piercing the one cover 5 through a seal ring 11. Further, inner part of the tube 1 is evacuated to vacuum by a vacuum pump 13 connected with a hose 14. Next, the truck 18 is advanced on a rail 17 by a motor 21 having reduction gear, and the roller 20 is revolved to move the tube 1 spirally. Plasma is generated from a plasma gun 25 fitted at top end part of the conduit 9 by a plasma source 31, an operation gas supplying apparatus 32, to plasma spray metal powder such as Ti, ceramic powder, etc., supplied from a covering material supplying apparatus 33 to inner surface of the tube 1.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method of coating the inner surface of a metal tube.

(Prior Art) Metal pipes, particularly steel pipes and cast iron pipes, are widely used for everyday purposes such as water pipes and gas pipes, and for industrial purposes such as oil country tubular goods and oil transport pipes. If steel pipes or cast iron pipes are used as they are, corrosion and abrasion will cause water and gas leaks, so the inner surface of the pipes is generally galvanized, coated with plastic, or painted.

(Problems to be Solved by the Invention) Small diameter pipes (100 mm or less) used for water pipes and gas pipes can be plated by immersion, but medium diameter pipes (100°~
40hm) and large diameter pipes (400-2500mm) are difficult to immerse in plating. Therefore, among these, large-diameter pipes that are painted without being plated are widely used, but their corrosion resistance and abrasion resistance are not very good. Some metal thermal spraying is also carried out, but since it is carried out in the atmosphere, there are many pinholes and the corrosion resistance is low.Also, low-pressure thermal spraying in a vacuum container can provide a dense coating, but it is difficult to coat general metal pipes, such as oil pipes. This method has not been put to practical use because a large vacuum container is required for long items such as tubes that are several meters long.

Furthermore, seamless stainless steel pipes are widely used for oil country tubular goods, but because there is no good coating method, they are used without coating. Furthermore, as slurry transport pipes, seamless stainless steel pipes whose inner surfaces are coated are currently used.

Therefore, these steel pipes do not have sufficient wear resistance to withstand long-term use.

It is expected that various fluids will be transported in the future, but the performance of conventional galvanizing or coating films has limitations, and there is a growing need for coatings with even better corrosion and wear resistance.

(Means for Solving the Problems) The method of coating the inner surface of a metal tube of the present invention utilizes the metal tube itself as an atmosphere container, and creates a non-oxidizing gas atmosphere inside the tube.
It is characterized by plasma spraying metal or ceramic onto the inner surface of the tube.

Argon, helium, nitrogen, hydrogen, etc. are used as the gas forming the non-oxidizing gas atmosphere, and the pressure of the gas atmosphere is 1 atmosphere or less, preferably 100 Torr (1,333 Torr).
X104Pa) or less.

As the thermal spraying material, an appropriate material is selected from metals and ceramics depending on the application.

Conventional methods are used for plasma spraying, but the high-speed, low-pressure plasma arc method (for example, Japanese Patent Application Laid-Open No. 58-87448)
is appropriate.

(Function) Particles of metal or ceramic powder, which is the thermal spraying material, become minute droplets due to the heat of the plasma and are deposited on the inner surface of the tube.

The laminated droplets solidify to form a coating on the inner surface of the tube. Depending on the properties of the sprayed material, the coating exhibits corrosion resistance, heat resistance, or wear resistance.

(Example) The inner surface of a steel pipe to be coated is degreased, cleaned and descaled in advance. Solvent cleaning or alkaline cleaning is used for degreasing, and blasting is used for descaling.

Then, preheat to about 500°C. As a preheating method, it is also possible to heat with a thermal spray flame, for example.

As shown in FIG. 1, both ends of the steel pipe l covering the inner surface are covered with covers 4.5 to isolate the inside of the steel pipe from the atmosphere. A conduit 9 supported by a pedestal 7 penetrates one cover 5, and the penetrating portion is sealed by a seal ring 11. Also,
A vacuum pump 13 is connected to the cover 5 via a hose 14.

The steel pipe 1 prepared as described above is placed on the cart 18 via the rollers 20 supported by the bearing stand 18. Then, the vacuum pump 13 moves the inside of the steel pipe l to 0°1? orr
The pressure is reduced to 20 Torr during thermal spraying. Next, the roller 20 is moved forward on the rail 17 in the tube axis direction by the motor 21 with a reducer.
When is driven to rotate, the steel pipe l moves in a spiral manner.

A plasma gun 25 is attached to the tip of the conduit 9. As shown in FIG. 2, the plasma gun 25 consists of a tungsten electrode 2B and a nozzle 27 placed directly below the tungsten electrode 2B. Electrode 26 and nozzle 27 are connected to a negative electrode and an anode of plasma main power source 31, respectively. A working gas supply device 32 is connected to the nozzle 27 of the plasma gun 25 . Further, the nozzle 27 of the plasma gun 25 is provided with a coating material supply hole 28, to which a coating material supply device 33 is connected.

While the steel pipe 1 whose interior has been depressurized as described above is fed in a spiral manner, a required voltage is applied between the electrode 26 and the nozzle 27 to generate an arc 35. A mixed gas of argon and helium is supplied from the operating gas supply device 32 into the arc 35 to generate plasma. A plasma jet 38 is ejected from the nozzle 27 toward the inner surface 2 of the tube. In this state, titanium powder is supplied to the nozzle 27 from the coating material supply hole on the second day.

The particles of titanium powder ejected into the nozzle 27 turn into minute droplets due to the heat of the plasma, stack on the inner surface 2 of the tube, and solidify, forming a coating 3 on the inner surface 2 of the tube. Since the steel pipe 1 is fed in a spiral so that the strip-shaped coating 3 slightly overlaps the adjacent coating strip, the entire inside of the tube can be coated uniformly.

Note that the nozzle 27 and steel pipe l are connected to a transitional arc power source (
(not shown) to clean or heat the steel pipe 1.

Similarly, ceramic powder, for example M, is supplied from the nozzle 27.
By thermal spraying o/Mo2G powder, a coating with excellent wear resistance can be obtained.

This invention is not limited to the above embodiments. For example, the required material may be thermally sprayed onto the inner surface of the tube as described above while the tube to be coated is housed in a cylindrical atmosphere chamber. In this case, the atmosphere chamber is maintained in an inert gas atmosphere. Ru.

(Effects of the Invention) According to the method of the present invention, a metal or ceramic is thermally sprayed onto the inner surface of the tube to form a coating, so that a metal tube with excellent corrosion resistance, heat resistance, or wear resistance can be obtained. Further, the present invention can be applied to pipes with an inner diameter of 45 mm or more, and it is possible to form a required coating on large pipes, which conventionally could not be plated.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating an embodiment of the present invention, and FIG. 2 is a sectional view of a main part of a plasma gun used in the above embodiment. ■... Steel pipe, 2... Tube inner surface, 3... Coating, 4.5
... Cover, 9 ... Conduit, 13 ... Vacuum pump,
18... Trolley, 20... Roller, 25... Plasma gun, 2B... Electrode, 27... Nozzle, 28...
...Coating material supply hole, 31...Plasma main power supply, 32.
...Operating gas supply device, 33...Coating material supply device, 3
5...Arc, 36...Plasma jet.

Claims (1)

[Claims] 1. A method for coating the inner surface of a metal tube, which comprises creating a non-oxidizing gas atmosphere inside the metal tube and plasma spraying a metal or ceramic onto the inner surface of the metal tube.