JPS597038A - Powdered-body epoxy resin coated steel pipe with protective film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel pipe whose outer surface is coated with a thermosetting resin, such as a powdered epoxy resin, and which is further coated with a protective layer of synthetic resin.

Steel pipes whose exterior surfaces are completely coated with powder epoxy resin are used in large quantities in the United States and Canada for pipelines that transport oil and gas, and there are several painting factories that handle everything from small diameter pipes to large diameter pipes. Painted steel pipes are manufactured. This powder Evokin resin-coated steel pipe has characteristics such as high production speed, especially when painting large-diameter steel pipes, and easy repair work on the eaves that occur in the coating. It has the following drawbacks, and improvements are desired.

Firstly, pinholes are likely to occur in the powder epoxy resin coating. The film thickness of powder epoxy resin coating is generally specified around 0.35mm, and depends on the particle size distribution of the epoxy resin, the curing reaction rate, or the surface roughness and surface after grid blasting of the steel pipe surface. Pinholes are likely to occur depending on the minute residual flaws in the coating, and it is rare for more than 2 pinholes/m2 to be detected during inspection with a 200QV DC pinhole tickter. If there is, the insulation resistance of the coating will decrease, so the required current for cathodic protection after buried piping must be increased.

The next problem is that holes are likely to form in the coating film due to abrasion.When steel pipes coated with powder epoxy resin are transported in bales, the parts where the surfaces of the steel pipes are in contact with each other rub against each other due to vibration during transport. This causes scratches on the paint film and pinholes.

As a way to solve these problems, two or three rubber bands made in the United States by cutting old tires are wrapped around the circumference of the painted steel pipe in the length direction. are prevented from coming into contact with each other. however,
In Japan, due to the distribution system for old tires, it is difficult to use large quantities of rubber bands made from old tires, and even if it is difficult to use rubber bands made from old tires, it is difficult to use them. Because the shape is not uniform, it is difficult to wrap the rubber band around the outer circumference of the steel pipe, making it difficult to reduce labor costs. There are problems such as poor loading efficiency when old steel pipes are loaded onto freight cars for transport, and there remains a need for improvement.

The next problem is that it has poor impact resistance. In the case of pipelines laid on the seabed, a concrete coating approximately 10 cm thick is used on top of the epoxy resin coating to suppress underwater buoyancy, but the fastest coating speed is applied to the outer surface of the epoxy resin-coated steel pipe. It is known that when concrete is coated using a large spray method, the gravel in the concrete hits the epoxy resin coating, resulting in numerous pinholes in the coating. To solve these problems, when concrete coating is applied to powder epoxy resin-coated steel pipes, a mold forming method is used, which is less productive.

Another problem is that the curve of the coating film has poor characteristics. When laying steel pipes, there are times when the pipes have to be bent depending on the terrain.
In the temperature range from 5° C. to +60° C., it is said that the thread membrane must have the ability to not cause cracks or pinholes even when bent at a circumferential angle of 3° or more with respect to an arc equivalent to the diameter of the pipe. However, since the epoxy resin coating becomes brittle as the temperature decreases, powder epoxy resin-coated steel pipes that can be bent by 3 degrees at -45°C have not yet been put into practical use. Therefore, currently, during the winter when the temperature drops, pipes must not be bent while the pipe is standing still, or the pipe must be heated while it is being bent. Whether individual solutions have been implemented for the above four problems, as mentioned above, one can be said to be insufficient.

The object of the present invention is to solve the problems of conventional powder epoxy resin coated steel pipes which have the above-mentioned drawbacks, and to improve the quality of the coating film as a corrosion-resistant steel pipe.

Next, the protective coating of the painted steel pipe of the present invention will be explained with reference to the drawings. Fig. 1 shows a cross-sectional view of the steel pipe when a shield coating is applied to the I'i-painted steel pipe. Fig. 2 shows a steel pipe coated with a polyolefin resin extruded from a die on the same line as when powder epoxy resin is applied to the steel pipe. The figure shows the Coating method is copper pipe 1
is traveling forward in the direction of the arrow while rotating in the direction of the tube axis on the transport roll 6, while the paint is sprayed from the powder epoxy resin coating nozzle 4, and as necessary,
．． A semi-molten polyolefin resin 3 is extruded from an extrusion die 5 onto the outer surface of the coated steel pipe to a thickness of 2 to 0.5 mm, and is wrapped around the coated steel pipe to cover it. This polyolefin resin has soft and sticky properties compared to the hard and brittle properties of powdered epoxy resin paints, so it
It has the ability to buffer against external forces such as contact between surfaces of steel pipes during transport and earth and sand during underground piping construction. Since polyolefin resin is relatively inexpensive compared to powder epoxy resin coating, it may be economically worthwhile to increase the coating thickness to a certain extent, so polyolefin resin is used for powder epoxy resin coating. The combination of using resin as a protective coating provides the ability to coat steel pipes to cover each other's weak points. The thickness of the coating is to compensate for the above problems, prevent the occurrence of troubles, and provide an ideal coating for coated steel pipes.

[Brief explanation of drawings]

Figure 1 shows a cross-sectional view of the steel pipe when a protective coating is applied to the painted steel pipe, and Figure 2 shows the same line in which the steel pipe is coated with powder epoxy resin, and a polyolefin resin is extruded from a die and coated. Show the diagram. l・・・・・Steel pipe 2・・・・Powder epoxy resin 3・・・・Polyolefin resin 4・・・・
Powder epoxy resin coating nozzle 5...Polyolefin resin extrusion die 6...Bag conveyance roll Applicant: Nippon Steel Corporation

Claims (1)

[Claims] Apply 200 to 500 powder epoxy resin to the outer surface of the steel pipe.
A powder epoxy resin coated steel pipe having a protective coating, characterized in that the coated steel pipe is coated with a thickness of 10.tt, and then a polyolefin resin coated with a thickness of 0.1 to 20 mm is formed on the coated steel pipe to protect the coating.