JPS60245545A - Steel pipe coated with plastic - 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 [Technical Field] The present invention relates to a plastic-coated steel pipe that exhibits stable anti-corrosion coating ability over a wide temperature range of about -50°C to +120°C.

[Technical background]

Plastic-coated steel pipes are widely used in a variety of applications, and among them, polyolefin-based plastic-coated steel pipes are used at a stable rate around the world as transportation pipelines for supplying energy such as oil and gas. ing.

By the way, in recent years, as these resources have been transported under high-temperature heating, the temperature of the coated steel pipes themselves has often increased, and more specifically, cases of temperatures reaching temperatures of around 120°C are increasing. .

In general, pipelines for transporting fluids, and pipelines for transporting oil and gas in particular, are often operated continuously for a long period of 20 to 30 years after installation, so it is natural that It is also desirable that the anticorrosion coating applied can maintain a long service life.

It is also thought that this anti-corrosion coated steel pipe will be left piled up outdoors for a long period of time, from several months to over a year depending on the case, until it is actually used for installation. It would be bad if the performance of the anti-corrosion coated steel pipe deteriorated. For example, in extremely cold regions, the temperature can drop to around 150 degrees Celsius, and in extremely cold regions, the temperature can drop to around 50 degrees Celsius, but even under these environmental conditions, products have certain characteristics such as impact resistance, weather resistance, and water resistance. It is necessary to maintain the

However, with conventional polyethylene-coated steel pipes, the outermost coating, which is an anti-corrosion layer, is made of polyethylene, and its thermal deformation temperature is as low as about 80°C, so the upper limit temperature for use is naturally limited, and it cannot be used under high-temperature conditions of 120°C. It could not withstand long-term use.

Under these circumstances, it was considered to cover the outermost anti-corrosion layer with polypropylene, which has excellent heat deformation resistance, but this polypropylene has a glass transition temperature or embrittlement temperature of 0°C. Since the temperature is approximately +20°C, stable use is difficult because there is a fear that the stock will be frequently damaged if it is exposed to impact when left in an extremely cold region.

Furthermore, if polypropylene is made into a material copolymerized with polyethylene in order to improve its low-temperature properties, it may be possible to use it at -50°C or lower, but this time the heat distortion temperature will drop to around 100°C and 120°C. It will not be able to withstand long-term use at ℃.

Separately, in order for plastic-coated steel pipes to maintain their weather resistance even when left outdoors for long periods of time, it is necessary to apply some kind of weather-resistance treatment to the outermost layer, but weather-resistance treatment agents have a heat deterioration resistance. may cause a decrease in

For example, plastics blended with color pigments such as common carbon black can greatly improve weather resistance, but this leads to a decrease in heat deterioration resistance.

As mentioned above, weather resistance and heat deterioration resistance are contradictory properties, so conventional plastic-coated steel pipes with an anti-corrosion layer as the outermost layer have been improved to the point where they can be used in practice. It was difficult to obtain.

[Purpose of the invention]

An object of the present invention is to provide a polyolefin-based plastic-coated steel pipe that can be used for a long period of time under high-temperature conditions of approximately 150 to 50°C in a stockyard before installation and in a trench of 120°C after installation. It is something.

[Analysis of the invention]

In order to achieve the above-mentioned object, the present inventors investigated various types of materials and, as a result, formed a layer in which a polypropylene composition treated with heat-resistant stability was tightly adhered to the outer circumferential surface of a steel pipe, and the outer surface of the steel pipe was We have achieved a plastic-coated steel pipe characterized by forming a plastic layer with a weather-resistant formulation.

Due to its chemical structure, polypropylene contains 6th class carbon, so it has problems with thermal stability, especially thermal oxidation stability, and in order to enable long-term use at high temperatures, it is necessary to perform heat-resistant stability treatment. .

This will be explained below based on the drawings. FIG. 1 is a partial cross-sectional view of a plastic-coated steel pipe constructed according to the present invention.

In the figure, 1 is a steel pipe that has been subjected to blasting or pickling treatment, and 2
6 is a modified polypropylene layer, 4 is a polypropylene layer, and 5 is a plastic layer having a glass transition temperature or embrittlement temperature of 150° C. or lower. It is necessary that the mutually contacting layers between the steel pipe 1 and the polypropylene layer 4 are in strong contact, but the polypropylene layer 4 and the plastic layer 5 do not necessarily need to be in sufficient contact with each other. .

[Embodiments of the invention]

100 °C and 120 °C, respectively, for 3.0 m thick polypropylene according to DIN 30670 (polypropylene (1) with IL 2.5% and polyethylene with 2.5% carbon black values) When a thermal deformation test was conducted on the sample, the following results were obtained.

Resin 100℃ 120℃ + 0.06mm 0.15ゝ II O, 04 questions 0.12cm ■ 0.28mm ) 0.5 m These resins are used to make plastic-coated steel pipes as shown in Figure 1. Created. For this sample, ASTM
An impact resistance test in accordance with G-14K was conducted and the following results were obtained.

*1 Example 1 Example 2 Comparative example 1 Comparative example 2*3 3 Mod, PP Same left Same left Mod, PE4117
m + thickness ■ 2.2 throat thickness ■ 2.7 familiar thickness ■ 2.7 simple thickness 5
K1.0m thickness Anal 0.5 printing thickness ---Low temperature impact strength - 10℃ >5. '0 > 5.0) 5.0 5.6-
'50℃ >5.0 )5.0 0.6 )5.0*1
The numbers indicate the same parts as the figure numbers in FIG.

*230 μm thick, *30.3-As is clear from the thickness table, Comparative Example 2 has good low-temperature properties, but since the outermost layer, which is an anti-corrosion layer, is made of high-density polyethylene, its thermal deformation properties are poor. It is difficult to use the temperature between 120°C and 120°C. Furthermore, it is recognized that Comparative Example 1 is not practical in terms of low-temperature characteristics.

In contrast, the products of Examples 1 and 2 were found to have sufficiently good performance in impact resistance at low temperatures up to -50°C and heat deformation resistance at high temperatures up to 120°C. It has become possible to leave it outdoors in extremely cold regions, and at the same time, it can withstand long-term use as a high-temperature pipeline of about 120°C.

〔Effect of the invention〕

The plastic-coated steel pipe obtained according to the present invention exhibits the following effects.

1. The outermost layer is a plastic layer with a heat-resistant formula and a glass transition temperature or embrittlement temperature of 150°C or less, so it has excellent impact resistance in the temperature range of -50°C to 50°C when left outdoors before installation. , is weather resistant and therefore not susceptible to damage.

2. Since the polypropylene layer with a heat-resistant stability formula is used as an anti-corrosion layer, when the Vibrine line is actually operated after installation,
It can be used for long periods at high temperatures of around 0°C.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a plastic-coated steel pipe obtained according to the present invention. DESCRIPTION OF SYMBOLS 1...Steel pipe, 2...Single layer of primer, 3...Modified polypropylene layer, 4...Polypropylene layer, 5...Glass transition temperature or embrittlement temperature is 150°C
Plastic layer below. Representative Patent Attorney Sanro Kimura Figure 1 2

Claims (1)

[Claims] A plastic-coated steel pipe characterized by forming a tightly adhered layer of a heat-resistant and stabilized polypropylene composition on the outer peripheral surface of the steel pipe, and forming a plastic layer with a weather-resistant formulation on the outer surface. .