JPH0486255A - Polyolefin coated steel pipe for high temperature buried piping for controlling heat oxidative deterioration of coating generated by sand and earth - Google Patents

Abstract

PURPOSE:To control oxidative deterioration of polyolefin coating generated by sand and earth under the high temperature burying to a large extent by laminating modified polyolefin containing a specified essential oxidation inhibitor and polyolefin successively on the outer surface of a substrate treated steel pipe. CONSTITUTION:The outer surface of a steel pipe is ground with grit blasting or the like and rust is removed, and the substrate treatment is performed by the chromate treatment or the combination of chromate and epoxy primer treatment. Then, a two-pack cured type epoxy primer or a dicyandiamide family one-pack type epoxy primer is applied on said surface of pipe for heat curing. Then, the steel pipe coated with the epoxy primer is preheated, and modified polyolefin containing two components in the formula (a) and formula (b) as an essential oxidation inhibitor are laminated successively. Then, said surface is coated with polyolefin.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to the heat-resistant life of polyolefin-coated steel pipes,
More specifically, the present invention relates to a polyolefin-coated steel pipe that suppresses thermal deterioration of the polyolefin-coated steel pipe promoted by sand and soil under high-temperature burial.

(Prior art) Polyolefins such as polyethylene and polypropylene are
Due to its excellent anti-corrosion properties, it has been used as a heavy-duty anti-corrosion coating for steel pipes. Such polyolefin coatings deteriorate due to oxidative deterioration. In general, to prevent oxidative deterioration of polyolefins, antioxidants such as phenolic antioxidants and sulfur-based antioxidants are blended with polyolefins.
Generally, the method used is to follow JIS K 7212J, measure the life at high temperatures at three or more points by varying the test temperature, and estimate the life near room temperature by extrapolating the Arrhenius plot of the test temperature and measured life. .

(Problem to be solved by the invention) However, these polyolefin coatings have recently been applied to pipes that transport high-temperature fluids underground, such as oil transport pipes that transport high-temperature heating and conduit pipes of steam pipes for district heating and cooling. When steel pipes are used, the deterioration of polyolefin due to thermal oxidation occurs over a short period of time, which is a problem, but no antioxidant has been found that is effective in preventing the deterioration of polyolefin coatings under high-temperature burial.

(Means for Solving the Problems) As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a polyolefin coating and a modified polyolefin for bonding the coating to a steel pipe contain a specific phenolic antioxidant and a specific We have discovered that by combining amine-based antioxidants, adsorption and escape of antioxidants by sand and soil under burial can be suppressed, and the thermal oxidative deterioration resistance of the coating can be dramatically improved. It's arrived.

That is, in the present invention, on the outer surface of a steel pipe that has been subjected to surface treatment,
Thermal deterioration promoted by sand and soil of a polyolefin coating under high-temperature burial, characterized by sequentially laminating a modified polyolefin containing the following two components (a) and (b) as essential antioxidants and a polyolefin. This invention relates to polyolefin-coated steel pipes that suppress

(a) 1,3,5-trismethyl-2,4,6-1
-lis(3,5-di-tart-butyl-4-hydroxybenzyl)benzene or 4,4゛-diobis(3
(b) Poly((6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine- Amine-based oxidation of 2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino)] or poly-2.2.4-1-lysothyl-1,2-dihydroquinoline The present invention will now be described in detail regarding the use of inhibitors, either singly or in mixtures.

The steel pipe used in the present invention is a steel pipe made of alloy steel such as carbon steel and stainless steel. Also, for the purpose of improving the corrosion resistance of steel pipes, the outer surface of steel pipes.

Plating of zinc, aluminum, nickel, etc. on the inner surface, zinc-iron, zinc-aluminum, zinc-nickel, zinc-
It is also possible to use alloy plating such as Nitsukel-cobalt, or dispersion plating in which fine inorganic particles such as silica or titanium oxide are dispersed in the plating or alloy plating.

For surface treatment of steel pipes, the outer surface of the steel pipe is degreased, pickled, blasted using Glyph 1-blasting, sandblasting, etc. to remove rust, and then chromate treatment is applied to maintain interfacial adhesion at high temperatures for a long time. It is effective to treat the base with a combination of S-ri or chromate treatment and evogishibrimer treatment.

The chromate treatment agent used in the present invention is a chromate treatment agent with fine particle silica added, or phosphoric acid added to the chromate treatment agent, from the viewpoint of maintaining the interfacial adhesive strength between the polyolefin coating and the steel pipe at high temperatures for a long time. It is more effective to use a phosphoric acid chromate treatment agent.

In order to maintain the interfacial adhesion between the polyolefin coating and the steel pipe at high temperatures for a long time, the adhesive primer of the present invention is a two-component epoxy primer or a dicyandiamide-based primer with a dicyandiamide-modified curing agent added. It is more effective to use type epoxy primer.

Polyolefins include polyethylene, polypropylene, polybutene, ethylene and propylene, 1-
Butene, 1-hexene 4-methyl-1-pentene, 1-
A copolymer with α-olefin such as octene is used. Further, as the modified polyolefin, an adhesive polyolefin obtained by modifying the polyolefin with an unsaturated carboxylic acid or its anhydride is used. Specific examples of the unsaturated carboxylic acid or anhydride thereof used for modification include maleic anhydride, citraconic anhydride, itaconic anhydride, maleic acid,
Acrylic acid, methacrylic acid, etc. are not mentioned, but among these, from the viewpoint of maintaining interfacial adhesive strength at high temperatures for a long time,
Maleic anhydride is particularly preferred. The following two components (a) and (b) are added to the polyolefin and modified polyolefin as essential antioxidants.

(a) The following phenolic antioxidants alone or in mixtures 1.3.5-hlismethyl-2,46-1-lis(3
,5-di-t,er t-butyl-4-hydroxybenzyl)benzenediyl 1((2,2,6,8-teI-ramethyl-4-piperidyl)imino)], and as a general commercial product I made by CIBA-GEIGY
X1330 etc. can be used for RG8N.

or 4,4゛-thio-bis-(3-methyl6-te
rt--butylphenol), and commercially available products include Antique Crystal manufactured by Kawaguchi Chemical Co., Ltd. and S manufactured by Sumitomo Chemical Co., Ltd.
Umilizer G80, Yoshinox SR manufactured by Yoshitomi Pharmaceutical Co., Ltd., etc. can be used.

(b) The following amine-based antioxidants alone or as a mixture poly[(6-(+,1,3゜3-tetramethylbutyl)
Imino-1,3,5-triazine-2,4-, CTB
CH [ASSORB 944LD manufactured by A-GEIGY
CHIMASSORB 944FD etc. can be used.

or poly-2,2,4-1-dimethyl-12-dihydroquinoline, Antige RD manufactured by Kawaguchi Chemical Co., Ltd., A manufactured by Sumitomo Chemical Co., Ltd.
ntigene RD-G etc. can be used.

Adsorption of antioxidants from polyolefins and modified polyolefin coatings by sand and soil under high-temperature burial occurs only when the above antioxidants (a) and (b) are combined and added to polyolefins and denatured polyolefins.・
It is extremely effective in suppressing escape and thermal oxidative deterioration of both coatings. Phenol-based antioxidants, amine-based antioxidants, sulfur-based antioxidants, etc. other than those used in kneading are easily adsorbed and released by sand and soil, causing the polyolefin and modified polyolefin coating to deteriorate in a short period of time, causing cracks and coating. Clumped collapse occurs and corrosion protection is impaired. As for the amounts of (a) and (b) added, it is desirable that each of (a) and (b) be added to the polyolefin in an amount of more than 0.05% by weight and less than 5% by weight.

The polyolefin used in the present invention contains an antioxidant to prevent deterioration during melt extrusion using an extruder, and a weathering stabilizer 1 to provide weather resistance during the outdoor exposure period until buried piping construction.
Pigments that provide color, inorganic or organic fibers and fillers that provide scratch resistance, flame retardants, anti-blocking agents,
Compounding agents, such as slip agents, which are usually added to polyolefins may be added to the extent that they do not impair the object of the present invention.

Next, a method for producing a polyolefin-coated steel pipe for high-temperature burial according to the present invention will be explained.

First, the outer surface of the steel pipe is polished by grid blasting or the like to remove rust, and a chromate treatment agent or phosphoric acid chromate treatment agent containing particulate silica is applied and baked by heating. The chromate treatment agent is applied using the methods normally used for applying chromate treatment agents, such as ironing and spray painting. From the viewpoint of retention, it is desirable that the total amount of chromium deposited be in the range of more than 100 mg/m2 and less than 1000 mg/m2.

Next, a two-component curing epoxy primer or a dicyandiamide-based wave-type epoxy primer is applied to the surface and cured by heating.

These epoxy primers are applied using the methods normally used for epoxy primer application, such as spray painting and ironing, but the film thickness of the epoxy primer to be applied is such that it maintains interfacial adhesion for a long time under high temperatures. From this viewpoint, a range of more than 10μ and less than 200μ is preferable.

Next, the steel pipe coated with the epoxy primer is preheated by a method commonly used for preheating steel pipes, such as high frequency induction heating.
Coating modified polyolefin and polyolefin. Methods for coating modified polyolefin include electrostatic coating of modified polyolefin in the form of an object, extrusion coating from a T-die or round die, and extrusion coating with polyolefin in two layers from a two-layer T-die or two-layer round die. The coating is carried out by a method commonly used for polyolefin coating, such as, but the thickness of the modified polyolefin to be coated is preferably in the range of more than 50 μm and less than 350 μm from the viewpoint of maintaining interfacial adhesive strength at high temperatures for a long period of time.

Then, coat the surface with polyolefin. Conventional polyolefin coating methods are used for coating, such as extrusion coating from a T-die or round die, and electrostatic coating of powdered polyolefin. From the viewpoint of long-term retention, 1mm over 10
A range of less than mm is preferred.

A partial cross-section of the polyolefin-coated steel pipe according to the present invention obtained as described above is as shown in FIGS. 1 and 2, where 1 indicates degreasing and pickling.

A steel pipe from which oil, rust, etc. have been removed by grid blasting, sandblasting, etc., 2 is a chromate coating obtained by applying a chromate treatment agent containing fine silica particles or a phosphoric acid chromate treatment agent containing phosphoric acid added to the chromate treatment agent and baking it. , 3 indicates an epoxy brimer coating film obtained by applying and curing a two-component curing type epoxy brimer or a dicyandiamide-based wave-type epoxy brimer, 4 indicates a modified polyolefin, and 5 indicates a polyolefin.

In addition, 2 in the figure is total chromium (100 to 1000 in -1 coating amount)
Good results are obtained when the coating amount is mg/m2, 3 is a film thickness of 10 to 200 μm, 4 is a film thickness of 50 to 350 μm, and 5 is a film thickness of 1 to 10 mm.

(Example) Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 The outer surface of a steel plate (24mmφ x 50mm length x 5mmt) was grid-blasted, and a chromate treatment agent containing silica particles was applied to the surface to give a total chromium adhesion of 500.
It was coated with a hard coat to give a concentration of mg/m2, and was preheated to 190°C and baked. Next, a two-component curing epoxy primer was applied to the surface to a thickness of 50 μm and cured, and then a film of maleic anhydride-modified polyolefin powder added with the antioxidant according to the present invention shown in Table 2 was applied. Thickness is 2
It was electrostatically coated to a thickness of 00μ and melted. Then,
The polyolefin coated with the antioxidant according to the present invention shown in Table 2 was extrusion coated on the surface using a circular die to a film thickness of 2.5 mm. 24 were manufactured.

As a comparative example, modified polyolefins and polyolefins added with antioxidants other than those of the present invention shown in Table 3 were used.
Comparative polyolefin-covered steel pipes 1 to 22 shown in Table 1 were manufactured in the same manner as above. The thus obtained polyolefin-coated steel pipe according to the present invention and the comparative polyolefin-coated steel pipe were placed in a glass container containing sand (inner diameter 75rnmφ×
Depth 150mm, silica sand No. 8 or soil 100m deep
buried in a glass container (filled up to m) at 140°C.
An accelerated test was conducted by placing the sample in an oven, and after 5,000 hours, the appearance of the coated surface was observed (presence or absence of lump-like collapse, presence or absence of cracks). The results are shown in Table 4.

From the results shown in Table 4, it is clear that the phenolic antioxidant according to the present invention was applied to modified polyolefins and polyolefins.
RGANOX1330, 1,3,5-trismethyl-
2,4,6-1-lis(3,5-di-tert-butyl-4-hydroxyhensyl)benzene or antique crystal, 4,4'-thio-bis-(3-medyl-6
- tert-butylphenol) and CIII MASSOR B944LD, poly((
8-(1,1,3,3-tetramethylbutyl)imino-
1,3,5-triazine-2,4-diyl) ((2
,2,8,6-tetramethyl-4-piperidyl)imino)hexamethylene(2,2,6,6-tetramethyl-4
-Piperidyl)imino)] or]Antage RD, Poly2.2.4-Only when adding in combination trimethyl-12-dihydroquinoline, oxidative deterioration of the sand coating was suppressed even in the accelerated burial test at 140°C. It is possible to prevent the coating from collapsing in chunks and from generating cracks.

4 is a modified polyolefin, 5 is polyolefin.

Other 4 people (Effects of the invention) As is clear from the examples, the polyolefin-coated steel pipe according to the present invention can significantly suppress the oxidative deterioration of the polyolefin coating caused by sand and soil when buried at high temperatures, so it has unprecedented durability. This has the remarkable effect of providing a polyolefin-coated steel material with a certain level of properties.

[Brief explanation of drawings]

1 and 2 are partial cross-sectional views of a polyolefin-coated steel pipe according to the present invention. 1 is a steel pipe that has had oil, rust, etc. removed by degreasing, pickling, plus treatment, etc. 2 is a steel pipe that has been coated with a chromate treatment agent containing silica fine particles or a phosphoric acid chromate treatment agent that is obtained by adding phosphoric acid to the chromate treatment agent. Chromate coating obtained by baking; 3. Epoxy primer coating obtained by applying and curing a two-component curing epoxy primer or dicyandiamide-based wave-type epoxy primer; 1. Oil content removed by degreasing, pickling, fur treatment, etc. The steel pipe 2 from which rust etc. have been removed is coated with a chromate treatment agent containing silica fine particles or a phosphoric acid chromate treatment agent in which phosphoric acid is added to the chromate treatment agent. Epoxy primer coating film 4 obtained by applying and curing Gici primer or dicyandiamide-based liquid epoxy primer 4 Modified polyolefin 5 Polyolefin

Claims (1)

[Claims] 1. A modified polyolefin containing the following two components (a) and (b) as essential antioxidants and a polyolefin are sequentially laminated on the outer surface of a steel pipe that has been subjected to surface treatment. (a) 1,3,5-trismethyl-2,4,6-tris (3,5-di-tert-butyl-4) (b) Poly[{6-(1,1,3 ,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl)imino}] or poly-2,2, 4-trimethyl-
1,2-dihydroquinoline amine antioxidant alone or mixture 2 Polyolefin is polyethylene, polypropylene,
The sand according to claim 1, which is polybutene or a copolymer of ethylene and an α-olefin such as propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, or 1-octene. A polyolefin-coated steel pipe 3 for high-temperature buried piping that suppresses thermal oxidative deterioration of the coating caused by soil.A claim characterized in that the modified polyolefin is an adhesive polyolefin obtained by modifying the polyolefin according to claim 2 with an unsaturated carboxylic acid or its anhydride. 4. A polyolefin-coated steel pipe for high-temperature buried piping that suppresses thermal oxidative deterioration of the coating made of sand and soil according to claim 1. The sand according to claim 1, characterized in that chromate treatment is applied to the outer surface of the steel pipe as a base treatment for the steel pipe. A polyolefin-coated steel pipe for high-temperature buried piping that suppresses thermal oxidative deterioration of the coating due to dirt and soil.Claim 1, characterized in that as a base treatment for the steel pipe, the outer surface of the steel pipe is subjected to a chromate treatment, and then an epoxy primer treatment is applied. Polyolefin-coated steel pipe for high-temperature underground piping that suppresses thermal oxidative deterioration of the coating due to sand and soil described above.