RU2087507C1 - Insulation coating for protection pipes against underground corrosion - Google Patents

Abstract

FIELD: paint and varnish industry, particularly anticorrosion protection of pipelines. SUBSTANCE: insulation coating for protection pipes against corrosion is manufactured of three layers. The first one which represents priming layer is manufactured on the base of bitumen and rubber. The second intermediate layer is manufactured of composition which comprises, %: butadiene methyl styrene rubber, 10.0-20.0; 4,4′, 4″-triphenylmethane triisocyanate, 0.04-0.2; sulfur, 0.2-0.7; organic solvent, the balance. The third layer being protective one is manufactured of extruded polyethylene. Pipe is preliminary heated before priming layer is applied on it. EFFECT: improved protection against corrosion. 3 cl, 2 tbl

Description

 The invention relates to insulating structures used for insulation of pipes in a factory by extrusion coating on a primed surface of a pipe of molten polyethylene.

 The closest in technical essence and the achieved result to the insulating structure according to the invention is an insulating structure, providing for the application on the pipe surface of one layer of primer composition and the outer layer of polyethylene.

 A disadvantage of the known insulation design is that the primer composition, providing high adhesive strength to the surface of the metal, does not have a sufficiently high cohesive strength and insufficiently high adhesion strength and a polyethylene coating.

 An object of the invention is to increase the adhesive and cohesive strength of the coating.

 The technical result is achieved in that the insulation coating for protecting pipes from underground corrosion consists of a primer layer and a protective polyethylene layer, characterized in that between the primer and protective layers it contains an intermediate layer made of a thermosetting composition, including, by weight.

styrene butadiene rubber 10.0 20.0
4,4 ', 4 "-triphenylmethane triisocyanate 0.04 0.2
sulfur 0.2 0.7
organic solvent rest
The primer layer is made of bitumen-rubber mastic (II), and the protective layer is made of extruded polyethylene.

 The technology for preparing the thermoset composition is as follows. Butadiene-methyl styrene rubber is rolled on cold rollers and loaded into a mixer. In the mixer, the rubber is mixed with sulfur and the resulting mixture is dissolved at room temperature or under slight heating. 4,4 ', 4 "triphenylmethanetriisocyanate is dissolved up to 20% concentration in dichloroethane or ethylene glycol. The solutions are mixed immediately before applying the primer to the pipe.

 An insulation coating is prepared as follows.

For pre-cleaned, fat-free and warmed to a temperature of 50
80 ^o C the surface of the pipe is applied sequentially with a primer layer, then the intermediate layer is dried with a stream of air, and then a polyethylene melt (melt temperature 200 -230 ^o C) is applied with stocking or side extrusion.

 A primer coating layer is applied to ensure high adhesive strength of the coating with the metal, as well as to inhibit the surface of the metal from corrosion.

 The coating layer is applied in order to ensure high adhesive strength of the primer with an outer layer of polyethylene, as well as to increase the cohesive strength of the primer.

 The feasibility of applying two layers of primer is also determined by the need to comply with technical requirements for the thickness of the primer. The surface of the insulated pipe and the surface of the extrudable polyethylene are not perfectly flat. Therefore, part of the applied primer is spent on filling surface defects, and the required thickness of its layer is not provided. An increase in the amount of primer applied in one layer above certain values does not allow it to be rubbed uniformly on the surface of the pipe on existing equipment. Primer clots form, the primer does not have time to dry by the time the polyethylene melt is applied. Applying a primer in two stages, but with "thin" layers solves these problems.

 The formation of a high adhesive strength of the primer coating with the outer layer of polyethylene and an increase in the cohesive strength of the primer coating is achieved by introducing vulcanizing additives into the composition of the intermediate layer, which provide chemical crosslinking of rubber at elevated temperatures.

 As a result of the high thermodynamic compatibility of the components of the primer and the intermediate layers of the primer coating, a partial interpenetration of the first and second layers occurs, thereby increasing the cohesive strength of the entire coating.

A feature of the application of the insulation coating on the pipe is the application of a primer layer on the pipe preheated to 50 80 ^o C. Providing pre-heating of the pipe to this temperature ensures, firstly, the complete evaporation of the organic solvent from the primers by the time the polyethylene melt is applied to the pipe, which eliminates the bubbling of the polyethylene coating on the pipe surface under the influence of evaporation of the residual organic solvent. Secondly, ensuring the heating of the pipe additionally contributes to the reaction of chemical crosslinking of the coating layers.

 The layers are applied in accordance with the technology for producing an insulating coating according to GOST 9.015-74.

 Composite polyethylene of grades according to GOST 16337-77 is used in the construction.

 The thickness of the main polyethylene layer is set in accordance with GOST 9.015-74, depending on the diameter of the insulated pipe and the operating conditions of the pipeline.

 SKMS-30 ARC rubber according to GOST 15621-79, obtained jointly by polymerization with a-methylstyrene or with styrene in an emulsion at low temperature, is used as butadiene-methylstyrene rubber.

 Soot PM-100 according to GOST 78885-77 is used as a heat stabilizer of polyethylene.

 As vulcanizing agents, 4.4 ', 4 "-triphenylmethane triisocyanate (TU 6-14-95-85) and sulfur (TU 127-76E) are used.

 As a solvent for a mixture of rubber with sulfur, BR-1, BR-2, B-70, gasane, hexane or other saturated hydrocarbons can be used. 4.4 ', 4 "triphenylmethane triisocyanate is dissolved in dichloroethane or ethylene glycol.

 In the table. 1 shows the formulation of the compositions for the primer and intermediate layers.

 Example number 1 characterizes the known composition based on the primer PG-887, applied in a single layer.

The coating was formed on a steel plate (steel grade St-3), heated to 60 ^o C. The drying time of the first coat of primer was 1 min. The drying time of the second primer layer was 1 min. The melt temperature of the polyethylene was 200 ^o C. the Force pressing the polyethylene to the primer provided a pressure of 0.4 MPa. The coating formation time was 1 min.

 In the table. 2 presents data on the study of the adhesion strength of coatings to a metal surface.

Claims (1)

 1. The insulation coating for protecting pipes from underground corrosion, made of a primer layer based on bitumen and rubber and a protective layer of extruded polyethylene, characterized in that between the primer and protective layers it contains an intermediate layer made of a composition comprising, by weight. Styrene butadiene rubber 10.0 20.0
4.4 ', 4''- Triphenylmethane triisocyanate 0.04 0.2
Sulfur 0.2 0.7
Organic solvent Else
2. A method of obtaining an insulating coating to protect pipes from underground corrosion by applying a primer layer based on bitumen and rubber and a protective layer of extruded polyethylene, characterized in that before applying the primer layer, the pipe is preheated to a temperature of 50 to 80 ^o C and additionally between the primer and a protective layer is applied an intermediate layer of a composition comprising, by weight. Styrene butadiene rubber 10.0 20.0
4.4 ', 4''- Triphenylmethane triisocyanate 0.04 0.2
Sulfur 0.2 0.7
Organic Solvent

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