JPS62231723A - Rust prevention of steel material - Google Patents

Abstract

PURPOSE:To obtain a rust preventive method displaying favorable rust preventive capacity even to a high-temperature steel material, by a method wherein an undercoating agent contains more than a specific quantity of a curing agent which is capable of curing an epoxy resin composite at the normal temperature, in a method applying lap winding of a thermosetting tape, obtained by forming an adhesive agent layer composed of an epoxy resin composite having adhesion at the normal temperature on one side of a polyolefin layer, to the surface of the steel material by forming the undercoating agent layer containing an organic flux on the surface. CONSTITUTION:An undercoating agent layer containing an organic solvent is formed on the surface of a steel material. Then before volatilization of the organic solvent of an undercoating agent, an adhesive polyolefin layer is formed on both sides of a heat-resistant polyolefin film. Then lap winding of a thermosetting tape, which is composed of a matter that an adhesive agent layer composed of an epoxy resin composite having adhesion at the normal temperature is formed, is applied to one side of an adhesive polyolefin layer. Then the undercoating agent is capable of curing the epoxy resin composite at the normal temperature. A compounding quantity of a curing agent is more than 1wt% of the whole quantity of the undercoating agent. In the case where the compounding quantity does not come up to the 1wt%, wetness between a steel pipe and adhesive agent layer of a rust preventive tape becomes insufficient and it may happen that deterioration in adhesion is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for preventing corrosion of steel materials, and more particularly to a method of preventing corrosion of steel materials using an anticorrosion tape.

[Prior art]

2. Description of the Related Art One method of transporting fluids such as oil and gas is to construct pipelines using steel pipes.

One problem with such methods is that the steel pipes corrode.

Various methods have been adopted so far to prevent corrosion of the steel 11.

One method is to protect the surface of the steel pipe with bituminous material. However, this method has the problem that the τ material layer is easily damaged by external impact.

In recent years, as a method to solve the problems of such methods, plastics such as polyethylene and polyvinyl chloride have been used on the steel pipe surface.
A method has been adopted to cover the

The following three methods are generally known for coating the surface of steel pipes with plastics.

l) A method in which a steel pipe is heated, an undercoat composition is applied to the surface thereof, and the surface is coated with molten plastic, and then cooled.

2) A method in which a cylindrical heat-shrinkable pipe is processed in advance from a plus-thousand pipe, which is attached to a steel pipe coated with a surface undercoating composition, and the pipe is heated to shrink and coat the pipe.

3) Preliminarily form a plastic material into a tape shape and form an adhesive layer on one surface of the tape, and apply a portion of it in a spiral shape to the surface of the steel pipe, which has been coated with an undercoat composition. This is the so-called anti-corrosion tape construction method, which involves wrapping and wrapping.

Compared to the coated steel pipes protected with bituminous material, this coated steel pipe protected with I, Unifiscus, and Tn has remarkable effects in terms of corrosion prevention effect and service life. has.

However, the undercoat or adhesive layer used in these methods is either a thermoplastic resin or a rubber-based material, and at high temperatures the coating 1yj softens and becomes weak against physical impact, causing it to break. It may also lose its adhesion to metals and cause damage.
Defects such as f→ shift and peeling occur. The problem is that water and oxygen enter through such defective parts, causing corrosion and progressing, that is, the corrosion resistance deteriorates.

Furthermore, in pipelines for transporting petroleum and m/Il+W- fluids, the fluid is usually pressurized and heated to lower its viscosity and improve its transport efficiency. When using a plastic coating with poor heat resistance, there is also a limit to the temperature at which it can be used.In order to solve this drawback of plastic coatings, various measures have been devised in the past. In the anti-corrosion tape construction method, the following 8sE has also been implemented.For example, in the anti-corrosion tape method, the support material for the anti-corrosion tape used, PLASTIC-7-NOTE, has a higher softening point. 'f
Use plastic-1, and in some cases, plastic.

Attempts have also been made to attach a heat-resistant release base material to the comb. This product is excellent in improving the heat resistance of the support for anticorrosion tape.

However, regarding the adhesive layer ζ, if the adhesive component that constitutes this is rubber or thermoplastic 6 (a fat that does not easily soften at high temperatures), it will exhibit adhesive properties at the temperature at which the tape is applied, usually at room temperature. , the steel pipe must be heated during construction.This greatly impairs the workability and simplicity that are the advantages of the tape construction method.

Therefore, attempts have been made to use TAM hardening resin for the adhesive layer of anti-corrosion tapes, but for example, when using a dense-layer hardening type 2/& type thermosetting resin, the pot life, so-called bot life, is limited. It was extremely short, and as the curing progressed, it became difficult to roll the tape around, resulting in poor workability, and it was not satisfactory in terms of heat resistance and heat resistance.

Furthermore, in the case of heat-setting two-component thermosetting resins, the pipe must be heated while being installed, which also causes the above-mentioned ridge spots.

[Invention is a fan! Problems to be resolved]

The problem to be solved by the present invention is that the conventional plastic
The purpose of this project is to solve the above-mentioned difficulties of anti-corrosion coating, especially the above-mentioned disadvantage of the anti-corrosion tape method. The objective is to develop a corrosion protection method that does not require corrosion.

[Means for solving problems]

This problem arises when an anti-corrosion tape consisting of a specific polyolefin film and an adhesive layer is used whose adhesive jH is made of an epoxy resin composition, and the epoxy resin composition is used as an undercoat at room temperature. This is achieved by using a numbing agent that can be cured with. That is, the present invention forms an undercoat layer containing a white organic solvent on the surface of the steel material, and then, while the organic solvent of the undercoat does not volatilize, an adhesive polyolefin layer is formed on both sides of the heat-resistant polyolefin film. A method in which a thermosetting tape comprising an adhesive layer made of an epoxy resin composition that is adhesive at room temperature is formed on one of the negative and hexa-polyolefin layers, and the undercoat is made of the above-mentioned epoxy resin composition. A curing agent that can cure the resin composition at room temperature is +, offi
The present invention relates to a method for preventing corrosion of steel, characterized in that it contains fa% or more.

[Structure and operation of the invention]

The anticorrosive tape used in the present invention has a heat-resistant polyolefin film as a support that does not soften under the operating temperature environment, and an adhesive layer of an epoxy resin composition whose glass transition temperature after curing is higher than that of the operating temperature environment. The combination of an adhesive polyolefin layer that ensures adhesion between the polyolefin film and the adhesive layer provides excellent anti-corrosion performance even when heated.

In addition, after coating the surface of the steel pipe with an undercoat containing an i:I curing agent that cures the adhesive layer in item 1 at room temperature, each time the anti-corrosion tape is wrapped, the wetting between the adhesive layer and the steel pipe is improved. The curing agent contained in the undercoat allows the adhesive layer to be hardened at least in the vicinity of the steel pipe in a short time. As a result, anticorrosion performance is achieved immediately after wrapping the anticorrosion tape, and as the temperature of the steel pipe rises, the thermosetting resin composition progresses in hardening due to the heat treatment J5, resulting in anticorrosion performance at high temperatures. do.

The anticorrosion method of the present invention basically consists of applying an undercoat and wrapping an anticorrosive tape in layers.

The undercoat used in the present invention contains as an essential component a curing agent that can cure the epoxy resin composition that forms the adhesive layer of the anticorrosive tape at room temperature, and also contains a curing accelerator and diluent as necessary. Agents, organic solvents, fillers, softeners, adhesion agents, colorants, antioxidants, flow control agents, etc. are used.

In this case, a wide variety of curing agents can be used that act as a curing agent for the adhesive layer of the anticorrosive tape used, and those that are compatible with the adhesive layer are particularly preferred. As the curing agent, a normal curing agent for curing at room temperature that can cure epoxy resin at room temperature is used.More specifically, polyamide polyamine,
Examples include aliphatic polyamines, aromatic polyamines, and alicyclic polyamines. It is of course possible to use other curing agents and curing accelerators, such as acid anhydrides, polyamides, sulfuric acid resins, phenolic resins, urea, melamine resins, etc. + Iu condensates, dicyandiamide, etc. , catalytically used tertiary amine order, boron trifluoride -
Amine combrenox etc. can also be used. These curing agents may be used singly, fffi, or in combination of two or more.

The amount of the curing agent is such that the total QO of the undercoat is greater than 1% by weight, preferably 2% by weight or more. If the blending amount does not reach 1% by weight, wetting between the steel pipe and the adhesive layer of the anticorrosion tape may be insufficient, resulting in a decrease in adhesive properties.

Diluents used in the primer of the present invention include high boiling point solvents such as glycols and esters, plasticizers such as phthalate esters and phosphate esters, non-reactive diluents such as pine oil and coal tar, butyl glycidyl ether, etc. monoepoxy compounds, polyepoxy compounds such as diglycidyl ether, vinyl compounds such as styrene and diallyl slate,
Epoxidized vinyl monomers such as glycidyl methacrylate, triphenyl phosphite, tetrahydrofuran
8. Poly; Reactive diluents such as sails and lactones are used.

The fT IXt solvent used in the undercoat is one that can dissolve the above-mentioned curing agent and diluent and is compatible with the epoxy resin. For example, toluene, xylene, cyclohexanone, methyl cellosolve, ethyl se[I solder, butyl cellosolve, cellosolve acetate, ethyl acetate, methyl ethyl ketone, butyl ketone, dioxane, methylene chloride, acetone, etc.
A species or two or more species are selected, and a curing agent and a diluent are dissolved and dispersed to be used as a τ pulling agent f6 liquid. The solid content in the primer solution is set so that the viscosity is suitable for applying the primer solution with a brush, spray, etc.
Usually about 10 to 50% is preferable. The coating amount of the undercoat solution is such that the thickness of the undercoat layer after 11 shots of the organic solvent is 0.002 to 0.2I, preferably 0.005 to 0.1m.
Adjust so that it becomes m.

As shown in Figure 1, the thermosetting anticorrosive tape used in the present invention has adhesive polyolefin layers (2) and (2') formed on both sides of a heat-resistant polyolefin film (1). It has a structure in which an adhesive layer (3) made of an epoxy resin composition having adhesive properties at room temperature is formed on one side (2) of the polyolefin layer.

The epoxy resin composition forming the adhesive rri (3) of the thermosetting anticorrosion tape of the present invention contains as essential components an epoxy resin and/or a modified epoxy resin, and a curing agent for curing this. Curing accelerators, fillers,
Softeners, adhesion agents, colorants, thermoplastic resins, rubber,
It contains various additives such as anti-aging agents and coupling agents.

Epoxy IΔ (As the fat, it is preferable to use an epoxy resin that is liquid at room temperature and an epoxy resin that is solid at room temperature in combination to provide adhesiveness at room temperature. Epoxy resins that can be used include bisphenol-based and novolak-based epoxy resins. There are epoxy resins such as glycidyl ether type, glycidyl ester type, and glycidyl amine type.Modified epoxy resins include epoxy urethane resin, epoxy ester resin, epoxy alkyd resin, epoxy phenol resin, epoxy alkyd melamine resin, and rubber-modified epoxy resin. etc. One type of these is used alone, or two or more types are used in combination.

As the curing agent for curing these, the curing agent normally used for epoxy resins is commonly used, but in consideration of the parts where it is used, it is cured at 120°C or less.i! It's good to have J. For example, aromatic diamines such as diaminodiphenylamine, condensates of aliphatic amines and aliphatic dicarboxylic acids, amine curing agents such as dicyandiamide, imidazoles, tetrahydrophthalic anhydride, benzophenone tetracarboxylic anhydride,! ! 1 (organic acid anhydride curing agents such as water trimellitic acid, phenolic resins, phenol curing agents such as bisphenol Δ, etc.).These curing agents may be used alone or in combination of two or more.

In addition, when selecting an epoxy resin and its curing agent, it is preferable that the cured product has a glass transition temperature higher than the temperature environment in which the anticorrosive construction product is used.

Further, the epoxy resin composition can contain various additives such as those described below, if necessary. For example, for the purpose of adjusting the viscosity of the adhesive layer and improving the strength after curing, calcium carbonate, curk, ashest, silicic acids, carbon black, etc.
A filler such as colloidal silica is used. The compounding amount is
The amount may normally be about 0 to 300 parts by weight per 100 parts by weight of the epoxy resin. Furthermore, for the purpose of lowering the viscosity and improving wettability, reactive diluents such as butyl glycidyl ether and monoglycidyl ether of long-chain alcohols, fucric acid plasticizers such as diocdylphthale-1, and i-refrigidyl phosphate are added. A phosphoric acid plasticizer such as -1. can be added. The amount of these components is preferably about 0 to 3011 parts by weight per 100 parts by weight of the epoxy resin.

Also contact, 6 sex bo'tlz7'r71'jii (2
), (2'),! : In order to improve the adhesion of the adhesive layer (3), the epoxy resin composition can also contain Jiff, which is used for the adhesive polyolefin layer. In this case, the amount of the adhesive polyolefin to be blended is preferably about θ to 30 ffifilt parts to 100 i1i parts of the epoxy resin.

Next, it is necessary that the heat-resistant polyolefin film (1) forming the support of the anticorrosion tape of the present invention does not soften at the usage environment temperature, and preferably the Vicat softening point (AS
TM-D l 525, using polypropylene or polyethylene whose Ikg load m) is 120°C or higher,
These can be used alone or in combination or in combination. Further, the gJ4-resistant polyolefin layer may contain various additives such as colorants, antioxidants, fillers, etc., if necessary. In addition, the support usually has a thickness of 5 to 1000 μm, preferably 10 to 100 μm, in order to ensure flexibility as a tape.
[Make it 100 μm thick.

In general, many plastic films that have a high softening temperature themselves have poor flexibility, and if the thickness of the support is made too thick, the flexibility of the tape becomes extremely poor, and tape winding may reduce workability. Easy to wake up.

As explained in FIG. 1, in the anticorrosion tape of the present invention, the heat-resistant polyolefin film (1) has an adhesive layer on both sides with adhesive polyolefin layers (2) and (2') interposed therebetween. (3) is formed.

Heat-resistant polyolefin film (1) has very low water permeability and is extremely effective in preventing deterioration of the adhesive layer due to water absorption. Therefore, it is necessary to apply an adhesive treatment to the surface of the heat-resistant polyolefin film (1), and one of the typical uses of the tape of the present invention is to wrap pipes, etc. Because it can be used for winding (overlapping), modified polyolefin layers (2), (
2') must be formed.

The polyolefin resin used here is a modified polyolefin resin in which an unsaturated carboxylic acid or its anhydride or an unsaturated epoxy tn polymer is grafted onto a polyolefin resin as a modifying agent, and the amount of the modifying agent is determined by the modification. 0.1 to 20i per 100 parts by weight of polyolefin resin
The amount is preferably 0.2 to 15 parts, more preferably 0.5 to 10 parts.

One of the above-mentioned modified polyolefins (polyolefin resins that form the base of the oil include polyethylene, polypropylene, ethylene-ethyl acrylate copolymer, and ethylene-vinyl acetate copolymer (thermoplastic) (car body polyester).

In addition, the unsaturated carboxylic acids and their anhydrides used as the above-mentioned modification agents include acrylic acid, methacrylic acid, maleic acid, fumaric acid, maleic anhydride, fumaric anhydride, itaconic acid, etc., and the unsaturated epoxy monomers include Examples include glycidyl acrylate, glycidyl methacrylate, mono-, di- and triglycidyl esters of itaconic acid, acrylic glycidyl ether, 3,4-epoxy-1-butene, etc., preferably acrylic acid, methacrylic acid, maleic acid,
Maleic anhydride, glycidyl acrylate, glycidyl methacrylate, etc. are used.

The thickness of the adhesive polyolefin layer (2), (2') is 10 to 8 Q It m, preferably 15 to 50 μm.
It is about m. If this thickness is too small, the heat-resistant polyolefin film (1) and adhesive JRII (3
), and if the thickness is too large, moisture will easily enter between the iJ j 4% polyolefin film (1) and the adhesive layer (3), resulting in a high temperature and high humidity environment. This may cause problems with durability.

In addition, in order to ensure adhesive strength at the usage environment temperature, the resin has a softening point of [0].
It is preferable that the temperature is 0°C or higher.

An example of a method for manufacturing the thermosetting tape of the present invention having such a configuration is as follows. First, the manufacturing method for the support layer of the tape is as follows: (a) Heat-resistant polyolefin resin is calendered or extruded to eliminate defects such as pinballs! u4t,) 1 layer or 21'f! A method of laminating a film with a structure of i or more to an adhesive polyolefin film made by inflation molding or the like, (b) a heat-resistant polyolefin resin and an adhesive polyolefin resin are formed by a multilayer extrusion method to produce a heat-resistant polyolefin There are methods such as forming a multilayer film with adhesive polyolefin layers on both sides of the layer, and these methods can create a support layer for the tape.

Next, an epoxy resin composition layer formed into a sheet by an extrusion molding method, a calendering method, etc. is laminated to the tape support layer to obtain the mesh-curable tape of the present invention.

In both cases, the thickness of the adhesive layer is determined to ensure good adhesion.
It is preferably 20μI11 or more in order to reduce the heat resistance. In addition, if it is difficult to unwind when using it as a tape, it is possible to apply 1Ml 1-type film to the adhesive layer in advance.
When using the product, wrap the tape around the piping while releasing the release film (it is preferable to wrap the tape around the piping).

A method of carrying out the method of the present invention will be explained below using a steel pipe for convenience. First, the outer surface of the steel pipe to be constructed is subjected to rust removal and surface conditioning using blasting, sandpaper, etc. as necessary. Next, apply the above primer by appropriate means such as using a spatula, brush, spray, etc. Better.

The thickness should be 0.01 to 0.2 mm. If the amount of undercoat applied is too small, it is undesirable because it will reduce the wettability and the adhesion at the interface between the steel pipe and the adhesive layer of the tape. In addition, if too much coating 11 is applied, unreacted curing agent will remain at the interface between the steel pipe and the 18 agent layer, reducing adhesion, even if the curing agent is highly compatible with the thermosetting resin. This is not desirable because it causes

Next, immediately wrap anti-corrosion tape in a spiral shape on the back side where the organic solvent of the undercoat will not volatilize. It is preferable to temporarily secure the beginning and end of the winding with heat-resistant tape such as fluorine resin tape.

Furthermore, in cases where a large force is applied from the outside, such as when buried underground, a more complete anti-corrosion performance can be ensured by further wrapping a protective tape around the outside of the tape. In this case, the protective tape has a support of plastiphthalate or rubber seam that has a high elastic modulus within the range that can be handled as a tape.・The adhesive layer is preferably a viscous compound containing non-polar rubber as a main component. The protective tape has the effect of protecting the tape from external forces such as earth pressure and stones, and preventing the tape from shifting and wrinkles, at least until the adhesive layer of the anticorrosion tape of the present invention hardens.

〔Example〕

The present invention will be explained below with reference to Examples. +f1 parts means parts by weight.

Example 1 Undercoat standing nails 02-ethyl-4-methylimida... 10 parts Sol 0 di-n-butyl phthalate 3
0 parts 0 toluene・・・・・・・・・・・・・・・・・・
・・・・・・・・・ 60 parts grade food source Niepao is 0 heat resistant polyolefin layer: Vikant softening point 155°C
, polypropylene with a melt flow index of 0.5 g/lO, thickness 3001! m.

0 Adhesive polyolefin layer; Modified polypropylene (polyprolene l OOTfz) in which maleic anhydride is grafted onto the above-mentioned polypropylene, amount of maleic anhydride added to the seams is 2.0 mm, Vikano 1 softening point is 140°C, melt flow index is 0.8 g /10 minutes), thickness 30μ
m: Formed on both sides of the heat-resistant polyolefin layer.

0 Adhesive 1d: Thickness 300 parts m JLM-agent'r@h:, AZnhQ Q Bisphenol A type epoxy resin...100 parts (
Evogin equivalent ■90) 0 Phenoquine 411 fat・・・・・・・・・・・・・・・
...20 parts (molecular weight 40000) 0 Butyl diglycidyl ether ...10
Part 0 Weimatsumi Talc・・・・・・・・・・・・・・・・・・
・・・・・・ 50 parts Q vinylon staple fiber ・・・・・・・・・
・・・・・・・・・・・・100 parts (thickness 20μm, average length 201) O carbon short fibers・・・・・・・・・・・・・・・・・・
... 50 parts (thickness 108 m, average length 20 parts) OT-glycidoxypropylmethyl... 1 part Jetoxysilane 0 Dicyandiamide...
・・ Part 5 02 Undecylimidazole・・・・・・
... After sanding the surface of a steel pipe with an outer diameter of 5011I11 with sandpaper (#240), apply an undercoat prepared using the above formulation until the thickness of the undercoat after the luene evaporates is 0.
．． Immediately after, Ill 50 nun tape having the above structure was wrapped half-wrap, and the end of the winding was temporarily wrapped with +L tape with fluororesin tape.

Example 2 In Example 1, the structure of the anticorrosive tape and the composition of the adhesive layer were as shown below, and the other conditions were the same as in Example 1.

Ami C and Nib J Shoulder Wajo fiJ4 Thermal polyolefin layer: Vicat softening point 128℃, melt flow index 0.5g/IO minute high-density polyethylene, thickness 300μm・0 adhesive polyolefin layer: -2 polyethylene Modified polyethylene containing meccrylic acid (3.0 parts of methacrylic acid added to 100 parts of polyethylene, Vicat softening point 120°C, melt [1-index 0.8 g/lo min), Pl size 30 p. m, formed on both sides of the heat-resistant polyolefin layer.

O18 adhesive layer: 300 μm thick Combined with Sokuyu f JL coating/Nbisphenol Δ type epoxy resin... 70 parts (epoxy equivalent 190) 0 Bisphenol A type epoxy resin... 30 parts (epoxy equivalent 1700) 0 Adding carboxyl groups to both ends... 20 parts acrylonitrile butadiene copolymer (average molecule ♀ 4000) 0 Solid adhesive powder...・
...100 parts (average particle size 20 μm) 0 glass, u fiber...
......100 copies (thickness 10 μm, IL average length 2
0mm) 0γ-aminopropyltrimethquine...
1 part silane 0 adipic acid hydrazide
Part 5 02 Methylimidazole・・・・・・・・・
... 1 part Example 3 In Example 1, the structure of the anticorrosion tape and the composition of the adhesive TfA were as follows, and (I was treated in the same manner as I in the experiment).

A typical polyolefin layer: Vicat softening point 15
Polypropylene with a melt flow index of 0.7 g/IO at 0°C and high density polyethylene with a Vicat softening point of 128°C and a melt flow index of 0.5 g/10 min are mixed in a weight ratio of 1:1. Thickness: 300μtn.

O-adhesive polyolefin layer: Modified resin made by adding glycidyl methacrylate to ethylene ethyl acrylate (Graph 1) (Additional amount of glycidyl methacrylate to 1 part of ethylene ethyl acrylate 5-Om)
'Q section, Vika 7 softening point 110℃, melt flow index 1. 0g/10 min), Pl level 20 pm, formed on both sides of the heat-resistant polyolefin layer.

・・Adhesive layer: IV depth 300 μm, W agent layer 0ffi, finely divided bisphenol Δ type epoxy (name 1 resin... 40
parts (epoxy equivalent 190) ・O bisphenol Δ type epoxy 1 mura fat... 30
Part (1700 for epoxy) ・・Evokinourethane resin・・・・・・・・・・・・・
・ 30 parts (epoxy equivalent: 600) Crystalline warping force 4'5) end...
・・・・80 parts (average particle size 20〆zm) ・・Glass short fiber・・・・・・・・・・・・・・・・・・・
...1 o o rr++ (person I OII river, engineering 1 visit ni sa 20 m+) 0T-aminopropyl trime I kin... 1 part silanelydicyandiamide...・・・・・・
・・Part 302-Undecylimidazole・・・・
... 2 parts Example 4 In Example 1, the undercoat formulation was changed to the following formulation, and the other conditions were the same as in Example 1.

Egomi U town! Synthetic curing agent・・・・・・・・・・・・・・・・・・・
... 20 parts (mixture of aromatic amine and aliphatic amine, active hydrogen equivalent: 40) 0 dioctyl phthalate...
40 parts 0 methyl ether ketone...
40 parts Comparative Example 1 In Example I, the tape was wound without using a primer. The rest was treated in the same manner as in Example 1.

Comparative Example 2 The same tape as in Example 1 was wound without forming an adhesive polyolefin layer. The rest was treated in the same manner as in Example 1.

Comparative Example 3 The tape in which the adhesive polyolefin layer was formed only on one side of the heat-resistant polyolefin layer (only on the adhesive I side) in Example 1 was wound. The rest was treated in the same manner as in Example 1.

Comparative Example 4 In Example 1, a tape without an adhesive layer was wound. The rest was treated in the same manner as in Example 1.

The steel pipes of the above examples and comparative examples were heated at 40"C for 2 hours.
After leaving it for 0 hours, the following al test was performed and the results shown in Table 1 were obtained.

(1) Water test: RR! After the steel pipe was immersed in 100'c''i water for 20 hours, the occurrence of bulges in the wave layer was observed, and the occurrence of pinholes was confirmed using a pinhole tester at AC 10 KV.

(2) Burial test: Heat-resistant, FFJ (pressure hoses) are attached to both ends of the Jliff pipe so that the heat medium oil can flow inside the coated steel pipe, and the heat medium oil at +00°C is buried 1 m underground. After continuing to flow for 20 mouths at a flow rate of 7!/min, the corrugated steel pipe was taken out and returned to room temperature, and changes in appearance such as blisters and wrinkles of the coating were observed.

(Effects of the Invention) As is clear from the above examples, according to the anticorrosion method of the present invention, anticorrosion-treated steel materials having excellent heat resistance can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an example of a thermosetting anticorrosive tape used in the method of the present invention. (1)...F-resistant, pH-resistant polyolefin film (2) (2')...Adhesive polyolefin layer (3)...Epoxy + Jl Adhesive I- (L) consisting of a fat composition

Claims (3)

[Claims] (1) Form an undercoat layer containing an organic solvent on the surface of the steel material, and then, while the organic solvent of the undercoat does not volatilize,
A thermosetting tape consisting of an adhesive polyolefin layer formed on both sides of a heat-resistant polyolefin and an adhesive layer made of an epoxy resin composition that is tacky at room temperature formed on one side of the adhesive polyolefin layer is wrapped in an overlapping manner. A method for preventing corrosion of steel materials, characterized in that the undercoat contains 1.0% by weight or more of a curing agent capable of curing the epoxy resin composition at room temperature. (2) the heat-resistant polyolefin film constituting the thermosetting tape is made of polypropylene and/or polyethylene having a Vicat softening point of 120°C or higher, and the adhesive polyolefin layer has a Vicat softening point of 100°C or higher; Further, a patent characterized in that the epoxy resin composition that is sticky at room temperature contains an epoxy resin and/or a modified epoxy resin and a curing agent as essential components, and is curable at a temperature of 120°C or lower. A method for preventing corrosion of steel according to claim 1. (3) The thickness of the undercoat layer after the organic solvent has evaporated is 0.
3. The corrosion prevention method according to claim 1, wherein the corrosion resistance is 0.002 to 0.2 mm.