JP2002267049A - HOT DIP Sn COATED STEEL TUBE FOR WATERWORKS AND HOT WATER SUPPLY SERVICE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot dip Sn coated steel pipe which is less easily subjected to mechanical damages such as damages in the execution environment and the embedding environment of pipes for waterworks and hot water supply services, and has excellent corrosion resistance. SOLUTION: In the hot dip Sn coated steel pipe for waterworks and hot water supply services, the deposition of a hot dip Sn coating layer is 100-600 g/m<2> in terms of Sn on an inner surface and/or an outer surface of the steel pipe. In addition, an organic synthetic resin film or a polyolefin coating is provided on the hot dip Sn coating layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip Sn-coated steel pipe used for water supply / hot water supply pipe.

[0002]

2. Description of the Related Art In recent years, hot water supply facilities have spread from buildings to single-family houses due to improvements in urban living environments. Also,
From the viewpoint of energy conservation, the spread of district cooling and heating systems is also being promoted. Therefore, durability of transport pipes for high-temperature fluid such as hot water is regarded as important. As a pipe material for transporting water and the like, in addition to steel pipes such as forged steel pipes and electric resistance welded steel pipes, thermoplastic resin pipes such as polyvinyl chloride, polyethylene, polypropylene, and polybutene are used alone. Steel pipes have higher mechanical strength than these resin pipes, so they have excellent shock resistance during construction and compression resistance even when buried under heavy traffic, etc. By comparison, the pressure resistance is sufficiently large and excellent, and it is not easily burned like a resin tube, so that it is excellent without being spread by fire even when used for indoor use.

However, in applications where prevention of fluid turbidity or blockage of pipelines due to corrosion of steel is required, resin tubes that do not cause corrosion are used. As a pipeline having both advantages, there is known a composite pipe of a resin and steel in which a resin pipe is inserted into the inner surface of a steel pipe to prevent corrosion. For example, a composite pipe of steel and soft polyvinyl chloride utilizing inexpensive polyvinyl chloride is widely used as a water supply pipe, and a composite pipe of steel and hard polyvinyl chloride is widely used as a hot water supply pipe.

However, the release of environmental hormones, which are said to affect the reproductive function of living organisms, has been recognized in polyvinyl chloride, and their use in water supply pipes and hot water supply pipes has been threatened in recent years. Furthermore, there is a problem that dioxin is generated at the time of incineration and disposal of composite pipe remaining material generated during on-site piping work. Therefore, a composite pipe used for a water supply pipe or a hot water supply pipe without using polyvinyl chloride has been desired. Therefore, a molten Sn-plated steel pipe was manufactured using Sn which is used for plating of tableware and has no problems of elution of environmental hormones and generation of dioxin. However, it is difficult to realize long-term corrosion resistance in a construction environment of a water supply / hot water supply pipe or a buried environment in which the plating is mechanically damaged such as a flaw.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention provides a molten Sn for water and hot water supply which has excellent corrosion resistance even in a construction environment of a water / hot water supply pipe or a used buried environment.
A plated steel pipe is provided.

[0006]

Means for Solving the Problems The present inventors focused on Sn which is used for plating of tableware and has no problems of dissolving environmental hormones and generating dioxins, and then examined the construction environment and use of piping for water supply and hot water supply. Considering mechanical damage to plating such as flaws in the embedded environment to be performed, limiting the amount of adhesion of the molten Sn plating layer, further providing an organic synthetic resin coating on the molten Sn plating layer, or By sequentially laminating an epoxy primer layer, a polyolefin adhesive layer, and a polyolefin layer, it has been found that a hot-dip hot-dip hot-dip Sn-coated steel pipe with excellent corrosion resistance is possible, and has led to the present invention. to place the water, characterized in that it comprises 100 to 600 / m ² at the inner surface and / or the outer surface, the adhesion amount of Sn converted molten Sn plating layer (1) steel tube And hot water supply for melting Sn-plated steel pipe.

(2) The hot-dip hot-dip steel pipe for tap water and hot water supply according to the above (1), further comprising an organic synthetic resin coating film on the hot-dip Sn plating layer. (3) The hot-dip hot-dip hot-dip steel pipe according to (1), wherein an epoxy primer layer, a polyolefin adhesive layer, and a polyolefin layer are sequentially laminated on the hot-dip Sn plating layer. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Melt Sn for water supply and hot water supply of the present invention
First, the surface of the plated steel pipe is degreased, pickled, and cleaned, and then subjected to a pretreatment by an appropriate method. The pre-treatment can be performed by a known method such as a method using a ZnCl ₂ / NH ₄ Cl-based flux or a method of heating in a hydrogen-containing atmosphere. Next, hot-dip Sn plating is performed on the steel pipe pretreated as described above. In addition to the expected long-term corrosion resistance of the steel pipe, the amount of molten Sn-plated It is preferable that the amount be 100 g / m ² or more in terms of Sn in consideration of a large damage. If the thickness is more than necessary, the smoothness of the surface of the hot-dip Sn plating may be impaired. Therefore, the upper limit is preferably set to 600 g / m ² .

[0009] The temperature of the molten Sn plating bath is 240 ° C or higher. If the temperature is lower than 240 ° C., the fluidity of the molten Sn plating bath is low, and a good plating appearance cannot be obtained. The upper limit of the temperature of the hot-dip Sn plating bath is not particularly specified, but when the strength of the steel pipe is required, a temperature not exceeding 500 ° C. is preferable. Molten Sn
The immersion time of the steel pipe in the plating bath is preferably 5 to 600 seconds.
If the time is less than 5 seconds, non-plating occurs and the adhesion of plating decreases. On the other hand, if it exceeds 600 seconds, the alloy becomes brittle because alloying of Fe and Sn proceeds.

Next, it is preferable to apply an organic synthetic resin paint on the molten Sn plating layer. As a paint,
Acrylic-based, chlorinated rubber-based, vinyl chloride-based, polyurethane-based commercially available products may be used, but it is preferable to use an epoxy-based paint because of high adhesion of the coating film and excellent mechanical strength. . The composition of the epoxy-based paint may be adjusted appropriately, but if it is necessary to complete a series of steps from coating to film formation within a limited time in a continuous production coating line, use a bake hardening type Is preferred.

The epoxy resin used for the coating material preferably has an average molecular weight of 300 to 4,000 and an epoxy equivalent of 70 to 5,000, and the number of oxirane rings at the molecular terminals is two or more per epoxy molecule. Further, those obtained by appropriately modifying these epoxy resins may be used. The curing agent is appropriately selected from diamine derivatives (including dicyandiamide and imidazole derivatives), acid anhydrides, phenol derivatives, amine salts, and various modifications thereof.

An appropriate mixing ratio of the epoxy resin and the curing agent is as follows:
Since it differs depending on the combination of the compounds used, it cannot be specified unconditionally. For example, when a primary amine compound is used as the curing agent, the active hydrogen of the curing agent is about 8 parts with respect to 10 parts of the oxirane ring of the epoxy resin. It is good to do. Furthermore, in order to impart strength and flexibility to the coating film,
An inorganic additive such as silica may be added, or the mixture may be diluted with an organic solvent to facilitate the coating operation. However, an organic solvent that does not cause a chemical reaction with an epoxy resin or a curing agent to be used is used.

The coating is performed by immersing the steel pipe in the coating or by a spraying method using an appropriate coating machine, but other methods may be used. After coating, it is preferable to lighten and rub with a rubber spatula or the like as necessary to make the coating film thickness uniform.
It is important that the required coating film thickness be individually determined in consideration of the corrosive environment of the water supply / hot water supply pipes, etc., and thus is not particularly limited here. However, in order to have anticorrosion properties, the thickness is preferably at least 5 μm or more.

Further, a chemical conversion coating such as chromate, phosphate, organic zirconium salt, organic titanium salt, zirconium salt, etc. may be interposed between the molten Sn plating layer and the organic synthetic resin coating. When performing the chemical conversion treatment, it is preferable to perform the degreasing after the plating surface is sufficiently degreased. As a chemical solution used for degreasing, a volatile organic solvent or a commercially available product for exclusive use can be used, and a chemical conversion treatment method is preferably performed by an immersion method, a spray method, or another appropriate method.

Further, instead of coating an organic synthetic resin paint on the hot-dip Sn plating layer, an epoxy primer,
A polyolefin adhesive and a polyolefin may be sequentially coated. As the epoxy primer, for example, a mixture of epoxy, a pigment and a curing agent is used. As the epoxy, for example, diglycidyl ether of bisphenol A or diglycidyl ether of bisphenol F is used. Fine particles such as silica and titanium oxide are used as the pigment. When the amount of these pigments is in the range of 3 to 30 parts by weight with respect to 100 parts by weight of epoxy, good water-resistant adhesion can be obtained.

The curing agent includes an alicyclic group such as butyl glycidyl ether adduct of 3,9-bis (3-aminopropyl) -2,4,8,10-tetraoxaspiro (5,5) undecane. Amine, aromatic amines such as condensates of meta-xylene diamine and epichlorohydrin, and dicyandiamide can be used. When an alicyclic amine or an aromatic amine is used as the curing agent, the curing agent is mixed at a ratio of the epoxy equivalent of the epoxy to the active hydrogen equivalent of the curing agent.

When dicyandiamide is used as a curing agent, modified imidazole is added as a curing accelerator to reduce the curing temperature. As the modified imidazole, for example, 2-methylimidazole, 2-phenylimidazole and the like can be used. In this case, when the curing agent is added in an amount of 3 to 10 parts by weight of dicyandiamide and 1 to 3 parts by weight of modified imidazole with respect to 100 parts by weight of epoxy, good water resistance adhesion can be obtained.

The epoxy primer is applied by preheating the molten Sn-plated steel pipe by high-frequency induction heating, burner heating, or the like, and spray-coating, roll-applying, or brush-applying the epoxy primer on the surface. After applying an epoxy primer to the surface of the plated steel pipe at room temperature, the steel pipe may be heated to cure the epoxy primer. In any of the above methods, the preheating temperature of the hot-dip Sn-plated steel pipe is preferably about 140 to 230 ° C. If the preheating temperature of the steel pipe is lower than 140 ° C., the adhesive strength of the polyolefin coating decreases. Further, from the viewpoint of workability and economy, the upper limit of the steel pipe preheating temperature is preferably about 230 ° C.

The thickness of the epoxy primer is 30 to
It is preferably about 250 μm. If the film thickness is less than 30 μm,
Adhesion of polyolefin coating decreases in immersion test. From the viewpoint of workability and economy, the upper limit of the film thickness is 250
About μm is good. Next, as a polyolefin adhesive, an ethylene homopolymer or an α-polymer such as ethylene and propylene, 1-butene, 1-hexene, 1-octene, etc.
An ethylene-α-olefin copolymer obtained by copolymerizing an olefin alone or a modified polyolefin obtained by modifying a mixture thereof with maleic anhydride, itaconic anhydride, or the like is used.

The rate of addition of maleic anhydride is from 0.05 to
Good adhesion is obtained in the range of 0.5% by weight. These polyolefin adhesives are laminated by extrusion coating on the outer surface of a steel pipe coated with an epoxy primer layer using a T die or a round die. The thickness of the polyolefin adhesive is 80 to 4
When the thickness is about 00 μm, good adhesiveness can be obtained. Further, as the polyolefin, an ethylene homopolymer, or an ethylene-α-olefin copolymer obtained by copolymerizing ethylene and an α-olefin such as propylene, 1-butene, 1-hexene, or 1-octene, or a homopolymer thereof; A mixture obtained by mixing a pigment with the mixture is used.

The pigments include, for example, carbon black (black), phthalocyanine green (green), isoindolinone yellow (yellow), quinacridone red (red),
Commercially available organic pigments such as perinone red (red) and phthalocyanine blue (blue), titanium oxide (white), chromium oxide (green), iron oxide (yellow, red), titanium yellow (yellow),
A commercially available inorganic pigment such as cobalt oxide (blue, purple) or the like is appropriately selected and mixed to give a desired color.

These polyolefins are extrusion-coated and laminated on the outer surface of a steel pipe coated with a polyolefin adhesive layer by a T-die or a round die, and a two-layer T-die or a two-layer A method of extrusion coating from a round die can also be used. When the thickness of the polyolefin is about 1 to 10 mm, good corrosion resistance is obtained. Further, a chemical conversion coating such as chromate, phosphate, organic zirconium salt, organic titanium salt, zirconium salt, etc. may be interposed between the molten Sn plating layer and the epoxy primer layer. When performing the chemical conversion treatment, it is preferable to perform the degreasing after the plating surface is sufficiently degreased. As a chemical solution used for degreasing, a volatile organic solvent or a commercially available product for exclusive use can be used, and a chemical conversion treatment method is preferably performed by an immersion method, a spray method, or another appropriate method.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on embodiments. A steel pipe having an outer diameter of 20 A, a thickness of 2.8 mm and a length of 600 mm degreased with a commercially available alkaline degreasing agent is immersed in 15% hydrochloric acid at 40 ° C. for 25 minutes and pickled, then ZnCl ₂ , NH ₄
Cl, NaCl, and SnCl ₂ were immersed in an aqueous treatment liquid in which 150 g, 50 g, 38 g, and 12 g were mixed per liter of water, respectively. The temperature of the treatment liquid was 50 ° C., and the immersion time was 5 minutes. After immersion, it was left to dry in an oven set at 180 ° C. for 6 minutes. Next, the bath temperature was raised to 260 ° C.
Was dipped in a hot-dip Sn plating bath set for 1 minute to perform hot-dip Sn plating. Molten Sn
The amount of plating was controlled by adjusting the pulling speed of the steel pipe from the molten Sn plating bath.

On the other hand, an organic synthetic resin paint was prepared as follows. First, 5% by weight of fumed silica as an extender is mixed with a bifunctional epoxy resin having an average molecular weight of 380 and an epoxy equivalent of 190, and 50% by weight of toluene.
Diluted. Thereto, bis-aminopropyl-tetraoxa-spiro-undecane was added as a curing agent so that the weight ratio with the epoxy resin became 2.8 to 3.0: 1. This organic synthetic resin paint was applied to the outer surface of the hot-dip Sn-plated steel pipe by a spray method using a coating machine, and then kept in a drying oven at 230 ° C. for an arbitrary time. The thickness of the coating was about 10 μm.

An epoxy primer (100 parts by weight of diglycidyl ether of bisphenol A, 3,9-bis (3-aminopropyl) -2,4,8,10-tetraoxalate) was coated on the outer surface of the hot-dip Sn-coated steel pipe. A mixture of spiro (5,5) undecane butyl glycidyl ether adduct 50 parts by weight and titanium oxide 20 parts by weight) is applied with a brush, and the molten Sn-plated steel pipe is heated to 200 ° C. by high frequency induction heating to obtain an epoxy primer layer. Was formed. The thickness of the epoxy primer was 50 μm.

Immediately thereafter, the polyethylene adhesive and polyethylene were extruded and coated from a double-layer round die in two layers.
The thicknesses of this polyethylene adhesive and polyethylene were 200 μm and 3 mm, respectively. Dropping sand impact using these molten Sn-plated steel pipes, steel pipes coated with an organic synthetic resin paint on the molten Sn-plated layer, and steel pipes coated on the molten Sn-plated layer with epoxy primer, polyethylene adhesive and polyethylene in order. Test (ASTM G 13
After that, a salt water spray test (according to JIS Z 2371) was performed to determine the time until rust was generated. Table 1 shows the results.

[0027]

[Table 1]

[0028] From Table 1, if the adhesion amount of the molten Sn plating 100 g / m ² or more, less susceptible to mechanical damage, has good corrosion resistance, the adhesion amount of the molten Sn plating 100 g / m ² , The corrosion resistance was found to be significantly reduced. Further, from Table 1, it can be seen that when the amount of the molten Sn plating adhered is 600 g / m ² or less, the appearance is good, but when it exceeds 600 g / m ² , fine unevenness occurs on the surface of the molten Sn plating or the gloss decreases. It was found that the smoothness was impaired. In addition, from Table 1, the melting S
It has been found that a steel pipe having an n-plated layer coated with an organic synthetic resin paint and a steel pipe having a molten Sn-plated layer coated with an epoxy primer, a polyethylene adhesive and polyethylene in this order have better corrosion resistance.

[0029]

By using the present invention, it is possible to use
It is possible to provide a hot-water supply / hot water supply hot-dip Sn-plated steel pipe that is hardly damaged by mechanical damage such as flaws in a construction environment of a hot water supply pipe or a used buried environment and has excellent corrosion resistance.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B32B 15/18 B32B 15/18 4K044 C23C 2/38 C23C 2/38 28/00 28/00 A F16L 58 / 08 F16L 58/08 (72) Inventor Yasuhiro Sueuchi 1 Kimitsu, Kimitsu-shi, Chiba F-term in Kimitsu Works of Nippon Steel Corporation (Reference) 3H024 AB07 EA01 EA02 EC04 EC11 ED04 ED05 ED08 EE02 3H111 AA01 BA02 CB05 CB08 CC12 CC13 DA08 DB03 4D075 AE03 BB87X CA13 CA33 DA15 DA20 DB01 DC05 EA41 EB13 EB15 EB22 EB33 EB38 4F100 AB03A AB21B AB21E AK01C AK01E AK03D07 AK03E AK53C AK53E BA02 BA03 E10 BA10 BA10 BA07 BA10 BA07 BA10 BA07 BA10 BA07 BA10 BA07 AB06 AB46 AC02 4K044 AA02 AB03 BA10 BA21 BB03 BB04 BC02 CA04 CA11 CA53

Claims (3)

[Claims] 1. A coating of a hot-dip Sn plating layer on the inner surface and / or outer surface of a steel pipe in an amount of 100 to 600 g / Sn in terms of Sn.
A hot-dip Sn-coated steel pipe for water supply and hot water supply, characterized by having m ² . 2. The hot-dip hot-dip galvanized steel pipe according to claim 1, further comprising an organic synthetic resin coating film on the hot-dip Sn plating layer. 3. The hot-dip hot-dip steel pipe for water supply and hot water supply according to claim 1, wherein an epoxy primer layer, a polyolefin adhesive layer, and a polyolefin layer are sequentially laminated on the hot-dip Sn plating layer.