JP6399056B2 - Polyethylene-coated steel pipe and method for producing the same - Google Patents
Polyethylene-coated steel pipe and method for producing the same Download PDFInfo
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- JP6399056B2 JP6399056B2 JP2016150647A JP2016150647A JP6399056B2 JP 6399056 B2 JP6399056 B2 JP 6399056B2 JP 2016150647 A JP2016150647 A JP 2016150647A JP 2016150647 A JP2016150647 A JP 2016150647A JP 6399056 B2 JP6399056 B2 JP 6399056B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 117
- 239000010959 steel Substances 0.000 title claims description 117
- -1 Polyethylene Polymers 0.000 title claims description 99
- 239000004698 Polyethylene Substances 0.000 title claims description 98
- 229920000573 polyethylene Polymers 0.000 title claims description 98
- 238000004519 manufacturing process Methods 0.000 title claims description 10
- 239000011247 coating layer Substances 0.000 claims description 43
- 239000000428 dust Substances 0.000 claims description 25
- 239000006087 Silane Coupling Agent Substances 0.000 claims description 21
- 238000010438 heat treatment Methods 0.000 claims description 20
- 239000010410 layer Substances 0.000 claims description 19
- ZCDOYSPFYFSLEW-UHFFFAOYSA-N chromate(2-) Chemical compound [O-][Cr]([O-])(=O)=O ZCDOYSPFYFSLEW-UHFFFAOYSA-N 0.000 claims description 17
- 238000000034 method Methods 0.000 claims description 16
- 239000000853 adhesive Substances 0.000 claims description 14
- 230000001070 adhesive effect Effects 0.000 claims description 14
- 230000007547 defect Effects 0.000 claims description 12
- 239000011248 coating agent Substances 0.000 claims description 8
- 238000000576 coating method Methods 0.000 claims description 8
- 239000002335 surface treatment layer Substances 0.000 claims description 7
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 4
- 238000001035 drying Methods 0.000 claims description 4
- 238000005422 blasting Methods 0.000 claims description 3
- 238000010191 image analysis Methods 0.000 claims description 3
- 239000007864 aqueous solution Substances 0.000 claims description 2
- 239000011780 sodium chloride Substances 0.000 claims description 2
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 description 11
- 238000005259 measurement Methods 0.000 description 9
- 230000007797 corrosion Effects 0.000 description 8
- 238000005260 corrosion Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 8
- 239000007788 liquid Substances 0.000 description 7
- 229920000298 Cellophane Polymers 0.000 description 6
- 239000004593 Epoxy Substances 0.000 description 6
- 239000002390 adhesive tape Substances 0.000 description 6
- 230000006698 induction Effects 0.000 description 5
- 229920013716 polyethylene resin Polymers 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 125000003700 epoxy group Chemical group 0.000 description 4
- 239000011347 resin Substances 0.000 description 4
- 229920005989 resin Polymers 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 3
- 238000004210 cathodic protection Methods 0.000 description 3
- 230000007613 environmental effect Effects 0.000 description 3
- 238000005507 spraying Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- BPSIOYPQMFLKFR-UHFFFAOYSA-N trimethoxy-[3-(oxiran-2-ylmethoxy)propyl]silane Chemical compound CO[Si](OC)(OC)CCCOCC1CO1 BPSIOYPQMFLKFR-UHFFFAOYSA-N 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 125000003277 amino group Chemical group 0.000 description 2
- 238000007664 blowing Methods 0.000 description 2
- 239000010408 film Substances 0.000 description 2
- 229920001903 high density polyethylene Polymers 0.000 description 2
- 239000004700 high-density polyethylene Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 229920003023 plastic Polymers 0.000 description 2
- 239000004033 plastic Substances 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 229920000098 polyolefin Polymers 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000004381 surface treatment Methods 0.000 description 2
- 125000003396 thiol group Chemical group [H]S* 0.000 description 2
- WYTZZXDRDKSJID-UHFFFAOYSA-N (3-aminopropyl)triethoxysilane Chemical compound CCO[Si](OCC)(OCC)CCCN WYTZZXDRDKSJID-UHFFFAOYSA-N 0.000 description 1
- IKYAJDOSWUATPI-UHFFFAOYSA-N 3-[dimethoxy(methyl)silyl]propane-1-thiol Chemical compound CO[Si](C)(OC)CCCS IKYAJDOSWUATPI-UHFFFAOYSA-N 0.000 description 1
- SJECZPVISLOESU-UHFFFAOYSA-N 3-trimethoxysilylpropan-1-amine Chemical compound CO[Si](OC)(OC)CCCN SJECZPVISLOESU-UHFFFAOYSA-N 0.000 description 1
- UUEWCQRISZBELL-UHFFFAOYSA-N 3-trimethoxysilylpropane-1-thiol Chemical compound CO[Si](OC)(OC)CCCS UUEWCQRISZBELL-UHFFFAOYSA-N 0.000 description 1
- 239000006096 absorbing agent Substances 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N acrylic acid group Chemical group C(C=C)(=O)O NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 239000012790 adhesive layer Substances 0.000 description 1
- 239000003963 antioxidant agent Substances 0.000 description 1
- 239000002216 antistatic agent Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000003086 colorant Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000006482 condensation reaction Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000032798 delamination Effects 0.000 description 1
- ZBCBWPMODOFKDW-UHFFFAOYSA-N diethanolamine Chemical class OCCNCCO ZBCBWPMODOFKDW-UHFFFAOYSA-N 0.000 description 1
- OTARVPUIYXHRRB-UHFFFAOYSA-N diethoxy-methyl-[3-(oxiran-2-ylmethoxy)propyl]silane Chemical compound CCO[Si](C)(OCC)CCCOCC1CO1 OTARVPUIYXHRRB-UHFFFAOYSA-N 0.000 description 1
- PKTOVQRKCNPVKY-UHFFFAOYSA-N dimethoxy(methyl)silicon Chemical compound CO[Si](C)OC PKTOVQRKCNPVKY-UHFFFAOYSA-N 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000007765 extrusion coating Methods 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 239000003063 flame retardant Substances 0.000 description 1
- 239000012634 fragment Substances 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 1
- 239000004850 liquid epoxy resins (LERs) Substances 0.000 description 1
- 239000000314 lubricant Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000000049 pigment Substances 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000003566 sealing material Substances 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- JXUKBNICSRJFAP-UHFFFAOYSA-N triethoxy-[3-(oxiran-2-ylmethoxy)propyl]silane Chemical compound CCO[Si](OCC)(OCC)CCCOCC1CO1 JXUKBNICSRJFAP-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Rigid Pipes And Flexible Pipes (AREA)
- Laminated Bodies (AREA)
- Other Surface Treatments For Metallic Materials (AREA)
Description
本発明は、ポリエチレン被覆層の密着性に優れたポリエチレン被覆鋼管およびその製造方法に関する。また、本発明は、ガス管、水道管、ケーブル保護管、ラインパイプ等に用いられる外面ポリエチレン被覆鋼管に関する。 The present invention relates to a polyethylene-coated steel pipe excellent in adhesion of a polyethylene coating layer and a method for producing the same. The present invention also relates to an outer polyethylene-coated steel pipe used for gas pipes, water pipes, cable protection pipes, line pipes and the like.
鋼管表面に防食層としてポリエチレン被覆層を被覆したポリエチレン被覆鋼管は、防食性に優れ各種配管に利用されている。ポリエチレン被覆鋼管は特に海底や地下への埋設用途が増大しており、その場合、電気防食が併用されることが多い。電気防食の効果によってポリエチレン被覆鋼管の鋼管は防食されるが、一方でポリエチレン被覆層が鋼管外表面から剥離しやすくなる問題があり、この問題は陰極剥離として知られている。 A polyethylene-coated steel pipe having a steel pipe surface coated with a polyethylene coating layer as an anticorrosion layer has excellent anticorrosion properties and is used for various pipes. Polyethylene-coated steel pipes are increasingly used for embedment in the seabed and underground, and in that case, anticorrosion is often used in combination. Although the steel pipe of the polyethylene-coated steel pipe is anticorrosive due to the effect of cathodic protection, there is a problem that the polyethylene coating layer tends to peel from the outer surface of the steel pipe, and this problem is known as cathodic peeling.
このような陰極剥離を抑制する方法として、クロメート処理が有効であることが知られている。例えば、特許文献１には、鋼材表面にクロメート層を有するクロメート被覆鋼材であって、エポキシプライマー層、無水マレイン酸変性ポリオレフィン層及びポリオレフィン層を順次積層した樹脂被覆重防食鋼材が開示されている。また、特許文献２には、鋼材の表面に特定のエポキシプライマーを適用するとともに、下地処理としてクロメート処理を施すことが示されている。 It is known that chromate treatment is effective as a method for suppressing such cathode peeling. For example, Patent Document 1 discloses a resin-coated heavy-duty anticorrosive steel material that is a chromate-coated steel material having a chromate layer on the surface of the steel material, in which an epoxy primer layer, a maleic anhydride-modified polyolefin layer, and a polyolefin layer are sequentially laminated. Patent Document 2 discloses that a specific epoxy primer is applied to the surface of a steel material and that chromate treatment is performed as a base treatment.
また、近年では環境負荷の観点からクロメート処理を施さない、すなわち、ノンクロメート処理を施した耐食性に優れた有機被覆鋼材が望まれている。特許文献３には、ノンクロメート処理を施した耐食性に優れた有機被覆鋼板が示されている。 In recent years, there has been a demand for an organic coated steel material excellent in corrosion resistance that is not subjected to chromate treatment, that is, subjected to non-chromate treatment, from the viewpoint of environmental load. Patent Document 3 discloses an organic coated steel sheet that is non-chromated and has excellent corrosion resistance.
特許文献１、２の方法では、鋼管を被覆する場合は環境負荷の高いクロメート処理を必要とする問題がある。特許文献３の方法はめっき鋼板を処理して耐食性を向上させるものであり、また、陰極剥離を抑制するものでもないという問題がある。 In the methods of Patent Documents 1 and 2, there is a problem that a chromate treatment with a high environmental load is required when coating a steel pipe. The method of Patent Document 3 has a problem that the plated steel sheet is treated to improve the corrosion resistance and does not suppress the cathode peeling.
したがって本発明の目的は、以上のような従来技術の課題を解決し、ポリエチレン被覆層の耐陰極剥離性に優れるとともに、クロメート処理を施すことなく製造することができるポリエチレン被覆鋼管を提供することにある。 Accordingly, an object of the present invention is to provide a polyethylene-coated steel pipe that solves the problems of the prior art as described above, is excellent in the cathode peel resistance of the polyethylene coating layer, and can be manufactured without performing chromate treatment. is there.
本発明者らは、上記課題を解決するために鋭意研究を重ね、鋼管外表面とポリエチレン被覆層の間に存在する粉じん量が陰極剥離に影響することを突き止めた。そこで、複数の鋼管外表面の粉じん付着状態のポリエチレン被覆鋼管を製造し、その耐陰極剥離性との関係の検討を行って、本発明を完成させた。 The inventors of the present invention have made extensive studies to solve the above-mentioned problems, and have found that the amount of dust existing between the outer surface of the steel pipe and the polyethylene coating layer affects the cathode peeling. Thus, a plurality of dust-coated polyethylene-coated steel pipes on the outer surface of the steel pipe were manufactured, and the relationship with the cathode peeling resistance was examined to complete the present invention.
本発明の要旨は以下のとおりである。 The gist of the present invention is as follows.
［１］鋼管外表面にポリエチレン被覆層を有するポリエチレン被覆鋼管であって、前記鋼管外表面と前記ポリエチレン被覆層間に含まれる粉じん量が、剥離したポリエチレン被覆層の鋼管外表面に接していた面をＸＰＳで測定したＦｅの表面元素割合が１．０％以下となる量である、ポリエチレン被覆鋼管。 [1] A polyethylene coated steel pipe having a polyethylene coating layer on the outer surface of the steel pipe, wherein the amount of dust contained between the outer surface of the steel pipe and the polyethylene coating layer is in contact with the outer surface of the peeled polyethylene coating layer. A polyethylene-coated steel pipe in which the Fe surface element ratio measured by XPS is 1.0% or less.
［２］電気防食とともに使用される、［１］に記載のポリエチレン被覆鋼管。 [2] The polyethylene-coated steel pipe according to [1], which is used together with cathodic protection.
［３］海底または地下への埋設用である、［１］または［２］に記載のポリエチレン被覆鋼管。 [3] The polyethylene-coated steel pipe according to [1] or [2], which is for embedding in the seabed or underground.
［４］ブラスト処理後、ＪＩＳ Ｚ０３１３（２００４）に規定された方法で粘着媒体に鋼管外表面の粉じんを付着させ、その粘着媒体を白色紙に貼り付け、画像解析により、２５６階調での輝度を測定し、その平均値が２２０以上である鋼管に、ポリエチレン被覆をする、ポリエチレン被覆鋼管の製造方法。 [4] After the blast treatment, dust on the outer surface of the steel pipe is adhered to the adhesive medium by the method specified in JIS Z0313 (2004), the adhesive medium is pasted on white paper, and the brightness at 256 gradations is determined by image analysis. A method for producing a polyethylene-coated steel pipe, in which a steel pipe having an average value of 220 or more is coated with polyethylene.
［５］前記輝度の平均値が２２０以上である鋼管の外表面にシランカップリング剤を塗布し、乾燥させる下地処理を行い、その後前記ポリエチレン被覆をする、［４］に記載のポリエチレン被覆鋼管の製造方法。 [5] The polyethylene-coated steel pipe according to [4], wherein the outer surface of the steel pipe having an average value of 220 or more is coated with a silane coupling agent and dried, and then coated with polyethylene. Production method.
［６］前記シランカップリング剤の乾燥を、赤外線加熱、誘導加熱、もしくは熱風加熱のいずれか、またはこれらの組み合わせにて行う、［５］に記載のポリエチレン被覆鋼管の製造方法。 [6] The method for producing a polyethylene-coated steel pipe according to [5], wherein the silane coupling agent is dried by any one of infrared heating, induction heating, hot air heating, or a combination thereof.
［７］前記シランカップリング剤の乾燥を、赤外線加熱にて行う、［６］に記載のポリエチレン被覆鋼管の製造方法。 [7] The method for producing a polyethylene-coated steel pipe according to [6], wherein the silane coupling agent is dried by infrared heating.
なお、本発明において、ポリエチレン被覆層の密着性に優れたとは、後述の実施例に記載の試験において、陰極剥離距離の平均値が２０ｍｍ以下であることを意味する。 In the present invention, the excellent adhesion of the polyethylene coating layer means that the average value of the cathode peeling distance is 20 mm or less in the test described in the examples described later.
本発明のポリエチレン被覆鋼管は、電気防食が併用された場合において、ポリエチレン被覆層の陰極剥離が効果的に抑制され、優れた防食性を発揮する。このように本発明のポリエチレン被覆鋼管は、優れた耐陰極剥離性を有するため、特に海底や地下への埋設用途に好適である。 In the polyethylene-coated steel pipe of the present invention, when the anticorrosion is used in combination, the cathode peeling of the polyethylene coating layer is effectively suppressed, and excellent anticorrosion properties are exhibited. Thus, since the polyethylene-coated steel pipe of the present invention has excellent cathode peeling resistance, it is particularly suitable for embedding in the seabed or underground.
以下本発明の構成を説明する。本発明のポリエチレン被覆鋼管は、優れた耐陰極剥離性を発揮するため、鋼管外表面の粉じん量の規定が必要となる。該粉じんはＦｅを主成分とし、通常、ブラスト処理粒子の破片、ブラスト処理によって剥離した鋼管の破片、鋼管外表面に残存したスケール等を含んでいることが多い。 The configuration of the present invention will be described below. Since the polyethylene-coated steel pipe of the present invention exhibits excellent cathode peeling resistance, it is necessary to define the amount of dust on the outer surface of the steel pipe. The dust is mainly composed of Fe, and usually contains blast-treated particles, steel pipe fragments peeled off by blasting, and scales remaining on the outer surface of the steel pipe.
１．鋼管外表面に付着した粉じん量について
陰極剥離は鋼管外表面とポリエチレン被覆層間で生じる。鋼管外表面にブラスト処理等で付着した粉じんが多量に付着していると、その部分で鋼管外表面とポリエチレン被覆層の密着が十分なされないため、陰極剥離が生じやすくなる。そのため、以下のように鋼管外表面の粉じん付着量を制御することにより、優れた耐陰極剥離性を発揮する。
1. Cathodic delamination occurs between the outer surface of the steel pipe and the polyethylene coating layer with respect to the amount of dust adhering to the outer surface of the steel pipe. If a large amount of dust adhered by blasting or the like adheres to the outer surface of the steel pipe, the outer surface of the steel pipe and the polyethylene coating layer are not sufficiently adhered to each other, so that the cathode is easily peeled off. Therefore, excellent cathode peeling resistance is exhibited by controlling the amount of dust adhering to the outer surface of the steel pipe as follows.
例えば、ポリエチレン被覆鋼管のポリエチレン被覆層を強制剥離し、剥離した被覆層の鋼管外表面に接していた面をＸＰＳ（Ｘ線光電子分光分析）により分析し、Ｆｅの表面元素割合が１．０％以下であることとする。後述の製造方法において記載のとおり、例えば鋼管外表面のエアブロー等により鋼管外表面に付着した粉じん量を低減できる。ポリエチレン被覆層を強制剥離する方法は、特に限定されるものではないが、例えばポリエチレン被覆鋼管の一部２０ｍｍ×５０ｍｍほどを切り出し測定用片とし、測定用片を液体窒素中に浸漬した後、取り出してポリエチレン被覆層をプラスチックハンマーで叩くなどすると、ポリエチレン被覆層が鋼管外表面から剥離する。剥離したポリエチレン被覆層の鋼管外表面に接していた面１０ｍｍ×１０ｍｍを以下の条件でＸＰＳにより分析する。Ｆｅの表面元素割合を１．０％以下とすることでポリエチレン被覆層と鋼管外表面との密着性が向上し、陰極剥離が発生し難くなる。Ｆｅの表面元素割合が１．０％を超える場合、ポリエチレン被覆層と鋼管外表面との密着性が低下し、陰極剥離が発生し易くなる。Ｆｅの表面元素割合は好ましくは０．５％以下、さらに好ましくは０．３％以下である。 For example, the polyethylene coating layer of a polyethylene coated steel pipe is forcibly peeled, and the surface of the peeled coating layer that is in contact with the outer surface of the steel pipe is analyzed by XPS (X-ray photoelectron spectroscopy). It shall be as follows. As described in the manufacturing method described later, the amount of dust attached to the outer surface of the steel pipe can be reduced by, for example, air blowing on the outer surface of the steel pipe. The method for forcibly peeling the polyethylene coating layer is not particularly limited. For example, a part of a polyethylene-coated steel pipe having a size of about 20 mm × 50 mm is cut out and used as a measurement piece, and the measurement piece is immersed in liquid nitrogen and taken out. When the polyethylene coating layer is hit with a plastic hammer, the polyethylene coating layer is peeled off from the outer surface of the steel pipe. The 10 mm × 10 mm surface of the peeled polyethylene coating layer in contact with the outer surface of the steel pipe is analyzed by XPS under the following conditions. By making the surface element ratio of Fe 1.0% or less, the adhesion between the polyethylene coating layer and the outer surface of the steel pipe is improved, and the cathode peeling is less likely to occur. When the surface element ratio of Fe exceeds 1.0%, the adhesion between the polyethylene coating layer and the outer surface of the steel pipe is lowered, and the cathode peeling tends to occur. The surface element ratio of Fe is preferably 0.5% or less, more preferably 0.3% or less.
−ＸＰＳ分析条件−
（１）ＸＰＳの分析条件は、光電子脱出角度を４５度として、測定範囲を約５ｍｍ×５ｍｍの範囲とし、光電子エネルギーを０〜１１００ｅＶの範囲でスキャンすることで存在元素情報を得ることが出来る。（２）得られた全元素ピーク強度に対するＦｅのピーク強度の比からＦｅ元素割合を求めることができる。
-XPS analysis conditions-
(1) The XPS analysis conditions are such that the photoelectron escape angle is 45 degrees, the measurement range is about 5 mm × 5 mm, and the photoelectron energy is scanned in the range of 0 to 1100 eV to obtain the existing element information. (2) The ratio of Fe element can be obtained from the ratio of the peak intensity of Fe to the total peak intensity of all elements obtained.
２．鋼管について
本発明で用いられる母材鋼管の種類や寸法などに特に制限はなく、鋼管の種類としては、例えば、電縫鋼管、スパイラル鋼管、ＵＯＥ鋼管、プレスベンド鋼管等が挙げられるが、これらに限定されるものではない。強度や経済性の面から母材鋼管は電縫鋼管が好ましい。
2. There are no particular restrictions on the type and dimensions of the base steel pipe used in the present invention for the steel pipe, and examples of the type of steel pipe include an electric-welded steel pipe, a spiral steel pipe, a UOE steel pipe, and a press-bend steel pipe. It is not limited. The base steel pipe is preferably an electric resistance steel pipe from the viewpoint of strength and economy.
３．ポリエチレン被覆について
ポリエチレン被覆には一般的な材料を用いることができる。ポリエチレン被覆層は鋼管外表面に接する側から順にプライマー層、接着性ポリエチレン層、ポリエチレン層を形成することで作製できる。なお、ポリエチレン被覆層は後述のシランカップリング剤を使用して形成した表面処理層を更に含んでもよい。本発明のポリエチレン被覆層は、クロメート処理により形成した表面処理層を含まない。
3. Regarding the polyethylene coating, common materials can be used for the polyethylene coating. The polyethylene coating layer can be produced by forming a primer layer, an adhesive polyethylene layer, and a polyethylene layer in this order from the side in contact with the outer surface of the steel pipe. The polyethylene coating layer may further include a surface treatment layer formed using a silane coupling agent described later. The polyethylene coating layer of the present invention does not include a surface treatment layer formed by chromate treatment.
プライマー層を形成するためのプライマーとして例えば、エポキシプライマー(ＪＩＳ Ｇ３４７７−１：２０１２)等を用いることができる。 As a primer for forming the primer layer, for example, an epoxy primer (JIS G3477-1: 2012) can be used.
接着性ポリエチレン層を形成するための接着性ポリエチレン樹脂としては、例えば無水マレイン酸変性ポリエチレン、不飽和カルボン酸変性ポリエチレン等を用いることができる。 Examples of the adhesive polyethylene resin for forming the adhesive polyethylene layer include maleic anhydride-modified polyethylene and unsaturated carboxylic acid-modified polyethylene.
ポリエチレン層を形成するためのポリエチレン樹脂としては低密度、中密度、高密度のいずれを用いてもよいが、特に高密度ポリエチレン樹脂（０．９４〜０．９７ｇ／ｃｍ３）が防食性の観点から望ましい。ポリエチレン樹脂には、必要に応じて酸化防止剤、紫外線吸収剤、難燃剤、顔料、充填剤、滑剤、帯電防止剤、着色剤等の添加剤を加えることができる。 As the polyethylene resin for forming the polyethylene layer, any of low density, medium density, and high density may be used, and in particular, high density polyethylene resin (0.94 to 0.97 g / cm 3 ) is a viewpoint of corrosion resistance. Desirable from. If necessary, additives such as antioxidants, ultraviolet absorbers, flame retardants, pigments, fillers, lubricants, antistatic agents, and colorants can be added to the polyethylene resin.
ポリエチレン被覆層は厚さ１ｍｍ〜５ｍｍ程度が防食性と経済性の面から好ましい。防食性の面から、さらに好ましい下限は２．５ｍｍである。 The polyethylene coating layer preferably has a thickness of about 1 mm to 5 mm from the viewpoint of corrosion resistance and economy. From the standpoint of corrosion resistance, a more preferred lower limit is 2.5 mm.
４．製造方法について
以下に本発明のポリエチレン被覆鋼管の製造方法について説明する。まず、鋼管外表面をブラスト処理する。その後エアブロー等で鋼管外表面の粉じんを除去する。次いでエアブロー後の鋼管外表面における粉じんを、ＪＩＳ Ｚ０３１３（２００４）に規定された方法で粘着媒体であるセロハン粘着テープ（ＪＩＳ Ｚ１５２２：２００９）に付着させ、その粘着媒体を白色紙に貼り付け、画像解析により、２５６階調での輝度を測定し、その平均値が２２０以上であることを確認する。また、あらかじめ、輝度が２２０以上であることを確認した見本サンプルと比較し、粉じんの除去状況を確認しても良い。上記粘着媒体は、粘着力１．８Ｎ／１０ｍｍ以上の粘着層を有する透明の薄膜である。
4). About a manufacturing method The manufacturing method of the polyethylene covering steel pipe of this invention is demonstrated below. First, the outer surface of the steel pipe is blasted. Thereafter, dust on the outer surface of the steel pipe is removed by air blow or the like. Next, the dust on the outer surface of the steel pipe after air blowing is attached to the cellophane adhesive tape (JIS Z1522: 2009), which is an adhesive medium, by the method specified in JIS Z0313 (2004), and the adhesive medium is attached to white paper, and the image By analysis, luminance at 256 gradations is measured, and it is confirmed that the average value is 220 or more. Further, the dust removal status may be confirmed by comparing with a sample sample that has been confirmed to have a luminance of 220 or more in advance. The adhesive medium is a transparent thin film having an adhesive layer having an adhesive strength of 1.8 N / 10 mm or more.
上記白色紙は、白色度９０％〜９５％である（後述の実施例では白色普通紙とも称する）。使用可能の白色紙として、例えば、ＪＩＳ Ｐ０００１：１９９８ に示されるＰＰＣ用紙やインクジェット用紙等がある。 The white paper has a whiteness of 90% to 95% (also referred to as white plain paper in the examples described later). Usable white paper includes, for example, PPC paper and inkjet paper shown in JIS P0001: 1998.
輝度の測定は２５６階調でおこなう。より具体的には、輝度の測定は、例えば複合機などを用い白色紙上に貼り付けたセロハン粘着テープをスキャンし、Ａｄｏｂｅ社製画像解析ソフトＰｈｏｔｏｓｈｏｐＣＳ６を用いて、セロハン粘着テープ画像の任意の位置を指定し、その範囲輝度の平均値を測定することができる。 The luminance is measured with 256 gradations. More specifically, the brightness is measured by, for example, scanning a cellophane adhesive tape affixed on white paper using a multifunction machine or the like, and using Adobe image analysis software Photoshop CS6 to locate an arbitrary position of the cellophane adhesive tape image. The average value of the range luminance can be measured.
画像解析のサイズは特に限定されないが、簡便さの観点から２０ｍｍ×２０ｍｍとすることが好ましい。また、輝度の平均値を求めるにあたり、測定回数は２以上とする。測定回数は、好ましくは、２〜５である。 The size of the image analysis is not particularly limited, but is preferably 20 mm × 20 mm from the viewpoint of simplicity. Further, in obtaining the average value of luminance, the number of measurements is 2 or more. The number of measurements is preferably 2-5.
粉じんの付着量が多い場合、輝度の平均値は低くなる。輝度の平均値が２２０以上となる粉じんの少ない状態でポリエチレン被覆を行うと、鋼管外表面とポリエチレン被覆層の密着性が向上し、陰極剥離が発生し難くなる。輝度の平均値が２２０未満の場合、ポリエチレン被覆層と鋼管外表面との密着性が低下し、陰極剥離が発生し易くなる。輝度の平均値は好ましくは２３０以上、さらに好ましくは２４０以上である。 When the amount of dust attached is large, the average value of luminance is low. When polyethylene coating is performed in a state where the average value of luminance is 220 or less and the amount of dust is small, the adhesion between the outer surface of the steel pipe and the polyethylene coating layer is improved, and the cathode peeling hardly occurs. When the average value of the luminance is less than 220, the adhesion between the polyethylene coating layer and the outer surface of the steel pipe is lowered, and cathode peeling is likely to occur. The average value of luminance is preferably 230 or more, and more preferably 240 or more.
ポリエチレン被覆層の形成方法は特に限定されない。例えば、外表面の粉じんが除去された鋼管にエポキシプライマーを塗布し、所定温度（例えば１３０〜１７０℃）まで誘導加熱装置、熱風炉等で加熱し、更に外側に極性を有する接着性ポリエチレン層と、ポリエチレン層を順次、丸ダイス、Ｔダイス等より押出し被覆層を形成後、冷却するといった方法がある。また、外表面の粉じんが除去された鋼管にエポキシプライマーを塗布、加熱後、接着性ポリエチレン層とポリエチレン層を同時に丸ダイス、Ｔダイス等より押出し被覆するといった方法等も挙げられる。この場合、２層の被覆層が一度に形成されることになる。特に、この場合はポリエチレン被覆鋼管とした後のポリエチレン被覆層の接着性が優れたものになる。ポリエチレン被覆層は厚さ１ｍｍ〜５ｍｍ程度が防食性と経済性の面から好ましい。防食性の面から、さらに好ましい下限は２．５ｍｍである。 The method for forming the polyethylene coating layer is not particularly limited. For example, an epoxy primer is applied to a steel pipe from which dust on the outer surface has been removed, heated to a predetermined temperature (for example, 130 to 170 ° C.) with an induction heating device, a hot air furnace, etc., and an adhesive polyethylene layer having polarity on the outside There is a method in which a polyethylene layer is sequentially extruded from a round die, a T die, or the like, and a coating layer is formed, followed by cooling. In addition, there may be mentioned a method in which an epoxy primer is applied to a steel pipe from which dust on the outer surface has been removed, and after heating, the adhesive polyethylene layer and the polyethylene layer are simultaneously extruded and coated with a round die, a T die or the like. In this case, two coating layers are formed at a time. In particular, in this case, the adhesiveness of the polyethylene coating layer after forming the polyethylene-coated steel pipe is excellent. The polyethylene coating layer preferably has a thickness of about 1 mm to 5 mm from the viewpoint of corrosion resistance and economy. From the standpoint of corrosion resistance, a more preferred lower limit is 2.5 mm.
さらに、耐陰極剥離性を向上させるため、鋼管を加熱後、上記ポリエチレン被覆層を形成するための樹脂を被覆する前に、０．５〜２質量％程度に希釈したシランカップリング剤をスプレー等で塗布し、乾燥させて表面処理層を形成しても良い。シランカップリング剤は特に限定されるものではないが、エポキシ基、メルカプト基、アミノ基などの官能基をもつものを用いることができる。エポキシ基をもつシランカップリング剤としては、例えば、３−グリシドキシプロピルトリメトキシシラン、３−グリシドキシプロピルメチルジエトキシシラン、３−グリシドキシプロピルトリエトキシシラン、３−グリシドキシプロピルメチルジメトキシシランなどがある。メルカプト基をもつシランカップリング剤としては、例えば、３−メルカプトプロピルメチルジメトキシシラン、３−メルカプトプロピルトリメトキシシランなどがある。アミノ基をもつシランカップリング剤としては３−アミノプロピルトリメトキシシラン、３−アミノプロピルトリエトキシシランなどがある。シランカップリング剤の乾燥条件は、適宜選択可能である。 Furthermore, in order to improve the cathode peel resistance, a silane coupling agent diluted to about 0.5 to 2% by mass is sprayed after the steel tube is heated and before the resin for forming the polyethylene coating layer is coated. May be applied and dried to form a surface treatment layer. Although a silane coupling agent is not specifically limited, What has functional groups, such as an epoxy group, a mercapto group, and an amino group, can be used. Examples of the silane coupling agent having an epoxy group include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 3-glycidoxypropyl. Examples include methyldimethoxysilane. Examples of the silane coupling agent having a mercapto group include 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltrimethoxysilane. Examples of the silane coupling agent having an amino group include 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane. The drying conditions for the silane coupling agent can be selected as appropriate.
シランカップリング剤の乾燥には赤外線加熱、誘導加熱、熱風加熱、もしくはこれら組み合わせを用いることが出来る。シランカップリング剤は加熱乾燥されることにより、水分が除去されるとともに、鋼表面の水酸基などと縮合反応し、耐陰極剥離性を向上させる。
シランカップリング剤の乾燥を赤外線加熱で行った場合には、耐陰極剥離性が他の加熱方法を採用した場合に比べて向上する。よって、より良好な耐陰極剥離性を求められる用途には赤外線加熱を行うのが有利である。
For drying the silane coupling agent, infrared heating, induction heating, hot air heating, or a combination thereof can be used. When the silane coupling agent is dried by heating, moisture is removed and a condensation reaction with a hydroxyl group on the steel surface and the like improves the resistance to cathodic peeling.
When the silane coupling agent is dried by infrared heating, the resistance to cathodic stripping is improved compared to the case where other heating methods are employed. Therefore, it is advantageous to perform infrared heating for applications that require better cathode peel resistance.
以上のとおり、本発明のポリエチレン被覆鋼管は、電気防食とともに使用されることが好ましい。また、本発明のポリエチレン被覆鋼管は、海底や地下への埋設用途に好適である。本発明のポリエチレン被覆鋼管は、海底や地下へ埋設され、かつ、電気防食とともに使用されることがより好ましい。 As described above, it is preferable that the polyethylene-coated steel pipe of the present invention is used together with an anticorrosion. Moreover, the polyethylene-coated steel pipe of the present invention is suitable for use in the seabed or underground. It is more preferable that the polyethylene-coated steel pipe of the present invention is embedded in the seabed or underground and used together with cathodic protection.
以下に、本発明の実施例を説明する。本実施例では、以下の方法により、鋼管外表面における粉じん付着量が異なるＮｏ．１〜１５のポリエチレン被覆鋼管について試験した。なお、本発明の技術的範囲は以下の実施例に限定されない。 Examples of the present invention will be described below. In this example, the number of dust deposits on the outer surface of the steel pipe is different by the following method. 1-15 polyethylene coated steel tubes were tested. The technical scope of the present invention is not limited to the following examples.
（輝度測定）
ブラスト処理したＪＩＳ ＳＧＰ ４００Ａ鋼管について、エアブローで外表面に付着した粉じんを除去し、ＪＩＳ ＪＩＳ Ｚ０３１３（２００４）に規定された方法でセロハン粘着テープ（サイズ：２４ｍｍ×２００ｍｍ）に鋼管外表面の粉じんを付着させ、そのセロハン粘着テープを白色普通紙に貼り付けた。白色普通紙に貼り付けたテープはその後スキャナで電子データとし、画像解析ソフト（Ａｄｏｂｅ社製ＰｈｏｔｏｓｈｏｐＣＳ６）で上述の方法によりセロハン粘着テープの輝度を求めた。なお、鋼管１本につき３回輝度を測定し、その平均値を求めた。
(Brightness measurement)
Dust on the outer surface of the blasted JIS SGP 400A steel pipe is removed by air blow, and the dust on the outer surface of the steel pipe is applied to the cellophane adhesive tape (size: 24 mm x 200 mm) by the method specified in JIS JIS Z0313 (2004). The cellophane adhesive tape was attached to white plain paper. The tape affixed to the white plain paper was then converted into electronic data by a scanner, and the brightness of the cellophane adhesive tape was determined by the above-described method using image analysis software (Photoshop CS6 manufactured by Adobe). In addition, the brightness | luminance was measured 3 times per steel pipe, and the average value was calculated | required.
（ポリエチレン被覆）
上記エアブロー処理した鋼管外表面に、市販の液状エポキシ樹脂（三菱化学（株）製「基本液状タイプ８２８」）と硬化剤（三菱化学（株）製「変性脂肪族アミングレードＴ」）を混合したエポキシプライマーを膜厚が４０μｍとなるようにスプレー塗布し、誘導加熱により表面温度１５０℃まで加熱し硬化させた。
(Polyethylene coating)
A commercially available liquid epoxy resin (“Basic Liquid Type 828” manufactured by Mitsubishi Chemical Corporation) and a curing agent (“Modified Aliphatic Amine Grade T” manufactured by Mitsubishi Chemical Corporation) were mixed on the outer surface of the steel pipe subjected to the air blow treatment. The epoxy primer was applied by spraying so as to have a film thickness of 40 μm, and was cured by induction heating to a surface temperature of 150 ° C.
その後、市販の接着性ポリエチレン樹脂（三井化学（株）製「アドマーＮＥ０６５」）、ポリエチレン樹脂（プライムポリマー（株）製「ＨＩ−ＺＥＸ５１００Ｅ」、高密度ポリエチレン樹脂である）を押出被覆により被覆して、ポリエチレン被覆層の厚さが３ｍｍとなるポリエチレン被覆鋼管を作製した。 Thereafter, a commercially available adhesive polyethylene resin (“Admer NE065” manufactured by Mitsui Chemicals, Inc.), a polyethylene resin (“HI-ZEX5100E” manufactured by Prime Polymer Co., Ltd., which is a high density polyethylene resin) is coated by extrusion coating. A polyethylene-coated steel pipe having a polyethylene coating layer thickness of 3 mm was produced.
（表面処理層形成）
また、一部の鋼管には上記エアブロー処理した鋼管にシランカップリング剤として、エポキシ基をもつ３−グリシドキシプロピルトリメトキシシラン（信越化学工業（株）製「ＫＢＭ−４０３」）を用い、シランカップリング剤が１質量％となるように純水で希釈した処理液をスプレーで塗布し、その後赤外線加熱、誘導加熱、熱風加熱それぞれの装置により処理液が完全に乾燥するように加熱し、表面処理層を形成した後、上記のポリエチレン被覆を行った。表面処理層を有するものは、表１において、「表面処理液」欄に「エポキシシラン」と記載した。
(Surface treatment layer formation)
In addition, for some steel pipes, 3-glycidoxypropyltrimethoxysilane having an epoxy group (“KBM-403” manufactured by Shin-Etsu Chemical Co., Ltd.) having an epoxy group is used as a silane coupling agent for the above-described air blow-treated steel pipe. A treatment liquid diluted with pure water so that the silane coupling agent is 1% by mass is applied by spraying, and then heated so that the treatment liquid is completely dried by each apparatus of infrared heating, induction heating, and hot air heating, After forming the surface treatment layer, the above polyethylene coating was performed. Those having a surface treatment layer are described as “epoxysilane” in the “surface treatment liquid” column in Table 1.
（ＸＰＳ測定）
ポリエチレン被覆後鋼管の端部２０ｍｍ×５０ｍｍを切り出し測定用片とし、測定用片を液体窒素中に浸漬した後、取り出して被覆層をプラスチックハンマーで叩いてポリエチレン被覆層を鋼管外表面から剥離した。剥離したポリエチレン被覆層の鋼管外表面側１０ｍｍ×１０ｍｍを上述の方法によりＸＰＳ測定し、Ｆｅの表面元素割合を測定した。
(XPS measurement)
After the polyethylene coating, the end 20 mm × 50 mm of the steel pipe was cut out and used as a measurement piece. After the measurement piece was immersed in liquid nitrogen, it was taken out and hit with a plastic hammer to peel off the polyethylene coating layer from the outer surface of the steel pipe. XPS measurement was performed on the outer surface side 10 mm × 10 mm of the peeled polyethylene coating layer by the above-described method, and the surface element ratio of Fe was measured.
（参考例：Ｎｏ．１５）
参考例としてクロメート処理を施した鋼管を用いたポリエチレン被覆鋼管を作製した。上記のシランカップリング剤の代わりに、クロメート処理液（関西ペイント（株）製「コスマー１００」）を純水で１／５（質量％）に希釈したものを使用し、鋼管外表面にＣｒ換算付着量が３００ｍｇ／ｍ２となるようスプレー塗布し、鋼管表面到達温度が１００℃となるよう加熱乾燥させてクロメート層を形成した。それ以外は、他の実施例と同様とし、ポリエチレン被覆鋼管を作製した。Ｃｒ換算付着量は、クロメート層を形成したダミー板を作製し、所定面積のクロメート皮膜を１０％ＮａＯＨで剥離した後、剥離溶液中のＣｒ量を吸光光度法で測定し、これを元に１ｍ２当たりのＣｒ換算付着量を算出した。
(Reference example: No. 15)
As a reference example, a polyethylene-coated steel pipe using a steel pipe treated with chromate was prepared. Instead of the above silane coupling agent, a chromate treatment solution (“Cosmer 100” manufactured by Kansai Paint Co., Ltd.) diluted with pure water to 1/5 (mass%) is used, and Cr is converted to the outer surface of the steel pipe. The chromate layer was formed by spray-coating so that the adhesion amount was 300 mg / m 2 and heating and drying so that the steel tube surface temperature reached 100 ° C. Other than that was carried out similarly to the other Example, and produced the polyethylene covering steel pipe. The amount of Cr equivalent deposited is 1 m based on the measurement of the amount of Cr in the stripping solution by absorptiometry after a dummy plate with a chromate layer is prepared and the chromate film of a predetermined area is stripped with 10% NaOH. The amount of Cr equivalent adhesion per 2 was calculated.
（陰極剥離試験）
ポリエチレン被覆鋼管から適当な大きさの試験片を採取し、以下の方法で陰極剥離距離を測定し、耐陰極剥離性を評価した。試験片の中央部に直径６ｍｍφの円形の人工欠陥部を形成し、鋼管外表面を露出させた。人工欠陥部を中心にして直径７０ｍｍφのアクリル製の円筒をポリエチレン被覆層上に縦に設置してシール材でポリエチレン被覆層に固定し、円筒内部を３質量％ＮａＣｌ水溶液で満たし、セルを作成した。
(Cathode peeling test)
A test piece of an appropriate size was taken from the polyethylene-coated steel tube, and the cathode peeling distance was measured by the following method to evaluate the cathode peeling resistance. A circular artificial defect having a diameter of 6 mmφ was formed at the center of the test piece, and the outer surface of the steel pipe was exposed. An acrylic cylinder having a diameter of 70 mmφ centered on the artificial defect portion was vertically installed on the polyethylene coating layer, fixed to the polyethylene coating layer with a sealing material, and the inside of the cylinder was filled with a 3% by mass NaCl aqueous solution to form a cell. .
対極に白金を使用して人工欠陥部の鋼管の電位を−１.５Ｖ ｖｓＳＣＥにポテンシオスタットを使用して保持した。このまま６０℃の恒温槽内に試験片を静置し、２８日間電位を保持した。 Platinum was used as the counter electrode, and the potential of the steel pipe at the artificial defect portion was maintained at -1.5 V vs SCE using a potentiostat. The test piece was left still in a constant temperature bath at 60 ° C., and the potential was maintained for 28 days.
以上の試験により、試験片には陰極剥離が生じている。次いで、試験片を回収後、セルをはずし、人工欠陥部の周囲をたがねとカッターを使用して強制的に剥離した。人工欠陥部の周辺部はポリエチレン被覆層が鋼管外表面から剥離し、鋼管の表面が露出した。人工欠陥部を中心とした４方向（管軸方向を１２時方向として、１２時、３時、６時、９時方向)で人工欠陥部端部からのポリエチレン被覆層剥離部の距離を測定して、その平均値を陰極剥離距離（ｍｍ）とした。この陰極剥離距離は、値が小さいほど良好であり、「２０ｍｍ以下」を合格とした。合格であるポリエチレン被覆鋼管は、海底や地下への埋設用途に好適である。表１に試験結果を示す。 As a result of the above test, cathode peeling occurred on the test piece. Next, after collecting the test piece, the cell was removed, and the periphery of the artificial defect portion was forcibly separated using a chisel and a cutter. At the periphery of the artificial defect portion, the polyethylene coating layer was peeled off from the outer surface of the steel pipe, and the surface of the steel pipe was exposed. Measure the distance of the peeling part of the polyethylene coating layer from the edge of the artificial defect part in 4 directions centered on the artificial defect part (12 o'clock, 3 o'clock, 6 o'clock, 9 o'clock direction with the tube axis direction being 12 o'clock) The average value was defined as the cathode separation distance (mm). The smaller the value of the cathode peeling distance, the better, and “20 mm or less” was considered acceptable. The accepted polyethylene-coated steel pipe is suitable for embedment in the seabed or underground. Table 1 shows the test results.
本発明例Ｎｏ．４、７、１０では、陰極剥離距離が目標の２０ｍｍ以下を満足し、優れた耐陰極剥離性を示している。シランカップリング剤を有する処理液を赤外線加熱で乾燥させた発明例はいずれも陰極剥離距離が１１．５ｍｍを下回り、優れた耐陰極剥離性を精度良く実現した。 Invention Example No. In Nos. 4, 7, and 10, the cathode peeling distance satisfies the target of 20 mm or less, and exhibits excellent cathode peeling resistance. In all of the inventive examples in which the treatment liquid having a silane coupling agent was dried by infrared heating, the cathode peeling distance was less than 11.5 mm, and excellent cathode peeling resistance was accurately realized.
Ｎｏ．１１〜１４は比較例である。Ｎｏ．１１、１２は鋼管外表面粉じん付着量が多く、ＸＰＳ測定結果が１．０％を超え、輝度の平均値も２２０未満であり、陰極剥離距離は目標値を満足しない。Ｎｏ．１３、１４は表面処理としてシランカップリング剤を用いたが、鋼管外表面粉じん付着量が多く、ＸＰＳ測定結果が１．０％を超え、輝度の平均値も２２０未満であり、陰極剥離距離は目標値を満足しない。 No. 11 to 14 are comparative examples. No. Nos. 11 and 12 have a large amount of dust on the outer surface of the steel pipe, the XPS measurement result exceeds 1.0%, the average value of luminance is less than 220, and the cathode peeling distance does not satisfy the target value. No. 13 and 14 used a silane coupling agent as the surface treatment, but the amount of dust on the outer surface of the steel pipe was large, the XPS measurement result exceeded 1.0%, the average value of luminance was less than 220, and the cathode peeling distance was The target value is not satisfied.
Ｎｏ．１５は参考例のクロメート処理材である。クロメート処理材は鋼管外表面の粉じん付着量が多く、ＸＰＳ測定結果が１．０％を超えているが、陰極剥離距離は目標値を満足する。ただし、環境負荷が高いため、望ましくない。 No. Reference numeral 15 denotes a chromate treatment material of a reference example. The chromate treatment material has a large amount of dust on the outer surface of the steel pipe, and the XPS measurement result exceeds 1.0%, but the cathode separation distance satisfies the target value. However, it is not desirable because the environmental load is high.
Claims (4)
ただし、陰極剥離距離とは、ポリエチレン被覆鋼管から採取した試験片の中央部に円形の人工欠陥部を形成し、鋼管外表面を露出させ、３質量％ＮａＣｌ水溶液中で人工欠陥部の鋼管の電位を−１.５Ｖ ｖｓＳＣＥにポテンシオスタットを使用して保持し、このまま６０℃の恒温槽内に試験片を静置し、２８日間電位を保持した試験片を回収後、人工欠陥部を剥離し、人工欠陥部を中心とした４方向（管軸方向を１２時方向として、１２時、３時、６時、９時方向)で人工欠陥部端部からのポリエチレン被覆層剥離部の距離を測定し、その平均値をいう。 The surface of the polyethylene coated steel pipe having a polyethylene coating layer on the outer surface of the steel pipe, the amount of dust contained between the outer surface of the steel pipe and the polyethylene coating layer being in contact with the outer surface of the steel pipe of the peeled polyethylene coating layer is measured by XPS. the amount der surface element ratio of the Fe is 1.0% or less is, has a surface treatment layer of a silane coupling agent between the polyethylene-coated layer and the steel tube outer surface, cathodic disbondment distance 11. Polyethylene-coated steel pipe that is less than 5 mm and has no chromate layer .
However, the cathode peeling distance is the potential of the steel tube at the artificial defect portion in a 3% by mass NaCl aqueous solution, in which a circular artificial defect portion is formed at the center of the test piece taken from the polyethylene-coated steel tube, and the outer surface of the steel tube is exposed. -1.5V vs. SCE using a potentiostat, leave the test piece in a constant temperature bath at 60 ° C as it is, collect the test piece holding the potential for 28 days, and then peel off the artificial defect. Measure the distance of the peeling part of the polyethylene coating layer from the edge of the artificial defect in 4 directions centered on the artificial defect (12 o'clock, 3 o'clock, 6 o'clock, 9 o'clock) And the average value.
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