JPS6114930B2 - - Google Patents
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- Publication number
- JPS6114930B2 JPS6114930B2 JP54085721A JP8572179A JPS6114930B2 JP S6114930 B2 JPS6114930 B2 JP S6114930B2 JP 54085721 A JP54085721 A JP 54085721A JP 8572179 A JP8572179 A JP 8572179A JP S6114930 B2 JPS6114930 B2 JP S6114930B2
- Authority
- JP
- Japan
- Prior art keywords
- steel pipe
- polyethylene
- coating layer
- layer
- polyethylene coating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 229910000831 Steel Inorganic materials 0.000 claims description 122
- 239000010959 steel Substances 0.000 claims description 122
- 239000004698 Polyethylene Substances 0.000 claims description 107
- 229920000573 polyethylene Polymers 0.000 claims description 107
- -1 polyethylene Polymers 0.000 claims description 106
- 239000011247 coating layer Substances 0.000 claims description 72
- 238000000034 method Methods 0.000 claims description 31
- 239000000853 adhesive Substances 0.000 claims description 28
- 230000001070 adhesive effect Effects 0.000 claims description 28
- 238000001816 cooling Methods 0.000 claims description 26
- 239000010410 layer Substances 0.000 claims description 26
- 239000003507 refrigerant Substances 0.000 claims description 21
- 239000002344 surface layer Substances 0.000 claims description 19
- 238000000576 coating method Methods 0.000 claims description 18
- 239000011248 coating agent Substances 0.000 claims description 16
- 230000002093 peripheral effect Effects 0.000 claims description 11
- 239000000463 material Substances 0.000 description 15
- 239000000498 cooling water Substances 0.000 description 8
- 239000007921 spray Substances 0.000 description 6
- 238000005260 corrosion Methods 0.000 description 4
- 239000012790 adhesive layer Substances 0.000 description 3
- 239000010426 asphalt Substances 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 230000007797 corrosion Effects 0.000 description 3
- 238000001125 extrusion Methods 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 229920001971 elastomer Polymers 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 239000002313 adhesive film Substances 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 229920005549 butyl rubber Polymers 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000002826 coolant Substances 0.000 description 1
- 238000005536 corrosion prevention Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 229920006332 epoxy adhesive Polymers 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000012943 hotmelt Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- 230000008719 thickening Effects 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Lining Or Joining Of Plastics Or The Like (AREA)
Description
【発明の詳細な説明】
この発明は、加熱された鋼管の外周面に接着剤
を被覆し、次いで、ポリエチレンシート状物をそ
の鋼管に螺旋状に巻き付けて被覆した後の被覆鋼
管の冷却方法を改善した鋼管の被覆方法に係るも
のである。
従来、石油、天然ガスなどの天然資源を輸送し
たり、あるいは通信または送電用のケーブルを通
したりするためのパイプラインを形成する大口径
の鋼管は、地球上のあらゆる場所（例えば、地
中、河川、沼地、海水中、または寒冷地から熱帯
地方など）に埋設または設置される可能性があ
り、数十年におよぶ長期間の使用が期待されてい
る。このため、この種鋼管は、地球上の種々の気
象条件、または設置条件に適応できるものでなけ
ればならず、鋼管の耐久性、特に鋼管の鋼材の腐
食性が大きな問題であつた。したがつて、パイプ
ライン用の鋼管の防食方法としては、従来から
種々の方法が提案されてきた。
特に、パイプライン用の鋼管の防食方法とし
て、あらかじめ予熱された鋼管に接着剤を被覆
し、次いで押出成形機から押出されたばかりのポ
リエチレンシート状物を前記鋼管に螺旋状に巻き
付けて被覆し、その後被覆鋼管を冷却してポリエ
チレン被覆層を固化することによつて、鋼管をポ
リエチレン被覆層でカバーする防食方法が、鋼管
の防食効果が高く安定しているため世界的に採用
されつつある。
ポリエチレンシート状物の巻き付けによる鋼管
の被覆方法では、約130〜300℃に予熱された加熱
鋼管に、接着剤を被覆し、次いで約150〜300℃の
半溶融または軟化状態のポリエチレンシート状物
を巻き付けて被覆するので、その被覆直後の被覆
鋼管がかなり高温となつていて何らかの方法で冷
却しなければならない。その冷却方法としては、
従来、被覆直後の被覆鋼管にポリエチレン被覆層
の外表面から多量の冷却水を供給して水冷する方
法が行なわれていた。しかしながら、この従来公
知の冷却方法では、伝熱係数の小さなポリエチレ
ン被覆層の外表面に冷却水を供給し、熱容量の大
きな内側の鋼管の高熱をポリエチレン被覆層経由
で除去する冷却法であるため、被覆鋼管の全体が
冷却するまでに非常に長い冷却時間を要し、よつ
て生産性が悪かつたのである。また、従来公知の
冷却方法では、鋼管の外面に巻き付けられた半溶
融状態または軟化状態のポリエチレン被覆層が冷
却して固化する際に、まずポリエチレン被覆層の
外表面層が固化し、次いで次第に内周部層が固化
していくので、ポリエチレン被覆層の外表面層か
ら内周部に向つて締め付ける力が生じ、固化が不
充分で軟化状態にある被覆層の内周部が流動また
は移動してしまい、特に鋼管の熔接継目部分のよ
うに鋼管の表面より盛り上つている個所では前述
の流動または移動が起り易く、結局、鋼管の熔接
継目部分のポリエチレン被覆層の厚さが薄くなつ
て被覆鋼管の防食性能の悪化を招くという欠点が
あつた。
そこで、発明者らは、前記の公知の冷却方法に
よる鋼管の被覆方法の欠点を改良することを鋭意
研究した結果、ポリエチレンシート状物で被覆し
た直後の被覆鋼管を、その外表面および内表面の
両側から特定の条件で、冷媒を供給して冷却する
ことによつて、前述の各欠点を解消することがで
きることを見出し、この発明を完成した。
すなわち、この発明は、加熱された鋼管の外周
面に接着剤を被覆し、次いで半溶融または軟化状
態のポリエチレンシート状物を鋼管に螺旋状に巻
き付けて被覆した後、
そのポリエチレンシート状物で被覆された鋼管
のポリエチレン被覆層の外周面および被覆鋼管の
内表面に冷媒を供給し、
前記ポリエチレン被覆層の全体が固化するまで
は、ポリエチレン被覆層の外表面層の温度が、ポ
リエチレン被覆層の最内周層の温度より低くなる
ようにし、しかも、そのポリエチレン被覆層の最
内周層の冷却速度が10℃／分以上となるようにし
て、
そのポリエチレン被覆鋼管の内外両側から冷却
することを特徴とする鋼管の被覆方法を提供する
ものである。
この発明の方法によれば、被覆鋼管の内外面の
両側から冷媒によつて被覆鋼管の高熱を除去して
奪い去つているので、従来方法と比較して冷却時
間が大幅に短縮され、鋼管の被覆の生産性が向上
するのである。
また、この発明の方法によれば、被覆鋼管のポ
リエチレン被覆層の外表面層の温度低下に追随す
るようにポリエチレン被覆層の内周層の温度を低
下させているので、ポリエチレン被覆層の外表面
層の固化による収縮力の存在下においてもポリエ
チレン被覆層の内周層が流動変形に対して抵抗力
を有することになり、したがつて、鋼管の継目部
でのポリエチレン被覆層の厚さの減少（減肉また
は薄化）が大幅に防止されたのである。
さらに、この発明の方法によれば、被覆鋼管の
ポリエチレン被覆層の全体が冷却固化するまで、
そのポリエチレン被覆層の外表面層の温度がその
ポリエチレン被覆層の最内周層の温度より低くな
るように、被覆鋼管の内外面両側から冷却してい
るので、ポリエチレン被覆層の外表面層から内周
部へ向つて順次固化および収縮が起り、またポリ
エチレン被覆層の全体が鋼管を締め付ける状態で
冷却するので、鋼管とポリエチレン被覆層とが充
分に緊密に密着し、両者の接着力が充分に高い値
を示すのである。
次に、この発明の被覆方法を、図面も参考にし
て、詳しく説明する。
なお、第１図は、鋼管に、ポリエチレンシート
状物を螺旋状に巻き付けて被覆している状況の一
例を概略示す斜視図であり、第２図は、その被覆
鋼管を内外両側から冷却している状況の一例を示
す斜視図である。第３図は、被覆鋼管の断面を示
す断面図である。第４図は被覆鋼管を内外両側か
ら冷却している状況の他の一例を示す側面図であ
る。
この発明の方法では、第１図に示すように、ま
ず、加熱された鋼管１の接着剤を被覆し、次いで
半溶融または軟化状態のポリエチレンシート状物
２を前記の鋼管１に螺旋状に巻き付けて被覆する
のである。
前記接着剤およびポリエチレンシート状物２を
加熱鋼管１へ順次被覆する方法は、従来公知の鋼
管の被覆方法と同様の方法で行えばよい。この被
覆方法としては、被覆をすべき鋼管１を130〜300
℃、特に150〜250℃に予め加熱しておき、その予
熱された鋼管１の外周面に、液状の接着剤を塗布
または吹き付けるか、粉末状の接着剤を吹き付け
て溶融するか、あるいは半溶融または軟化状態の
接着剤膜状ないしはシート状物を巻き付けるかし
て、接着剤を予熱鋼管１の外周面の全体に被覆
し、次いで、押出成形機のＴダイ６から150〜300
℃の吐出温度で押出された半溶融または軟化状態
のポリエチレンシート状物２を適当な緊張または
伸張状態で、第１図に示す矢印の方向に前進およ
び自転している前記予熱鋼管１に、ポリエチレン
シート状物２の一部を互に重ね合わせながら螺旋
状に巻き付けて被覆する方法を好適に挙げること
ができる。
前記鋼管は、石油、天然ガスなどの資源を輸送
するため、または電信用のケーブルを通すための
パイプライン用に使用され、管の長手方向に沿つ
て熔接継目１０の盛り上り部を有する鋼鉄製の大
口径管である。その鋼管は、外径が約100〜2000
mmであつて、厚さが３〜40mmのものであればよ
い。
前記接着剤としては、300℃以下で、特に250℃
以下で、液状ないしは軟化状態になりうるもので
あつて、約60℃以下に冷却されれば優れた接着性
能を有する接着剤であればよく、例えばブチルゴ
ム系接着剤、ポリエチレン系接着剤（変性ポリエ
チレン系接着剤を含む）、エポキシ系接着剤、変
性アスフアルト系接着剤（ゴム入アスフアルト系
接着剤を含む）などを挙げることができ、特にポ
リエチレン系ホツトメルトタイプの接着剤が好ま
しい。
前記のポリエチレンシート状物としては、150
〜300℃の温度で半溶融または軟化状態のポリエ
チレンシート状物を形成できれば、どのような種
類のポリエチレン（例えば、高圧法ポリエチレ
ン、中圧法または低圧法ポリエチレンなど）から
得られたシート状物であればよい。このシート状
物の形状およびサイズは、特に限定されるもので
はないが、長手方向に対して直角方向の両端部が
薄くなつている帯状のものが好ましく、その幅が
100〜1500mmであつて、厚さ（中央部）が0.5〜５
mmであるものがよく用いられている。
この発明の方法では、前述のようにして予熱鋼
管１に接着剤およびポリエチレンシート状物を被
覆した後、このポリエチレンシート状物で被覆さ
れた鋼管（被覆鋼管とも言う）１のポリエチレン
被覆層３の外表面４および被覆鋼管１の内表面５
に冷媒を供給し、前記ポリエチレン被覆層３の全
体が固化するまでは、ポリエチレン被覆層３の外
表面層の温度がポリエチレン被覆層３の最内周層
の温度より低くなるようにし、しかも、このポリ
エチレン被覆層３の最内周層の冷却速度が10℃／
分以上となるようにして、前記のポリエチレンの
被覆鋼管１の内外両側から冷却するのである。
ここでポリエチレン被覆層３の外表面層とは、
鋼管１を被覆しているポリエチレン被覆層３の全
体の厚さの1/2倍の厚さを想定したポリエチレン
被覆層３の表皮層のことであり、このポリエチレ
ン被覆層３の外表面層の温度とは、被覆層３の厚
さの1/2倍の厚さの外表面層の平均温度である。
またポリエチレン被覆層３の最内周層とは、ポ
リエチレン被覆層３が接着剤層９を介して鋼管１
の外周面に接着しているポリエチレン被覆層３の
接着面の薄層部分のことであつて、その最内周層
（接着面層）は、ポリエチレン被覆層３の全体の
厚さの約0.001倍に相当する厚さを想定した。
このポリエチレン被覆層３の最内周層の温度
は、鋼管１の外周部の温度で近似することができ
る。
この発明の方法において使用する冷媒は、気体
状の冷媒、液状の冷媒、霧状の冷媒などいずれの
状態のものであつてもよく、温度が約50℃以下、
特に30℃以下である冷却水を噴霧したり噴出した
り、あるいは、被覆した鋼管を冷却水中に浸漬し
たりして使用することが最適である。
被覆鋼管１へ冷媒を供給する方法は、この発明
の冷却における限定条件を満たすことができれ
ば、特に限定されない。しかし、この発明の方法
では、被覆鋼管１のポリエチレン被覆層３の外表
面４へ冷媒を供給するには、前述のようにして予
熱鋼管１に接着剤およびポリエチレンシート状物
２を被覆した直後から約10分間以内、特に被覆直
後から５分間以内に、第２図に示す矢印の方向に
自転している被覆鋼管１に、その上方に設置した
スプレーノズル７から噴霧またはシヤワーリング
して冷却水を供給することが好ましい。また前記
の自転をしていない被覆鋼管では、その鋼管の上
下左右の周辺に設置されたスプレーノズルから冷
却水を噴出してもよい。ポリエチレン被覆層３の
外表面４へ供給する冷媒の種類および使用量は、
その外表面４への冷媒の供給を開始してからポリ
エチレン被覆層３の全体が固化するまでの間、そ
のポリエチレン被覆層３の外表面層の冷却速度が
約30〜150℃／分、特に50〜100℃／分となるよう
に適当に選択することが好ましい。
また、被覆鋼管１の内表面５に冷媒を供給する
には、被覆鋼管１のポリエチレン被覆層３の外表
面４に冷媒を供給し始めてから10分間以内、特に
9.5分間以内に、そして予熱鋼管へのポリエチレ
ンシート状物の被覆直後から20分間以内、特に15
分間以内に、第２図あるいは第４図に示すように
して行うことが好ましい。
すなわち、第２図に示す方法では、矢印の方向
に自転している被覆鋼管１の片側または両側に設
置された噴出ノズル８から被覆鋼管１の内部の内
表面５に向つて、冷媒を噴出しており、被覆鋼管
１の外表面４へのシヤワーリングをそのまま継続
している。また、第４図で示す方法では、0.5〜
３゜傾斜した平面上に設けられ搬送ロール１１上
を被覆鋼管１が矢印の方向に移動し、所定の位置
で被覆鋼管１の下部が冷却水１２中に浸漬し、被
覆鋼管１の自転によつて被覆鋼管１の内外両側が
全周にわたつて冷却されている。
第２図で示すような方法で、被覆鋼管１の内表
面５へ供給する冷媒の種類および使用量、あるい
は第４図で示すような浸漬方法で、被覆鋼管１の
浸漬の速度、傾斜角度または冷却水の状態は、ポ
リエチレン被覆層３の最内周層（接着面層）の冷
却速度が10℃／分以上、特に10〜200℃／分とな
り、しかも、ポリエチレン被覆層３の全体が固化
するまでは、ポリエチレン被覆層３の外表面層
（表皮層）の温度がその最内周層の温度より低く
なるように適当に選択しなければならない。
この発明の方法において、被覆鋼管１のポリエ
チレン被覆層３の外表面４へ供給する冷媒と、被
覆鋼管１の内表面５へ供給する冷媒との関連は、
それぞれの冷媒の種類および使用量、ならびに冷
媒の供給開始時期などにおいて、ポリエチレン被
覆層３の全体が固化するまでの間、ポリエチレン
被覆層３の外表面層の温度が、被覆鋼管３の最内
周層の温度より常に低くなるように、調整しなけ
ればならない。前述のようにポリエチレン被覆層
３の外表面層と最内周層との温度関係を維持する
ように、被覆鋼管１の内外両側に供給する冷媒を
調整することは、固化しつつあるポリエチレン被
覆層３が鋼管１を締め付ける力を適当に保持させ
ることになり、ポリエチレン被覆層３と鋼管１と
が接着剤層９を介して強力・緊密に接合すること
になるので重要である。
この発明の方法によれば、特定の制約条件があ
るが、被覆鋼管１の内外両側から冷却しているの
で、被覆鋼管１の全体の冷却時間が大幅に短縮さ
れ生産性が向上した。この発明の方法では、被覆
鋼管１を常温近くまで冷却する時間を、約30分間
以内、特に20分間以内にすることができ、冷却条
件を適当に選択すれば冷却時間を15分間以内にす
ることができた。
また、この発明の方法によれば、被覆鋼管１の
ポリエチレン被覆層３の外表面層と最内周層との
温度差を小さくすることができたので、ポリエチ
レン被覆層３の外表面層が鋼管を冷却中に締め付
ける力を緩和することができ、また、ポリエチレ
ン被覆層３の内周部の流動性を減少させることも
できたために、鋼管の熔接継目部分１０でのポリ
エチレン被覆層３の厚さの減肉（薄化）を防止す
ることができた。
なお、この発明の方法では、ポリエチレン被覆
層３の全体が冷却・固化してしまつた後には、前
述のこの発明の冷却時の制約にかまわず、無制限
に自由に冷却することができ、その後の冷却によ
つて被覆鋼管１を常温近くまで冷却すればよい。
以下、実施例および比較例を示す。
実施例および比較例において、接着力は、被覆
鋼管からポリエチレン被覆層の一部を引き剥が
し、その一部引剥がした部分を保持して鋼管の外
周の接線方向に引張つて、さらに被覆層を引き剥
すのに要する力（Kg／cm）で示し、減肉率（薄化
率）Ａは、次式のように被覆鋼管１の平たん部の
ポリエチレン被覆層の厚さD0から熔接継目部分
のポリエチレン被覆層の厚さD1を差し引いた値
を、前記の熔接継目部分の以外の平たん部のポリ
エチレン被覆層の厚さD0で割つて、さらに100倍
して得られる値である。
Ａ＝Ｄ０−Ｄ１／Ｄ０×100（％）
実施例１〜６および比較例１〜４
鋼管の外径が1422mmであり、鋼管の厚さが19mm
であり、しかも長さが12ｍである鋼管を、250℃
に予熱し、ポリエチレン系接着剤を被覆し、次い
で高圧法ポリエチレン（密度；0.925ｇ／cm3、
MI；0.15ｇ／10分）97.5重量％およびカーボンブ
ラツク2.5重量％を含有するポリエチレン組成物
を使用して押出成形機のＴダイから250℃の吐出
温度で押出したポリエチレンシート状物（鋼管に
巻き付け時の厚さ約1.5mm、幅約500mm）を、前記
予熱鋼管に巻き付けて一部シート状物を重ね合わ
せながら螺旋状に被覆した。第１図、第２図に示
すような方法で、第１表に示すような冷却の開始
時間、ポリエチレン被覆層の外表面層および最内
周層の冷却速度で、20℃の冷却水を被覆鋼管の内
外両側から噴出することによつて、前述の被覆鋼
管をその全体の温度50℃となるまで冷却した。そ
の結果、被覆鋼管のポリエチレン被覆層の冷却時
間、ポリエチレン被覆層の接着力および減肉率を
第１表に示す。なお、ポリエチレン被覆層の全体
は厚さは約３mmであつた。
【表】DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for cooling a coated steel pipe after coating the outer peripheral surface of a heated steel pipe with an adhesive and then wrapping a polyethylene sheet material around the steel pipe in a spiral manner. This invention relates to an improved method of coating steel pipes. Traditionally, large-diameter steel pipes, which form pipelines for transporting natural resources such as oil and gas, or for carrying communication or power transmission cables, have been constructed in all parts of the world, e.g. They can be buried or installed in rivers, swamps, seawater, or in cold to tropical regions, and are expected to last for decades. Therefore, this type of steel pipe must be able to adapt to various weather conditions and installation conditions on the earth, and the durability of the steel pipe, particularly the corrosivity of the steel material of the steel pipe, has been a major problem. Therefore, various methods have been proposed to prevent corrosion of steel pipes for pipelines. In particular, as a method for preventing corrosion of steel pipes for pipelines, a preheated steel pipe is coated with an adhesive, then a polyethylene sheet freshly extruded from an extrusion molding machine is wrapped around the steel pipe in a spiral shape, and then the steel pipe is coated with an adhesive. A corrosion prevention method of covering a steel pipe with a polyethylene coating layer by cooling the coated steel pipe and solidifying the polyethylene coating layer is being adopted worldwide because it is highly effective and stable in preventing corrosion of steel pipes. In the method of coating steel pipes by wrapping a polyethylene sheet, a heated steel pipe that has been preheated to about 130 to 300°C is coated with an adhesive, and then a semi-molten or softened polyethylene sheet at about 150 to 300°C is coated. Since the coating is wrapped around the tube, the coated steel pipe becomes quite hot immediately after coating, and must be cooled down by some method. The cooling method is
Conventionally, a method has been used to water-cool a coated steel pipe immediately after coating by supplying a large amount of cooling water from the outer surface of the polyethylene coating layer. However, in this conventionally known cooling method, cooling water is supplied to the outer surface of the polyethylene coating layer, which has a small heat transfer coefficient, and high heat from the inner steel pipe, which has a large heat capacity, is removed via the polyethylene coating layer. It took a very long time to cool down the entire coated steel pipe, resulting in poor productivity. In addition, in conventional cooling methods, when the semi-molten or softened polyethylene coating layer wrapped around the outer surface of the steel pipe cools and solidifies, the outer surface layer of the polyethylene coating layer first solidifies, and then the inner surface layer gradually solidifies. As the peripheral layer solidifies, a tightening force is generated from the outer surface layer of the polyethylene covering layer toward the inner peripheral part, and the inner peripheral part of the covering layer, which is insufficiently solidified and is in a softened state, flows or moves. In particular, the above-mentioned flow or movement is likely to occur in areas that rise above the surface of the steel pipe, such as the welded joints of the steel pipes, and as a result, the thickness of the polyethylene coating layer at the welded joints of the steel pipes becomes thinner, and the coated steel pipes become thinner. The disadvantage was that it caused a deterioration in the anti-corrosion performance of the steel. Therefore, as a result of intensive research into improving the drawbacks of the method of coating steel pipes using the above-mentioned known cooling method, the inventors discovered that the outer and inner surfaces of coated steel pipes immediately after being coated with a polyethylene sheet-like material were It was discovered that each of the above-mentioned drawbacks could be overcome by supplying refrigerant from both sides under specific conditions for cooling, and the present invention was completed. That is, this invention coats the outer peripheral surface of a heated steel pipe with an adhesive, then wraps a semi-molten or softened polyethylene sheet material around the steel pipe in a spiral pattern, and then covers the steel pipe with the polyethylene sheet material. A refrigerant is supplied to the outer peripheral surface of the polyethylene coating layer of the coated steel pipe and the inner surface of the coated steel pipe, and until the entire polyethylene coating layer is solidified, the temperature of the outer surface layer of the polyethylene coating layer is maintained at the highest temperature of the polyethylene coating layer. It is characterized by cooling the polyethylene-coated steel pipe from both the inside and outside so that the temperature is lower than that of the inner circumferential layer, and the cooling rate of the innermost circumferential layer of the polyethylene coating layer is 10°C/min or more. The present invention provides a method for coating steel pipes. According to the method of this invention, the high heat of the coated steel pipe is removed and taken away by the refrigerant from both the inner and outer surfaces of the coated steel pipe, so the cooling time is significantly shortened compared to the conventional method, and the heat of the coated steel pipe is This improves coating productivity. Furthermore, according to the method of the present invention, the temperature of the inner circumferential layer of the polyethylene coating layer is lowered to follow the temperature decrease of the outer surface layer of the polyethylene coating layer of the coated steel pipe. Even in the presence of shrinkage forces due to layer solidification, the inner peripheral layer of the polyethylene coating layer will have resistance to flow deformation, thus reducing the thickness of the polyethylene coating layer at the joint of the steel pipe. (Thickening or thinning) was largely prevented. Furthermore, according to the method of the present invention, until the entire polyethylene coating layer of the coated steel pipe is cooled and solidified,
The coated steel pipe is cooled from both the inner and outer surfaces so that the temperature of the outer surface layer of the polyethylene coating layer is lower than the temperature of the innermost layer of the polyethylene coating layer. Solidification and shrinkage occur sequentially toward the periphery, and the entire polyethylene coating layer is cooled while tightening the steel pipe, so the steel pipe and polyethylene coating layer are brought into close contact with each other, and the adhesive strength between the two is sufficiently high. It shows the value. Next, the coating method of the present invention will be explained in detail with reference to the drawings. Note that FIG. 1 is a perspective view schematically showing an example of a situation in which a steel pipe is coated with a polyethylene sheet material wrapped spirally, and FIG. FIG. 2 is a perspective view showing an example of a situation in which FIG. 3 is a sectional view showing a cross section of the coated steel pipe. FIG. 4 is a side view showing another example of a situation in which a coated steel pipe is cooled from both the inside and outside. In the method of the present invention, as shown in FIG. 1, first, a heated steel pipe 1 is coated with an adhesive, and then a semi-molten or softened polyethylene sheet 2 is spirally wrapped around the steel pipe 1. It is then coated. The heating steel pipe 1 may be sequentially coated with the adhesive and the polyethylene sheet 2 in the same manner as the conventionally known method for coating steel pipes. In this coating method, the steel pipe 1 to be coated is
℃, especially 150 to 250℃, and apply or spray a liquid adhesive on the outer peripheral surface of the preheated steel pipe 1, or spray a powdered adhesive and melt it, or semi-melt it. Alternatively, the entire outer circumferential surface of the preheated steel pipe 1 is coated with the adhesive by wrapping a softened adhesive film or sheet, and then 150~300 mm is applied from the T-die 6 of the extrusion molding machine.
A semi-molten or softened polyethylene sheet material 2 extruded at a discharge temperature of A preferred method is to wrap a portion of the sheet-like material 2 in a spiral manner while overlapping each other. The steel pipe is used for pipelines for transporting resources such as oil and natural gas or for passing cables for telecommunications, and is made of steel and has a raised part of welded joints 10 along the length of the pipe. This is a large diameter pipe. The steel pipe has an outer diameter of about 100~2000
mm and the thickness is 3 to 40 mm. The adhesive may be used at temperatures below 300°C, especially at 250°C.
Below, any adhesive that can be in a liquid or softened state and has excellent adhesive performance when cooled to below about 60°C may be used, such as butyl rubber adhesives, polyethylene adhesives (modified polyethylene (including rubber-containing asphalt adhesives), epoxy adhesives, modified asphalt adhesives (including rubber-containing asphalt adhesives), and polyethylene hot melt type adhesives are particularly preferred. As the polyethylene sheet-like material, 150
Any sheet of polyethylene obtained from any type of polyethylene (e.g., high-pressure polyethylene, medium-pressure polyethylene, or low-pressure polyethylene) can be used as long as it can form a semi-molten or softened polyethylene sheet at a temperature of ~300°C. Bye. The shape and size of this sheet-like material are not particularly limited, but it is preferable that it be a strip-like material that is thinner at both ends in the direction perpendicular to the longitudinal direction.
100-1500mm, thickness (center) 0.5-5
mm is often used. In the method of the present invention, after coating the preheated steel pipe 1 with an adhesive and a polyethylene sheet as described above, the polyethylene coating layer 3 of the steel pipe (also referred to as coated steel pipe) 1 coated with the polyethylene sheet is applied. Outer surface 4 and inner surface 5 of coated steel pipe 1
The temperature of the outer surface layer of the polyethylene coating layer 3 is lower than the temperature of the innermost layer of the polyethylene coating layer 3 until the entire polyethylene coating layer 3 is solidified. The cooling rate of the innermost layer of the polyethylene coating layer 3 is 10℃/
The polyethylene-coated steel pipe 1 is cooled from both the inside and outside for a time of at least 1 minute. Here, the outer surface layer of the polyethylene coating layer 3 is:
This refers to the skin layer of the polyethylene coating layer 3, which is assumed to have a thickness of 1/2 of the total thickness of the polyethylene coating layer 3 that covers the steel pipe 1, and the temperature of the outer surface layer of this polyethylene coating layer 3. is the average temperature of the outer surface layer with a thickness 1/2 times the thickness of the coating layer 3. In addition, the innermost layer of the polyethylene coating layer 3 means that the polyethylene coating layer 3 is attached to the steel pipe through the adhesive layer 9.
The thin layer of the adhesive surface of the polyethylene coating layer 3 that is adhered to the outer peripheral surface of The thickness was assumed to be equivalent to . The temperature of the innermost layer of the polyethylene coating layer 3 can be approximated by the temperature of the outer circumference of the steel pipe 1. The refrigerant used in the method of the present invention may be in any state, such as a gaseous refrigerant, a liquid refrigerant, or a mist refrigerant, and has a temperature of about 50°C or less,
In particular, it is best to spray or squirt cooling water at a temperature of 30°C or lower, or to immerse the coated steel pipe in cooling water. The method of supplying the refrigerant to the coated steel pipe 1 is not particularly limited as long as it can satisfy the limiting conditions for cooling of the present invention. However, in the method of the present invention, the refrigerant is supplied to the outer surface 4 of the polyethylene coating layer 3 of the coated steel pipe 1 immediately after the preheated steel pipe 1 is coated with the adhesive and the polyethylene sheet material 2 as described above. Within about 10 minutes, particularly within 5 minutes immediately after coating, coolant water is sprayed or showered from the spray nozzle 7 installed above onto the coated steel pipe 1, which is rotating in the direction of the arrow shown in Figure 2. It is preferable to supply. Furthermore, in the case of the coated steel pipe that does not rotate, cooling water may be jetted from spray nozzles installed around the top, bottom, right and left of the steel pipe. The type and amount of refrigerant supplied to the outer surface 4 of the polyethylene coating layer 3 are as follows:
From the start of supply of refrigerant to the outer surface 4 until the entire polyethylene coating layer 3 is solidified, the cooling rate of the outer surface layer of the polyethylene coating layer 3 is approximately 30 to 150°C/min, particularly 50°C/min. It is preferable to appropriately select the temperature to be 100° C./min. Furthermore, in order to supply the refrigerant to the inner surface 5 of the coated steel pipe 1, it is necessary to supply the refrigerant to the outer surface 4 of the polyethylene coating layer 3 of the coated steel pipe 1 within 10 minutes, especially within 10 minutes.
within 9.5 minutes and within 20 minutes immediately after coating the preheated steel pipe with the polyethylene sheet, especially within 15 minutes.
It is preferable to carry out the process as shown in FIG. 2 or 4 within minutes. That is, in the method shown in FIG. 2, the refrigerant is jetted toward the inner surface 5 inside the coated steel pipe 1 from the jet nozzle 8 installed on one or both sides of the coated steel pipe 1 that is rotating in the direction of the arrow. The shearing of the outer surface 4 of the coated steel pipe 1 continues as it is. In addition, in the method shown in Figure 4, 0.5 to
The coated steel pipe 1 moves in the direction of the arrow on the conveyor roll 11 provided on a plane inclined by 3 degrees, and at a predetermined position, the lower part of the coated steel pipe 1 is immersed in the cooling water 12, and due to the rotation of the coated steel pipe 1, the coated steel pipe 1 moves in the direction of the arrow. Both the inner and outer sides of the coated steel pipe 1 are cooled over the entire circumference. The type and amount of refrigerant supplied to the inner surface 5 of the coated steel pipe 1 in the method shown in FIG. 2, or the dipping speed, inclination angle, or The state of the cooling water is such that the cooling rate of the innermost layer (adhesive surface layer) of the polyethylene coating layer 3 is 10°C/min or more, especially 10 to 200°C/min, and the entire polyethylene coating layer 3 is solidified. Up to this point, the temperature of the outer surface layer (skin layer) of the polyethylene coating layer 3 must be selected appropriately so that it is lower than the temperature of its innermost peripheral layer. In the method of this invention, the relationship between the refrigerant supplied to the outer surface 4 of the polyethylene coating layer 3 of the coated steel pipe 1 and the refrigerant supplied to the inner surface 5 of the coated steel pipe 1 is as follows:
Depending on the type and amount of refrigerant used, and the timing at which refrigerant supply is started, the temperature of the outer surface layer of the polyethylene coating layer 3 will be around the innermost periphery of the coated steel pipe 3 until the entire polyethylene coating layer 3 is solidified. It must be adjusted so that it is always lower than the temperature of the layer. As mentioned above, adjusting the refrigerant supplied to both the inner and outer sides of the coated steel pipe 1 so as to maintain the temperature relationship between the outer surface layer and the innermost layer of the polyethylene coating layer 3 is to control the temperature of the polyethylene coating layer that is solidifying. 3 is important because it maintains an appropriate tightening force on the steel pipe 1, and the polyethylene coating layer 3 and the steel pipe 1 are bonded strongly and tightly via the adhesive layer 9. According to the method of the present invention, although there are certain constraints, since the coated steel pipe 1 is cooled from both the inside and outside, the overall cooling time of the coated steel pipe 1 is significantly shortened and productivity is improved. In the method of the present invention, the time for cooling the coated steel pipe 1 to near room temperature can be reduced to approximately 30 minutes or less, particularly 20 minutes or less, and if cooling conditions are appropriately selected, the cooling time can be reduced to 15 minutes or less. was completed. Furthermore, according to the method of the present invention, the temperature difference between the outer surface layer and the innermost layer of the polyethylene coating layer 3 of the coated steel pipe 1 can be reduced, so that the outer surface layer of the polyethylene coating layer 3 is The thickness of the polyethylene coating layer 3 at the welded joint portion 10 of the steel pipe was It was possible to prevent wall thinning (thinning). In addition, in the method of this invention, after the entire polyethylene coating layer 3 has been cooled and solidified, it can be freely cooled without any restrictions, regardless of the above-mentioned restrictions on cooling of this invention, and the subsequent The coated steel pipe 1 may be cooled to near room temperature by cooling. Examples and comparative examples are shown below. In the Examples and Comparative Examples, the adhesive strength was determined by peeling off a part of the polyethylene coating layer from the coated steel pipe, holding the partially peeled off part and pulling it in the tangential direction of the outer circumference of the steel pipe, and then pulling the coating layer. It is expressed as the force required for peeling (Kg/cm), and the thickness reduction rate (thinning rate) A is calculated from the thickness D 0 of the polyethylene coating layer on the flat part of the coated steel pipe 1 to the thickness of the welded joint part as shown in the following formula. This value is obtained by subtracting the thickness D 1 of the polyethylene coating layer, dividing the value by the thickness D 0 of the polyethylene coating layer in the flat portion other than the welded joint portion, and then multiplying the result by 100. A=D 0 −D 1 /D 0 ×100 (%) Examples 1 to 6 and Comparative Examples 1 to 4 The outer diameter of the steel pipe is 1422 mm, and the thickness of the steel pipe is 19 mm.
Moreover, a steel pipe with a length of 12m was heated to 250℃.
preheated to 100 ml, coated with polyethylene adhesive, and then coated with high-pressure polyethylene (density: 0.925 g/cm 3 ,
A polyethylene sheet (wrapped around a steel pipe) extruded from a T-die of an extruder at a discharge temperature of 250°C using a polyethylene composition containing 97.5% by weight (MI; 0.15g/10min) and 2.5% by weight of carbon black. (approximately 1.5 mm in thickness and approximately 500 mm in width) was wound around the preheated steel pipe to coat the preheated steel pipe in a helical manner while partially overlapping sheet-like materials. Using the method shown in Figures 1 and 2, and at the cooling start time and cooling rate of the outer surface layer and the innermost layer of the polyethylene coating layer shown in Table 1, the coating is coated with cooling water at 20°C. The above-mentioned coated steel pipe was cooled to a total temperature of 50° C. by jetting from both the inside and outside of the steel pipe. As a result, the cooling time of the polyethylene coating layer of the coated steel pipe, the adhesive strength of the polyethylene coating layer, and the thinning rate are shown in Table 1. The total thickness of the polyethylene coating layer was approximately 3 mm. 【table】
第１図は鋼管にポリエチレンシート状物を螺旋
状に巻き付けて被覆している状況の一例を概略示
す斜視図、第２図は被覆鋼管を内外両側から冷却
している状況の一例を示す斜視図、第３図は被覆
鋼管の断面を示す断面図、第４図は被覆鋼管を内
外両側から冷却している状況の他の一例を示す斜
視図である。
１……鋼管、２……ポリエチレンシート状物、
３……ポリエチレン被覆層、４……ポリエチレン
被覆層の外表面、５……ポリエチレン被覆鋼管の
内表面、６……押出成形機のＴダイ、７……スプ
レーノズル、８……噴出ノズル、９……接着剤
層、１０……熔接継目。
Figure 1 is a perspective view schematically showing an example of a situation in which a steel pipe is coated with a polyethylene sheet material wrapped spirally, and Figure 2 is a perspective view showing an example of a situation in which a coated steel pipe is cooled from both the inside and outside. FIG. 3 is a sectional view showing a cross section of the coated steel pipe, and FIG. 4 is a perspective view showing another example of a situation in which the coated steel pipe is cooled from both the inside and outside. 1...Steel pipe, 2...Polyethylene sheet material,
3... Polyethylene coating layer, 4... Outer surface of polyethylene coating layer, 5... Inner surface of polyethylene coated steel pipe, 6... T-die of extrusion molding machine, 7... Spray nozzle, 8... Ejection nozzle, 9 ... Adhesive layer, 10 ... Welded joint.
Claims (1)
次いで、半溶融または軟化状態のポリエチレンシ
ート状物を鋼管に螺旋状に巻き付けて被覆した
後、 そのポリエチレンシート状物で被覆された鋼管
のポリエチレン被覆層の外表面および被覆鋼管の
内表面に冷媒を供給し、 前記のポリエチレン被覆層の全体が固化するま
では、ポリエチレン被覆層の外表面層の温度が、
ポリエチレン被覆層の最内周層の温度より低くな
るようにし、しかも、そのポリエチレン被覆層の
最内周層の冷却速度が10℃／分以上となるように
して、 そのポリエチレン被覆鋼管の内外両側から冷却
することを特徴とする鋼管の被覆方法。[Claims] 1. Coating the outer peripheral surface of a heated steel pipe with an adhesive,
Next, a semi-molten or softened polyethylene sheet is wrapped spirally around the steel pipe to cover it, and then a refrigerant is applied to the outer surface of the polyethylene coating layer of the steel pipe covered with the polyethylene sheet and the inner surface of the coated steel pipe. Until the entire polyethylene coating layer is solidified, the temperature of the outer surface layer of the polyethylene coating layer is
The temperature is lower than that of the innermost layer of the polyethylene coating layer, and the cooling rate of the innermost layer of the polyethylene coating layer is 10°C/min or more, and the temperature is lower than that of the innermost layer of the polyethylene coating layer, and the cooling rate of the innermost layer of the polyethylene coating layer is 10°C/min or more. A method for coating steel pipes, which is characterized by cooling.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8572179A JPS5610422A (en) | 1979-07-06 | 1979-07-06 | Method of sheathing steel pipe |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8572179A JPS5610422A (en) | 1979-07-06 | 1979-07-06 | Method of sheathing steel pipe |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS5610422A JPS5610422A (en) | 1981-02-02 |
| JPS6114930B2 true JPS6114930B2 (en) | 1986-04-21 |
Family
ID=13866697
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP8572179A Granted JPS5610422A (en) | 1979-07-06 | 1979-07-06 | Method of sheathing steel pipe |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5610422A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS62178320A (en) * | 1986-01-31 | 1987-08-05 | Nisshin Steel Co Ltd | Method of adhesion between denatured polyolefin resin and metal |
| KR100372267B1 (en) * | 2000-12-01 | 2003-02-26 | 한미아 | T-die extrusion type coating method for steel pipe and apparatus thereof |
| KR100822147B1 (en) | 2007-01-26 | 2008-04-15 | 주식회사 이니텍기계 | Metal tubing clothing system |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS505221A (en) * | 1973-05-21 | 1975-01-20 | ||
| JPS5455064A (en) * | 1977-10-11 | 1979-05-01 | Nippon Kokan Kk <Nkk> | Production of metal pipe coated with plastics |
-
1979
- 1979-07-06 JP JP8572179A patent/JPS5610422A/en active Granted
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS505221A (en) * | 1973-05-21 | 1975-01-20 | ||
| JPS5455064A (en) * | 1977-10-11 | 1979-05-01 | Nippon Kokan Kk <Nkk> | Production of metal pipe coated with plastics |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5610422A (en) | 1981-02-02 |
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