Method for manufacturing seamless pipe

Claim 1

A method for manufacturing a seamless pipe, comprising the steps of: (a) preparing a billet made of an alloy steel or an alloy having a main component selected from the group consisting of Cr, Ni and Mo; (b) joining a steel plate at least to an end surface of the billet at which a piercing of the billet is to be commenced; (c) preparing a piercing plug, the piercinc plug comprising (i) a main body made of Mo, a Mo alloy or a heat resisting steel and (ii) a hard laver formed on the surface of the main body, wherein said hard layer is made of any one selected from the group consisting of stellite, a ceramic obtained by adding tungsten carbide to stellite, a ceramic obtained by adding a mixture composition of tungsten carbide and cobalt to stellite and a ceramic obtained by adding a compound of chromium and carbon to stellite; (d) hot-piercing the billet at a hot-piercing temperature, to which the steel plate is Joined, with the piercing plug by a Mannesmann piercing to produce a hollow shell, an oxide scale being formed from said steel plate, at the hot-piercing temperature, the oxide scale lubricating the piercing plug during the hot-piercing; and (e) rolling the hollow shell to produce a seamless pipe.

Claim 2

A method for manufacturing a seamless pipe, comprising the steps of: (a) preparing a billet made of an alloy steel or an alloy having a main component selected from the group consisting of Cr, Ni and Mo; (b) joining a steel plate at least to an end surface of the billet at which a piercing of the billet is to be commenced; (c) preparing a piercing plug, the piercinc plug comprising (i) a main body made of Mo, a Mo alloy or a heat resisting steel and (ii) a hard laver formed on the surface of the main body, wherein said hard layer is made of any one selected from the group consisting of stellite, a ceramic obtained by adding tungsten carbide to stellite, a ceramic obtained by adding a mixture composition of tungsten carbide and cobalt to stellite and a ceramic obtained by adding a compound of chromium and carbon to stellite; (d) hot-piercing the billet at a hot-piercing temperature, to which the steel plate is Joined, with the piercing plug by a Mannesmann piercing to produce a hollow shell, an oxide scale being formed from said steel plate, at the hot-piercing temperature, the oxide scale lubricating the piercing plug during the hot-piercing; and (e) rolling the hollow shell to produce a seamless pipe.

Claim 5

A method for manufacturing a seamless pipe, comprising the steps of: (a) preparing a billet made of an alloy steel or an alloy having a main component selected from the group consisting of Cr, Ni and Mo; (b) joining a steel plate at least to an end surface of the billet at which a piercing of the billet is to be commenced; (c) preparing a piercing plug, the piercing plug comprising (i) a plug body made of Mo, a Mo alloy or a heat-resisting steel and (ii) a plug head formed at a leading end of the plug body, the plug head being made of Mo, a Mo alloy or a heat resisting steel, the plug body having a hard layer formed on a surface of the plug body, wherein said hard layer is made of any one selected from the group consisting of stellite, a ceramic obtained by adding tungsten carbide to stellite, a ceramic obtained by adding a mixture composition of tungsten carbide and cobalt to stellite and a ceramic obtained by adding a compound of chromium and carbon to stellite; (d) hot-piercing the billet at a hot-piercing temperature, to which the steel plate is joined, with the piercing plug by a Mannesmann piercing to produce a hollow shell, an oxide scale being formed from said steel plate, at the hot-piercing temperature, the oxide scale lubricating the piercing plug during the hot-piercing; and (e) rolling the hollow shell to produce a seamless pipe.

Claim 6

A method for manufacturing a seamless pipe, comprising the steps of: (a) preparing a billet made of an alloy steel or an alloy having a main component selected from the group consisting of Cr, Ni and Mo; (b) joining a steel plate at least to an end surface of the billet at which a piercing of the billet is to be commenced; (c) preparing a piercing plug, the piercing plug comprising (i) a plug body made of Mo, a Mo alloy or a heat-resisting steel and (ii) a plug head formed at a leading end of the plug body, the plug head being made of Mo, a Mo alloy or a heat resisting steel, the plug body having a hard layer formed on a surface of the plug body, wherein said hard layer is made of any one selected from the group consisting of stellite, a ceramic obtained by adding tungsten carbide to stellite, a ceramic obtained by adding a mixture composition of tungsten carbide and cobalt to stellite and a ceramic obtained by adding a compound of chromium and carbon to stellite; (d) hot-piercing the billet at a hot-piercing temperature, to which the steel plate is joined, with the piercing plug by a Mannesmann piercing to produce a hollow shell, an oxide scale being formed from said steel plate, at the hot-piercing temperature, the oxide scale lubricating the piercing plug during the hot-piercing; and (e) rolling the hollow shell to produce a seamless pipe.

Claim 7

A method for manufacturing a seamless pipe, comprising the steps of: (a) preparing a billet made of an allov steel or an alloy having a main component selected from the group consisting of Cr, Ni and Mo; (b) joining a steel plate at least to an end surface of the billet at which a piercing of the billet is to be commenced; (c) preparing a piercing slug, the piercing plug comprising (i) a plug body made of Mo, a Mo alloy or a heat-resisting steel and (ii) a plug head formed at a leading end of the plug body, the plug head being made of Mo, a Mo alloy or a heat resisting steel, the plug head having a hard layer formed on a surface of the plug head, wherein said hard layer is made of any one selected from the group consisting of stellite, a ceramic obtained by adding tungsten carbide to stellite, a ceramic obtained by adding a mixture composition of tungsten carbide and cobalt to stellite and a ceramic obtained by adding a compound of chromium and carbon to stellite; (d) hot-piercing the billet at a hot-piercing temperature, to which the steel plate is joined, with the piercing plug by a Mannesmann piercing to produce a hollow shell, an oxide scale being formed from said steel plate, at the hot-piercing temperature, the oxide scale lubricating the piercing plug during the hot-piercing; and (e) rolling the hollow shell to produce a seamless pipe.

Claim 8

A method for manufacturing a seamless pipe, comprising the steps of: (a) preparing a billet made of an allov steel or an alloy having a main component selected from the group consisting of Cr, Ni and Mo; (b) joining a steel plate at least to an end surface of the billet at which a piercing of the billet is to be commenced; (c) preparing a piercing slug, the piercing plug comprising (i) a plug body made of Mo, a Mo alloy or a heat-resisting steel and (ii) a plug head formed at a leading end of the plug body, the plug head being made of Mo, a Mo alloy or a heat resisting steel, the plug head having a hard layer formed on a surface of the plug head, wherein said hard layer is made of any one selected from the group consisting of stellite, a ceramic obtained by adding tungsten carbide to stellite, a ceramic obtained by adding a mixture composition of tungsten carbide and cobalt to stellite and a ceramic obtained by adding a compound of chromium and carbon to stellite; (d) hot-piercing the billet at a hot-piercing temperature, to which the steel plate is joined, with the piercing plug by a Mannesmann piercing to produce a hollow shell, an oxide scale being formed from said steel plate, at the hot-piercing temperature, the oxide scale lubricating the piercing plug during the hot-piercing; and (e) rolling the hollow shell to produce a seamless pipe.

Claim 9

A method for manufacturing a seamless pipe, comprising the steps of: preparing a billet made of an alloy steel or an alloy having a main component selected from the group consisting of Cr, Ni and Mo; joining a steel plate at least to an end surface of the billet at which a piercing of the billet is to be commenced, the steel plate being subjected to an oxidation treatment; heating the billet to which the steel plate is joined; hot-piercing the heated billet at a hot-piercing temperature with a piercing plug by a Mannesmann piercing to produce a hollow shell; an oxide scale being formed from said steel plate, at the hot-piercing temperature, the oxide scale lubricates the piercing plug during the hot-piercing; and rolling the hollow shell to produce a seamless pipe.

Claim 10

A method for manufacturing a seamless pipe, comprising the steps of: preparing a billet made of an alloy steel or an alloy having a main component selected from the group consisting of Cr, Ni and Mo; joining a steel plate at least to an end surface of the billet at which a piercing of the billet is to be commenced, the steel plate being subjected to an oxidation treatment; heating the billet to which the steel plate is joined; hot-piercing the heated billet at a hot-piercing temperature with a piercing plug by a Mannesmann piercing to produce a hollow shell; an oxide scale being formed from said steel plate, at the hot-piercing temperature, the oxide scale lubricates the piercing plug during the hot-piercing; and rolling the hollow shell to produce a seamless pipe.

Claim 17

A method for manufacturing a seamless pipe, comprising the steps of: preparing a billet made of an alloy steel or an alloy having a main component selected from the group consisting of Cr, Ni and Mo; heating the billet in a heating furnace; joining a steel plate at least to an end surface of the billet at which a piercing of the billet is to be commenced, the steel plate being subjected to an oxidation treatment; hot-piercing the heated billet at a hot-piercing temperature, to which the steel plate is joined, with a piercing plug by a Mannesmann piercing to produce a hollow shell; an oxide scale being formed from said steel plate, at the hot-piercing temperature, the oxide scale lubricates the piercing plug during hot-piercing; and rolling the hollow shell to produce a seamless pipe.

Claim 18

A method for manufacturing a seamless pipe, comprising the steps of: preparing a billet made of an alloy steel or an alloy having a main component selected from the group consisting of Cr, Ni and Mo; heating the billet in a heating furnace; joining a steel plate at least to an end surface of the billet at which a piercing of the billet is to be commenced, the steel plate being subjected to an oxidation treatment; hot-piercing the heated billet at a hot-piercing temperature, to which the steel plate is joined, with a piercing plug by a Mannesmann piercing to produce a hollow shell; an oxide scale being formed from said steel plate, at the hot-piercing temperature, the oxide scale lubricates the piercing plug during hot-piercing; and rolling the hollow shell to produce a seamless pipe.

Claim 25

A method for manufacturing a seamless pipe, comprising the steps of: preparing a billet made of a high alloy steel or a high alloy; preparing a piercing plug having a plug rolling portion and a plug reeling portion, the plug reeling portion is adjacent to the plug rolling portion, the piercing plug satisfies the following equation: 0.80°≦α-β≦1.51°, wherein α is an angle of the plug reeling portion and β is an angle at an outlet portion of a piercing roll; hot-piercing the billet with the piercing plug to produce a hollow shell; and rolling the hollow shell to produce a seamless pipe.

Claim 26

A method for manufacturing a seamless pipe, comprising the steps of: preparing a billet made of a high alloy steel or a high alloy; preparing a piercing plug having a plug rolling portion and a plug reeling portion, the plug reeling portion is adjacent to the plug rolling portion, the piercing plug satisfies the following equation: 0.80°≦α-β≦1.51°, wherein α is an angle of the plug reeling portion and β is an angle at an outlet portion of a piercing roll; hot-piercing the billet with the piercing plug to produce a hollow shell; and rolling the hollow shell to produce a seamless pipe.