Patent Number: 
Section: claims

1. A method for heat treating a metal tube or pipe, comprising:heat treating a metal tube or pipe which is accommodated in a heat treatment furnace, the metal tube or pipe being laid down on a plurality of cross beams, the plurality of cross beams being arranged along a longitudinal direction of the metal tube or pipe such that a distance between adjacent ones of the cross beams is in a range of 200 to 2500 mm, the metal tube or pipe being in contact with the cross beams, whereinas the cross beams, cross beams having a convex top surface are used, the convex top surface having a radius of curvature in a range of 50 to 300 mm. 2. A method for heat treating a metal tube or pipe comprising:heat treating a metal tube or pipe, which is accommodated in a heat treatment furnace, the metal tube or pipe being laid down on a plurality of the cross beams with spacers having a convex top surface interposed therebetween, the plurality of cross beams being arranged along a longitudinal direction of the metal tube or pipe such that a distance between adjacent ones of the cross beams is in a range of 200 to 2500 mm, the metal tube or pipe being in contact with the spacers, whereinthe convex top surface has a radius of curvature in a range of 50 to 300 mm. 3. The method for heat treating a metal tube or pipe according to claim 1, wherein the metal tube or pipe has a composition consisting of, in mass %, C: 0.15% or less, Si: 1.00% or less, Mn: 2.0% or less, P: 0.030% or less, S: 0.030% or less, Cr: 10.0% to 40.0%, Ni: 8.0% to 80.0%, Ti: 0.5% or less, Cu: 0.6% or less, Al: 0.5% or less, and N: 0.20% or less, the balance being Fe and impurities. 4. A heat treatment furnace that performs heat treatment on a metal tube or pipe, the metal tube or pipe being accommodated in the heat treatment furnace in a state where the metal tube or pipe is laid down on a plurality of cross beams, the plurality of cross beams being arranged along a longitudinal direction of the metal tube or pipe such that a distance between adjacent ones of the cross beams is in a range of 200 to 2500 mm, the metal tube or pipe being in contact with the cross beams whereinas the cross beams, cross beams having a convex top surface are used, the convex top surface having a radius of curvature in a range of 50 to 300 mm. 5. A heat treatment furnace, that performs heat treatment on a metal tube or pipe, the metal tube or pipe being accommodated in a heat treatment furnace in a state where the metal tube or pipe is laid down on a plurality of cross beams with spacers having a convex top surface interposed therebetween, the plurality of cross beams being arranged along a longitudinal direction of the metal tube or pipe such that a distance between adjacent ones of the cross beams is in a range of 200 to 2500 mm, the metal tube or pipe being in contact with the spacers, whereinthe convex top surface has a radius of curvature in a range of 50 to 300 mm. 6. The method for heat treating a metal tube or pipe according to claim 2, wherein the metal tube or pipe has a composition consisting of, in mass %, C: 0.15% or less, Si: 1.00% or less, Mn: 2.0% or less, P: 0.030% or less, S: 0.030% or less, Cr: 10.0% to 40.0%, Ni: 8.0% to 80.0%, Ti: 0.5% or less, Cu: 0.6% or less, Al: 0.5% or less, and N: 0.20% or less, the balance being Fe and impurities.