Thin walled stainless steel pipe is harder to cut than copper and aluminum tubing, but you can still cut the stainless steel pipe with tubing tools. There are tubing tools, specifically tubing cutters, that are designed to cut stainless steel pipe and stainless steel tubing. If you already own a tubing cutter that the stainless steel pipe will fit into, you need to change one component to use your tubing cutter to square cut the end of the stainless steel pipe. The cutting wheel is the most important component when cutting stainless steel tubing.

The present invention is explained based on FIG. 1 and FIG. 2 and in this case, a double-wound stainless steel pipe is explained as an embodiment of this invention.

First, a multi-wound stainless steel pipe producing apparatus used for producing the above-described double-wound stainless steel pipe is explained.

In a double-wound forming apparatus 11 shown in FIG. 2, a guide roll 11-1 for guiding a hoop material 1, which is formed to a double-wound pipe, to a forming step, many pairs of pipe-making or forming rolls 11-2 of forming the hoop material 1 to a double-wound pipe from a sheet form, and finishing and regulating rolls 11-3 successively disposed and a plug-attached rod 11-4 is disposed from the side of the above-described guide roll 11-1.

As a heating apparatus 12, for example, a resistant heating system by plural electric current passing rolls (rotary electrodes) disposed in the line direction with a proper interval is employed. The inside of the heating apparatus is a non-oxidative atmosphere or a reducing gas atmosphere.

Also, press rolls 13 as a means of press-welding the double-wound walls each other in the diameter direction has a structure of uniformly pressing the outer surface of the double-wound pipe 15 formed by the above-described forming apparatus 11 in the diameter direction from outside and the disposing position thereof is an inlet side of a cooling apparatus 14 from the heating apparatus 12.

The cooling apparatus 14 is disposed just behind the heating apparatus and has a structure that many cooling medium spraying nozzles (not shown) are disposed such that the outer surface of the double-wound pipe 15 can be uniformly and quickly cooled. Specifically, for example, the cooling apparatus of a structure of a cooling jacket type having formed many nozzle holes at the inside wall such that a cooling medium is sprayed from the nozzle holes onto the double-wound pipe passing through the inside thereof is used. As the cooling medium, a gas is mainly used but a liquid such as water, etc., can be used.

Also, as a primary cooling means for cooling the double-wound pipe 15 as quick as possible, nozzles 16 are disposed just behind the heating apparatus and by spraying a cooling medium from the nozzles, the brazing material can be quickly cooled to about the solidifying point thereof.

As described above, as the cooling apparatus, it is preferred to constitute the apparatus by the primary cooling means composed of nozzles 16 and the secondary cooling means composed of the cooling apparatus 14 disposed at the down stream side of said nozzles but both quick cooling to about the solidifying point of the brazing material and cooling of the double-wound pipe can be carried out in the cooling apparatus 14.

In the multi-wound pipe producing apparatus of the above-described construction, the hoop material 1 made of a stainless steel sheet 1-1 both surfaces of which are applied with Cu plating is unwound from an uncoiler (not shown), is formed to a pipe 15 having double walls by the double-wound forming apparatus 11, and is introduced into the heating apparatus 12. In the heating apparatus 12, from a d.c. power source, an electric current is applied to the pipe through plural electric current passing rolls 12-1 to heat the pipe until the state that by the resistant heat of the pipe, Cu as the brazing material between the walls is melted and the diffusion of the molten brazing material into the walls proceeds is attained. In this case, the temperature is usually from 1083° C. to 1200° C.

The double-wound pipe 15 from the heating apparatus 12 is cooled by the cooling apparatus 14 disposed just behind the press rolls, whereby the diffusion bonding of the brazing material between the walls is finished.

In addition, as the heating means of the multi-wound pipe, a high-frequency heating coil may be employed in place of the above-described resistant heating system and also, a general heating furnace may be used as a brazing furnace.

Also, although it is not shown in the figure, when a press rolls are formed just behind the heating apparatus, because one end side (seamed portion side) of the outermost wall of the double-wound pipe is forcibly pressed by the press rolls from outside, the wall is adapted and adhered to the wall of the inner side and releasing of the outer seamed portion is prevented.

In the double-wound stainless steel pipe of this invention produced by the above-described apparatus, as a part of the cross-sectional structure shown in FIG. 1, between an inside wall 1-1 and an outside wall 1-2, and at the inside/outside surfaces of said steel pipe are formed Cu-brazing material layers 1-3, and at the inside surface and the outside surface of the inside wall 1-1 and at the inside surface and the outside surface of the outside wall 1-2 are formed diffused layers 1-4 having a thickness of from 0.5 μm to 15 μm. Also, in the double-wound stainless steel pipe, the concentration of Cu of the Cu-brazing material layers 1-3 remaining between the inside wall 1-1 and the outside wall 1-2, and at inside/outside surfaces of said steel pipe is at least 75% and the thickness of the Cu-brazing material layers 1-3 remaining between the inside wall 1-1 and the outside wall 1-2 is at least 0.5 μm.

As described above, in the double-wound stainless steel pipe of this invention, by diffusing the Cu-brazing material between the walls of the pipe and the Cu-brazing material at the inside surface and the outside surface of the pipe into the base material, the bonding force of the Cu-brazing material and the base material (stainless steel sheet) is increased and the deterioration of the SUS base material can be prevented. Also, by ensuring at least 75% of the Cu concentration of the Cu-brazing material after brazing, the strength such as the ductility, etc., of the Cu-brazing material can be maintained. As a matter of course, these effects are also similarly obtained in multi-wound stainless steel pipes other than the double-wound stainless steel pipe.