Patent ID: 7708319

Claim:
A piping joint structure in which an end of a first tubular material and an end of a second tubular material, which is located adjacent to the first tubular material, are joined by butt welding, wherein an inner fitting portion is formed along a circumferential direction on an end face of said first tubular material, and a first bevel is formed on the radial outside of said inner fitting portion around the circumference, and an outer fitting portion, which is fitted to the radial outside of said inner fitting portion, is formed on an end face of said second tubular material, and a second bevel is formed around the circumference at a location that is at the end of said outer fitting portion and that faces said first bevel, wherein the shape of the cross-section of the face of said inner fitting portion located on the radial outside, and the shape of the cross-section of the face of said outer fitting portion located on the radial inside, are processed such that each is completely round with a curvature that is constant around the whole circumference, wherein the first tubular material and said inner fitting portion are integrally molded, wherein the second tubular material and said outer fitting portion are integrally molded, and wherein a thickness of the first tubular material increases gradually between the both ends of the first tubular material along a direction of fluid flow within the piping joint structure.