Provided is an + titanium alloy welded pipe excellent in the strength and the rigidity in the pipe longitudinal direction, the + titanium alloy welded pipe having a composition consisting of, in mass %, Fe: 0.8% to 1.5%, N: 0.02% or less, and the balance: Ti and impurities, and satisfying Q shown in Formula (1) being 0.34 to 0.55. A tensile strength in a pipe longitudinal direction is more than 900 MPa and a Young's modulus in the pipe longitudinal direction is more than 130 GPa.

Q=[O]+2.77[N]+0.1[Fe](1)

where [Fe], [O], and [N] represent the amounts of the respective elements contained [mass %].

Provided is an + titanium alloy welded pipe excellent in the strength and the rigidity in the pipe longitudinal direction, the + titanium alloy welded pipe having a composition consisting of, in mass %, Fe: 0.8% to 1.5%, N: 0.02% or less, and the balance: Ti and impurities, and satisfying Q shown in Formula (1) being 0.34 to 0.55. A tensile strength in a pipe longitudinal direction is more than 900 MPa and a Young's modulus in the pipe longitudinal direction is more than 130 GPa.

Q=[O]+2.77[N]+0.1[Fe](1)

where [Fe], [O], and [N] represent the amounts of the respective elements contained [mass %].

According to one aspect, a tubular structure may include a base and a wrap. The base may have a first surface and second surface opposite one another, the first surface defining an elongate cavity, and the base having a tubular shape defining a longitudinal axis extending along the elongate cavity. The wrap may be supported on the second surface of the base, the wrap including a plurality of layers, and each layer having a first longitudinal edge and a second longitudinal edge coupled to one another along a respective spiral seam associated with the given layer and extending about the longitudinal axis of the base.

According to one aspect, a tubular structure may include a base and a wrap. The base may have a first surface and second surface opposite one another, the first surface defining an elongate cavity, and the base having a tubular shape defining a longitudinal axis extending along the elongate cavity. The wrap may be supported on the second surface of the base, the wrap including a plurality of layers, and each layer having a first longitudinal edge and a second longitudinal edge coupled to one another along a respective spiral seam associated with the given layer and extending about the longitudinal axis of the base.

A rolling apparatus for an annular workpiece includes roller, a rolling wheel device, a base, and a stand. The roller has two circular frames that holds the annular workpiece therein using removable fixing members. After an outer circumferential surface of the annular workpiece is tightly wrapped by an investment material, the fixing members are removed to leave a through hole at the center of the investment material and the annular workpiece has its inner circumferential surface exposed at the through hole. The cylindrical rolling wheel of the rolling wheel device passes through the through hole of the investment material and rolls on the inner circumferential surface of the annular workpiece against a rolling platform of the base to increase the density of the annular workpiece. During the rolling operation, the investment material positions the annular workpiece and protects textures and patterns preformed on the outer circumferential surface.

A rolling apparatus for an annular workpiece includes roller, a rolling wheel device, a base, and a stand. The roller has two circular frames that holds the annular workpiece therein using removable fixing members. After an outer circumferential surface of the annular workpiece is tightly wrapped by an investment material, the fixing members are removed to leave a through hole at the center of the investment material and the annular workpiece has its inner circumferential surface exposed at the through hole. The cylindrical rolling wheel of the rolling wheel device passes through the through hole of the investment material and rolls on the inner circumferential surface of the annular workpiece against a rolling platform of the base to increase the density of the annular workpiece. During the rolling operation, the investment material positions the annular workpiece and protects textures and patterns preformed on the outer circumferential surface.