Improving the bending behaviour of mechanically-lined rigid pipe
A method of making mechanically-lined pipe with primary expansion by plastically expanding a liner sleeve within an outer pipe, under lining pressure applied internally to the liner sleeve. On relieving the lining pressure, elastic radial contraction of the outer pipe makes a mechanical bond between the outer pipe and the liner sleeve. Then, secondary expansion of the outer pipe is performed under fixing pressure, which may be greater than the lining pressure, applied internally to the liner sleeve at an end portion of the pipe. This makes or strengthens a mechanical bond at the end portion. The resulting pipe joint has an end portion and a body portion inboard of the end portion. The body portion has a first, lesser bonding pressure between the outer pipe and the liner sleeve. The end portion has a second, greater bonding pressure between the outer pipe and liner sleeve.
1. A method of making mechanically-lined rigid pipe, comprising:
inserting an end plug into an end portion of an outer pipe to seal an open end of the outer pipe, the outer pipe surrounding a liner sleeve;
in a primary radial expansion, expanding the outer pipe by plastically expanding the liner sleeve against an inner surface of the outer pipe, under a lining pressure applied internally to the liner sleeve while the end plug shields the liner sleeve within the end portion of the outer pipe from plastic expansion under the lining pressure;
relieving the lining pressure to permit elastic radial contraction of the outer pipe around the plastically-expanded liner sleeve, that contraction making a mechanical bond between the outer pipe and the liner sleeve at a body portion of the outer pipe inboard of the end portion that contains the end plug;
removing the end plug from the end portion of the outer pipe;
placing an external annular backing ring around the end portion of the outer pipe; and
subsequently, performing a secondary radial expansion of the end portion of the outer pipe by local plastic expansion of the liner sleeve within the end portion of the outer pipe against the inner surface of the end portion of the outer pipe, under a fixing pressure applied internally to the liner sleeve within the end portion of the outer pipe, wherein the fixing pressure is greater than the lining pressure.
2. The method of claim 1 , wherein the outer pipe is at least partially expanded plastically during the secondary expansion.
3. The method of claim 1 , followed by applying an overlay at which the liner sleeve is chemically or metallurgically bonded to the outer pipe.
4. The method of claim 1 , comprising inserting an expander apparatus into the end portion of the outer pipe after relieving the lining pressure, and activating the expander apparatus after insertion to apply the fixing pressure to the liner sleeve within the end portion of the outer pipe.
5. The method of claim 1 , wherein the fixing pressure is applied to the liner sleeve over a length of less than 50 cm of the outer pipe.
6. The method of claim 1 , wherein the secondary radial expansion is performed to make or to strengthen a mechanical bond between the liner sleeve and the outer pipe.
7. Mechanically-lined rigid pipe made by the method of claim 1 .