It is known that the life and performance of new and existing pipelines can be extended and optimised by lining lengths of metal pipe with polymer liners. For example, the Applicant's Swagelining® pipe lining service allows existing pipelines to be remediated and new pipelines to be provided with corrosion resistance by installing a polymer liner that remains in tight contact with the inside of a host pipe.
In a typical pipe lining process of this kind, a polymer liner pipe is drawn into a host pipe via a die which reduces it in diameter. The liner pipe is drawn by a pulling device such as a winch connected to the end of the pipe by a cable and pulling cone arrangement. When pulling tension is removed, the liner pipe undergoes a process known as “reversion” in which the memory characteristics of the material of the liner pipe cause it to undergo radial expansion as it reverts towards its original dimensions and until it contacts the inner surface of the host pipe. As a result of selecting a liner pipe of an outer diameter equal to or, preferably, greater than the inner diameter of the host pipe, the host pipe is provided with an extremely close fitting lining.
When lining a long section of host pipe, it may be the case that the liner pipe is constructed from a number of sections that are successively butt-welded, as the liner pipe is drawn through the host pipe, to produce a liner pipe of sufficient length. Regardless of whether the liner pipe is so constructed on-site, taken from a spooled or continuous length of liner pipe on indeed extruded on demand, there is a risk that the liner pipe may contain one or more leaks. It is well understood that at the butt-weld locations there may be leaks, or weaknesses that could result in leaks, but it is also understood that there may be perforations or damage to the liner pipe itself (or liner pipe sections) which presents the risk of leak.
Understandably, if the liner pipe is perforated or ruptured or exhibits any kind of leak (whether at the location of a butt-weld or elsewhere) then the integrity of the corrosion barrier provided by the liner pipe is compromised. At present, internal corrosion barriers for pipelines—be they liners, sprayed polymer, painted epoxies or other forms of surface coating for example—are difficult to test with anything approaching complete reliability. Even a small hole in a protective coating can result in so-called “pin hole corrosion” that can very rapidly produce a hole through the wall of a steel host pipe.
One known method of testing the integrity of polymer lined pipe is to allow the reversion process to complete, and attach special end connectors to each end of the pipe which is then flooded with water for the purposes of leak detection. The pressurised water will escape through any perforations or ruptures and into the annular space between the liner and the host steel pipe. The end connectors provide vent points for the annular space and if water is detected at the vents then the liner has been compromised. This is a costly exercise, and requires the production and controlled disposal of the water used in the test. Furthermore, the process is slow because it may take several days for a liner to revert fully, and it may then take several days to perform the test.
An alternative method of testing the integrity of a (non-conductive) protective coating is to perform a so-called Holiday or Continuity test in which a low voltage is applied across a test area; if electrical current is detected in the test area this is indicative of the presence of discontinuities in the coating (for example, pinholes or ruptures). However, these methods are generally performed on external coatings and it would be extremely difficult to perform them on internal coatings where direct access is limited.
U.S. Pat. No. 4,273,605 relates to a method of lining and sealing hollow ducts in which a flattened flexible tube is inflated to contact a pipeline interior wall. This pressure may subsequently be used to test the integrity of the lined pipeline.
Similarly, GB2186340 A discloses a pipe lining and a closure that can be used for pressure testing of a liner pipe. The internal wall of the liner pipe is pressurised to expand it into engagement with the internal wall of the host pipe—in this case for enforced reversion rather than inflation. Thereafter, pressurisation may be used to test the integrity of the lined pipeline.
US 2009/0205733A1 discloses a “core pipe” which is deformable into a C-shape to facilitate insertion into a host pipe. The deformed pipe is wrapped in Mylar to hold it in that shape. Subsequent to insertion in the host pipe, the core pipe is sealed and pressurised to overcome the resistance provided by the Mylar wrap and reform the pipe into its original circular cross-section. Post re-forming, and while the core pipe is still sealed, a full hydrostatic test at operational pressure may be performed to verify pipe integrity.
It is an object of at least one aspect of the present invention to provide a method of testing the integrity of a pipe lining. Embodiments of aspects of the present invention are intended to realise this object and to obviate or mitigate one or more disadvantages of existing integrity tests.
Further aims and objects of the invention will become apparent from reading the following description.