The inside story
Internal pipe-joint repairs avoid difficult excavation and high service costs, Stephen Taylor of PMP reports
Most repairs to leaking pipeline joints give engineers a choice – repair using a trenchless method or by excavation. Although various factors might make that decision far from straightforward, trenchless technology now allows for extremely durable repairs without digging.
For larger-diameter pipelines, in which man-access is possible, leaking joints and radial cracks in the pipe wall can now be repaired to last out the pipe’s working life, without any excavation whatsoever. The benefits are obvious in situations in which the alternative of putting in a large trench, in order to fit a repair clamp, would create disruption at ground level, or require costly surface reinstatement.
Not surprisingly, under the Confined Space Regulations 1997, the inside of a pipeline is considered to be a confined space, with at least one of the following risks:
n limited access,
n the space may contain hazardous or toxic substances,
n the air may be irrespirable or explosive,
n there may be a potential for entrapment, engulfment or in-rush.
Therefore, any activities carried out by personnel working within a pipe must comply with the regulations. The regulations require avoidance of entry into confined spaces or, if this is unavoidable, that an employer should set up a safe system of work and make emergency arrangements. So it is common practice to employ a specialist
contractor for internal pipe repairs.
Commissioning a confined-spaces contractor has recently become a much simpler exercise. Previously, the Policies, Procedures and Arrangements (PPAs) for confined-space working that were developed within the various water companies were, in some cases, adapted to provide specific instructions to contractors. This led to the inconsistent specification of skills, training and equipment requirements facing contractors working for more than one water company.
As a result of the confusion over diverse PPAs, Water UK set up a Confined Spaces Rationalisation Project, to work with the HSE, which has resulted in guidance that provides a single national standard when specifying work to contractors. A similar rationalisation in
training standards has also engendered more consistency.
A contract solution
The internal pipe-repair system recommended and installed by PMP is the Amex-10-Seal, which, because it is mechanically fitted and has an integral test facility, can also be used as a joint tester for systematically checking suspect joints before any repairs are commissioned. One of the reasons for the longevity of this repair method is that it bridges the leaking area, between the upstream and downstream pipe walls, with
a tough, flexible seal that allows for future ground movement and
misalignment of the pipe joint.
Basically the repair seal is created by a low-profile, made-to-measure rubber hoop, which spans the joint, crack or localised damage. In potable water and sewerage applications, the rubber used is an extruded EPDM profile, and the seals can be made for all pipe sizes from 600mm up to 4m, provided that human access can be achieved. No chemical joint sealants or strip adhesives are involved, as the seal is securely compressed against the pipe wall, not bonded to it. This is achieved by experienced fitters, using compact hydraulic equipment to insert two stainless steel compression rings. A further benefit of having no reliance on chemical adhesives or coatings is that the seal can be installed and tested relatively quickly.
Suitable for pipe materials including steel, ductile iron, concrete and GRP, the seals can withstand pipeline pressures up to 20bar, as rated by the manufacturer, Amex GmbH. PMP has successfully installed 900mm and 1,100mm diameter seals in a treated water pipeline with a working pressure of 16bar and a test pressure of 20bar. The Amex-10-Seal has recently undergone an exhaustive test carried out by RAPRA, the leading rubber testing centre, which confirmed that the service life of the seal is at least 50 years. No other pipe joint repair system has undergone the same test.
When the seal has been fitted, it is pneumatically tested. For this step, a portable air tester is connected to the seal to inflate the rubber with compressed air. Then a soap solution is applied around the interface between the seal rubber and the pipe to check for leaks. Since air seeks an escape path far more efficiently than water, a pneumatic test provides an extremely reliable indicator of the repair’s success.
A great advantage of this repair method is that, because the seal is fitted to the upstream pipe wall independently of the downstream pipe wall, the 120mm of rubber that spans the pipe joint is free to adjust to any subsequent movement. The seals can accommodate expansion, contraction, displacement or rotation and, if the pipe joint movement is excessive (outside the limits of the rubber) for example due to land slippage, the problem can be rectified. An installation engineer can return to the seals to release the stainless steel retaining bands, reposition the rubber and refit the seals.
Steep test for Amex-10
The seals were recently required by AMCO Construction, in carrying out remedial works to a number of joints on a pipeline buried on a hillside. The pipeline forms the penstock for one of Scotland’s newest hydroelectric schemes at Kingairloch, which is located on the Morvern peninsula, southwest of Fort William.
Kingairloch Hydro Scheme has a generation capacity of 3.5MW with a gross operating head of 143m. The scheme is located within the Abhainn na Coinnich river catchment and includes a storage reservoir at Loch Uisge, with water diverted from a number of the river’s tributaries.
The penstock includes approximately 4.5km of buried pipe made up from approximately 3.5km of 1,200mm diameter and 1km of 900mm diameter. The pipeline is buried in a trench over upland terrain at variable gradients up to 50% and is rated between PN 6 and PN 25. As the pipeline had to be laid to tight dimensional tolerances, a number of the joints between sections of the pipeline did not conform to the specification.
PMP used roped access skills to fit the unique Amex-10-Seals from within the pipe. By completing all repairs internally, difficult excavation and high service costs were avoided. Roped access was required to reach down to pipe joints where the operating pressure approached 25bar. Gaining access from a removed section of the 900mm pipe, the PMP engineer was lowered to the location of each leaking joint, in order to carry out the preparation and fitting of the seals. In total, 28 seals were fitted over a period of two to three months.
Although undertaking this method of joint repair is subject to the Confined Spaces Regulations 1997, it does not rely on chemical bonding, and is free from associated contamination hazards and health risks. It is purely a mechanical method, which is highly adaptable due to its simple concept. Already its application has extended beyond pipelines, with the successful repair of a leaking box culvert recently completed in the UK.