Steam cure inversion lining minimizes environmental impact on Scottish countryside

Drybridge is a village laying some 6 1/2 miles east of Kilmarnock in Scotland, UK. Recently, on farmland near the village, Insituform Technologies Ltd (Insituform) once again showed its experience and expertise in the pipeline rehabilitation sector when it undertook and successfully completed a difficult project to line a 1,200 mm diameter, 42 m long pipeline running across a pipe bridge spanning the River Irvine.

The pipebridge section was the last remaining element of an 1,800 m long rehabilitation/replacement scheme for part of the Irvine Valley Trunk Sewer, which is owned and operated by Scottish Water. The project was being carried out by Morrison Construction as Main Contractor. Several options, including a new pipebridge and sewer, had been considered but rejected due to various constraints, not least being the inaccessibility of the downstream end of the pipe deep below the village of Drybridge. Morrison called in ITL for advice.

Following initial introduction, Morrison Construction's Site Agent, Greg Adamson, and Insituform's Project Engineer, Rob Mckay, working closely together, developed a strategy that met with Scottish Water's directive for a pipe rehabilitation solution that negated the requirement for intrusive engineering works at the site. It was decided that, due to time restrictions imposed regarding flow control within the pipe, the only viable option for completing the work would be to utilise air inversion of the lining with steam curing, as this would reduce the operating window required to complete the installation to a minimum. Having gained Scottish Water's approval, Morrison formally engaged ITL as lining sub-contractor for the pipebridge section.

The pipe bridge crossing the River Irvine.The proposed work site was also of interest because the pipe being lined passes over the River Irvine which feeds into a harbor classified as 'Blue Flag' according to European Standards and as such the work generated a great of interest from various parties with an environmental interest in maintaining this status.

Access to the site proved to be extremely challenging, with the pipe bridge access being located on farmland with only one pedestrian access point via a flight of stairs from the main road through the village. This meant that the only option was to utilize the temporary access road, some 2,000 m long, built by Morrison across farmland for the other sections of the work.

Lining Operation
Various pieces of equipment were considered as the planning stages progressed as well as during the implementation of the project. The primary equipment used for the actual liner inversion process included Insituform's Dual Gland Air Inversion (DGAI) unit and a Supporting Steam Boiler.

The liner installation equipment set-up.The DGAI unit was developed by Insituform to overcome some of the limitations encountered with other air inversion systems. The DGAI unit allows air inversion and steam cure of diameters as large as 2 meters and lengths in excess of 300 meters can be installed in a single operation.

The new system takes a factory impregnated liner directly off the delivery truck on site, eliminating any need to confine it in any way. The inversion process involves attaching the free end of the liner to the DGAI unit. The liner is inverted through a gland in the unit, which is designed to provide a seal to allow air pressure to be applied to the inside of the inverting liner. The 'gland' design maintains the internal pressure required for inversion to proceed whilst allowing the free movement of the liner through the 'gland' during the inversion process.

The access point opened on the Dry Bridge main.Given the complexities of the site, project timings were planned with the intention that the lining operation would be carried out over a 3-day period. This would involve Day 1 for travel to the site; Day 2 as site set up and preparation for the lining operation; and Day 3 being used to complete the inversion procedure. However, due to the pipe's operational requirements, the project was extremely weather-sensitive as the flows within the pipe being rehabilitated would increase considerably during any period of rainfall. With this in mind, the overall planning schedule included procedures to enable Insituform to accelerate these timings if a suitable weather window was presented. The entire operation was ultimately carried out and completed in just 25 hours, including travel to site, site set up and completion of the inversion process.

During the course of this 25-hour window of operation, no problems were encountered. This, according to the site personnel, was a testament to the precise planning of the works and the efficient way in which the actual installation was carried out, both on the part of Morrison Construction and Insituform.

Steam curing was completed well into the night.Environmental ManagementThere were some special arrangements that had to be undertaken for the project that were mainly related to environmental concerns. As the pipe bridge was suspended over a river which led to a blue flag harbor, there were concerns regarding any possible contamination. Morrison Construction, working closely with specialist pumping sub-contractor, SLD, devised a pumping operation that would be able to deal with expected flows within the pipe under repair based on specific dry weather conditions prior to and during the lining operation. A number of contingency measures, including continuous monitoring by Morrison and SLD, were put in place to handle any dramatic change in weather conditions and, therefore, flows in the pipeline, which could reach in excess of 1,200 l/sec. Everything was planned and executed exactly as required, and the lining operation was completed in what was described by the site personnel as 'comfortable conditions'.

For the main contractor, Morrison Construction, Site Agent Greg Adamson, stated: "We always knew this would not be any easy installation to complete. However, the recent development of the larger diameter steam lining option by Insituform, the minimal impact at the site and reduced access requirements this allowed, enabled us to successfully complete a lining operation at a remote, difficult to access location in environmentally-sensitive conditions in a timescale significantly less than conventional water curing methods - given the complexity of the overpumping operation and the proximity to a major watercourse; this was a key factor in the successful completion of the operation.. We were very satisfied with the outcome achieved. The close cooperation between all the teams involved was a major factor in this success of this project over and above the efficient application of the lining system by Insituform's crew."

Commenting on the work, Insituform's Project Engineer, Rob McKay, said: "This operation was an astounding success despite initially being a very difficult prospect. Working closely with Morrison to produce a very detailed plan and by making sure our preparations were good (a process that took approximately 4 months), we were able to successfully complete the lining operation, once again enhancing ITL's position in the rehabilitation industry. We met and surpassed Morrison's expectations and have been acknowledged by Scottish Water for every aspect of the operation."

August 2008

###