Paignton-based Exjet has been serving the sewer market for the past 27 years providing drainage solutions to the construction industry, civil engineering, government departments, health authorities, the retail industry, Wessex Water and South West Water. Over this time the company has become a leading operator at the forefront of the industry across the South West of England. Whilst for many years the company’s core market has been drain cleaning and unblocking services, including 24/7 blockage removal, the range of services now offered has been expanded to include CCTV surveying to WTI standards and includes light line profiling; drain repair, including in-situ pipe lining and pitch fibre pipe rehabilitation; open cut excavations and high volume water jetting using jet vac units.
As part of this service expansion, over the past few years Exjet has, as part of its CCTV survey operations, increasingly employed the use of laser-based light line surveys to improve the range of information that can be made available to clients during pipeline surveys. Most recently the company has invested in a triple laser light unit for even greater accuracy of data in larger diameter pipes from such surveys than has been previously available using a single laser system. The company utilises a Clearline laser profiling system with its associated analysis software.
WESSEX WATER PROJECT
An example of the type of work being undertaken for water companies using light line profile surveying was one completed recently for Wessex Water to examine the interior of an existing concrete pipeline prior to the commencement of a rehabilitation operation. The project involved surveying a 68 m long, 1,050 mm diameter pipeline with an invert 300 mm diameter low-flow channel built in which runs under the M5 motorway near Banwell that was earmarked for rehabilitation. The survey was required after the pipe had been deep cleaned to established residual wall thickness and therefore residual pipe strength around which a rehabilitation and redesign of the pipe use took place. The plan subsequently selected for the pipeline was to install a full circular CIPP liner in the low-flow channel using a glass-fibre, UV cured liner. The pipe was then part filled with 200 mm depth of grout onto which were laid two SDR11 PE100 HDPE over-pumping pipelines which were ultimately grouted into place permanently by grout filling the remainder of the pipe.
The lining work was to be carried out by main contractor Onsite, but the light line profile survey was subcontracted to Exjet given its previous experience with light line profiling. The physical survey of the pipe itself was completed in just one day utilising a standard technique used by Exjet whereby a visual/laser profile is completed on the outward run through the pipe from the start shaft. This allows a full visual check to be made within the pipe for defects, protrusions and other faults at the same time as a light line survey is undertaken. Once this run is complete, a second light line profile only survey is completed on the reverse run as the tractor is retrieved through the pipe to verify the outward run data. The data collected from the twin-run survey is then fed into the analysis software.
According to Exjet General Manager, Rob Dowell: “The real work begins once the practical survey is done. It is the highly sophisticated software that brings out the true depth available from the results of the survey data and that is usually done back at the office. With the output potential from the software system clients then see just how clever and useful this type of survey can be.” Knowing how the survey unit was set up in the pipe, the software finds the centreline of the light ring and starts to check data at 2 degree intervals around the ring at a rate of between 28 and 30 time per second (about 4 million measurements over a 30 minute survey). Once the basic data has been established the analysis can begin.
The level of data can be varied to give the client the information it is seeking over a wide range of options. The Quick Analysis shows variance of diameter using colour difference along the pipe length showing increase or decrease of diameter in relation to the nominal diameter of the pipe. For greater detail of the pipe condition the software can also produce an ovality check, minimum and maximum diameter measurements an XY cross-section at any point in the pipe length surveyed, the potential capacity loss or gain and as in the case for Wessex Water residual pipe wall thickness. The software can also then generate a 3D image of the pipe over the survey length with again colour difference on the image showing variations from those expected.
In the case of the Banwell survey it was also possible to split the data stream to analyse just the smaller diameter low-flow profile in the invert as a separate part of the overall analysis. In the event the Banwell data showed that the pipe had sufficient residual strength to be rehabilitated successfully and redesigned in accordance with future company needs. At the end of the processing run the client then receives the full analysis results or the set of results requested prior to the survey.
The type of data produced using a light line profile survey can be offer significant increase in the base understanding of any pipeline length. This not only enables site operations to run more smoothly once works begin on site simply because there is a greater understanding of what to expect, but also the survey can a provide solid foundation on which liner design and liner type can based.
Rob Dowell went on the say: “The target of all water company contractors today is to get the job done quickly and efficiently and least cost to the client and therefore ultimately to the water company’s customers. Whilst a standard CCTV survey can often give the results required for general information like state of cleanliness, obvious defects like cracks/fractures and displaced joints, there is often a need for more detailed information in relation to future repair/maintenance and rehabilitation options that we as a company, over the years, have found difficult if not impossible to gain using visual survey techniques alone. This is why we have moved towards the use of light line profiling, and more recently in larger diameters, where more detailed information is required. All we ask is a clean pipe at the start, man-entry access to enable us to set up our equipment and preferably, but not necessarily, two-point access at either end of the survey run. We will then do our best to get our clients all the information they could need.”
Commenting on the Banwell project Julian Britton, Senior Engineer for Wessex Water said: “The use of the light line profile system in this instance (at Banwell) gave us all the information we required to establish the residual strength of the pipeline. This enabled the type of rehabilitation/reconstruction we needed for the pipeline under the M5 to be confirmed. Ultimately we utilised the rehabilitated low-flow channel for existing flow management whilst utilising the remainder of the pipe with a view to future operations by using it to house two over-pumping mains. We are looking to use light line profile surveys for a number of other aspects of our planning and reconstruction/rehabilitation effort over the coming years as well as continuing to work with survey contractors for this type of information as we have in the past for works such as checking ovality in flexile pipe structures etc.”