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Pipe Penetrating Radar Void Detection

Project: Millenium Main
Scope: Inspect and measure for voids outside of host-pipe
Location: Central London

On a ground-breaking project for a long-standing client, WSG were requested to provide Pipe Penetrating Radar (PPR) to locate and measure voids formed between a 1000mm GRP liner and the 1100mm internal diameter of the concrete host pipe. WSG were subsequently asked to check the alignment of the GRP sections to 1 degree accuracy and to test for ovality using LiDAR.

Developments:

We designed and built a 360-degree rotational PPR manipulator with retractable arm to mount on our long-range crawler. This mechanical rotator allowed for the precise placement of the radar head at any point around the circumference of the pipeline.

On Site Trails:

The initial trial survey was carried out using a circumferential scanning method. This caused a few unforeseen complications with interpreting the data. Subsequently technical improvements were made to the manipulator head to facilitate a series of longitudinal scans rather than circumferential scans. Longitudinal scans of the pipe and its surroundings were taken at every 22.5 degrees thereby providing 16 scans of the pipe and circa 200mm of surrounding material. A fixed-frequency radar head was used to produce highly accurate images of both liner/host pipes and the presence or absence of material between them.

Access challenges

From the outset, extreme access restrictions necessitated the robot being dismantled into its component parts in order to pass is through a standard 600 x 600mm access manhole and then had to be re-assembled within the section of the water main to be surveyed. Access into the main was often restricted to openings as small as 480mm in width which was only just wide enough to squeeze the components of the robot through.

Results:

Nearly 25km of useable radar data was recorded from the 12-sections of the asset that were surveyed. 16 scans of circa 1.5km of the water main.

This method proved to be both effective and accurate with voids being located (to within 10mm), measured, and subsequently verified by sample hole drilling. The holes were subsequently utilised as injection points for the pumped resin chosen to fill the voids.

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Tunnel Vision faced setbacks and challenges during the initial site trials with the robot’s manipulator arm and with the data collection and interpretation. Their team demonstrated a positive approach to overcoming the challenges and went on to successfully complete what was the most technically challenging and complex survey that we have undertaken to date and a vital part of the project. The accuracy of the information delivered enabled key decisions to be made on the project delivery. I highly recommend them and look forward to working together on other projects.

Paul Garland, Project Manager – Morrison WS

FAQs

Frequently Asked Question

What was the objective of this survey?

To locate and measure voids between a 1000 mm GRP liner and the 1100 mm concrete host pipe using PPR, then check GRP section alignment to 1 degree and test ovality with LiDAR.

We designed a 360-degree rotational PPR manipulator with a retractable arm mounted on a long-range crawler, allowing precise head placement around the circumference.

Longitudinal scans improved data interpretation and quality. We captured 16 passes at 22.5-degree intervals, recording the pipe and about 200 mm of surrounding material.

Voids were located to within about 10 mm and verified by sample drilling. The drill holes were then used as injection points for resin fill.

The robot was dismantled to pass through 600 x 600 mm entries and reassembled underground, with some openings as small as 480 mm.

Nearly 25 km of usable radar traces were recorded across 12 sections, covering roughly 1.5 km of the main with 16 scans per traverse.