Non-Destructive Testing (NDT)

Project: Guernsey Public Utilities
Scope: Condition assessment on cast iron mains
Location: Belle Greve and Red Lion outfalls

The highly specialised non-destructive testing project was carried out in conjunction with our partnering company and the chosen NDT discipline was Magnetic Flux Leakage (MFL), to locate and measure pin holing, graphitisation levels and thickness of remaining material on surface run pipes, submerged risers and submerged pipe sections.

An ultrasonic wall thickness probe and MFL system was designed specifically for the project and was used by our divers working within a flooded shaft to assess the condition of the riser; the non-destructive testing probe was subsequently mounted on a medium range PIV to assess the condition of sections of the  pipe that were running through the flooded tunnel.

To meet project specific requirements, we modified one of our ultrasonic wall thickness probes to measure HDPE pipe wall thickness and designed and built a remote manipulator arm and cleaning head to fit a small diameter PIV’s to facilitate the inspection and remote non-destructive testing of a 400m long HDPE pipe section which formed an extension to the existing outfall.

Working from a GPU vessel, the PIV was launched into the outfall by our dive team and the control cable tended by a diver throughout the survey.

The project was entirely successful and provided the Client with the level of information they required for future planning of outfall remedial programme.

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They were recommended by Black & Veatch, our Consulting engineers for the Belle Greve project, as the ideal people for the job. Site conditions resulted in the project protracting and PSD’s requirements evolving; TV provided a timely solution for every problem that we encountered on the project even to the point of modifying some testing equipment to measure the wall thickness of a section of HDPE pipe. They provided us with total client support at every stage of the project.

FAQs

Frequently Asked Question

Which NDT techniques did you apply and why?

Magnetic Flux Leakage (MFL) to screen for pin-holing, graphitisation and wall loss on cast-iron sections, plus ultrasonic wall-thickness measurement for quantified remaining wall.

Divers operated an ultrasonic/MFL probe in a flooded shaft for the riser, then the probe was mounted on a medium-range PIV to survey flooded tunnel sections.

We modified an ultrasonic probe for HDPE, added a remote manipulator and cleaning head to a small PIV, and surveyed the 400 m section under controlled conditions.

From a GPU vessel: the dive team launched the PIV into the outfall and a diver tended the control cable throughout the survey.

Evolving scope and mixed environments (surface runs, submerged risers, flooded tunnels) drove custom probe design, a cleaning head, and purpose-built mounts for reliable data capture.

The condition dataset underpinned future remedial planning for the outfalls, prioritising interventions by location and severity.