Feature 3 | REPAIR & MAINTENANCE
Novel defect detection technique to be used on T-class submarine
An innovative engineering solution developed to address a costly and time-consuming issue in submarine maintenance programmes is to be applied for the first time since being qualified for use, on the Trafalgar class submarine HMS Trenchant.
T
he new technique will be used during the ongoing Revalidation and Maintenance Period (RAMP)
being undertaken on HMS Trenchant by Babcock at Devonport Royal Dockyard. The new development is a technique
deploying leading-edge Non Destructive Testing (NDT) technology to enable the propulsion tailshaſt on HMS Trenchant to be inspected for defects and revalidated in-situ, with significant benefits over conventional removal methods. A rigorous inspection regime is required
to ensure safety and operational effectiveness. (The tailshaft operates in a high-fatigue salt water environment which can cause problems if seawater has been able to seep beneath the protective glass-reinforced plastic (GRP) layer). Traditionally this has involved removal
of the tailshaſt (which may be up to 20m long and weighs some 20-25tonnes), and machining off the GRP layer, to inspect and revalidate it. This is a costly and time-consuming process, and will often find no problems. Te new method saves considerable time and money, as well as avoiding potential delays during docking periods, thereby contributing to improved submarine availability. Te novel solution was developed by a
Babcock-led team including the Ministry of Defence Maritime Equipment Services team (who had approached Babcock to find a solution), Frazer-Nash Consultancy, and NDT industry partners Imes and Sonovation. Instead of removal for external inspection,
the new technique enables the tailshaft to be inspected from inside the tailshaſt bore, using advanced NDT technology to penetrate the wall thickness and identify defects on the external surface from within. Tis is technically extremely challenging,
22 The carriage and sensor carrier are inserted into the tailshaft.
as the sensors have to be able to identify small defects (typically 1.5mm) through a comparatively thick wall (50-200mm), and must distinguish between corrosion pits, cracks, and welded machining repairs. Specially developed equipment is fed into the hollow tailshaſt through a 4inch
Maintenance programmes for Trafalgar class submarines will be less costly and time consuming thanks to the new technique.
aperture at the outboard end of the shaſt, featuring a section of track held between two centralising spider assemblies. A transducer carrier with ultrasonic probes moves up and down the track and sweeps round, indexing 1-2 degrees at a time around the full 360degrees.
Warship Technology July/August 2010
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