Corrosion protection for Rosyth caisson

This was partially in response to the new shape of the dock floor, which had been re-profiled to accommodate the hull form of the new flat bottomed carriers, making the floor effectively 9m wider.

A caisson at the entrance to No 1 Dock was protected against corrosion using the combined resources of Corrintec and UMC International, who created an alliance last year which enabled the specialist diving services of UMC International to be used for the installation and maintenance of corrosion protection systems supplied by Cathelco and its Corrintec division.

The work at Rosyth involved installing a sacrificial anode system on a sliding caisson which has been widened by the addition of a new middle section as part of the major dock extension scheme.

The caisson, measuring 42.7 metres wide and 13.4 metres high, has been protected against corrosion by 48 sacrificial anodes mounted on either side. Corrintec have also supplied anodes which are fitted to internal ballast tanks within the caisson.

‘The aim is to bring the corrosion protection in the new section of the caisson to the same level as in the original sections, therefore the anodes are of the same type and have been positioned in the same configuration as previously to conform to DNV RP 401 standards’, said Aneel Mumtaz, a corrosion engineer at Corrintec.

The sacrificial anodes have been mounted on the caisson using pre-fabricated steel plates with threads. They have been attached to the submerged surface by UMC divers using a specialised underwater welding procedure that was specifically written by their design and consultancy to support the underwater installation of anode support brackets.

The anodes were then bolted into position by the divers, who also made a CCTV recording of their work to confirm that it was performed to the required standard.

‘This is the third caisson that Corrintec has protected as part of the Rosyth dock extension and modernisation scheme. It is particularly satisfying to be involved in this project as Corrintec are also supplying their most technologically advanced impressed current cathodic protection systems for the two aircraft carriers which will be integrated at the yard’, said Ian Pownall, manager of the Corrintec division.