Cathelco corrosion protection for arctic drilling platforms

Tag : Bio Disc


Two massive semi-submersible drilling rigs, designed to operate in the arctic conditions of the Barents Sea, will be protected against corrosion using Cathelco Jotun cathodic protection systems. In addition, Cathelco will be supplying marine pipework anti-fouling systems to protect seachests and pipework against bio-fouling. The rigs will be constructed at the Vyborg yard in Russia for Gazflot, a subsidiary of the Russian energy giant Gazprom. The order for the Cathelco equipment has been won by Marine Bridge & Navigation Systems, the company's well established agent in St Petersburg.

The semi-submersibles are based on the versatile Moss Maritime CS 50 design. Cathelco Jotun has supplied cathodic protection equipment for Moss Maritime platforms in the past and this experience has led to the new contract. "We are delighted to have received the orders for both the cathodic protection and anti-fouling systems on the strength of our experience in this field and the on-going relationship with Moss Maritime", said Kevin Ward, Cathelco Jotun's sales manager. The semi-submersibles have a displacement of 55,000 tonnes and are designed with two 118 metre long pontoons with six stabilising columns supporting the upper hull in conjunction with four horizontal and diagonal trusses.

Because of the arduous operating conditions, the central part of the rig consists of a riser column to protect the riser from damage by pack ice. "In terms of the cathodic protection system, the riser column increases the size of the surface area and we have taken this into account in our design", said Aneel Mumtaz of Cathelco Jotun who has been responsible for the technical aspects of the project.

"In this rig the complex geometry, especially around the bracings and riser column, might create a potential ‘hot spot' vulnerable to ‘under protection; despite the ICCP system providing optimum protection to the whole structure. This issue has been overcome by placing sacrificial anodes to the ‘hot spot' areas eliminating any risk of ‘under protection' to the structure due to its complex shape", Aneel commented.

He explained that Cathelco Jotun would be supplying four 800 amp ICCP thyristor control panels serving a total of 12 mounted rod anodes and 12 large disc anodes, all designed to be diver changeable. "The structure of rig creates complex shapes which cannot be fully protected with an ICCP system alone and therefore the design incorporates the use of sacrificial anodes to provide comprehensive corrosion protection", Aneel explained.

In total 780 sacrificial anodes will be supplied to protect the port and starboard water ballast tanks, submerged cross members and seachests. Cathelco pipework anti-fouling systems, using copper and aluminium anodes, will safeguard against bio-fouling in four seachests with flow rates of 2, 280 cubic metres per hour. The first of the platforms will be delivered in 2010 and the second in 2011. They have been designed to operate in the Barents Sea and Kara Sea drilling to a depth of 7.5 kilometres in up to 500 metres of water. It is known that these areas can be threatened by icebergs of up to 4 million tonnes in weight, a factor which has an important influence on the design and construction of the rig.