Gassco inspected the Knarr gas pipeline earlier this month, the inaugural outing for its Surveyor Interceptor remotely operated vehicle, proving that the technology works.

Specially built by Kystdesign in Haugesund for a joint venture between MMT and ReachSubsea, Surveyor Interceptor's unique design and outfitting allow it to acquire stable data at high speed.

Gassco, which operates the gas transport system that delivers Norwegian gas to continental Europe and the UK through more than 8000 kilometres of pipelines, said the trials were successful.

As the company responsible for operating and maintaining this network, it is constantly looking for cost-effective solutions which provide the highest quality.

"Most of the gas pipelines lie on the seabed, and ROVs controlled from surface vessels must therefore be used for maintenance and monitoring work," the transport network's vice president Kristin Kinn Kaste explained.

"Such operations are basically expensive. Factors affecting the price include the offshore vessel, the ROV's efficiency and the choice of inspection technology. Using new, world-leading technology is therefore cost-efficient for us."

Inspection of the 106km Knarr gas pipeline took place in the northern North Sea at water depths of 140-400m to check the external condition of the pipeline and the rock berm protection after laying, but the work had to be completed before the pipeline could kill with gas.

The Knarr inspection job took just 17 hours, giving an average speed of 3.33 knots (6.2 kilometres per hour), and the ROV was operated at a top speed of 4.5 knots (8.3 kph) - about three times the speed formally achieved in similar water depths.

Surveyor Interceptor performed stably during the inspection, and the data acquired was of very good quality.

Data was processed and analysed continuously on the Edda Fonn support vessel in order to provide a field report to Gassco on demobilisation.

The Knarr field is located about 100kms north of Brent in the northern-most North Sea.

The 12-inch pipeline has since been tied into the existing Far North Liquids and Associated Gas System [Flags] pipeline, which will soon carry rich gas to St Fergus in Scotland via the Shell-Esso Gas and Liquids [Segal] system.

The technical capacity of the pipeline is 5.6 million cubic feet per day.

Gassco operates the pipeline, while the field is operated by BG.

It also recently repaired the valves at the metering station in St Fergus without the need for a shutdown, proving a new method for repairing valves while in service.

"A new line of products, combined with a high level of expertise with valves, was required to develop this new, effective and purposeful repair method. It definitely represents an important breakthrough," Kaste explained.

The products used are gel-based and spread through the lubrication channels to the entire seat and ball surfaces.

Klyde Consultant, a valve maintenance and consultancy company, was an important partner during the project.

Without this method, the 12 valves would have had to be sent to a workshop for repair.

Another option considered was to build a new metering station with new valves at an estimated cost of NOK 100 million ($A16 million).