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Nord Stream retrospective, part 2

Published by
World Pipelines,

Ruurd Hoekstra, Maintenance Director at Nord Stream AG, talks about integrity and maintenance strategies for the Nord Stream gas pipeline: how is the operator tackling the first stages of integrity management?

Who is Nord Stream partnering with to ensure repair capabilities?

Nord Stream has secured the services of specialised offshore construction company Saipem as Main Repair Contractor (MRC).The MRC, together with Nord Stream’s own in-house technical specialist support, has conducted significant levels of detailed engineering to develop the necessary operational procedures and definition of equipment needs to ensure that, in the event of an incident, MRC is ‘ready to act’ to return the pipeline system back to full operational capacity.

Saipem has the inherent advantage that it was the main contractor involved in the construction of the offshore pipeline system and therefore has the familiarity. It can also potentially provide the necessary types of marine vessel spread to undertake recovery and repair of the damaged section of the pipeline.

Another significant element of the Nord Stream Repair Strategy is its membership to the Pipeline Repair and Subsea Intervention (PRSI) Pool, which is administered by Statoil. Through the membership, Nord Stream has access to a range of specialised services and equipment technically suited for performing large diameter subsea repairs, including a remotely operable habitat, pipeline support frames and auxiliary support systems which were already deployed for the hyperbaric weld tie-in of the 48 in. diameter pipeline sections.

Further suppliers were contracted to develop specialised equipment, among them Oil States Industries and TDW Offshore Services.

What special tools have been developed?

We have invested in the development of tools and are currently in the delivery and system integration testing (SIT) phases of a full complement of state of the art pipeline repair tools.

Specific tooling developed by TDW for Nord Stream AG includes SmartPlug isolation tools, pipeline recovery tools (PRT) with dewatering and pig catcher functionality and pipeline end sealing plugs (PEPs), all suited for 48 in. diameter. These would be used if major offshore repairs with the need to isolate sections of the pipeline.

Other specialist tooling and equipment developments through 2015 into 2016 include a clamp-on pig stopper and SmartPlug launcher (CPS/CSL), an activated sealing pig (ASP), subsea mechanical tie-in flange assemblies, as well as a liquid/gas separator.

We are also in the process of developing two structural and pressure containment pipeline repair clamps, which can be externally fitted over an area of damage in order to provide a permanent repair solution. Here we partnered with Oil States Industries. For the installation of the repair clamps, we designed a dedicated installation system, which suspends the clamp and positions it precisely over the pipeline for installation. It can be operated by ROV and can be used in depth up to 214 m.

Now that Nord Stream has been in operation for almost four years, what are the first learnings from a maintenance perspective?

The conditions in the Baltic Sea are certainly unique – as is our pipeline. Nord Stream is the longest large-diameter gas pipeline built to-date. However, the pipeline technology and maintenance have been tried and tested in the North Sea and elsewhere. So there were no surprises.

The results of our surveys show that the pipeline is in good condition: as expected, material integrity shows no sign of corrosion. The pipeline shows the expected signs of settling into the seabed from its own weight and slight shifts.

What we learned is that it has certainly paid off to start setting up organisational structures, find expert personnel and contract suppliers early on. Also important was to instil into the organisation a sense that the cause of integrity management and maintaining an asset goes beyond checking for corrosion but includes many functions within the company. Everyone is pulling in the same direction on this.

Written by Ruurd Hoekstra, Maintenance Director at Nord Stream AG and edited by Elizabeth Corner. This article was published in full in the August 2015 issue of World Pipelines. To read the full article, click here.

Click here to read part 1.

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