Similar operations will get under way at Eupec’s Kotka plant in Finland during the second half of 2009. The Korean-owned, French-based company was awarded the contract for concrete weight-coating (CWC) and logistics services by the Nord Stream consortium in July 2008, and since that time progress has been rapid.

Within a surprisingly short timeframe of only seven months, EUPEC set up its two CWC plants at either end of the 1,220km pipeline route. EUPEC is currently establishing five ‘marshalling’ yards for the storage and load-out to the pipeline installation contractor of the concrete coated pipes at intervals of approximately 200–250 km along the route. Two of these marshalling yards are nearby the CWC plants, and the others are at Hanko in Finland, and at Slite and Karlskrona in Sweden.

All five sites were chosen to optimise the distance travelled by the pipe-carrier vessels that will be used during the pipelaying operations of the two parallel 1,220 km gas pipelines.

The concrete coating process

The CWC aspect of EUPEC’s work is impressive. The highly-automated CWC plant has been designed to increase the weight of each pipe from 11 tonnes to approximately 25 tonnes with an impinged application of concrete with a 3,040 kg per cubic metre density up to 110 mm thick. What makes even more impact is the logistical operation that will be required for this project. The plan is for approximately 200,000 pipe lengths to be received at the CWC plants and for them to be stored, concrete coated, and then stacked ready for trans-shipment to one of the five marshalling yards. The Mukran site will supply Karlskrona and Slite, Kotka will supply Hanko.

For the first line, anti-corrosion coated pipes from the manufacturer in Germany arrive in Mukran by train. In Kotka they arrive from the Russian manufacturer by train and from the German manufacturer by sea. Each pipe has a bar code, which is immediately recorded upon arrival. The pipes, with wall thicknesses ranging from 26.8 to 41 mm, are unloaded and stored according to the order in which they will eventually be needed by the laybarge.

Upon entering the CWC plant, having been transported in pairs from the storage yards by lorry, the pipes embark on what is essentially a semi-automated journey through the plant, which takes around 24 hours for each pipe. The pipes are first cleaned – internally and externally – inspected, and measured for weight and precise length. This data is then entered into EUPEC’s pipe-tracking system, which forms the critically important heart of the overall operation.

The next stage in the coating process involves each pipe length being inserted into a pre-formed steel reinforcement cage, tailored precisely to fit each individual pipe length. With its surrounding cage, and with the necessary spacers having been installed to ensure the correct position of the cage, the pipe is then moved to the coating application unit which, in less than five minutes, sprays on the required thickness of concrete for that particular pipe. The concrete is made up of a mixture of iron ore aggregate, cement and water, and has been specially developed by EUPEC for this operation. Each pipe is then measured and its coating inspected, following which the pipes enter one of the four curing tunnels.

The curing process is designed to rapidly cure the concrete to provide a significant strength gain so that the concrete coated pipes can then be safely transported and stacked. The curing tunnels use steam: the pipes are slowly brought up to the curing temperature of 50°C, and are then ‘soaked’ in 95–98 per cent humidity for at least nine hours, before being gradually cooled down and emerging from the tunnel after nearly 24 hours.

At this stage, each pipe and its new concrete coating are subjected to further detailed dimensional and quality testing, after which it is colour-coded (according to the concrete and pipe-wall thicknesses), and fitted with end caps to ensure the internal coated pipe and the cutbacks remain clean. Each end cap contains an ‘e-box’, which allows continuity in pipe tracking.

After this final inspection and processing, the pipes are transported individually by road to nearby storage areas, ready for the final period of curing and onward transportation to the marshalling yards.

In parallel with the coating application to the majority of the pipes, around one tenth are separated out as they arrive at the plant to be fitted with zinc or aluminium anodes. Although this is also a highly-automated process, it requires some manual activities, and involves the half-circle anodes being installed on the pipe and the copper cables pin-brazed to the pipe, and shorter reinforcement cages installed on either side. The anodes are designed to be the same thickness as the weight-coating, and are protected by plastic sheeting during the coating application process. After coating application the anode surfaces are cleaned prior to the pipe entering the curing tunnels.

Pipe coating success

The site at Mukran and its nearby storage areas are well-suited to the requirements of the project, with easy access to the nearby port of Sassnitz, and ample space at disused railway yards, for Nord Stream and its contractor. Planning permission for the use of the site was straightforward, as it was already a part of the Sassnitz industrial area, and consequently the establishment of the plant took place with few delays.

EUPEC’s site manager Gerard Vogel points out with quiet pride that this is a truly international job. Although some skilled expatriate engineers were initially required, EUPEC now employs around 200 people at Mukran, approximately 25 of whom are not from the local region. The statistics at Kotka reflect this same approach, which is augmented by the fact that EUPEC’s project in Germany has resulted in more than 100 new jobs at its 30 or so local subcontractors.

Tremendously detailed planning, a high-quality international team, and great enthusiasm have meant that the project has been implemented “without screaming”, according to Mr Vogel. This is a significant testimony to the plant and project management skills, and to well-co-ordinated teamwork, underpinned by the high quality of the work that the two CWC plants are producing.