Pipe Making: Rigorous Quality Standards from Start to Finish
With over 200,000 steel pipe joints needed to build the Nord Stream 2 Pipeline through the Baltic Sea, the importance of pipe quality cannot be overstated. From the carefully tested plate materials from which they are formed, to the precise roundness of their shape, superior pipe joints are essential to the safe and efficient construction and operation of the pipeline.
After a rigorous international tendering process that involved multiple trial productions and on-site tests, Nord Stream 2 chose some of the world's leading suppliers to produce the impressive quantity of 12-metre pipe joints that will ultimately become the more than 1,200 kilometre long twin Nord Stream 2 pipelines.
Russian companies OMK and Chelpipe, along with Germany's Europipe, were chosen to produce the more than 2 million tonnes of steel pipes thanks to their modern high-capacity facilities, broad experience and ability to meet Nord Stream 2's demanding quality standards.
But quality assurance doesn't stop with the selection of capable suppliers. At each production facility, Nord Stream 2 continuously monitors every critical step in the manufacturing process outlined below.
Materials and Coating
Before the project began, our engineers specified the required properties and parameters of plates, pipes and coating in detail. A special high-tensile, low-alloyed carbon steel is needed to ensure that the plates are tough enough for offshore welding, for example. During production we then sacrifice more than 25,000 tonnes of this steel for laboratory testing to confirm that material properties like strength, toughness and chemistry are fulfilled.
After the plates have been formed into pipes, longitudinally welded and thoroughly tested and measured in the pipe mills, they receive both an internal flow coating and an external anti-corrosion coating, followed by a layer of concrete weight-coating that keeps the pipes safely on the seafloor. At each step along the way, the pipes are carefully monitored by specialists.
Pipe Roundness and Consistency
Perfect and consistent roundness of the pipe joints is another crucial element in the pipe making process. The pipes are designed to have a constant internal diameter of 1,153 millimetres and a wall thickness of up to 41 millimetres. Nord Stream 2 allows a maximum ovality, also called out-of-roundness (OOR), of up to 5.0 mm. OOR expresses the deviation from a perfect circle, and we require that 50 percent or more of the pipes show an OOR less than 3.0 mm.
This level of precision means that all pipe joints will then fit perfectly together during offshore welding. With virtually all of the welds making it past inspection without repair, we not only optimise quality, but also significantly reduce the construction time to stay on schedule.
Another important element to ensure a seamless offshore pipelay process is the installation of "buckle arrestors," typically one every 1 km in the deep water sections. Buckle arrestors are extra thick pipe segments that prevent a propagating buckle that could accidentally occur during pipeline installation.
Though propagating buckles are rare, the consequences can be significant. Without buckle arrestors, such an incident could result in pipeline sections needing to be removed and reinstalled again, with serious commercial and scheduling impacts. But with protection installed at regular intervals, the maximum pipeline section lost from a potential buckle would be limited to the 1 km distance between two buckle arrestors, making their installation a critical risk reducing measure during the pipelay process.
Teamwork and Expertise
To achieve this high level of efficiency and quality, Nord Stream 2 relies on an experienced team of engineers and technicians during pipe manufacture to guarantee that all Nord Stream specifications are met. We also employ between 100 and 150 full-time inspectors to approve each pipe joint along each step of its journey. Together they make a vital contribution to the intricate logistical and engineering efforts required to execute a project of this magnitude.