Pipelines, the Norwegian deep sea and digital radiography

16/05/2019

Imagine an early August morning on a remote Norwegian fjord coast. The North Sea Giant, a 150 m-long pipe-laying vessel, is being readied to lay down an 8.4 km gas pipeline onto the seabed of the Norwegian Sea. The massive ship will leave the shores of Orkanger and start its journey at sea to reach the Åsgard field, which is 200 km away.

This subsea, umbilicals, risers and flowlines (SURF) project commissioned by Equinor, previously Statoil, the oil & gas company, was entrusted to TechnipFMC, a global leader in subsea, onshore, offshore and surface oil & gas technology, and Axess Group, a Norwegian quality control and inspection solutions provider within the SURF business.

The tube that is reeled at the rear of the North Sea Giant is assembled in a factory twice the size of a football field, where 12 m pipes go through a series of working stations to be preheated, welded, tested and coated. In total, the project consists of 700 double joint welds and 700 other main-line welds, as well as onshore and offshore tie-in welds.

As you can imagine, this complex enterprise can go wrong in a variety of ways. A slight mistake anywhere in the process inevitably delays the production, which can cause tremendous financial losses. Therefore, human errors or equipment failures are to be avoided at all cost.

From the outset, the two partners were looking for reliable, hands-on and easily implemented solutions to ensure seamless execution of the assembly line work that was to be carried out in the Norwegian plant.

An operation of this magnitude calls for extensive examinations of each weld that holds the several kilometres of pipeline together. Indeed, the viability of the entire project relies on the strength and quality of the different junctions that compose the pipe. Therefore, highly qualified operators and state-of-the-art quality control equipment are paramount.

Axess, a quality control contractor always on the lookout for innovative and reliable tools, was in the market for a high-definition digital X-ray system that would allow the inspection team to carry out the thousands of X-ray shots in record time, but with unequalled precision and quality.

The Norwegian company eventually settled on the GO-SCAN 1510 XR radiographic testing equipment from Teledyne ICM, a Belgian X-ray expert. This 15 x 10 cm, 49.5 µm complementary metal oxide semiconductor (CMOS) digital detector coupled with a CP225D, a 225 kV constant potential X-ray generator also from Teledyne ICM, was revealed to be the ideal partner for the task.

“The Teledyne ICM system was very well adapted to the Åsgard and Trestakk projects. It proved to be effective, reliable and accurate,” said Hjalmar Holmen, Senior Surveyor at DNV GL.

To meet Axess’s high expectations in terms of image quality, engineers at Teledyne ICM worked hand in hand with experts from Axess. Teledyne’s Sherlock™ image processing software was tailored to meet the client’s need and comply with the EN ISO 17636-2 standard covering radiographic inspection using digital imaging solutions. The system also had to comply with the very demanding specification for subsea pipeline, DNV-OS-F101. To the Axess experts, the features implemented in the software, such as signal-to-noise ratio (SNR) and measuring tools, were also very welcome additions to Sherlock as they greatly improved the understanding of each X-ray shot.

On top of the high-resolution images, the portability and versatility of the entire system became a great asset when Axess installed the X-ray source and detector on the TechnipFMC production line.
Thanks to Axess’s expertise, the team developed solutions for the Teledyne ICM generator and detector, which enabled two quick X-ray exposures that covered the complete weld in a few seconds. The set-up greatly satisfied the requirements connected to subsea pipeline, with high expectations for process speed, quality and durability.

Besides the incomparable speed at which digital radiography (DR) delivers images compared to film, the magic of digital radiography, and especially the Sherlock software, resides in the fact that all of the images, studies and edits can be shared with colleagues, clients and advisors all over the world in an instant.

“It [the system] was very fast and the sensitivity was also very good. It was a big advantage for me to be able to contribute in scan interpretations from my Oslo office simultaneously with the welds being produced in Orkanger,” commented Bent Arild Aspeli, Senior Specialist Engineer NDT and NDT Responsible Level 3 at TechnipFMC.

The CP225D X-ray generator delivered all of its promises and more. With its output voltage ranging from 10-225 kV and its current range going from 1-10 mA, this tube was highly versatile. Weighing only 12 kg, the unit was very easy to carry around and install on the main line.

“The in-built shielding system in the tube and the fact that we were able to achieve very low radiation dose rates within the relatively limited space we had available was incredible,” said Vidar Grønning, NDT Operator and HSE Selected Delegate, Axess.

In September, all of the 12 m tubes that formed the 8.4 km sea pipeline were ready to be rolled onto the massive reel at the rear of the North Sea Giant, with the pipe-laying vessel leaving the harbour to start its expedition to Åsgard.

The Axess and TechnipFMC teams were extremely satisfied with their equipment of choice. They concluded that this digital X-ray system would be capable of meeting all applications given the tremendous success and complexity of the Åsgard project.

It took four weeks, thousands of welds and close to 100 operators to complete this project. The Equinor pipeline is now laying at the bottom of the Norwegian Sea. Axess and TechnipFMC are once again at work using the equipment provided by Teledyne ICM and the North Sea Giant is out on new missions in Scandinavian waters.

www.teledyne.com

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