Foto: Statoil/Ole Jørgen Bratland

Cast nozzle delivers increased life span

A gigantic cast nozzle, a diffusor of about 1 tonne, will be installed on oil rigs operated by Norway’s Statoil Petroleum. In cooperation with the subcontractor Mjørud and Österby Foundry, Swerea managed to develop a cast design of the previously welded component.

Increased demands on the service life of one of their products led Mjørud AS to investigate the possibility of casting as a manufacturing method instead of welding. The product, a diffusor, is installed after the gas turbine and serves to minimise the turbulent flow of gas before it passes a heat exchanger.

“The project has taken us a major step in the right direction. Together we are stretching the boundaries in an industry with a high focus on energy optimisation, reduced CO2 emissions, and robust solutions with long service lives. Through systematic development work, together with Swerea and Österby Foundry, we have now solved most of the technical challenges. I am very pleased with the process and the results,” says Stian Martinsen, project manager for the work at Mjørud AS.

The challenge was to cast a complex geometry as thin as possible. It was thought possible to cast a dominant thickness of 8 mm and, several casting simulations later, a well-functioning gating system had been produced, which Swerea felt confident in recommending.

Together with Österby Foundry, cast alloy was selected as suitable. The sand mould parts were supplied by Karlebo Foundry Technology and manufactured in a 3D printer from ExOne. The mould was too big and too complex to print as one part, thus it was printed in many minor pieces and later assembled.

In April 2018, the first diffusor was installed on an oil platform, according to plan. A further two to four nozzles will be replaced each year.

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