RMS 3D prints large centrifugal compressor impellers

RMS, an aftermarket turbomachinery company, was recently contracted by a refining customer to undertake a critical project focused on replacing two riveted impellers for a centrifugal compressor in plant air service. Facing tight time constraints due to an impending outage, RMS and the customer decided to 3D print the replacement impellers using LPBF – resulting in the reported largest and first-ever 3D printed centrifugal compressor impellers used in a refining application.

The project presented several challenges. The existing impeller design used a riveted construction and measured 23.5 inches in diameter. However, the largest printing bed available was limited to a 23-inch diameter. To address this, RMS engineers needed to redesign the impeller geometry to overcome the reduction in head that would naturally occur from decreased diameter. RMS’s Aero team designed the impellers to achieve the customer’s performance requirements, instead of simply duplicating the riveted impeller geometry.

Extensive engineering was required to ensure that the new impellers would deliver comparable performance despite their reduced size. The high tip speeds required for the impellers (>1000 ft/s) necessitated careful evaluation of stresses to ensure reliable operation. RMS’s Analytical Team conducted comprehensive modeling activities, including full structural and aerodynamic analysis using CFD, to ensure the new designs met the customer’s stringent process requirements.

RMS worked to develop an impeller design that leverages the design freedom afforded by 3D printing. The impellers featured shallow cover angles of 3.8 degrees for the stage 3 wheel and 2.5 degrees for the stage 4 wheel. The impeller was manufactured using Inconel 718 and the latest API 20S Standard, a material known for its exceptional strength and durability. This choice of material resulted in a final product that was significantly stronger and more reliable than the previous riveted impellers – ensuring superior performance for the refineries’ application.

To guarantee the performance and reliability of the 3D printed impellers, multiple test bars were produced during the printing process. To ensure quality in all directions, the test bars were printed from each laser, and oriented in each axis to ensure consistent quality in all directions. These test bars underwent rigorous testing to confirm that the metal met all necessary performance standards. This comprehensive process and series of protocols were paramount in validating the new impeller manufacturing process.