Powder Metallurgy and Additive Manufacturing for Compressors and Pumps: A New Manufacturing Paradigm for Corrosion and Heat Resistant Alloys
Authors: Stella Piergiorgio , Ceccanti Filippo , Cappuccini Filippo , Bellacci Michelangelo , Kemble Simon , Biccari Duilio Vincenzo , Masi Gabriele 
Published: October 2022

The work describes two representative case-studies: a centrifugal compressor impeller made by Alloy N0726 through Hot Isostatic Pressing and a Centrifugal pump impeller made by Alloy 718 through Laser powder-bed Additive manufacturing. Two basic powder metallurgy approaches were developed at Baker Hughes to manufacture Centrifugal-Compressor impellers: near and net shape. Applicability and benefits of both routes are discussed. Powder metallurgy Alloy N07626 was selected for its outstanding corrosion properties, superior to Alloy 718, as an alternative to conventional Alloy 718 forgings. For the 3D pump impeller, the material Alloy 718 was selected to produce spare impellers that mimics or exceeds the mechanical and corrosion resistance properties of conventional equivalent alloyed steels produced by castings. The pump Impellers were redesigned for printing to keep the flow-path and even increasing the stage performance. Additional post-processing steps of surface finishing and heat-treatment were applied to achieve microstructure and mechanical properties which complied with API, ASTM and customer standards.

A mild Net Shape approach was released, referred as "Close Net Shape" (CNS). It is discussed how the CNS solution was down-selected as the optimum compromise in term of overall process cost and intrinsic variability. The alloy N07626 material properties are outlined with an emphasis on new collected experimental data regarding corrosion behavior and resistance to liquid droplet erosion. The results of manufacturing the 3D-printed pump impeller are discussed and compared to conventional manufacturing routes.

One of the main challenges of the Oil & Gas Energy industry is facing more and more harsh environment that requires increasing use of corrosion and heat resistant alloys, similar or even better than well-known Inconel 718. These materials are still relatively difficult to machine with slow and expensive manufacturing routes. Conventional machining methods faces intrinsic technological limitation to obtain complex shapes that prevent the adoption of novel design. Furthermore, lead time of forgings can be long when a customized production route is preferred instead of standardized series. The development and spreading of revolutionary manufacturing methods based on additive manufacturing and powder metallurgy is changing this picture. In particular, additive manufacturing, more suite for relatively small parts and complex components, presents itself as complementary to more mature powder metallurgy technologies like pressure-assisted sintering by Hot Isostatic Pressing. These novel technologies bring two key benefits: 1) a more effective and versatile manufacturing routes and 2) a faster and more responsive supply-chain with shorter time-to-market. The advantages apply in new units with novel and more efficient design as well as in Service operations when shorter time-to-market is more critical.