The International HIP committee (IHC) presented its ‘HIP Parts of Excellence’ award winners at HIP’14, the 11th International Conference on Hot Isostatic Pressing, Stockholm, Sweden, June 9-13. GE Oil & Gas, Italy, together with Synertech PM, Inc. and LNT PM, Inc. received the Grand Prize in the competition for an Alloy 625M shrouded impeller manufactured for use in centrifugal compressors used in the oil and gas industry.
Designed specifically for sour applications, for example environments where high concentrations of hydrogen sulfide, carbon dioxide and chlorides create a particularly aggressive environment, the nickel based superalloy component exhibited exceptional dimensional control for such a large PM component.
As shown in Fig. 2, the shrouded impeller design, with solid sections covering an array of complex, internal vanes, is a challenging shape to manufacture by any method. The complexity of the part makes it well suited for production using selective-surface HIP Powder Metallurgy net shape techniques. By this method solid, machined cores made from mild steel are positioned within a capsule during the capsule assembly process. Powder fills the remaining voids within the capsule and after HIP, the mild steel core and capsule materials are removed in an acid bath. The as-HIPed superalloy component, as shown in Fig. 2b, remains. Heat treating and an external machining step produce the finished product.
Tests performed during product development included: high cycle fatigue, fracture toughness, fatigue crack growth rate, tensile strength, impact strength, notch sensitivity, and sulfide stress corrosion cracking. Sulfide stress corrosion cracking testing was performed in accordance with NACE TM0177 and ASTM G39-99 with no failures. Fatigue crack growth and fracture toughness thresholds were intermediate between forgings and castings of similar alloy (Fig. 3).
GE Oil & Gas cited high material utilisation as an advantage for the HIP PM approach with the weight of the as-HIPed part only weighing 1.1 times the weight of the finished product while the weight of a forged preform was five times greater than that of the finished part . GE Oil and Gas has established all process and quality control parameters and production using the HIP PM approach is anticipated to begin in 2015 at a nominal rate of 300 parts per year.
The combination of part complexity, part size, and dimensional control were stated as being factors in this part being named the grand prize winner in the competition.
Read our full report from the HIP’14 conference in the Autumn 2014 issue of Powder Metallurgy Review