GE Oil & Gas wins top award for nickel base shrouded impeller

November 5, 2014

November 5, 2014

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.


Fig. 1 Gabriele Masi, Materials & Processes Principal Engineer for GE Oil and Gas, Florence, Italy (center left) and Dr Federico Iozzelli, Low Temperature Materials Engineering Manager for GE Oil and Gas (center right) receive the Samovar from IHC Awards Chair, Dr Victor Samarov (left) and award certificate from IHC Chairman, Dr Stephen Mashl (right), for winning the grand prize in the IHC HIP Parts of Excellence Competition

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.


Fig. 2 As shown in the left-most CAD image, (a), the shrouded impeller consists of a number of complex vanes sandwiched between solid surfaces. The part is difficult to machine from a solid billet. As seen on the right, (b), HIP PM net shape techniques offer a method by which the complex inner surfaces can be manufactured to net shape dimensions, leaving only the easily accessed outer surfaces that require machining. The alloy is a NACE-MR0175 compliant material,  that exhibits outstanding corrosion properties and resists liquid droplet erosion. HIP and Heat Treatment parameters were optimised for Alloy 625M and sour acid gas applications

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).


Fig. 3 Data from the fatigue crack growth rate assessment of the GE shrouded impeller showed that fatigue crack growth behaviour was intermediate between forgings and castings

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

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November 5, 2014

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