Generally speaking, the technologies of impellers, rotors, turbines and compressors are not new. The core concept of the rotor in its various applications has remained unchanged through decades so that the modern engineering challenge is to make incremental advances that will have a positive impact on performance. At GE, we have always strived for and maintained the highest levels of design and manufacturing quality possible using available technology, and often by developing new technologies. This philosophy of unrelenting improvement is what sets our equipment apart to this day.

From the ground up
When a 19-ton steel shaft spins at 3,000 RPMs generating 31 bar of pressure, the smallest vibration can spell disaster – or at the very least,
lost profit from inefficiency.

Rotor vibration can be caused by manufacturing defects, operation at incorrect speed ranges, and by installation and on-site balancing errors. Even relatively slight vibration can lead to severe machine damage. Results can include costly repairs or replacements, lost revenue, and grave danger for the environment and human life.

The core idea behind our most recent innovation to combat this ongoing and costly challenge was simple: replace the traditional welded rotor with a single piece of finely machined steel. One-piece construction would eliminate the weaknesses inherent in even the most precisely welded impeller, delivering a significantly stronger, more stable and better balanced rotor.

Single piece versus welded construction may have been simple in theory, but executing the idea was quite an involved process.

Rotors can be milled from either stainless steel or carbon steel, depending upon the application, and can have from 1 to 8 impellers. With single-piece impeller technology there are no power limits on the single compression stage, since the weakest point between hub and shroud is automatically eliminated. Moreover, the manufacturing process, itself, is more efficient and reliable than traditional welded methods.
 
Our single-piece impellers are manufactured using a combination of proprietary CAD systems and a sophisticated computer-controlled 5-axis milling process. Starting with a precisely engineered model, all toolpaths are automatically generated using CAM tools. A machining strategy which uses a variety of different sized mills, operating from both the inducer and exducer side, and backed by simulation and accessibility programs, ensures the tightest possible tolerances for improved performance and greater process control from design through manufacturing.

Continuous automated feedback loop
Not only are many of our rotors now seamless, but so too are the processes by which we create them. Our redesigned manufacturing plant in Florence features a new workflow system that includes more than 200 integrated computer terminals on the shop floor. Every work station is now fully equipped to monitor quality throughout the entire manufacturing process.

Traditionally, rotor design would be undertaken based on a series of performance specifications before moving on to manufacturing. Once complete, final testing would confirm the level of conformity between the finished piece and its design specifications.

Our new approach uses fully integrated design, modeling, programming and machining technologies that feed the same precise parameters through all software and system components. Specifications are continually tested and confirmed at every stage so that even minute inconsistencies can be identified and corrected automatically throughout the process to ensure that actual performance is consistent with design specifications.

GE’s automated CAD/CAM process (l/r): Design, Modeling, Programming and Machining. The fully integrated process ensures the continuous and automatic verification of all parameters at every stage of rotor design and manufacturing.

Fully integrating the engineering and manufacturing processes results in significantly less wasted time and materials, which has a dramatic effect on project budgeting. As well, work that used to require five days now takes a mere five hours to complete.

Our Engineering department designs 3D models using Unigraphics software, and then our manufacturing programs automatically break them down and define the manufacturing process to be followed. The result is defect-free manufacturing that is exactly on spec with the 3D engineering drawings. We know in advance how the as-built machine is going to perform at the customer’s facility – and can commit to performance standards with significantly greater confidence.

The net outcome of all these efforts - is that GE is now the only company
in the world manufacturing single-piece forged steel rotors – designing, building, testing and installing them for some of the industry’s most demanding operations.

The capability comes from a serious commitment to invest in the equipment, staff training and procedural modifications needed to reach new heights. We also have the advantage of unparalleled research and development capabilities through regularly sharing knowledge and technology with GE’s Aviation and Healthcare businesses. When a customer purchases a GE compressor, they can rely on a package of equipment, software and operating technology that has undergone the most stringent development process – not only in the oil and gas industry, but in three of the most advanced technology-based industries in the world.

Real benefits
All these advancements are a direct result of our corporate mission – to create value defined only in customer terms. That means success is measured by delivering on spec and on time. To that end, manufacturing cycle times have been reduced by 30-50%, while final delivery times have improved sevenfold.

For more information, contact:
Giulio Favilla
giulio.favilla@ge.com