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FEATURE
3D PRINTING/ADDITIVE MANUFACTURING
Keeping legacy equipment in peak operational condition is very important to maintain productivity. But what happens if significant repairs are needed? Dr. Yogiraj Pardhi, global lead for Additive Manufacturing for Sulzer, looks at how additive manufacturing (AM) can be used to create spare parts
IS AM KEY TO
KEEPING LEGACY EQUIPMENT RUNNING?
R
otating equipment – such as gas or steam turbines and compressors – play an
important role in modern industry. But due to long service lives, the necessary support may no longer be available. However, continuous advancements in maintenance engineering mean that specialist solutions can now be quickly reverse engineered. Take gas turbine airfoils as an example. Gas turbines are often used for driving larger
pumps and compressors. Those manufactured in the 1960s and 1970s use legacy materials and technology, such as fabricated nozzles, which are made from several individual parts. Today, the modern equivalents are made from cast components to improve reliability. However, with the older machines now having
little to no support, the operators are looking for replacement parts from new sources – meaning the equipment can be repaired cost-effectively and parts inventories can be updated with the introduction of modern materials.
SUPPORTING INDUSTRIES New parts for gas turbine airfoils are typically made using a casting process, but this requires a considerable amount of time to develop and qualify the finished product, and the cost is affected by the volume of parts required. So, repair specialists, such as Sulzer, are looking to use the latest available technology to create new components cost- effectively, even in small quantities. Additive manufacturing (AM) is supporting many industries, but qualifying new materials and achieving the necessary quality standards is a complex procedure requiring the highest levels of technical expertise. In a recent project, a gas pipeline operator was
looking to update a turbine that was powering a gas compressor. This needed two stator rings, each containing 42 airfoils.
38 DESIGN SOLUTIONS FEBRUARY 2022 Thanks to its
experience of using additive manufacturing (AM) for replacement parts, Sulzer recommended using this technique to make airfoils using
cobalt-based superalloy Mar M 509 material. When made using selective laser melting (SLM), this material offers a number of benefits including high strength levels, good resistance to hot corrosion and excellent creep behaviour at high temperatures. These attributes are paramount, since the stator ring airfoils will typically experience firing temperatures of 760˚C.
QUALIFICATION Having established that the material is suitable, the next stage is to qualify the components. This involves in-depth trials and first article inspection work to perfect the manufacture of this component. Additive manufacturing for advanced engineering applications such as this requires each material to be properly tested and qualified before it can be approved for use in an AM design. One of the biggest challenges was refining the manufacturing process to fit the properties of the material. Sulzer used selective laser melting, which takes metallic powder and melts it in thousands of 2D layers with a laser, before rapidly cooling it to create the component from a 3D model. The fast cooling process during SLM requires careful management of residual stresses by selection of a suitable laser scanning strategy. Selective laser melting of complex superalloys
like Mar M 509 is a technological feat that has only been achieved by a few. Sulzer is able to
apply many years of experience in working with complex hot gas path superalloys to develop and qualify process parameters for this material. The resulting process is very accurate and the final dimensions can be attained without requiring additional machining. The surface finish, internal and external, is achieved through careful selection of proprietary finishing techniques. The final properties of SLM material are achieved using an optimum heat treatment routine that was defined using extensive investigation into the effects of heat treatment parameters on material properties. After establishing the required SLM process and post processing routine, and on completion of First Article Inspection, the first set of 42 airfoils were delivered within eight weeks. In cases like this where no original drawings
are available, the designs for the new components need to be created using Sulzer’s in-house reverse engineering process. In this particular example, Sulzer created the new airfoils using a parent material which would withstand the high operating temperatures. On top of this, an additional thermal barrier coating was applied. The final dimensions are established by the
accuracy of the manufacturing process and, from this point, the new airfoils are ready to be installed into the stator ring and welded in place. Post fabrication machining of the stator ring and application of the thermal barrier coating was completed in-house before reassembly into the gas turbine. This therefore shows how operators of legacy machinery, which is still more than capable of delivering reliable service, can take advantage of modern maintenance engineering and enhance the supply of spare parts for the future.
Sulzer
www.sulzer.com
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