REMANUFACTURING IN TURBOMACHINERY

SOME COMPONENTS ARE WORTH REMANUFACTURING WHILE OTHERS SHOULD BE REPLACED. HOW DO YOU MAKE THE DECISION?

BY DEREK VANEK

Remanufacturing is the rebuilding of a product to specifications of the original manufactured product using a combination of reused, repaired and new parts. And it requires the repair or replacement of worn out or obsolete components and modules. The definition, developed by King, Burgess and others, defines a remanufacturing process as, “the only process where used products are brought at least to Original Equipment Manufacturer (OEM) performance specification from the customer’s perspective and, at the same time, are given warranties that are equal to those of equivalent new products.”

The U.S. is the largest remanufacturer in the world. Between 2009 and 2011, the value of U.S. remanufactured production grew by 15% to at least $43.0 billion, supporting 180,000 full-time jobs, according to the U.S. International Trade Commission.

Remanufacturing, though, might not be right for every application. Sitting at the heart of the decision is the used part that is at the end of its service life. A part that was removed due to failure is considered the same as a part that was disassembled from that same application due to obsolescence.

There are four main strategies for remanufacturing, each of which comes down to value and type of component, according to a study on “Remanufacturing Inspection Models,” by Exeter University, UK. It states: “If cores [end of service life components] are relatively cheap, disposal is an effective way of increasing the reliability of the population as a whole. If cores are expensive they must be processed almost regardless of cost. In the case of low value cores, there is often a new alternative that can be purchased in its place.”

Ultimately, the decision to remanufacture a component is made by the OEM or by the company that owns and uses the equipment. This decision depends on the lead time to make a new part. In order to create a new component for an existing turbine, the base material needs to be the same, which is not always accessible if the component is made out of an alloy.

To assess whether it is worth remanufacturing, the value of the part helps determine if it is worth repairing. Compare the cost of repair to the cost to remake the component. If the repair costs more than 25% of the value to remake the part, remanufacturing is not an option. It is more effective to replace the part. Remanufacturing of a component, then, should be assessed on a case-by-case basis. Different processes might be used in the remanufacturing process than were used in manufacturing the original equipment or part. Further, a repair may result in transportation costs.

Due to the high cost of turbomachinery equipment combined with the lead time required to purchase new equipment, remanufacturing generally remains an option. Nevertheless, there can still be instances when remanufacturing is not viable, because it costs more in time and energy to restore a part than to replace. In some cases, remanufacturing cannot be considered due to the wear, corrosion, or other damage to the part. In other cases, there may be dimensional limits in the design scheme that hinders the ability to perform a selective plating application.

As remanufacturing can add as many as ten or more years to part life, it can be of assistance in minimizing repair times. Remanufactured components may be available with a shorter lead time than those that are manufactured-to-order in overseas locations. Surface treatment in remanufacturing NACE estimated the cost of corrosion to U.S. industry to reach as much as $540 billion in 2015. Surface treatment is a cost effective and common method of restoring a component back to its original specification.

Many processes are available, including tank plating, thermal spray and selective plating. Tank plating immerses the components in a solution. To accomplish this, parts are typically removed and shipped to the plating company. Thermal spray, on the other hand, provides a mechanical bond. Once the spraying is done, machining is done to bring the component to the required dimension. Selective plating, also known as brush plating, is commonly applied via a handheld tool. The operator soaks the tool in the plating solution and applies it via an absorbent cover wrapped over the anode of the plating tool. It can be carried out in situ and creates an atomic bond.

Steam compressor housings and stages, for example, experience corrosion due to the build-up of condensation. Similarly, when leaks form in the seal areas of a turbine, pressure builds and steam releases at such high power, that it gouges or cuts any exposed component. Surface deterioration of metal components can lead to premature failure with the risk of unscheduled downtime. When a turbocompressor operates at full load, ensuring the correct dimensions of turbine shafts and housing covers is essential to optimal output. It is impossible to resist wear on these components, but there is a way to restore them to size with a nickel alloy without the need for post machining. The pinion gear is an essential part in a gear train assembly. If not maintained regularly, lubricant in the pinion gear can leak out of the seal, ultimately causing the bearing to seize and gall to the shaft. When the seized bearing is removed it can also remove excess material from the journal resulting in a gouge to the surface. Plating can prevent galling and raise surface hardness.

With many surface finishing options available, including thermal spray processes, IVD, PVD, tank plating and selective brush plating, choosing the right one for a particular application can be difficult. Selective plating, for example, is best suited for localized areas on inside and outside component diameters or flat surfaces. Take the case of rotor resizing. One major power generator uses selective plating for the maintenance of turbines. This saves it 50 per cent of the time required to return equipment to service. It builds up rotors with nickel to prevent erosion or wear on the shaft and permit optimal performance. Selective plating technicians use the OEM specification to determine the deposit to be plated and thickness required. If the shape is out of round or pitting has occurred, post machining is required. If only a small amount of deposit is needed, selective plating can be used to plate to size.

Derek Vanek is the Technical Manager for SIFCO Applied Surface Concepts, a company that provides selective brush plating solutions to improve part performance and reduce manufacturing costs through corrosion protection, increased wear resistance, increased hardness, improved conductivity, anti-galling or slip. The SIFCO Process is an application of selective plating used by many in the turbomachinery industry. For more information, visit www.sifcoasc.com