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There are many sources out there offering aftermarket parts, often at rates far below those of the OEM. Yet most OEMs are understandably against the practice of finding replacement parts anywhere else. They typically state performance benefits of their own products as well as warranty objections to those tempted to stray from the path.

“Our goal is to help our customers optimize the performance of our equipment throughout its life cycle,” said Dave Taylor, Director of Engineering for Services at Rolls-Royce Energy. “It is important to note that product warranty can only be maintained through the use of OEM parts. As well as benefiting from the deep domain expertise only Rolls-Royce can provide as the OEM, there is a clear performance guarantee and commercial advantage to operators.”

Rolls-Royce products are aero-derivative machines and, as such, are removed and returned to an authorized service center when an overhaul is required. A replacement unit is installed at this time. Users do not conduct overhaul work themselves other than to install the replacement gas generator or power turbine. For power turbines, the overhaul life is either 50,000 or 100,000 hours when the turbine is removed and returned to the service center.

“Parts that have a defined life are replaced during the service overhaul,” said Taylor. “Life sampling is carried out on these parts to improve our knowledge of performance in the field, enabling us to gather data to further extend the part’s life.”

Rolls-Royce recently introduced an upgrade for the Avon gas generator called the Avon 200. Its new turbine assembly allows the operator a 10% increase in power or a 20% increase in life. Taylor said over 80 units have been sold to date (Figure 1).

“We are working on a similar upgrade for the RB211, called Gzero, which should be available in early 2013,” said Taylor. “We can also offer combustor upgrades (gas-only to dual fuel or DLE) to increase fuel flexibility or reduce emissions.” Ken Kihara of Kawasaki Heavy Industries (KHI) confirms that his company has a similar policy regarding replacement parts. “In the past, we have a seen a few cases when the end user went to a third party for a major overhaul as well as replacing or refurbishing the internal parts,” he said. “Soon after start up, they encountered unexpected situations of failures which that supplier couldn’t resolve.”

Kihara pushes the virtues of a Long Term Service Agreement (LTSA), which covers the scope of parts and services during a preset period of the contract. “Upon request, contracts may take several weeks or months in some cases before the purchase order is formally issued,” said Kihara. “The LTSA concept is better if you really need the parts and services quickly, especially upon an unexpected plant shutdown, and want to reinstate the compressor.”


Service bulletin needs

Pat Loveland, Director of Parts Marketing for North America at Siemens Energy Service, made the point that timing of spare part replacement is primarily driven by intervals for scheduled minor and major maintenance inspections as laid out in service bulletins. Spare parts lists are developed for each type of inspection called out in the bulletins.

Siemens recommends replacement parts be ordered based on standard manufacturing lead times. The company has developed an online parts catalog system, including pricing and estimated lead times. Users could then plan for parts purchase in advance of an outage.

“Only original manufactured parts should be used in Siemens units, installed in accordance with OEM standard processes and using specially designed OEM tooling,” said Loveland. “Scheduled inspection intervals help customers optimize the performance capability of their hardware configuration through our system-based approach to engine component and auxiliaries design.”

Long Term Service Agreements (LTSA) available from Siemens mean that new and repaired parts can be maintained in a fleet pool so ready spares are available fleetwide. In addition to hardware, Siemens also stocks open and close kits for most major frame families, which provide a range of minor material as a contingency available on-site during an outage. The user pays for what is used from the parts kit and the rest is returned.

Further, upgrades for performance, emissions, or operational flexibility are available to owners of Siemens turbines. One example is Si3D (Siemens Innovative Three Dimensional) turbine blades and vanes. These rotating and stationary blades had been created utilizing three-dimensional design tools. Enhancements to aerodynamics, materials, coatings and internal cooling patterns are said to provide higher power output and efficiency. They are drop-in replacements for originally supplied hardware (Figure 2).

“Use of third-party components can impact the ability to obtain benefits from these Siemens designed upgrades or may not be compatible with the upgrades at all,” said Loveland. “Furthermore, continued long-term operation using non-Siemens parts would not allow users to benefit from design enhancements that are regularly incorporated into new generations of Siemens baseline components.”

Buyer Beware

The OEMs have their own tales to warn users who are tempted into the non-OEM aftermarket. At a recent user conference, for example, one plant manager discussed the consequence of using non-OEM second stage buckets on a GE 7EA, commissioned during the 1980s. During the next outage, maintenance staff noticed that half the tip shrouds were gone from the new buckets. They had to be changed out. “We never found out what went wrong, but we have been careful of buying second-stage buckets ever since,” said the plant manager.